Onset of entrainment in transitional round fountains |
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| Authors: | Wenxian Lin SW Armfield |
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| Affiliation: | 1. School of Earth Science and Resources, China University of Geosciences Beijing, No. 29 Xueyuan Road, Haidian District, Beijing 100083, China;2. Department of Earth Sciences, University of Adelaide, South Australia 5005, Australia;3. Institute of Geomechanics, Chinese Academy of Geological Science, Beijing 100081, China;4. Institute of Geology, Chinese Academy of Geological Sciences, No. 26 Baiwanzhuang Road, Beijing 100037, China;1. School of Sciences, Chang''an University, 710064 Xi''an, PR China;2. School of Aeronautics, Northwestern Polytechnical University, 710072 Xi''an, PR China;3. School of Mathematics, Yunnan Normal University, 650500 Kunming, PR China;4. School of Mathematics and Statistics, Xi''an Jiaotong University, 710049 Xi''an, PR China |
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| Abstract: | It is of fundamental interest to understand the behavior of transitional fountains with intermediate Froude and Reynolds numbers, together with the associated entrainment and turbulence. In this work, the transient behavior of axisymmetric fountains with 1 ? Fr ? 8 and 200 ? Re ? 800 is studied by direct numerical simulation. It is found that at Re ? 200, there is little entrainment present at the upflow–downflow interface and at the downflow–ambient interface, even for a value of Fr as high as 8; however, at Re > 200, entrainment is present at these interfaces and the extent increases with Re, which clearly demonstrates that entrainment is strongly dependent on Re whereas the contribution from the Fr effect is relatively much smaller. The DNS results also show that zm, which is the maximum fountain penetration height, fluctuates, even when the flow reaches full development, due to the entrainment at the upflow–downflow and the downflow–ambient interfaces, and the averaged zm scales with for 1 < Fr ? 8 and 100 ? Re ? 800. |
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