Hybrid algorithm for modeling of fluid-structure interaction in incompressible, viscous flows

The objective of this paper is to present and to validate a new hybrid coupling （HC） algorithm for modeling of fluid-structure interaction （FSI） in incompressible, viscous flows. The HC algorithm is able to avoid numerical instability issues associated with artificial added mass effects, which are often encountered by standard loosely coupled （LC） and tightly coupled （TC） algorithms, when modeling the FSI response of flexible structures in incompressible flow. The artificial added mass effect is caused by the lag in exchange of interfacial displacements and forces between the fluid and solid solvers in partitioned algorithms. The artificial added mass effect is much more prominent for light/flexible struc- tures moving in water, because the fluid forces are in the same order of magnitude as the solid forces, and because the speed at which numerical errors propagate in an incom- pressible fluid. The new HC algorithm avoids numerical instability issues associated with artificial added mass effects by embedding Theodorsen＇s analytical approximation of the hydroelastic forces in the solution process to obtain better initial estimates of the displacements. Details of the new HC algorithm are presented. Numerical validation studies are shown for the forced pitching response of a steel and a plastic hydrofoil. The results show that the HC algorithm is able to converge faster, and is able to avoid numerical insta- bility issues, compared to standard LC and TC algorithms, when modeling the transient FSI response of a plastic hydrofoil. Although the HC algorithm is only demonstrated for a NACA0009 hydrofoil subject to pure pitching motion, the method can be easily extended to model general 3-D FSI response and stability of complex, flexible structures in turbulent, incompressible, multiphase flows.

WEAK SOLUTION TO THE INCOMPRESSIBLE VISCOUS FLUID AND A THERMOELASTIC PLATE INTERACTION PROBLEM IN 3D

In this paper we deal with a nonlinear interaction problem between an incompressible viscous fluid and a nonlinear thermoelastic plate.The nonlinearity in the plate equation corresponds to nonlinear elastic force in various physically relevant semilinear and quasilinear plate models.We prove the existence of a weak solution for this problem by constructing a hybrid approximation scheme that,via operator splitting,decouples the system into two sub-problems,one piece-wise stationary for the fluid and one time-continuous and in a finite basis for the structure.To prove the convergence of the approximate quasilinear elastic force,we develop a compensated compactness method that relies on the maximal monotonicity property of this nonlinear function.

On the pressure and stress singularities induced by steady flows of incompressible viscous fluids

Design for structural integrity requires an appreciation of where stress singularities can occur in structural configurations. While there is a rich literature devoted to the identification of such singular behavior in solid mechanics, to date there has been relatively little explicit identification of stress singularities caused by fluid flows. In this study, stress and pressure singularities induced by steady flows of viscous incompressible fluids are asymptotically identified. This is done by taking advantage of an earlier result that the Navier-Stokes equations are locally governed by Stokes flow in angular corners. Findings for power singularities are confirmed by developing and using an analogy with solid mechanics. This analogy also facilitates the identification of flow-induced log singularities. Both types of singularity are further confirmed for two global configurations by applying convergence-divergence checks to numerical results. Even though these flow-induced stress singularities are analogous to singularities in solid mechanics, they nonetheless render a number of structural configurations singular that were not previously appreciated as such from identifications within solid mechanics alone.

Investigation into the Interaction of Centrifugal Compressor Impeller and Vaneless Diffuser

Centrifugal compressors with parallel-wall and contracting wall vaneless diffuser are designed by using centrifugal compressor computer-aided integrated design system. The internal flow fields of the compressor are calculated by solving three-dimensional Navier-Stokes equation. Four aspects are investigated and calculation results show that the total efficiencies and total pressure ratios of the compressor with contracting wall vandess diffuser is higher than that of the compressor with parallel-wall. The jet and wake don＇t mix rapidly inside vandess diffuser. The outlet blade lean angle doesn＇t affect the compressor performance. The greater the mass flow rate through impeller, the more uneven the velocity distribution at impeller outlet is.

On the pressure and stress singularities induced by steady flows of a pair of nonmiscible,incompressible,viscous fluids in contact with a wall

Design for structural integrity requires an appreciation of where stress singularities can occur in structural configurations. While there is a rich literature devoted to the identification of such singular behavior in solid mechanics, only of late has there been much in the way of corresponding identifications of flow-induced stress singularities in fluid mechanics. These recent asymptotic identifications are for a single incompressible viscous fluid： Here the asymptotic approach is extended to apply to a configuration entailing two such fluids, For this configuration, various specifications leading to power or log singularities are determined. These results demonstrate that flow-induced stress singularities can occur in a structural container at a location where no singularities are identified within solid mechanics alone.

