Study On The Nonlinear Acoustic Field Of Exponential Shaped Thermoacoustic Resonator

Thermoacoustic refrigerator is the new machine which has a great development potential and application prospect. With the development of the thermoacoustic refrigerator practical process, the requirement of thermoacoustic refrigeration efficiency more and more highly. Resonator is an important part of a thermoacoustic refrigerator, the sound pressure amplitude and pressure ratio in resonator has great influence on the cooling efficiency of thermoacoustic refrigerator. Under the same driving condition, high sound pressure amplitude and pressure ratio can improve the acoustic power, so that the refrigeration efficiency of refrigerator was improved. The exponential shaped resonator can improve pressure ratio. But when the sound pressure amplitude of resonator is larger, the linear thermoacoustic theory cannot explain some nonlinear phenomenon under large pressure amplitude. However, the sound field of exponential resonator simulation is mostly based on one dimensional model, and also lack methods to enhance the performance of exponential shaped resonator.The two-dimensional nonlinear acoustic field of exponential shaped resonator was simulated with a computational fluid dynamics software-Fluent. The sound pressure amplitude of the resonator is the largest when driving frequency equal to the resonance frequency of the tube, so the resonance frequency was studied and the pipe type which has the largest sound pressure amplitude and pressure ratio was obtained. The advantages of the exponential shaped resonator in increasing the sound power consumption was verified by comparison with the acoustic field of cylindrical resonators after get the resonance frequency of exponential shaped resonator. Meanwhile, the characteristics of acoustic and flow field of exponential resonator are analyzed and the influences of wall boundary temperature on acoustic field was also explored. At last, puts forward suggestions for improve performance of resonator, so as to provide reference for efficient thermoacoustic refrigerator design.In this thesis, the main work includes the following several aspects:(1) The feasibility of using Fluent to simulating thermal thermoacoustic problem and the correctness of the calculation model was verified by analysis for the acoustic field in a cylindrical straight resonator and compared with the literature results.(2) The two-dimensional nonlinear acoustic field of six exponential shaped resonators(m = 2.0, 2.2, 2.0, 2.2, 2.8 and 3.0) was simulated. The influence of driving frequency and driving intensity on pressure in resonator as well as its actual resonance frequency was studied. The relationship between actual resonance frequency and theoretical calculation resonance frequency was also explored.(3) The acoustic field of the exponential shaped resonator of m=2.2 was calculated and simulated, the ability of the exponential shaped resonator in increasing pressure ratio and inhibition of harmonics was verified by comparison with acoustic fields of an equal diameter straight resonator and an equal volume straight resonator. The characteristics of the structure of flow field and acoustic field are analyzed. Finally, the influences of wall boundary temperature on acoustic field of exponential shaped resonators was explored and the best boundary temperature which can improve the performance of resonators was obtained.