Geometric scale effect of the subsonic-supersonic shear layer based on a sinusoidal lobed splitter plate

Passive flow control tools have been widely used to enhance shear layer mixing in ramjet engines. Lobed mixer is an excellent method in mixing enhancement performance, while there is no comprehensive consensus on its mixing enhancement mechanism in a subsonic-supersonic shear layer. In this work, a sinusoidal lobed mixer is used to increase mixing between the subsonic and supersonic flows, and large eddy simulation (LES) is used to research the potential flow control mechanisms. Parameter experiments were carried out and the mixing performance was obtained. The numerical conclusions show good similarity with experimental conclusions. The impact of the geometric scales of the modified lobed mixer in the evolution of shear layer is investigated. It is found that sinusoidal lobed splitter plate with wavelength 10 mm and amplitude 2 mm shows the best mixing thickness experimentally and numerically, where compared with other cases, it is 3.3 times thicker than that of the flat plate. It is demonstrated that the sinusoidal lobed mixer performance is affected by its amplitude and wavelength. Large amplitude increases the initial disturbance, induces large scale streamwise vortex and enhances its mixing effectively. The number and size of large scale coherent vortices are inversely proportional to the wavelength. Smaller wavelength can accelerate the transformation process of the vortex structure, but it causes the slow development of shear layer downstream. Sinusoidal lobed mixer can promote the generation of large-scale streamwise vortices, significantly shorten the transition distance, and achieve better shear layer mixing.