IMECH-IR  > 流固耦合系统力学重点实验室
流动干扰对颤振的影响研究
Alternative TitleEffect Investigation of Flow Interference on Flutter
姜倩
Thesis Advisor赵桂林
2019-05-29
Degree Grantor中国科学院大学
Place of Conferral北京
Subtype硕士
Degree Discipline工程力学
Keyword颤振 干扰流动 CFD/CSD耦合 复杂结构
Abstract

颤振是一种典型的气动弹性动不稳定现象,表现为弹性结构在非定常气动力作用下的振动发散。颤振发生时会造成严重的后果,轻则引起结构破坏,重则造成人员伤亡,因此预测颤振边界、划分安全范围在颤振研究中是一项极为重要的工作。在工程设计中,由于几何外形的复杂性,各部件之间普遍存在着流场干扰的现象。然而为了降低仿真分析工作难度,提高效率,目前的工程颤振计算中往往并不关注这种流动干扰对实际模型颤振特性的影响,只针对单一部件进行分析,这样的简化难以准确评估模型的真实颤振边界。在学术研究领域,针对复杂外形颤振问题,已有其他学者开展了一些研究工作,但是有关流动干扰对颤振影响的研究工作则屈指可数。本文针对这个问题,通过人为改变弹性部件的来流条件、添加干扰因素等手段,验证了流动干扰对颤振边界的影响,并研究了其中引起颤振边界变化的主要原因。同时在工程结构的颤振计算中,充分考虑干扰流动的重要影响作用,从而准确解决实际的工程问题。本文就这些内容展开了一系列的研究工作。

本文所采用的颤振计算方法结合了计算流体力学(Computational Fluids dynamic, CFD)和计算结构力学(Computational Structural Dynamics, CSD),是基于CFD/CSD耦合的颤振计算方法,通过将Navier-Stokes方程与结构运动方程分别求解,采用紧耦合的耦合方式实现二阶时间精度;以径向基函数(Radial Basis Function, RBF)的插值方法实现CFD/CSD之间的数据交换,其中包括在耦合界面上的载荷传递和位移传递,并引入虚功原理以满足能量守恒原则;在每一步完成从结构到流场的位移传递并得到物面的网格变形之后,便通过RBF插值的方式将物面的网格变形量插值到空间网格节点,实现空间上的网格变形,在这其中采用贪婪算法精简网格控制点从而降低计算量。

首先对机翼的颤振进行了研究。通过对国际公认颤振计算模型AGARD445.6机翼的颤振边界预测,验证了本文所采用的基于CFD/CSD耦合的颤振计算方法能够较好地与实验吻合。并且探究了机翼颤振边界对底层粘性网格高度变化的敏感度,以及在不同攻角下机翼颤振边界的变化。

然后研究了导弹舵面受到不同情况的流动干扰时颤振边界发生的变化,包括导弹弹身的干扰、弹身半径的变化、导弹的飞行攻角变化、导弹舵面的不同安装位置以及存在前后两组舵面时前后舵面的交错形式和距离等。

通过这两部分的研究,发现了对弹性结构颤振边界影响较大的因素,比如膨胀波、激波、漩涡分离流动等这些流场的非线性特性,都将改变弹性部件的局部来流状态,改变压力梯度的分布情况,从而引起颤振边界的变化。因此采用均匀来流模拟复杂流场中弹性结构的颤振特性所得结果是不够准确的,为了得到更精确的仿真结果,需要将所研究的部件置于完整的复杂流场中进行颤振数值模拟。

由于干扰流动对颤振边界的重要影响,本文在对高速列车外风挡的颤振计算问题进行求解时高度还原了高速列车的头车、尾车、车厢以及地面等真实流动状态,对比研究了安装不同设计方案的外风挡时的气动特性,然后通过变模态频率的方式搜索了外风挡的颤振边界,并研究了影响外风挡模态频率的相关变量,为工程设计单位对相关产品的优化设计,提供了具有指导意义的仿真数据。

