Cavitation and Draft Tube Analysis of Pump Running in Turbine Mode

Abstract

Conserving energy while exploring renewable, environmentally-friendly energy resources is critical in the quest to keeping up with increasing energy demand. Hydropower is the top most renewable energy source and micro hydro power plant is one of the best solutions for energy crisis in remote, rural and hilly areas. The pump running in turbine mode is the excellent alternative of turbine for micro hydro power plant. Several methods for predicting the behaviour of pumps as turbine (PAT) have been developed. Investigations for the entire range of specific speeds have been carried out also computational fluid dynamics (CFD) is also used to study the reverse operation of centrifugal pumps by many researchers.

In the present study, introduction of small hydro power schemes and PAT is given. The literature review pertaining to PAT is presented. Analytical and numerical investigations for different types of draft tubes were carried out. For CFD analysis 3-D computational model of PAT was prepared and analysis was done in ANSYS CFX- software. The study revealed that diverging draft tube with inlet cone angle 6 is suitable at the exit of PAT. Experimental investigation carried out on pump (Head 15 m, Discharge 1500 liter/min) running in turbine mode is presented. Parametric studies viz. effect of speeds on various parameters like efficiency, power and head is carried out. Vibration analysis of system with two types of draft tubes viz. straight and diverging was carried out.

Experimental investigations for cavitation analysis were carried out including artificial suction creating system (ASCS). Sigma test was carried out at rated speed and critical cavitation factor is defined for the existing system. Different cavitation detection techniques like visual observation, vibration measurement and acoustic measurement were applied and traveling bubble cavitation at the end of the PAT and vortex rope cavitation was detected at the entrance of the draft tube.