Ground Effect of Transonic and Supersonic Projectiles: Influence of Mach Number and Ground Clearance

2017 ◽  
pp. 635-640
Author(s):  
C. Sheridan ◽  
J. Young ◽  
Harald Kleine ◽  
Koju Hiraki ◽  
Satoshi Nonaka
Keyword(s):  
Mach Number ◽  
Ground Effect ◽  
Ground Clearance

Experimental Investigation of the Effect of Camber on the Aerodynamic Characteristics of Airfoils in Ground Effect

2003 ◽  
Author(s):  
M. R. Ahmed ◽  
G. M. Imran ◽  
S. D. Sharma
Keyword(s):  
Experimental Investigation ◽  
Angle Of Attack ◽  
Ground Effect ◽  
Chord Length ◽  
Wake Region ◽  
Trailing Edge ◽  
Mean Velocity ◽  
Large Defect ◽  
Freestream Velocity ◽  
Ground Clearance

In the present paper, results from an experimental investigation of aerodynamic ground effect on two airfoils are presented. The flow characteristics over a symmetrical airfoil (NACA 0015) and a cambered airfoil (NACA 4415) were studied in a low speed wind tunnel. Experiments were carried out by varying the angle of attack from 0° to 10° and ground clearance from zero to one chord length. Pressure distribution on the surface of the airfoil was obtained with the help of pressure tappings. Mean velocity distributions were obtained over the surface of the airfoil. Profiles of mean velocity and turbulence intensity were obtained in the wake region at 0.5 and 1.0 chord length downstream of the trailing edge. It is found that pressure increases on the lower surface as the ground is approached. The flow accelerates over the airfoil, and a considerably higher mean velocity is observed near the suction peak location. For the symmetrical airfoil, the mean velocity over the surface was found to increase by nearly 30%, while for the cambered airfoil, an increase of nearly 60% was recorded for an angle of attack of 7.5°. The flow was found to separate almost near the trailing edge for angles of attack upto 10°, resulting in a thinner wake region and lower turbulence intensities for the symmetrical airfoil; while for the cambered airfoil, an early separation for an angle of attack of 10° was observed. Measurements in the wake region showed a defect in mean velocity profile at the corresponding values of ground clearance. For lower angles of attack, turbulence levels were higher in the wake region for the symmetrical airfoil, while for an angle of attack of 10°, very large defect in velocity was observed for the cambered airfoil model and the minimum velocity reduced to 20% of the freestream velocity.

scholarly journals The onset of compressibility effects for aerofoils in ground effect

2007 ◽  
Vol 111 (1126) ◽  
pp. 797-806 ◽  
Author(s):  
G. Doig ◽  
T. J. Barber ◽  
E. Leonardi ◽  
A. J. Neely
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Subsonic Flow ◽  
Flow Characteristics ◽  
Ground Effect ◽  
Aerodynamic Performance ◽  
Computational Studies ◽  
Pressure Gradients ◽  
Cfd Simulations ◽  
Compressibility Effects

Abstract The influence of flow compressibility on a highly-cambered inverted aerofoil in ground effect is presented, based on two-dimensional computational studies. This type of problem has relevance to open-wheel racing cars, where local regions of high-speed subsonic flow form under favourable pressure gradients, even though the maximum freestream Mach number is typically considerably less than Mach 0·3. An important consideration for CFD users in this field is addressed in this paper: the freestream Mach number at which flow compressibility significantly affects aerodynamic performance. More broadly, for aerodynamicists, the consequences of this are also considered. Comparisons between incompressible and compressible CFD simulations are used to identify important changes to the flow characteristics caused by density changes, highlighting the inappropriateness of incompressible simulations of ground effect flows for freestream Mach numbers as low as 0·15.

Experimental Aerodynamic Characteristics of a Compound Wing in Ground Effect

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Saeed Jamei ◽  
Adi Maimun Abdul Malek ◽  
Shuhaimi Mansor ◽  
Nor Azwadi Che Sidik ◽  
Agoes Priyanto
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Center Of Pressure ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Ground Effect ◽  
Reynolds Numbers ◽  
Aerodynamic Characteristics ◽  
Ground Clearance

Wing configuration is a parameter that affects the performance of wing-in-ground effect (WIG) craft. In this study, the aerodynamic characteristics of a new compound wing were investigated during ground effect. The compound wing was divided into three parts with a rectangular wing in the middle and two reverse taper wings with anhedral angle at the sides. The sectional profile of the wing model is NACA6409. The experiments on the compound wing and the rectangular wing were carried to examine different ground clearances, angles of attack, and Reynolds numbers. The aerodynamic coefficients of the compound wing were compared with those of the rectangular wing, which had an acceptable increase in its lift coefficient at small ground clearances, and its drag coefficient decreased compared to rectangular wing at a wide range of ground clearances, angles of attack, and Reynolds numbers. Furthermore, the lift to drag ratio of the compound wing improved considerably at small ground clearances. However, this improvement decreased at higher ground clearance. The drag polar of the compound wing showed the increment of lift coefficient versus drag coefficient was higher especially at small ground clearances. The Reynolds number had a gradual effect on lift and drag coefficients and also lift to drag of both wings. Generally, the nose down pitching moment of the compound wing was found smaller, but it was greater at high angle of attack and Reynolds number for all ground clearance. The center of pressure was closer to the leading edge of the wing in contrast to the rectangular wing. However, the center of pressure of the compound wing was later to the leading edge at high ground clearance, angle of attack, and Reynolds number.

