Flow visualization studies of VTOL aircraft models during Hover in ground effect

2013

This paper presents a detailed experimental study of a plunging jet on a free liquid surface. An experimental characterization facility is designed and constructed for generating a vertical round water jet impinging on a free surface of a pool. The experimental analysis focuses on the jet penetration depth, its relation to impact velocity V j and free jet falling length L j . The results obtained are compared with previous studies. The flowmap for four different regimes, in terms of impact jet velocity is obtained. The details of the two-dimensional velocity field below the pool liquid free surface under a no-entrainment regime, are obtained using Particle Image Velocimetry (PIV) and reveal the spatial extent of the entrained region. The initial impact process and air cavity features are also investigated and compared with previous semi-theoretical results.

20th Atmospheric Flight Mechanics Conference, 1995

_Abstract Results of an unsteady thin-layer Navier-Stokes simulation of a 0.658-scale V-22 rotor and wing configuration in hover are presented. All geometric components of the flapped-wing and rotor test rig, including rotor blades, are accurately modeled. Rotor motion and rotor/ airframe interference effects are simulated directly using moving body overset grid methods. Tiltrotor hover aerodynamics are visualized via unsteady particle trace images. Wing download predictive ability is demonstrated. Simulation results are compared with experimental data. No effort was made to account for the tunnel walls, overhead doors, etc. in the computation. t Staff Scientist, Member AIAA

This paper discusses the use of advanced flow field structure extraction methods for a comprehensive understanding of the flow field structure presented on a case of a simplified helicopter fuselage. The turbulent flow is modeled via RANS (Reynolds-averaged Navier-Stokes) approach solved by means of Finite Volume Method on an unstructured type hybrid grid using the commercial software FLUENT 6. Two flight scenarios are presented here: cruise flight at a negative angle of attack with low influence of the induced velocity field of the rotor; and hovering flight when only the velocity field of the rotor plays a role. In cruise flight the flow field was found to be steady, thus non-linear RANS approach was reliably applied, however in the case of hovering, large scale unsteadiness was expected and the flow field was traced by means of URANS (Unsteady RANS) method. Post-processing of the results is based on the simultaneous observation of streamlines, wall-streak lines, vortex cores and the iso-surfaces of the second invariant of the velocity gradient tensor (usually denoted by Q). Applying these methods, one can not only show the structure of separated flow regions but can determine which of these structures are relevant regarding the aerodynamic characteristics of an aerospace vehicle or its components. The gathered additional information may extend the support of design engineers in making conceptual or optimization decisions.

Comprehensive information of fluid and flight dynamics of an aircraft is vital for most aircraft handlers, especially when it comes to more complex aircraft which are capable of flying at wider flight envelopes. In the case of trainer aircraft, it delivers valuable information to both student and trainers. A majority of aircraft manufacturers do no disclose such information to relevant stake holders due to various reasons. As such an information gap exists between handlers and designers as far as the aircraft’s aerodynamics is concerned. In this research, an aerodynamic comparison will be done between the most frequently flown configurations of the Chinese built Karakorum-08 aircraft. Selected armament configuration for this research is the 250 Litre Drop Tank attached to the underside of the aircraft with the help of two outboard Pylons. Present work involved in extending the previous work in the area to model a three dimensional surface model and computational mesh of the aircraft including a drop tank and Outboard Pylon using solid modelling software. A 1:48 scaled model was created for the complete aircraft with and without external stores. A CFD tool models the flow physics involved in flight in both configurations, thus rendering performance parameters which are available only through trial and error in the present context. The results provide new insights into the behaviour of the wing-body combination, thus enabling means of enhancing performance and handling qualities of the aircraft for both designers and pilots. Keywords: Aerodynamics, Aircraft Performance, CFD, Flow Physics, Solid Modelling.

