Aerodynamics

We show that the upscaling of wind turbines from rotor diameters of 15-20 m to presently large rotors of 150-200 m has changed the requirements for the aerodynamic blade element momentum (BEM) models in the aeroelastic codes. This is because the typical scales in the inflow turbulence are now comparable with the rotor diameter of the large turbines. Therefore, the spectrum of the incoming turbulence relative to the rotating blade has increased energy content on 1P , 2P , . . . , nP , and the annular mean induction approach in a classical BEM implementation might no longer be a good approximation for large rotors. We present a complete BEM implementation on a polar grid that models the induction response to the considerable 1P , 2P , . . . , nP inflow variations, including models for yawed inflow, dynamic inflow and radial induction. At each time step, in an aeroelastic simulation, the induction derived from a local BEM approach is updated at all the stationary grid points covering the swept area so the model can be characterized as an engineering actuator disk (AD) solution. The induction at each grid point varies slowly in time due to the dynamic inflow filter but the rotating blade now samples the induction field; as a result, the induction seen from the blade is highly unsteady and has a spectrum with distinct 1P , 2P , . . . , nP peaks. The load impact mechanism from this unsteady induction is analyzed and it is found that the load impact strongly depends on the turbine design and operating conditions. For operation at low to medium thrust coefficients (conventional turbines at above rated wind speed or low induction turbines in the whole operating range), it is found that the grid BEM gives typically 8 %-10 % lower 1 Hz blade root flapwise fatigue loads than the classical annular mean BEM approach. At high thrust coefficients that can occur at low wind speeds, the grid BEM can give slightly increased fatigue loads. In the paper, the implementation of the grid-based BEM is described in detail, and finally several validation cases are presented. Comparisons with blade loads from full rotor CFD, wind tunnel experiments and a field experiment show that the model can predict the aerodynamic forces in half-wake, yawed flow, dynamic inflow and turbulent inflow conditions.

This article shows qualitatively the yaw stability of a free yawing downwind turbine and the ability of the turbine to align passively with the wind direction, using a two degree of freedom model. An existing model of a Suzlon S111 upwind 2.1 MW turbine is converted into a downwind configuration with a 5 • tilt and a 3.5 • downwind cone angle. The analysis shows that the static tilt angle causes a wind speed dependent yaw misalignment of up to -19 • due to the projection of the torque onto the yaw bearing and the skewed aerodynamic forces caused by wind speed projection. With increased cone angles, the yaw stiffness can be increased for better yaw alignment and the stabilization of the free yaw motion. The shaft length influences the yaw alignment only for high wind speeds and cannot significantly contribute to the damping of the free yaw mode within the investigated range. Asymmetric flapwise blade flexibility is seen to significantly decrease the damping of the free yaw mode, leading to instability at wind speeds higher than 19 ms -1 . It is shown that this additional degree of freedom is needed to predict the qualitative yaw behaviour of a free yawing downwind wind turbine.

This article shows qualitatively the yaw stability of a free yawing downwind turbine and the ability of the turbine to align passively with the wind direction, using a two degree of freedom model. An existing model of a Suzlon S111 upwind 2.1 MW turbine is converted into a downwind configuration with a 5 • tilt and a 3.5 • downwind cone angle. The analysis shows that the static tilt angle causes a wind speed dependent yaw misalignment of up to -19 • due to the projection of the torque onto the yaw bearing and the skewed aerodynamic forces caused by wind speed projection. With increased cone angles, the yaw stiffness can be increased for better yaw alignment and the stabilization of the free yaw motion. The shaft length influences the yaw alignment only for high wind speeds and cannot significantly contribute to the damping of the free yaw mode within the investigated range. Asymmetric flapwise blade flexibility is seen to significantly decrease the damping of the free yaw mode, leading to instability at wind speeds higher than 19 ms -1 . It is shown that this additional degree of freedom is needed to predict the qualitative yaw behaviour of a free yawing downwind wind turbine.

