Flow Mechanism Analysis Of Confined And Unconfined Compressible Turbulent Jets

Compressible turbulent jets can be divided into three types: free jet,semi-confined jet and confined jet.In this paper,three typical methods of supersonic free jet,impinging jet and ejector are studied by scale adaptive method and large eddy simulation method respectively,and the flow mechanism of the jet is analyzed.The flow field structure and flow mechanism of a supersonic free jet are studied by numerical simulation of a planar jet and an axisymmetric jet.The results show that the phenomenon of shock series exists in the supersonic free jet.In the flow dissipation,the dissipative part of the spiral is dominant,which is larger than the expansion dissipation.In the near-field region of supersonic jet,the vortex structure presents a circular tube shape.Then,in the unstable region of the jet,the vortex structure is severely fractured after the circumferential breakage of the vortex structure,so the turbulent kinetic energy reaches the maximum value in the mixing zone.The flow field structure and turbulence characteristics are studied by numerical simulation of an supersonic impinging jet.The calculation results show that there is a Maher disk and an oblique shock wave in the flow field.Due to the effect of Maher disk and oblique shock wave,the air flow formed the inner shear layer and formed the reflux zone near the impact plate.The vortex structure in the reflux region is more complex,and the whole is distributed in a spiral tube.In the area outside the stagnation zone of the jet,the vortex structure is distributed in a circular tube.Through numerical simulation of the subsonic jet impacting the concave wall,the results show that the Reynolds stress value at the shear layer of the jet is the largest,and the fluid will deflect along the concave wall to both sides,and it will move away from the concave surface.Through the numerical simulation of the subsonic plane ejector,the internal flow structure of the ejector is obtained.The calculation results show that there are shock series in the ejector,and the instability of the main jet is the same as that of the free jet,which is also divided into growth stage,instability stage and mixing stage.The dissipative fraction of the turbulent flow in the flow field is dominated by the dissipative part,and the dissipative part of the expansion can be ignored.