Fluid dynamics and convective heat transfer in impinging jets through implementation of a high resolution liquid crystal technique: Part II: Navier-Stokes Computation of Impulsively Starting Heat Transfer Experiments

The current numerical/analytical effort is a continuation of the experimental study described in 'Fluid Dynamics and Convective Heat Transfer in Impinging Jets Through Implementation of a High Resolution Liquid Crystal Technique - Part I”. The Navier Stokes predictions of the flow field and heat transfer in a round, heated jet impinging on a flat plate provide insight in interpreting the flow field and convective heating pattern. The present numerical model predicts the mean velocity field in an excellent manner when compared to the experimental data. The radial distributions of jet axial velocity, the jet centerline velocity and static pressures in the free jet zone are predicted successfully through the numerical solution of Navier-Stokes equations using a low Reynolds number turbulence model based on a kinetic energy/dissipation rate model. There is reasonably good agreement between the predictions and the measured data in the wall jet region where the free jet stagnates and turns about 90 degrees to form a wall jet. The energy equation is solved in a manner that a complete transient liquid crystal experiment is numerically simulated. For this case, the unsteady energy equation is solved separately using the steady state flow field solutions, assuming constant fluid transport properties. During the time iterative energy equation solution, the local wall temperatures of the impingement plate are updated by using the same semi-infinite wall heat conduction model which is employed in transient liquid crystal experiments. A complete numerical simulation of the heat transfer experiments using chiral nematic liquid crystals produced results which compare well with the specific experiments in a range of Reynolds numbers and jet to wall distances. The specific numerical study is valuable in supporting the current transient heat transfer experiments in an effort to understand the details of convective heat transfer mechanisms in impinging jets.