An LDA Study of the Backward-Facing Step Flow, Including the Effects of Velocity Bias

Abstract

The subsonic, backward-facing step flow was studied experimentally to provide structural information and test data for modelers. A single-component laser-Doppler anemometer was the primary measurement instrument. The effects of velocity bias on the LDA results were examined in detail. It was concluded that velocity bias was small (< 4 percent) in the uncorrected measurements and nonexistent when a periodic sampling strategy was employed. The measurements show that the pressure gradient at reattachment is lower in the present experiment than in most previous work, due to the thick boundary layer at separation. Turbulence levels in the separated shear layer are also reduced by the thick upstream boundary layer. Scaling of the streamwise coordinate on the reattachment length produced the best agreement with previous data. Agreement of turbulence quantities was particularly good downstream of reattachment.