Effect of Surface Roughness on Jet Pump Performance(<Special Issue>Jets, Wakes and Separated Flows)

The jet pump generally needs a long throat to mix the driving and induced fluids and transfer the momentum of driving fluid to induced fluid. Simultaneously, the energy loses when the fluids flow through the long throat because the friction loss occurs inside of the throat wall. Therefore, it is known that the throat length largely affects the jet pump efficiency. In this study, experimental studies are performed for a typical single nozzle jet pump using water at room temperature. It is revealed that surface roughness located nearer the throat inlet has a greatest effect on the jet pump efficiency because the local skin friction coefficient nearest the throat inlet is the largest. The best efficiency and its flow rate ratio decrease linearly as surface roughness increases. The frictional resistance coefficient in the throat for each roughness is made clear by fitting a one-dimensional theoretical prediction equation to the experimental results.