Numerical study of unsteady shock/mixing interaction in confined space

Unsteady shock wave enhancement is an effective technical approach to achieve air/fuel mixing under high speed and compressible conditions. However, unsteady shock/mixing interactions are always accompanied by complex wave structures, so the height of the combustion chamber will inevitably have a significant impact on shock waves and engine performance. In this regard, shock/mixing interactions in confined space are studied in this article by direct numerical simulation to investigate the effect of wall constraint on shock wave enhancement. Shock wave structure, total pressure loss, thickness of mixing layer, and turbulence intensity of flow field with different confinement degrees are calculated and compared. The results show that the unsteady shock wave can dramatically enhance the thickness of the mixing layer and the turbulence intensity, thus improving the mixing efficiency. In addition, as the wall constraint increases, the intensity of the shock wave and the total pressure loss increase; the flow field is more prone to Mach reflection. The average total pressure loss caused by steady shock wave and unsteady shock wave is essentially the same for an identical wall height, but the total pressure distortion caused by the unsteady shock wave is more substantial. Furthermore, the enhancements of mixing efficiency by the shock wave are also affected significantly by the degree of wall constraint; therefore, a suitable wall height needs to be determined in order to achieve the highest mixing efficiency.