Investigation of Closed Valve Operation Using Computational Fluid Dynamics

Abstract

Predicting the head of a centrifugal pump operating at closed valve remains a difficult task. The nature of the flow regime and the influence of geometric features on this flow is uncertain. In this paper both the flow regime and the influence on that regime by geometry is investigated using a commercially available CFD RANS code. A CFD methodology is presented that takes account of the difficult boundary conditions. This methodology is then used to present the flow regime in a volute pump against the background of available research. The theory of solid body rotation, as a major influence on the closed valve head, is shown by the CFD simulations to be analogous to but not representative of the actual flow regime. The nature of the flow is impulsive and unsteady with fluid interchange occurring between the pump collector and the impeller vane passages. At the inlet the pump impeller experiences a strong steady outflow from the impeller blade tip. This spiralling flow must be accommodated within the computational solution. The impeller outlet is filled with a vortex driven by the flow which cannot be accommodated within the stalled stator passageways. The annular gap between the impeller and collector is filled with a pulsating flow whose frequency is determined by the number of vanes within the impeller. Model validation was carried out by reference to experimental papers and time averaged closed valve head values obtained under standard performance testing.

Flow performance analysis on shutoff condition in centrifugal pump based on CFD simulation

“…Re cently, some CFO simulation investigations were carried out for shutoff's flow field of centrifugal pumps. Oyson [5] performed an unsteady numerical calculation on a 3-blade centrifugal pump to investigate shutoff's flow and pump head with the boundary condition using pump's leakage flow rate (1% -5% of Qd). Huang P [6] and Wu X [7] employed Dyson's approach to simulate shutoff flow in a centrifugal pump with specific speed 65.…”

Design and Test for High Specific Speed Mixed Flow Pump with Volute

“…Relativity examination of grid number is done for each model. When the effect of grid number on pump characteristics is less than 0.1 percentage [10] ，the effect is ignored. Finally, the mesh number of impeller, fixed diffuser, and volute are 820 000, 390 000, and 670 000 respectively.…”

Experimental Study on Transient Startup Characteristics of a Super Low Specific Speed Centrifugal Pump

“…Some studies on centrifugal pumps under unsteady states have been conducted. The inner flow field and external characteristics of a single stage double volute centrifugal pump under shut-off condition was investigated by numerical simulation, and the results were compared with experimental results (Dyson and Teixeira, 2009). The influence of the inertia of the centrifugal pump impeller and the fluid during the startup period on performance has been studied, and the results showed that the pressure and the pump speed during the startup period would be only a little higher than the stable value when the rotational inertia of the rotating parts was less than the flow inertia (Grover and Koranne, 1981).…”