A high-order upwind scheme has been developed to capture the vortex wake of a helicopter rotor in the hover based on chimera grids. In this paper, an improved fifth-order weighted essentially non-oscillatory （WENO） ...A high-order upwind scheme has been developed to capture the vortex wake of a helicopter rotor in the hover based on chimera grids. In this paper, an improved fifth-order weighted essentially non-oscillatory （WENO） scheme is adopted to interpolate the higher-order left and right states across a cell interface with the Roe Riemann solver updating inviscid flux, and is compared with the monotone upwind scheme for scalar conservation laws （MUSCL）. For profitably capturing the wake and enforcing the period boundary condition, the computation regions of flows are discretized by using the struc- tured chimera grids composed of a fine rotor grid and a cylindrical background grid. In the background grid, the mesh cells located in the wake regions are refined after the so- lution reaches the approximate convergence. Considering the interpolation characteristic of the WENO scheme, three layers of the hole boundary and the interpolation boundary are searched. The performance of the schemes is investigated in a transonic flow and a subsonic flow around the hovering rotor. The results reveal that the present approach has great capabilities in capturing the vortex wake with high resolution, and the WENO scheme has much lower numerical dissipation in comparison with the MUSCL scheme.展开更多
In this paper,an intelligent control method applying on numerical virtual flight is proposed.The proposed algorithm is verified and evaluated by combining with the case of the basic finner projectile model and shows a...In this paper,an intelligent control method applying on numerical virtual flight is proposed.The proposed algorithm is verified and evaluated by combining with the case of the basic finner projectile model and shows a good application prospect.Firstly,a numerical virtual flight simulation model based on overlapping dynamic mesh technology is constructed.In order to verify the accuracy of the dynamic grid technology and the calculation of unsteady flow,a numerical simulation of the basic finner projectile without control is carried out.The simulation results are in good agreement with the experiment data which shows that the algorithm used in this paper can also be used in the design and evaluation of the intelligent controller in the numerical virtual flight simulation.Secondly,combined with the real-time control requirements of aerodynamic,attitude and displacement parameters of the projectile during the flight process,the numerical simulations of the basic finner projectile’s pitch channel are carried out under the traditional PID(Proportional-Integral-Derivative)control strategy and the intelligent PID control strategy respectively.The intelligent PID controller based on BP(Back Propagation)neural network can realize online learning and self-optimization of control parameters according to the acquired real-time flight parameters.Compared with the traditional PID controller,the concerned control variable overshoot,rise time,transition time and steady state error and other performance indicators have been greatly improved,and the higher the learning efficiency or the inertia coefficient,the faster the system,the larger the overshoot,and the smaller the stability error.The intelligent control method applying on numerical virtual flight is capable of solving the complicated unsteady motion and flow with the intelligent PID control strategy and has a strong promotion to engineering application.展开更多
The joint grid system, which consists of the developed collar grid, the virtual grid and other grids, was used in the embedding technique to solve the problem of finding interpolating cells of the internal and externa...The joint grid system, which consists of the developed collar grid, the virtual grid and other grids, was used in the embedding technique to solve the problem of finding interpolating cells of the internal and external boundary points near the joint regions. With different boundary plane generated along different fixed surface, the collar grid obtained using hyperbolic partial equations can ensure to generate high quality grids and to provide real interpolating cells for the boundary points in the blanking regions. The virtual grid was used to convert solid wall boundary conditions into an interface condition, however, no fluid flow computations were conducted within the virtual grid. The computational result of body strake wing shows that the current developed embedding technique with joint grid system can effectively treat the geometry and can more accurately predict the flow over complexconfiguration with intersecting surfaces.展开更多
The virtual grid method used in the embedding technique to solve the problem of finding interpolating cells of the inner and outer boundary points near joint regions was developed for calculating the viscous flows aro...The virtual grid method used in the embedding technique to solve the problem of finding interpolating cells of the inner and outer boundary points near joint regions was developed for calculating the viscous flows around a wing with control surface. The main purpose of the virtual grid is to effectively treat the geometry of the crossed facial planes at the interface, and to convert a solid wall boundary condition into an interface condition, however, no fluid flow computations are conducted within the virtual grid. Navier Stokes computations were performed for transonic flow over a clipped delta wing with control surface, and the computed results compare well with the experimental data.展开更多
