Stability and Mixing of a Vertical Axisymmetric Buoyant Jet in Shallow Water

The stability, mixing and effect of downstream control on axisymmetric turbulent buoyant jets discharging vertically into shallow stagnant water is studied using 3D Reynolds-averaged Navier–Stokes equations (RANS) combined with a buoyancy-extended k –ε model. The steady axisymmetric turbulent flow, temperature (or tracer concentration) and turbulence fields are computed using the finite volume method on a high resolution grid. The numerical predictions demonstrate two generic flow patterns for different turbulent heated jet discharges and environmental parameters (i) a stable buoyant discharge with the mixed fluid leaving the vertical jet region in a surface warm water layer; and (ii) an unstable buoyant discharge with flow recirculation and re-entrainment of heated water. A stratified counterflow region always appears in the far-field for both stable and unstable buoyant discharges. Provided that the domain radius L exceeds about 6H, the near field interaction and hence discharge stability is governed chiefly by the jet momentum length scale to depth ratio l_M/H, regardless of downstream control. The near field jet stability criterion is determined to be l_M/H = 3.5. A radial internal hydraulic jump always exists beyond the surface impingement region, with a 3- to 6-fold increase in dilution across the jump compared with vertical buoyant jet mixing. The predicted stability category, velocity and temperature/concentration fields are well-supported by experiments of all previous investigators.     

天津市地表水体与沉积物中7种高关注酚类化合物的污染特征与生态风险分析

为探究地表水体与沉积物中酚类化合物的污染分布特征和生态风险,选择天津市3个水源地与6条主要河流,采集了26个地表水样与6个沉积物样品,利用固相萃取与超声萃取、高效液相色谱-串联质谱法(HPLC-MS/MS)测定了水样及沉积物中1-萘酚(1-naphthol)、壬基酚(nonylphenol, NP)、双酚A(bisphenol A, BPA)、2-苯基苯酚(biphenyl-2-ol)、3,4-二氯酚(3,4-dichlorophenol)、四溴双酚A(tetrabromobisphenol A, TBBPA)和对叔丁基苯酚(p-tert-butylphenol, PTBP)等7种高关注酚类化合物的浓度水平,并应用物种敏感性分布(species sensitivity distribution, SSD)法和熵值法(ecological risk quotient, RQ)评估7种酚类化合物水环境和沉积物的生态风险。结果表明,地表水样中7种酚类化合物均全部检出;其中壬基酚的检出浓度最高,其次为四溴双酚A、对叔丁基苯酚、1-萘酚、2-苯基苯酚、3,4-二氯酚和双酚A。沉积物中酚类化合物的污染分布规律与水样相似,除双酚A外的目标物全部检出。其中,壬基酚浓度比其他物质浓度高2个数量级。风险评估结果显示,壬基酚对水环境与沉积物存在不可接受的风险;而四溴双酚A、对叔丁基苯酚、1-萘酚、2-苯基苯酚、3,4-二氯酚和双酚A则对环境具有较低风险或者存在一定的风险。