Evolution of Shear and Buoyancy Driven Vortices of an Inclined Negatively Buoyant Jet

Turbulent mixing plays a vital role in the behavior of submerged inclined negatively buoyant jets (INBJ) discharged from desalination plants. In this regard,investigation of turbulent flow structures of INBJs could be useful. In this work, large eddy simulation (LES) is performed to study the formation and evolution of shear and buoyancy driven vortices of a ۳۰° INBJ. The growth of shear layer coherent vortices and spanwise fluctuations of the INBJ are studied using the Q-criterion. Our results show that after the shear layer breakdown, the buoyancy force dominates the jet, bending its trajectory and generating buoyancy-induced vortices. Since the velocity in the buoyancy-driven region is smaller than in the momentum-driven one, buoyancy-induced vorticesare bigger in size and weaker in strength compared with shear layer vortices. Also, another reason for the difference in the coherent structures’ sizes between the momentum and buoyancy driven regions is that the spanwise and vertical fluctuations grow downstream, stretching the buoyancy-induced vortices. The transformation of the shear layer vortices to the buoyancy-induced ones is well illustrated in crosssectional vorticity contours of the INBJ, showing the growth in the fluctuations and stretching the vortical structures downstream.

کلیدواژه ها:

Large eddy simulation (LES) ، Inclined negatively buoyant jet (INBJ) ، Coherent structures ، Shear layer ، Buoyancy–induced instabilities