Aerodynamics

Previously made evaluations show confinement of fire coal waste dumps to geodynamically dangerous zones which in this work are considered as borders of active blocks of the earth crust. According to the hypothesis under development, when disposing the dumps in geodynamically dangerous zones (GDZ), which have a high penetrating, aerodynamic relation of the dumps with the environment occurs, хmaking the dumps firing possible. Firing of the dumps inflicts environmental, social and material damage. This research is aimed to study possible mechanism of gas mass transfer through GDZ into the body of dump on the base of computer modeling of aerodynamic processes. A relevant geometry model is developed, borderline conditions are proven and modeling of aerodynamic process is shown in the work. Taking into account actual data on location and characteristics of firing dumps of a region of Eastern Donbas (Rostov region, Russia) calculation are performed by means of ANSYS software. A dump located in GDZ is modeled. The GDZ is set in the model as a highly penetrating linear zone in the rock, which has a deep emplacement. The GDZ crosses mine fields and has an expression in relief of the Earth surface. Temperature of the rock within the dump may reach 420 degrees Centigrade. Petrophysical characteristics are taken into account in the model (porousness and permeability) of its main structural elements, dimensions of the dump, width of GDZ, difference of relief heights, depth of mine workings location under the dump. The results of the modeling show influence of the dump temperature, petrophysical characteristics of the model structural elements, depth of the mine openings location on aerodynamic processes within the dump mass. Operability of the model at the preset border conditions allows to deeply argue the hypothesis of the air intake into the dump body with consideration of the local geodynamics. According to the results obtained, geodynamic conditions of mining area where coal waste dumps are disposed, may be and are an important factor, which has an effect on creation conditions for spontaneous combustion of dumps and its further impact on environment.

This paper presents analyses of the effect of blowing flow control and variations on front geometry towards the reduction of aerodynamic drag on vehicle models. Blowing flow control is an alternative measure in modifying the onset of flow separation in the boundary layer on the surface of the vehicle. The modification is expected to reduce the dominating influence of the separation area on the total drag. Conducted in computational and experimental approaches, the research investigated the effect of frontal slant angle variations (θ) of 25°, 30° and 35° towards the reduction of aerodynamic drag on vehicle models on the application of blowing flow control with upstream and blowing speed of 16.7 m/s and 0.5 m/s, respectively. Load cells were used in the experimental method to validate the reduction of aerodynamic drag obtained from computational method. It is indicated that the effects of blowing flow control and variations on front geometry are significant in the increasing on pressure coefficients and the reduction of aerodynamic drag on vehicle models. The largest increase on pressure coefficients of 38.93% is indicated on the vehicle model with θ=35°, while the largest reduction of aerodynamic drag occurred on the same model with the values of 14.81 and 12.54 for computational and experimental methods, respectively.

A cycling peloton is the main group of cyclists riding closely together to reduce aerodynamic drag and energy expenditure. Previous studies on small groups of in-line drafting cyclists showed reductions down to 70 to 50% the drag of an isolated rider at same speed and these values have also been used for pelotons. However, inside a tightly packed peloton with multiple rows of riders providing shelter, larger drag reductions can be expected. This paper systematically investigates the drag reductions in two pelotons of 121 cyclists. High-resolution CFD simulations are performed with the RANS equations and the Transition SST-k-ω model. The cyclist wall-adjacent cell size is 20 μm and the total cell count per peloton is nearly 3 billion. The simulations are validated by four windtunnel tests, including one with a peloton of 121 models. The results show that the drag of all cyclists in the peloton decreases compared to that of an isolated rider. In the mid rear of the peloton it reduces down to 5%-10% that of an isolated rider. This corresponds to an "equivalent cycling speed" that is 4.5 to 3.2 times less than the peloton speed. These results can be used to improve cycling strategies.

A cycling peloton is the main group of cyclists riding closely together to reduce aerodynamic drag and energy expenditure. Previous studies on small groups of in-line drafting cyclists showed reductions down to 70 to 50% the drag of an isolated rider at same speed and these values have also been used for pelotons. However, inside a tightly packed peloton with multiple rows of riders providing shelter, larger drag reductions can be expected. This paper systematically investigates the drag reductions in two pelotons of 121 cyclists. High-resolution CFD simulations are performed with the RANS equations and the Transition SST-k-ω model. The cyclist wall-adjacent cell size is 20 μm and the total cell count per peloton is nearly 3 billion. The simulations are validated by four windtunnel tests, including one with a peloton of 121 models. The results show that the drag of all cyclists in the peloton decreases compared to that of an isolated rider. In the mid rear of the peloton it reduces down to 5%-10% that of an isolated rider. This corresponds to an "equivalent cycling speed" that is 4.5 to 3.2 times less than the peloton speed. These results can be used to improve cycling strategies.

