Shock Waves DOI 10.1007/s00193-017-0722-z ORIGINAL ARTICLE Effect of shock interactions on mixing layer between co-flowing supersonic flows in a confined duct S. M. V. Rao 1 · S. Asano 2 · I. Imani 2 · T. Saito 2 Received: 21 March 2016 / Revised: 31 March 2017 / Accepted: 4 April 2017 © Springer-Verlag Berlin Heidelberg 2017 Abstract Experiments are conducted to observe the effect of shock interactions on a mixing layer generated between two supersonic streams of Mach number M 1 = 1.76 and M 2 = 1.36 in a confined duct. The development of this mixing layer within the duct is observed using high-speed schlieren and static pressure measurements. Two-dimensional, com- pressible Reynolds averaged Navier–Stokes equations are solved using the k-ω SST turbulence model in Fluent. Fur- ther, adverse pressure gradients are imposed by placing inserts of small (<7% of duct height) but finite (> boundary layer thickness) thickness on the walls of the test section. The unmatched pressures cause the mixing layer to bend and lead to the formation of shock structures that interact with the mixing layer. The mixing layer growth rate is found to increase after the shock interaction (nearly doubles). The strongest shock is observed when a wedge insert is placed in the M 2 flow. This shock interacts with the mixing layer excit- ing flow modes that produce sinusoidal flapping structures which enhance the mixing layer growth rate to the maximum (by 1.75 times). Shock fluctuations are characterized, and it is Communicated by F. Lu. B S. M. V. Rao srisha.raomv@gmail.com S. Asano 14042003@mmm.muroran-it.ac.jp I. Imani eysma.ahamad@gmail.com T. Saito saito@mmm.muroran-it.ac.jp 1 Department of Aerospace Engineering, Indian Institute of Science, Bengaluru, India 2 Department of Aerospace Engineering, Muroran Institute of Technology, Muroran, Japan observed that the maximum amplitude occurs when a wedge insert is placed in the M 2 flow. Keywords Supersonic flows · Mixing layers · Shock interactions · Mixing enhancement 1 Introduction The gas dynamics of the interaction between two gaseous streams at high Mach numbers in a varying area duct is crucial for devices such as supersonic ejectors and high- speed air breathing engines. There are mutual interactions between shocks, boundary layers at the walls, and mixing layers, leading to complex gas dynamic phenomena. The effects of compressibility on turbulent shear layers includ- ing the mixing layer have been summarized by Bradshaw [1]. The mixing layer, which is primarily responsible for mass, momentum, and energy transfer between the gaseous streams, is also the area for heat release during combustion. The significance of these components on the dynamics of the compressible mixing layer is elucidated in the monograph by Dimotakis [2]. Shock waves interacting with turbulence lead to mutual changes to structure and intensity of shocks and turbulence [3]. Boundary layers on the wall are also signifi- cantly affected by shock interactions [4]. Experimental studies were conducted in compressible mixing layer facilities that generated streams of different Mach number within the test section [5–8]. The experimental setup was designed such that the static pressures across the mixing layer were the same. The development of the mixing layer was primarily observed by flow visualization and char- acterized by the visually determined thickness of the layer. The compressibility effect was characterized by the intro- duction of the convective Mach number. Most importantly, it 123