Offshore wind turbines are designed and analyzed using comprehensive simulation tools (or codes) that account for the coupled dynamics of the wind inflow, aerodynamics, elasticity, and controls of the turbine, along with the incident waves, sea current, hydrodynamics, mooring dynamics, and foundation dynamics of the support structure. This paper describes the latest findings of the code-to-code verification activities of the Offshore Code Comparison Collaboration Continuation project, which operates under the International Energy Agency Wind Task 30. In the latest phase of the project, participants used an assortment of simulation codes to model the coupled dynamic response of a 5-MW wind turbine installed on a floating semisubmersible in 200 m of water. Code predictions were compared from load case simulations selected to test different model features. The comparisons have resulted in a greater understanding of offshore floating wind turbine dynamics and modeling techniques, and be...

The objective of the present work is to present the latest results in effects of including large blade deflections in aeroelastic calculations and to quantify the errors of the linearized approach for a modern flexible mega-watt sized turbine. In this paper three nonlinear approaches have been used to quantify the effects of large deflections. One approach is a rather simple extension of the already existing aeroelastic code HAWC, which changes the calculation basis so that small deflections are assumed around an initially large deflected blade shape. The second approach is based on a multibody formulation of the beam element used in HAWC, where nonlinear effects are included as a result of modelling the blade using several interconnected bodies. The third approach is a corotational finite element formulation where each element can be regarded as linear and the nonlinear effects are included by translation and rotation of the local element coordinate system. The results from the three nonlinear approaches are compared with results obtained by the existing HAWC, and the impact on the following main effects (due to large deflections) are addressed: 1. The reduction of the effective radius. 2. The reduction of power production due to the reduced effective radius. 3. The effect of increased torsional inertia of the blade due to the deflected shape. 4. The change of blade frequencies due to changes in inertia and coupling effects.

The present research study presents the results of the aerodynamic analysis of a USB AERO aircraft using computational fluid dynamics (CFD) in operational conditions of cruise flight at an angle of attack of 3.5 degrees. The ANSYS FLUENT computational tool was used, with which the lift, drag and longitudinal momentum coefficients were determined. Additionally, the aircraft was analyzed at different angles of attack in order to determine aerodynamic characteristics such as the highest lift coefficient and the loss angle, in addition to establishing the maximum aerodynamic efficiency.

Understanding the performance of penetrators and aerodynamic bodies of revolution (missiles, rockets, aircraft noses, etc.) requires a close look at the drag and the heat transfer characteristics at a wide range of supersonic flight conditions. This research utilizes computational study and compares the aerothermal loads of supersonic flows around a new penetrator geometry, derived based on the optimization of the nose factor, to those of other common projectile shapes: conical, tangent-ogive, and power series nose geometries. The abundance of research on 0.3-caliber projectile made the choice for this research simple in order to maximize our ability to compare to the existing data. The comparison of our 0.3 caliber cylindrical projectile with other geometries shows that within the range of 500–1500 m/s flight speed the new geometry has the lowest aerodynamic drag, lowest body temperature, and least amount of heating.

In the current study, a rigid body penetrator nose shape that is optimized for minimum penetration drag (Jones et al., 1998) has been tested to determine the aerodynamic drag of such a penetrator in comparison to three additional nose shapes. Other nose shapes ...

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The phenomenon of flutter is a self-excited aeroelastic vibration which can occur on flexible aerodynamic structures moving within a fluid domain, whereby the structure absorbs energy from the fluid; this phenomenon is related to variations in configuration with respect to the relative wind that the structure undergoes as a consequence of its oscillations. Based on the aeroelastic model of a three-degree-of-freedom airfoil, an adaptive controller for flutter suppression is designed and investigated in this work. A population decline swarm optimization P D SO is used to find the optimal parameters of the controller to set a gain scheduling approach to make the control adaptive in velocity. The integral of time absolute error is minimized to attribute a greater weight to the divergence error that can manifest far after the disturbing instant. Numerical results are reported to show how the gain scheduling control allows to obtain damped oscillation beyond the critical speed without destructive picks.

