Response of buoyant plumes to transient discharges investigated using an adaptive solver

The behavior of buoyant plumes driven by variable momentum inputs were examined using an adaptive Navier‐Stokes solver (Gerris). Boundary conditions were representative of an idealized stratified, coastal environment. Salinity ranged from 5 to 30 in the top 5 m of the water column to replicate the strong vertical gradients experienced in fjord environments. Two‐dimensional simulations examined the response of the buoyant plume driven by zero, steady, and variable momentum fluxes. The behavior was quantified in terms of the characteristic features of a buoyant plume, the thickness of the nose (or head of gravity current), and the trailing tail. Both the nose and tail of the plume were substantially thicker for the variable momentum run, whereas elongation and thinning of the plume was evident for the steady and zero momentum inputs. Furthermore, an order of magnitude difference in available potential energy was found for the variable momentum run. Validation of the Boussinesq approximation initially utilized the classic lock‐exchange experiment with excellent agreement to previous numerical and theoretical experiments. Frontal speeds of the gravity current converged toward the theoretical value of Benjamin (1968). The adaptive mesh permitted lock‐exchange simulations at Reynolds number (Re) of ∼10,500 and are some of the highest Re runs to date. Moreover, improved computational efficiency was achieved using the adaptive solver with simulations completed in 20% of the time they took on a static, high‐resolution grid.