Clean-full mixed flow FVM simulation method based on gradual change narrow slit method

The invention discloses an open-full mixed flow FVM simulation method based on a gradual change slit method. The open-full mixed flow FVM simulation method comprises the following steps: constructing a one-dimensional flow control equation of unsteady open-full mixed flow of a pipeline based on the gradual change slit method; a finite volume method is adopted to solve a one-dimensional unsteady open-full mixed flow control equation adopting a gradual change narrow slit method, and a precise Riemann solver is adopted for a discontinuous problem in the FVM solving process, so that the problem of inaccuracy of approximate solving is avoided; an accurate Riemannian solution is solved by using a derivative-free third-order iteration method, so that the problem that the function has no derivative is avoided; and finally performing model evaluation verification. According to the invention, the gradual change narrow slit method is utilized to simulate the bright-full mixed flow, so that the problem of virtual numeric