The key demand on future space transportation systems is the concurrent reduction of Earth-to-orbit launch costs and increase of launcher reliability and operational efficiency. A common way of slightly improving performance of gas-generator open-cycle engines is the injection of the turbine exhaust gas into the nozzle divergent section, which is also used for wall film cooling. The present study focuses on a numerical parametric analysis of the film-cooling efficiency in dual-bell nozzles. The secondary gas injection is made in the first bell, and it is found that the expansion fan originating from the inflection helps the film to better protect the wall. The results of fully-attached-flow simulations are also used to study the influence of film cooling on the expected behavior of nozzle side loads during operation with separated flow in the second bell.
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Martelli et al. (2009) studied this question.
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