37th AIAA Fluid Dynamics Conference and Exhibit, 2007

The Pegasus wing-glove flight experiment 1-4 was designed to provide crossflow transition data at high Mach numbers, specifically to help validate stability based predictions for transition onset in a flight environment. This paper provides an analysis of the flight experiment, with emphasis on computational results for crossflow disturbances and the correlation of disturbance growth factors with in-flight transition locations via the method. Implications of the flight data for attachment line stability are also examined. Analysis of the thermocouple data reveals that transition (from turbulent to laminar flow) was first detected during the ascending flight of the rocket when the free stream Mach number exceeded about 4. Therefore, computations have been performed for flight Mach numbers of 4.13, 4.35, 4.56 and 4.99. Due to continually decreasing unit Reynolds number at higher altitudes, the entire wing-glove boundary layer became laminar at the highest flight Mach number computed above. In contrast, the boundary layer flow over the inboard tile region remained transitional up to and somewhat beyond the time of laminarization over the instrumented glove region. Linear stability predictions confirmed that the tile boundary layer is indeed more unstable to crossflow disturbances than the much colder stainless steel glove boundary layer. The transition locations based on thermocouple data from both the glove and the tile regions are found to correlate with stationary-crossflow N-factors within the range of 7 to 12.4 and with traveling mode N-factors between 7.6 and 14.1. Data from the thermocouples and hot film sensors indicates that transition from turbulent to laminar flow (i.e., laminarization) at a fixed point over the glove is generally completed within a flight time interval of 3 seconds. However, the times at which transition begins and ends as inferred from the hot film sensors are found to differ by about 2 seconds from the corresponding estimates based on the thermocouple data. N e

Aerospace Science and Technology

Lift and drag flight test data is presented from the National Flying Laboratory Centre, Jetstream 31 aircraft. The aircraft has been modified as a flying classroom for completing flight test training courses, for engineering degree accreditation. The straight and level flight test data is compared to data from 10% and 17% scale wind tunnel models, a Reynolds Averaged Navier Stokes steady-state computational fluid dynamics model and an empirical model. Estimated standard errors in the flight test data are ±2.4% in lift coefficient, ±2.7% in drag coefficient. The flight test data also shows the aircraft to have a maximum lift to drag ratio of 10.5 at Mach 0.32, a zero lift drag coefficient of 0.0376 and an induced drag correction factor of 0.0607. When comparing the characteristics from the other models, the best overall comparison with the flight test data, in terms of lift coefficient, was with the empirical model. For the drag comparisons, all the models under predicted levels of drag by up to 43% when compared to the flight test data, with the best overall match between the flight test data and the 10% scale wind tunnel model. These discrepancies were attributed to various factors including zero lift drag Reynolds number effects, omission of a propeller system and surface excrescences on the models, as well as surface finish differences.

2016

This work is devoted to the visualization and characterization of twin air jet flow when impinging vertically to a solid surface, which is important to understand the phenomenon relevant to Vertical/Short Take-Of and Landing (V/STOL) type of aircraft when they are operating on short distances from the ground, landing or taking-off, and could be helpful to improve the performance and stability of this kind of aircrafts. The major concern of this work is characterizing the fountain upwash region, which is a distinctive fan-shape flow that is formed on the collision region. The parameters analysed on this work are the separation distance between the jets and the jet height. Have been observed significant changes in the flow pattern and properties in the fountain upwash region due to the changes in the parameter studied. To be possible the realization of this work an experimental facility has been built. The facility supports an adjustable mechanical system which can accommodate twin stainless steel barrels with different diameters, which are the jets. Within this mechanical system, the barrels horizontal distance and height can be independently adjusted. The working fluid is the air, and to be possible the flow visualization a seeding generator have been projected and built. The flow visualization has been supported by an algorithm developed on the "Image Processing toolbox of Matlab" software, where have been made the post processing of the images. vi Resumo Este trabalho baseia-se na visualização e caracterização do escoamento desenvolvido por dois jactos paralelos e verticalmente disposto em relação a uma superfície sólida. Estes fenómenos estão associados com aeronaves de descolagem e aterragem vertical ou curta (V/STOLvertical/short take-of and landing). Particularmente, interessa a caracterização da região conhecida como "fountain upwash", que é uma forma característica do escoamento que se forma na região da colisão. Os parâmetros analisados neste trabalho foram a distância horizontal entre os jactos e a altura destes à superfície de impacto. Foram observados diferenças significativas no padrão e propriedades do escoamento na região de "fountain upwash" devido à variação dos parâmetros em estudo. Para a realização deste estudo foi construída uma instalação experimental. A instalação é ajustável mecanicamente, contendo dois tubos de aço, com diâmetro variável. O sistema mecânico permite o ajustamento, independentemente, a distância horizontal entre os jactos e a altura dos mesmos. Como neste trabalho se vai trabalhar com ar, para ser possível visualizar o escoamento é necessário marcar o escoamento. Nesse sentido foi desenvolvido um gerador de "seeding". Para uma melhor e mais precisa visualização do escoamento foi desenvolvido um algoritmo no "Matlab" usando "Image Processing toolbox", onde as imagens captadas foram pós processadas. vii Acknowledgment Alone this work was not possible to do, have been many people that help, with his work, dedication patience or just a friendly word. I would like to take this opportunity to express my thanks and appreciation to my supervisors Professor Doctor Jorge Manuel Martins Barata and Professor André Resende Rodrigues Silva, for their support guidance, encouragement and for all i learned with them. I want to express my thanks to the "Departamento de Ciencias Aeroespaciais da Universidade da Beira Interior", especially to laboratory technician Rui Paulo for his help and contribution in the construction of the experimental facility. Thanks to my friends and colleagues who have made the last years spatial and for the support and good moments. The last but not the least, i am very great full by the support and encouragement of the people that are always there on the best and warts days: Armando,

