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978-3-8439-1214-3, Reihe Raumfahrt
Numerical Investigation of Film and Transpiration Cooling
131 Seiten, Dissertation Rheinisch-Westfälische Technische Hochschule Aachen (2013), Softcover, A5
In thrust chambers of rocket engines the walls are exposed to high temperatures. In order to avoid material damage effective cooling concepts are necessary. Active cooling techniques, that are currently common in gas turbines, are a promissing approach also in certain components of rocket engines. However, the knowledge of physical effects gained concerning the use in gas turbines cannot be easily transfered to thrust chambers of rocket engines. Therefore, basic research leading to a detailed comprehension of the underlying physical effects is necessary for development of reliable active cooling systems.
In this thesis, two technical concepts of active cooling techniques for rocket engines are considered: Firstly, film cooling could be applied to the walls of the thrust nozzle, where the flow is supersonic in contrast to gas turbines. A very homogenous cooling film can be generated by injecting the coolant through large spanwise slots. Secondly, transpiration cooling is considered by using porous materials for the combustion chamber lining instead of solid materials with boreholes or slits for the cooling gas injection.
Computational results of film cooling through formally infinite and finite slots in laminar and turbulent supersonic flow are compared with shock tube experiments. Furthermore, cooling gas injection through a porous ceramic matrix composite mounted into the side wall of a subsonic hot gas channel has been simulated and compared to experimental data.
The essential results gained from the locally high-resolved three-dimensional simulations are the following: Considering film cooling through a finite slot a region downstream from the edge of the slot was revealed that is heated instead of cooled due to the rotation in the flow field induced by the injection. Especially, the underlying flow mechanism could be explained due to the high resolution. This region could not be detected in experiments. The numerical investigations of transpiration cooling provided an estimation of the influences resulting from the sidewalls of the channels. In contrast to other numerical investigations, less restrictive assumptions have been made here. Therefore, the legitimacy of some of these assumptions could be reviewed. These simulations could only be performed with affordable computational costs due to the usage of efficient, reliable and robust numerical tools.