Author(s): Ruben Nerella, Venkata Rathnam Erva
Linked Author(s): Venkata Rathnam Erva
Keywords: Fluid transients, wave speed, pumping main, specific speed, liquid column separation.
Abstract: Pumping mains that are conveying large quantity of water from lower elevation to higher elevations over long distance may experience undesirable water hammer pressures and are also referred to as hydraulic transients. They may arise due to abrupt operations like sudden opening or closing of valves or power failure to pump in pumping mains. Unplanned power tripping generates water hammer pressure that may fluctuates from minimum pressures or vacuum pressures to maximum transient pressures. Liquid column separation is the phenomena which may occur in a pumping mains when the pressure head decreases to vapour pressure of the flowing liquid and this analysis is important for planning transient mitigation devices. This paper presents a study on numerical simulation of water hammer with column separation events. A case study of pumping main of JCR Devadula Lift Irrigation Project, Telangana, India is presented. Discrete vapour cavitation model (DVCM) was applied to simulate the transient pressures in pumping mains for pump trip scenario. The effect of wave speed (500-1200m/s) and specific speed of the pump (17-52) on the developed transient pressures were investigated. The water hammer equations were solved using Method of Characteristics (MOC) approach. The effect of unsteady friction was neglected. Then, discrete vapour cavity equations were incorporated at each computational grid (node) to simulate cavitation locations, along delivery length of pumping main. The results show that when the specific speed of the pump increases, the minimum pressure head near pump delivery increased and cavitation event does not occur. Similarly, the maximum pressure head decreases as the specific speed increases. Moreover, results show that the maximum transient's pressures heads are increasing and minimum pressures are decreasing for higher value of wave speeds
Year: 2017