Visualization of Mechanical Processes, 2011

This paper presents the collection of the fluid flow pattern along a two-dimensional NACA 2415 airfoil and four modifications of this one. Results allowed obtaining the location of the separation and reattachment point in some cases for different angles of attack by means of experimental visualization techniques such as oil and smoke. The experiments were held at a Reynolds number of 10 5 . Finally, experimental results were compared with numerical references and found to be in good agreement.

2015

This paper is devoted to the study of a 1/20-scale model of wingsail in a wind tunnel environment. This study deals with the methodology to achieve accurate comparisons between numerical and experimental data. A particular care is brought in the numerical simulation to reproduce the wind tunnel effects on the model. The experimental results did not match with preliminary numerical simulations performed in a freestream domain. The reason is that the wind tunnel domain introduces some modifications in the flow field, around the wingsail, especially near the tip. As a consequence, a study has been done first to set the correct configuration to model the real vein conditions. Then numerical simulations based on a RANS approach have been run to study the flow around the wing in the wind tunnel environment, at different operating conditions in terms of inlet flow angles and wingsail cambers. A comparison of the numerical predictions with experimental data established the accuracy of the s...

International Journal of Engineering Materials and Manufacture, 2018

This paper presents a step by step verification and validation process of a vertical round submerged jet into a cylindrical bath. Taking advantage of the axi-symmetric domain, Navier-Stokes equation of primary is solved by finite volume method (FVM) using commercial computational fluid dynamics, CFD (Fluent) software. For verification and to minimise the computational error, step by step grid independence tests were performed. For validation, experimental data was produced using laser Doppler velocimetry (LDV). Among the turbulence model, SST was found to predict the flow behaviour better than k-e- realization or RSM models.

