scholarly journals Eddy diffusivity of quasi-neutrally-buoyant inertial particles

2018 ◽  
Vol 3 (4) ◽  
Author(s):  
Marco Martins Afonso ◽  
Paolo Muratore-Ginanneschi ◽  
Sílvio M. A. Gama ◽  
Andrea Mazzino
Keyword(s):  
Eddy Diffusivity ◽  
Inertial Particles ◽  
Neutrally Buoyant

scholarly journals Experimental Observation of Inertial Particles through Idealized Hydroturbine Distributor Geometry

Water ◽  
2019 ◽  
Vol 11 (3) ◽  
pp. 471 ◽  
Author(s):  
Samuel Harding ◽  
Marshall Richmond ◽  
Robert Mueller
Keyword(s):  
High Speed ◽  
Laboratory Data ◽  
Bead Geometry ◽  
Inertial Particles ◽  
Video Cameras ◽  
Through Flow ◽  
Flow Speeds ◽  
Biological Performance ◽  
Neutrally Buoyant ◽  
Collision Target

To increase and maintain existing hydropower capacity within biological performance-based regulations, predictive simulation methods are needed that can reliably estimate the risk to fish passing through flow passage routes at hydropower facilities. One of the central challenges is to validate the software capabilities for simulating the trajectories, including collisions, of inertial particles against laboratory data. In this work, neutrally buoyant spherical- and rod-shaped beads were released upstream of laboratory-scale geometries representative of the distributor of a hydroturbine. The experimental campaign involved a test matrix of 24 configurations with variations in bead geometry, collision target geometry, flow speeds, and release locations. A total of more than 10,000 beads were recorded using high-speed video cameras and analyzed using particle tracking software. Collision rates from 1–7% were observed for the cylinder geometry and rates of 1–23% were observed for the vane array over the range of test configurations.

scholarly journals Eddy diffusivities of inertial particles under gravity

2012 ◽  
Vol 694 ◽  
pp. 426-463 ◽  
Author(s):  
Marco Martins Afonso ◽  
Andrea Mazzino ◽  
Paolo Muratore-Ginanneschi
Keyword(s):  
Particle Velocity ◽  
Large Scale ◽  
Particle Concentration ◽  
Mass Density ◽  
Concentration Field ◽  
Eddy Diffusivity ◽  
Inertial Particles ◽  
Differential Problem ◽  
Carrier Flow ◽  
Eddy Diffusivities

AbstractThe large-scale/long-time transport of inertial particles of arbitrary mass density under gravity is investigated by means of a formal multiple-scale perturbative expansion in the scale-separation parameter between the carrier flow and the particle concentration field. The resulting large-scale equation for the particle concentration is determined, and is found to be diffusive with a positive definite eddy diffusivity. The calculation of the latter tensor is reduced to the resolution of an auxiliary differential problem, consisting of a coupled set of two differential equations in a $(6+ 1)$-dimensional coordinate system (three space coordinates plus three velocity coordinates plus time). Although expensive, numerical methods can be exploited to obtain the eddy diffusivity, for any desirable non-perturbative limit (e.g. arbitrary Stokes and Froude numbers). The aforementioned large-scale equation is then specialized to deal with two different relevant perturbative limits: (i) vanishing of both Stokes time and sedimenting particle velocity; (ii) vanishing Stokes time and finite sedimenting particle velocity. Both asymptotics lead to a greatly simplified auxiliary differential problem, now involving only space coordinates and thus easily tackled by standard numerical techniques. Explicit, exact expressions for the eddy diffusivities have been calculated, for both asymptotics, for the class of parallel flows, both static and time-dependent. This allows us to investigate analytically the role of gravity and inertia on the diffusion process by varying relevant features of the carrier flow, such as the form of its temporal correlation function. Our results exclude a universal role played by gravity and inertia on the diffusive behaviour: regimes of both enhanced and reduced diffusion may exist, depending on the detailed structure of the carrier flow.

scholarly journals Dynamics of inertial particles in a turbulent von Kármán flow

2011 ◽  
Vol 668 ◽  
pp. 223-235 ◽  
Author(s):  
R. VOLK ◽  
E. CALZAVARINI ◽  
E. LÉVÊQUE ◽  
J.-F. PINTON
Keyword(s):  
Turbulent Flows ◽  
Laser Doppler Velocimetry ◽  
Reynolds Numbers ◽  
Probability Density Functions ◽  
Density Functions ◽  
Inertial Particles ◽  
Von Karman ◽  
Kolmogorov Scale ◽  
Von Kármán ◽  
Neutrally Buoyant

We study the dynamics of neutrally buoyant particles with diameters varying in the range [1, 45] in Kolmogorov scale units (η) and Reynolds numbers based on Taylor scale (Reλ) between 590 and 1050. One component of the particle velocity is measured using an extended laser Doppler velocimetry at the centre of a von Kármán flow, and acceleration is derived by differentiation. We find that the particle acceleration variance decreases with increasing diameter with scaling close to (D/η)−2/3, in agreement with previous observations, and with a hint for an intermittent correction as suggested by arguments based on scaling of pressure spatial increments. The characteristic time of acceleration autocorrelation increases more strongly than previously reported in other experiments, and possibly varying linearly with D/η. Further analysis shows that the probability density functions of the acceleration have smaller wings for larger particles; their flatness decreases as well, as expected from the behaviour of pressure increments in turbulence when intermittency corrections are taken into account. We contrast our measurements with previous observations in wind-tunnel turbulent flows and numerical simulations.

scholarly journals Settling velocity of quasi-neutrally-buoyant inertial particles

2018 ◽  
Vol 346 (2) ◽  
pp. 121-131 ◽  
Author(s):  
Marco Martins Afonso ◽  
Sílvio M.A. Gama
Keyword(s):  
Settling Velocity ◽  
Inertial Particles ◽  
Neutrally Buoyant

Focusing of inertial particles after the shock-wave intersection point

2007 ◽  
Vol 5 ◽  
pp. 145-150
Author(s):  
I.V. Golubkina
Keyword(s):  
Shock Wave ◽  
Mass Concentration ◽  
Gas Flow ◽  
Intersection Point ◽  
Plane Shock ◽  
Inertial Particles ◽  
Dusty Gas ◽  
Focusing Effect ◽  
Aerodynamic Focusing ◽  
Particle Mass Concentration

The effect of the aerodynamic focusing of inertial particles is investigated in both symmetric and non-symmetric cases of interaction of two plane shock waves in the stationary dusty-gas flow. The particle mass concentration is assumed to be small. Particle trajectories and concentration are calculated numerically with the full Lagrangian approach. A parametric study of the flow is performed in order to find the values of the governing parameters corresponding to the maximum focusing effect.

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