The SPARK3D and SPARK3D-PNS computer programs have been developed to model 3-D supersonic, chemically reacting flow-fields. The SPARK3D code is a full Navier-Stokes solver, and is suitable for use in scramjet combnstors and other regions where recirculation

The work presents a correction technique to compute unsteady transonic pressure distributions and aeroelastic stability in this flow regime. The methodology is based on corrections of pressure distributions by the weighting of the lifting surface self-induced downwash, resulting from aeroelastic structural displacements or prescribed motions. The correction of pressure distributions through the weighting of the lifting surface self-induced downwash is also known as downwash weighting method. This method has been enhanced leading to a new downwash correction technique. This extended downwash correction method led to a rational formulation named as "successive kernel expansion method" (SKEM). The unsteady pressures and aeroelastic stability boundaries computations using such method led to good agreement with experimental measurements. This procedure is a rapid form to compute the transonic flutter speed boundaries, compared to computational aeroelasticity and experimental techniques.

Small unmanned aerial vehicles (UAVs) face flying quality problems different from those encountered by larger aircraft. The lower airspeeds and small dimensions make these vehicles more susceptible to gusts and stability and control issues, which may render the aircraft difficult to fly. Moreover, due to many factors, UAVs are often built with a considerable degree of uncertainty regarding their aerodynamic properties and flying quality. The resulting aircraft may present poor stability and handling characteristics. This work presents the conceptual design of a robust stability augmentation system (SAS), aimed at increasing stability characteristics and protecting aircraft prone to flying quality problems. In order to deal with parametric uncertainties, the controller was designed with the robust H-infinity technique. The design process is presented, and a parametric aircraft model is provided, together with longitudinal stability and control derivatives. Simulations are presented t...

Three-dimensional, compressible turbulent boundary-layer calculations have been performed for the finite supercritical wing of the NASA modified F8 transonic research airplane. Data on the boundary-layer thickness, displacement thickness, skin friction components, and integrated streamwise skin friction are presented for points along the streamwise stations of which the pressure measurements were previously made. Representative velocity profiles are shown, and boundary-layer-thickness contour plots and skin-friction vector plots are presented. Results are given for a Reynolds number of 1.5 million per foot, and for Mach numbers of 0.50 and 0.99.

While many experimental studies use springs to model the bending and torsional motions of a fluttered wing in wind tunnel experiments, the mass of the spring is often neglected in flutter calculation. In large test facilities, the spring mass is usually small compared to the mass of the wing. For smaller wind tunnels, however, the mass of the springs is larger relative to the mass of the test wing, and so perhaps should not be neglected. The purpose of this dissertation is to determine the sensitivity of flutter measurements to non-negligible spring mass effects, and thereby qualify a source of uncertainty present in a wide range of flutter experiments reported in the literature. For this purpose of research, two sets of experimental apparatus were designed and built to demonstrate classical two-degree of freedom flutter in open-return, low-speed wind tunnel in the Aerospace and Engineering Mechanics Department at university of Minnesota. In the first set-up, torsion and tension springs were used to provide the pitch and plunge motions, while in the second set-up, tension springs only were used. This apparatus was used to experimentally determine flutter speed for a range of supporting springs. Classical aerodynamic theory was used to calculate flutter speeds to determine how to model added mass due to supporting springs so as to make theory and experiment agree.

An Effective Dimensional Inspection Method Based on Zone Fitting. (December 2004) Nachiket Vishwas Pendse, B. Eng., Government College of Engineering, Pune, India Co-Chairs of Advisory Committee: Dr. Richard Alexander Dr. Jyhwen Wang Coordinate measuring machines are widely used to generate data points from an actual surface. The generated measurement data must be analyzed to yield critical geometric deviations of the measured part according to the requirements specified by the designer. However, ANSI standards do not specify the methods that should be used to evaluate the tolerances. The coordinate measuring machines employ different verification algorithms which may yield different results. Functional requirements or assembly conditions on a manufactured part are normally translated into geometric constraints to which the part must conform. Minimum zone evaluation technique is used when the measured data is regarded as an exact copy of the actual surface and the tolerance zone is ...

The multi-copters are one of the important aircrafts in the world because they are used in both military and civil application. The problem of these aircrafts is the low efficiency of its propellers. That's why, it is necessary to study the aerodynamic structure around every rotor. In this paper, a computer simulation has been done to study the aerodynamic structure around a NACA 6409 airfoil rotor. The numerical model is based on the resolution of the Navier -Stockes equations with a standard k-ε model. Then, the finite volume discretization of these equations leads to solve it. The local characteristics of the aerodynamic structure are extracted using the software Solidworks Flow Simulation and the validation is done with comparison with anterior result of Alexandrov .

