Experiment to Support the Formulation and Validation of Compressor-Face Boundary Conditions

Abstract

The reliability of unsteady inlet e ow computations may be seriously degraded by the lack of experimentally validated compressor-face (outeow) boundary conditions. The commonly imposed oute ow conditions require a e ow variableto beconstant (pressure, velocity, Mach number,etc. )at theoute owboundary, butthereis littleif any documented evidenceto support theseassumptions, norarethey likely to actually occurduring a rapid transient of arealinlet/enginesystem.Measurementsarepresentedofacousticree ectioncoefe cientsforanoperatingmultistage compressor, a quantity appropriate for the characterization of the compressor face for computational purposes. The experiment used an impulse method, in which short-duration, large-amplitude acoustic pulses (1 ms, with a peak value of nearly 4% of the mean static pressure, respectively ) were generated in a constant-area, annular inlet. The pulse and its ree ection from the compressor face were tracked by fast-response pressure transducers. Frequency-domain analysis of the data yields transfer functions that may be thought of as frequency-resolved ree ection coefe cients. None of the currently availablecompressor-face boundary conditions accurately predict the data obtained in this study, indicating that current practices concerning oute ow boundary conditions are in need of revision.