A method of unstructured dynamic overset grids is developed for the numerical simulation of helicopter unsteady rotorairframe aerodynamic interaction.For the effective treatment of the relative motion between the roto...A method of unstructured dynamic overset grids is developed for the numerical simulation of helicopter unsteady rotorairframe aerodynamic interaction.For the effective treatment of the relative motion between the rotor and the airframe,the domain of flowfield is divided into two overset subzones,namely,a rotational subzone containing the blades and a stationary subzone containing the airframe.The overset part of two subzones is used to convect the flow variables of the two zones.The Taylor series expansion is used to obtain a second-order spatial accuracy,and dual-time stepping is adopted to improve the solution accuracy.Mesh deformation from the blade motion in forward flight is treated by using a spring analogy.Validation is made by numerically simulating the flows around a wind tunnel configuration and comparing the predicted time-averaged and instantaneous inflow and airframe surface pressure distributions with the experimental data.It shows that the present method is efficient and robust for the prediction of complicated unsteady rotor-airframe aerodynamic interaction phenomena.展开更多
Fully nonlinear water entry of a cone into waves with gravity effect has been analyzed based on a three-dimensional(3D)higher-order boundary method(HOBEM).The total velocity potential at the initial time is divided in...Fully nonlinear water entry of a cone into waves with gravity effect has been analyzed based on a three-dimensional(3D)higher-order boundary method(HOBEM).The total velocity potential at the initial time is divided into the incident and scattering components.In the subsequent time steps,the solution of the velocity potential is defined as a whole through instantaneous boundary conditions.Based on the image theory,a modified Green function is applied to establish the integral equations so that only half of the calculation domain is considered and the seabed can be excluded.The free surface elevation is tracked along a given azimuth plane in the polar coordinate system,while the horizontal motion of the water particle is updated by using a segment-spring analogy method,which redistributes nodes and maintains mesh connectivity according to linear stiffness.An auxiliary function is applied to solve the pressure distribution,instead of directly calculating time derivative of the velocity potential.The high accuracy of the present numerical method is achieved through a detailed convergence study and comparison with results in the literature.Simulations are emphatically performed to examine the effects of gravity,wave nonlinearity,entry location,and oblique entry.展开更多
基金supported by the Basic Research Program of Northwestern Polytechnical University (Grant No. JC201219)the Postdoctoral Science Foundation of China (Grant No. 20100481368)
文摘A method of unstructured dynamic overset grids is developed for the numerical simulation of helicopter unsteady rotorairframe aerodynamic interaction.For the effective treatment of the relative motion between the rotor and the airframe,the domain of flowfield is divided into two overset subzones,namely,a rotational subzone containing the blades and a stationary subzone containing the airframe.The overset part of two subzones is used to convect the flow variables of the two zones.The Taylor series expansion is used to obtain a second-order spatial accuracy,and dual-time stepping is adopted to improve the solution accuracy.Mesh deformation from the blade motion in forward flight is treated by using a spring analogy.Validation is made by numerically simulating the flows around a wind tunnel configuration and comparing the predicted time-averaged and instantaneous inflow and airframe surface pressure distributions with the experimental data.It shows that the present method is efficient and robust for the prediction of complicated unsteady rotor-airframe aerodynamic interaction phenomena.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52025112,51861130358,and 51609109)the State Key Laboratory of Ocean Engineering,China(Shanghai Jiao Tong University)(Grant No.1905)+1 种基金the Newton Advanced Fellowships(Grant No.NAF\R1\180304)by the Royal Societythe Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX20_3156).
文摘Fully nonlinear water entry of a cone into waves with gravity effect has been analyzed based on a three-dimensional(3D)higher-order boundary method(HOBEM).The total velocity potential at the initial time is divided into the incident and scattering components.In the subsequent time steps,the solution of the velocity potential is defined as a whole through instantaneous boundary conditions.Based on the image theory,a modified Green function is applied to establish the integral equations so that only half of the calculation domain is considered and the seabed can be excluded.The free surface elevation is tracked along a given azimuth plane in the polar coordinate system,while the horizontal motion of the water particle is updated by using a segment-spring analogy method,which redistributes nodes and maintains mesh connectivity according to linear stiffness.An auxiliary function is applied to solve the pressure distribution,instead of directly calculating time derivative of the velocity potential.The high accuracy of the present numerical method is achieved through a detailed convergence study and comparison with results in the literature.Simulations are emphatically performed to examine the effects of gravity,wave nonlinearity,entry location,and oblique entry.