Estimativa de parâmetros aerodinâmicos em estruturas com a utilização da dinâmica dos fluidos computacional / Carlos Vitor da Silva Sarmento. -Recife: O Autor, 2015. 200 folhas, il., gráfs., tabs. Em primeiro lugar, agradeço a Deus por todo o projeto que tem em minha vida, que vem sendo consolidado cada dia que passa e a cada fase que venço nesta jornada acadêmica. A minha mãe, Inês, por ser minha fortaleza e refúgio, me inspirando com seu jeito determinado de guiar a vida. Por me alimentar com seu amor e carinho, que me fortifica para as dificuldades diárias. Também destaco sua tolerância a minha ausência. Ao meu irmão, Carlos Felipe, por inspirar-me através de seu domínio da matemática pura e seu raciocínio lógico. Ainda destaco um espaço a minha cunhada, Sheyla e a meu sobrinho Rafael, que terá boas inspirações em sua árvore genealógica. Agradeço ainda a todos da minha família, por me apoiar e servir de exemplo com tantos pesquisadores e professores sempre a motivar-me. A minha namorada, Danielle, por sua paciência e compreensão à minha ausência. Pela ajuda nas horas difíceis e apoio constante nas dificuldades inerentes de uma pós graduação. Também pelo seu companheirismo em congressos e viagens. A meus amigos por compreenderem a minha ausência e me apoiarem sempre. E a meus colegas de trabalho por me apoiarem sempre. Principalmente Paulo Alison pela sua experiência em CFD. A todos os professores do programa de pós graduação em engenharia civil da UFPE que realizam suas atividades com grande dedicação. Destaco também o agradecimento a quem está por trás do funcionamento operacional da pós da UFPE, as servidoras Andrea e Claudiana, que sempre foram atenciosas e prestativas em seu trabalho. Ao meu coorientador, professor Antônio Oscar, por acreditar em mim, desde a graduação, onde iniciamos estudos ligados à ação do vento em edificações. Sou muito grato ao professor Oscar pela paciência e contribuição nos estudos, que foram de grande tamanho devido à sua larga experiência e conhecimento técnico. Em especial agradeço ao meu orientador, professor Paulo Marcelo Ribeiro, por toda a sua paciência e dedicação à pesquisa. Sou infinitamente grato pela sua contribuição na formação de um pesquisador. Com o prof. Paulo Marcelo aprendi bem mais que equações diferenciais ordinária ou método dos elementos finitos. Aprendi na verdade que ser professor extrapola a barreira da sala de aula, expandindo ao campo da curiosidade epistemológica. Sou extremamente grato pelo seu tempo gasto em diversas pesquisas em diversos campos da física e em especial na aerodinâmica de edificações, assunto que não é comumente abordado por engenheiros civis, principalmente calculistas, mas que foi um desafio abraçado por nós, que resultou em um final extremamente satisfatório. Professor Paulo Marcelo e Antônio Oscar, são as pessoas mais geniais que já conheci. Consegui unir os dois para um trabalho em um assunto que tenho grande apreço e curiosidade. Agradeço também a banca pela sua colaboração e dedicação para a melhoria deste trabalho. "A matemática é a única linguagem que temos em comum com a natureza". Stephen Hawking "A mente que se abre a uma nova ideia jamais voltará ao seu tamanho original".

Estimativa de parâmetros aerodinâmicos em estruturas com a utilização da dinâmica dos fluidos computacional / Carlos Vitor da Silva Sarmento. -Recife: O Autor, 2015. 200 folhas, il., gráfs., tabs. Em primeiro lugar, agradeço a Deus por todo o projeto que tem em minha vida, que vem sendo consolidado cada dia que passa e a cada fase que venço nesta jornada acadêmica. A minha mãe, Inês, por ser minha fortaleza e refúgio, me inspirando com seu jeito determinado de guiar a vida. Por me alimentar com seu amor e carinho, que me fortifica para as dificuldades diárias. Também destaco sua tolerância a minha ausência. Ao meu irmão, Carlos Felipe, por inspirar-me através de seu domínio da matemática pura e seu raciocínio lógico. Ainda destaco um espaço a minha cunhada, Sheyla e a meu sobrinho Rafael, que terá boas inspirações em sua árvore genealógica. Agradeço ainda a todos da minha família, por me apoiar e servir de exemplo com tantos pesquisadores e professores sempre a motivar-me. A minha namorada, Danielle, por sua paciência e compreensão à minha ausência. Pela ajuda nas horas difíceis e apoio constante nas dificuldades inerentes de uma pós graduação. Também pelo seu companheirismo em congressos e viagens. A meus amigos por compreenderem a minha ausência e me apoiarem sempre. E a meus colegas de trabalho por me apoiarem sempre. Principalmente Paulo Alison pela sua experiência em CFD. A todos os professores do programa de pós graduação em engenharia civil da UFPE que realizam suas atividades com grande dedicação. Destaco também o agradecimento a quem está por trás do funcionamento operacional da pós da UFPE, as servidoras Andrea e Claudiana, que sempre foram atenciosas e prestativas em seu trabalho. Ao meu coorientador, professor Antônio Oscar, por acreditar em mim, desde a graduação, onde iniciamos estudos ligados à ação do vento em edificações. Sou muito grato ao professor Oscar pela paciência e contribuição nos estudos, que foram de grande tamanho devido à sua larga experiência e conhecimento técnico. Em especial agradeço ao meu orientador, professor Paulo Marcelo Ribeiro, por toda a sua paciência e dedicação à pesquisa. Sou infinitamente grato pela sua contribuição na formação de um pesquisador. Com o prof. Paulo Marcelo aprendi bem mais que equações diferenciais ordinária ou método dos elementos finitos. Aprendi na verdade que ser professor extrapola a barreira da sala de aula, expandindo ao campo da curiosidade epistemológica. Sou extremamente grato pelo seu tempo gasto em diversas pesquisas em diversos campos da física e em especial na aerodinâmica de edificações, assunto que não é comumente abordado por engenheiros civis, principalmente calculistas, mas que foi um desafio abraçado por nós, que resultou em um final extremamente satisfatório. Professor Paulo Marcelo e Antônio Oscar, são as pessoas mais geniais que já conheci. Consegui unir os dois para um trabalho em um assunto que tenho grande apreço e curiosidade. Agradeço também a banca pela sua colaboração e dedicação para a melhoria deste trabalho. "A matemática é a única linguagem que temos em comum com a natureza". Stephen Hawking "A mente que se abre a uma nova ideia jamais voltará ao seu tamanho original".

