Time discretization methods in the computation of unsteady flow

For the numerical computation of unsteady flow, the computational accuracy and efficiency would have a significant difference with different time discretization methods. This paper based on the summarize of the development situation of time discretization methods at present, briefly introduces the time discretization methods developed in recent years like the nonlinear frequency domain method, harmonic balance method, time spectral method, time spectral element method, time finite difference method and so on. Based on the difference between discrete versions, the time discretization methods can be divided into four types: time domain marching method, frequency domain harmonic method, time domain collocation method and hybrid method. This paper briefly introduces the mathematical thought and study progress of each discretization method, and selective compare the accuracy, efficiency, and scope of application of each time discretization method in the computation of unsteady flow. Then we systematically summarize the characteristic of each time discretization method and advise how to choose appropriate time discretization methods in different unsteady flow problems. Finally, briefly introduce the application of current time discretization methods in the projects and discuss the development directions of the time discretization method in the future.