In this paper, a computer simulation has been done to study the aerodynamic structure around a X5C-02 main blades propeller. The numerical model is based on the resolution of the Navier-Stokes equations with a standard k-ε model. The local characteristics are determined using the software "Solidworks Flow Simulation". The software gives us the opportunity to extract the global result of this system which is the force of the thrust. The validation of this result has been done using an experimental protocol designed in the laboratory named brushless motor test bench. In this paper, we have described the experimental set up and we have compared it with the numerical curve using two meshes.

When multiple instruments are used in tandem it is possible to obtain more complete information on particle transport and physicochemical properties than can be obtained with a single instrument. This article discusses tandem measurements in which submicrometer particles classified according to electrical mobility are then characterized with one or more additional methods. Measurement combinations that are summarized here include mobility plus mass, aerodynamic (or vacuum aerodynamic) diameter, integrated or multiangle light scattering, composition by single particle mass spectrometry, electron microscopy, and so on. Such measurements enable intercomparisons of different measures of size including mobility diameter, optical size, aerodynamic diameter, volume (for agglomerates and nanowires), length (for nanowires), and mass, even for particles that are morphologically and chemically complex. In addition, the article summarizes the use of tandem techniques to measure various transport properties (e.g., dynamic shape factor, sedimentation speed, diffusion coefficient) and physicochemical properties (e.g., mixing state, shape, fractal dimension, density, vapor pressure, equilibrium water content, composition). In addition to providing an overview of such tandem measurements we describe previously unreported results from several novel tandem measurement methods.

Uncertainty in aerodynamic load prediction is an important parameter driving the price of wind energy, especially for offshore locations. Blade Element Momentum (BEM) theory is the current standard for estimating the wind forces in load case calculations. The variety between the several engineering extensions used in different BEM implementations is huge. In addition to that, the assumption of radial independence of the annuli and the lack of wake modelling are well known shortcomings of this method. A more detailed approach to model the rotor aerodynamics is presented by a vortex line method with a free vortex wake. Contrary to the BEM method, it is possible to accurately simulate innovative rotor geometries exhibiting distributed control or non-straight blades. A survey is made to investigate the influence of the various modelling options for several operating conditions. Firstly a rigid turbine is subject of investigation by means of a comparison to the NASA-AMES and MEXICO wind ...

The present paper addresses the process of preliminary design of low pressure fan and outlet guide vane (OGV) of a boundary layer ingestion propulsion system. The tail-cone thruster systems of NASA's STARC_ABL adopts axisymmetric BLI type inlet as opposed to other embedded engine systems. Thus, the focus of the present work is placed on maximizing the efficiency of the fan and OGV stages under a significant radial distortion. A parameterization with B-spline function for camber line angles, metal chord, thickness distribution and stacking axis of blades are presented. The flowpath lines are also parameterized by B-spline function and aggregated in the design system of blades. The design optimization with evolutionary algorithm is performed with constraints of fan pressure ratio, OGV exit swirl angle and nozzle exit properties. The inlet conditions for the turbo-machinery CFD domain and the design goal of the fan stage are driven by propulsion airframe integration (PAI) model that uses a 3-D unstructured RANS solver and actuator disk model. The expected power saving of the BLI propulsor is quantified via PAI analysis and the resulting preliminary design of the fan stages is compared with clean inlet flow propulsor.

A parallelized design optimization approach is presented for a subsonic S-shaped intake using aerodynamic sensitivity analysis. Two-equation turbulence model is adopted to predict the strong counter vortices in the S-shaped duct more precisely. Sensitivity analysis is performed for the three-dimensional Navier-Stokes equations coupled with two-equation turbulence models using a discrete adjoint method. For code validation, the result of the flow solver is compared with experiment data and bench marking data of other computation researches. To study the influence of turbulence models and grid refinement in the duct flow analysis, the results using several turbulence models are compared with each other on various grid systems. The adjoint variable code is validated by comparison with the complex step derivative results. And to guarantee a sufficient design space, NURBS equations are applied as a new shape function to modify the duct geometry freely. The capability and the efficiency of the present design tools are successfully demonstrated in three-dimensional subsonic inlet flow analysis and design optimization.

