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Flow Confinement Effects on the Wake Structure behind a Pitching Airfoil： A Numerical Study Using an Immersed Boundary Method

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Journal of Bionic Engineering 2017年第1期14卷 88-98页

作者： ali akbar hosseinjani ali Ashrafizadeh Faculty of Mechanical Engineering K. N. Toosi University of Technology Tehran P.O.B. 19395-1999 Iran

The flow patterns and wake structures behind a pitching airfoil in an un-bounded domain have been studied extensively. In contrast, the flow phenomena associated with a pitching airfoil near a solid boundary have not been adequately studied or reported. This paper aims at filling this research gap by considering the flow confinement effects on the flow pattern around a pitching airfoil. To achieve this goal, the flow fields around a flapping airfoil in un-bounded, bounded and semi-bounded domains are studied and compared. Numerical simulations are carried out at a fixed Reynolds number, Re = 255, and at a fixed oscillation frequency corresponding to St = 0.22. An accurate immersed boundary method is employed to calculate the unsteady flow fields around the airfoil at various flapping amplitudes. It is argued that two flow mechanisms, here called ＂the interaction effect＂ and ＂the induced reverse flow effect＂ are responsible for the variations of the flow field due to the presence of a nearby solid boundary.

关键词： immersed boundary method pitching airfoil vortex street induced momentum aligned vortex

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An extended iterative direct-forcing immersed boundary method in thermo-fluid problems with Dirichlet or Neumann boundary conditions

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Journal of Central South University 2017年第1期24卷 137-154页

作者： ali akbar hosseinjani ali Ashrafizadeh Faculty of Mechanical Engineering K.N.Toosi University of TechnologyP.O.B.19395-1999 TehranIran

An iterative direct-forcing immersed boundary method is extended and used to solve convection heat transfer *** pressure,momentum source,and heat source at immersed boundary points are calculated simultaneously to achieve the best *** of convection heat transfer problems with both Dirichlet and Neumann boundary conditions are *** approaches for the implementation of Neumann boundary condition,*** and indirect methods,are introduced and compared in terms of accuracy and computational *** test cases include forced convection on a heated cylinder in an unbounded flow field and mixed convection around a circular body in a lid-driven ***,the proposed method is applied to study the mixed convection around a heated rotating cylinder in a square enclosure with both iso-heat flux and iso-thermal boundary *** results show that the order of accuracy of the indirect method is less than the direct ***,the indirect method takes less computational time both in terms of the implementation of the boundary condition and the post processing time required to compute the heat transfer variables such as the Nusselt *** is concluded that the iterative direct-forcing immersed boundary method is a powerful technique for the solution of convection heat transfer problems with stationary/moving boundaries and various boundary conditions.

关键词： Dirichlet 诺伊曼边界条件边界法浸入迭代流体问题对流换热计算效率

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