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

Abstract

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.

Influence of wing span on the aerodynamics of wings in ground effect

“…Grid inde pendence of the three-dimensional hexahedral mesh þ (approximately 8 x 10 6 cells, y of approximately 1 on the wing) has previously been verified through extensive comparison to experiment. 6 Figure 1 shows the domain extent and an example mesh (for the original wing span). For this study, wing transition was not imposed (as it was in the original experiments) so as to eliminate it as an influence on the results -a real-world racing car wing would feature free transition and future work, consider ing the effect of span on this variable would be useful.…”

The effects of simplifications on isolated wheel aerodynamics

“…For this reason, additional simulations were run as transient (unsteady RANS) and the flowfields were time-averaged in order to assess the suitability of steady-state simulations for the present investigation. Because of a similar industry standard, all simulations were run as incompressible, although local density changes, particularly in the contact patch region, may have a slight influence on the flow (Doig et al, 2011;Doig, 2014;Keogh et al 2014).…”

Hydrogen car fill-up process modeling and simulation

“…According to [11], fluids experience compressible flow effects at Mach numbers greater than 0.3. At hydrogen's high and low pressure/flowrate conditions during the fill-up, 415.00 bar/0.006 kg/s and 360.00 bar/0.002 kg/s respectively (mass flowrate values shown with gram precision), it can be shown that the resulting Mach number are 0.004 for high conditions and 0.002 for low conditions.…”