基于ANSYS/CFX耦合的机翼颤振分析

在飞行器飞行气动特性的研究中,为避免传统方法进行颤振点预测时的"准模态"假设,能够更加准确地仿真机翼在流场中的真实运动情况,根据CFD/CSD一体化设计思想,采用了ANSYS/CFX紧耦合算法,对国际标准气动弹性模型AGARD 445.6机翼作了颤振分析,验证性地研究了亚音速和跨音速颤振机理,将仿真计算结果和实验数据进行了比较.表明耦合计算所得的颤振速度和颤振频率和实验值吻合,在亚音速阶段,机翼颤振主要是机翼的弯曲扭转耦合运动引起,而跨音速阶段则主要是机翼的弯曲运动的不稳定性引起,与理论定性分析得到的结果一致,证明ANSYS/CFX全耦合的应用为求解非线性流固耦合问题提供了有效的方法.     

基于CFD-CSD耦合的机翼跨音速颤振计算

采用CFD-CSD耦合计算是预计机翼跨音速颤振特性的主流方法。以跨音速颤振国际标准模型AGARD 445.6机翼为研究对象,利用ANSYS.MFX多场耦合求解器对Euler方程进行求解来获得作用在机翼表面上的非定常气动力;对结构振动方程采用HHT方法直接数值积分以获得结构响应。通过CFD和CSD的耦合,计算了AGARD 445.6机翼的跨音速颤振特性。数值模拟结果与NASA风洞实验结果符合良好,表明利用ANSYS.MFX计算机翼跨音速颤振问题是可行的。     

风扇/压气机动叶流固耦合特性分析

在叶轮机械的设计中,流固耦合效应对叶轮机气动性能与结构特性的影响较大.为提高航空发动机的性能,气压机的叶片要增长,负载随之增加,结构强特性也要进行优化.采用计算流体力学与计算结构动力学相结合的方法,通过三维线性插值与常体积转换两种不同的数据交换,用CFD与CSD计算之间的气动力与变形位移数据的相互传递,并对气动与结构计...     

基于CFD系统辨识的气弹分析及GPU并行算法初探

通过求解Euler方程获得运动翼段的非定常流场,并用CUDA语言对流场求解器进行GPU并行计算.使用ARMA(auto-regressive-moving-average)模型对非定常气动力进行辨识,由系统辨识模型得到的结果与全阶CFD计算结果十分吻合.基于降阶气动模型与结构的耦合,计算了具有S型颤振边界的气动弹性标准算例-Isogai Wing的跨音速颤振.本文给出的方法可以在保证气动弹性计算精度的前提下大幅提高计算效率.     

超音速舵面热气动弹性仿真

为研究弹翼气动加热效应对结构气动弹性稳定性的影响,建立了热气动弹性仿真模型。根据分层求解的原理,首先采用平板参考温度法进行气动加热计算,进而分析热环境下结构的固有特性,并利用当地流活塞理论计算非定常气动力,在状态空间进行热颤振求解。对某弹性边界全动舵进行了超音速巡航段的热颤振特性分析;结果表明,随着时间的推移,热效应使舵面的固有频率逐渐降低,导致颤振边界下降;一段时间后,固有特性及热颤振特性趋于稳定。分析方法简捷有效,为飞行器结构设计提供了一种工程分析手段。     

计算流体力学在化学反应器模拟中的应用进展

计算流体力学(CFD)能够准确地描述流体流动、混合、传热规律,近年来逐渐开始耦合到化学反应中应用于化学工程领域,并表现出巨大潜力。本文综述了CFD在不同化学反应器中针对不同反应体系模拟的基本原理以及应用。相比于传统的面向理想反应器的反应动力学模拟和单纯面向流动传递的CFD模拟方法而言,采用CFD耦合化学反应动力学的方法同时考虑了传递过程和反应过程,能够对非理想化学反应器的操作特性(转化率、选择性、分子量及其分布等)进行模拟、分析与预测,在化工过程强化和化工产品控制方面优势明显。开发新的耦合数学模型和数值算法、考虑亚格子尺度的微观过程和采用直接数值模拟等方法,将是利用CFD深入研究非理想反应器特性的重要方向。     

高超声速飞行器参数化几何建模研究

针对高超声速飞行器设计由于采用吸气式冲压发动机带来的机体/推进系统一体化而带来的优化设计问题,同时也为了进行总体优化布局,必须建立参数化几何模型.通过采用部件分解法,拟合曲线,坐标变换和旋转,拉伸截面,从而建立了高超声速飞行器类乘波体的完整的参数化几何模型.同时采用工程算法和CFD软件对其进行气动特性计算,工程算法的思路是先采用面元法对其进行无粘气动力计算,再通过经验公式来计算粘性阻力系数.两者结果显示类乘波体气动特性良好.     

