Impinging Wall Curvature Effects on Flow and Screech Tones in Choked Under Expanded Supersonic Jets

Supersonic jets exhibit distinct dominant temporal scales and coupled spatial oscillations. These scales are jet parameter dependent and can be sensitive to the Impinging wall curvature. The present study aims towards investigating the influence of impingement wall curvature on flow unsteadiness and the scaling of screech tones in impinging supersonic jets. We focus on an under-expanded supersonic jet operating at an ideally expanded Mach number of 1.56 and Reynolds number of 6 × 104. Dented walls with three-dimensional Gaussian surface geometry are being used to introduce both positive and negative curvature on to the impinging surface. Three configurations featuring convex, flat, and concave impinging walls are presented in this paper. Large Eddy Simulations are conducted to assess dominant spatio-temporal scales. A good agreement of mean flowfield and a reasonable agreement of screech frequency was observed between the present numerical calculations and the experimental measurements. Our preliminary results, presented in this manuscript, indicate that as the concavity of the impinging surface is increased, the dominant screech frequency is reduced (from St=0.8 to St=0.25 in the specific cases studied) with mode staging occurring in between from dominant flapping B-mode in convex case to dominant toroidal mode in flat and concave cases. On the other hand the absolute screech amplitude (pressure fluctuation magnitude) is increased by about two times in the concave case compared to the convex case. Furthermore, the concave case featured cyclic changes in flow structure with highly unsteady Mach stem and dynamic pressure loading on the impinging surface. Future work will explore additional configurations with various levels of convexity and concavity, along with the inclusion of an inlet nozzle and a turbulent nozzle exit boundary layer.