Structure and Dynamics of Small-Scale Turbulence in Stably Stratified Homogeneous Shear Flows

  • Peter J. Diamessis
  • Keiko K. Nomura
Part of the Fluid Mechanics and Its Applications book series (FMIA, volume 58)

Abstract

The collapse of vortex structures in stably stratified homogeneous sheared turbulence is explained through the coupled dynamics of vorticity w, rate of strain S, and scalar (density) gradientG.Conditional sampling of direct numerical simulation (DNS) results is used in the analysis. In homogeneous shear flow without buoyancy, high-amplitude rotation-dominated regions consist of tube-like structures with distinct spatial orientation due to the presence of mean shear. With buoyancy, these structures tend to flatten and orient along a horizontal plane. The associatedwis predominantly horizontal due to active scalar gradient dynamics. Early time dynamics in these regions are similar to those in the flow without buoyancy:wand S interact with the mean shear and fluctuations ofGare generated by reorientation of the mean scalar gradient by w. Further development inGleads to the prevalence of positive vertical scalar gradient fluctuations G3. In the presence of buoyancy, positive G3 enhances compressive straining in the vertical direction through differential acceleration. This results in a strong attenuation of the vertical vorticity fluctuations 4. At the same time, buoyancy introduces baroclinic torque which at early times, acts as a sink for horizontal w while at later times, may act as a source for spanwise cot. In general, interaction ofwand S in shear flow promotes cvi and 4. The combined effects result in the observed collapse ofwin these flows.

Keywords

Vortex Torque Attenuation Stratification Vorticity 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Gerz, T. (1991a). Coherent structures in stratified turbulent shear flows deduced from direct simulations. In Turbulence andCoherent Structurespages 449–468, Grenoble, France. Turbulence 89: Organized structures and turbulence in fluid mechanics.Google Scholar
  2. Gerz, T. (1991b). Evolution of coherent vortex structures in sheared and stratified homogeneously turbulent flows. Munich, Germany. Eighth Symposium on Turbulent Shear Flows.Google Scholar
  3. Gerz, T., Howell, J., and Mahrt, L. (1994). Vortex structures and microfronts.Phys. Fluids6:1242–1251.ADSMATHCrossRefGoogle Scholar
  4. Gerz, T., Schumann, U., and Elghobashi, S. (1989). Direct simulation of stably stratified homogeneous turbulent shear flows.J. Fluid Mech.200:563–594.ADSMATHCrossRefGoogle Scholar
  5. Jacobitz, F. (1998). Direct numerical simulation of turbulent stratified shear flow.Ph.D Dissertation University of California San Diego. Google Scholar
  6. Jacobitz, F., Sarkar, S., and Van Atta, C. (1997). Direct numerical simulations of the turbulence evolution in a uniformly sheared and stably stratified flow.J. Fluid Mech.342:231–261.ADSMATHCrossRefGoogle Scholar
  7. Kida, S. and Tanaka, M. (1994). Dynamics of vortical structures in a homogeneous shear flow.J. Fluid Mech.274:43–68.MathSciNetADSMATHCrossRefGoogle Scholar
  8. Majda, A. and Grote, M. J. (1997). Model dynamics and vertical collapse in decaying strongly stratified flows.Phys. Fluids9:2932–2940.MathSciNetADSMATHCrossRefGoogle Scholar
  9. Nomura, K. K. and Diamessis, P. J. (1999). The interaction of vorticity and rate of strain in homogeneous sheared turbulence.Submitted to Phys. Fluids. Google Scholar
  10. Nomura, K. K. and Post, G. K. (1998). The structure and dynamics of vorticity and rate of strain in incompressible homogeneous turbulence.J. Fluid Mech.377:65–97.MathSciNetADSMATHCrossRefGoogle Scholar
  11. Nomura, K. K., Post, G. K., and Diamessis, P. (1997). Characterization of small-scale motion in incompressible homogeneous turbulence.28th AIAA Fluid Dynamics Conference Snowmass Village CO.AIAA-97–1956.Google Scholar
  12. Rogers, M. M. and Moin, P. (1987). The structure of the vorticity field in homogeneous turbulent flows.J. Fluid Mech.176:33–66.ADSCrossRefGoogle Scholar
  13. Tanaka, M. and Kida, S. (1993). Characterization of vortex tubes and sheets.Phys. FluidsA5:2079–2082.ADSGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2000

Authors and Affiliations

  • Peter J. Diamessis
    • 1
  • Keiko K. Nomura
    • 1
  1. 1.Department of Applied Mechanics and Engineering SciencesUniversity of California at San Diego, La JollaUSA

Personalised recommendations