|Ph.D Student||Aviad Gofer|
|Subject||Investigation of Performance and Basic Phenomena in Air|
Augmented Waterjet Propulsion
|Department||Department of Aerospace Engineering||Supervisor||Professor Emeritus Gany Alon|
|Full Thesis text - in Hebrew|
This research presents analysis, experiment, and prediction of the performance of a unique marine propulsion concept, the air augmented waterjet, having a revolutionary potential for significant thrust augmentation and boost capability of waterjet systems. Related phenomena were also analytically and experimentally analyzed.
Analytical model for the two-phase air-water flow in the mixing chamber and following nozzle was developed.
A new expression for stagnation pressure is revealed, yielding more accurate values than the common expression, , in which is the average water-bubble mixture density. Stagnation pressure measurements at the exit cross-section were found to be in good agreement with the theoretical Bernoulli like expression in converging nozzles.
An analysis of the influence of distributed air bubbles introduction into a water flow in a constant and non-constant cross-section duct on the variation of the two-phase flow properties has been done. For a constant cross-section duct the analysis revealed an analogy between the relation of air-to-water mass ratio and Mach number in two phase flow and Rayleigh Line (correlation between temperature ratio due to heat addition and Mach number) in air-only flow.
A simple differential equation was found for velocity and Mach number distributions for a non-constant area cross-section duct. Numerical solution has been obtained for two-phase flow in a converging nozzle and in a diverging nozzle. For the case of subsonic two-phase flow in a converging nozzle a good agreement between numerical solution and experimental results was demonstrated.
This research also presents experimental investigation of bubbly low and high speed
air-water two-phase flow in converging and converging-diverging nozzles.
At higher mass ratios (between 0.08% and 0.32%), pressures higher than the ambient pressure were detected at the nozzle throat in both converging and converging-diverging nozzles, indicating choking conditions.
Converging-diverging two phase nozzle flows indicate behavior which is typical to supersonic flows, namely, a pressure decrease along the diverging section, reaching sub-atmospheric values. Results in two-phase flow showed negligible decrease in stagnation pressure between the inlet and throat cross-section area of the nozzle and significant decrease, up to 30%, in stagnation pressure in the diverging section of the nozzle, between the throat and the exit cross-section area of the nozzle.
The research presents innovative analytical solutions, enabling simple prediction of two-phase bubbly flows in nozzles. The experiments results revealed phenomena that have not been published in previous experimental works on two-phase flows.