Numerical simulations were carried out to investigate the effects of synthetic jet actuation frequency on the separated flow in a diffusing S-duct.The Reynolds number based on the entrance height was9.78×105.At f...Numerical simulations were carried out to investigate the effects of synthetic jet actuation frequency on the separated flow in a diffusing S-duct.The Reynolds number based on the entrance height was9.78×105.At first,the numerical model was validated with experimental data,and then,the interaction between the separated flow and the synthetic jets at different frequencies was discussed.The results demonstrate that the control effect is significantly dependent on the momentum mixing enhancement between inside of the separated boundary layer and the outer flow.There exists a narrow range of actuation frequency,in which effective separation control can be achieved using synthetic jets.A dimensionless frequency F+=1.0is identified as the optimal frequency,with a momentum coefficient of 1.62×10-3,the separation area is reduced about46%,and the aerodynamic performance of the S-duct is also greatly improved compared to uncontrolled case.Further analysis reveals that the choice of actuation frequency is mainly determined by the momentum flux produced by a single ejection and the spacing between adjacent ejections,the optimal frequency case can be understood as a balance between the two factors.In addition,it is found that the synthetic jets can also suppress the secondary flows while decreasing the separation.展开更多
Heat transfer characteristics of oscillating turbulent air flow in a pipe heated with constant heat flux were experimentally investigated.The experiments were performed over a range of 245.7 to 902 of the kinetic Reyn...Heat transfer characteristics of oscillating turbulent air flow in a pipe heated with constant heat flux were experimentally investigated.The experiments were performed over a range of 245.7 to 902 of the kinetic Reynolds number and 25 to 175 of the dimensionless oscillation amplitude.The effects of these two dimensionless parameters were analyzed.The results show that the cycle-averaged local Nusselt number increases with both the kinetic Reynolds number and the dimensionless oscillation amplitude.The space-cycle averaged Nusselt number also effectively increases with the kinetic Reynolds number and the dimensionless oscillation amplitude.Based on the experimental data,a correlation equation of the space-cycle averaged Nusselt number for air in terms of these two dimensionless parameters has been obtained.展开更多
文摘Numerical simulations were carried out to investigate the effects of synthetic jet actuation frequency on the separated flow in a diffusing S-duct.The Reynolds number based on the entrance height was9.78×105.At first,the numerical model was validated with experimental data,and then,the interaction between the separated flow and the synthetic jets at different frequencies was discussed.The results demonstrate that the control effect is significantly dependent on the momentum mixing enhancement between inside of the separated boundary layer and the outer flow.There exists a narrow range of actuation frequency,in which effective separation control can be achieved using synthetic jets.A dimensionless frequency F+=1.0is identified as the optimal frequency,with a momentum coefficient of 1.62×10-3,the separation area is reduced about46%,and the aerodynamic performance of the S-duct is also greatly improved compared to uncontrolled case.Further analysis reveals that the choice of actuation frequency is mainly determined by the momentum flux produced by a single ejection and the spacing between adjacent ejections,the optimal frequency case can be understood as a balance between the two factors.In addition,it is found that the synthetic jets can also suppress the secondary flows while decreasing the separation.
文摘Heat transfer characteristics of oscillating turbulent air flow in a pipe heated with constant heat flux were experimentally investigated.The experiments were performed over a range of 245.7 to 902 of the kinetic Reynolds number and 25 to 175 of the dimensionless oscillation amplitude.The effects of these two dimensionless parameters were analyzed.The results show that the cycle-averaged local Nusselt number increases with both the kinetic Reynolds number and the dimensionless oscillation amplitude.The space-cycle averaged Nusselt number also effectively increases with the kinetic Reynolds number and the dimensionless oscillation amplitude.Based on the experimental data,a correlation equation of the space-cycle averaged Nusselt number for air in terms of these two dimensionless parameters has been obtained.
