Film cooling with sister holes in a rotating detonation combustor: Thermal performance and vortex mechanism assessment

The walls of rotating detonation combustors (RDCs) are subjected to intense periodic thermal loads, and film cooling is widely regarded as an effective thermal protection approach. This study applies a film cooling configuration using sister holes to an RDC and numerically compares its cooling performance with that of a conventional cylindrical hole configuration. Particular attention is given to whether the anti-kidney vortex mechanism established for sister holes under steady crossflow remains applicable in the strongly unsteady and highly periodic RDC environment. The results show that the configuration with sister holes provides broader and more continuous thermal protection, while its cooling performance varies non-monotonically with blowing ratio. A structure resembling an anti-kidney vortex is observed before detonation ignition; however, after a stable rotating detonation wave is established, no persistent classical kidney vortex or anti-kidney vortex pair is resolved. Therefore, the advantage of the configuration with sister holes is attributed more to coolant redistribution, enhanced lateral coverage, and improved axial continuity than to sustained suppression of the counter-rotating vortex pair (CRVP). These findings provide a useful reference for analyzing multi-jet film cooling under strongly unsteady RDC conditions.