Improved CFD simulation of dual jet flow past a heated surface

A dual jet flow comprises a wall jet discharged immediately parallel to a solid boundary flowing alongside a parallel offset jet. Dual jets have application in aircraft noise suppression and process cooling and more recently are of interest regarding electronics cooling. To date, of the published dual jet studies that have investigated wall heat transfer, most have been conducted using computational fluid dynamics simulations (CFD). However, recently published experimental data shows those numerical works do not accurately predict the wall heat transfer. Such discrepancies motivate the current study, which details the development of experimentally validated CFD simulations that can accurately predict the hydrodynamic and thermal characteristics for dual jet air flow past a surface heated with uniform heat flux. The effects of the chosen turbulence model and turbulence model inputs are investigated under steady flow conditions for jet Reynolds numbers of Re = 5500 , 9000 , 12000 , at an offset ratio of 3 where the jet velocity ratio is maintained at 1. The major aspects of a dual jet flow field are observed for all simulated cases. Importantly, the simulations predict the separation of the wall jet from the boundary, as observed by reference experimental studies but not by previous computational efforts. The local Nusselt number ( N u x ) profiles along the boundary are in good agreement with the reference experimental dataset, where the local N u x minimum and maximum are simulated successfully. The N u x profiles are found to be very sensitive to the choice of turbulence model and model inputs, indicating why previous attempts in the literature reporting heat transfer behaviours of dual jet flows may be inaccurate. A set of model inputs including turbulence intensity, turbulent viscosity ratio, and turbulent Prandtl number are presented and calibrated to relevant experimental data for the specific case of a jet offset ratio of 3 and jet velocity ratio of 1. The present study provides improvements to the two-dimensional simulation of steady, wall-bounded dual jet flow, where the resulting wall heat transfer behaviour can be considered more reliable and better aligned with physical reality for the specific case investigated. Yet, the study is not without its limitations. Results show a consistent underprediction of the rate of jet development, with the combined point predicted to exist further downstream than that observed in experiments. Moreover, the validity of calibrated input parameters outside the stated values of offset ratio and velocity ratio is unknown and requires further study.