M.Sc Thesis

M.Sc StudentMiller Lior
SubjectDevelopment of Integrated Geometry Nozzles for Rocket Motors
DepartmentDepartment of Aerospace Engineering
Supervisor PROF. Benveniste Natan
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


The rocket motor nozzle is a critical part in a missile system and should be designed adequately in order to maximize the rocket performance, taking also into consideration additional parameters, such as weight and price.

The most common and efficient form of a rocket nozzle has an axisymmetric, convergent-divergent shape. Advanced rocket motor nozzles aspire to improve the rocket motor performance by various means or nozzles of non-conventional geometries. These nozzles can be designed and assembled in different and non-conventional shapes or configurations.

In the present research, an experimental investigation was conducted along with CFD analysis to study the effect of changing the rocket motor nozzle cross section from round to rectangular on its ballistics performance.

The CFD analysis indicated that the higher wetted surface at the rectangular nozzle causes higher energy losses due to surface friction, thermal losses and due to 3D vortexes created at the corners. A theoretical comparison between equilibrium flow and frozen flow in both types of nozzles was performed and showed small differences in the flow profile and nozzle performance.

Firing tests were conducted using a BEM (Ballistic Evaluation Motor) and a full-size rocket motor. The ballistics performance of BEM and the full size rocket motor was predicted using both Rafael ballistics performance software and the NASA CEA code.

The research focused on three different rocket motor chamber pressure levels: 60, 90 and 130 bar. For each pressure level, three nozzles were examined: an axisymmetric nozzle, a rectangular nozzle with one-dimensional divergence plane and a rectangular nozzle with two dimensional divergence planes. All nozzles were designed to have the same ratio between the exit plane area and the throat area.

The BEM static firing test analysis indicated an average loss of 1.5% in the specific impulse for the rectangular nozzle, in comparison to the axisymmetric nozzle and an average loss of 2.5% in the total impulse, for the same firing conditions. The results of the full-size rocket motor static firing test analysis indicated a loss of 2% in the specific impulse for the rectangular nozzle in comparison to the axisymmetric nozzle and a loss of 0.6% in the burn time.

The analysis of the experimental results showed that an adequate rectangular nozzle design, which takes into consideration factors that affect the anticipated losses in performance, can significantly reduce the performance losses.