Numerical simulation of Holmboe waves in intrusive gravity current using LES method

Gravitational currents are important currents in atmospheric and oceanic studies. Gravity current is caused when a fluid with different density moves into another fluid. If the fluid of a given density enters the stratified ambient, such that its density is lower than the underneath layers and higher than the upper layers, the gravity current is of the intrusive type. The Kelvin-Helmholtz and the Holmboe instabilities are seen in the interface. The decisive parameters in the type of instability are the Richardson number local (J) and the ratio of shear layer thickness to the density layer (R). In this study, two-dimensional numerical simulation of the shear instabilities (Holmboe waves) with the Eulerian-Eulerian approach on intrusive gravitational flow is investigated. OpenFOAM code was used to perform this simulation, and due to the turbulence of the flow, the LES method was used to model the turbulence. The obtained results show that with increasing the intrusive current density, the value of Richardson number decreases and the R parameter increases. Also, as the density increases, the frequency of the Holmboe waves first increases, then decreases. An increase in the wavelength of Holmboe waves is observed with increasing the intrusive current density but in the wave number of the waves, the opposite behavior is seen. The phase velocity of Holmboe waves also does not have a specific trend with density changes.