Title: Implications of compressibility effects for Reynolds-scaled testing of an inverted wing in ground effect

Authors: Graham Doig; Tracie J. Barber; Sammy Diasinos

Addresses: School of Mechanical and Manufacturing Engineering, The University of New South Wales, NSW 2052, Sydney, Australia ' School of Mechanical and Manufacturing Engineering, The University of New South Wales, NSW 2052, Sydney, Australia ' Department of Engineering, Macquarie University, North Ryde, NSW 2109, Sydney, Australia

Abstract: The influence of compressibility around an isolated inverted wing at a fixed Reynolds number was examined as relevant to the issue of wind tunnel scaling effects. Three-dimensional simulations were conducted for low ground clearances, at: full scale and a Mach number of 0.088, at 50% scale at Mach 0.176, and at 25% scale at Mach 0.352. As the scale was reduced, the increasing peak local Mach number between the wing and the ground resulted in a higher propensity of the flow to separate towards the trailing edge, and for incompressible or full-scale CFD to underestimate the lift and drag coefficients by an ever-increasing margin. The lower vortex path was less affected. The results suggest that compressible CFD of a scale experiment ought to be conducted at the same Reynolds number and Mach number as the tunnel test for the best possible correlation at free-stream Mach numbers beyond 0.15.

Keywords: ground effect; CFD; computational fluid dynamics; compressible flow; fixed Reynolds number; inverted wing; downforce; compressibility effects; wind tunnel scaling; 3D simulation; Mach number; lift coefficient; drag coefficient.

DOI: 10.1504/IJAD.2014.067578

International Journal of Aerodynamics, 2014 Vol.4 No.3/4, pp.135 - 153

Received: 12 Jul 2013
Accepted: 15 Sep 2013
Published online: 28 Feb 2015 *

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