Inhibition of supersonic mixing layer growth rate via a micro vortex generator array

In the past, various flow control methods have been used to enhance the growth rate of the supersonic mixing layer (SML), yet suppression strategies remain underexplored. The flow fields of the free SML (FSML) and the SML controlled by the micro vortex generator (MVG) array (CSML) were obtained via flow visualisation and large-eddy simulations, which show that the CSML’s growth rate is substantially lower. The upper Q Q $Q$ -criterion analysis confirms that under MVG control, the dominant vortical structures in the initial stage of SML transition from spanwise to streamwise vortices. Circulation analysis shows that streamwise circulation upper Gamma Subscript x Γ x $\varGamma _x$ and transverse circulation upper Gamma Subscript y Γ y $\varGamma _y$ are significantly enhanced in the CSML, thereby facilitating energy redistribution. Dynamic mode decomposition reveals that the first two dominant modes of the FSML exhibit spanwise periodic structures. However, the dominant modes exhibit ‘comb-like’ patterns in the initial stage of the CSML, while the spanwise vortices regain dominance further downstream. The interaction between streamwise and spanwise vortices dominates the spatial growth of the CSML, which is in contrast to the sole dominance of Kelvin–Helmholtz vortices in the FSML. By suppressing the Reynolds normal stress left angle bracket v prime v Superscript prime Baseline right angle bracket ⟨ v ′ v ′ ⟩ $\langle {v'v'} \rangle$ and restructuring the turbulent kinetic energy (TKE) transport process, MVGs enhance the central amplitudes of TKE transport terms, and narrow their spanwise distribution width. Therefore, the diffusion of TKE towards the high- and low-speed flows is inhibited, thereby reducing the SML’s growth rate. This study offers a viable approach and insights for applications that require inhibiting the SML’s growth rate.