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Turbulence model sensitivity and scour gap effect of unsteady flow around pipe: a CFD study.

Ali A, Sharma RK, Ganesan P, Akib S - ScientificWorldJournal (2014)

Bottom Line: A numerical investigation of incompressible and transient flow around circular pipe has been carried out at different five gap phases.Flow equations such as Navier-Stokes and continuity equations have been solved using finite volume method.Unsteady horizontal velocity and kinetic energy square root profiles are plotted using different turbulence models and their sensitivity is checked against published experimental results.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia.

ABSTRACT
A numerical investigation of incompressible and transient flow around circular pipe has been carried out at different five gap phases. Flow equations such as Navier-Stokes and continuity equations have been solved using finite volume method. Unsteady horizontal velocity and kinetic energy square root profiles are plotted using different turbulence models and their sensitivity is checked against published experimental results. Flow parameters such as horizontal velocity under pipe, pressure coefficient, wall shear stress, drag coefficient, and lift coefficient are studied and presented graphically to investigate the flow behavior around an immovable pipe and scoured bed.

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Turbulent kinetic energy square root () at different locations, (a) X/D = −3.0, (b) X/D = 1.0, (c) X/D = 1.5, and (d) X/D = 2.0, — standard k-ε, ⋄ RNG k-ε, △ realizable k-ε, × standard k-ω, + SST k-ω, and □ Reynolds stress model (RSM), Red Jensen.
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fig6: Turbulent kinetic energy square root () at different locations, (a) X/D = −3.0, (b) X/D = 1.0, (c) X/D = 1.5, and (d) X/D = 2.0, — standard k-ε, ⋄ RNG k-ε, △ realizable k-ε, × standard k-ω, + SST k-ω, and □ Reynolds stress model (RSM), Red Jensen.

Mentions: Cases 1–30 are used to predict the horizontal velocity profile (Ux) and the turbulent kinetic energy (TKE) at some axial length (i.e., X/D = −3.0, 1.0, 1.5, and 2.0) using different type of turbulence models and the results are presented in Figures 5 and 6, respectively. For comparisons, the experimental results reported in Chang [2] are also presented in the figure. Note that the location of the axial position covers the front and rear part of the pipe (or obstruction). Referring to Figures 5(a)to 5(d), which is presented at X/D = −3.0, 1.0, 1.5, and 2.0, respectively, the standard k-ɛ turbulence model prediction is much closer to the experimental data at various water depths; some of them overlap each other. Nearly the same can be said for the realizable k-ɛ model and RSM model but some deviation seen at some of water depths, for example, at water depths below 0.01 m and those between 0.03 and 0.04 m at X/D = 2.0 (Figure 5(d)) for the both models. RNG k-ɛ model prediction is quite accurate for X/D = −3.0 and 1.0 (Figures 5(a) and 5(b)), but this is not the case for X/D = 1.5 and 2.0 (Figures 5(c) and 5(d)); overprediction of the velocity is seen at water depths between 0.01 and 0.03 m. Relatively, standard k-ω and SST k-ω models are the most inaccurate among the turbulence models studied. Significant under prediction of the velocity is seen at water depths from 0 to 0.04 m at X/D = 1.0, 1.5, and 2.0. Referring to Figure 6, the TKE is well predicted by standard k-ɛ turbulence with some deviation at X/D = 2.0 (Figure 6(d)) in comparison to other turbulence models. RNG k-ɛ model and RSM model also reasonably predict TKE especially for X/D = 1.5 and 2.0 and realizable k-ɛ model has a good prediction only at X/D = 1.0. On overall, realizable k-ɛ model, standard k-ω, and SST k-ω models can be regarded as the least accurate among the turbulence models studied in predicting the turbulence kinetic energy.


Turbulence model sensitivity and scour gap effect of unsteady flow around pipe: a CFD study.

Ali A, Sharma RK, Ganesan P, Akib S - ScientificWorldJournal (2014)

Turbulent kinetic energy square root () at different locations, (a) X/D = −3.0, (b) X/D = 1.0, (c) X/D = 1.5, and (d) X/D = 2.0, — standard k-ε, ⋄ RNG k-ε, △ realizable k-ε, × standard k-ω, + SST k-ω, and □ Reynolds stress model (RSM), Red Jensen.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4129154&req=5

fig6: Turbulent kinetic energy square root () at different locations, (a) X/D = −3.0, (b) X/D = 1.0, (c) X/D = 1.5, and (d) X/D = 2.0, — standard k-ε, ⋄ RNG k-ε, △ realizable k-ε, × standard k-ω, + SST k-ω, and □ Reynolds stress model (RSM), Red Jensen.
Mentions: Cases 1–30 are used to predict the horizontal velocity profile (Ux) and the turbulent kinetic energy (TKE) at some axial length (i.e., X/D = −3.0, 1.0, 1.5, and 2.0) using different type of turbulence models and the results are presented in Figures 5 and 6, respectively. For comparisons, the experimental results reported in Chang [2] are also presented in the figure. Note that the location of the axial position covers the front and rear part of the pipe (or obstruction). Referring to Figures 5(a)to 5(d), which is presented at X/D = −3.0, 1.0, 1.5, and 2.0, respectively, the standard k-ɛ turbulence model prediction is much closer to the experimental data at various water depths; some of them overlap each other. Nearly the same can be said for the realizable k-ɛ model and RSM model but some deviation seen at some of water depths, for example, at water depths below 0.01 m and those between 0.03 and 0.04 m at X/D = 2.0 (Figure 5(d)) for the both models. RNG k-ɛ model prediction is quite accurate for X/D = −3.0 and 1.0 (Figures 5(a) and 5(b)), but this is not the case for X/D = 1.5 and 2.0 (Figures 5(c) and 5(d)); overprediction of the velocity is seen at water depths between 0.01 and 0.03 m. Relatively, standard k-ω and SST k-ω models are the most inaccurate among the turbulence models studied. Significant under prediction of the velocity is seen at water depths from 0 to 0.04 m at X/D = 1.0, 1.5, and 2.0. Referring to Figure 6, the TKE is well predicted by standard k-ɛ turbulence with some deviation at X/D = 2.0 (Figure 6(d)) in comparison to other turbulence models. RNG k-ɛ model and RSM model also reasonably predict TKE especially for X/D = 1.5 and 2.0 and realizable k-ɛ model has a good prediction only at X/D = 1.0. On overall, realizable k-ɛ model, standard k-ω, and SST k-ω models can be regarded as the least accurate among the turbulence models studied in predicting the turbulence kinetic energy.

Bottom Line: A numerical investigation of incompressible and transient flow around circular pipe has been carried out at different five gap phases.Flow equations such as Navier-Stokes and continuity equations have been solved using finite volume method.Unsteady horizontal velocity and kinetic energy square root profiles are plotted using different turbulence models and their sensitivity is checked against published experimental results.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia.

ABSTRACT
A numerical investigation of incompressible and transient flow around circular pipe has been carried out at different five gap phases. Flow equations such as Navier-Stokes and continuity equations have been solved using finite volume method. Unsteady horizontal velocity and kinetic energy square root profiles are plotted using different turbulence models and their sensitivity is checked against published experimental results. Flow parameters such as horizontal velocity under pipe, pressure coefficient, wall shear stress, drag coefficient, and lift coefficient are studied and presented graphically to investigate the flow behavior around an immovable pipe and scoured bed.

Show MeSH
Related in: MedlinePlus