Numerical Analysis of Impeller-Volute Tongue Interaction and Unsteady Fluid Flow in a Centrifugal Pump

Abstract

Unsteady flow analysis has been carried out within a centrifugal pump with six twisted blade impeller to study the impeller/volute tongue interaction. The numerical analysis is done by solving the three-dimensional RANS codes with standard k-ɛ two-equations turbulence model. The wall regions are modeled with a scalable log-law wall function. The numerical simulation is carried out with multiple frames of reference (MFR). Dissimilar tetrahedral mesh for the impeller/volute casing has been used and is connected via Transient Rotor Stator interface. Current investigation will study the unsteady fluid flow interaction between impeller/volute tongue and the casing at various operating point. The results of the numerical analysis are used to predict and visualize the unsteady flow interaction between the impeller and volute casing. From the numerical analysis, it shows that a recirculation zone near to suction-front shroud side just after the leading edge even at design point due to non-tangential inflow condition. The flow within the impeller passage is very smooth and congruent with the curvature of the blade in stream-wise direction. When the flow is discharged into volute casing circumferentially from the impeller exit, the high velocity flow is severely distorted and formed a spiral flow pattern within the volute casing. The axisymmetrical, dual core vortex flow developed inside the volute near the tongue will slowly evolved into non-axisymmetrical, non-equal dual core vortex flow near volute exit in angular flow direction. Near volute tongue region, the impeller/volute tongue strong interaction is observed based on the periodically fluctuating pressure at outlet. The uneven pressure distribution is observed at impeller outlet circumferential position. The existing analysis results showed that the pressure fluctuation periodically is due to the position of impeller blade relative to tongue and the flow field within the volute casing is always unsteady and turbulent.