A numerical study on the stability of a vertical plane buoyant jet in confined depth

A plane turbulent buoyant jet discharging vertically into confined depth is studied using the Renormalization Group(RNG) k – ∊ model. The steady two-dimensional turbulent flow and temperature field are computed using the finite volume method on an unstructured triangular mesh. The numerical predictions demonstrate three generic flow patterns for different jet discharge and environmental parameters: i) a flow with circulation cells of alternate rotation for non-buoyant discharge; ii) a stable buoyant discharge with the mixed fluid leaving the near-field in a surface warm water layer; and iii) 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. The near field interaction and hence discharge stability is governed by only two dimensionless parameters - the discharge densimetric Froude number and the relative depth. The computed velocity and temperature fields agree well with the laboratory flow-visualization and temperature measurements, and the theoretical predictions of Jirka & Harleman (1979).