基金supported by the National Natural Science Foundation of China(No.10802046)
文摘A high-order upwind scheme has been developed to capture the vortex wake of a helicopter rotor in the hover based on chimera grids. In this paper, an improved fifth-order weighted essentially non-oscillatory （WENO） scheme is adopted to interpolate the higher-order left and right states across a cell interface with the Roe Riemann solver updating inviscid flux, and is compared with the monotone upwind scheme for scalar conservation laws （MUSCL）. For profitably capturing the wake and enforcing the period boundary condition, the computation regions of flows are discretized by using the struc- tured chimera grids composed of a fine rotor grid and a cylindrical background grid. In the background grid, the mesh cells located in the wake regions are refined after the so- lution reaches the approximate convergence. Considering the interpolation characteristic of the WENO scheme, three layers of the hole boundary and the interpolation boundary are searched. The performance of the schemes is investigated in a transonic flow and a subsonic flow around the hovering rotor. The results reveal that the present approach has great capabilities in capturing the vortex wake with high resolution, and the WENO scheme has much lower numerical dissipation in comparison with the MUSCL scheme.
文摘In this paper,an intelligent control method applying on numerical virtual flight is proposed.The proposed algorithm is verified and evaluated by combining with the case of the basic finner projectile model and shows a good application prospect.Firstly,a numerical virtual flight simulation model based on overlapping dynamic mesh technology is constructed.In order to verify the accuracy of the dynamic grid technology and the calculation of unsteady flow,a numerical simulation of the basic finner projectile without control is carried out.The simulation results are in good agreement with the experiment data which shows that the algorithm used in this paper can also be used in the design and evaluation of the intelligent controller in the numerical virtual flight simulation.Secondly,combined with the real-time control requirements of aerodynamic,attitude and displacement parameters of the projectile during the flight process,the numerical simulations of the basic finner projectile’s pitch channel are carried out under the traditional PID(Proportional-Integral-Derivative)control strategy and the intelligent PID control strategy respectively.The intelligent PID controller based on BP(Back Propagation)neural network can realize online learning and self-optimization of control parameters according to the acquired real-time flight parameters.Compared with the traditional PID controller,the concerned control variable overshoot,rise time,transition time and steady state error and other performance indicators have been greatly improved,and the higher the learning efficiency or the inertia coefficient,the faster the system,the larger the overshoot,and the smaller the stability error.The intelligent control method applying on numerical virtual flight is capable of solving the complicated unsteady motion and flow with the intelligent PID control strategy and has a strong promotion to engineering application.
文摘The joint grid system, which consists of the developed collar grid, the virtual grid and other grids, was used in the embedding technique to solve the problem of finding interpolating cells of the internal and external boundary points near the joint regions. With different boundary plane generated along different fixed surface, the collar grid obtained using hyperbolic partial equations can ensure to generate high quality grids and to provide real interpolating cells for the boundary points in the blanking regions. The virtual grid was used to convert solid wall boundary conditions into an interface condition, however, no fluid flow computations were conducted within the virtual grid. The computational result of body strake wing shows that the current developed embedding technique with joint grid system can effectively treat the geometry and can more accurately predict the flow over complexconfiguration with intersecting surfaces.
文摘The virtual grid method used in the embedding technique to solve the problem of finding interpolating cells of the inner and outer boundary points near joint regions was developed for calculating the viscous flows around a wing with control surface. The main purpose of the virtual grid is to effectively treat the geometry of the crossed facial planes at the interface, and to convert a solid wall boundary condition into an interface condition, however, no fluid flow computations are conducted within the virtual grid. Navier Stokes computations were performed for transonic flow over a clipped delta wing with control surface, and the computed results compare well with the experimental data.
