Effect of Injector Wall Heat Flux on Cryogenic Injection

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Kurzfassung

This paper reports on numerical investigation and discussion of a cryogenic injection test case. This is a first step towards a numerical model for high pressure liquid rocket engine injection. Experiments with nitrogen injection at supercritical pressures are an accepted way of studying flow phenomena relevant for high pressure liquid rocket engines without introducing the complexities of mixing and combustion. CFD simulations of these cryogenic injection cases are found to typically agree on predicting a region of constant high density, extending some 10 injector diameters downstream into the chamber. This is in agreement with the traditional interpretation of liquid injection where instabilities on the phase boundary grow until the jet disintegrates. However, many experiments do not show this behavior: exceeding the critical pressure of the injected fluid, phase interfaces seize to exist, the jet tends to behave more like a dense gas jet with a rapid drop off of density starting at the injector exit. It is thus unclear whether the concept of a liquid core length is still true for thermodynamic states at temperatures near the critical point and supercritical pressures. To study this, experimental and numerical boundary conditions have been analyzed. Computations have been carried out using the DLR TAU code extended by a treatment for real gas thermodynamics. It has been found that the absence of a dense core, as found in experiments, can be reproduced numerically if numerical boundary conditions are chosen appropriately: taking into account heat transfer inside the injector leads to a preheating of the cryogenic stream and the development of a distinct radial density profile. This preheated jet then shows the more realistic immediate reduction of density instead of a dense core.

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• Effect of Injector Wall Heat Flux on Cryogenic Injection. (deposited 17 Aug 2010 15:25) [Gegenwärtig angezeigt]