THE INTERACTIONS BETWEEN WAVE-CURRENTS AND OFFSHORE STRUCTURES WITH CONSIDERATION OF FLUID VISCOSITY

Study of the how held around the large scale offshore structures under the action of waves and viscous currents is of primary importance for the scouring estimation and protection in the vicinity of the structures. But very little has been known in its mechanism when the viscous effects is taken into consideration. As a part of the efforts to tackle the problem, a numerical model is presented for the simulation of the how held around a fixed vertical truncated circular cylinder subjected to waves and viscous currents based on the depth-averaged Reynolds equations and depth-averaged k-epsilon turbulence model. Finite difference method with a suitable iteration defect correct method and an artificial open boundary condition are adopted in the numerical process. Numerical results presented relate to the interactions of a pure incident viscous current with Reynolds number Re = 10(5), a pure incident regular sinusoidal wave, and the coexisting of viscous current and wave with a circular cylinder, respectively. Flow fields associated with the hydrodynamic coefficients of the fixed cylinder, as well as corresponding free surface profiles and wave amplitudes, are discussed. The present method is found to be relatively straightforward, computationally effective and numerically stable for treating the problem of interactions among waves, viscous currents and bodies.

SHORT-AND RESONANT-RANGE INTERACTIONS BETWEEN SCALES IN TURBULENCE AND THEIR APPLICATIONS

Interactions between different scales in turbulence were studied starting from the incompressible Navier-Stokes equations. The integral and differential formulae of the short-range viscous stresses, which express the short-range interactions between contiguous scales in turbulence,were given. A concept of the resonant-range interactions between extreme contiguous scales was introduced and the differential formula of the resonant-range viscous stresses was obtained. The short- and resonant-range viscous stresses were applied to deduce the large-eddy simulation (LES) equations as well as the multiscale equations, which are approximately closed and do not contain any empirical constants or relations. The properties and advantages of using the multiscale equations to compute turbulent flows were discussed. The short-range character of the interactions between the scales in turbulence means that the multiscale simulation is a very valuable technique for the calculation of turbulent flows. A few numerical examples were also given.

WAKE GEOMETRY CALCULATIONS FOR TILT-ROTOR USING VISCOUS VORTEX METHOD

A tilt-rotor unsteady flow analytical method has been developed based upon viscous vortex-particle method.In this method,the vorticity field is divided into small assembled vortex particles.Vortex motion and diffusion are obtained by solving the velocity-vorticity-formed incompressible Navier-Stokes equations using agrid-free Lagrangian simulation method.Generation of the newly vortex particles is calculated by using the Weissinger-L lifting surface model.Furthermore,in order to significantly improve computational efficiency,a fast multiple method(FMM)is introduced into the calculation of induced velocity and its gradient.Finally,the joint vertical experimental(JVX)tilt-rotor is taken as numerical examples to analyze.The wake geometry and downwash are investigated for both hover and airplane modes.The proposed method for tilt-rotor flow analysis is verified by comparing its results with those available measured data.Comparison indicates that the current method can accurately capture the complicated tilt-rotor wake variation and be suitable for aerodynamic interaction simulation in complex environments.Additionally,the aerodynamic interactional characteristics of dual-rotor wake are discussed in different rotor distance.Results show that there are significant differences on interactional characteristics between hover mode and airplane mode.

A Structured Mesh Euler and Interactive Boundary Layer Method for Wing/Body Configurations

To compute transonic flows over a complex 3D aircraft configuration, a viscous/inviscid interaction method is developed by coupling an integral boundary-layer solver with an Eluer solver in a ＂semi-inverse＂ manner. For the turbulent boundary-layer, an integral method using Green＇s lag equation is coupled with the outer inviscid flow. A blowing velocity approach is used to simulate the displacement effects of the boundary layer. To predict the aerodynamic drag, it is developed a numerical technique called far-field method that is based on the momentum theorem, in which the total drag is divided into three component drags, i.e. viscous, induced and wave-formed. Consequently, it can provide more physical insight into the drag sources than the often-used surface integral technique. The drag decomposition can be achieved with help of the second law of thermodynamics, which implies that entropy increases and total pressure decreases only across shock wave along a streamline of an inviscid non-isentropic flow. This method has been applied to the DLR-F4 wing/body configuration showing results in good agreement with the wind tunnel data.