2012

This thesis investigates the application of CFD techniques to the aerodynamic analysis of a Ushaped JETC. Investigations were carried out to determine the flow patterns present at a number of locations within the structure of a full U-shaped JETC. The CFD solutions produced in these investigations used recommendations from the literature in the setup of the CFD solver, and provided the computational component towards problem-specific validation of the CFD techniques used. A structured series of CFD-aided investigation and design processes were then performed. These processes were based around a series of analyses that evaluated the influence of a number of cell parameters in terms of cell airflow efficiency and velocity distortion. Four cell components; the inlet and exhaust stack baffle arrangements, the turning-vanes, the rear of the working section and augmenter entrance, and the lower exhaust stack, including the BB, were investigated in individual analyses. Throughout the investigations the value of CFD as a design tool was constantly assessed. 1 Project Overview and Motivation This section discusses the impetus behind the initiation of this project and the subjects covered within. In the latter part of this section the scope of the investigations that were performed is presented, along with a brief discussion of the layout of this thesis. 1.1 Formulation and Impetus of Project The formulation of this project was born out of the relationship between the University of Canterbury (UoC) and the Christchurch Engine Centre (CHCEC) during a final year undergraduate project in 2005 (Agmen, Bosworth, Gilmore, & Hager, 2005). The work carried out in that project performed an aerodynamic analysis of the (at the time) new Jet Engine Test Cell (JETC) at the CHCEC base in Christchurch, New Zealand. The work performed by (Agmen et al., 2005) aimed to introduce and investigate the use of Computational Fluid Dynamics (CFD) techniques to the analysis of the CHCEC JETC. Such techniques had not been employed previously by the cell designers, CENCO, or by the engineers in the alliance formed by Air New Zealand and Pratt & Whitney in the creation of the CHCEC. Upon completion of the work performed by (Agmen et al., 2005), a desire was shown by both the Mechanical Engineering Department at the UoC and the CHCEC to develop the findings of the final year project, and the general application of CFD techniques to the analysis of JETCs. This project was therefore born out of the desire to create an ongoing relationship between the two parties that would utilise the academic resources of the UoC in combination with the full-scale 'real-world' test bed that the CHCEC offered. 1.2 The Christchurch Engine Centre The CHCEC is situated at Christchurch International Airport with the main administration facilities located alongside the domestic terminal. The company provides maintenance, repair, overhaul (MRO) and testing facilities for a range of aircraft engines. These include the Rolls-Royce Dart, Pratt & Whitney JT8-STD, and JT8-200 amongst others. An additional facility was completed at 115/117 Orchard Road in 2005, also within the vicinity of the airport.

28th National Heat Transfer Conference, 1992

Miltary Technical College-Egypt 2012 , 2013

This work aims to study and simulate the behavior of flow over SAFAT-01's wing using numerical simulation based on solving Reynolds's Averaged Navier-Stokes equations coupled with K-ω turbulent model. The wing model is simple rectangular with elliptical ends. In the present work, aerodynamics characteristics and different flow phenomena were predicted at different design conditions (e.g at different angles of attack) and at Re=5.2×10 6 . The present study analysis the vortices which occur over wing and captured their effective regions at critical design conditions. This study indicates that the maximum lift coefficient for SAFAT-01's wing is 1.44 occur at stall angle of attack 12 o , maximum lift to drag ratio (L/D) is 26 which occur at -4 o , and the zero lift drag coefficient is 0.0142. For the purpose to validate this numerical simulation, a typical wing which found in was analyzed, a comparison between predicted results and available results indicate that this numerical simulation has high ability for predicting the aerodynamics characteristics.

1997

The behavior of jet fuel and its vapor under different sets of conditions was studied as part of the National Transportation Safety Board's (NTSB's) investigation into the cause of the TWA Flight 800 accident (DCA96MA070; the crash of a 747-131, N93119). An important goal of this study was to provide technical information about the properties of jet fuel and its vapor under conditions that might have existed in the Flight 800 center wing fuel tank at the time of the explosion. Specifically, we wanted to address the question of fuel flammability under flight conditions at 14,000 feet. Headspace gas chromatography was used to measure component partial pressures and total vapor pressures for twelve jet fuel samples (Jet-A, Jet-A1) taken from the center wing tanks of commercial aircraft. Measurements were made at 32-33.5, 40, and 50•C and at vapor volume-to-liquid volume (V/L) ratios of 274, 136.5, 26.5, and 1.2 for four of the samples. Measurements were also made at 40, 50, a...

The Melbourne Metropolitan Fire Brigade are exploring the fitment of Hazardous Materials sensors to a quadrotor Unmanned Aircraft System (UAS). The aim of this paper is determine whether the flow structures surrounding the quadrotor would be sufficient to support measurements made by the sensor. Flow visualisation techniques (Schilieren) and point flow-rate measurements were used to characterise the complex flow structure surrounding the shroud. A number of viable regions for locating the inlet to the gas sensor were identified. Future work will explore the pressure at various locations on the inside of the duct.