 

Other Abstract

Flutter is a typical dynamic instability phenomenon in aeroelastic field, which manifests as the vibration divergence of the elastic structure under unsteady aerodynamic forces. When flutter occurs, it will cause serious consequences, slightly structural damage, and heavily casualties, so in the flutter research, the task of predicting flutter boundary seems much important. In engineering design, flow field interference widely exists among structural components due to the complexity of engineering configuration. However, in order to reduce the difficulty of simulation analysis and improve the efficiency, the effect of this flow field interference on the flutter characteristics of the actual model are often neglected in current engineering flutter calculation, and only the single component is analyzed there. This simplification usually leads to the inaccuracy of flutter prediction. In the academic research, some scholars have done the study work on flutter of complex shape, but there are few effects of flow interference on flutter. For this problem, by means of changing inflow conditions of elastic components and adding interference factors artificiallythis paper proves the important influence of interference flow on flutter boundary, and explores the main reasons for the change of flutter boundary. At the same time, the important influence of interference flow is fully considered in flutter calculation of engineering structures to solve practical engineering problems. Therefore, in this paper a series of research tasks have been carried out on these contents.

The flutter calculation method adopted in this paper combines Computational Fluids dynamic (CFD) and Computational Structural Dynamics(CSD). In other words, this is the means based on the CFD/CSD coupling. About this method, The Navier-Stokes equations and structural equations of motion are solved respectively, and tight coupling method between the CFD and CSD models is used to achieve second-order time accuracy. Besides, a Radial Basis Function (RBF) Interpolation is applied for the data exchange at the interface of fluid and structural models, both the displacements transfer and loads transfer included. Meanwhile, the principle of virtual work is introduced to satisfy the energy conservation here. After the displacements transfer from structure to flow field is completed and the mesh deformation of the structural surface is obtained at each step, the spatial mesh is deformed by the RBF Interpolation according to the revised wall mesh, and the greedy algorithm is applied to simplify the mesh control points and reduce the computational complexity.

First of all, the study on wing flutter is carried out. By calculating the flutter boundary of AGARD445.6 wing, which is an international recognized flutter model, it is proved that the data of wing flutter boundary calculated in this paper via the method based on CFD/CSD coupling agree well with that in experiment. In addition, the sensitivity of the wing flutter boundary to the initial aerodynamic cell height and the change of the wing flutter boundary at different angles of attack are investigated.

Then the researches on the changes of flutter boundary of missile rudder in interference flow that under different situations are carried out, including the interference of missile body, the change of missile body radius, the change of missile operation angle of attack, different installation positions of missile rudder, the staggered forms and distances between the front and rear rudders when there are two groups of rudders on the missile.

After the studies of these two parts, the factors that influence the flutter boundary of elastic structures are found, such as expansion wave, shock wave and eddy separation flow, etc. These nonlinear characteristics of the flow fields will change the local inflow state of elastic components, and change the distribution of pressure gradient, and finally change the flutter boundary. Therefore, it is not accurate to simulate the flutter characteristics of elastic structures in complex flow field by only using uniform inflow. Instead, for getting more accurate simulation results, it is necessary to place the component studied in a complete complex flow field for flutter numerical simulation.

Because of the important influence of interference flow on the flutter boundary, this paper also simulates as much as possible the most real flow state of the carriages on high speed train as well as the ground effect when solving the flutter problem of the external windshield. In this paper, the aerodynamic characteristics of the external windshield with different design schemes are compared, and the flutter boundary of the external windshield is searched by changing the modal frequencies, also the relevant variables affecting the modal frequencies of the external windshield are explored. The study in this part can provide meaningful reference value for engineering application.

Language中文
Document Type学位论文
Identifierhttp://dspace.imech.ac.cn/handle/311007/79110
Collection流固耦合系统力学重点实验室
Recommended Citation
GB/T 7714
姜倩. 流动干扰对颤振的影响研究[D]. 北京. 中国科学院大学,2019.
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