Impact of Vertical, Turbulent, Planar, Negatively Buoyant Jet With Rigid Horizontal Bottom Boundary

The results of a series of laboratory modeling experiments are presented for the case of a vertical, turbulent, plane, negatively buoyant jet impinging on a horizontal solid surface placed a distance H below the jet source. The results show that the impingement results in the generation of a complex two-dimensional disturbance field at the site of the impact and the generation of a buoyancy-driven boundary current carrying away fluid from the impingement zone. The disturbance field is seen to extend vertically along the time-averaged axis of the incident buoyant jet, thereby distorting the vertical velocity and concentration fields over a vertical distance that depends upon the value of the parameter $F{d}_0^{-4/3}\text{,}$ where $F{d}_0$ is the source Froude number of the buoyant jet. Transverse velocity and concentration profiles taken at different axial distances from the source reveal systematic departures from the far-field Gaussian similarity profiles as the solid boundary is approached. Such departures are utilized to quantify and parameterize the vertical distance $z*$ from the boundary at $z=0$ beyond which the impingement of the buoyant jet does not affect significantly the incident flow. Measurements indicate that $z*/b\sim 0.4F{d}_0^{4/3}\text{.}$ For distances $z<z*\text{,}$ the degree of distortion of the vertical velocity profile within the jet (1) increases strongly with decreasing values of $(z/b)F{d}_0^{-4/3}$ and (2) shows a weak dependence upon the Froude number $F{d}_0\text{.}$ Measurements of (1) the rebound height of the disturbance field in the impingement zone and (2) the maximum horizontal velocity in the spreading gravity current confirm the ubiquity of the $F{d}_0^{-4/3}$ scaling for other aspects of the impingement flow. Data indicate also that the thickness of the current reaches a constant value $h_b$ outside the immediate impact zone, with $h_b/H$ depending linearly upon $F{d}_0\text{.}$