Large-eddy simulation of flows past a flapping airfoil using immersed boundary method

The numerical simulation of flows past flapping foils at moderate Reynolds numbers presents two challenges to computational fluid dynamics: turbulent flows and moving boundaries. The direct forcing immersed boundary (IB) method has been devel- oped to simulate laminar flows. However, its performance in simulating turbulent flows and transitional flows with moving boundaries has not been fully evaluated. In the present work, we use the IB method to simulate fully developed turbulent channel flows and transitional flows past a stationary/plunging SD7003 airfoil. To suppress the non-physical force oscillations in the plunging case, we use the smoothed discrete delta function for interpolation in the IB method. The results of the present work demonstrate that the IB method can be used to simulate turbulent flows and transitional flows with moving boundaries.

Large-eddy simulation of flows past a flapping airfoil using immersed boundary method

The numerical simulation of flows past flapping foils at moderate Reynolds numbers presents two challenges to computational fluid dynamics: turbulent flows and moving boundaries. The direct forcing immersed boundary (IB) method has been developed to simulate laminar flows. However, its performance in simulating turbulent flows and transitional flows with moving boundaries has not been fully evaluated. In the present work, we use the IB method to simulate fully developed turbulent channel flows and transitional flows past a stationary/plunging SD7003 airfoil. To suppress the non-physical force oscillations in the plunging case, we use the smoothed discrete delta function for interpolation in the IB method. The results of the present work demonstrate that the IB method can be used to simulate turbulent flows and transitional flows with moving boundaries.

跨音速翼型反设计的一种大范围收敛方法

求解跨音速翼型的反设计问题时,传统的梯度型方法一般均为局部收敛.为增大求解的收敛范围,依据同伦方法的思想,通过构造不动点同伦,将原问题的求解转化为其同伦函数的求解,并依据拟Sigmoid函数调整同伦参数以提高计算效率,进而构造出一种具有较高计算效率的大范围收敛反设计方法.数值算例以RAE2822翼型的表面压力分布为拟合目标,分别采用B样条方法,PARSEC方法及正交形函数方法等3种不同的参数化方法,并分别以NACA0012,OAF139及VR15翼型为初始翼型进行迭代计算.计算结果证明,该方法适用于多种参数化方法,且具有较好的计算效率,从多个不同的初始翼型出发,经较少次数迭代后,均能与目标翼型很好地拟合,是一种高效的大范围收敛方法.

Numerical investigation of dynamic stall of an oscillating aerofoil

The flow structure around an NACA 0012 aerofoil oscillating in pitch around the quarter-chord is numerically investigated by solving the two-dimensional compressible N-S equations using a special matrix-splitting scheme. This scheme is of second-order accuracy in time and space and is computationally more efficient than the conventional flux-splitting scheme. A 'rigid' C-grid with 149 x 51 points is used for the computation of unsteady flow. The freestream Mach number varies from 0.2 to 0.6 and the Reynolds number from 5000 to 20,000. The reduced frequency equals 0.25-0.5. The basic flow structure of dynamic stall is described and the Reynolds number effect on dynamic stall is briefly discussed. The influence of the compressibility on dynamic stall is analysed in detail. Numerical results show that there is a significant influence of the compressibility on the formation and convection of the dynamic stall vortex. There is a certain influence of the Reynolds number on the flow structure. The average convection velocity of the dynamic stall vortex is approximately 0.348 times the freestream velocity.

Euler Solution Using Adaptive Cartesian Grid With A Gridless Boundary Treatment

A quadtree-based adaptive Cartesian grid generator and flow solver were developed. The grid adaptation based on pressure or density gradient was performed and a gridless method based on the least-square fashion was used to treat the wall surface boundary condition, which is generally difficult to be handled for the common Cartesian grid. First, to validate the technique of grid adaptation, the benchmarks over a forward-facing step and double Mach reflection were computed. Second, the flows over the NACA 0012 airfoil and a two-element airfoil were calculated to validate the developed gridless method. The computational results indicate the developed method is reasonable for complex flows.

Numerical investigation on a transition prediction model

A new transition prediction model is introduced, which couples the intermittency effect into the turbulence transport equations and takes the characteristics of fluid transition into consideration to mimic the exact process of transition. Test cases include a two-dimensional incompressible plate and a two-dimensional NACA0012 airfoil. Performance of this transition model for incompressible flows is studied, with numerical results consistent to experimental data. The requirement of grid resolution for this transition model is also studied.

压电纤维复合材料铺层用于翼面设计的驱动特性与刚度影响

压电纤维复合材料驱动器在形状控制、振动控制、颤振抑制与抖振控制等方面有广泛的应用前景. 首先简单介绍了压电应变驱动的比拟载荷方法, 并采用该方法讨论了压电陶瓷片状驱动器与压电纤维复合材料驱动器在驱动特性上的主要差异. 在此基础上, 对压电纤维复合材料在不同铺设方式、铺设角度与铺设层数下的驱动特性进行了分析, 在刚度影响方面展示了不同铺设角度下模型刚轴的移动. 分析结果表明: 对称铺设反向电场可以同时获得弯曲与扭转变形, 而反对称铺设同向电场主要获得扭转变形; 两种铺设方式下45°铺设角均获得最大弦向转角, 而0°铺设角将获得最大挠度; 多铺层可以增加驱动载荷, 但总体变形效果还取决于结构系统的刚度比例; 对称铺设方式下铺设角对结构刚轴移动的影响非常明显, 在气动弹性控制中应着重关注.