Aerodynamic response of internal passages to pulsating inlet supersonic conditions

Abstract

Abstract Supersonic flow passages benefit from high specific mass-flow rate, which can potentially be used in fluid machinery with the highest power density. Currently, the maximization of the propulsive efficiency, on forthcoming power plant systems, requires reduced engine cores, while for distributed local-power plant units, small gas turbine engines are ideal. Hence, ultra-compact fluid machinery is an enabling technology for future propulsion and power generation applications. In this context, the use of supersonic flow within internal passages allows the downsizing of the turbomachinery. However, the efficient operation of supersonic internal passages is a challenge due to shock losses and a constrained operability. Therefore, fully supersonic internal passages are typically discarded, and their unsteady operation scarcely documented. This paper presents a detailed characterization of the unsteadiness experienced across internal flow passages exposed to pulsating supersonic conditions. The analysis was performed in a wide range of excitation frequencies. To generalize the results the fluctuations are expressed in terms of a non-dimensional reduced frequency, i.e. ratio of excitation period to the propagation wave time. This aerodynamic characterization was performed with three-dimensional unsteady Reynolds-Averaged Navier Stokes simulations, revealing a hysteresis like behavior and amplitude modulation between the inlet and the outlet distinct from the steady prediction. The paper provides a numerical approach, based on a one-dimensional Euler solver that can predict the unsteady response of internal passages to the inlet varying conditions.