Incident shock wave–boundary layer interaction generated by twin-uniform-2-dimensional-flow interaction

The expansion fan originating at the termination of the shock generating wedge may affect the results of incident shock wave–boundary layer interaction (SWBLI). This paper draws on the method of generating shock wave by forming discontinuities in computational fluid dynamics (CFD), and studies incident SWBLI using an oblique shock wave generated by twin-uniform-2-dimensional-flow (twin-uniform-2D-flow) interaction. This configuration can also be regarded as an exploration of SWBLI in a combined nozzle. The slip line generated by twin-uniform-2D-flow interaction is equivalent to a shock generator of sufficient length to intersect with the reflection shock (inviscid) or separation shock (viscous), thereby minimizing the influence of downstream flow structure. Furthermore, as the slip line constitutes an aerodynamic boundary, it prevents the occurrence of unstart phenomenon. Varying the pressure ratio between two jets enables the generation of different incident shock wave intensities without physical hardware modifications, while enabling the acquisition of deflection angles with higher resolution. The feasibility of this method to study SWBLI is validated through pressure distribution analysis, regular reflection–irregular reflection transition, and low-frequency oscillation characteristics. Experimental results align with classical free interaction theory and the detachment criterion. The influence of the Reynolds number is investigated by maintaining the nozzle pressure ratio while systematically varying ambient pressure and nozzle total pressure. Experimental results indicated that Reynolds number simulation is critical for twin-uniform-2D-flow interaction studies in a combined nozzle. Additionally, cumulative upstream disturbances collectively govern the incoming boundary layer parameters of the interaction region, which is a distinct feature compared to the conventional flat plate incident SWBLI configuration. Finally, the study concludes with practical suggestions for experimental improvement.