STRUCTURE DETECTION AND ANALYSIS OF NON-CIRCULAR IMPINGING JETS IN A SEMI-CONFINED ARRAY CONFIGURATION

摘要

The modal kinetic energy distribution and instantaneous vortex field of an impinging confined jet array is investigated. The jet array consists of 7-by-7 equally spaced orifice nozzles, using two nozzle cross sections: circular and cusped ellipse. Digital Particle Image Velocimetry (DPIV) is used to determine the velocity field of the impinging jets along the center row in the plane parallel with the cross flow direction. Proper Orthogonal Decomposition (POD) and vortex detection algorithms are used to analyze the results of 50 instantaneous velocity fields in the impingement regions for each of several jets located along the crossflow direction. The energetic content of the flow is evaluated based on the POD eigenvalue distribution, the number of POD modes necessary to reconstruct the instantaneous velocity field, and the modal turbulent kinetic energy distributions. Vortex detection algorithms are used to locate and quantify the nature of the instantaneous vortices within the flow. Results of the vortex identification and the associated kinetic energy distribution within the flows are used to indicate the overall sensitivity to the nozzle geometry. The results suggest that the cusped ellipse nozzle when oriented with its major axis parallel to the flow, because of axis switching, can provide increased surface interactions which may lead to enhanced rates of heat and mass transfer.