The entrainment due to a turbulent fountain at a density interface

We describe new experiments to measure the penetrative entrainment by a turbulent fountain in a steady two-layer stratification. A theoretical model was established by assuming that the stratification consists of two uniform layers, and the penetrative entrainment rate is estimated quantitatively by three independent formulae. Two quasi-uniform layers were observed in the steady state in the laboratory experiments. Experimental results gave a nearly constant dimensionless penetrative entrainment rate (0.65 +/- 0.17) across a density interface when the local Richardson number is smaller than 1.2.