Numerical investigation of film cooling hole design effects on the cooling performance of an expansion-deflection nozzle pintle

초록

This study performed a numerical investigation into the film cooling performance required to ensure the thermal stability of a pintle exposed to high-temperature combustion gases inside an expansion-deflection (ED) nozzle. Coolant dispersion characteristics were examined through single-hole analysis by comparing the coolant behavior under freestream conditions and the nozzle internal flow. The effects of the contraction streamline and mass flux of the main flow on the coolant distribution were also examined. The dominant film cooling mechanisms for each pintle section were identified, thereby confirming the need for a section-specific pintle cooling design. Two-dimensional axisymmetric simulations for the straight section determined the baseline cooling efficiency trends as functions of the axial injection angle and slit width. Three-dimensional computations evaluated the influence of the circumferential injection angle and hole arrangement and characterized the governing cooling mechanisms in the deflection and head sections. Convection driven by the internal flow of the plenum chamber is the primary factor controlling pintle cooling inside the ED nozzle. Static pressure in the plenum chamber and the coolant mass flow rate are key design parameters. Furthermore, the cooling performance in the straight section was governed by the interaction between the counter-rotating vortex system and attached film layer, whereas in the deflection and head sections, the main flow became dominant, requiring different cooling hole configurations for each region. This study improves understanding of the film cooling behavior in complex confined flow environments and provides foundational guidance for the thermal management design of ED nozzle systems.

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