76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023;
Washington, DC
Session R27: Geophysical Fluid Dynamics: Stratified Flows I
1:50 PM–3:21 PM,
Monday, November 20, 2023
Room: 151B
Chair: Daniel Lecoanet, Northwestern
Abstract: R27.00006 : Analysis and modeling of slow and rapid pressure correlations in stably stratified turbulence*
2:55 PM–3:08 PM
Abstract
Presenter:
Young R Yi
(Princeton University)
Authors:
Young R Yi
(Princeton University)
Jeffrey R Koseff
(Stanford Univ)
Elie R Bou-Zeid
(Princeton University)
In many turbulent flows, pressure fluctuations play a key role of redistributing the more energetic (normal) Reynolds stresses to the less energetic ones. For stably stratified turbulence, the damping of vertical fluctuations by the buoyancy force implies that this redistribution process will play a significant role in the generation of vertical Reynolds stresses, and therefore have important effects on the vertical buoyancy flux as well. In this study, we consider four datasets of direct numerical simulations (DNS) of stably stratified turbulence (one without shear forcing and three with shear forcing) across a wide range of stratification strengths. The three shear forcing datasets correspond to different turbulence generation scenarios: (i) vertically sheared mean horizontal flow, (ii) horizontally sheared mean vertical flow, (iii) laterally sheared horizontal flow. We decompose the pressure fluctuations into the slow and rapid components and analyze their contributions to the pressure-strain correlations and the pressure scrambling terms, which appear in the Reynolds stress and buoyancy flux budgets, respectively. For example, the dataset without shear forcing has a single slow and rapid pressure component associated with nonlinear and buoyancy effects, and we observe the following changes as stratification is increased: (i) the pressure-strain correlations are dominated by the slow component even as the rapid component becomes finite and switches signs; (ii) the pressure scrambling term undergoes a sign change as it becomes dominated by the rapid component and acts a source of vertical buoyancy flux. The other three datasets involve an additional rapid pressure component due to shear forcing, resulting in different behaviors with increasing stratification. Lastly, we test the performance of commonly used closures such as Rotta's return-to-isotropy model and evaluate the model coefficients as a function of stratification strength with the goal of improving subgrid-scale models used in large-scale models.
*This work was supported by the Stanford Civil and Environmental Engineering Department's Charles H. Leavell Fellowship.