# Entrainment induced by waves at a density interface impinged by a turbulent jet

## TL;DR

This study demonstrates that turbulence-driven gravity waves at a density interface, rather than baroclinic instabilities, primarily cause erosion and mixing when impacted by a turbulent jet, supported by experiments and a new scaling model.

## Contribution

It reveals that interfacial gravity waves, amplified by turbulent fluctuations, are the main mechanism of entrainment, contrasting with previous baroclinic instability models.

## Key findings

- Gravity waves induce mixing and erosion.
- Scaling model varies from $Fr_i^3$ to $Fr_i$ with Froude number.
- Experimental validation supports the wave-driven entrainment mechanism.

## Abstract

Using water/salty-water laboratory experiments}, we investigate the mechanism of erosion by a turbulent jet impinging on a density interface, for moderate Reynolds and Froude numbers. Contrary to previous models involving baroclinic instabilities, we show that the entrainment is driven by interfacial gravity waves, which break and induce mixing. The waves are generated by the turbulent fluctuations of the jet and are amplified by a mechanism of wave-induced stress . Based on the physical observations, we introduce a scaling model which varies continuously from the $Fr_i^3$ to the $Fr_i$ power law from small to large Froude numbers, in agreement with some of the previous laboratory data.