Experimental and numerical study on flow separation control in rectangle diffuser

To investigate the mechanism of active control for flow separation in rectangle diffuser by vortex generator jets (VGJs) method, numerical analysis with large-eddy simulation and experimental measurement by particle image velocimetry (PIV) were carried out for the flow field. The numerical results show good agreement with experimental data. The two dimensional vortical structure was discussed in detail via the analysis of their velocity and vorticity distribution. Based on the three dimensional identification of vortex, several vortical structure, with emphasis on the dynamic process of its generation and development, was also discussed. The results show that the jet shear-layer vortices evolved from vortex loops to vortex rings as time go on. Horseshoe vortices wrap around the jet nozzle have the strong stability. The counter-rotating vortex pair has mean-flow definition although they may also have unsteady components. Moreover, to investigate the effect of VGJs on separation control, the surface pressure coefficient, the length of separation zone, the flow characteristics in diffuser and pressure power spectra were compared with and without VGJs. It revealed the longitudinal vortices generate at the downstream of jet increase cross-stream mixing of streamwise momentum and then suppress or delay the separation in diffuser.