The Numerical Analysis Of Vibration Wall Flow Control Method

Recently, with the development of researching aircraft and the improvement of flow control technology itself, people is paying more and more attention on using flow control technology on different kinds of internal and external air fluid machinery. Compare to other flow control method like the synthetic jet and the periodic blowing, the vibration wall flow control method has advantages of without the external flow path, the light weight and the potential of flow control. This article based on the numerical simulation of vibration wall flow control method, introduced the method for analysis of discrete data Lynapunov exponent and the proper orthogonal decomsition analysis method, and carried out the research of controlling the flow separation of diffuser with unsteady excitation, the main work is as follows:1?Use the Large Eddy Simulation method to simulate the flow field of diffuser channel, and put vibration wall near the separation point. Use moving mesh technology to simulate the vibrating process. Spring-based smoothing model can be used for reconstructing the mesh, and be solved with the flow field. This can simulate the process of interact between the vortex and the vibration wall, and gained the flow structure under this process.2?Due to the unsteady flow in structure diffuser is complex, it is difficult to direct analyse, this paper introduces the proper orthogonal decomposition method(POD) to analyze the unsteady flow field, using the POD method to separate vortex structure in different scales thus the large scale vortex structure which plays a major role in the separation can be researched targetedly.3?The POD of uncontrolled flow results show that first mode and other modes are essentially different, it accounts for the largest share of energy, other than the first mode at least higher one order of magnitude; the second and third modes reflect the large scale structure in the channel, the periodicity is also close to the main separation vortex; flow field energy is mainly concentrated in the low modes, through the analysis of low order modes can have flow characteristics research on diffuser channel flow field.4?Study on effect of flow control for the effect of frequency shows that, when the vibration frequency is close to the separation vortex flow frequency, the main frequency is far greater than the no control case, and the spectrum characteristics of the control flow is greatly improved. After the POD decomposition of energy spectrum, reasonable vibration frequency enables the separation vortex energy transfer to the average flow energy, and weakened the high order mode share of energy from the whole, to suppress the complex flow structure in the channel corresponding to the higher order modes, to achieve the purpose of flow separation control.5?For the effects of different amplitude on the flow structure, with larger amplitude the channel relative total pressure loss coefficient firstly r educes and then increases, which shows that there is an optimum total pressure loss with an amplitude. The POD results of different amplitude show that over large amplitude although weakens the high modes, but also disrupts the mean flow, prompted the energy of average flow into the pulse energy.6?By introducing the Lyapunov exponent of Chaos Theory to analsy the unsteady flow field. Use the Takens delay embedding theorem to reconstruct the phase space, and C-C algorith to the estimate the time delay, finally calculate the maximum Lyapunov exponent by using Wolf method. And use the classical insect population model to verify the accuracy of the calculation program, based on which to analsy the time series of pressure fluctuation in the flow field of the monitoring points.