Measurements of characteristics by means of a two-component Laser DopplerVelocimeter (LDV) were carried out in turbulent boundary layers over both a symmetric V-shapedribbed plate and a smooth one in a low speed wind ...Measurements of characteristics by means of a two-component Laser DopplerVelocimeter (LDV) were carried out in turbulent boundary layers over both a symmetric V-shapedribbed plate and a smooth one in a low speed wind tunnel. The present results clearly indicate thatthe logarithmic velocity profile over the riblets surface is shifted upward with a 30. 9% increasein the thickness of the viscous sublayer. Also a change in the log-law region is found. And themaximum value of streamwise velocity fluctuations is reduced by approximately 17%. The skewness andflatness factors do not show any change besides those in the region of y^+ 【 0. 6 . It is evidentthat the Reynolds shear stress over the riblets is reduced. Further more, in log-law region, theReynolds shear stress has a larger reduction of up to 18%.展开更多
The velocities of boundary layer flows between two parallel oscillating plates separated by small distance, i.e., in so called narrow channel, were theoretically and experimentally studied. The focus was on the lamina...The velocities of boundary layer flows between two parallel oscillating plates separated by small distance, i.e., in so called narrow channel, were theoretically and experimentally studied. The focus was on the laminar case where the Reynolds number ReA is much smaller than the transition value. The theoretical analysis of the Stokes layer in oscillating flow over a narrow channel was made first. Then Laser Doppler Velocimeter （LDV） was employed to measure the Stokes boundary layer above an oscillating flat plate and inside the oscillating narrow channel at various ReH numbers. At the same time, the phase angle difference along the vertical direction in both analysis and experiment were provided. The good agreements are shown between the measured results and the theoretical solution.展开更多
The turbo air classifier is widely used powder classification equipment in a variety of fields. The flow field characteristics of the turbo air classifier are important basis for the improvement of the turbo air class...The turbo air classifier is widely used powder classification equipment in a variety of fields. The flow field characteristics of the turbo air classifier are important basis for the improvement of the turbo air classifier＇s structural design. The flow field characteristics of the rotor cage in turbo air classifiers were investigated trader different operating conditions by laser Doppler velocimeter（LDV）, and a measure diminishing the axial velocity is proposed. The investigation results show that the tangential velocity of the air flow inside the rotor cage is different from the rotary speed of the rotor cage on the same measurement point due to the influences of both the negative pressure at the exit and the rotation of the rotor cage. The tangential velocity of the air flow likewise decreases as the radius decreases in the case of the rotor cage＇s low rotary speed. In contrast, the tangential velocity of the air flow increases as the radius decreases in the case of the rotor cage＇s high rotary speed. Meanwhile, the vortex inside the rotor cage is found to occur near the pressure side of the blade when the rotor cage＇s rotary speed is less than the tangential velocity of air flow. On the contrary, the vortex is found to occur near the blade suction side once the rotor cage＇s rotary speed is higher than the tangential velocity of air flow. Inside the rotor cage, the axial velocity could not be disregarded and is largely determined by the distances between the measurement point and the exit.展开更多
文摘Measurements of characteristics by means of a two-component Laser DopplerVelocimeter (LDV) were carried out in turbulent boundary layers over both a symmetric V-shapedribbed plate and a smooth one in a low speed wind tunnel. The present results clearly indicate thatthe logarithmic velocity profile over the riblets surface is shifted upward with a 30. 9% increasein the thickness of the viscous sublayer. Also a change in the log-law region is found. And themaximum value of streamwise velocity fluctuations is reduced by approximately 17%. The skewness andflatness factors do not show any change besides those in the region of y^+ 【 0. 6 . It is evidentthat the Reynolds shear stress over the riblets is reduced. Further more, in log-law region, theReynolds shear stress has a larger reduction of up to 18%.
基金Project supported by the Hongkong SAR Government under the RGC (Grant No. 6165/98E)the RIG (Grant No. R195/96.EG15)supported by the HKUST (Grant No. 6254/02E).
文摘The velocities of boundary layer flows between two parallel oscillating plates separated by small distance, i.e., in so called narrow channel, were theoretically and experimentally studied. The focus was on the laminar case where the Reynolds number ReA is much smaller than the transition value. The theoretical analysis of the Stokes layer in oscillating flow over a narrow channel was made first. Then Laser Doppler Velocimeter （LDV） was employed to measure the Stokes boundary layer above an oscillating flat plate and inside the oscillating narrow channel at various ReH numbers. At the same time, the phase angle difference along the vertical direction in both analysis and experiment were provided. The good agreements are shown between the measured results and the theoretical solution.
基金supported by National Natural Science Foundation of China (Grant No. 50474035)
文摘The turbo air classifier is widely used powder classification equipment in a variety of fields. The flow field characteristics of the turbo air classifier are important basis for the improvement of the turbo air classifier＇s structural design. The flow field characteristics of the rotor cage in turbo air classifiers were investigated trader different operating conditions by laser Doppler velocimeter（LDV）, and a measure diminishing the axial velocity is proposed. The investigation results show that the tangential velocity of the air flow inside the rotor cage is different from the rotary speed of the rotor cage on the same measurement point due to the influences of both the negative pressure at the exit and the rotation of the rotor cage. The tangential velocity of the air flow likewise decreases as the radius decreases in the case of the rotor cage＇s low rotary speed. In contrast, the tangential velocity of the air flow increases as the radius decreases in the case of the rotor cage＇s high rotary speed. Meanwhile, the vortex inside the rotor cage is found to occur near the pressure side of the blade when the rotor cage＇s rotary speed is less than the tangential velocity of air flow. On the contrary, the vortex is found to occur near the blade suction side once the rotor cage＇s rotary speed is higher than the tangential velocity of air flow. Inside the rotor cage, the axial velocity could not be disregarded and is largely determined by the distances between the measurement point and the exit.
