Numerical study on the overall cooling effectiveness of the rotating impingement effusion cooling structure under low Reynolds number conditions

The operating Reynolds numbers (Re) of high-altitude unmanned aerial vehicles (UAVs) reduces to around 2 × 104. However, existing low Re experiments differ significantly from the extremely low Re environment of UAVs. The additional forces affect internal impingement flow and heat transfer of impingement effusion cooling structure (IECS) under rotational conditions. Conclusions on whether rotation enhances or weakens heat transfer remain inconsistent. However, the current lack of comprehensive research on the coupling effect of low Re and rotation has not been given sufficient attention. This paper investigates the influence of low Re, rotation, rotation direction on the internal and external flow, and heat transfer characteristics of IECS. Results show that under stationary conditions, compared to high Re, the counter-rotating vortex pair (CRVP) at film hole outlet dissipates faster at low Re, increasing mixing between jet and mainstream. At low Re, the stable CRVP inside film hole interacts with the external CRVP, further lifting the film. Under rotational conditions, Coriolis and centrifugal forces deflect jet radially outward, improving film coverage between holes. The spanwise-averaged film cooling effectiveness (η) obtained under forward rotation decreases from 25.63% to 13.43% when Re drops from 5 × 105 to 2 × 104. At low Re, the shear vortices at film hole outlet and the downstream CRVP become asymmetric. The CRVP detachment from the surface is reduced than the stationary state, and the mutual disturbance of CRVP increases dissipation and reduces η. Changing rotation direction alters Coriolis force, and reverse rotation increases film wake deflection and enhances η compared to forward rotation.