Experimental investigation of outflow boundary conditions used in unsteady inlet flow computations

The adequate representation of compressor dynamics through a boundary condition has been a long-standing problem in the computation of rapid inlet flow transients. No experimental information is available to validate any of the numerous compressor-face conditions currently in use. The present paper alleviates this shortage by offering experimental data focused on the inlet/engine interface problem. The data describe a rapid transient in a system comprising a constant-area, annular inlet and an axial, multistage compressor. An acoustic expansion pulse of short duration and large amplitude (1 msec, 3 kPa) is generated within the inlet and allowed to propagate to the compressor face. The incident pulse and its reflection are monitored and compared using high response pressure transducers mounted on the hub and the casing. At low axial Mach numbers the compressor face behaves as an attenuated hard wall termination.