The aquatic plants are often found in natural rivers,and they affect the channel flow structure significantly.To study the effects of the vegetation density a(the frontal area per volume)on the flow velocity character...The aquatic plants are often found in natural rivers,and they affect the channel flow structure significantly.To study the effects of the vegetation density a(the frontal area per volume)on the flow velocity characteristics,rigid bamboo circular cylinders are chosen as the model emergent vegetation.In the experiments,the density of the vegetation takes various values while all other flow parameters are kept constant.A 3-D acoustic Doppler velocimeter(ADV)is used to measure the local flow velocities for different vegetation densities.The results show that the existence of the vegetation patch leads to an increase of the depth-averaged velocity on the right and left sides behind the vegetation patch,and it increases monotonically with the vegetation density.For different vegetation densities,the lateral distribution of the stream-wise velocity behind the vegetation patch follows approximately an S-shaped profile when a≤60 m-1,and a logarithmic profile if a>60 m-1.The vertical distribution of the stream-wise velocity along the channel varies with the vegetation density and also follows an S-shaped distribution in a certain range,with the locations and the ranges being affected by the vegetation density.展开更多
A RNG numerical model together with a laboratory measurement with Micro ADV are adopted to investigate the flow through a 180o curved open channel（a 4 m straight inflow section,a 180o curved section,and a 4m straight...A RNG numerical model together with a laboratory measurement with Micro ADV are adopted to investigate the flow through a 180o curved open channel（a 4 m straight inflow section,a 180o curved section,and a 4m straight outflow section）partially covered with rigid vegetations on its inner bank.Under the combined action of the vegetation and the bend flow,the flow structure is complex.The stream-wise velocities in the vegetation region are much smaller than those in the non-vegetation region due to the retardation caused by the vegetation.For the same reason,no clear circulation is found in the vegetated region,while in the non-vegetation region,a slight counter-rotating circulation is found near the outer bank at both 90o and downstream curved cross-sections.A comparison between the numerical prediction and the laboratory measurement shows that the RNG model can well predict the flow structure of the bend flow with vegetation.Furthermore,the shear stress is analyzed based on the numerical prediction.The much smaller value in the inner vegetated region indicates that the vegetation can effectively protect the river bank from scouring and erosion,in other words,the sediment is more likely to be deposited in the vegetation region.展开更多
The three-dimensional （3D） reacting flow in a staged supersonic combustor is examined numerically. In order to obtain the optimum stream-wise vortices, a swept ramp injector is chosen as the second-stage wall inject...The three-dimensional （3D） reacting flow in a staged supersonic combustor is examined numerically. In order to obtain the optimum stream-wise vortices, a swept ramp injector is chosen as the second-stage wall injection combined with the first-stage central strut injection. The performance of the two-staged injection is compared with that of a one-staged injection, while the strut is kept installed in both cases. The two-staged injections can make full use of the residual oxygen near the wall and release more heat. The second-stage injection further downstream avoids the strong shock waves in the isolator and results in a rising wall pressure and good burning effects after the wall injection. Therefore, it allows more fuel to be injected into the supersonic combustor without causing thermal choking. Parallel injection from the second-stage swept ramp shows low total pressure loss and the best burning efficiency, compared with the other injection angles.展开更多
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
Results from a series of studies on the stream-wise vibration of a circular cylinder verifying Japan Society of Mechanical Engineers Standard S012-1998, Guideline for Evaluation of Flow-induced Vibration of a Cylindri...Results from a series of studies on the stream-wise vibration of a circular cylinder verifying Japan Society of Mechanical Engineers Standard S012-1998, Guideline for Evaluation of Flow-induced Vibration of a Cylindrical Structure in a Pipe, are summarized and discussed in this paper. Experiments were carried out in a water tunnel and in a wind tunnel using a two-dimensional cylinder model elastically supported at both ends of the cylinder and a cantilevered cylinder model with a finite span length that was elastically supported at one end. These cylinder models were allowed to vibrate with one degree of freedom in the stream-wise direction. In addition, we adopted a cantilevered cylinder model that vibrated with two degrees of freedom in both the stream-wise and cross-flow directions under the same vibration conditions as an actual thermocouple well. The value of the Scruton number (structural damping parameter) was changed over a wide range, so as to evaluate the value of the critical Scruton number that suppressed vibration of the cylinder. For the two-dimensional cylinder, two different types of stream-wise excitations appeared in the reduced velocity range of approximately half of the resonance-reduced velocity. For the stream-wise vibration in the first excitation region, due to a symmetric vortex flow, the response amplitudes were sensitive to the Scruton number, while the shedding frequency of alternating vortex flow was locked-in to half of the Strouhal number of vibrating frequency of a cylinder in the second excitation region. In addition, the effects of the aspect ratio of a cantilevered cylinder on the flow-induced vibration characteristics were clarified and compared with the results of a two-dimensional cylinder. When a cantilevered circular cylinder with a finite length vibrates with one degree of freedom in the stream-wise di-rection, it is found that acylinder with a small aspect ratio has a single excitation region, whereas a cylinder with a large aspect ratio has two excitation regions. Furthe展开更多
