In the course of studying on aerodynamic change and its effect on steering stability and controllability of an automobile in passing, because of multi interaction streams, it is difficult to use traditional methods, s...In the course of studying on aerodynamic change and its effect on steering stability and controllability of an automobile in passing, because of multi interaction streams, it is difficult to use traditional methods, such as wind tunnel test and road test. If the passing process of an automobile is divided into many time segments, so as to avoid the use of moving mesh which takes large calculation resource and CPU processing time in calculating, the segments are simulated with computational fluid dynamics （CFD） method, then the approximate computational results about external flow field will be obtained. On the basis of the idea, the change of external flow field of wagon-shaped car at the moment of passing is simulated through solving three-dimensional, steady and uncompressible N-S equations with finite volume method. Numerical simulation analysis of side force coefficient, stream lines, body surface pressure distribution of wagon-shaped car are presented and a preliminary discussion of aerodynamic characteristics of correlative situations is obtained. Finally, the C3 -x/l curve of side force coefficient（C3） of car following relative distance （x/l） between cars is obtained. By comparison, the curve is coincident well with the experimental data, which shows creditability of numerical simulation methods presented.展开更多
The drag and side force coefficients of a half-submerged cylinder in a free-surface flow were calculated through numerical simulations,with the aim of supporting the numerical modelling of log transport in rivers.The ...The drag and side force coefficients of a half-submerged cylinder in a free-surface flow were calculated through numerical simulations,with the aim of supporting the numerical modelling of log transport in rivers.The variability of these coefficients with the yaw angle with respect to the flow direction and with the ratio between the flow depth and the diameter of the cylinder were investigated.Simulations were performed with the three-dimensional code ANSYS/CFX,employing the volume of fluid multiphase technique to reproduce the critical interaction between the free surface and the cylinder.The numerical tests,showing the rise of the drag force coefficient for increasing yaw angles passing from flow-parallel to flow-perpendicular cylinder and the peak of the side force coefficient for flow-oblique cylinder,were validated by comparison with the results of laboratory experiments.The simulations were then extended to conditions with significant blockage in the vertical direction which had not been previously experimented,revealing a strong increase in the force coefficients for decreasing ratios between the flow depth and the cylinder diameter.A detailed description of the reproduced flow features in the proximity of the cylinder for the different cases was furthermore obtained.Such report,in addition to the analysis of the force coefficients,could serve a much wider range than that of log transport,i.e.,any case in which a floating cylinder interacts with free-surface flow.展开更多
基金National Natural Science Foundation of China(No. 50275052).
文摘In the course of studying on aerodynamic change and its effect on steering stability and controllability of an automobile in passing, because of multi interaction streams, it is difficult to use traditional methods, such as wind tunnel test and road test. If the passing process of an automobile is divided into many time segments, so as to avoid the use of moving mesh which takes large calculation resource and CPU processing time in calculating, the segments are simulated with computational fluid dynamics （CFD） method, then the approximate computational results about external flow field will be obtained. On the basis of the idea, the change of external flow field of wagon-shaped car at the moment of passing is simulated through solving three-dimensional, steady and uncompressible N-S equations with finite volume method. Numerical simulation analysis of side force coefficient, stream lines, body surface pressure distribution of wagon-shaped car are presented and a preliminary discussion of aerodynamic characteristics of correlative situations is obtained. Finally, the C3 -x/l curve of side force coefficient（C3） of car following relative distance （x/l） between cars is obtained. By comparison, the curve is coincident well with the experimental data, which shows creditability of numerical simulation methods presented.
基金The authors greatly appreciate the financial support received by Dr.M.I.
文摘The drag and side force coefficients of a half-submerged cylinder in a free-surface flow were calculated through numerical simulations,with the aim of supporting the numerical modelling of log transport in rivers.The variability of these coefficients with the yaw angle with respect to the flow direction and with the ratio between the flow depth and the diameter of the cylinder were investigated.Simulations were performed with the three-dimensional code ANSYS/CFX,employing the volume of fluid multiphase technique to reproduce the critical interaction between the free surface and the cylinder.The numerical tests,showing the rise of the drag force coefficient for increasing yaw angles passing from flow-parallel to flow-perpendicular cylinder and the peak of the side force coefficient for flow-oblique cylinder,were validated by comparison with the results of laboratory experiments.The simulations were then extended to conditions with significant blockage in the vertical direction which had not been previously experimented,revealing a strong increase in the force coefficients for decreasing ratios between the flow depth and the cylinder diameter.A detailed description of the reproduced flow features in the proximity of the cylinder for the different cases was furthermore obtained.Such report,in addition to the analysis of the force coefficients,could serve a much wider range than that of log transport,i.e.,any case in which a floating cylinder interacts with free-surface flow.
