An Experimental Investigation of the Transitory Stall Regime in Two-Dimensional Diffusers

Abstract

A study of flow behavior of transitory stall in two-dimensional diffusers at low Mach numbers is reported. The changes in flow patterns from stall inception to full-stall are described; the geometries for maximum fluctuations are located. The mean times and distribution of stall build-up and wash-out periods are given for a series of units of varying total angle. The mean times are found to scale on total stall volume, and a nondimensional correlation of stall period is given. The distribution of stall periods, for random inlet fluctuations, is found to be broad and strongly skewed toward lower periods. Comparable results are found in water for R∼104 and in air at R∼105. A further series of tests with periodic inlet disturbances indicates that the stall behavior is modified strongly when the pulsing period is 0.5 to 1.0 times the natuarl mean period, but not otherwise. Details of flow patterns and blockage are summarized.