Local Froude Number Research Articles

Forced plume in a stratified fluid

A turbulent buoyant jet operating in a linearly stratified fluid is investigated. By requiring similarity forms for the velocity, density difference, and shear stress and by adopting an integral representation of the governing equations, the rate of entrainment of ambient fluid into the plume is found to be an explicit function of the dependent variables. The entrainment is a function of the Reynolds stress, the form of the similarity profiles, and the local mean densimetric Froude number. The Reynolds stress term is shown to be related to the constant obtained if the entrainment rate is assumed to be proportional to the mean centerline velocity. A critical parameter of the analysis is the ratio of the form of the velocity profile to the form of the density difference profile. Values of this parameter near unity seem most appropriate. Numerical solutions are compared with experimental results to suggest values for the Reynolds stress term.

Salinity Intrusion Effects in Estuary Shoaling

In the salinity intrusion region of an estuary the internal velocity distribution in the longitudinal direction is modified by the density effects. If the velocities are averaged over a tidal cycle the result is an increase in the surface velocities in the downstream (ebb) direction and a reversal of the near-bottom velocities so that the net velocity is in the upstream (flood) direction. The region of heavy shoaling in an estuary is shown to be related to the location of the null point at which the near-bottom velocity reverses from a net landward to a net seaward direction. The location of the null point is shown to be related to the longitudinal salinity distribution through a correlation based on the local densimetric Froude number. A method is developed for predicting the longitudinal change in the region of heavy shoaling due to changes in channel depth or fresh water discharge. The method is developed from laboratory data obtained at M.I.T. and W.E.S. (Vicksburg) and is applied to the Savannah and Delaware estuaries.