Aerodynamic bearings have received considerable attention in recent decades and are increasingly being used in applications where high speed, low loads and high precision are required. Aerodynamic applications mainly concern auxiliary power units (APU) and air-conditioning machines (ACM). From the industrial point of view, the static and dynamic characteristics of these bearings rotating at very high speed must be determined. According to the literature, studies carried out on this type of bearing consider the elastic deformations of the foils due to the pressure generated in the air film. The linear approach is from time to time adopted for the prediction of the dynamic behavior of these bearings, which is not always justified. This paper aims to present a step towards a better mastery of the non-linear dynamic behavior of a flexible rotor-air bearing system. We will focus on finite element modeling (FEM) of the non-linear isothermal elasto-aerodynamic lubrication problem in the ca...

The determination of Lagrangian Coherent Structures (LCS) is becoming very important in several disciplines, including cardiovascular engineering, aerodynamics, and geophysical fluid dynamics. From the computational point of view, the extraction of LCS consists of two main steps: The flowmap computation and the resolution of Finite Time Lyapunov Exponents (FTLE). In this work, we focus on the design, implementation, and parallelization of the FTLE resolution. We offer an in-depth analysis of this procedure, as well as an open source C implementation (UVaFTLE) parallelized using OpenMP directives to attain a fair parallel efficiency in shared-memory environments. We have also implemented CUDA kernels that allow UVaFTLE to leverage as many NVIDIA GPU devices as desired in order to reach the best parallel efficiency. For the sake of reproducibility and in order to contribute to open science, our code is publicly available through GitHub. Moreover, we also provide Docker containers to ease its usage.

This article considers the distribution of the pressure coefficient on the surface of a modular house model in order to further assess the possibility of operation of a thermosyphon solar collector integrated into the external protection. The experiment was planned to estimate the factors influencing the value of the aerodynamic coefficient. The results of experimental studies conducted in a wind tunnel are presented. The obtained graphical dependences were compared with the results of computer simulations and convergence was evaluated.

This dissertation presents a simulation-based analysis of the influence of hub cavities on the performance of shrouded stator axial compressors. The study investigates the impact of hub cavities on the efficiency of a three-stage axial compressor, utilizing Computational Fluid Dynamics (CFD) tools, including CAD for geometry creation, TurboGrid for meshing, and ANSYS CFX for the simulation. The methodology encompasses the modelling of two configurations: one with hub cavities and one without, allowing for a comparative analysis of compressor performance. Key performance indicators, such as efficiency, static pressure distribution, and leakage flow through streamlines, are analysed in detail. Static entropy plots are used to identify loss areas, while total pressure analysis from hub to shroud offers further insights into the effects of hub cavity presence on the overall flow behaviour. The results indicate that the inclusion of hub cavities influences compressor efficiency and blade loading, which is critical for optimizing axial compressor design. This study provides a comprehensive understanding of the role of hub cavities in axial compressors, offering valuable insights for future advancements in turbine and compressor technologies.

A mixed-type discontinuous Galerkin (DG) framework based on the second-order Boltzmann kinetic equation [1] is presented for hypersonic rarefied and low Mach number microscale gas flows. An explicit modal DG scheme on unstructured triangular/tetrahedral meshes is considered for solving the multi-dimensional conservation laws in conjunction with non-Newtonian type nonlinear coupled constitutive relations (NCCR) arising from the high degree of thermal non-equilibrium [2-5]. The verification of the DG scheme was achieved by comparing numerical solutions of a stiff problem of the shock structure with corresponding analytical solutions for all Mach numbers; not only the inner shock structure profiles but also the differential and integral quantities of the shock structure like the thickness, the asymmetry, and the density-temperature separation distance. In addition, the DG scheme was validated by investigating the hypersonic rarefied and low-speed microscale gas flows past cylinder, sph...

The ability to calculate aerodynamic heating and surface temperature is essential to ensure proper design of aircraft components in high speed flight. In this study, various empirical formulas for efficiently calculating aerodynamic heating of aircraft were first analyzed. A simple computational code based on empirical formulas was developed and then compared with commercial codes; ANSYS FLUENT based on the Navier-Stokes-Fourier equation, and ThermoAnalytics MUSES based on an empirical formula. The code was found to agree well with the results of FLUENT in the wall and stagnation point temperatures. It also showed excellent agreement with MUSES, within 1% and 5% in temperature and heat flux, respectively.