The "input-output desideratum", outlined in the New Athens Charter, sets new requirements for urban designers. Nowadays, using modern techniques, we can solve weighty contemporary urban problems using such system of designing, which balances quantitative and qualitative parameters of the urban matter. The text presents the part of the designing system that uses methodology of the meteorology. Proper use of this system allows to control and design parameters of the socalled urban canopy. The urban canopy covers the area of reduced energy consumption and increased comfort of using the public space between the buildings constituting urban tissue. Urban canopy is characterized by multiplier effects, obtained -among others -thanks to the use of aerodynamics in urban design. Shaping buildings, supported by empirical method (with use of models), allows to implement the so-called filters and regulators postulated in the Charter: the elements that maintain the city's structure in balance

The “input-output desideratum”, outlined in the New Athens Charter, sets new requirements for urban designers. Nowadays, using modern techniques, we can solve weighty contemporary urban problems using such system of designing, which balances quantitative and qualitative parameters of the urban matter. The text presents the part of the designing system that uses methodology of the meteorology. Proper use of this system allows to control and design parameters of the socalled urban canopy. The urban canopy covers the area of reduced energy consumption and increased comfort of using the public space between the buildings constituting urban tissue. Urban canopy is characterized by multiplier effects, obtained - among others - thanks to the use of aerodynamics in urban design. Shaping buildings, supported by empirical method (with use of models), allows to implement the so-called filters and regulators postulated in the Charter: the elements that maintain the city's structure in balance.

In order to predict the laminar/turbulent transition on a hypersonic vehicle forebody at Mach numbers 4 and 6, the three-dimensional (3D) modal linear stability analysis is applied, coupled with the e N method. Nevertheless, N factors are unknown for wind tunnel conditions. Experimental investigations have been carried out on a §at plate in the blowdown wind tunnel T-313 of ITAM RAS (Novosibirsk). At M ∞ = 2 to 6, the position of laminar/turbulent transition was measured by both Pitot tube and thermocouples. Then, stability analysis allows computing N factors at transition on the §at plate: they are about 3 ∼ 4, typical of conventional wind tunnels. These §at plate correlations can then be used to predict the transition on the forebody in the same wind tunnel. Experiments for the forebody are currently in progress and will allow checking the predicted transition location.

This paper presents the coupled analysis performed in the frequency and time domain, considering a multi-purpose floating structure suitable for offshore wind and wave energy source exploitation. The floating structure encompasses an array of hydrodynamically interacting Oscillating Water Column (OWC) devices, moored through tensioned tethers as a Tension Leg Platform (TLP), and supports a 10 MW Wind Turbine (WT). The analysis is built to incorporate properly the solutions of the diffraction and the pressure- and motion-dependent radiation problems around the floating structure, the mooring lines characteristics, the OWCs characteristics, and the aerodynamics of the WT by accounting for the aerodynamic modelling of the rotor, the elastic modelling of the turbine components, namely the blades, the drive train, and the tower. Numerical results are obtained through the developed analysis methods, presenting the fundamental hydrodynamic properties of the platform, as well as the ultimat...

This paper summarizes the coupled hydro-aero-elastic analysis of a multi-purpose floating structure suitable for offshore wind and wave energy exploitation. The analysis incorporates properly the solutions of the diffraction and the pressure- and motion- dependent radiation problems around the floating structure and the aerodynamics of a 5 MW Wind Turbine (WT). Finite water depths are considered, the structure being floating under the action of regular surface waves. The platform encompasses three hydrodynamically interacting Oscillating Water Column (OWC) devices consisting of concentric vertical cylinders, moored through tensioned tethers in a TLP concept. Details concerning the numerical and experimental modelling of the system are presented and the numerical results are compared against experimental data. 

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Cross-flow fan propulsion has not been seriously considered for aircraft use since an Vought Systems Division (VSD) study for the U.S. Navy in 1975. A recent conceptual design study of light-weight, single seat VTOL aircraft suggest that rotary-engine powered cross-flow fans may constitute a promising alternative to the conventional lift-fan vertical thrust augmentation systems for VTOL aircraft. The cross-flow fan performance data obtained by VSD supported the hypothesis that they could be improved to the point where their thrust augmentation could be used in a VTOL aircraft. In this paper we report results of a NASA Glenn supported experimental and computational cross-flow fan investigation which is currently in progress and we provide an assessment of the potential suitability of crossflow fans for VTOL aircraft propulsion. The tests are carried out in the Turbopropulsion Laboratory of the Naval Postgraduate School, using an existing Turbine Test Rig as a power source to drive the crossflow fan. A 0.305 m (12-inch) diameter, 38.1 mm (1.5-inch) span cross-flow fan test article was constructed to duplicate as closely as possible the VSD fan so that baseline comparison performance data could be obtained. Performance measurements were taken over a speed range of 1,000 to 7,000 RPM and results comparable to those measured by Vought Systems Division were obtained. At 3,000 RPM a 2:1 thrust-to-power ratio was measured which dropped to one as the speed was increased to 6,000 RPM. Performance maps were experimentally determined for the baseline configuration as well as one with both cavities blanked off, for the speed range from 2,000 to 6,000 rpm. Using Flo++, a commercial PC-based computational fluid dynamics software package by Softflo, 2-D numerical simulations of the flow through the cross-flow fan were also obtained. Based on the performance measurements it was concluded that the optimum speed range for this rotor configuration was in the 3,000 to 5,000 rpm range. The lower speed producing the best thrust-to-power ratio and the upper speed range producing the highest efficiency over sizeable throttling range.

