Extracting energy from unsteady flows through vortex control
Extracting energy from unsteady flows through vortex control
复制标题
通过涡流控制从不稳定流中提取能量
DOI：
10.1575/1912/5563
复制
发表时间：
1994
影响因子：
4.1
通讯作者：
K. Streitlien
中科院分区：
文献类型：
--
作者：
K. Streitlien
涡流控制是流体力学中的一种新的范例，其应用于推进和减少尾流。在有来流涡阵的流场中放置一个升沉和俯仰的水翼，可以获得很高的推进效率和减小的尾流特征。具有规则涡列的流动的典型例子是Krman涡街，这是我们的翼型入流模型。本文用理论模型和数值模拟方法研究了置于Krmin涡街中的振荡翼型的问题。理论模型是对非定常翼型的经典线性理论的一种修改。它结合了非均匀入流和翼型运动的影响来预测产生的推力、升力和力矩。数值计算过程考虑了翼型之间的非线性相互作用，进行大振幅振荡，和迎面而来的涡街。该方法是基于二维势流和复变函数理论。仔细制定的速度潜力，和封闭形式的表达的力和力矩的Joukowski翼型在点涡的存在下，允许快速评估的流体动力学性能。理论和仿真结果在他们的主要结论一致：为了最佳性能。翼片应该试图拦截迎面而来的旋涡，同时保持在迎面而来的旋涡列的边界内。该模式与组合尾流中相反符号的涡流之间的高度相互作用相关，导致尾流特征减少。当翼片避免靠近涡流时，预测效率最低，这里的组合尾流由一排交替符号的非常强的涡流组成。该理论还表明，振荡翼片可以恢复更多的能量包含在涡街比一个固定的，但这还没有得到证实，在模拟。采用一个简化的模型，对尾流中的相互作用过程进行了详细的研究：将翼型尾流模拟为一个小而有限的均匀剪切层
Vortex control is a new paradigm in fluid mechanics, with applications to propulsion and wake reduction. A heaving and pitching hydrofoil placed in a flow with an array of oncoming vortices can achieve a very high propulsive efficiency and reduced wake signature. The canonical example of flow with regular arrays of vortices is the Krman vortex street, and this is our model for the inflow to the foil. The problem of an oscillating foil placed within a Krmin vortex street is investigated with a theoretical model and numerical simulation. The theoretical model is an adaptation of the classical linear theory for unsteady aerofoils. It combines the effects of nonuniform inflow and foil motion to predict the resulting thrust, lift, and moment. The numerical procedure allows for nonlinear interaction between the foil, performing large amplitude oscillations, and the oncoming vortex street. The method is based on two-dimensional potential flow and the theory of functions of a complex variable. Careful formulation of the velocity potential, and closed form expressions for force and moment on a Joukowski foil in the presence of point vortices, permits rapid evaluation of hydrodynamic performance. The theory and simulation results agree in their main conclusion: For optimum performance. the foil should try to intercept the vortices head on. while remaining inside the border of the oncoming vortex street. This mode is associated with a high degree of interaction between oppositely signed vorticitv in the combined wake leading to reduced wake signature. The lowest efficiency is predicted when the foil avoids coming close to the vortices, here the combined wake consists of a row of very strong vortices of alternate sign. The theory also indicates that an oscillating foil can recover more of the energy contained in the vortex street than a stationary one, but this has not been confirmed in simulation. The interaction process in the wake is studied in more detail, using a much simplified model: the foil wake is modeled as a uniform shear laver of small but finite