Shape effects on turbulent modulation by large nearly neutrally buoyant particles

Gabriele Bellani, Margaret Byron, Audric G. Collignon, Colin R. Meyer, Evan A. Variano

    Research output: Contribution to journalArticle

    56 Citations (Scopus)

    Abstract

    We investigate dilute suspensions of Taylor-microscale-sized particles in homogeneous isotropic turbulence. In particular, we focus on the effect of particle shape on particle-fluid interaction. We conduct laboratory experiments using a novel experimental technique to simultaneously measure the kinematics of fluid and particle phases. This uses transparent particles having the same refractive index as water, whose motion we track via embedded optical tracers. We compare the turbulent statistics of a single-phase flow to the turbulent statistics of the fluid phase in a particle-laden suspension. Two suspensions are compared, one in which the particles are spheres and the other in which they are prolate ellipsoids with aspect ratio 2. We find that spherical particles at volume fraction Øv = 0. 14% reduce the turbulent kinetic energy (TKE) by 15 % relative to the single-phase flow. At the same volume fraction (and slightly smaller total surface area), ellipsoidal particles have a much smaller effect: they reduce the TKE by 3 % relative to the single-phase flow. Spectral analysis shows the details of TKE reduction and redistribution across spatial scales: spherical particles remove energy from large scales and reinsert it at small scales, while ellipsoids remove relatively less TKE from large scales and reinsert relatively more at small scales. Shape effects are far less evident in the statistics of particle rotation, which are very similar for ellipsoids and spheres. Comparing these with fluid enstrophy statistics, we find that particle rotation is dominated by velocity gradients on scales much larger than the particle characteristic length scales.

    Original languageEnglish (US)
    Pages (from-to)41-60
    Number of pages20
    JournalJournal of Fluid Mechanics
    Volume712
    DOIs
    StatePublished - Dec 10 2012

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    Kinetic energy
    Modulation
    Statistics
    modulation
    Fluids
    Volume fraction
    single-phase flow
    ellipsoids
    kinetic energy
    statistics
    Spectrum analysis
    Aspect ratio
    Refractive index
    Kinematics
    Turbulence
    fluids
    Water
    homogeneous turbulence
    isotropic turbulence
    Experiments

    All Science Journal Classification (ASJC) codes

    • Condensed Matter Physics
    • Mechanics of Materials
    • Mechanical Engineering

    Cite this

    Bellani, Gabriele ; Byron, Margaret ; Collignon, Audric G. ; Meyer, Colin R. ; Variano, Evan A. / Shape effects on turbulent modulation by large nearly neutrally buoyant particles. In: Journal of Fluid Mechanics. 2012 ; Vol. 712. pp. 41-60.
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    abstract = "We investigate dilute suspensions of Taylor-microscale-sized particles in homogeneous isotropic turbulence. In particular, we focus on the effect of particle shape on particle-fluid interaction. We conduct laboratory experiments using a novel experimental technique to simultaneously measure the kinematics of fluid and particle phases. This uses transparent particles having the same refractive index as water, whose motion we track via embedded optical tracers. We compare the turbulent statistics of a single-phase flow to the turbulent statistics of the fluid phase in a particle-laden suspension. Two suspensions are compared, one in which the particles are spheres and the other in which they are prolate ellipsoids with aspect ratio 2. We find that spherical particles at volume fraction {\O}v = 0. 14{\%} reduce the turbulent kinetic energy (TKE) by 15 {\%} relative to the single-phase flow. At the same volume fraction (and slightly smaller total surface area), ellipsoidal particles have a much smaller effect: they reduce the TKE by 3 {\%} relative to the single-phase flow. Spectral analysis shows the details of TKE reduction and redistribution across spatial scales: spherical particles remove energy from large scales and reinsert it at small scales, while ellipsoids remove relatively less TKE from large scales and reinsert relatively more at small scales. Shape effects are far less evident in the statistics of particle rotation, which are very similar for ellipsoids and spheres. Comparing these with fluid enstrophy statistics, we find that particle rotation is dominated by velocity gradients on scales much larger than the particle characteristic length scales.",
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    Shape effects on turbulent modulation by large nearly neutrally buoyant particles. / Bellani, Gabriele; Byron, Margaret; Collignon, Audric G.; Meyer, Colin R.; Variano, Evan A.

    In: Journal of Fluid Mechanics, Vol. 712, 10.12.2012, p. 41-60.

    Research output: Contribution to journalArticle

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