Prediction And Analysis Of Fluctuating Pressure At Transonic Mach Numbers And Nonlinear Characteristic Of RB Convection System

Two parts are included in the thesis:1 The Analysis and Prediction of Fluctuating Pressure at Transonic Mach Numbers. Fluctuating Pressure provides an important basis for the analysis of structure response. The fluctuating pressure loads can induce danger aeroacoustic environment to the crew or equipments on the vehicles and cause potential structural failure.The thesis is based on demand for analysis of structural stability. After analyzing the existing techniques for the prediction of fluctuating pressure, we conclude that the combination of numerical simulation with the empirical models, which are based on the experiments, will be a more effective and more economical method with the advancement of the computer performance and the improvement of the reliability and the accuracy of the numerical technique. Based on this conception, numerical studies are conducted to provide necessary flow field data for the fluctuating pressure models through solving the 3D compressible mass weight-averaged Navier-Stokes equations. The time and space two order NND2M scheme is utilized to discrete the equations. Based on the numerical results and previous experiment data, different engineering models are adopted to predict the fluctuating pressure loads on the aerocraft surface so as to provide basic references for structural design of aerocraft. After serious reliability check, this model as well as the models for the surface area is incorporated into integrated software used as references to engineering.2 Nonlinear Characteristic Analysis of Rayleigh Benard (RB) Convective System Using Direct Simulation Monte Carlo (dsmc) Method. As a nonlinear dissipative system far from thermodynamics equilibrium, the onset and the structure of it are related to divarication and chaos. At present, the study for turbulence has been brought into the higher level-nonlinear research science. Rayleigh Benard system as a simple model of nonlinear system is so interesting that more and more researchers intend to show their interest for it in order to draw some conclusion about the onset of the turbulence. In general, they should get some experiment data or numerical data, and then the data is used to analyze the nonlinear characteristic of the system. Based on the idea, Rayleigh Benard is numerically simulated using Dsmc method, and the numeric result is nonlinearly analyzed, followed with some conclusions. In the thesis, the value of critical Rayleigh number by numeric simulation is near to the theoretical value. Another result is one route to chaos in RB. And the chaotic characteristic is also analyzed in order to further study.