In-flight icing is a critical technical issue for aircraft safety and, in particular, ice accretions on aircraft surfaces can drastically impair aerodynamic performances and control authority. In order to investigate icing effects on the aerodynamic characteristics of KC-100 aircraft, a state-of-the-art CFD code, FENSAP-ICE, was used. A main wing section and full configuration of KC-100 aircraft were considered for the icing analysis. Also, shapes of iced area were calculated for the design of anti-/de-icing devices. The iced areas around leading edge of main wing and horizontal tail wing were observed maximum 7.07% and 11.2% of the chord length of wing section, respectively. In case of wind shield, 16.7% of its area turned out to be covered by ice. The lift of KC-100 aircraft were decreased to 64.3%, while the drag was increased to 55.2%. 초 록

For the Mach reflection (MR) of symmetric shock waves of opposite families, only the wave configuration of an overall Mach reflection (oMR) consisting of two direct Mach reflections (DiMR+DiMR) is theoretically admissible. For asymmetric shock waves, an oMR composed of a DiMR and an inverse Mach reflection (InMR) is possible if the two slip layers assemble a converging-diverging stream tube, while an oMR including two inverse Mach reflections (InMR+InMR) is absolutely impossible. In this paper, an overall Mach reflection configuration with double inverse MR patterns is computationally confirmed using the computational fluid dynamics technique. The aerodynamic mechanism behind such an abnormal wave pattern is illustrated. Classical two- and three-shock theories are also applied for the theoretical analysis.

Ceiling fans play a pivotal role in indoor cooling and thermal comfort. In this paper a computational framework, validated by experimental data, is presented for the design enhancement of ceiling fan blades with the objective of enhancing energy efficiency. A parametric study is performed by steady-state numerical simulation of three-dimensional airflow. Specifically, the parameters considered in the study are rake angle, bend angle and bend position. Rated air delivery, power consumption and service value at different rotational speeds are set as performance measure. The recommended geometry from the parametric study is tested and compared with the original geometry. The results indicate that airflow and service value increase by 21% and 54% respectively at 300 revolutions per minute and power consumption is reduced by 22%.

This paper aims to present specific methods for optimizing the design of micro propellers for small Reynolds numbers. In order to better understand the aim of this contribution, the effects of a micro propeller on the aerodynamic surfaces of a micro air vehicle (for example a flying wing configuration) are presented together with the analysis of the specific tools for the design of micro propellers. The final part aims to renew the interest in predicting the influence of the propeller-wing flow interaction on the aerodynamic characteristics of deflected slipstream and small flying wing MAV.

Summary This paper presents an overview of results from the wind tunnel test of a 1/4-scale V-22 proprotor in the Duits-Nederlandse Windtunnel (DNW) in The Netherlands. The small-scale proprotor was tested on the isolated rotor configuration of the Tilt Rotor Aeroacoustic Model (TRAM). The test was conducted by a joint team from NASA Ames, NASA Langley, U.S. Army Aeroflightdynamics Directorate,

Spatio-Temporal Flow Structure over a NACA-0015 Airfoil under the influence of ZNMF Jet Flow Control CALLUM ATKINSON, NICO-LAS BUCHMANN, JULIO SORIA, Monash University -The spatio-temporal flow structure associated with Zero Net Mass Flux (ZNMF) jet forcing at the leading edge of a NACA-0015 airfoil (Re = 30000, AoA = 18 deg) is investigated using highrepetition rate Particle Image Velocimetry (HR-PIV). In the absence of forcing, flow separation occurs at the leading edge, while ZNMF jet forcing at a frequency of f+ = 1.3 leads to a nearly complete reattachment with a 45% lift increase. The structure and dynamics associated with both the forced and unforced case are considered and the dominant frequencies are identified. A triple-decomposition of the velocity field is performed to identify the spatio-temporal perturbations produced by the ZNMF jet forcing. This forcing results in a reattachment of the flow, which is caused by the generation of large-scale vortices that entrain high momentum fluid from the freestream. Forcing produces a series of vortices that are advected parallel to the airfoil surface. Potential mechanisms by which these vortices affect the flow reattachment are discussed.

