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Licentiate seminar

Flow processes in rocket engine nozzles with focus on flow separation and side loads


Defendant Main Advisor Extra Advisor Date
Jan Östlund Barbro Klingmann 2002-06-13

Opponent
Ardeshir Hanifi, KTH, Mekanik

Evaluation committee

Abstract

The increasing demand for higher performance in rocket launchers promotes the development of nozzles with higher performance, which is basically achieved by increasing the expansion ratio. However, this may lead to flow separation and ensuing unstationary, asymmetric forces, so-called side-loads, which may present life-limiting constraints on both the nozzle itself and other engine components. Substantial gains can be made in the engine performance if this problem can be overcome, and hence different methods of separation control have been suggested, however none has so far been implemented in full scale, due to the uncertainties involved in modelling and predicting the flow phenomena involved. The present thesis presents a comprehensive, up-to-date review of supersonic flow separation and side-loads in internal nozzle flows with ensuing side-loads. In addition to results available in the literature, it also contains previously unpublished material based on this author¹s work, whose main contributions are (i) discovery the role of transition between different separation patterns for side-load generation, (ii) experimental verification of side-loads due to aeroelastic effects and (iii) contributions to the analysis and scaling of side-loads. A physical description of turbulent shock wave boundary layer interactions is given, based on theoretical concepts, computational results and experimental observation. This is followed by an in-depth discussion of different approaches for predicting the phenomena. This includes methods for predicting shock-induced separation, models for predicting side-load levels and aeroelastic coupling effects. Examples are presented to illustrate the status of various methods, and their advantages and shortcomings are discussed. The third part of the thesis focuses on how to design sub-scale models that are able to capture the relevant physics of the full-scale rocket engine nozzle. Scaling laws like those presented in here are indispensable for extracting side-load correlations from sub-scale tests and applying them to full-scale nozzles. The present work was performed at VAC`s Space Propulsion Division within the framework of European space cooperation. //Keywords: turbulent, boundary layer, shock wave, interaction, intermittent, overexpanded, rocket nozzle, flow separation, side-load, models, criteria, prediction, review.
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