Reynolds Average Navier-Stokes Formulation Applied to Single and Two-phase Flows in a Centrifugal Pump
Keywords:
Numerical simulation, Head curves, multiphase flow, centrifugal pump, cavitation, NPSHAbstract
In this work numerical simulation of single and bi-phase flows are carried out in a centrifugal pump. The main goal is to simulate both head and the efficiency curves for different angular velocities face single and two phase flows. To achieve such goals commercial Ansys CFX platform was employed. The physical model was discretized into finite volumes and the turbulence model employed was k-ω SST along with Rayleigh-Plesset to model the bubble increasing for cavitation modelling. At the first stage both head and the efficiency curves were simulated under single phase flow for three different angular velocities, 1250, 1500 and 2000 RPM. In sequence bi-phase flow was prescribed at the pump inlet to analyse the same head and efficiency curves under the light of the vapour/liquid mixture. During the simulation only liquid and/or vapour water, at 25°C were employed. As the main results the vapour-water was seen to increase as the leading to a head decrease in comparison with the single phase flow, does not matter which the angular velocity prescribed. The required NPSH was then computed and compared with the based on the open literature formula, through the Thoma factor, s. Despite of the certain scattering of the data the Thoma factor was found to be fitted by exponential curve as s=C nq4/3, being C the constant and nq the specific pump rotation.
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