This paper describes tuning concepts for passive devices aimed at load alleviation in wind turbines. Two types of tuning are considered: inertial and aerodynamic. The first concept is illustrated with reference to a passive flap, while the second with reference to a passive tip. In both cases, the goal is to reduce loads with devices that are as simple as possible, and do not require sensors nor actuators. The main features and critical issues of each concept are highlighted and illustrated with reference to a large conceptual 10 MW wind turbine.

This paper describes tuning concepts for passive devices aimed at load alleviation in wind turbines. Two types of tuning are considered: inertial and aerodynamic. The first concept is illustrated with reference to a passive flap, while the second with reference to a passive tip. In both cases, the goal is to reduce loads with devices that are as simple as possible, and do not require sensors nor actuators. The main features and critical issues of each concept are highlighted and illustrated with reference to a large conceptual 10 MW wind turbine.

This paper investigates the load alleviation capabilities of an articulated tip device, where the outermost portion of the blade can rotate with respect to the rest of the blade. Passive, semi-passive and active solutions are developed for the tip rotation. In the passive and semi-passive configurations tip pitching is mainly driven by aerodynamic loads, while for the active case the rotation is obtained with an actuator commanded by a feedback control law. Each configuration is analyzed and tested using a high-fidelity aeroservoelastic simulation environment, by considering standard operative conditions as well as fault situations. The potential benefits of the proposed blade tip concepts are discussed in terms of performance and robustness.

Wind energy is one of the renewable energy resources that is gaining attention from industry players and researchers. In the last few years, there is an increasing interest in small-scale wind turbines as a power generator in built environments as the urgency to reduce carbon footprint in urban areas increases as well as reducing adverse effects of fossil fuels on human health and the environment. Generally, wind turbines can be categorized into two categories which are horizontal axis wind turbines (HAWTs) and vertical axis wind turbines (VAWTs). VAWTs have good potentials to be developed considering their suitability to be used in complex wind conditions associated with built environments. However, the number of research, publications, as well as basic understanding of flow phenomena associated to the performance of VAWTs such as dynamic stall, flow separation, flow curvature effect and blade-wake interaction are scarce. These flow phenomena are attributed by operational and geometrical parameters that significantly affect the overall performance of VAWTs that includes turbine power generation and aerodynamic characteristics. This paper provides a review and discussion of the effects of various design parameters such as blade profile, blade pitch angle and turbine solidity on the performance of VAWTs and serves as a basic guideline to the designer in designing an ideal VAWT.

Tenaga angin merupakan salah satu sumber tenaga keterbaharuan yang berpotensi sebagai alternatif kepada penjanaan tenaga secara konvensional melalui pembakaran arang batu dan bahan api fosil yang menjadi penyumbang utama kepada perubahan iklim. Sejak kebelakangan ini, kajian tentang turbin angin lebih tertumpu kepada turbin angin paksi menegak jenis Darrieus berskala kecil yang lebih sesuai untuk digunakan di kawasan angin berkelajuan rendah. Justeru, kajian ini dijalankan bertujuan untuk menganalisa secara berangka, kesan kepaduan, dengan mengubah diameter turbin, terhadap prestasi kuasa VAWT menggunakan teknologi perkomputeran dinamik bendalir (CFD). Satu siri simulasi CFD dua dimensi telah dijalankan ke atas VAWT 3-bilah yang diperlengkap dengan bilah jenis NACA0018. Penilaian prestasi kuasa terhadap 3 konfigurasi turbin dengan diameter yang berbeza, iaitu 1.0 m, 0.6 m dan 0.43 m telah dijalankan pada julat operasi kelajuan yang besar dengan kelajuan pengaliran masuk angin ditetapkan pada 8.0 m/s. Hasil simulasi jelas memperlihatkan bahawa turbin angin berdiameter besar menunjukkan prestasi yang baik pada nilai λ yang tinggi dan mempunyai julat operasi yang besar manakala turbin angin berdiameter kecil menjana kuasa lebih banyak pada nilai λ yang rendah dan mempunyai keupayaan mula diri yang lebih baik. Hasil kajian ini dapat membantu para penyelidik memahami dengan lebih mendalam kesan kepaduan turbin terhadap prestasi VAWT seterusnya menghasilkan rekaan ideal VAWT yang boleh beroperasi dalam keadaan angin yang kompleks.