基于流固耦合的叶片颤振分析

研究航空发动机性能问题,叶片颤振过程属于流固耦合问题,为了对叶片颤振进行预测和分析,保证发动机稳定,在提出对流固耦合原理和求解过程进行分析的基础上,采用 ANSYS 进行结构计算,CFX 进行流场计算,并利用两者间的数据交互平台传递流场压力载荷和结构位移数据,实现了流固耦合数值仿真计算.在不同来流速度及攻角下进行叶片和流场的耦合计算,根据得到的叶片振动位移响应判断叶片是否会发生颤振.计算结果表明,颤振频率与叶片低阶固有频率一致,证明来流速度和攻角是影响叶片气动弹性稳定性的重要因素,并可做为叶片颤振的预测依据.     

鸟体力学模型仿真研究

为使鸟撞飞机结构数值计算中鸟体模型更贴近实际,基于非线性动力学有限元分析程序的Lagrange算法、Euler算法和SPH算法,以及弹塑性和流体动力学本构模型,建立了三种鸟体有限元模型,并进行了由低速到高速的鸟撞平板仿真研究.结果表明:鸟撞击速度低于100m/s时,采用模型一方法仿真鸟体较合理;鸟撞击速度高于100m/s时,鸟体的仿真宜采用模型三方法;综合计算精度和计算成本两个方面,当鸟撞击速度高于145m/s时,模型一方法也是可接受的方法.鸟撞平板仿真验证了分析结果的正确性,为鸟撞仿真中鸟体的建模提供了参考依据.     

CFD方法在压水堆安全分析中的应用现状和发展趋势

为更好地利用CFD方法解决压水堆安全分析问题,简要介绍CFD方法,着重阐述其在硼稀释、混合和热分层以及受压热冲击等压水堆安全分析问题的应用现状,并提出CFD与系统程序的耦合计算、流固耦合计算和CFD与中子动力学程序的耦合计算将是CFD方法在该领域的发展重点.     

Optimum design of composite plate wings for aeroelastic characteristics using lamination parameters

The present paper treats the flutter and divergence characteristics of composite plate wings with various sweep angles. First, the effect of laminate configuration on the flutter and divergence characteristics is investigated for composite plate wings. To examine the effect of laminate configuration, the flutter and divergence characteristics are represented on the lamination parameter plane. Next, a minimum weight design of composite plate wings subjected to the constraints on the flutter and divergence speeds is conducted by using a genetic algorithm in which lamination parameters are used as design variables. The effectiveness of aeroelastic tailoring is demonstrated through the optimization results.     

Multidisciplinary Simulation of the Maneuvering of an Aircraft

A computational methodology for the simulation of the transient aeroelastic response of an unrestrained and flexible aircraft during high-G maneuvers is presented. The key components of this methodology are: (a) a three-field formulation for coupled fluid/structure interaction problems; (b) a second-order time-accurate and geometrically conservative flow solver for CFD computations on unstructured dynamic meshes; (c) a corotational finite element method for the solution of geometrically nonlinear and unrestrained structural dynamics problems; (d) a robust method for updating an unrestrained and unstructured moving fluid mesh; and (e) a second-order time-accurate staggered algorithm for time-integrating the coupled fluid/structure semi-discrete equations of motion. This computational methodology is illustrated with the simulation on a parallel processor of several three-dimensional high-G pullup maneuvers of the Langley Fighter in the transonic regime, using a detailed finite element aeroelastic model.     

