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Research Papers: Multiphase Flows

Improvements of Particle Near-Wall Velocity and Erosion Predictions Using a Commercial CFD Code

[+] Author and Article Information
Yongli Zhang1

Department of Mechanical Engineering, University of Tulsa, 800 South Trucker Drive, Tulsa, OK 74104yongli-zhang@utulsa.edu

Brenton S. McLaury, Siamack A. Shirazi

Department of Mechanical Engineering, University of Tulsa, 800 South Trucker Drive, Tulsa, OK 74104

1

Corresponding author.

J. Fluids Eng 131(3), 031303 (Feb 05, 2009) (9 pages) doi:10.1115/1.3077139 History: Received November 16, 2007; Revised December 19, 2008; Published February 05, 2009

The determination of a representative particle impacting velocity is an important component in calculating solid particle erosion inside pipe geometry. Currently, most commercial computational fluid dynamics (CFD) codes allow the user to calculate particle trajectories using a Lagrangian approach. Additionally, the CFD codes calculate particle impact velocities with the pipe walls. However, these commercial CFD codes normally use a wall function to simulate the turbulent velocity field in the near-wall region. This wall-function velocity field near the wall can affect the small particle motion in the near-wall region. Furthermore, the CFD codes assume that particles have zero volume when particle impact information is being calculated. In this investigation, particle motions that are simulated using a commercially available CFD code are examined in the near-wall region. Calculated solid particle erosion patterns are compared with experimental data to investigate the accuracy of the models that are being used to calculate particle impacting velocities. While not considered in particle tracking routines in most CFD codes, the turbulent velocity profile in the near-wall region is taken into account in this investigation, and the effect on particle impact velocity is investigated. The simulation results show that the particle impact velocity is affected significantly when near-wall velocity profile is implemented. In addition, the effects of particle size are investigated in the near-wall region of a turbulent flow in a 90 deg sharp bend. A CFD code is modified to account for particle size effects in the near-wall region before and after the particle impact. It is found from the simulations that accounting for the rebound at the particle radius helps avoid nonphysical impacts and reduces the number of impacts by more than one order-of-magnitude for small particles (25μm) due to turbulent velocity fluctuations. For large particles (256μm), however, nonphysical impacts are not observed in the simulations. Solid particle erosion is predicted before and after introducing these modifications, and the results are compared with experimental data. It is shown that the near-wall modification and turbulent particle interactions significantly affect the simulation results. Modifications can significantly improve the current CFD-based solid particle erosion modeling.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Wall function region in FLUENT

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Figure 2

Determining variables at particle location (for inner cells)

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Figure 3

u+ comparison between calculated (CFD) and standard wall-function (linear law and log law) velocity profiles

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Figure 4

Schematics of rebound at wall and rebound at particle radius

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Figure 5

Schematic of flow loop (from Ref. 11)

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Figure 6

Material specimen wall thickness measurement (from Ref. 11)

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Figure 7

90 deg sharp bend used in simulations

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Figure 8

Mesh around the corner and on the inlet of the 90 deg sharp bend

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Figure 9

Predicted erosion using different types of mesh

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Figure 10

Effect of the number of particles being simulated

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Figure 11

Effects of the modifications on erosion pattern (test 1, 50 ft/s, 256 μm): left column: upstream; right column: downstream; first row: experimental data; second row: prediction without modifications; and third row: prediction with both modifications

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Figure 12

Effects of the modifications on erosion pattern (test 2, 50 ft/s, 25 μm): left column: upstream; right column: downstream; first row: experimental data; second row: prediction without modifications (note the change in scale); and third row: prediction with both modifications

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Figure 13

Effects of the modifications on erosion pattern (test 3, 85.8 ft/s, 25 μm): left column: upstream; right column: downstream; first row: experimental data; second row: prediction without modifications (note the change in scale); and third row: prediction with both modifications

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Figure 14

Effects of the modifications on erosion pattern (test 4, 85.8 ft/s, 256 μm): left column: upstream; right column: downstream; first row: experimental data; second row: prediction without modifications; and third row: prediction with both modifications

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Figure 15

Nonphysical particle trajectory near the wall

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