Shock-Stationary Application of Pseudoshock Models During High-Amplitude Combustion-Driven Unsteadiness

The isolator pseudoshock provides necessary compression within a dual-mode scramjet engine and is typically ejected during unstart. Quasi-one-dimensional (1-D) flux-conserved models are reduced-order models for designing dual-mode scramjet isolators and could be extended to control the pseudoshock in real time. A flexible quasi-1-D flux-conserved pseudoshock model, the Fiévet flux-conserved model, is extracted from the literature as a representative of the state of the art. When the pseudoshock moves within the isolator, these models are typically applied by instantaneously “freezing” the isolator state as “quasi steady.” The efficacy of this process is evaluated against data from a combustor-driven, direct-connect isolator experiment. The experiment exhibited strong unsteadiness that produced weak, upstream propagating shocks into the isolator. Although this configuration resulted in atypical unsteadiness, it provides an opportunity to evaluate the flux-conserved modeling assumptions in a transient edge case. Such transients could occur during throttling or unexpected combustor events. The Fiévet flux-conserved model is fit within laboratory and shock-stationary reference frames using Bayesian inference. Model performance is analyzed over a range of measured shock train speeds up to 20% of the isolator freestream velocity. It is concluded that to produce consistent isolator pressure profile estimates in an unsteady environment, flux-conserved models should be implemented in a shock-stationary reference frame. Doing so guides the isolator design to an optimal length with the desired safety factor. Furthermore, such modeling corrections can aid in the robust control of the isolator–combustor system by providing a more accurate prediction of control feedback variables.