טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentAviad Gofer
SubjectInvestigation of Performance and Basic Phenomena in Air
Augmented Waterjet Propulsion
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Emeritus Gany Alon
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

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.