|Alternative Title||Effect Investigation of Flow Interference on Flutter|
|Place of Conferral||北京|
|Keyword||颤振 干扰流动 CFD/CSD耦合 复杂结构|
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。
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 artificially，this 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.
|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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