Hydrodynamic Characterisation of Reservoir with Specific Reference to Vortex

Abstract

For smooth operation of large-capacity pumps, flow to suction nozzle should be eddy or newlinevortex free. Standards and guidelines available to design such a system lack theoretical newlineanalysis; hence many times, vortex or eddy formation takes place when flow rates are altered. newlineIt is proposed to use guided vanes, anti-vortex devices and maintain sufficient water level to newlineavoid such conditions. Many parameters like flow rate, critical submergence, and suction newlinepipe location were investigated in the literature to understand the vortex forming conditions. newlineIn the present work, a computational and experimental study was conducted to characterize newlinethe highly intermittent nature of surface vortex in the reservoir. CFD based study was newlineconducted to identify the Large eddy simulation (LES) model as the reliable model compares newlineto the k-and#969; and Detached Eddy Simulation (DES) model for analyzing the underline flow newlinephysics. A rectangular reservoir was considered for experimental and numerical analysis of newlinevortex forming conditions with Reynolds number 3.2x104 and Froude number 2.5 for varying newlinecritical submergence. The strength of the surface vortex was analyzed by applying the Fast newlineFourier Transform (FFT) analysis on the pressure fluctuations measured at the core of the newlinevortex experimentally and numerically. A numerical assessment was conducted to measure newlinethe effectiveness of the Anti-vortex devices in minimizing the vortex forming conditions. A newlinecorrelation was proposed for calculating critical submergence in terms of Froude number, newlineWeber number, and hD/D for a specific range of hD/D (10-150). Critical submergence was newlinefound to be dependent on the top/free surface draining rate. A parametric study was also newlineconducted to develop a correlation for vortex depth in the mixing vessel under constant newlinewithdrawal rate. Experiments were conducted for a paddle blade, pitch blade, and retreat newlinecurve impeller with impeller diameter from Di/Do = 0.3 to 0.5 and tip speed from 120-700 newlinefpm.