Aerodynamic Behavior of a Compound Wing Configuration in Ground Effect

2014 ◽  
Vol 66 (2) ◽  
Author(s):  
Saeed Jamei ◽  
Adi Maimun ◽  
Shuhaimi Mansor ◽  
Agoes Priyanto ◽  
Nor Azwadi ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Ground Effect ◽  
Tip Vortex ◽  
Aerodynamic Coefficients ◽  
Ground Clearance ◽  
Reverse Taper ◽  
Current Experimental Data ◽  
Computational Fluid Dynamics Cfd ◽  
Ram Effect ◽  
Wing In Ground Effect

The aerodynamic coefficients of wing in ground effect can be affected with its design which can be the main parameter for efficiency of wing-in-ground effect craft. In this study, the aerodynamic coefficients of a compound wing were numerically determined in ground effect. The compound wing was divided into three parts with one rectangular wing in the middle and two reverse taper wings with an anhedral angle at the sides. An NACA6409 airfoil was employed as a section of wings. Three dimensional (3D) computational fluid dynamics (CFD) was applied as a numerical scheme. A realizable k-ε turbulent model was used for simulation the turbulent flow around the wing surfaces. For validation purpose, the numerical results of a compound wing with aspect ratio 1.25, at ground clearance of 0.15 and different angles of attack were compared with the current experimental data. Then, the aerodynamic coefficients of the compound wings were computed at various ground clearances and angle of attack of 4°. According to pressure and velocity distribution of air around wing surfaces, ground clearance had considerable effects on ram effect pressure and tip vortex of the compound wing, and aerodynamic coefficients of the compound wing had some improvements as compared with the rectangular wing.

scholarly journals Aerodynamics of an aerofoil in transonic ground effect: Methods for blowdown windtunnel scale testing

2012 ◽  
Vol 116 (1180) ◽  
pp. 599-620 ◽  
Author(s):  
G. Doig ◽  
T. J. Barber ◽  
A. J. Neely ◽  
D. D. Myre
Keyword(s):  
Wind Tunnel ◽  
Ground Plane ◽  
Ground Effect ◽  
Mirror Image ◽  
Navier Stokes ◽  
Oncoming Flow ◽  
Ground Clearance ◽  
Mach Numbers ◽  
Reynolds Averaged Navier Stokes ◽  
Symmetry Method

Abstract Experimental aerodynamic testing of objects in close ground proximity at high subsonic Mach numbers is difficult due to the construction of a transonic moving ground being largely unfeasible. Two simple, passive methods have been evaluated for their suitability for such testing in a small blowdown wind tunnel: an elevated ground plane, and a symmetry (or mirror-image) approach. The methods were examined using an unswept wing of RAE2822 section, with experiments and Reynolds-Averaged Navier Stokes CFD used synergistically to determine the relative merits of the techniques. The symmetry method was found to be a superior approximation of a moving ground in all cases, with mild discrepancies observed only at the lowest ground clearance. The elevated ground plane was generally found to influence the oncoming flow and distort the flowfield between the wing and ground, such that the method provided a less-satisfactory match to moving ground simulations compared to the symmetry technique.

scholarly journals Effect of Ground Proximity on Aerodynamic Characteristics of NACA 4412 Airfoil.

2022 ◽  
pp. 96-104
Author(s):  
Aditi Deekshita Pallay ◽  
Abdul Wahab ◽  
Akhil Shesham ◽  
Y D Dwivedi
Keyword(s):  
Wind Tunnel ◽  
Flow Behavior ◽  
Ground Effect ◽  
Aerodynamic Characteristics ◽  
Aerodynamic Performance ◽  
Vital Role ◽  
Ground Clearance ◽  
Induced Drag ◽  
Good Accordance ◽  
Low Speed Wind Tunnel

Ground effect plays a vital role in modulating the flow behavior over any streamlined body. The most widely used wing-in ground effect (WIG) aircrafts and seaplanes utilize this phenomenon in order to enhance the aerodynamic performance during the landing and take-off phases of flight. This paper investigates the aerodynamics of ground effect on a NACA 4412 rectangular wing without end plates. The experiment was conducted in a low-speed wind tunnel at Re=2×105 for the ground clearance of 1 and 0.5 of the chord, measured from the maximum thickness position on the airfoil. The pressure distribution over the chord length was recorded for α=3° and 6° to verify the effect of ground clearance during takeoffs. The results have shown to be in good accordance with the literature, as the coefficient of lift augmented with increase in ground proximity and the induced drag was minimized.

