A threedimensional unsteady CFD simulation method was established based on the RANS equations and Spalart-Allmaras turbulence model by varying rotating speed of reference frame and sliding mesh techniques to simulate the transient flow in an axial pump unit model in the runaway caused from power failure. The governing equations of fluid flow are discretized with the finite volume method; the temporal item is approximated with a firstorder backward difference implicit scheme, a secondorder central difference scheme is applied to the source and diffusion items, a secondorder upwind scheme is for the convection items, and the velocitypressure coupling method is chosen to be SIMPLEC. A steady simulation was performed first for providing an initial condition to the transient case. The results showed that the pump attained its runway speed in 20.35 s. The estimated runway speeds were 1 610 r/min and 1 989 r/min by two techniques, comparing with the experimental speed of 1 720 r/min. Additionally, the pump rotational speed, flow rate, torque and static pressure at monitor points against time were revealed during the transient period. These data will provide a reference for pump design and operation of pumping station.
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