An experimental investigation of effects of a kind of streamwise-grooved blade on the unsteady flow field at an exit of an axial-flow fan was performed. The flow field at 25% chord downstream from the trailing edge at...An experimental investigation of effects of a kind of streamwise-grooved blade on the unsteady flow field at an exit of an axial-flow fan was performed. The flow field at 25% chord downstream from the trailing edge at hub was measured using a fast-response five-hole pressure probe at different mass-flow conditions. The unsteady flow of the grooved blades was compared with that of the smooth blades. The measurement results indicate that： （1） the grooved blades restrain the velocity fluctuation and the pressure fluctuation by modulating the blade boundary layers, which contributes to the flow loss reduction in the hub region and in the rotor wake region at the design condition; （2） the stream-wise grooves play an important role in restraining the radial migration in the blade boundary layer and abating the tip flow mixing, which contributes to the flow loss reduction in the tip region at the design condition; （3） at the near stall condition, the grooved surface can not reduce the flow loss, even increase the loss nearby when the separation happens in the blade boundary layer.展开更多
With the development of the offshore deep water oil industry many researchers are focusing on the vortex-induced vibrations （VIV） of deep risers. In the present work, Reynolds-averaged Navier-Stokes （RANS） equatio...With the development of the offshore deep water oil industry many researchers are focusing on the vortex-induced vibrations （VIV） of deep risers. In the present work, Reynolds-averaged Navier-Stokes （RANS） equations were combined with the SST κ-ω turbulent model to simulate the stream-wise and transverse motion of an elastically mounted cylinder with a low mass-ratio, a natural frequency ratio of fx/fy = 1 and an Re number between 5 300 and 32 000, The four-order Runge-Kutta method was applied to solve the oscillating equation of the cylinder. The relationship between reduced velocity and parameters of the cylinder, including the lift coefficient, the drag coefficient, displacement and the vortex structure were then compared with recent experimental results and discussed in detail. The present numerical simulation reproduced effects have been observed in experiments, such as the lock-in phenomenon, the hysteretic phenomenon and beating behavior.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51539007,51479128 and 51609160)the National Key Research and Development Program of China(Grant No.2016YFC0402302).
文摘The aquatic plants are often found in natural rivers,and they affect the channel flow structure significantly.To study the effects of the vegetation density a(the frontal area per volume)on the flow velocity characteristics,rigid bamboo circular cylinders are chosen as the model emergent vegetation.In the experiments,the density of the vegetation takes various values while all other flow parameters are kept constant.A 3-D acoustic Doppler velocimeter(ADV)is used to measure the local flow velocities for different vegetation densities.The results show that the existence of the vegetation patch leads to an increase of the depth-averaged velocity on the right and left sides behind the vegetation patch,and it increases monotonically with the vegetation density.For different vegetation densities,the lateral distribution of the stream-wise velocity behind the vegetation patch follows approximately an S-shaped profile when a≤60 m-1,and a logarithmic profile if a>60 m-1.The vertical distribution of the stream-wise velocity along the channel varies with the vegetation density and also follows an S-shaped distribution in a certain range,with the locations and the ranges being affected by the vegetation density.
基金supported by the Natural National Science Foundation of China(Grant Nos.11172218,10972163,51079102and50979078)
文摘A RNG numerical model together with a laboratory measurement with Micro ADV are adopted to investigate the flow through a 180o curved open channel（a 4 m straight inflow section,a 180o curved section,and a 4m straight outflow section）partially covered with rigid vegetations on its inner bank.Under the combined action of the vegetation and the bend flow,the flow structure is complex.The stream-wise velocities in the vegetation region are much smaller than those in the non-vegetation region due to the retardation caused by the vegetation.For the same reason,no clear circulation is found in the vegetated region,while in the non-vegetation region,a slight counter-rotating circulation is found near the outer bank at both 90o and downstream curved cross-sections.A comparison between the numerical prediction and the laboratory measurement shows that the RNG model can well predict the flow structure of the bend flow with vegetation.Furthermore,the shear stress is analyzed based on the numerical prediction.The much smaller value in the inner vegetated region indicates that the vegetation can effectively protect the river bank from scouring and erosion,in other words,the sediment is more likely to be deposited in the vegetation region.
