Effects of Wavy Channel Entrance Design on Streamwise Counter-rotating Vortices: a Visualization Study


1 Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576

2 Reactive Flow Modeling Laboratory Group in Clean Combustion Research Center, King Abdullah University of Science and Technology, Thuwal 23955, Kingdom of Saudi Arabia

3 Institute of Ophthalmology, University College London, London EC1V 9EL, United Kingdom

4 Faculty of Engineering, Universitas Diponegoro, Tembalang Campus, Semarang 50275, Indonesia


Two different channel entrance designs, code named Valley First (VF) and Peak First (PF), were experimentally visualized by means of smoke-wire visualization technique to observe their effects towards the streamwise counter-rotating vortices generated. The spanwise wavelength of the vortices was pre-set by modifying the leading edge. The investigation was carried out on the laminar boundary-layer flow in a rectangular channel with one-sided wavy surface that has amplitude a and wavelength λ of 7.5 mm and 76 mm, respectively. The vortices in the channel with VF design preserve farther downstream than those on the PF design, which might be caused by the large favorable pressure gradient between the entrance flat plate and the first peak location. The counter-rotating vortices could still be observed at non-dimensionalized streamwise distance χ (= x/λ) = 2.47 for Reynolds number Re (= UH/ν) = 9900 in channel with VF design. For lower Re, the vortices could preserve further downstream. In contrast, in channel with PF design, the structures were only visible clearly up to approximately χ = 1.32 for Re = 4700 and χ = 0.39 for Re = 5200.