The Structure of A Turbulent Jet in A Crossfiow--Effect of Jet-Crossfiow Velocity
摘要
A comprehensive numerical study on the three-dimensional structure of a turbulent jet in crossflow is performed. Thejet-to-crossflow velocity ratio (R) varies in the range of 2 ～ 16; both vertical jets and inclined jets without excess streamwisemomentum are considered. The numerical results of the standard two-equation k-~ model show that the turbulent structurecan be broadly categorised according to the jet-to-crossflow velocity ratio. For strong to moderate jet discharges, i.e. R >4, the jet is characterized by a longitudinal transition through a bent-over phase during which the jet becomes almost parallelwith the main freestream, to a sectional vortex-pair flow with double concentration maxima; the computed flow details andscalar mixing characteristics can be described by self-similar relations beyond a dimensionless distance of around 20 ～ 60.The similarity coefficients are only weakly dependent on R. The cross-section scalar field is kidney-shaped and bifurcated,with distinct double concentration maxima; the aspect ratio is found to be around 1.2. A loss in vertical momentum is ob-served and the added mass coefficient of the jet motion is found to be approximately 1. On the other hand, for weak jets instrong crossflow, i.e. R≤ 2, the lee of the jet is characterized by a negative pressure region. Although the double vortexflow can still be noted, the scalar field becomes more symmetrical and no longer bifurcated. The similarity coeffcients are al-so noticeably different. The predicted jet flow characteristics and mixing rates are well supported by experimental and field data