Research Of Theory And Application For Sound Radiation With Gas-Structure Coupling

Noise is included aerodynamic noise and structure noise. The vibration force acting on the fluid directly comes into being the aerodynamic noise. One of the important factors affecting the aerodynamic noise is the result of the interaction of the gas and structure called gas-structure coupling,inducing sound radiation. The phenomenon is that the equation of motion describing coupling system is included some variable describing the gas field and the structure field when the question is researched. At the same time, the gas force acting on the interaction interface and the structure displacement on the interaction interface all don't be known. Because the equation can not be solved in the gas field or the structure field if the gas variable or the structure variable eliminate apparently. The variable can be known in the gas field and the structure field when the system equation of motion is solved. After solving the system equation, the structure vibration and the distributing surrounding in the gas field can be researched advanced. The mechanism of aerodynamic noise and structure noise can be researched. The major factors producing the noise can be controlled. So noise can be controlled more reasonably. In the dissertation, the frequency and sound radiation characteristic of thin plate structure in different surrounding medium is researched at first. Based on the thin plate structure and its surrounding medium shape, iso-parametric element is used to discretize the structure and the surrounding medium. The interaction equation between thin plate and the surrounding medium is founded using the Galerkin method which can be calculated the pressure of the arbitrary point in the surrounding medium. The calculating model and tested model are compared in different surrounding medium. There are some difference between the calculating result and the tested result. And the law of the natural frequency and the sound radiation of the thin plate in different medium can be obtained. The method can be used to research on similar structure frequency characteristic of the fan blade with complexity shape. So the virtual mass method is used to research on the fan blade frequency characteristic. The Wilson-θmethod with well stability is used to solve the equation of air-blade coupling. The mode analysis theory is used to analyze the fan blade chattering and the sound radiation characteristic etc. The gas-structure coupling characteristic is researched. The results can be used for researching on the law of the fan blade period noise and broad band noise caused by the sound radiation for the fan blade gas-structure coupling. For the fan blade period noise and broad band noise research, the fan blade should satisfy the leading function at first. Based on the fan blade shape theory, the sound field characteristic of movement sound source, the fan blade gas-structure coupling sound radiation and nonlinear pulsate lift affection, the fan blade period noise and broad noise models with the gas-structure coupling induced sound radiation effect are made. The gas-structure coupling sound radiation affecting the period and broad band noise is research. The frequency characteristic of the two noises is gained. It simulates the characteristic of fan blades noise when the model parameters (number of blades, rotation of fan, camber angle, spanwise radius of fan, section parameter of fan etc.) are changed. The law can be used during the course of low noise design and noise prediction of fans. Based on the frontal theory study, embedded-type air conditioner's indoor unit structure is considered. The indoor unit noise is controlled by the structure sound radiation controlled theory. Running separately and spectrum analysis etc. are used during the course of noise sources diagnosing. To ensure the indoor unit performance, a blast defector with perforation structure is used to put in practice. It also analyzes the noise control result by zwicker theory. It shows that the noise control is effective. The thin plate is used widely. So there is a good chance for researching on the interaction characteristic between the thin plate and its surrounding medium. In pipeline elimination noise system, there are many columniform thin plates in the muffler structure. The speed of the flow, noise source characteristic and the composition of the flow in the muffler affect the muffler performance. Based on the Corialis inertia force phenomenon of the flow in the pipeline, considering the gas-structure coupling induced sound radiation, the Hamilton theory and variational principle are used to model the coupling vibration equation of the exhaust pipeline. The exhaust pipeline gas-structure coupling frequency characteristic is researched by solving the coupling equation. The appearance of the gas-structure coupling inducing sound radiation of the exhaust pipeline is tested under the special surrounding. The rich data can be got together in order to exert the muffler characteristic. Because the exhaust pipeline characteristic should be researched at first before the gas-structure coupling of the exhaust pipeline is researched. The evaluating model of the muffler function (transfer loss model, insertion loss model and pressure loss model) model is made by the limited cubage method. The muffler evaluating target can be calculated by the developed "the automobileexhaust system CAD/CAE". The structural parameter can be modified by the affecting factor of the gas-structure coupling sound radiation. The research can provide the enterprise to design the optimization muffler and trial-manufacture the muffler.