Model for Multistage Compressors to Predict Unsteady Inlet-Compressor Interactions

Abstract

The design of supersonic airbreathing propulsion systems must include an assesment of how the inlet/engine combination responds to flow disturbances that might affect the system during operation. The movement of the terminal normal shock is of particular concern because excessive upstream displacement can cause inlet instabilities. The engineering approach to this problem is to use an unsteady computational fluid dynamics (CFD) code to analyze the inlet flowfield in conjunction with an outflow boundary condition, imposed at the compressor face. If the characteristic time scale of the disturbance is short, then internal reverberations within the compressor may play an important role in the transients. In this case only a simultaneous, coupled inlet‐compressor computation is capable of yielding the correct result. The complexity of unsteady compressor flows currently makes such computations impractical within the constraints of engineering projects. This article offers a simple, one-dimensional compressor model that utilizes the acoustic reflection and transmission coefficients of individual compressor components as building blocks. Incorporation of the model into existing unsteady inlet CFD codes would eliminate the need for a boundary condition at the compressor face, with no significant impact on overall computational time. Calculated results agree well with experimental data.