Characteristics Of The Unstart States Of Typical Hypersonic Inlets

As an unstarted state of the hypersonic inlet may result in serious damages to the engine, the hypersonic inlet is required to be started during all the operation process so as to work normally and efficiently. Hence, the inlet is quite important to a hypersonic airbreathing ramjet. However, causes of the inlet unstart are very complex and the unstart state of inlets is inevitable during the development of hypersonic airbreathing propulsion system. So it is necessary to make a further study on the unstart state as well as predict the unstarted phenomena.Firstly, this thesis numerically studies both the started and unstarted phenomena on a two-dimensional hypersonic inlet. A comparison is made between the computational and experimental results. It's found that the flow structure and the pressure distributions along the wall are in well agreement, indicating that the computational approach is credible. Then the approach is conducted both on a two-dimensional hypersonic inlet and a side-wall hypersonic inlet. Furthermore, the influences on the buzz characteristics of different configuration parameters and the freestream conditions, such as throttling ratio, the length of simplified dump combustor, the height of backstep, the total temperature and the freestream Mach number, are studied numerically and the reasons are discussed at the same time. Finally, the process of a two-dimensional hypersonic inlet from start to unstart is experimentally demonstrated by recording the corresponding time history of the wall static pressure. Then the pressure signals are analyzed by means of such time-frequency signal-processing methods as short-time Fourier transform (STFT) and wavelet transform (WT). What's more, two change-detection algorithms, i.e. the cumulative sum (CUSUM) and generalized likelihood ratio (GLR), are utilized to predict the buzz phenomenon. According to the experimental data, the alarm time calculated by CUSUM and GLR methods are both approximately 220 ms ahead of the big buzz, which verifies the feasibility of the methods adopted.