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Experimental and Numerical Visualization of Counter Rotating Vortices

[+] Author and Article Information
Jeongmoon Park

Texas A&M University, College Station, Texas, USA
park469@email.tamu.edu

Axy Pagan-Vazquez

University of Illinois Urbana-Champaign, Urbana, Illinois, USAU.S. Army Construction Engineering Research Laboratory (CERL), Champaign, Illinois, USA
Axy.Pagan-Vazquez@erdc.dren.mil

Jorge L. Alvarado

Texas A&M University, College Station, Texas, USA
jorge.alvarado@tamu.edu

Leonardo P. Chamorro

University of Illinois Urbana-Champaign, Urbana, Illinois, USA
lpchamo@illinois.edu

Scott Lux

U.S. Army Construction Engineering Research Laboratory (CERL), Champaign, Illinois, USA
scott.m.lux@usace.army.mil

Charles Marsh

University of Illinois Urbana-Champaign, Urbana, Illinois, USAU.S. Army Construction Engineering Research Laboratory (CERL), Champaign, Illinois, USA
Charles.P.Marsh@usace.army.mil

1Corresponding author.

J. Heat Transfer 138(8), 080908 (Jul 08, 2016) (1 page) Paper No: HT-16-1218; doi: 10.1115/1.4033825 History: Received April 20, 2016; Revised May 09, 2016

Abstract

Visualization of the flow structure generated by passive vortex generators continues to be a matter of research in the fluid mechanics and heat transfer communities. In this study, self-sustaining counter-rotating vortex pairs (CVP) generated from a series of vortex generators (VG) have been characterized numerically and experimentally to understand the effects of the VG parameters on vortical flow structure formation. Four different types of VGs were considered by varying the taper angle from 0° to 19.3° at a fixed inclination angle of 24.5° and a Reynolds number of 1965. Flow fields were experimentally visualized using a smoke technique. Each VG induced a coherent CVP flow structure in the wake region despite the fact that the upstream flow was laminar. CVPs initially dominate flow dynamics over a certain streamwise length; however, Kelvin-Helmholtz (KH) instability appears to affect the spatial evolution of CVP longitudinally. The CVP within the stability region were reconstructed digitally in 3D by interpolating several 2D smoke images taken at various spanwise planes. The smoke results indicate that as taper angle decreases, the onset location of KH instability decreases. Furthermore, the CVP trajectory within the stability region was observed to be predominantly controlled by a two-dimensional inviscid process, while the effects by the free stream were not significant. Based on the experimental observations and the numerically reconstructed 3D CVP flow structures, VG with smaller taper angle results in CVPs with higher circulation, which is a positive aspect for mass and heat transfer applications. Preliminary numerical simulations based on RANS have shown that heat transfer enhancement is about 50% in the region near the rectangular vortex generator.

Copyright © 2016 by ASME
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