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 Fd ₀-^4/3, where Fd O 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*/bsimilar to0.4Fd(0)(4/3). For distances z <z*, the degree of distortion of the vertical velocity profile within the jet (1) increases strongly with decreasing values of (z/b) Fd ₀^-4/3 and (2) shows a weak dependence upon the Froude number Fd(0). 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 Fd(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 Fd₀.