Laser-Doppler velocimetry measurements through a one millimeter hole in the casing of an annular turbine cascade were performed in the endwall region downstream of the blade row. Complementary threehole pressure probe measurements were also taken downstream of the nozzle blades, as well as blade surface pressure measurements. The object of this study was to devise methods for the measurement close to an endwall and to overcome the problems associated with optical access window contamination. The eventual aim of the project was to perform laser anemometry measurements in the tip leakage region of an operating turbine of comparable size. Good comparisons with numerical predictions of the flowfield were also obtained. P static pressure Pt stagnation pressure Po reference stagnation pressure Prat inlet total -to-exit static (at the hub) pressure ratio U mean axial velocity u' fluctuating axial velocity V mean circumferential velocity Vexit maximum exit plane velocity v' fluctuating circumferential velocity X axial direction Y tangential direction * Associate Professor, Member AIAA ** Lt. US Navy *** LCDR. US Navy

This study investigated the performance of blown airfoil. Two types of blown airfoil were developed. The integrated parts of the airfoils were investigated in the subsonic wind tunnel to study the aerodynamic forces. Each airfoil was implemented with a blower at different locations on the upper surface and was tested in the wind tunnel, with different Reynolds numbers, and with and without blower. The results showed that the airfoil with air blower produced a very significant additional 35% lift force compared to airfoil without air blower. The experimental result also exhibited 7% higher lift coefficient for air blower compared to numerical analysis.

The objective of this study is to develop direct numerical simulations (DNS) to investigate the aerodynamic performance, transition to turbulence, and to capture the laminar separation bubble occurring on a wind turbine blade. Simulations are conducted with spectral/hp element method to investigate the details of flow separation bubble over wind turbine blades with NACA-4412 airfoil at wide range of design parameters. This airfoil is chosen because recent studies have shown that it is challenging to capture the details of the flow instabilities and pressure fluctuations in the separated shear layer of wind turbines by experimental methods. Furthermore, owing to more accurate development of DNS, the separated bubbles at high Reynolds numbers are captured. The results show that the vortex structures shed from the trailing edge of the airfoil by raising the angle of attack (𝛼). Consequently, the fully turbulent flow develops downstream of the trailing edge (Karman vortex). Moreover, the pressure fluctuation significantly increased by raising 𝛼 . However, some rolling up of the flow structures, similar to Kelvin-Helmholtz rolls, on the pressure surface near the trailing edge, are observed at 𝛼 > 12 °. The separation point was delayed from Xsep/C=0.19 to 0.58 by decreasing 𝛼 from 16 to 0 at Re=5×10 4 .

Shape optimization is an indispensable step in any aerodynamic design. However, the inherent complexity and non-linearity associated with fluid mechanics as well as the high-dimensional design space intrinsic to such problems make airfoil shape optimization a challenging task. Current approaches relying on gradient-based or gradient-free optimizers are data-inefficient in that they do not leverage accumulated knowledge, and are computationally expensive when integrating Computational Fluid Dynamics (CFD) simulation tools. Supervised learning approaches have addressed these limitations but are constrained by user-provided data. Reinforcement learning (RL) provides a data-driven approach bearing generative capabilities. We formulate the airfoil design as a Markov decision process (MDP) and investigate a Deep Reinforcement Learning (DRL) approach to airfoil shape optimization. A custom RL environment is developed allowing the agent to successively modify the shape of an initially provided 2D airfoil and to observe the associated changes in aerodynamic metrics such as lift-to-drag (L/D), lift coefficient (C l ) and drag coefficient (C d ). The learning abilities of the DRL agent are demonstrated through various experiments in which the agent's objectivemaximizing L/D, maximizing C l or minimizing C d -as well as the initial airfoil shape are varied. Results show that the DRL agent is able to generate high performing airfoils within a limited number of learning iterations. The strong resemblance between the artificially produced shapes and those found in the literature highlights the rationality of the decision-making policy learned by the agent. Overall, the presented approach demonstrates the relevance of DRL to airfoil shape optimization and brings forward a successful application of DRL to a physics-based aerodynamics problem. As demand for air travel continues to grow, so are concerns regarding the environmental impacts of aviation. For aircraft, aerodynamic drag represents the main source of energy losses 1 . As such, its reduction could represent a 20 to 25% decrease in fuel burn 2 and lead to fewer emissions. An optimization process leading to an increase in the aerodynamic efficiency of aircraft components is needed. Here, we focus on the optimization of airfoil shapes. Relying on fluid mechanics, aerodynamic related problems exhibit non-linearity and are complex in nature 1,3 . Specifically, the problem at hand involves generating airfoils that achieve a desired performance. Formally, airfoil inverse design is described as the prediction of airfoil shapes based on given desired performance metrics 4 , making our problem an inverse design problem. Solving inverse problems is generally more difficult due to the non-injective nature of the physical phenomena 3 . In simpler terms, for a given desired performance, multiple shapes can exist 5 . Since there is a potentially infinite number of airfoil shapes, the problem is characterized by high-dimensionality. All together, airfoil shape optimization is a challenging task . In exploring the associated high-dimensional design space, current approaches iteratively evaluate the performance of a large number of airfoils through either physical testing (wind tunnel testing) or numerical simulations (Computational Fluid Dynamics or CFD). With numerical simulations, a gradient-based or gradient-free optimizer is used to guide the search towards the optimal shape. However, these approaches are limited due to the high dimension of the design space to be explored as well as the prohibitive computational cost of running a large number of high-fidelity aerodynamic simulations 9 . Moreover, both gradient-based and gradient-free approaches are data-inefficient since they do not utilize the knowledge gained from previous experiments 3 . To cope with this, supervised machine learning approaches to computational aerodynamic problems have been developed and have proven successful in addressing these limitations . In particular, a data-driven approach to the problem at hand could help alleviate the high complexity associated with the underlying physics 10 . However, since these methods rely on provided

