Large-Eddy Simulation Of Hydraulic Characteristics Of Turbulent Offset Jet Impinging On Inclined Wall

Offset jet is a typical flow in hydraulic engineering,such as dam discharge into stilling basin,flood discharge pipeline outflow,etc.At present,the research on the flow characteristics of impinging inclined wall offset jet is still insufficient,especially the reports on the vortex dynamic characteristics are few.In order to improve the understanding of the flow mechanism of the offset turbulent jet impinging on the inclined wall,the large eddy simulation method is used to simulate the Reynolds number re=15000,the offset ratio H/d=3.5～6.5 and the wall inclination α= 0°～20°.The effects of the key factors on the time averaged flow field,turbulent statistics and vortex structure of the offset jet are analyzed,and the effects of the vortex structure on the time averaged field and turbulent field are preliminarily revealed.(1)The research results on the time-averaged characteristics of the jet centerline,wall static pressure coefficient,velocity expansion and decrease,etc.show that: the wall static pressure coefficient decreases with the increase of offset ratio and wall inclination,and the relationship between the length of recirculation zone and offset ratio and wall inclination is fitted.The centreline curvature,the maximum axial velocity decay rate and the half width of velocity in the pre-impinging region are basically independent of the wall inclination.With the increase of the offset ratio,the centerline curvature and the maximum axial velocity decay rate of the pre-impinging region decrease;The velocity half width expansion rate and the axial maximum velocity decay rate in the wall jet region decrease as a whole.The velocity distribution in the wall jet region has strong self similarity.(2)The turbulent characteristics such as turbulence intensity,Reynolds stress,turbulent kinetic energy flux and flatteness factor show that the turbulence of offset jet is significant in the pre-impinging region and impinging region,and the turbulence in the wall jet region is unconspicuous.With the increase of the offset ratio and the wall inclination angle,as the range of the pre-impinging region increases and the interaction between the fluid in the recirculation zone and the jet are compromised,the radial turbulence intensity in the inner shear layer,the turbulence intensity and the Reynolds stress in the recirculation zone decrease in the pre-impinging region,the turbulence intensity and the Reynolds stress in the barotropic zone decrease,and the peak Reynolds stress varies from negative to zero and changes to positive,and the turbulence intensity and Reynolds stress in the wall jet zone change little.Turbulent kinetic energy flux and flattening factor first increase and then decrease in the pre-impinging region and impinging region;The turbulent kinetic energy flux in the wall jet region is basically zero,and the flatness factor fluctuates around 3.(3)Through the analysis of vortex structure,the effects of offset and wall inclination on the time averaged flow field and turbulent field are summarized: the increase of offset ratio and wall inclination increases the length of the development section of the preimpinging zone,the number of vortex structures in the development section of the preimpinging zone increases,and the initial dissipation of energy is generated by entrainment and mixing with the ambient fluid,so that the number of vortex structures in the impinging zone and the energy carried by them are reduced,and the pulsation in the impinging zone is weakened;When impinging the wall,the vortex breaks up and releases the energy at the vortex core,and the energy is further dissipated;The vortices in the recirculation zone and the broken vortices in the impinging region fuse again,but the number of vortices and the energy carried by them are significantly reduced,and the entrainment effect on the jet vortex structure in the pre-impinging region is reduced,so that the jet deflection curvature is reduced,the velocity attenuation rate in the preimpinging region is reduced,the radial turbulence intensity in the inner shear layer is weakened,and the turbulence intensity and Reynolds stress in the recirculation zone are reduced;For the wall jet region,the turbulence is small because of the small vortex intensity.