Abstract
Compared with the periodic unsteady flow induced by single-stage centrifugal pump, the internal flow state of multistage centrifugal pump is more complicated and the flow is more disordered. In this paper, the start-up process is divided into two stages: the closed-valve transition and the open-valve transition. The transient operation process is simulated numerically, and the pump characteristics and the evolution characteristics of the internal flow field are analyzed. It is found that when the impeller does the same work, compared with the steady state at the same speed, the mechanical energy in the internal flow field is converted into more kinetic energy and less pressure, which is a typical performance of the transient effect during the start-up process of the closed-valve transition. Compared with the steady state at the same flow rate, in the initial stage of the open-valve start-up phase, the stall group in the impeller flow channel is larger and the number of stall groups is more during the transient process, which exacerbates the rotational stall of the internal flow of the impeller, and the flow is more disordered. As a result, the amplitude of the hump fluctuation is greater than that under the same flow steady state.
Highlights
Multi-stage centrifugal pumps need to be started frequently due to changes in operating conditions
The start-up process of low specific speed multistage centrifugal pump is divided into two stages: variable speed closed-valve transition and variable flow open-valve transition
(1) According to the theoretical analysis, the centrifugal pump impeller has transient effects caused by two kinds of additional heads, a rotational acceleration head and a flow inertia head during the pump-start transient operation
Summary
Multi-stage centrifugal pumps need to be started frequently due to changes in operating conditions. Compared with the stable speed start-up process at corresponding time, the area of low-pressure vortices is larger, the central pressure is lower, the pressure gradient is larger and the number is larger It shows that the internal flow condition of the startup process of the closed-valve transient is more turbulent and more complicated than the steady-state steady state at the corresponding moment. This is because the impeller does have a certain functional force when the rotational speed is kept constant. With the development of the open-valve process, the flow rate gradually increases, internal flows have gradually stabilized
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