Experimental Identification of Transient Dynamics for Supersonic Inlet Unstart

Abstract

Successful realization of dual-mode scramjet engines will require closed-loop control schemes to eliminate the occurrence of inlet unstart. An important step toward this goal is the development of dynamic models for shock system motion inside the inlet isolator under varying flow conditions. In this paper, shock motion models are developed based on fast-response pressure measurements made along the wall of the isolator (straight channel) downstream of a Mach 1.8 nozzle. The shock system can be perturbed by changing the stagnation pressure with an upstream valve and/or by changing the backpressure with a downstream flap. In particular, the shock’s transient dynamics are modeled, which govern the unstart process and are induced by changing pressure-boundary conditions, by employing system identification techniques. The result is a partially nonlinear dynamic model that reveals the possibility of partitioning the nonlinear behavior from the linear dynamics with relative ease. A second dynamic model is then generated, where the nonlinear portion has been prespecified, leaving only the linear portion to be determined by system identification. The modeling and identification process specific to the experimental unstart data used are discussed and successful models are presented for both the full system identification and the partitioned model cases.