The flow inside the impeller of the high temperature molten salt pump is a complex three-dimensional turbulent flow. The flow law is affected by the curvature of the blade, the rotation of the impeller and its boundary conditions. At present, the real flow law can’t be obtained by the analytical method. So the experimental measurement and numerical simulation are the two main methods to study the complex internal flow. Especially under the influence of the device conditions and variable conditions, it appears a lot of flow phenomenon that they are not in the design conditions, which it has a great impact on the scope of allowing the pump to run and characteristics. In this paper, the calculation results under different working conditions are compared and analyzed, so as to further understand of the flow field inside the impeller for high temperature molten salt pump, and it provides the reference for two-phase flow in impeller
    1.The boundary conditions of the inlet

    According to the characteristics of the centrifugal pump inlet, the axial velocity is determined by mass conservation and no rotation. The tangential velocity and the radial velocity are assumed to be zero, and the rotating coordinate system is set at the impeller inlet. The first boundary condition is adopted at the inlet of the calculation domain, and the inlet velocity is determined by the flow rate under the three operating conditions. The turbulent kinetic energy at the inlet is taken as 1.0% of the average kinetic energy at the inlet.
    2. Results of the analysis
    After the iterative calculation, the relative velocity distribution and pressure distribution of the flow field in the impeller flow channel were obtained under different conditions.
   3.Relative speed

    Comparing the distribution of relative velocity under different working conditions, we can see that with the increase of the flow rate, the relative velocity is increasing and the relative velocity is getting smaller and smaller, but the velocity gradient is getting bigger and bigger. Import speed dues to the impeller high-speed rotation, rotating the wall drives the liquid particle to rotation, the relative movement of liquid becomes a spin movement.
    4.Conclusion

    In this paper, CFD software Fluent was used to simulate the internal flow field of IH65 centrifugal chestnut impeller. The numerical calculation results under different working conditions are compared and analyzed, and the flow of centrifugal pump impeller is analyzed preliminarily
    Field, the following conclusions can be drawn:
    (1) The internal flow field of the impeller that it is obtained by the numerical calculation is in accordance with the general law of the internal flow of the impeller.
    (2) Due to the impeller flow channel diffusion and the presence of the secondary flow inside the impeller, it will lead to the blade surface boundary layer separation to result in separation losses.
    (3) For the high temperature molten salt pump running in the clear water, the analysis of the internal flow field provides a valuable reference for its two-phase flow study.