Three dimensional numerical simulations of long-span bridge aerodynamics, using block-iterative coupling and DES

The design of long-span bridges often depends on wind tunnel testing of sectional or full aeroelastic models. Some progress has been made to find a computational alternative to replace these physical tests. In this paper, an innovative computational fluid dynamics (CFD) method is presented, where the fluid-structure interaction (FSI) is solved through a self-developed code combined with an ANSYS-CFX solver. Then an improved CFD method based on block-iterative coupling is also proposed. This method can be readily used for two dimensional (2D) and three dimensional (3D) structure modelling. Detached-Eddy simulation for 3D viscous turbulent incompressible flow is applied to the 3D numerical analysis of bridge deck sections. Firstly, 2D numerical simulations of a thin airfoil demonstrate the accuracy of the present CFD method. Secondly, numerical simulations of a U-shape beam with both 2D and 3D modelling are conducted. The comparisons of aerodynamic force coefficients thus obtained with wind tunnel test results well meet the prediction that 3D CFD simulations are more accurate than 2D CFD simulations. Thirdly, 2D and 3D CFD simulations are performed for two generic bridge deck sections to produce their aerodynamic force coefficients and flutter derivatives. The computed values agree well with the available computational and wind tunnel test results. Once again, this demonstrates the accuracy of the proposed 3D CFD simulations. Finally, the 3D based wake flow vision is captured, which shows another advantage of 3D CFD simulations. All the simulation results demonstrate that the proposed 3D CFD method has good accuracy and significant benefits for aerodynamic analysis and computational FSI studies of long-span bridges and other slender structures.     

Aerodynamic and aeroelastic analyses on the CAARC standard tall building model using numerical simulation

The simulation of the wind action over the CAARC (Commonwealth Advisory Aeronautical Council) standard tall building model is performed in the present work. Aerodynamic and aeroelastic analyses are reproduced numerically in order to demonstrate the applicability of CFD techniques in the field of wind engineering. A major topic in this paper is referred to one of the first attempts to simulate the aeroelastic behavior of a tall building employing complex CFD techniques. Numerical results obtained in this work are compared with numerical and wind tunnel measurements and some important concluding remarks about the present simulation are also reported.     

A canonic-signed-digit coded genetic algorithm for designing finite impulse response digital filter

In this paper, the genetic algorithm (GA) based on Canonic Signed Digit (CSD) code was used to find the optimum design of a finite impulse response digital filter (FIR). By using the characteristics of the CSD structure, the circuit was able to be simplified and also the calculation speed was raised to increase the hardware's efficiency. However, CSD structure cannot be guaranteed by a general GA after the evolution of chromosomes. Thus in this research an algorithm was proposed which the CSD structure can be maintained. A CSD coded GA was used to the evolution of chromosome to reduce the time wasted by trials and errors during the evolution and then to accelerate the training speed. In this paper, a new hybrid code for the filter coefficients was proposed to improve the precision of the coefficient of FIR. An example is shown in this paper to verify the efficiency of the proposed algorithm.     

Conceptual design of aeroelastic structures by topology optimization

A topology optimization methodology is presented for the conceptual design of aeroelastic structures accounting for the fluid–structure interaction. The geometrical layout of the internal structure, such as the layout of stiffeners in a wing, is optimized by material topology optimization. The topology of the wet surface, that is, the fluid–structure interface, is not varied. The key components of the proposed methodology are a Sequential Augmented Lagrangian method for solving the resulting large-scale parameter optimization problem, a staggered procedure for computing the steady-state solution of the underlying nonlinear aeroelastic analysis problem, and an analytical adjoint method for evaluating the coupled aeroelastic sensitivities. The fluid–structure interaction problem is modeled by a three-field formulation that couples the structural displacements, the flow field, and the motion of the fluid mesh. The structural response is simulated by a three-dimensional finite element method, and the aerodynamic loads are predicted by a three-dimensional finite volume discretization of a nonlinear Euler flow. The proposed methodology is illustrated by the conceptual design of wing structures. The optimization results show the significant influence of the design dependency of the loads on the optimal layout of flexible structures when compared with results that assume a constant aerodynamic load.     

