CONTROLLING THE SPACING OF STREAMWISE VORTICES ON CONCAVE WALLS

The wavelength of Gortler streamwise vortices was changed by a factor of three by varying the amount of tunnel side wall boundary-layer removal just upstream of the concave wall test section's leading edge. Nondimensional wavelengths in the range 215 less-than-or-equal-to LAMBDA less-than-or-equal-to 900 were achieved with the larger wavelengths resulting from increased suction. The minimum wavelength compares well with the maximum amplification curve based on past theoretical studies. Low-speed streaks appeared to merge with other low-speed streaks or were weakened to the point of disappearing as the suction level was increased. The downstream location of secondary instability onset changed with variation in suction level and/or wavelength. The Gortler number and amplification factor for secondary instability onset, however, was approximately independent of suction level and/or wavelength.