Numerical simulation of side loads in an ideal truncated nozzle

The side loads induced by unsymmetrical and unsteady separation of the flow taking place in the nozzle extension during launch are a very important limiting factor for the performance of a rocket engine. The onset of suchloads is not yet a fully understood phenomenon because only a limited amount of experimental data is available due to test difficulties. A numerical study of the three-dimensional overexpanded nozzle flow during stationary operations has been undertaken to try to understand the origin of this phenomenon. The flow separation in an truncated ideal contoured nozzle is investigated together with the resulting side loads. Comparisons with experimental data are given. The numerical simulation relies on the resolution of the three-dimensional unsteady Reynolds-averaged Navier-Stokes equations. An algebraic turbulence model based on Baldwin-Lomax and Goldberg's backflow correction has been implemented in a three-zone formulation adapted to the flow topology of interest. The main features of the flowfield, side-loads mean value, and the separation point location are well estimated. With regard to the separation point location, the proposed method gives better results than the most commonly used semi-empirical criteria. Unsteady characteristics of the flowfield are presented.

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