Fly low: The ground effect of a barn owl (Tyto alba) in gliding flight

2020 ◽  
pp. 095440622094393
Author(s):  
Jialei Song
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Ground Effect ◽  
Barn Owl ◽  
Wake Vortex ◽  
Tyto Alba ◽  
Ground Clearance ◽  
Weight Support ◽  
Gliding Flight ◽  
Induction Model

Birds take advantage of the ground effect to improve their flight performance by flying low over ground. In this paper, we created a high-fidelity computational fluid dynamics model of a barn owl ( Tyto alba) to study its ground effect in gliding flight. A computational fluid dynamics simulation shows that the ground effect leads to increases in the lift/drag ratio and span efficiency. Interestingly, the span efficiency exceeds one when the bird is below a certain ground clearance ( h/ c = 0.8). Such an estimation is under the condition of different weight supports; hence, there is no fair comparison for many parameters. Therefore, we used a vortex induction model validated by computational fluid dynamics to estimate the aerodynamics at different ground clearances under a constant weight support. As the ground blocks the downwash of the bird, an image wake system can equivalently replace the ground, forming a vortex system with four components: the wake vortex, bound vortex, image wake vortex and image bound vortex. The vortex induction model shows the vertical flows induced by these four vortex components. Such vertical flow can be used to estimate the drag production on the bird. As the ground clearance decreases, the drag due to the wake vortex and its image counterpart as a whole decreases, while that due to the bound vortex and its image counterpart increases slightly and then decreases. The remaining drag, namely, the zero-lift drag, undergoes a shallow “U” shape as a function of the ground clearance. We also analyzed the streamwise flow induction using this model and showed that the streamwise flow is reduced due to the ground effect, which might cause insufficient weight support at low speeds.

The Influence of Compressibility on the Aerodynamics of an Inverted Wing in Ground Effect

2011 ◽  
Vol 133 (6) ◽  
Author(s):  
Graham Doig ◽  
Tracie J. Barber ◽  
Andrew J. Neely
Keyword(s):  
Mach Number ◽  
Ground Plane ◽  
Three Dimensional ◽  
Ground Effect ◽  
Angle Of Incidence ◽  
Flow Conditions ◽  
Race Car ◽  
Mach Numbers ◽  
Lift And Drag ◽  
Separation Behavior

For inverted wings in close ground proximity, such as race car configurations, the aerodynamic ground effect can produce local velocities significantly greater than the freestream and the effects of compressibility may occur sooner than would be expected for a wing that is not close to a ground plane. A three-dimensional computational fluid dynamics study was conducted, involving a modified NASA GA(W)-2 LS [1]-0413 MOD inverted wing with an endplate, to investigate the onset and significance of compressibility for low subsonic Mach numbers. With the wing angle of incidence fixed, Mach numbers from 0.088 to 0.4 were investigated, at ground clearances ranging from infinite (free flight) to a height-to-chord clearance of 0.067. The freestream Mach number at which flow compressibility significantly affects the predicted aerodynamic coefficients was identified to be as low as 0.15. Beyond this point, as the compressible flow conditions around the wing result in changed pressure distribution and separation behavior, treating the flow as incompressible becomes inappropriate and leads to consistent underprediction of lift and drag. The influence on primary vortex behavior of density changes around the wing was found to be relatively inconsequential even at the higher end of the Mach scale investigated. By a freestream Mach number of 0.4 and at low clearances, local supersonic flow regions were established close to the suction peak of the lower wing surface in compressible simulations; the formation of a normal shock wave between the wing and the ground was shown to result in significant increases in separation and therefore overall drag, as well as a distinct loss of downforce.

An Alternative Analytical Method for Ground-Effect Aerofoils

1976 ◽  
Vol 27 (4) ◽  
pp. 292-308 ◽  
Author(s):  
T Kida ◽  
Y Miyai
Keyword(s):  
Asymptotic Method ◽  
Analytical Method ◽  
Present Method ◽  
Solid Wall ◽  
Ground Effect ◽  
Jet Stream ◽  
Ground Clearance ◽  
Free Jet ◽  
Uniform Fluid ◽  
Interference Problems

SummaryAn alternative analytical method is applied to interference problems of an aerofoil very close to the ground, such as a free surface, a solid wall, and a slipstream. The method of matched asymptotic expansions on the small ground clearance is used in the governing integral equation and this analysis is different from Widnall and Barrows’s analysis. They used the matched asymptotic method in the differential equation. To show that the present method is reasonable, the problem of a ground-effect aerofoil in uniform fluid flow is considered and it is found possible to obtain the same results as those of Widnall and Barrows for the case of small ground clearance. By comparing with some earlier studies, it is found that the asymptotic method used with small ground clearance is valid for a clearance less than about 0.3 of the chord length. Next, the interference of ground-effect aerofoils in the channel wall, in a free jet stream, and in a slipstream are examined, and it is found that the present method can be easily applied to these problems.

Sign in / Sign up

Export Citation Format

Share Document