Efficient diffuser design for plasma wind tunnels with a large blockage model

Abstract

The operation of plasma wind tunnels requires an excessive pressure ratio owing to the excess total pressure loss in the hypersonic environment. This loss increases when a large blockage model is mounted on the test section. Therefore, designing a diffuser that can alleviate this total pressure loss by compressing the hypersonic flow efficiently is essential. However, the flow inside a plasma wind tunnel diffuser exhibits a low Reynolds number and a high Mach number, rendering the prediction of the flow and performance of a diffuser difficult. Furthermore, limited literature exists on the design of plasma wind tunnel diffusers. In the study, we propose an efficient plasma wind tunnel diffuser capable of testing despite a large blockage model. We carried out flow analysis and a parametric study on the shape of the diffuser and numerically investigated the influence of a large blockage model. Additionally, a performance analysis was conducted to estimate the pressure ratio required for the operation of the wind tunnel. Throughout the study, the newly proposed parameter, mass flow rate weighted average of the total pressure, was identified as the primary observation value because it was found helpful for improving diffuser efficiency in the design stage. Furthermore, several design considerations are recommended for the enhancement of plasma wind tunnel diffusers. The inflow Mach number and total pressure at the nozzle exit were 7 and 21.9 bar, respectively, corresponding to conditions of MW class large plasma wind tunnels. With limited related studies in current literature, we expect this study to serve as a reference when designing a plasma wind tunnel diffuser.