In this article,the processes of vans running into a one-way two-lane road tunnel are simulated numerically using the dynamic mesh technique and RNG k ？ ε turbulence model.The transient aerodynamic characteristics a...In this article,the processes of vans running into a one-way two-lane road tunnel are simulated numerically using the dynamic mesh technique and RNG k ？ ε turbulence model.The transient aerodynamic characteristics around vans are obtained in three cases：a single van,two vans side-by-side and two vans one after another running into the tunnel,respectively.Through a comparison with the results of the wind tunnel experiment,the transient simulation method is verified.The results show that,when a van runs into the tunnel,the aerodynamic drag coefficient increases near the tunnel entrance,and after entering the tunnel,the side force is generated,pointing to the tunnel wall nearer to the van.When two vans run into the tunnel side-by-side,their drag coefficients increase by 50%,and the side force varies sharply with directions changing twice near the tunnel entrance.When two vans run into tunnel one after another,the aerodynamic characteristics around the van in the front is similar to that of a single van,but the aerodynamic forces on the van behind do not have obvious change.Among the three cases,the aerodynamic forces have a sharp change when two vans run side-by-side,so driving side-by-side into a tunnel should be avoided for safety.展开更多
The flow in the positive displacement blower is very complex.The existing two-dimensional numerical simulation cannot provide the detailed flow information,especially flow characteristics along the axial direction,whi...The flow in the positive displacement blower is very complex.The existing two-dimensional numerical simulation cannot provide the detailed flow information,especially flow characteristics along the axial direction,which is unfavorable to improve the performance of positive displacement blower.To investigate the effects of spiral inlet and outlet on the aerodynamic performance of positive displacement blower,three-dimensional unsteady flow characteristics in a three-lobe positive displacement blower with and without the spiral inlet and outlet are simulated by solving Navier-Stokes equations coupled with RNG k-ε turbulent model.In the numerical simulation,the dynamic mesh technique and overset mesh updating method are used.The computational results are compared with the experimental measurements on the variation of flow rate with the outlet pressure to verify the validity of the numerical method presented.The results show that the mass flow rate with the change of pressure is slightly affected by the application of spiral inlet and outlet,but the internal flow state is largely affected.In the exhaust region,the fluctuations of pressure,velocity and temperature as well as the average values of velocity are significantly reduced.This illustrates that the spiral outlet can effectively suppress the fluctuations of pressure,thus reducing reflux shock and energy dissipation.In the intake area,the average value of pressure,velocity and temperature are slightly declined,but the fluctuations of them are significantly reduced,indicating that the spiral inlet plays the role in making the flow more stable.The numerical results obtained reveal the three-dimensional flow characteristics of the positive displacement blower with spiral inlet and outlet,and provide useful reference to improve performance and empirical correction in the noise-reduction design of the positive displacement blowers.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 10802042)the NaturalScience Foundation of Shandong Province (Grant No.Y2007A04)
文摘In this article,the processes of vans running into a one-way two-lane road tunnel are simulated numerically using the dynamic mesh technique and RNG k ？ ε turbulence model.The transient aerodynamic characteristics around vans are obtained in three cases：a single van,two vans side-by-side and two vans one after another running into the tunnel,respectively.Through a comparison with the results of the wind tunnel experiment,the transient simulation method is verified.The results show that,when a van runs into the tunnel,the aerodynamic drag coefficient increases near the tunnel entrance,and after entering the tunnel,the side force is generated,pointing to the tunnel wall nearer to the van.When two vans run into the tunnel side-by-side,their drag coefficients increase by 50%,and the side force varies sharply with directions changing twice near the tunnel entrance.When two vans run into tunnel one after another,the aerodynamic characteristics around the van in the front is similar to that of a single van,but the aerodynamic forces on the van behind do not have obvious change.Among the three cases,the aerodynamic forces have a sharp change when two vans run side-by-side,so driving side-by-side into a tunnel should be avoided for safety.
基金supported by Fundamental Research Funds for the Central UniversitiesChina(Grant No.xjj20100073)Science and Technology Innovation Project of Shaanxi Province of China(Grant No.2011KTCL01-04)
文摘The flow in the positive displacement blower is very complex.The existing two-dimensional numerical simulation cannot provide the detailed flow information,especially flow characteristics along the axial direction,which is unfavorable to improve the performance of positive displacement blower.To investigate the effects of spiral inlet and outlet on the aerodynamic performance of positive displacement blower,three-dimensional unsteady flow characteristics in a three-lobe positive displacement blower with and without the spiral inlet and outlet are simulated by solving Navier-Stokes equations coupled with RNG k-ε turbulent model.In the numerical simulation,the dynamic mesh technique and overset mesh updating method are used.The computational results are compared with the experimental measurements on the variation of flow rate with the outlet pressure to verify the validity of the numerical method presented.The results show that the mass flow rate with the change of pressure is slightly affected by the application of spiral inlet and outlet,but the internal flow state is largely affected.In the exhaust region,the fluctuations of pressure,velocity and temperature as well as the average values of velocity are significantly reduced.This illustrates that the spiral outlet can effectively suppress the fluctuations of pressure,thus reducing reflux shock and energy dissipation.In the intake area,the average value of pressure,velocity and temperature are slightly declined,but the fluctuations of them are significantly reduced,indicating that the spiral inlet plays the role in making the flow more stable.The numerical results obtained reveal the three-dimensional flow characteristics of the positive displacement blower with spiral inlet and outlet,and provide useful reference to improve performance and empirical correction in the noise-reduction design of the positive displacement blowers.
