On the numerical-experimental analysis and scaling of convective heat transfer to pulsating impinging jets

This paper presents a comprehensive numerical-experimental study performed on unsteady impinging jets with flow pulsation and builds on an experimentally validated numerical Reynolds-averaged Navier Stokes (RANS) CFD model for fluid flow and heat transfer simulations of steady impinging jets. The model accounts for intermittent pulsation with a square-wave form as the inlet velocity signal. Comparing against experimental local heat transfer data as reference, accurate CFD simulation results are presented. The study is performed over an extensive range of operating conditions for an axisymmetric air jet impinging on a flat surface for nozzle-to-surface distances 1 ≤ H/D ≤ 6, Reynolds numbers 1300 ≤ Re ≤ 2800 and Strouhal number 0.0029 ≤ Sr ≤  0.333 (pulsation frequency 5 Hz ≤ f ≤ 260 Hz). The numerical model is used to extend the findings beyond the experimental range and simulates considerably higher pulsation frequencies. The numerical results also provide a more detailed insight into the near-wall behaviour in the viscous sub-layer, which helps to understand the governing heat transfer mechanisms. Correlations for the averaged and stagnation point Nusselt number enhancement in pulsating flow have been least-square fitted to the numerical data as a function of suitably modified Strouhal numbers.