A body of work has grown around the use of small amplitude traveling waves on aerodynamic and hydrodynamic surfaces for boundary layer control. In particular, when the traveling wave speed exceeds the free stream velocity, significant drag reductions have been shown in simulation. Building viable prototypes to test these hypotheses, however, has proven challenging. In this paper, we describe a candidate system for constructing structural airfoils and hydrofoils with embedded electromagnetic actuators for driving high velocity traveling waves. Our approach relies on the fabrication of planar substrates which are populated with electromagnetic components and then folded into a prescribed three dimensional structure with actuators embedded. We first specify performance characteristics based on hydrodynamic requirements. We then describe the fabrication of fiber-reinforced polymer composite substrates with prescribed folding patterns to dictate three dimensional shape. We detail the development of a miniaturized single-phase linear motor which is compatible with this approach. Finally, we compare the predicted and measured force produced by these linear motors and plot trajectories for a 200 Hz driving frequency.

The knowledge of reentry vehicles (RV) §ight characteristics regarding geometrical shape, dimensions, and mechanical properties is essential for precise prediction of their §ight trajectory, impact point, and possible deviations according to simulation uncertainties. The §ight characteristic estimations of existing RV require both body dimensions and mechanical properties of the objects. Due to comparatively simple and reliable methods of specifying the vehicle outer dimensions, e. g., photos and videomaterials, the estimation of mechanical properties is a subject of higher uncertainties. Within this study, a generic medium range ballistic missile (MRBM) RV was examined for several modi¦cations such as center of gravity (CoG) position, weight moment of inertia, and initial reentry §ight states. Combinations of these variables with constant aerodynamic properties for maximal lateral accelerations will be determined. Basing on these, potential evasion maneuver capabilities of the RV will be described.

In this study, a time-dependent investigation has been conducted to numerically analyze the impact of wind-driven surface fire on an obstacle located on sloped terrain downstream of the fire source. Inclined field with different upslope terrain angles of 0, 10, 20, and 30 • at various wind-velocities have been simulated by FireFoam, which is a large eddy simulation (LES) solver of the OpenFOAM platform. The numerical data have been validated using the aerodynamic measurements of a full-scale building model in the absence of fire effects. The results underlined the physical phenomena contributing to the impact of varying wind flow and terrain slope near the fire bed on a built area. The findings indicated that under a constant heat release rate and upstream wind velocity, increasing the upslope terrain angle leads to an increase in the higher temperature areas on the ground near the building. It is also found that raising the inclined terrain slope angle from 0 to 30 • , results in an increase in the integrated temperature on the surface of the building. Furthermore, by raising the terrain slope from 0 to 30 • , the integrated temperature on the ground for the mentioned cases increases by 16%, 10%, and 13%, respectively.

The combined effects of percent slope and fire intensity of a wind driven line fire on an idealized building has been numerically investigated in this paper. The simulations were done using the large eddy simulation (LES) solver of an open source CFD toolbox called FireFOAM. A set of three fire intensity values representing different heat release rates of grassland fuels on different inclined fuel beds have been modeled to analyze the impact of factors, such as fuel and topography on wind-fire interaction of a built area. An idealized cubic structure representing a simplified building was considered downstream of the fire source. The numerical results have been verified with the aerodynamic measurements of a full-scale building model in the absence of fire effects. There is a fair consistency between the modeled findings and empirical outcomes with maximum error of 18%, which acknowledge the validity and precision of the proposed model. The results show that concurrent increase of fire intensity and terrain slope causes an expansion of the surface temperature of the building which is partially due to the increase of flame tilt angle upslope on the hilly terrains. In addition, increasing fire intensity leads to an increase in the flow velocity, which is associated with the low-pressure area observed behind the fire front. Despite limitations of the experimental results in the area of wind-fire interaction the result of the present work is an attempt to shed light on this very important problem of fire behavior prediction. This article is a primary report on this subject in CFD modeling of the collective effects of fire intensity and sloped terrain on wind driven wildfire and its interaction on buildings.

This paper presents an investigation on the effect of fire intensity of a wind driven surface fire, similar to a large wildfire, on an idealized structure located downstream from the fire source. A numerical simulation was conducted using an open source CFD code called FireFOAM, which is a transient solver for fire simulation and turbulent diffusion flames, supported by a large eddy simulation (LES) solver for incompressible flow. The numerical data were verified using the aerodynamic experimental data of a full-scale building model with no fire effects. An idealized cubic obstacle representing a simplified building with the dimension of 6 × 6 × 6 m; is considered downstream from the fire source. Different fire intensity values of the fire line representing different grassland fuels were simulated to analyse the impact of wind-fire interaction on a built area. To solve the problem, a coupled velocity and pressure method was applied through a PIMPLE scheme in FireFoam solver of OpenFoam platform. There is a good agreement between simulated results and experimental measurements with a maximum error of 18%, which confirms the validity and accuracy of the model. The results showed that by increasing the fire intensity; the velocity of the crosswind stream increases, which causes low-density air and generates an extra stream behind the fire plume. It was also found that increasing fire intensity from 10 MW/m to 18 MW/m raises the integrated temperature on the ground near the building and on the surface of the building by 26%, and 69%, respectively.

