Potential-enstrophy lengthscale for the turbulent/nonturbulent interface in stratified flow
| Autor: | Marco Boetti, Maarten van Reeuwijk, Alex Liberzon |
|---|---|
| Rok vydání: | 2021 |
| Předmět: |
TURBULENT ENTRAINMENT
Computational Mechanics Direct numerical simulation Enstrophy 01 natural sciences LAYERS 0203 Classical Physics 010305 fluids & plasmas Physics::Fluid Dynamics symbols.namesake Physics Fluids & Plasmas 0102 Applied Mathematics 0103 physical sciences Stratified flow 010306 general physics VORTICES Fluid Flow and Transfer Processes Physics Science & Technology Turbulence Kolmogorov microscales Reynolds number Mechanics Nonlinear Sciences::Chaotic Dynamics INTERNAL WAVES Modeling and Simulation Physical Sciences symbols Temperature stratification 0913 Mechanical Engineering |
| Zdroj: | Physical Review Fluids. 6 |
| ISSN: | 2469-990X |
| Popis: | We study properties of the turbulent/nonturbulent interface (TNTI) between two layers of stratified fluids through direct numerical simulations (DNSs). Zero mean shear forcing creates moderate turbulence in one of the layers with the Taylor microscale Reynolds numbers in the mixed region of Re λ = 35 , 44 . We focus on the similarities and differences of the properties of stratified TNTIs due to two distinct types of forcing: (a) convection due to a boundary heat source and (b) agitation resembling a vertically oscillating grid experiment. Similarly to other stratified flows, the small scale dynamics of the TNTI in the present DNSs differ from what would be expected in comparable yet unstratified TNTIs. The interface cannot be indeed uniquely identified by the commonly used vorticity ω . Instead, the potential enstrophy Π 2 is shown to be the most appropriate marker in these flow cases. It is emphasized that the Kolmogorov lengthscale η K ∼ √ ν / ω is not representative of the small scale dynamics of the interface. Hence, an alternative lengthscale, η Π , is defined, in analogy to the Kolmogorov scale, based on the potential enstrophy, η Π = ( ν 3 / Π ∗ ) 1 / 6 , being Π ∗ = | g / ρ 0 Π | . The conditionally averaged profiles of potential enstrophy Π 2 , enstrophy ω 2 , and turbulent kinetic energy dissipation ε of the two distinctly different turbulence forcing cases collapsed when scaled by η Π at different time instants in each simulation. This implies not only the self-similarity of the small scale statistics of the TNTI in either of the two cases, but also the similarity between the statistics of the two different turbulent flows in the proximity of TNTI. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|