We study the transition to turbulence of channel flow of finite-size particle suspensions at low volume fraction, i.e., φ ≈0.001. The critical Reynolds number above which turbulence is sustained reduces to Re ≈ 167...We study the transition to turbulence of channel flow of finite-size particle suspensions at low volume fraction, i.e., φ ≈0.001. The critical Reynolds number above which turbulence is sustained reduces to Re ≈ 1675, in the presence of few particles, independently of the initial condition, a value lower than that of the corresponding single-phase flow, i.e., Re ≈1775. In the dilute suspension, the initial arrangement of the particles is important to trigger the transition at a fixed Reynolds number and particle volume fraction. As in single phase flows, streamwise elongated disturbances are initially induced in the flow. If particles can induce oblique disturbances with high enough energy within a certain time, the streaks breakdown, flow experiences the transition to turbulence and the particle trajectories become chaotic, Otherwise, the streaks decay in time and the particles immigrate towards the channel core in a laminar flow.展开更多
The equation of two-dimensional fiber direction vector was solved theoretically to give the fiber orientation distri- bution in simple shear flow, flow with two direction shears, extensional flow and arbitrary planar ...The equation of two-dimensional fiber direction vector was solved theoretically to give the fiber orientation distri- bution in simple shear flow, flow with two direction shears, extensional flow and arbitrary planar incompressible flow. The Fok- ker-Planck equation was solved numerically to validify the theoretical solutions. The stable orientation and orientation period of fiber were obtained. The results showed that the fiber orientation distribution is dependent on the relative not absolute magnitude of the matrix rate-of-strain of flow. The effect of fiber aspect ratio on the orientation distribution of fiber is insignificant in most conditions except the simple shear case. It was proved that the results for a planar flow could be generalized to the case of 3-D fiber direction vector.展开更多
A non-stretchable fiber rotation in planar flows has been solved. The fiber will rotate periodically or run to the asymptotical direction decided by a discriminant defined in the paper involving the fiber aspect ratio...A non-stretchable fiber rotation in planar flows has been solved. The fiber will rotate periodically or run to the asymptotical direction decided by a discriminant defined in the paper involving the fiber aspect ratio and the flow characteristics. Subsequently the fiber orientation distribution is derived directly without the bother of solving the Fokker-Planck equation. The research clearly indicates the overall configuration of a fiber rotation movement in planar flows.展开更多
Abrasive suspension flow machining(ASFM)is an advanced finishing method that uses an abrasive suspension slurry for grinding and chamfering as well as the finishing of inaccessible components.This study examines the e...Abrasive suspension flow machining(ASFM)is an advanced finishing method that uses an abrasive suspension slurry for grinding and chamfering as well as the finishing of inaccessible components.This study examines the effect of back pressure on the grinding characteristics of an abrasive suspension flow during the grinding of slender holes.A numerical model was developed to simulate the abrasive suspension flow in a slender hole and was verified experimentally using injector nozzle grinding equipment under different grinding pressures and back pressures.It is shown that the ASFM with back pressure not only eliminates the cavitation flow in the spray hole,but also increases the number of effective abrasive particles and the flow coefficient.Increasing the back pressure during the grinding process can increase the Reynolds number of the abrasive suspension flow and reduce the thickness of the boundary layer in the slender hole.Moreover,increasing the back pressure can improve the flow rate of the injector nozzle and its grinding performance.展开更多
基金supported by the European Research Council Grant No.ERC-2013-CoG-616186,TRITOSthe Swedish Research Council(VR)
文摘We study the transition to turbulence of channel flow of finite-size particle suspensions at low volume fraction, i.e., φ ≈0.001. The critical Reynolds number above which turbulence is sustained reduces to Re ≈ 1675, in the presence of few particles, independently of the initial condition, a value lower than that of the corresponding single-phase flow, i.e., Re ≈1775. In the dilute suspension, the initial arrangement of the particles is important to trigger the transition at a fixed Reynolds number and particle volume fraction. As in single phase flows, streamwise elongated disturbances are initially induced in the flow. If particles can induce oblique disturbances with high enough energy within a certain time, the streaks breakdown, flow experiences the transition to turbulence and the particle trajectories become chaotic, Otherwise, the streaks decay in time and the particles immigrate towards the channel core in a laminar flow.
基金Project (No. 10372090) supported by the National Natural Science Foundation of China
文摘The equation of two-dimensional fiber direction vector was solved theoretically to give the fiber orientation distri- bution in simple shear flow, flow with two direction shears, extensional flow and arbitrary planar incompressible flow. The Fok- ker-Planck equation was solved numerically to validify the theoretical solutions. The stable orientation and orientation period of fiber were obtained. The results showed that the fiber orientation distribution is dependent on the relative not absolute magnitude of the matrix rate-of-strain of flow. The effect of fiber aspect ratio on the orientation distribution of fiber is insignificant in most conditions except the simple shear case. It was proved that the results for a planar flow could be generalized to the case of 3-D fiber direction vector.
基金Project (No. 10632070) supported by the Major Program of theNational Natural Science Foundation of China
文摘A non-stretchable fiber rotation in planar flows has been solved. The fiber will rotate periodically or run to the asymptotical direction decided by a discriminant defined in the paper involving the fiber aspect ratio and the flow characteristics. Subsequently the fiber orientation distribution is derived directly without the bother of solving the Fokker-Planck equation. The research clearly indicates the overall configuration of a fiber rotation movement in planar flows.
文摘Abrasive suspension flow machining(ASFM)is an advanced finishing method that uses an abrasive suspension slurry for grinding and chamfering as well as the finishing of inaccessible components.This study examines the effect of back pressure on the grinding characteristics of an abrasive suspension flow during the grinding of slender holes.A numerical model was developed to simulate the abrasive suspension flow in a slender hole and was verified experimentally using injector nozzle grinding equipment under different grinding pressures and back pressures.It is shown that the ASFM with back pressure not only eliminates the cavitation flow in the spray hole,but also increases the number of effective abrasive particles and the flow coefficient.Increasing the back pressure during the grinding process can increase the Reynolds number of the abrasive suspension flow and reduce the thickness of the boundary layer in the slender hole.Moreover,increasing the back pressure can improve the flow rate of the injector nozzle and its grinding performance.
