13:30
Multiphase and non-Newtonian flows 1
Chair: Jeanette Hussong
13:30
15 mins
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Experimental and numerical investigation of turbulent entrainment in dilute polymer solutions
Giacomo Cocconi, Bettina Frohnapfel, Elisabetta De Angelis, Mark Baevsky, Alex Liberzon
Abstract: Dilute polymer effects on the inter-scale energy transfer in turbulent flows is studied in this work with a major focus on the problem of turbulent entrainment across turbulent/non-turbulent interface. Polymers alter this region of flow significantly due to the large gradients at the interface and strong interaction of multiple scales - large scales that deflect the interface and the small scales that diffuse the vorticity and strain. An experimental (PIV) and numerical (DNS with FENE-P model) study has been performed to characterize the basic mechanisms of turbulent entrainment in Newtonian vs poly(ethylene oxide) solutions. We work on a localized patch of turbulent flow created numerically or by a small spherical oscillating grid, isolating the effects of boundary friction effects from the bulk effects. We analyze the patch initial growth, a steady state and the decay phase. The effects are quantified in terms of the reduced growth rates, turbulent kinetic energy and enstrophy balance, curvature of the interface and summarized by the reduced entrainment rates. Numerical model allows to reveal the underlying mechanism that controls the rates of turbulent energy transfer towards and across the interface and to further improve models of turbulent entrainment.
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13:45
15 mins
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Turbulence modulation in particle laden homogeneous shear flow: Exact Regularized Point Particle method
Paolo Gualtieri, Francesco Battista, Carlo Massimo Casciola
Abstract: This contribution presents a first evaluation of a new approach, dubbed the Exact Regularized Point Particle (ERPP) method
[Gualtieri et al., Exact regularized point particle method for multi-phase flows in the two-way coupling regime, arXiv preprint arXiv:1405.6969], designed to model the modulation of turbulence by hundred thousands of small inertial particles. The approach overcomes some intrinsic difficulties which arise in some circumstances in available approaches like, e.g., the Particle In Cell (PIC) method introduced by Crowe and coworkers since 1977.
Numerical results concerning a homogeneous shear flow at moderate values of the Reynolds number laden with hundred thousand of small inertial particles are discussed documenting the turbulence modification in the so-called two-way coupling regime, in a range of control parameters unaccessible to the available approaches.
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14:00
15 mins
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How the dispersion of a droplet cloud depends on its initial size
Dennis van der Voort, Guus Bertens, Humberto Bocanegra-Evans, Nico Dam, Willem van de Water
Abstract: A cloud of droplets evolves under the influence of strong turbulence.
The droplets are made from a phosphorescent fluid. From this cloud we
select at t = 0 a narrow line by exciting the droplets with a UV
laser, which causes them to glow for a few milliseconds. The
dispersion of this line is followed in time using a fast intensified
camera. A large range of droplet sizes (Stokes number St) was
measured. It appears that lines with St \approx 1 disperse
faster than a line of fluid tracers. Lines of droplets which are
narrowest initially, spread fastest.
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14:15
15 mins
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NUMERICAL MODELLING OF INTERMITTENCY REGION IN TURBULENT STRATIFIED AIR-WATER FLOWS
Marta Waclawczyk, Tomasz Waclawczyk
Abstract: The present work deals with the modelling of turbulent air-water flows, where the phases are separated by a deformable, but non-broken interface. We use a “mesoscopic” level of description, i.e. we aim to model the probabilty $\alpha$ of finding the water phase at a given point of the flow. The evolution equation for the function $\alpha$ is solved with the use of the conservative level-set method.
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14:30
15 mins
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Flow over partially liquid filled cavity
Andries C. van Eckeveld, Avinash K. Pancham, Jerry Westerweel, Christian Poelma
Abstract: Experiments have been carried out to investigate the effect of liquid cavity filling on the behavior of the gas flow over a flat plate cavity. PIV measurements in the gas phase reveal that cavity filling can affect vortex shedding in the cavity mouth. Shear layer vortices can break-up into smaller vortices, thereby losing their periodic interaction with the aft wall and, hence, their sound producing potential. Expected is that this is one of the mechanisms causing sound mitigation in corrugated pipes with liquid addition, observed in literature.
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14:45
15 mins
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EFFECTS OF PARTICLE SIZE AND SOLID-TO-FLUID DENSITY RATIO ON THE DYNAMICS OF PARTICLE-LADEN HOMOGENEOUS SHEAR TURBULENCE
Mitsuru Tanaka, Daisuke Teramoto
Abstract: Particulate turbulent flows are encountered in many natural and industrial situations. In the present study, we numerically investigate how the dynamics of particle-laden homogeneous shear turbulence depends on the particle size and solid-to-fluid density ratio in order to deepen the understanding of the interaction between particles and turbulent shear flows. We consider the situation where the particle diameter is five to ten times larger than the Kolmogorov scale of turbulence with a solid-to-fluid density ratio between 0.5 and 10. An immersed boundary method is adopted to represent the spherical finite-size particle. Numerical results show that small particles enhance the viscous dissipation inside viscous layers surrounding particles, which leads to the suppression of the growth of homogeneous shear turbulence. The viscous dissipation is further enhanced through the modification of turbulence structure. The enhancement of the viscous dissipation depends strongly on the solid-to-fluid density ratio as well as particle size. In the cases of high density ratio, the generation of vortex tubes is activated around the particles, which leads to the modification of vortex layers and the enhancement of the viscous dissipation.
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