Applications of a novel curve-fitting technique are presented to efficiently predict the motion of the vortex filament, which is trailed from a rigid body such as wings and rotors. The gov- erning equations of the mot...Applications of a novel curve-fitting technique are presented to efficiently predict the motion of the vortex filament, which is trailed from a rigid body such as wings and rotors. The gov- erning equations of the motion, when a Lagrangian approach with the present curve-fitting method is applied, can be transformed into an easily solvable form of the system of nonlinear ordinary dif- ferential equations. The applicability of Bezier curves, B-spline, and Lagrange interpolating polyno- mials is investigated. Local Lagrange interpolating polynomials with a shift operator are proposed as the best selection for applications, since it provides superior system characteristics with minimum computing time, compared to other methods. In addition, the Gauss quadrature formula with local refinement strategy has been developed for an accurate prediction of the induced velocity computed with the line integration of the Biot-Savart law. Rotary-wing problems including a vortex ring problem are analyzed to show the efficiency, accuracy, and flexibility in the applications of the pro- posed method.展开更多
The present hybrid vortex tube-vorton method is based entirely on the Full Multi-wake Vortex Lattice Method(FMVLM)concepts,which means detaching vorticity with pre-cise vortex strength and orientation along all separa...The present hybrid vortex tube-vorton method is based entirely on the Full Multi-wake Vortex Lattice Method(FMVLM)concepts,which means detaching vorticity with pre-cise vortex strength and orientation along all separation lines between each discretized element of a shell-body,including all external edges.Since the classic Vortex Particle Method(VPM)is unstable by itself because it does not conserve the total amount of circulation as time evolves(Kelvin’s circulation theorem),an isolated Vortex(regular-ized)Filament Method(VFM)approach is implemented to obtain advection of vorti-city,while the induced velocity field is obtained through its corresponding full vorton cloud.Further,a novel vortex squeezing/stretching scheme for such a vortex cylinder-sphere approach is proposed based on variation in time for vortex volumes in order to precisely(zero residual)conserve both circulation and vorticity at each time step(for each detached vortex element),while the viscous effect can be accounted for via the Core Spreading Method(CSM).展开更多
Experiments of a flexible filament in the wake of a cylinder and in free stream were conducted in a vertical soap film tunnel. The experiments distinctly visualized the movement of the filament. Based on the experimen...Experiments of a flexible filament in the wake of a cylinder and in free stream were conducted in a vertical soap film tunnel. The experiments distinctly visualized the movement of the filament. Based on the experimental kinematic results, a 2-d panel method was used to calculate the forces acting on the filament. The experiment and numerical results revealed that different from that in free stream, the filament in Karman vortex street flapped at the same frequency as the vortex street, and with smaller amplitude and larger curvature. The filament suffered an evident thrust in Karman vortex street, while a drag appeared in the case of free stream. The dependence of the drag coefficient on the phase relation between the movement of the filament and the Karman vortex street was also studied.展开更多
基金supported by the EDISON Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Science,ICT and Future Planning(No.2011-0020560)
文摘Applications of a novel curve-fitting technique are presented to efficiently predict the motion of the vortex filament, which is trailed from a rigid body such as wings and rotors. The gov- erning equations of the motion, when a Lagrangian approach with the present curve-fitting method is applied, can be transformed into an easily solvable form of the system of nonlinear ordinary dif- ferential equations. The applicability of Bezier curves, B-spline, and Lagrange interpolating polyno- mials is investigated. Local Lagrange interpolating polynomials with a shift operator are proposed as the best selection for applications, since it provides superior system characteristics with minimum computing time, compared to other methods. In addition, the Gauss quadrature formula with local refinement strategy has been developed for an accurate prediction of the induced velocity computed with the line integration of the Biot-Savart law. Rotary-wing problems including a vortex ring problem are analyzed to show the efficiency, accuracy, and flexibility in the applications of the pro- posed method.
基金This article was supported by the National Council for Science and Technology of Mexico(Consejo Nacional de Ciencia y Tecnologia—CONACyT).
文摘The present hybrid vortex tube-vorton method is based entirely on the Full Multi-wake Vortex Lattice Method(FMVLM)concepts,which means detaching vorticity with pre-cise vortex strength and orientation along all separation lines between each discretized element of a shell-body,including all external edges.Since the classic Vortex Particle Method(VPM)is unstable by itself because it does not conserve the total amount of circulation as time evolves(Kelvin’s circulation theorem),an isolated Vortex(regular-ized)Filament Method(VFM)approach is implemented to obtain advection of vorti-city,while the induced velocity field is obtained through its corresponding full vorton cloud.Further,a novel vortex squeezing/stretching scheme for such a vortex cylinder-sphere approach is proposed based on variation in time for vortex volumes in order to precisely(zero residual)conserve both circulation and vorticity at each time step(for each detached vortex element),while the viscous effect can be accounted for via the Core Spreading Method(CSM).
基金Supported by the National Natural Science Foundation of China (Grant No. 10832010)Innovation Project of Chinese Academy of Sciences (Grant No. KJCX2-YW-L05)
文摘Experiments of a flexible filament in the wake of a cylinder and in free stream were conducted in a vertical soap film tunnel. The experiments distinctly visualized the movement of the filament. Based on the experimental kinematic results, a 2-d panel method was used to calculate the forces acting on the filament. The experiment and numerical results revealed that different from that in free stream, the filament in Karman vortex street flapped at the same frequency as the vortex street, and with smaller amplitude and larger curvature. The filament suffered an evident thrust in Karman vortex street, while a drag appeared in the case of free stream. The dependence of the drag coefficient on the phase relation between the movement of the filament and the Karman vortex street was also studied.
