飞行器快速俯仰产生大迎角非定常气动力数学模型研究

在Goman提出的状态空间模型的基础上,开展了有关建立大迎角非定常气动力数学模型问题的研究。针对以往在运用状态空模型建立大迎角非定常气动力数学模型中存在的问题,通过分析状态方程中非定常影响参数与减缩频率（或无量纲俯仰角速率）的关系,建立了改进数学模型的基本思路。同时运用插值方法给出了二之间的关系,并将引结果引入状态方程中。经过辨识验算后表明,改进后的模型不仅改善了该模型对气动力的预测准确度,同时也提高了描述大迎角非定常气动力的能力。     

级间分离气动力特性数值研究

对超声速飞行弹体级间分离过程中的流场开展了数值模拟研究,得到了两级弹体在不同分离状态下的气动特性.计算中采用分区多块网格技术,并对计算所得的气动力结果进行摩擦阻力修正.根据计算结果,分析了主级通气和非通气两种状态下的流场结构和气动力变化特性;研究了弹体气动力随马赫数的变化规律.     

Vortices and Vortical Structures in InternalAerodynamics

INTRODUCTIoNfoicalofflowsinturbomachineryelemefits,i.e.inclosedcurvedchannels,cascades,etc.aretheirthree-dimensionalcharacterandvariousvorticalstructures(Fig.1).Theymakethewholefiowstructureverycom-plexandintroduceunknowneffectsonotherphenom-enaofinterest,ase.g.theflowseparation,choking,developmentofshockwavesandtheirinteraction,etc.Inclosedchannelsallthesephenomenainteractwitheachother(thesocalledstronginteraction)inamannernotyetfullyunderstood.Itshouldbestressedatthebegiedngthatvorticalf…     

Predictions of unsteady HAWT aerodynamics in yawing and pitching using the free vortex method

To predict the unsteady aerodynamic loads of horizontal-axis wind turbines (HAWTs) during operations under yawing and pitching conditions, an unsteady numerical simulation method is proposed. This method includes a nonlinear lifting line method to compute the aerodynamic loads on the blades and a time-accurate free-vortex method to simulate the wake. To improve the convergence property in the nonlinear lifting line method, an iterative algorithm based on the Newton–Raphson method is developed. To increase the computational efficiency and the accuracy of the calculation, a new wake vortex model consisting of the vortex core model, the vortex sheet model and the tip vortex model is used. Wind turbines with different diameters, such as NREL Phase VI, the TU Delft model turbine and the Tjæreborg wind turbine, are used to validate the method for rotors operating at given yaw and/or pitch angles and during yawing and/or pitching processes at different wind speeds. The results, including the blade loads, the rotor torque and the locations of the tip vortex cores in the wake, agree well with the measured data and the computed data. It is shown that the proposed method can be used for predictions of unsteady aerodynamic loads and rotor wakes in the operational processes of blade pitching and/or rotor yawing.     

Lift correction model for local shear flow effect on wind turbine airfoils

Wind turbines operate under various wind conditions in which turbulence virtually always exists. Therefore, unsteady wind turbine simulation methods to estimate wind loading in turbulent inflow conditions are very important for developing optimally designed wind turbines. Several methods have been developed for this purpose and are usually based on the blade element momentum theory (BEMT), which is used for calculation of the wind loading on turbine blades. The local shear flow effect induced by turbulence, however, is not explicitly considered in the popular BEMT-based simulations. Extreme situations can occur in a large-scale wind farm where the inflow field of a wind turbine may contain strong tip vortices generated from upstream turbines. In this study, the effects of idealized local shear flows around a two-dimensional airfoil, S809, on its aerodynamic characteristics were analyzed by CFD simulations. Various parameters including reference inflow velocity, shear rate, angle of attack, and cord length of the airfoil were examined. From the simulation results, several important characteristics were found. The shear rate in a flow causes some changes in the lift coefficient depending on its sign and magnitude, while the angle of attack does not have a distinguishable influence. The chord length and reference inflow also cause proportional and inversely proportional changes in the lift coefficient, respectively. Based on these observations, we adopted an analytic expression for the lift coefficient from the thin airfoil theory and proposed a lift correction model, which is easily applicable to the traditional load analysis procedure based on the BEMT.     

Goal-oriented model reduction of parametrized nonlinear partial differential equations: Application to aerodynamics

We introduce a goal-oriented model reduction framework for rapid and reliable solution of parametrized nonlinear partial differential equations with applications in aerodynamics. Our goal is to provide quantitative and automatic control of various sources of errors in model reduction. Our framework builds on the following ingredients: a discontinuous Galerkin finite element (FE) method, which provides stability for convection-dominated problems; reduced basis (RB) spaces, which provide rapidly convergent approximations; the dual-weighted residual method, which provides effective output error estimates for both the FE and RB approximations; output-based adaptive RB snapshots; and the empirical quadrature procedure (EQP), which hyperreduces the primal residual, adjoint residual, and output forms to enable online-efficient evaluations while providing quantitative control of hyperreduction errors. The framework constructs a reduced model which provides, for parameter values in the training set, output predictions that meet the user-prescribed tolerance by controlling the FE, RB, and EQP errors; in addition, the reduced model equips, for any parameter value, the output prediction with an effective, online-efficient error estimate. We demonstrate the framework for parametrized aerodynamics problems modeled by the Reynolds-averaged Navier-Stokes equations; reduced models provide over two orders of magnitude online computational reduction and sharp error estimates for three-dimensional flows.     

Sloshing effects on supersonic flutter characteristics of a circular cylindrical shell partially filled with liquid

This paper aims to revisit the effect of sloshing on the flutter characteristics of a partially liquid-filled cylinder. A computational fluid-structure interaction model within the framework of the finite element method is developed to capture fluid-structure interactions arising from the sloshing of the internal fluid and the flexibility of its containing structure exposed to an external supersonic airflow. The internal liquid sloshing is represented by a more sophisticated model, referred to as the liquid sloshing model, and the shell structure is modeled by Sanders' shell theory. The aerodynamic pressure loading is approximated by the first-order piston theory. The initial geometric stiffness due to prestresses in the initial configuration stemming from the fluid hydrostatic pressure, internal pressure, and axial compression load is also considered. The obtained results reveal that the sloshing of the internal fluid has little influence on the supersonic flutter boundary of a cylinder partially filled with liquid, at least for the case considered here. It is also shown that the critical freestream static pressure predicted by the sloshing model is negligibly larger than that calculated by the hydroelastic model of the internal fluid, which means that the sloshing of the internal fluid slightly overestimates the flutter boundary.     

基于响应面和遗传算法的翼型优化设计方法研究

文章针对气动优化设计中高效率和高精度的矛盾,综合响应面方法和遗传算法的优点和不足,采用多项式响应面模型代替原始遗传算法中计算量庞大的目标特性分析模型,建立了多项式响应面模型和遗传算法相结合的翼型优化设计方法,在采用N-S方程进行气动求解达到较高的精度情况下,求解次数显著减少,优化效率大大提高。研究了设计变量对优化设计效率的影响,文中方法在较少设计变量、较少N-S方程求解次数情况下,即可得到满意的优化设计结果。设计区间对响应面模型精度的影响显著,合适的设计区间既可保证模型精度,减少响应面预测结果和CFD计算结果的偏差,又可获得最佳优化结果。文中方法适用于翼型的单设计点和多设计点优化设计问题,具有原理简单、适应面宽、快速易行,且精度高等特点,可广泛应用于工程设计问题中。