High-resolution simulation for rotorcraft aerodynamics in hovering and vertical descending flight using a hybrid method

A high-resolution simulation tool for rotorcraft aerodynamics is developed by coupling CFD with a Vorticity Transport Model (VTM). An Eulerian-based CFD module is used to model the blade near body flowfield, and a Lagrangian-based VTM module is employed for vortex tracking in the far wake. The coupling procedure is implemented by transmitting vortex sources to the VTM module and feeding boundary conditions back to the CFD module. The presented CFD/VTM hybrid solver is firstly validated by hover cases of three different rotor configurations. Simulation results, including the blade surface pressure distribution, rotor downwash, and hover figure of merit, exhibit favorable correlations with available experimental data. Then, a rotor operated in vertical descending flight with a fixed collective pitch is investigated. It is shown that the CFD/VTM coupling method is suitable for rotor wake simulation. Wake instabilities (far wake breakdown in hover and toroidal wake pattern in the vortex ring state) are successfully demonstrated with a moderate computational cost.     

基于边界涡量流的二维叶型优化建模与求解

针对二维叶片整体造型优化问题,提出一种基于边界涡量流的二维叶型优化模型,并对该模型进行求解。建立以含参数的Bezier曲线定义的二维叶型型线为边界、以边界涡量流正峰值的最小化为目标函数的优化模型,通过分析边界涡量流的生成机制,把叶型型线边界信息代入边界涡量流中,将边界涡量流用叶型型线参数和型线上的气动参数表示,进而获得新的目标函数表达式。该目标函数表达式可直接对叶型型线参数求导,仅使用简单的定步长梯度算法即可对优化模型求解。结果表明:优化后的叶型型线上的边界涡量流的正峰值显著降低。     

The role of vorticity in 3D magnetic field annihilation

We show that magnetic field annihilation depends strongly on the behaviour of the vorticity and is quite different in 2D and 3D. In 3D the vorticity can be increased locally by the stretching of vortex lines (an effect that is absent in 2D). This leads to the onset ofcellular flow at quite low vorticities and the fragmentation of the simple current sheet.     

Global electric circuit modulation of winter cyclone vorticity in the northern high latitudes

Small changes in extended winter (November–March) 500 hPa vorticity area index (VAI) values for the 60–80°N latitude band are shown to be positively correlated with changes in a proxy for the high latitude ionosphere-to-surface current density _Jz$J_z$.     

垂直发射水下航行体的通气空化数值模拟研究

基于均相流模型对垂直发射水下航行体周围的通气空化流动进行了三维数值模拟,通过与试验得到的压力数据比较验证了数值方法的可靠性,并讨论了通气时序对通气空化流场的影响。结果表明:计算结果与试验吻合较好,通气能提高空泡内压力且不同位置压力一致,空泡末端存在回射高压;随着通气时刻提前,泡内压力和回射高压增大;空泡的发展过程伴随着旋涡的形成与演变,通入空泡的气体有3种流向,气体的运动导致空泡内产生多个旋涡,旋涡的种类可以分为3类。     

Euler computation of the nearfield wake vortex of an aircraft in take-off configuration

Numerical simulations based on the three-dimensional Euler equations are used to investigate the predictive capability of an Euler code for calculations of the nearfield wake of a narrow-body airliner wind tunnel model in take-off configuration up to a half span behind the wing tip trailing edge. Simulation results on both structured and unstructured grids are presented. The results on the block-structured grid were obtained within the scope of the EU-project EUROWAKE. The simulation quality of the vortex formation and spatial development is analysed by comparison to wind tunnel measurements of the spanwise lift distribution available from the EU-project DUPRIN II and to experimental PIV data available from the EU-project EUROWAKE.     

Helicity evolution during the life cycle of tropical cyclones formed over the north Indian Ocean

Tropical cyclones (TCs) are violent multiscale convections occurring in the atmosphere. The destructive impact of the TCs is commensurate to the helicity associated with their evolution. The evolution of helicity of three TCs viz. Fani, Luban, and Ockhi formed over the north Indian ocean have been analyzed in this study. The analysis of kinetic energy density of primary (EP), secondary (ES) circulation and total helicity has shown that TCs showed helical features when the secondary overturning circulation knotted with primary tangential circulation in a moist convective situation. This condition can be considered a starting of the self-sustained helical feedback process. At this time, the core region became a rotation-dominated region that suppressed strain-dominated surroundings. The Okubo-Weiss parameter demonstrates the similar qualitative behavior of deep convection as total helicity. The local maximas in helicity time series are related with the changes in tropical cyclones' stages (intensification/dissipation). Therefore, consideration of helicity analysis is essential to analyze the TC intensification and dissipation.