The impact of film cooling on the heat release within a rotating detonation combustor

Abstract

Rotating detonation combustors establish a detonation wave that continuously circulates inside a small annulus. The presence of the detonation wave and the downstream oblique shock within the small annulus coupled with high mass flow induces a high heat load to the combustor wall. Preliminary analysis shows that for higher thermal power, internal air cooling alone is not sufficient to remove the heat out of the walls to maintain them below the maximum temperature of the metal. A possible solution is to use film cooling to reduce the heat flux to the combustor walls. One issue, though, is that the introduction of film cooling provides additional air into the system that can influence the combustion process as well as providing a location for secondary combustion.This paper represents the first investigation to study the secondary implications on combustion of using film cooling in a rotating detonation combustor. The TU Berlin RDC architecture was modified with the introduction of 480 film cooling holes placed in the oblique shock region. High fidelity LES investigations were performed for different coolant plenum pressures to show the benefits of using film cooling. However, due to the presence of unburnt fuel in this post-detonation region, the coolant can result in additional combustion leading to an increase in temperature near the wall. One the one hand, these secondary reactions result in an increase of the overall heat release increasing combustion efficiency, however this also results in higher temperatures and reduced film cooling effectiveness. A simulation performed with nitrogen as a coolant enabled the effects of increased mixing caused by the ejection of coolant gases to be separated from the additional heat release. The simulation with nitrogen shows a reduction of 88% in the local heat release in the post detonation region resulting in similar performance as the uncooled case and significantly cooler walls.