High-speed ground effect aerodynamics

 

Ground effect

As an object passes through a compressible fluid such as air, the aerodynamics of the body are affected by density changes in the fluid around it. These aerodynamic effects are influenced – usually exaggerated - by proximity to a ground plane, in particular when shock waves reflect from the ground to interact with the body again one or more times. Traditionally, most aeronautical ground effect research (excluding study of vertical take-off and landing (VTOL)) has concentrated on the properties of wings in nominally-incompressible flows, i.e. at relatively low subsonic Mach numbers. Applications have included aircraft in landing or takeoff modes, aircraft designed specifically to fly in ground effect, or in the case of inverted wings, high-performance racing vehicles. In these cases, proximity to the ground serves to enhance the lift (or downforce) performance of the wing, and often the overall aerodynamic efficiency.

Blue Angels photo credit: Matt Niesen

 

How?

Recent developments in the understanding of the aerodynamic influence of compressible ground effects and of shock/ground interaction for ground effect problems are timely, particularly given new or recurring interest in high-speed subsonic (freestream Mach number, M∞ ≥ 0.4) wing-in-ground effect (WIG) aircraft, magnetic-levitation space vehicle launch systems, and high speed rail or tube transport systems. For more esoteric applications, it has also been speculated that the shock waves from an extremely-low-flying supersonic aircraft could potentially be used as a means to suppress large-scale uncontrolled fires such as forest fires, or that the use of a sonic boom from a low-flying supersonic jet could be used as a non-explosive weapon to injure or disorient humans as part of a military operation.

Original projectile movie: Kleine, Mudford, Purdon

 

The study of ground effect aerodynamics in the transonic and supersonic regime is an active area that shares flow similarities with several other fundamental and applied research areas in fluid mechanics. Considerable advances have been made in understanding flowfields featuring shock interactions with a ground plane and their reflection back onto the generating body one or more times.

Publications

Doig, G., Wang, S., Kleine, H., Young, J.
Aerodynamic Analysis of Projectiles in Ground Effect at Near-sonic Mach numbers.
AIAA Journal, Vol. 54, No. 1, pp. 150-160

Doig, G.
Transonic and Supersonic Ground Effect Aerodynamics.
Progress in Aerospace Sciences, Volume 69, pp. 1–28. DOI: dx.doi.org/10.1016/j.paerosci.2014.02.002

Doig, G., Barber, T.J., Diasinos, S
Implications of compressibility effects for Reynolds- scaled testing of an inverted wing in ground effect.
International Journal of Aerodynamics Vol. 4, 3/4, pp. 135–153. DOI: 10.1504/IJAD.2014.067578

Doig, G., Young, J., Wang, S., Kleine, H.
Aerodynamics of Transonic and Supersonic Projectiles in Ground Effect
52nd AIAA Aerospace Sciences Meeting, AIAA SciTech, National Harbor, MD, 13th-17th Jan 2014.

Doig, G., Barber T, Neely A.
Aerodynamic Characteristics of a Swept Wing in Close Ground Proximity at High Subsonic Mach Numbers.
Journal of Aerospace Engineering, 2012, 25, pp. 600-612.

Doig, G., Barber, T.J., Neely, A.J., Myre, D.D.
Aerodynamics of an Aerofoil in Transonic Ground Effect: Methods for Blowdown Wind Tunnel Scale Testing.
The Aeronautical Journal, 2012, 116 (1180). pp. 599-620.

Doig, G., Barber, T., Neely, A., Myre, D.D.
Aerodynamics of an Aerofoil in Transonic Ground Effect: Numerical Study at Full-scale Reynolds Numbers
The Aeronautical Journal, 2012, 116 (1178), pp. 407 - 430.

Doig, G., Barber, T.J., Neely, A.J.
Progress in Understanding Transonic and Supersonic Ground Effect.
28th International Congress of the Aeronautical Sciences, Brisbane, 23-28 Sept 2012.

Doig, G., Barber, T.J., Leonardi, E., Neely, A.J., Kleine, H.
Aerodynamics of a Supersonic Projectile in Proximity to a Solid Surface.
AIAA Journal, 2010, 48(12):pp. 2916-2930.

Doig, G., Barber, T., Neely, A.
The Influence of Compressibility on the Aerodynamics of an Inverted Wing in Ground Effect.
ASME J. Fluids Eng., 2011, 133 (6), pp. 1-12.

Doig, G., Barber, T.J., Leonardi, E., Neely, A.J., Kleine, H.
Methods for investigating supersonic ground effect in a blowdown wind tunnel

Shock Waves, 2008, 18(2): pp. 155- 159. DOI: 10.1007/s00193-008-0144-z

Doig, G., Barber, T.J., Leonardi, E. & Neely, A.J.
The onset of compressibility effects for aerofoils in ground effect.
The Aeronautical Journal, 2007; 111(1126): pp. 797 - 806.

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