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Transition and self-sustained turbulence in dilute suspensions of finite-size particles
KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik.
KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik.ORCID-id: 0000-0002-3943-8187
KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik.ORCID-id: 0000-0002-4346-4732
2015 (engelsk)Inngår i: Theoretical and Applied Mechanics Letters, ISSN 2095-0349, Vol. 5, s. 121-125Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

We study the transition to turbulence of channel flow of finite-size particle suspensions at low volume fraction, i.e., Φ ≈ 0.001. The critical Reynolds number above which turbulence is sustained reduces to Re ≈ 1675, in the presence of few particles, independently of the initial condition, a value lower than that of the corresponding single-phase flow, i.e., Re ≈ 1775. In the dilute suspension, the initial arrangement of the particles is important to trigger the transition at a fixed Reynolds number and particle volume fraction. As in single phase flows, streamwise elongated disturbances are initially induced in the flow. If particles can induce oblique disturbances with high enough energy within a certain time, the streaks breakdown, flow experiences the transition to turbulence and the particle trajectories become chaotic. Otherwise, the streaks decay in time and the particles immigrate towards the channel core in a laminar flow. 

sted, utgiver, år, opplag, sider
2015. Vol. 5, s. 121-125
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-177847DOI: 10.1016/j.taml.2015.04.004ISI: 000437286600006Scopus ID: 2-s2.0-84944751845OAI: oai:DiVA.org:kth-177847DiVA, id: diva2:874515
Merknad

QC 20151127

Tilgjengelig fra: 2015-11-27 Laget: 2015-11-27 Sist oppdatert: 2024-03-15bibliografisk kontrollert
Inngår i avhandling
1. Stability analysis and inertial regimes in complex  flows
Åpne denne publikasjonen i ny fane eller vindu >>Stability analysis and inertial regimes in complex  flows
2015 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

In this work we rst study the non-Newtonian effects on the inertial instabilities in shear flows and second the inertial suspensions of finite size rigid particles by means of numerical simulations.

In the first part, both inelastic (Carreau) and elastic models (Oldroyd-B and FENE-P) have been employed to examine the main features of the non-Newtonian fluids in several congurations; flow past a circular cylinder, in a lid-driven cavity and in a channel. In the framework of the linear stability analysis, modal, non-modal, energy and sensitivity analysis are used to determine the instability mechanisms of the non-Newtonian flows. Signicant modifications/alterations in the instability of the different flows have been observed under the action of the non-Newtonian effects. In general, shear-thinning/shear-thickening effects destabilize/stabilize the flow around the cylinder and in a lid driven cavity. Viscoelastic effects both stabilize and destabilize the channel flow depending on the ratio between the viscoelastic and flow time scales. The instability mechanism is just slightly modied in the cylinder flow whereas new instability mechanisms arise in the lid-driven cavity flow.

In the second part, we employ Direct Numerical Simulation together with an Immersed Boundary Method to simulate the inertial suspensions of rigid spherical neutrally buoyant particles in a channel. A wide range of the bulk Reynolds numbers, 500<Re<5000, and particle volume fractions, 0<\Phi<3, is studied while fixing the ratio between the channel height to particle diameter, 2h/d = 10. Three different inertial regimes are identied by studying the stress budget of two-phase flow. These regimes are laminar, turbulent and inertial shear-thickening where the contribution of the viscous, Reynolds and particle stress to transfer the momentum across the channel is the strongest respectively. In the inertial shear-thickening regime we observe a signicant enhancement in the wall shear stress attributed to an increment in particle stress and not the Reynolds stress. Examining the particle dynamics, particle distribution, dispersion, relative velocities and collision kernel, confirms the existence of the three regimes. We further study the transition and turbulence in the dilute regime of finite size particulate channel flow. We show that the turbulence can sustain in the domain at Reynolds numbers lower than the one of the unladen flow due to the disturbances induced by particles.

sted, utgiver, år, opplag, sider
Stockholm: KTH Royal Institute of Technology, 2015. s. x, 60
Serie
TRITA-MEK, ISSN 0348-467X
Emneord
non-Newtonian flow, global stability analysis, inertial suspensions, particle dynamics
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-177850 (URN)978-91-7595-782-1 (ISBN)
Disputas
2015-12-18, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:15 (engelsk)
Opponent
Veileder
Merknad

QC 20151127

Tilgjengelig fra: 2015-11-27 Laget: 2015-11-27 Sist oppdatert: 2022-06-23bibliografisk kontrollert

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