Instantaneous discharge of buoyant fluid in cross-flow

Artificial instantaneous discharge of buoyant fluid in ambient waters is usually carried out at the time of maximum cross-flow so that the resulting dilution is optimal. The determination of the characteristics of this problem is important for environmental impact study but has seldom been studied. To investigate the transport, mixing, and dilution of an isolated cloud of buoyant fluid in cross-flow ambient, a three-dimensional buoyancy extended k-ε model is employed. The computed results show that two flow regimes exist. First is the initial dumping regime in which the effect of crosscurrent and the associated turbulence on the longitudinal width and the average dilution is insignificant as compared to the effect of buoyancy on those quantities. The flow and mixing characteristics in this regime are close to those in the case of stagnant ambient. Second is the ultimate regime in which the effect of buoyancy on the longitudinal width and the average dilution is small as compared to the effect of cross-flow on those quantities. In the ultimate regime, the crosscurrent produces ambient turbulence that increases the longitudinal width of the cloud (and hence increases the dilution), but only slightly affects the vertical frontal position of the cloud. Laboratory experiments are also conducted for the verification of the model and both results are in reasonable agreement.