Numerical Simulation of Impinging Slot Air Jet in the Presence of a Cross Flow

Abstract

Abstract A numerical investigation is carried out to study the effect of cross flow on local heat transfer distribution of a flat surface impinged normally by a slot air jet using ANSYS Fluent commercial software. Initially an experimental validation study is conducted to validate the centerline Nusselt number and to fix numerical settings such as Turbulence model, optimal mesh size and solution strategy. During this study, it is observed that the k-ϵ realizable model predicts fairly accurate results (less than 10%) when compared with the experiment data and therefore used for all further simulations in the present work. Grid independence study was conducted to arrive at optimal grid size. Grid size was varied from 0.08 million cell size to 0.2 million cells with 3% variation in percentage of peak Nusselt number. It is ensured that minimum of five boundary layers are maintained in numerical grid with y+ not more than 5 for all the cases studied. Further, the influence of nozzle exit to impingement plate distance (z/d = 2 to 6) is studied for different cross flow velocity to the main jet velocity ratios (M = 0 to 1). The Reynolds number (Re) is varied from 5000 to 50000. Furthermore, the aspect ratio of the slot jet is also varied. The center-line distribution of Nusselt number along the crossflow direction is provided. From the present numerical investigations, it is found that the presence of cross flow jet may result in either increase or decrease of the peak Nusselt number. This is attributed to the vorticial structures generated from the interaction of the wall jet of the main flow jet with the cross-flow jet. For the smallest nozzle tip to plate spacing, Z/D = 2, the peak Nusselt number is observed for the highest cross flow, M = 1 at higher Reynolds number (Re = 20,000 and 50,0000). For the larger nozzle tip to plate spacing (Z/D = 4 and 6), the peak Nusselt number is observed for the intermediate cross flow (M = 1/2) at higher Reynolds number (Re = 20,000 and 50, 0000). For the highest aspect ratio of 2, it is observed that peak Nusselt number decreases with the increase in crossflow. On the contrary, the square nozzle with lowest aspect ratio of 1, it is observed that the peak Nusselt number increases with the increase in crossflow.