Experimental Study of an Air-Augmented Waterjet Propulsor

摘要

Compressed air can be added to the flow in a waterjet pump to increase the thrust. The gas bubbles expand as the pump mixture passes through the pressure gradient of the convergent discharge nozzle, imparting energy into the flow. In this experiment, air is injected into a pump fitted to a model boat and static thrust is measured for a range of void fractions using two nozzles. Air is injected between the rotor and stator and downstream of the stator stage. Measurements of the pump and air flow rates, thrust, pressures, and torque show how the injected air affects thrust, pump head rise and power. Results show that the thrust can be increased by 12%, and the pump operates at a lower flow coefficient and higher headrise. The energy balance shows that thrust can be increased with less shaft power than required for the same thrust increase using higher pump speed, but the energy required for the air injection offsets the savings in shaft power.