Large-eddy simulation of flow and heat transfer in an impinging slot jet

The flow field due to an impinging jet at a moderately high Reynolds number, emanating from a rectangular slot nozzle has been computed using a large eddy simulation (LES) technique. A dynamic subgrid-scale stress model has been used for the small scales of turbulence. Quite a few successful applications of the dynamic subgrid-scale stress model use planar averaging to avoid ill conditioning of the model coefficient. However, a novel localization procedure has been attempted herein to find out the spatially varying model coefficient of the flow. The flow field is characterized by entrainment at the boundaries. Periodic boundary conditions could not be used on all the boundaries. The results reveal the nuances of the vortical structures that are characteristic of jet flows. The stress budget also captures a locally negative turbulence production rate. The calibration of the model has been made through prediction of the normalized axial velocity profile and heat transfer on the impingement plate. The computed results compare favorably with the experimental observations, especially in the stagnation zone

Numerical investigation of heat transfer by rows of rectangular impinging jets

The velocity field and heat transfer in rows of rectangular impinging jets have been analyzed from the numerical solution of unsteady Navier-Stokes and energy equations. Jets emanating axially and radially from rectangular slot nozzles (feed tubes) have been considered. For the radial jets, the jet exit angle has also been varied. Steady flows have been obtained for Reynolds numbers smaller than a critical value above which periodic flows appear. At a higher Reynolds number than the critical value, the flow becomes unsteady and nonperiodic. For the laminar axial jets, an optimum relative nozzle area for maximum heat transfer, as experimentally observed for turbulent jets, is also obtained. For the radial jets, heat transfer monotonically increases with relative nozzle area. For the densely spaced jets, i.e.,for a large relative nozzle area, average heat transfer for the radial jets can be larger than that for the axial jets. Heat transfer can also be substantially increased by vectoring the radial jets toward the impingement surface. Densely packed and vectored radial jets can give 20%-30% more heat transfer than the axial jets, for the same mass flow ate

Numerical investigation of heat transfer in impinging axial and radial jets with superimposed swirl

The effect of swirl on heat transfer by axial and radial laminar jets impinging on a flat plate has been investigated numerically through the solution of Navier-Stokes and energy equations. Heat transfer is reduced substantially by the superposition of swirl on axial jets. Significant enhancement in heat transfer has been observed in the case of a radial jet with superimposed swirl on it. For a swirl number of unity, the heat transfer is enhanced by 77%

Prediction of heat transfer from impinging knife-jets using a dynamic subgrid stress model

The turbulent flow field and heat transfer due to the knife-jets impinging on a flat surface have been numerically investigated. The large-eddy simulation (LES) technique has been used to model the turbulent flow that has both large- and small-scale structures. A dynamic subgrid scale model has been used to account for the subgrid scale stresses and heat transfer. The Nusselt number distributions for the impinging jets emanating from an array of horizontal slot nozzles are presented within the Reynolds number range of 600-3000. Two different jet exit-angles, namely 0° and 60° have been considered. The reattachment of the horizontal-knife-jets is obtained due to the Coanda effect. The flow field on the impinging plate due to the horizontal-knife-jets culminates in an oscillatory flow dominated by vortical motions. Such motions play a significant role in enhancing heat transfer. Heat transfer due to the horizontal-knife-jet with 60° exit-angle has been found to be greater than that of the axial slot jet

Large Eddy Simulation in a Channel with Exit Boundary Conditions

The influence of the exit boundary conditions (vanishing first derivative of the velocity com-ponents and constant pressure) on the large eddy simulation of the fully developed turbulent channel flow has been investigated for equidistant and stretched grids at the channel exit. Results show that the chosen exit boundary conditions introduce some small disturbance which is mostly damped by the grid stretching. The difference between the fully developed turbulent channel flow obtained with LES with periodicity condition and the inlet and exit and the LES with fully developed flow at the inlet and the exit boundary condition is less than 10 % for equidistant grids and less than 5 % for the case grid stretching. The chosen boundary condition is of interest because it may be used in complex flows with backflow at exit

Flow Structure of an Impinging Plane Jet

Sixth Conference on Design and Modeling of Mechanical Systems (CMSM 2015), Hammamet, TUNISIA, MAR 23-25, 2015International audienceThe current study attempt to examine and investigate the flow field of a plane air jet impinging normally on a flat surface. In order to understand the development of the flow generated from a rectangle turbulent jet impinging a flat plate, a detailed dynamic and turbulent simulation is presented. The plate is appropriately larger than the nozzle exit diameter. The ground plate can be moved vertically in order to simulate the height ratio h/e=28. Another aim of this study is to explore the effect of the Reynolds number (Re=1000, 2000, 3000) on the flow structure. A Computational Fluid Dynamics study is performed using the Reynolds-averaged Navier-Stokes equations by means of the RSM (Reynolds Stress Model) second order turbulent closure model. The results include mean and turbulent velocities and quantify the large effects of flow distortion on the turbulent structure of complex, three-dimensional impingement flow