Currently the development of wind energy devices, either the horizontal or vertical axis wind turbines, are mainly focused on the use of orthogonal wind flows to generate on-site power. However, in an urban environment, the vertical axis wind turbine is thought to be better suited for building integrated applications due to its durability and better performance in skewed and turbulent flows compared to the more common horizontal axis wind turbine. Application of wind turbines in skewed flow is a subject of increasing interest due to the improved power output of turbines in this wind condition. Skewed flow in the built environment can be referred to as the deflected wind vector at a roof that is not horizontal. Therefore, there exists a potential for better diffusion of renewable energy in the urban built environment, especially in the implementation of vertical axis wind turbines on rooftops. This study provides a critical review of the skewed wind flow phenomena, the physical chara...

The technological possibility of changing the heat transfer resistance coefficient of window profiles made of various materials in various ways without changing the thickness of the profile and without changing equipment is shown.Показана технологічна можливість зміни коефіцієнта опору теплопередачі віконних профілів, виготовлених з різних матеріалів різними способами без зміни товщини профілю та без переналагодження обладнання.Метою даної роботи є пошук шляхів зміни опору теплопередачі віконного профілю виготовленого з різних матеріалів в залежності від потреб споживачів, які не потребують переналагодження обладнання

A number of existing and emerging concepts for formulating solution algorithms applicable to multidisciplinary inverse problems involving aerodynamics, heat conduction, elasticity, and material properties of arbitrary three-dimensional objects are briefly surveyed. Certain unique features of these algorithms and their advantages are sketched for use with boundary element and finite element methods.

This work is focused on studying the aerodynamic benefits of surface heating of airfoil in low Reynolds number flow. Numerical simulations of NACA 0012 airfoil in a flow of Reynolds number 2.5 10 5 were performed employing Transition SST turbulence model. The airfoil was heated at multiple zones and the heat supplied came via two sources: a constant heat source and a time-varying heat source. It was observed that heating the lower nose of the airfoil with a constant heat source shows drag reduction at all angles of attack and periodically heating the same zone gives more significant reduction for 0 o to 6 o AOA.

Compressible DNS of transitional and turbulent flow in a low pressure turbine cascade 1 RAJESH RANJAN, SURESH DESHPANDE, ROD-DAM NARASIMHA, JNCASR -Direct numerical simulation (DNS) of flow in a low pressure turbine cascade at high incidence is performed using a new in-house code ANUROOP. This code solves compressible Navier-Stokes equations in conservative form using finite volume technique and uses kinetic-energy consistent scheme for the flux calculations. ANUROOP is capable of handling flow past complex geometries using hybrid grid approach (separate grid topologies for the boundary layer and rest of the blade passage). This approach offers much more control in mesh spacing and distribution compared to elliptic grid technique, which is used in many previous studies. Also, in contrast to previous studies, focus of the current work is mainly on the boundary layer flow. The flow remains laminar on the pressure side of the blade, but separates in the aft region of the suction side leading to transition. Separation bubbles formed at this region are transient in nature and we notice multiple bubbles merging and breaking in time. In the mean flow however, only one bubble is seen. Velocity profiles very near to the leading edge of the suction side suggest strong curvature effect. Higher-order boundary layer theory that includes effect of curvature is found to be necessary to characterize the flow in this region. Also, the grid convergence study reveals interesting aspects of numerics vital for accurate simulation of this kind of complex flows.

Extensive unstructured-grid CFD analysis has been performed for predicting performance of a twin-engine commercial transport airplane in landing configuration. The objective of the work was to identify and resolve complex gridding and solver related issues relevant to accurate prediction of complex flow physics associated with airplane high-lift systems. A variety of grid generation and CFD solution techniques were investigated for their efficacy in predicting performance of a complete airplane including high-lift devices e.g., multiple flaps and slats, and nacelle chines. Both steady and unsteady Reynolds Averaged Navier-Stokes (RANS) solution techniques were utilized. The role of relevant flowphysics phenomena in attainment of maximum lift as well as computational requirements for adequately modeling these phenomena were investigated. Computed aerodynamic forces are compared with available wind-tunnel test data.