Study On Scaling Properties Of Turbulent Statistics In Low-Reynolds-Number Wall Turbulence

Wall turbulence is a typical turbulent shear flow,in wall turbulence,study on statistics in recent years has made many meaningful results,the study of wall turbulence statistics can help us to create turbulence model,it also provides theoretical basis for complex turbulent structure.At the same time,the similarity of wall turbulence statistics has been studied in recent years,including the study of the similarity of mean velocity,Reynolds stress,material functions,turbulent kinetic energy spectrum and so on.Based on direct numerical simulation database of low-Reynolds number fully developed channel flow,turbulent statistics,such as the first normal stress difference coefficient,the second method to stress difference coefficient,apparent viscosity,turbulent viscosity and dimensionless velocity gradient on the wall turbulence has been studied in this thesis.Secondly,the LES method has been applied to simulate asymmetric turbulent channel flow with ribs,and the similarity of statistical characteristics is also investigated.The main results obtained are as follows:(1)The dimensionless shear rate increases with the increase of wall distance,the near wall shear rate is constant which corresponding to the viscous sublayer.In the turbulent core area,shear rate follows logarithmic relationship.The general relationship between shear stress and shear rate and Reynolds stress and shear rate have similar characteristics,and only in the high shear rate area,there is little difference between the Reynolds number.The first normal stress difference coefficient and the second normal stress difference coefficient also have similar characteristics,and show scaling law in larger shear rate and small shear rate.The relationship between the viscosity and the shear rate also shows similar characteristics,and are constant in small the shear rate.The relaxation time and the Weissenberg number have similar characteristics,and in small shear rate,the relaxation time is straight,the slope of the line in low Reynolds number ratio and Reynolds number is small,the Weissenberg is constant in the shear rate less than 100,while in shear rate less than 100 Weissenberg number can be neglected.The constant area is corresponding to the region of turbulent flow.(2)The large eddy simulation results of asymmetric turbulent channel flow with ribs shows that the three Reynolds numbers of statistics has similar properties,mean velocity,Reynolds stress and root mean square fluctuating velocity are similar.The relationship between shear rate and wall distance is also different from that of the smooth channel,the region of smooth channel shear rate is constant,while there is a slight inclination in the asymmetric channel flow.(3)The large eddy simulation results of walls with a temperature difference and ribs asymmetric turbulent channel flow shows that the introduction of rib strengthen the turbulent mixing.Due to the driving force of buoyancy,plume is generated close the wall with high temperature and rising gradually.Finally the cold and hot fluid is fully mixed.And the ribs accelerate the generation of the plume and the turbulence fluctuating of bottom wall.