Numerical Solution of Lock-Release Gravity Current with Viscous Self-Similar Regime

Lock-release gravity currents with a viscous self-similar regime are simulated by use of the renormalization group(RNG) k - ε model for Reynolds-stress closure. Besides the turbulent regime with initially a slumping phase of a conslant current front speed and later an inviseid self-similar phase of front speed decreasing as t^-1/3(where t is the time measured from release), the viseous self-similar regime is satisfactorily reproduced with front speed decreasing as t^-4/5,consistent with well known experimental observations.     

The Structure of A Turbulent Jet in A Crossflow-Effect of Jet-Crossflow Velocity

A comprehensive numerical study on the three-dimensional structure of a turbulent jet in crossflow is performed. The jet-to-crossflow velocity ratio (R) varies in the range of 2 - 16; both vertical jets and inclined jets without excess streamwise momentum are considered. The numerical results of the Standard two-equation k-ε model show that the turbulent structure can 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 parallel with the main freestream, to a sectional vortex-pair flow with double concentration maxima; the computed flow details and scalar 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, vvith distinct double concentr     

Three-Dimensional Computations of Multiple Tandem Jets in Crossflow

1 .IntroductionAn effective method of wastewater disposal in estuarine and coastal watersisto discharge partiallytreated effluentthrougha submerged multiport diffuserlocated atthe end of a sea outfall .Atypical dif-fuser designinvolves multiple jets all discharginginthe same direction awayfromthe shoreline ,per-pendicular to an alongshore ambient current to minimize the environmental impact .This is one type ofa multiple jet groupin crossflow(MJGC) . Whenthe jets are arrangedintandem,withthe…     

The Structure of A Turbulent Jet in A Crossfiow--Effect of Jet-Crossfiow Velocity

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