不同截面形状淹没水平柱体上波浪力数值模拟研究

基于黏性流理论,采用有限体积法,考虑多种波浪参数和截面形状,计算淹没水平柱体在波浪作用下的受力.通过受力分解和局部流场特征分析,探究了波浪参数和截面形状对柱体受力的影响.结果表明,3种不同截面形状柱体受力主要由惯性力主导,柱体的淹没体积更大程度地决定了柱体所受波浪力的大小.在相同宽高比条件下,矩形柱淹没体积最大,其次是曲边矩形柱,最小的是椭圆柱.因此,综合考虑3种截面形状淹没水平柱体,矩形柱所受波浪力最大,椭圆柱所受波浪力最小,且随着宽高比的增大逐渐减小.

粘性润滑油冲击测试翅片的流固耦合分析研究

为解决风电齿轮箱润滑油在线监测难题,提出了用润滑油冲击翅片的方法测定润滑油粘度。与传统的粘度测量方法不同,应用计算流固耦合方法分析了不同粘度润滑油对待测翅片的冲击影响,研究了多种不同形状翅片对粘度流体冲击的变形敏感性,并在等温条件下通过CFD仿真得出不同流体粘度与翅片变形量之间关系,依据得到的变形量,对比粘度-变形量理想曲线,得到粘度的数值,利用得到的数值与标准质量指标进行对比,判断油液品质是否合格。该仿真研究可支撑风电润滑油粘度在线监测难题的解决,促进可持续发展。

Effect of expansion waves on cowl shock wave and boundary layer interaction in hypersonic inlet

The interaction of cowl shock wave and boundary layer has a crucial effect on the stability,operability and performance of hypersonic inlets.Many studies on inhibiting the sep-aration and managing the strength of the interaction of the shock wave and boundary layer with expansion corner have been conducted.However,the expansion waves near the circular arc shoulder to effectively control the interaction and cowl shock arrangement is little investigated.Therefore,the interaction of the cowl shock wave and boundary layer under thefluence of the expansion waves is studied by inviscid and viscous numerical simulations.The results reveal that the expansion waves have an important impact on the interaction between the cowl shock wave and boundary layer and the strength of shock wave,and that there are four types of inter-action processes with the change of the relative impingement positions of cowl shock wave.The expansion waves have a different influence on the shock wave and boundary layer inter-action at different incident points.When the incident point of the cowl shock wave goes far downstream from the end of the circular arc shoulder,the influence of expansion waves is weakened,and the magnitude of separation zone increases.However,when the expansion waves are applied to the interaction of the cowl shock wave and boundary layer on the circular arc shoulder,the separation can be effectively controlled.In particular,while the expansion waves interact with the shock wave and boundary layer in the back half of the circular arc shoulder,the separation is best inhibited.Compared with the upstream and downstream inci-dent points,the scale of separation area in the optimal control region is reduced by 65.3%at most.Furthermore,the total pressure recovery coefficientfirst increases and then decreases when the cowl moves from upstream to downstream,and the total pressure recovery coefficient reaches the maximum value of 68.36%at the incident position of cowl shock wave d Z 8.09d0.ª2024 The Authors.Publishing services by Elsevier B.V.on behalf of KeAi Communications Co.Ltd.

基于隔离非线性法-黏弹性人工边界的结构高效抗震分析方法

黏弹性人工边界是解决土-结构动力相互作用问题的有效手段之一,但其在分析过程中通常需要进行大量的非线性动力时程计算,效率较低。建立采用黏弹性人工边界求解土-结构动力相互作用问题控制方程求解的高效计算方法,为此,引入隔离非线性法高效求解思想,构造基于隔离非线性法-黏弹性人工边界的非线性土-结构动力相互作用分析模型,推导的动力控制方程在形式上与固定边界的隔离非线性动力控制方程基本一致,仅需将黏弹性人工边界的弹簧-阻尼器元件的刚度直接集成到近场土-结构模型的初始刚度矩阵与阻尼矩阵上即可。此外,结合Woodbury公式与组合近似法提出了改进Woodbury近似法,该改进方法能同时降低控制方程求解的时间复杂度与空间复杂度,实现了黏弹性人工边界求解土-结构动力相互作用问题动力控制方程的高效求解。研究方法同时保留了黏弹性人工边界与隔离非线性法的优点,数值算例验证了所提方法的正确性与高效性。

Gao's interacting shear flows( ISF) theory and its inferences and their applications

