EXPERIMENTS ON INSTABILITIES IN CURVED CHANNEL FLOW

Experimental results are reported from hot-wire measurements in a narrow gap, curved air channel with a spanwise aspect ratio of 29. The Reynolds numbers (Re) covered a range from 2 to 6.5 times the critical Re, i.e., the Re for which the flow becomes centrifugally unstable according to linear stability theory. For the lowest Re studied, the measurements showed a regular flow pattern of streamwise vortices, whereas at higher Re interaction occurred between vortex pairs. The streamwise disturbance velocity increased rapidly near the inlet section, thereafter the disturbance amplitude overshot before it finally reached a saturated level of the nonlinear stage. At even higher Re a secondary instability in the form of traveling waves appeared on top of the primary instability and was found to be localized between one pair of vortices at the inflow region from the concave wall.