Supersonic film cooling in generic rocket nozzles

  • Supersonische Filmkühlung in generischen Raketendüsen

Ludescher, Sandra Christine; Olivier, Herbert (Thesis advisor); Gülhan, Ali (Thesis advisor)

Aachen (2020)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020

Abstract

Rocket engines have to withstand high thermal loads. For guaranteeing a safe operation of the engine, these loads on the structure have to be minimized by applying cooling. However, the mass and costs of the cooling system are critical design parameters, since they affect the total cost-value ratio of the engine. In addition, reusability of the engine and the cooling system becomes more and more important. A possible cooling technique with low additional mass and high reusability is film cooling. It is based on a coolant film, which flows parallel to the wall and builds a protective layer between hot gas and structure. This technique is already applied in some rocket engines for the thermally less stressed components. By combining film cooling with other cooling methods, it is also used in regions of higher thermal loads. However, until now this technique bears a lot of uncertainties regarding its efficiency, which limits its application in the engine. The aim of this work is to reduce these uncertainties by providing a better understanding of the film cooling behavior under rocket-engine-like conditions. Therefore, supersonic, tangential film cooling in the expansion part of a conical nozzle is investigated and the most important influencing parameters on film cooling behavior are detected and explained. Supported by numerical simulations the similarity of the experimental hot gas conditions and the hot gas conditions in a real rocket engine is shown. For a theoretical investigation of the gained data the cooling efficiencies of each experiment are determined. Therefore, a model for calculating the heat transfer coefficients of the local hot gas-coolant mixture is developed. Additionally, the influence of several characteristic numbers on the cooling efficiency is investigated and correlation models for the experimental data are found. Based on this, a simple model for a rough design of a supersonic film cooling application in a nozzle is proposed and used for giving a first approximation of the coolant gas mass fluxes in a realistic engine. Furthermore, film cooling experiments in a dual-bell nozzle are conducted. The parameter of interest here is the influence of the contour inflection geometry on film cooling efficiency in the bell extension when the nozzle operates in altitude mode. These results can help in future design processes for this type of nozzles.

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