This paper presents an investigation into the impact of wind speed on the interaction of wind driven surface fire with an idealized building structure. The open-source large eddy simulation (LES) fire dynamic solver, FireFOAM, was used to simulate fires burning with an intensity of 10 MW/m under different wind speeds. The numerical data was validated using a wind only simulation which compared aerodynamic data to the previous full size experimental and numerical studies. The results show the aerodynamic flow characteristics and their interaction with the idealized structure located downstream of the fire source. Increase in wind speed showed a linear relationship to increase in the coefficient of lift on the building. The local coefficient of pressure on the building was calculated which indicated significant risk of damage due to aerodynamic lift caused by buoyant fire updraft. The results also show that at a constant fire intensity, increasing wind speed leads to an increase in the average temperature of the domain downstream of the fire to a certain value and then decreases.

The combined effects of percent slope and fire intensity of a wind driven line fire on an idealized building has been numerically investigated in this paper. The simulations were done using the large eddy simulation (LES) solver of an open source CFD toolbox called FireFOAM. A set of three fire intensity values representing different heat release rates of grassland fuels on different inclined fuel beds have been modeled to analyze the impact of factors, such as fuel and topography on wind-fire interaction of a built area. An idealized cubic structure representing a simplified building was considered downstream of the fire source. The numerical results have been verified with the aerodynamic measurements of a full-scale building model in the absence of fire effects. There is a fair consistency between the modeled findings and empirical outcomes with maximum error of 18%, which acknowledge the validity and precision of the proposed model. The results show that concurrent increase of f...

In this study, a time-dependent investigation has been conducted to numerically analyze the impact of wind-driven surface fire on an obstacle located on sloped terrain downstream of the fire source. Inclined field with different upslope terrain angles of 0, 10, 20, and 30° at various wind-velocities have been simulated by FireFoam, which is a large eddy simulation (LES) solver of the OpenFOAM platform. The numerical data have been validated using the aerodynamic measurements of a full-scale building model in the absence of fire effects. The results underlined the physical phenomena contributing to the impact of varying wind flow and terrain slope near the fire bed on a built area. The findings indicated that under a constant heat release rate and upstream wind velocity, increasing the upslope terrain angle leads to an increase in the higher temperature areas on the ground near the building. It is also found that raising the inclined terrain slope angle from 0 to 30°, results in an i...

This paper presents an investigation on the effect of fire intensity of a wind driven surface fire, similar to a large wildfire, on an idealized structure located downstream from the fire source. A numerical simulation was conducted using an open source CFD code called FireFOAM, which is a transient solver for fire simulation and turbulent diffusion flames, supported by a large eddy simulation (LES) solver for incompressible flow. The numerical data were verified using the aerodynamic experimental data of a full-scale building model with no fire effects. An idealized cubic obstacle representing a simplified building with the dimension of 6 × 6 × 6 m; is considered downstream from the fire source. Different fire intensity values of the fire line representing different grassland fuels were simulated to analyse the impact of wind-fire interaction on a built area. To solve the problem, a coupled velocity and pressure method was applied through a PIMPLE scheme in FireFoam solver of OpenF...

The paper presents CAE MBS analysis of aircraft front landing gear behaviour in unusual situations that can be caused by unpredictable obstacles. Numerical tools were applied, because real investigations can be relatively expensive and dangerous. One of unusual maintenance condition assumed increasing of the aircraft vertical velocity, caused by a loss of uplift forces (result of decreasing the horizontal velocity to shorten the airfield length needed to dissipate aircraft energy). The other analyzed maintenance condition assumed the aircraft landing with horizontal velocity, increased of a large percentage in comparison with its maximum value allowed by the aircraft manufacturer. Simulation also provided the gear dynamics analysis while crossing over obstacles placed on slightly damaged or makeshift airfield. During CAE tests, Lagrange spring/dumper elements used to simulate the behavior of deformable tyre and shock absorber oil-gas mixture. Simulations proved that increasing the vertical velocity of 25% and the horizontal one of 15% is safe for the aircraft and it can operate on damaged airfields. Investigations proved that aircraft maintenance conditions might be safely expanded, in comparison with its manufacturer suggestions. It enables the manufacturer to look for new and aircraft-safe applications that require special landing capabilities: Special Team Transport or Medical Evacuation.

Due to complex surface structure, the aerodynamic behaviour of a tennis ball is significantly different compared to other sports balls. This difference is more obvious when spin is involved. Although several studies have been conducted on drag and lift in steady state condition (no spin ...

The primary objective of this paper is to conduct a comparative study on the number of blade and different blade angles of a domestic savonius vertical axis wind turbine with semicircular shaped blades under a range of wind speeds. A domestic scale 6bladed Savonius Vertical Axis Wind Turbine was manufactured to investigate the effect of blade number and blade angle on the maximum power generation by the turbine. Maximum power curves as a function of wind speeds were established for each configuration. The results show that the blade angle has positive effect to increase the power output of a Savonius turbine to a significant amount. The most efficient configuration is the 6bladed turbine with an angle of attack of 10°. This configuration generated 27% more power compared to the 0° angle of attack at the wind speed from 10 to 15 km/h.

