Recent Aerodynamic Improvements at the Lockheed Martin Low Speed Wind Tunnel 960903

The Lockheed Martin Aeronautical Systems Company Low Speed Wind Tunnel has been used for aircraft testing and full scale automotive testing since 1967 In 1993, an improvement program was initiated to reduce background noise, improve test section flow quality, and reduce the aerodynamically induced vibrations affecting the main drive The initial aerodynamic work discussed here included optimizing the setting angles of the turning vanes in the first and second comers and modifying the orientation of the test section breather slots

Optimizing the turning vane setting angles was required to minimize flow irregularities in the circuit A CFD panel method program was used to study the effects of various turning vane setting angles While the computational study had limitations, it was used to identify large pressure gradients at the outer corners and qualitatively related the effects of flow constriction at the vane trailing edges to the rotation angle of the vanes Final decisions on vane setting angles were based on measured velocity profiles in the second diffuser and upstream of the fan The improved turning vane configurations minimized the separated flow in the second diffuser, increased the uniformity of the flow into the fan, and reduced the flow swirl angle in the test section by approximately 50% Modification of the breather slots and sealing leaks in the circuit reduced the pressure difference acting across the walls of the closed test section by 85% These actions reduced the test section longitudinal static pressure gradient by 33% and reduced the velocity of air leaking into the test section The reduced air leakage lowered the test section background noise 2 dB at frequencies above 2 kHz