Numerical Solutions of Single and Multiple Laminar Jets

Modern power plants discharge approximately 1.5 to 2kWhr of waste heat for every kWhr of electrical energy produced. Modern power plants discharge approximately 1.5 to 2kWhr of waste heat for every kWhr of electrical energy produced. Usually this heat is discharged to an adjacent water body which increases the water temperature near the outfall. In order to assess the ecological consequences of waste heat discharge one must first know the physical changes (temperature, velocity, salinity) induced by these discharges. It is with this later aspect, prediction of physical properties, that the current work is primarily concerned. Existing theoretical work on axisymmetric buoyant jets is confined to integral techniques developed by Morton in the early 1950’s. From these techniques only centerline velocities and temperatures can be calculated. Experimental data for this type of flow are essentially confined to centerline temperature measurements except for pure jet or plume data which constitute the extremes for a buoyant jet. The present work addresses the problem of developing a theoretical model for an axisymmetric laminar buoyant jet. The governing equations for an axisymmetric buoyant jet in rectangular co-ordinates are transformed into an orthogonal curvilinear co-ordinate system which moves along the length of the jet axis. The complete partial differential equations governing steady, incompressible laminar flow are solved in the new curvilinear co-ordinates using finite-difference techniques. This method is applicable to a much wider range of jet flows issued at arbitrary angles into quiescent or flowing ambience. This method is also applied to the case for multiple jets spaced by a finite distance apart. Results for the momentum jet, axial and radial distribution of velocity and temperature, show good agreement with published data.