In this paper, a special integrated plant/output-feedback controller optimization problem is studied, which optimizes a single plant parameter while satisfying open-and closed-loop static and dynamic performance requirements. Both polytopic model uncertainties and multi-mission optimization are considered in the integrated design optimization. A necessary and su cient condition is given for the solvability of such an optimization problem. Based on the condition, a design optimization method is presented in terms of linear matrix inequalities. An aircraft example is applied to demonstrate the proposed method.

Concerns on climate change and dwindling fossil fuel supply have renewed interest on alternative ways of harnessing renewable energy. Using rotating cylinders to generate lift from a fluid stream, a Magnus rotor can produce up to 10 times more lift compared to an airfoil. However, it is also producing more drag. Recent studies have demonstrated improvement on the aerodynamic efficiency of a Magnus rotor through the application of surface modifications such as grooves, bumps, dimples, and even changing the shape of the cylinder into a frustum. However, it is unknown which is most desirable among those modifications; moreover, if some may be combined for even better performance. This present study seeks to fill the mentioned research gap with the aid of computer simulation tool ANSYS CFX. Simulation results showed that modifying cylinder shape into a frustum generates the most lift force. However, it is also increasing the drag on the cylinder. Interestingly, a helical groove may be e...

In this paper we give a general framework for isotone optimization. First we discuss a generalized version of the Pool-Adjacent-Violators Algorithm (PAVA) to minimize a separable convex function with simple chain constraints. Besides of general convex functions we extend existing PAVA implementations in terms of observation weights, approaches for tie handling, and responses from repeated measurement designs. Since isotone optimization problems can be formulated as convex programming problems with linear constraints we then develop a primal active set method to solve such problem. This methodology is applied on specific loss functions relevant in statistics. Both approaches are implemented in the R package isotone.

Hybrid composite gear technology is being investigated to increase power density in rotorcraft drive systems. These gears differ from conventional steel gears in that the structural web material is replaced with a lightweight carbon fiber composite. Past studies have focused on performance of this technology under normal operating conditions, however, for this technology to be viable it must also withstand adverse conditions. The study presented here evaluates the performance of hybrid gears under loss-of-lubrication conditions in NASA Glenn Research Center's Contact Fatigue Test Facility. Two experiments are presented using small-scale 3.5 inch (8.9 cm) pitch diameter hybrid gears and compared to a baseline steel gear pair. Results of these tests show that there are limitations to the use of a hexagonal interlock pattern between the steel and composite. There is also evidence that the presence of polymer in the gear during an oil out event has a potential to increase time to failure. Further studies are planned to expand on these initial findings. ** This paper has been corrected from the original submitted to the conference. **

A computational fluid dynamics (CFD) method has been applied to gear configurations with and without shrouding. The goals of this work have been to validate the numerical and modeling approaches used for these applications and to develop physical understanding of the aerodynamics of gear windage loss. Several spur gear geometries are considered, for which experimental data are available. Various canonical shrouding configurations and free spinning (no shroud) cases are studied. Comparisons are made with experimental data from open literature, and data recently obtained in the NASA Glenn Research Center Gear Windage Test Facility, Cleveland, OH. The results show good agreement with the experiment. The parametric shroud configuration studies carried out in the Glenn experiments and the CFD analyses elucidate the physical mechanisms of windage losses as well as mitigation strategies due to shrouding and newly proposed tooth contour modifications.

An unstructured overset moving mesh CFD method is adapted, validated and applied to spinning gear systems with emphasis on predicting windage losses. Several spur gears and a disc, spinning in air at rotation rates up to 1200 s -1 are studied. It is observed that the CFD simulations return good agreement with measured windage power loss, as determined by the deceleration of the gears due to torques exerted by viscous and pressure forces on the gear surfaces. Turbulence modeling choices, the relative importance of viscous and pressure torques with gear speed, and the physics of the complex 3D unsteady flow field in the vicinity of the gear teeth are studied. The capabilities and challenges associated with the overset mesh approach for enclosed gear train applications are demonstrated.

High-Cycle Fatigue is a major problem facing the gas turbine industry today. It has been investigated by many researchers, using many different methods. Due to its highly complex nature, designers still do not have adequate tools to accurately predict the onset of high-cycle fatigue. A three-dimensional Navier-Stokes program was used to perform a study of the unsteady aerodynamics on a compressor rotor. The effect of aerodynamic detuning on the forced response of a rotor blade was compared to a baseline tuned rotor case. Detuning consisted of a ten percent decrease in circumferential spacing between alternate pairs of blades. The high-cycle fatigue effects of this detuning were investigated by examining the unsteady forces and moments on the rotor blades and inlet guide vanes. Computations were performed using a three-dimensional NASA research code (ADPAC) on a cluster of five desktop PCs. Computational times were on the order of several days for a grid of approximately 500,000 cells. These computations showed that detuning of the rotor blade could result in a reduction in the forced response of the IGV and rotor blades. This reduction came without much loss in overall performance (less than ten percent) and therefore may be a viable option to reduce high-cycle fatigue.

