Effect of velocity ratio on the streamwise vortex structures in the wake of a stack |
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| Authors: | MS Adaramola D Sumner DJ Bergstrom |
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| Institution: | 1. Division of Environmental Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, Saskatchewan, Canada S7N 5A9;2. Department of Mechanical Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, Saskatchewan, Canada S7N 5A9;1. College of Engineering and Technology, American University of the Middle East, Kuwait;2. Institute for Turbulence-Noise-Vibration Interaction and Control, Harbin Institute of Technology (Shenzhen), Shenzhen, 518055, China;3. Digital Engineering Laboratory of Offshore Equipment, Shenzhen, 518055, Guangdong, China;1. School of Civil Engineering, Central South University, China;2. National Engineering Laboratory for High-speed Railway Construction, Central South University, China;1. University Lille, CNRS, Centrale Lille, IEMN UMR 8520, Cité Scientifique, 59651 Villeneuve d’Ascq, France;2. IEMN UMR 8520, USTL, University Lille, Cité Scientifique, 59652 Villeneuve d’Ascq, France;3. Wave Research Center of A. Prokhorov General Physics Institute RAS, Russian 119991, Moscow, Russia;4. ONERA, chemin de la hunière 91123, Palaiseau, France;5. Thurmelec, Aire de la Thur, 68840 Pulversheim, France |
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| Abstract: | The time-averaged velocity and streamwise vorticity fields within the wake of a stack were investigated in a low-speed wind tunnel using a seven-hole pressure probe. The experiments were conducted at a Reynolds number, based on the stack external diameter, of ReD=2.3×104. The stack, of aspect ratio AR=9, was mounted normal to a ground plane and was partially immersed in a flat-plate turbulent boundary layer, where the ratio of the boundary layer thickness to the stack height was δ/H≈0.5. The jet-to-cross-flow velocity ratio was varied from R=0 to 3, which covered the downwash, crosswind-dominated and jet-dominated flow regimes. In the downwash and crosswind-dominated flow regimes, two pairs of counter-rotating streamwise vortex structures were identified within the stack wake. The tip vortex pair located close to the free end of the stack, and the base vortex pair located close to the ground plane within the flat-plate boundary layer, were similar to those found in the wake of a finite circular cylinder, and were associated with the upwash and downwash flow fields within the stack wake, respectively. In the jet-dominated flow regime, a third pair of streamwise vortex structures was observed, referred to as the jet-wake vortex pair, which occurred within the jet-wake region above the free end of the stack. The jet-wake vortex pair had the same orientation as the base vortex pair and was associated with the jet rise. The peak vorticity and strength of the streamwise vortex structures were functions of the jet-to-cross-flow velocity ratio. For the tip vortex structures, their peak vorticity and strength reduced as the jet-to-cross-flow velocity ratio increased. |
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