基金National Natural Science Foundation of China(50306011)the German Research Foundation (DFG) (GRK1095/1)
文摘The three-dimensional （3D） reacting flow in a staged supersonic combustor is examined numerically. In order to obtain the optimum stream-wise vortices, a swept ramp injector is chosen as the second-stage wall injection combined with the first-stage central strut injection. The performance of the two-staged injection is compared with that of a one-staged injection, while the strut is kept installed in both cases. The two-staged injections can make full use of the residual oxygen near the wall and release more heat. The second-stage injection further downstream avoids the strong shock waves in the isolator and results in a rising wall pressure and good burning effects after the wall injection. Therefore, it allows more fuel to be injected into the supersonic combustor without causing thermal choking. Parallel injection from the second-stage swept ramp shows low total pressure loss and the best burning efficiency, compared with the other injection angles.
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%.
文摘Results from a series of studies on the stream-wise vibration of a circular cylinder verifying Japan Society of Mechanical Engineers Standard S012-1998, Guideline for Evaluation of Flow-induced Vibration of a Cylindrical Structure in a Pipe, are summarized and discussed in this paper. Experiments were carried out in a water tunnel and in a wind tunnel using a two-dimensional cylinder model elastically supported at both ends of the cylinder and a cantilevered cylinder model with a finite span length that was elastically supported at one end. These cylinder models were allowed to vibrate with one degree of freedom in the stream-wise direction. In addition, we adopted a cantilevered cylinder model that vibrated with two degrees of freedom in both the stream-wise and cross-flow directions under the same vibration conditions as an actual thermocouple well. The value of the Scruton number (structural damping parameter) was changed over a wide range, so as to evaluate the value of the critical Scruton number that suppressed vibration of the cylinder. For the two-dimensional cylinder, two different types of stream-wise excitations appeared in the reduced velocity range of approximately half of the resonance-reduced velocity. For the stream-wise vibration in the first excitation region, due to a symmetric vortex flow, the response amplitudes were sensitive to the Scruton number, while the shedding frequency of alternating vortex flow was locked-in to half of the Strouhal number of vibrating frequency of a cylinder in the second excitation region. In addition, the effects of the aspect ratio of a cantilevered cylinder on the flow-induced vibration characteristics were clarified and compared with the results of a two-dimensional cylinder. When a cantilevered circular cylinder with a finite length vibrates with one degree of freedom in the stream-wise di-rection, it is found that acylinder with a small aspect ratio has a single excitation region, whereas a cylinder with a large aspect ratio has two excitation regions. Furthe
基金National Natural Science Foundation of China,Grant No.50376002the 111 Project,No.B07009
文摘An experimental investigation of effects of a kind of streamwise-grooved blade on the unsteady flow field at an exit of an axial-flow fan was performed. The flow field at 25% chord downstream from the trailing edge at hub was measured using a fast-response five-hole pressure probe at different mass-flow conditions. The unsteady flow of the grooved blades was compared with that of the smooth blades. The measurement results indicate that： （1） the grooved blades restrain the velocity fluctuation and the pressure fluctuation by modulating the blade boundary layers, which contributes to the flow loss reduction in the hub region and in the rotor wake region at the design condition; （2） the stream-wise grooves play an important role in restraining the radial migration in the blade boundary layer and abating the tip flow mixing, which contributes to the flow loss reduction in the tip region at the design condition; （3） at the near stall condition, the grooved surface can not reduce the flow loss, even increase the loss nearby when the separation happens in the blade boundary layer.
文摘With the development of the offshore deep water oil industry many researchers are focusing on the vortex-induced vibrations （VIV） of deep risers. In the present work, Reynolds-averaged Navier-Stokes （RANS） equations were combined with the SST κ-ω turbulent model to simulate the stream-wise and transverse motion of an elastically mounted cylinder with a low mass-ratio, a natural frequency ratio of fx/fy = 1 and an Re number between 5 300 and 32 000, The four-order Runge-Kutta method was applied to solve the oscillating equation of the cylinder. The relationship between reduced velocity and parameters of the cylinder, including the lift coefficient, the drag coefficient, displacement and the vortex structure were then compared with recent experimental results and discussed in detail. The present numerical simulation reproduced effects have been observed in experiments, such as the lock-in phenomenon, the hysteretic phenomenon and beating behavior.