Computational fluid dynamics was used to investigate particle aspiration efficiency in lowmoving air typical of occupational settings (0.1-0.4 m s -1 ). Fluid flow surrounding an inhaling humanoid form and particle trajectories traveling into the mouth were simulated for seven discrete orientations relative to the oncoming wind (0°, 15°, 30°, 60°, 90°, 135° and 180°). Three continuous inhalation velocities (1.81, 4.33, and 12.11 m s -1 ), representing the mean inhalation velocity associated with sinusoidal at-rest, moderate, and heavy breathing (7.5, 20.8, and 50.3 l min -1 , respectively) were simulated. These simulations identified a decrease in aspiration efficiency below the inhalable particulate mass (IPM) criterion of 0.5 for large particles, with no aspiration of particles 100 µm and larger for at-rest breathing and no aspiration of particles 116 µm for moderate breathing, over all freestream velocities and orientations relative to the wind. For particles smaller than 100 µm, orientation-averaged aspiration efficiency exceeded the IPM criterion, with increased aspiration efficiency as freestream velocity decreased. Variability in aspiration efficiencies between velocities was low for small (<22 µm) particles, but increased with increasing particle size over the range of conditions studied. Orientationaveraged simulation estimates of aspiration efficiency agree with the linear form of the proposed linear low-velocity inhalable convention through 100 µm, based on laboratory studies using human mannequins.

A flow visualization study of several configurations of a jet-powered vertical takeoff and landing (VTOL) aircraft model during hover in ground effect was conducted. A surface oil flow technique was used to observe the flow patterns on the lower surfaces of the model. There were significant configuration effects. Wing height with respect to fuselage, the presence of an engine inlet duct beside the fuselage, and nozzle pressure ratio are seen to have strong effects on the surface flow angles on the lower surface of the wing. This test was part of a program to improve the methods for predicting the hot gas ingestion (HGI) for jet-powered vertical/short takeoff and landing (V/STOL) aircraft. The tests were performed at the Jet Calibration and Hover Test (JCAHT) Facility at Ames Research Center.

HE shock-shock phenomena occurring at supersonic and hypersonic flows present critical challenges in the design of supersonic and hypersonic vehicles. Aerodynamic heating and increased pressure loads are two such challenges as highlighted in the cases of the X-15 ...

A new way of assessing student learning in an aerodynamics course through the use of portfolios is presented. The approach is portable to any engineering course, with a few modifications depending on content.The main idea is to allow students more responsibility for their own learning. Instead of having everyone in the class perform identical activities (homework, experiments, projects, tests, etc.), a cadre of assignments is made available to them. Students choose and perform (within reason) the ones that suit them better in terms of their own strengths and learning styles. The ultimate goal is for each student to demonstrate a minimum level of competence in analytical, computational, experimental, design, communication, and team skills, while pursuing excellence in at least one from the first four categories.The paper describes the various assignments and options the students have for achieving the learning objectives of the course. It also discusses my observations on the effects...

This paper presents a potential flow model for the leading edge vortex over a two-dimensional flat plate at an angle of attack. The paper is an extension of a model by Saffman and Sheffield (1977). A sink has been added in this model in an effort to satisfy the Kutta condition at both the leading edge and the trailing edge of the plate. The introduction of the sink was inspired by the fact that most steady vortices in nature appear in combination with a flow feature which can be interpreted as a sink at their cores when the flow is analyzed in a two-dimensional observation plane. As in the Saffman and Sheffield model, the presence of a vortex results in increased lift; however, in the current model a unique vortex/sink position is found at each angle of attack. A comparison has also been made between the lift and the drag of this model and the corresponding results for two classical solutions of flow over a flat plate: (a) the fully attached flow with the Kutta condition satisfied a...

This paper describes a videogrammctric technique for determining aerodynamic loads based on optical elastic deformation measurements. The data reduction methods are developed to extract the normal force and pitching moment from beam deformation data. The axial force is obtained by measuring the axial translational motion of a movable shaft in a spring/bearing device. Proof-of-concept calibration experiments are conducted to assess the accuracy of this optical technique.

This paper presents a critical evaluation of the physical aspects of lift generation to prove that no lift can be generated in a steady inviscid flow. Hence, the answer to the recurring question in the paper title is negative. In other words, the fluid viscosity is necessary in lift generation. The relevant topics include D' Alembert's paradox of lift and drag, the Kutta condition, the force expression based on the boundary enstrophy flux (BEF), the vortex lift, and the generation of the vorticity and circulation. The physical meanings of the variational formulations to determine the circulation and lift are discussed. In particular, in the variational formulation based on the continuity equation with the first-order Tikhonov regularization functional, an incompressible flow with the artificial viscosity (the Lagrange multiplier) is simulated, elucidating the role of the artificial viscosity in lift generation. The presented contents are valuable for the pedagogical purposes in aerodynamics and fluid mechanics.

This paper presents a critical evaluation of the physical aspects of lift generation to prove that no lift can be generated in a steady inviscid flow. Hence, the answer to the recurring question in the paper title is negative. In other words, the fluid viscosity is necessary in lift generation. The relevant topics include D' Alembert's paradox of lift and drag, the Kutta condition, the force expression based on the boundary enstrophy flux (BEF), the vortex lift, and the generation of the vorticity and circulation. The physical meanings of the variational formulations to determine the circulation and lift are discussed. In particular, in the variational formulation based on the continuity equation with the first-order Tikhonov regularization functional, an incompressible flow with the artificial viscosity (the Lagrange multiplier) is simulated, elucidating the role of the artificial viscosity in lift generation. The presented contents are valuable for the pedagogical purposes in aerodynamics and fluid mechanics.