Reliability-based design optimization of aeroelastic structures

Aeroelastic phenomena are most often either ignored or roughly approximated when uncertainties are considered in the design optimization process of structures subject to aerodynamic loading, affecting the quality of the optimization results. Therefore, a design methodology is proposed that combines reliability-based design optimization and high-fidelity aeroelastic simulations for the analysis and design of aeroelastic structures. To account for uncertainties in design and operating conditions, a first-order reliability method (FORM) is employed to approximate the system reliability. To limit model uncertainties while accounting for the effects of given uncertainties, a high-fidelity nonlinear aeroelastic simulation method is used. The structure is modelled by a finite element method, and the aerodynamic loads are predicted by a finite volume discretization of a nonlinear Euler flow. The usefulness of the employed reliability analysis in both describing the effects of uncertainties on a particular design and as a design tool in the optimization process is illustrated. Though computationally more expensive than a deterministic optimum, due to the necessity of solving additional optimization problems for reliability analysis within each step of the broader design optimization procedure, a reliability-based optimum is shown to be an improved design. Conventional deterministic aeroelastic tailoring, which exploits the aeroelastic nature of the structure to enhance performance, is shown to often produce designs that are sensitive to variations in system or operational parameters.     

Reliability-based shape optimization of structures undergoing fluid–structure interaction phenomena

Fluid–structure interaction phenomena are often roughly approximated when the stochastic nature of a system is considered in the design optimization process, leading to potentially significant epistemic uncertainty. In this paper, after reviewing the state-of-the-art methods in robust and reliability-based design optimization of problems undergoing fluid–structure interaction phenomena, a computational framework is presented that integrates a high-fidelity aeroelastic model into reliability-based design optimization. The design optimization problem is formulated pursuant to the reliability index and performance measure approaches. The system reliability is evaluated by a first-order reliability analysis method. The steady-state aeroelastic problem is described by a three-field formulation and solved by a staggered procedure, coupling a potentially detailed structural finite element model and a finite volume discretization of the Euler flow. The design and imperfection sensitivities are computed by evaluating the analytically derived direct and adjoint coupled aeroelastic sensitivity equations. The computational framework is verified by the optimization of three-dimensional wing structures. The lift-to-drag ratio is maximized, subject to stress constraints, by varying shape, thickness, and material properties. Uncertainties in structural parameters, including design parameters, operating conditions, and modeling uncertainties are considered. The results demonstrate the need for reliability-based optimization methods, for the design of structures undergoing fluid–structure interaction phenomena, and the applicability of the proposed framework to realistic design problems. Comparing the optimization results for different levels of uncertainty shows the importance of accounting for uncertainties in a quantitative manner.     

Aircraft morphing wing design by using partial topology optimization

A morphing wing concept has been investigated over the last decade because it can effectively enhance aircraft aerodynamic performance over a wider range of flight conditions through structural flexibility. The internal structural layouts and component sizes of a morphing aircraft wing have an impact on aircraft performance i.e. aeroelastic characteristics, mechanical behaviors, and mass. In this paper, a novel design approach is proposed for synthesizing the internal structural layout of a morphing wing. The new internal structures are achieved by using two new design strategies. The first design strategy applies design variables for simultaneous partial topology and sizing optimization while the second design strategy includes nodal positions as design variables. Both strategies are based on a ground structure approach. A multiobjective optimization problem is assigned to optimize the percentage of change in lift effectiveness, buckling factor, and mass of a structure subject to design constraints including divergence and flutter speeds, buckling factors, and stresses. The design problem is solved by using multiobjective population-based incremental learning (MOPBIL). The Pareto optimum results of both strategies lead to different unconventional wing structures which are superior to their conventional counterparts. From the results, the design strategy that uses simultaneous partial topology, sizing, and shape optimization is superior to the others based on a hypervolume indicator. The aeroelastic parameters of the obtained morphing wing subject to external actuating torques are analyzed and it is shown that it is practicable to apply the unconventional wing structures for an aircraft.     

基于iSIGHT平台的倾斜冲击射流传热特性优化

为了研究和优化半封闭倾斜射流中击移动平板的传热性能,采用iSIGHT与CFD软件的联合仿真,根据多岛遗传算法动态调整射流角度和平板移动速度,进行狭缝湍流冲击射流的数值模拟.结果表明,平板表面的传热效果主要是由板速决定的,低速时高角度下的平板表面的平均努塞尔数较高;初始设计时流场左侧的回流区和二次回流区消失,优化后的流场结构得到改善,移动平板表面的平均努塞尔数比初始设计结果提高7.62％,热传导更加均匀.