Author(s): Angelos Kokkinos; Panagiotis Prinos

Linked Author(s): Angelos Kokkinos, Panagiotis Prinos

Keywords: Collision; Gravity currents; Lock-exchange; Large Eddy Simulation

Abstract: In this work the collision of two opposing, horizontal gravity currents is examined numerically using Large Eddy Simulation (LES). Gravity current collision is important in many physical conditions and especially in atmospheric flows such as sea breezes, thunderstorm outflows, katabatic flows, etc. The classical lock-exchange configuration is considered using a partial depth setup which is believed to be a better approximation of the collision in deep environment of atmosphere. The focus is on the examination of symmetric collision (currents with same densities and heights). Maximum height and vertical velocity of the ascending front, which are the main parameters of collision in nature, are investigated. In addition, the energy balance is calculated, and mixing is evaluated using methods previously applied in gravity current propagation (Ottolenghi et al., 2016). The simulations are performed using the open source OpenFOAM package. The model solves the filtered Navier-Stokes equations along with a transport equation for concentration assuming Boussinesq approximation for density. A dynamic Smagorinsky SGS model is used for turbulence closure. The model is validated using available experimental and DNS data (Frantz et al., 2021) for the case of full depth lock-exchange gravity current. Numerical simulations of collision are performed for a wide range of Grashof numbers (10⁶-10¹²) which are beyond the range achieved in laboratory experiments. It is found that the dimensionless maximum height h/D (D= lock height) is slightly reduced with Gr number ranging from 1.57 for Gr=10⁶ to 1.36 for Gr=10¹². The same trend appears for the dimensionless maximum ascending front velocity Vf/Uf (Uf= front velocity before collision) which varies from 2.23 to 1.66. References Frantz, R. A. S., Deskos, G., Laizet, S., & Silvestrini, J. H. (2021). High-fidelity simulations of gravity currents using a high-order finite-difference spectral vanishing viscosity approach. Computers and Fluids. https://doi.org/10.1016/j.compfluid.2021.104902 Ottolenghi, L., Adduce, C., Inghilesi, R., Armenio, V., & Roman, F. (2016). Entrainment and mixing in unsteady gravity currents. Journal of Hydraulic Research, 54(5), 541–557. https://doi.org/10.1080/00221686.2016.1174961

DOI: https://doi.org/10.3850/IAHR-39WC252171192022409

Year: 2022