Helicity dynamics in stratified turbulence in the absence of forcing
A numerical study of decaying stably stratified flows is performed. Relatively high stratification (Froude number ≈10 - 2-10 - 1) and moderate Reynolds (Re) numbers (Re≈ 3-6×103) are considered and a particular emphasis is placed on the role of helicity (velocity-vorticity correlations), which is no...
Guardado en:
| Autor principal: | |
|---|---|
| Publicado: |
2013
|
| Materias: | |
| Acceso en línea: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_15393755_v87_n6_p_Rorai http://hdl.handle.net/20.500.12110/paper_15393755_v87_n6_p_Rorai |
| Aporte de: |
| id |
paper:paper_15393755_v87_n6_p_Rorai |
|---|---|
| record_format |
dspace |
| spelling |
paper:paper_15393755_v87_n6_p_Rorai2023-06-08T16:20:58Z Helicity dynamics in stratified turbulence in the absence of forcing Mininni, Pablo Daniel Boussinesq equations Energy distributions Initial conditions Large-scale coherent structures Phenomenological models Planetary boundary layers Stratified flows Stratified turbulence Aerodynamics Decay (organic) Fourier series Hydrodynamics Thermal stratification Shear flow A numerical study of decaying stably stratified flows is performed. Relatively high stratification (Froude number ≈10 - 2-10 - 1) and moderate Reynolds (Re) numbers (Re≈ 3-6×103) are considered and a particular emphasis is placed on the role of helicity (velocity-vorticity correlations), which is not an invariant of the nondissipative equations. The problem is tackled by integrating the Boussinesq equations in a periodic cubical domain using different initial conditions: a nonhelical Taylor-Green (TG) flow, a fully helical Beltrami [Arnold-Beltrami- Childress (ABC)] flow, and random flows with a tunable helicity. We show that for stratified ABC flows helicity undergoes a substantially slower decay than for unstratified ABC flows. This fact is likely associated to the combined effect of stratification and large-scale coherent structures. Indeed, when the latter are missing, as in random flows, helicity is rapidly destroyed by the onset of gravitational waves. A type of large-scale dissipative "cyclostrophic" balance can be invoked to explain this behavior. No production of helicity is observed, contrary to the case of rotating and stratified flows. When helicity survives in the system, it strongly affects the temporal energy decay and the energy distribution among Fourier modes. We discover in fact that the decay rate of energy for stratified helical flows is much slower than for stratified nonhelical flows and can be considered with a phenomenological model in a way similar to what is done for unstratified rotating flows. We also show that helicity, when strong, has a measurable effect on the Fourier spectra, in particular at scales larger than the buoyancy scale, for which it displays a rather flat scaling associated with vertical shear, as observed in the planetary boundary layer. © 2013 American Physical Society. Fil:Mininni, P.D. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. 2013 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_15393755_v87_n6_p_Rorai http://hdl.handle.net/20.500.12110/paper_15393755_v87_n6_p_Rorai |
| institution |
Universidad de Buenos Aires |
| institution_str |
I-28 |
| repository_str |
R-134 |
| collection |
Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) |
| topic |
Boussinesq equations Energy distributions Initial conditions Large-scale coherent structures Phenomenological models Planetary boundary layers Stratified flows Stratified turbulence Aerodynamics Decay (organic) Fourier series Hydrodynamics Thermal stratification Shear flow |
| spellingShingle |
Boussinesq equations Energy distributions Initial conditions Large-scale coherent structures Phenomenological models Planetary boundary layers Stratified flows Stratified turbulence Aerodynamics Decay (organic) Fourier series Hydrodynamics Thermal stratification Shear flow Mininni, Pablo Daniel Helicity dynamics in stratified turbulence in the absence of forcing |
| topic_facet |
Boussinesq equations Energy distributions Initial conditions Large-scale coherent structures Phenomenological models Planetary boundary layers Stratified flows Stratified turbulence Aerodynamics Decay (organic) Fourier series Hydrodynamics Thermal stratification Shear flow |
| description |
A numerical study of decaying stably stratified flows is performed. Relatively high stratification (Froude number ≈10 - 2-10 - 1) and moderate Reynolds (Re) numbers (Re≈ 3-6×103) are considered and a particular emphasis is placed on the role of helicity (velocity-vorticity correlations), which is not an invariant of the nondissipative equations. The problem is tackled by integrating the Boussinesq equations in a periodic cubical domain using different initial conditions: a nonhelical Taylor-Green (TG) flow, a fully helical Beltrami [Arnold-Beltrami- Childress (ABC)] flow, and random flows with a tunable helicity. We show that for stratified ABC flows helicity undergoes a substantially slower decay than for unstratified ABC flows. This fact is likely associated to the combined effect of stratification and large-scale coherent structures. Indeed, when the latter are missing, as in random flows, helicity is rapidly destroyed by the onset of gravitational waves. A type of large-scale dissipative "cyclostrophic" balance can be invoked to explain this behavior. No production of helicity is observed, contrary to the case of rotating and stratified flows. When helicity survives in the system, it strongly affects the temporal energy decay and the energy distribution among Fourier modes. We discover in fact that the decay rate of energy for stratified helical flows is much slower than for stratified nonhelical flows and can be considered with a phenomenological model in a way similar to what is done for unstratified rotating flows. We also show that helicity, when strong, has a measurable effect on the Fourier spectra, in particular at scales larger than the buoyancy scale, for which it displays a rather flat scaling associated with vertical shear, as observed in the planetary boundary layer. © 2013 American Physical Society. |
| author |
Mininni, Pablo Daniel |
| author_facet |
Mininni, Pablo Daniel |
| author_sort |
Mininni, Pablo Daniel |
| title |
Helicity dynamics in stratified turbulence in the absence of forcing |
| title_short |
Helicity dynamics in stratified turbulence in the absence of forcing |
| title_full |
Helicity dynamics in stratified turbulence in the absence of forcing |
| title_fullStr |
Helicity dynamics in stratified turbulence in the absence of forcing |
| title_full_unstemmed |
Helicity dynamics in stratified turbulence in the absence of forcing |
| title_sort |
helicity dynamics in stratified turbulence in the absence of forcing |
| publishDate |
2013 |
| url |
https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_15393755_v87_n6_p_Rorai http://hdl.handle.net/20.500.12110/paper_15393755_v87_n6_p_Rorai |
| work_keys_str_mv |
AT mininnipablodaniel helicitydynamicsinstratifiedturbulenceintheabsenceofforcing |
| _version_ |
1768541672742846464 |