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Semi-empirical model for supersonic flow separation in rocket nozzles
2005 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The commercial potential of space flight can be described as a quotient of system performance and system weight. The system costs are primarily dependent on this quotient. To increase the quotient focus has been on reducing the system weight. After exploiting numerous ways of reducing the system weight and finally reaching the limit of mechanical load capacities, the current aim is to increase the thrust-to-weight ratio of the rocket nozzle. This is achieved by reducing the divergent length and increase the specific momentum of the nozzle, i.e. increasing the expansion ratio. However, this may causes the nozzle to be overexpanded at sea level and thus provokes the flow to separate from the nozzle wall. The unsteady and asymmetric flow separation generates lateral forces on the nozzle wall, so called side loads, which can be of dimensioning size for the nozzle and the rocket structure and not at least for the payload. Extensive studies have been made through the years to understand the flow separation phenomena in overexpanded rocket nozzles. A better understanding could lead to better prevention or even control of flow separation. In addition, a reliable separation model is needed for accurate prediction of the side-loads experienced during start up and shut down of the engine. The aim of this thesis was to examine current separation models and try to develop a new semi-empirical model for hot gases. Focus was on the recirculation region where the flow is separated from the nozzle wall. A new model was developed to determine the pressure- and flow distribution in the recirculation region. The model includes various parameters of the jet- and ambient gas and can therefore be used for hot gases. Several steps of the model were validated with good agreement with experimental data and numerical results found in the literature. The complete model on the other hand showed poor agreement with experiment and further work must therefore be made before the model can be useful.

Place, publisher, year, edition, pages
Keyword [en]
Technology, shock waves, rocket nozzle, flow separation, Integral, method, recirculation region, ideal jet
Keyword [sv]
URN: urn:nbn:se:ltu:diva-51861ISRN: LTU-EX--05/128--SELocal ID: 90974b65-f5ce-4bda-8c5c-29a657e9c2fcOAI: diva2:1025225
Subject / course
Student thesis, at least 30 credits
Educational program
Space Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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