A Review of Flow Field and Heat Transfer Characteristics of Jet Impingement From Special‐Shaped Holes

Jet impingement cooling offers high convective heat transfer coefficients, making it effective for high‐heat‐flux applications. However, conventional circular impinging jets (CIJs) typically produce non‐uniform heat transfer distributions, with high Nusselt numbers ( Nu ) at the stagnation point that rapidly decline in the wall‐jet region, causing thermal stresses. This review critically analyzes the flow field and heat transfer performance of jet impingement from special‐shaped holes, including swirling (threaded and twisted‐tape), converging/diverging, lobed, chevron, cross‐shaped, and racetrack nozzles. It synthesizes experimental and numerical studies examining the effects of nozzle geometry on jet structure, vortex dynamics, entrainment, turbulence generation, and local/average Nu distributions. Swirling impinging jets (SIJs) introduce tangential velocity through helical inserts or twisted tapes, generating additional streamwise and azimuthal vortices. These enhance radial momentum redistribution and significantly improve thermal uniformity. Non‐circular orifices (lobed, chevron, and cross‐shaped) promote stronger entrainment and axis‐switching, yielding Nu enhancements of 25%–110% relative to circular jets, especially at low H / D ratios. The integration of nanofluids (Al 2 O 3 , CuO, TiO 2 , and hybrids) with both CIJs and SIJs is also examined. Nanofluids further augment heat transfer (typically 20%–75%) via increased thermal conductivity and microconvection, although they increase viscosity and pressure drop (Δ p ). Key parameters, including Reynolds number ( Re ), H / D , swirl number, and nanoparticle concentration, are systematically evaluated using compiled data and correlations. The review concludes that special‐shaped holes shift cooling from localized high‐heat‐transfer zones toward more uniform temperature distributions, making them suitable for gas turbine blades and electronics. Critical gaps remain in combined SIJ‐nanofluid systems on non‐planar surfaces and long‐term nanofluid stability under high‐shear conditions.