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Entrainment and mixing of water droplets across a shearless turbulent interface with and without gravitational effects

Published online by Cambridge University Press:  26 January 2011

S. GERASHCHENKO ,
G. GOOD  and
Z. WARHAFT
S. GERASHCHENKO
Affiliation:
Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA and International Collaboration for Turbulence Research
G. GOOD
Affiliation:
Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA and International Collaboration for Turbulence Research
Z. WARHAFT*
Affiliation:
Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA and International Collaboration for Turbulence Research
*
†Email address for correspondence: [email protected]
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Abstract

We describe experiments of the entrainment and mixing of water (sub-Kolmogorov scale) droplets across a turbulent–non-turbulent interface (TNI) as well a turbulent–turbulent interface (TTI) in shearless grid turbulence, over a time scale in which evaporation is insignificant. The flow is produced by means of a splitter plate with an active grid and water sprays on one side and screens or an active grid on the other side. The Taylor microscale Reλ on the turbulent side is 275 and the average dissipation scale Stokes number, Stη ≈ 0.2, and based on the integral scale, Stl ≈ 0.003. By changing the orientation of the grid system, gravitational effects may be excluded or included. We show that in the absence of gravity, for the Stokes number range studied (0.06 ≤ Stη ≤ 1.33), the droplet distribution does not change across the interface. With gravity, the larger drops are selectively mixed and this is more pronounced for the TNI than for the TTI. The particle concentration distribution is an error function for the TTI but departs significantly for the TNI due to the intermittency in the flow. In terms of particle concentration, the entrainment is most efficient for the TTI with gravity. The results are related to droplet entrainment in clouds.

JFM classification

Drops and Bubbles: Drops Turbulent Flows: Intermittency
Type
Papers
Information
Journal of Fluid Mechanics , Volume 668 , 10 February 2011 , pp. 293 - 303
Copyright
Copyright © Cambridge University Press 2011

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References

REFERENCES

Aliseda, A., Cartellier, A., Hainaux, F. & Lasheras, J. C. 2002 Effect of preferential concentration on the settling velocity of heavy particles in homogeneous isotropic turbulence. J. Fluid Mech. 468, 77–105.CrossRefGoogle Scholar
Ayyalasomayajula, S., Gylfason, A., Collins, L. R., Bodenschatz, E. & Warhaft, Z. 2006 Lagrangian measurements of inertial particle accelerations in grid-generated wind tunnel turbulence. Phys. Rev. Lett. 97, 144507.CrossRefGoogle ScholarPubMed
Dávila, J. & Hunt, J. C. R. 2001 Settling of small particles near vortices and in turbulence. J. Fluid Mech. 440, 117–145.CrossRefGoogle Scholar
Gerashchenko, S., Sharp, N. S., Neuscamman, S. & Warhaft, Z. 2008 Lagrangian measurements of inertial particle accelerations in a turbulent boundary layer. J. Fluid Mech. 617, 255–281.CrossRefGoogle Scholar
Hill, R. J. 2005 Geometric collision rates and trajectories of cloud droplets falling into a burgers vortex. Phys. Fluids 17, 037103.CrossRefGoogle Scholar
Kang, H. S. & Meneveau, C. 2008 Experimental study of an active grid-generated shearless mixing layer and comparisons with large-eddy simulation. Phys. Fluids 20, 125102.CrossRefGoogle Scholar
Larue, J. C. & Libby, P. A. 1981 Thermal mixing layer downstream of half-heated turbulence grid. Phys. Fluids 24, 597–603.CrossRefGoogle Scholar
Lavezzo, V., Soldati, A., Gerashchenko, S., Warhaft, Z. & Collins, L. R. 2010 On the role of gravity and shear on the acceleration of inertial particles in near-wall turbulence. J. Fluid Mech. 658, 229–246.CrossRefGoogle Scholar
Lázaro, B. J. & Lasheras, J. C. 1989 Particle dispersion in a turbulent, plane, free shear layer. Phys. Fluids 1, 1035–1044.CrossRefGoogle Scholar
Longmire, E. K. & Eaton, J. K. 1992 Structure of a particle-laden round jet. J. Fluid Mech. 236, 217–257.CrossRefGoogle Scholar
Ma, B.-K. & Warhaft, Z. 1986 Some aspects of the thermal mixing layer in grid turbulence. Phys. Fluids 29, 3114–3120.CrossRefGoogle Scholar
Maxey, M. R. & Corrsin, S. 1986 Gravitational settling of aerosol particles in randomly oriented cellular flow fields. J. Atmos. Sci. 43, 1112–1134.2.0.CO;2>CrossRefGoogle Scholar
Mydlarski, L. & Warhaft, Z. 1996 On the onset of high-Reynolds-number grid-generated wind tunnel turbulence. J. Fluid Mech. 320, 331–368.CrossRefGoogle Scholar
Pruppacher, H. R. & Klett, J. D. 1997 Microphysics of Clouds and Precipitation. Kluwer.Google Scholar
Rogers, R. R. & Yau, M. K. 1989 A Short Course in Cloud Physics. Pergamon, NY.Google Scholar
Shaw, R. A. 2003 Particle–turbulence interactions in atmospheric clouds. Annu. Rev. Fluid Mech. 35, 183–227.CrossRefGoogle Scholar
Siebert, H., Gerashchenko, S., Lehmann, K., Gylfason, A., Collins, L. R., Shaw, R. A. & Warhaft, Z. 2010 Towards understanding the role of turbulence on droplets in clouds: in situ and laboratory measurements. Atmos. Res. 97, 426–437.CrossRefGoogle Scholar
Townsend, A. A. 1976 The Structure of Turbulent Shear Flow. Cambridge University Press.Google Scholar
Veeravalli, S. & Warhaft, Z. 1989 The shearless turbulence mixing layer. J. Fluid Mech. 207, 191–229.CrossRefGoogle Scholar
Wang, L. P. & Maxey, M. R. 1993 Settling velocity and concentration distribution of heavy particles in homogeneous isotropic turbulence. J. Fluid Mech. 256, 27–68.CrossRefGoogle Scholar