Verification and validation of large-eddy simulations of heat transfer in a planar impinging jet

A significant portion of the energy produced by the burning plasma in diverted tokamaks will be dissipated on the plasma-facing components (PFC). Hence, cooling the PFC and recovering this energy is important for realizing magnetic fusion energy. The tungsten (W) targets of the divertor, which minimize plasma contamination, are subject to perhaps the highest surface heat loads—as great as 10 MW/m²—even though they lie outside the core plasma. The leading gaseous coolant for PFC is helium (He), and several divertor cooling schemes rely on planar He jets impinging on the W targets. Our initial studies consider the heat transfer in this canonical flow. A He jet exiting from a slot of width B at Reynolds numbers Re_B = O(10⁴) and impinging on a constant-temperature flat surface within 4B of the exit was simulated by wall-resolved large-eddy simulations (LES) using ANSYS Fluent and the wall-adapting local eddy-viscosity (WALE) subgrid-scale (SGS) viscosity model. Surface Nusselt number Nu and near-surface velocity distributions within 20B of the stagnation point are compared with previous experimental data, as well as earlier LES and DNS studies. Given the complex geometry of actual divertor designs, the LES results are also used to evaluate and verify RANS simulations using Fluent and various turbulence closures, including the k-ω shear stress transport (SST) with and without transition, realizable k-ε, and “untuned” GEKO models.