Impact of front surface area on the dynamics of planar gravity currents

Abstract: Direct numerical simulations (DNSs) of three-dimensional planar, full-depth release gravity currents in an unstratified ambient are conducted at Reynolds numbers Re = 3450 and 10000. The study investigates the influence of a sinusoidal variation in heavy fluid frontal surface with spanwise wavenumbers ranging from 0 to 8. At Re = 3450, gravity currents with zero spanwise wavenumber propagate slower compared to other cases, whereas at Re = 10000, the propagation of currents shows minimal variation among different spanwise wavenumbers. Density contours at the gravity current head reveal minimal effects of the initial front surface area on the mixing within the head. Remarkably, coherent structures influenced by the initial conditions persist throughout the evolution of the current into the self-similar phase at Re = 3450, where the number of spanwise instabilities equals the spanwise wavenumbers, termed 'memory' effect of the initial release of the heavy fluid. However, at Re = 10000, these coherent structures break down into smaller turbulence scales, diminishing the observed 'memory' effect present at lower Re cases Keywords: Direct numerical simulations, gravity current, surface area, spanwise wavenumbers