Gao＇s viscous/in-viscid interacting shear flows （ISF） theory, proposed by professor Gao Zhi in Institute of Mechanics, China Academy of Science, and its inferences and their applications in computational fluid dynamics （CFD） are reviewed and some subjects worthy to be studied are pro- posed in this paper. The flow-field and motion law of ISF, mathematics definition of strong viscous shear layer flow in ISF, ISF equations, wall-surface compatibility criteria （Gao＇s criteria ）, space scale variety law of strong viscous shear layer reveals flow mechanism and local space small scale triggered by strong interaction that cause some abnormal severe local pneumatic heating phenomenon in hypersonic flow. Gao＇s ISF theory was used in near wall flow, free ISF flow simulation and design of computing grids, Gao＇s wall-surface criteria were used to verify calculation reliability and accuracy of near wall flows, ISF theory approximate analytical result of shock waves-boundary layer interac- tion and ISF equations were used to obtain the numerical exact solution of local area flow （ such as stationary point flow）. Some new subjects, such as, improving near-wall turbulent models according to the turbulent flow simulation satisfying the wall-criteria and illustrating relation between grid-con- vergence based on the wall criteria and other convergence tactics, are suggested. The necessity of applying Gao＇s ISF theory and wall criteria is revealed. Difficulties and importance of hypersonic vis- cous/in-viscid interaction phenomenon were also emphasized.

考虑管-土-浆相互作用的管段施工过程力学模型

顶管法应用广泛,为更准确控制顶进过程的顶力,假定注浆浆液为粘时变流体,将注浆过程分为初注和满注2个阶段,初注时采用柱形渗透扩散模型,满注时采用管土部分接触模型,提出了基于浆液扩散面积和渗流速度的浆液状态判断准则,建立了考虑管土浆相互作用的管段全过程力学模型。浆液满注时,基于粘性流体力学和管土部分接触模型,得到了管段不同接触面剪应力大小。在此基础上将浆液产生的浮力与管段自身重力比较,来确定管土浆共同工作模式下管段形态,得到不同形态下管段所处状态的力学模型。进一步的计算实例证明,其他参数已知的条件下,可以通过本文提出的管段全过程力学模型计算出管段的顶进阻力。与实测及其他文献计算结果对比可知,提出的计算模型能够实时准确反应管段所处工作状态且计算结果更为精确。

典型参数对黏性干扰效应影响研究

针对航天飞行器高空高速飞行面临的黏性干扰问题,以尖楔外形和典型后缘舵航天飞行器为研究对象,采用计算流体力学手段,开展高度(雷诺数)、壁温(壁温比)对壁面边界层流动的影响研究,获得黏性干扰流场结构变化及影响规律。结果表明:随着高度、壁温增大,黏性干扰效应增强,边界层逐渐增厚,机翼对空气舵的干扰影响增强,可造成航天飞行器空气舵表面压强降低,舵效显著减小。

一种基于改进流固耦合力求解的浸没光滑点插值法

浸没光滑点插值方法(immersed smoothed point interpolation method,IS-PIM)是一种基于浸没类方法框架,采用光滑点插值方法(smoothed point interpolation method,S-PIM)作为固体求解器的流固耦合计算方法。在IS-PIM以及其它基于浸没类方法框架的方法中,流固耦合力是基于虚拟流体拉格朗日网格求解的,但这种求解方式忽略了流固边界节点的速度梯度,导致无法计算边界粘性力,尤其是在模拟低雷诺数流动时,会产生较大的数值误差。本文针对上面的问题,提出一种基于真实流体欧拉网格求解流固耦合力的新思路。经过算例证明,该方法无需额外修正即可有效计算流固边界的粘性力,提高了计算精度。

Inviscid Limit for Scalar Viscous Conservation Laws in Presence of Strong Shocks and Boundary Layers

In this paper, we study the inviscid limit problem for the scalar viscous conservation laws on half plane. We prove that if the solution of the corresponding inviscid equation on half plane is piecewise smooth with a single shock satisfying the entropy condition, then there exist solutions to the viscous conservation laws which converge to the inviscid solution away from the shock discontinuity and the boundary at a rate of ε1 as the viscosity ε tends to zero.

翼吊式双发民机机体/动力装置一体化数值分析

介绍了多块网格技术与流场分区求解方法在翼吊式双发民机机体／动力装置一体化研究中的应用．数值求解Ｅｕｌｅｒ方程模拟复杂组合体绕流．采用边界展方程／Ｅｕｌｅｒ方程耦合迭代技术进行器面粘性修正．为保持Ｅｕｌｅｒ方程求解中计算网格固定，粘流／无粘流耦合迭代采用表面源模型．该方法对某民用飞机模型跨音速绕流流场进行了数值模拟，机翼表面计算压力分布与实验吻合良好．

高超声速粘性干扰效应相关性研究

探讨了高超声速粘性干扰效应的相关性理论,采用CFD数值模拟方法对轨道器再入阶段的粘性干扰效应进行了研究,以此为基础考察了粘性干扰相关参数′∞的关联特性。对计算结果的分析表明:ν-′∞能够将轨道器外形气动力的地面风洞试验数据和飞行试验数据进行有效关联,从而为建立轨道器外形再入气动力天地换算方法奠定了基础。