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Research Papers: Techniques and Procedures

Comparison of Turbulence Modeling Strategies for Indoor Flows

[+] Author and Article Information
Ammar M. Abdilghanie, Lance R. Collins

Sibley School of Mechanical & Aerospace Engineering, Cornell University, Ithaca, NY 14853-7501

David A. Caughey1

Sibley School of Mechanical & Aerospace Engineering, Cornell University, Ithaca, NY 14853-7501dac5@cornell.edu

1

Corresponding author. Present address: Department of Mechanical & Aerospace Engineering, Cornell University, 248 Upson Hall, Ithaca, NY 14853-7501.

J. Fluids Eng 131(5), 051402 (Apr 15, 2009) (18 pages) doi:10.1115/1.3112386 History: Received June 14, 2008; Revised March 08, 2009; Published April 15, 2009

Abstract

Turbulence modeling techniques are compared for the simulation of low speed indoor air flow in a simple room. The effect of inlet turbulence intensity on the flow field is investigated using the constant coefficient large eddy simulation (LES) model with uniform mean inlet conditions at several levels of inlet turbulence intensities. The results show significant differences between the simulations with laminar inflow conditions and those in which turbulence was introduced at the inlet. For simulations with turbulent inlet conditions, it is noticed that the jet transitions to a state of fully developed turbulence wherein the dynamics of the flow become nearly insensitive to any further increase in the level of inlet turbulence. For laminar flow conditions, it is seen that the jet slowly spreads and mixes with the quiescent room air. As a result, the jet reaches a fully developed turbulent state further away from the inlet relative to the simulations with inlet turbulence. The effect of using experimental inlet profiles is also investigated. It is seen that, close to the inlet, the flow is sensitive to the inflow details, whereas further away from the inlet, these effects become less pronounced. The results from the constant coefficient and the dynamic LES models are compared. The most noticeable differences in the flow occur at the locations where the subgrid-scale’s contribution to the turbulent kinetic energy is highest. Finally, the results from the dynamic LES and the $k-ϵ$ models are compared. It is found that there are significant differences between the two models for the zero inlet turbulence limit where the flow is most probably transitional in nature and turbulence has not yet reached a fully developed state. It is seen that in the laminar inflow case the $k-ϵ$ model predicts a fully turbulent jet very close to the inlet and thus fails to capture the slow development of the jet found in LES. Accordingly, the $k-ϵ$ model results are nearly insensitive to the level of inlet turbulence especially far from the origin of the flow. It is also seen that for cases with nonzero inlet turbulence level, the $k-ϵ$ model predicts the general features of the mean flow reasonably well; however, the $k-ϵ$ model overpredicts the jet spreading rate and the turbulent kinetic energy close to the inlet. Furthermore, the $k-ϵ$ model under predicts the turbulence level near the corner of the ceiling as it fails to capture the complicated mean velocity and turbulent kinetic energy, most likely because of the highly intermittent flow pattern found there in LES.

Copyright © 2009 by American Society of Mechanical Engineers
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Figures

Figure 1

(a) Geometry of Indoor Flowfield Laboratory Chamber; dimensions are 244×183×244 cm3. (b) Top view; dimensions are in cm.

Figure 2

Computational grid for the Indoor Flowfield Laboratory Chamber: (a) side (x-z plane) and (b) top (x-y plane) views of the baseline grid

Figure 3

Comparison of mean velocity magnitude on the baseline and the refined grids at (a) z/L=−0.2 and (b) z/L=0.9375

Figure 4

Comparison of the rms of the velocity magnitude on the baseline and the refined grids at (a) z/L=−0.2 and (b) z/L=0.9375

Figure 5

Comparison of turbulent kinetic energy on the baseline and the refined grids at (a) z/L=−0.8 and (b) z/L=0.9375

Figure 6

(a) Instantaneous and (b) mean velocity contours on center plane; 0% inlet turbulence (units are in m/s)

Figure 7

(a) Instantaneous and (b) mean velocity contours on center plane; 5% inlet turbulence (units are in m/s)

Figure 8

(a) Instantaneous and (b) mean velocity contours on center plane; 13% inlet turbulence (units are in m/s)

Figure 9

Comparison of the mean velocity magnitude for three levels of inlet turbulence intensity at (a) z/L=−0.4 and (b) z/L=0.0; baseline grid

Figure 10

Comparison of the mean velocity magnitude for three levels of inlet turbulence intensity at z/L=0.75; baseline grid

Figure 11

Comparison of the rms velocity magnitude for three levels of inlet turbulence intensity at (a) z/L=−0.4 and (b) z/L=0.0; baseline grid

Figure 12

Comparison of the rms velocity magnitude for three levels of inlet turbulence intensity at (a) z/L=0.875 and (b) z/L=0.9375; baseline grid

Figure 13

Experimental data and curve fits along the (a) long and (b) short sides of the inlet. In (a), Ls is the half-length of the inlet section.

Figure 14

Fitted profile of the turbulent kinetic energy

Figure 15

Mean velocity magnitude at (a) z/L=−0.8 and (b) z/L=0.0; comparison of results with plug flow and experimentally determined inlet conditions

Figure 16

Mean velocity magnitude at (a) z/L=0.75 and (b) z/L=0.875; comparison of results with plug flow and experimentally determined inlet conditions

Figure 17

rms velocity magnitude at (a) z/L=−0.8 and (b) z/L=−0.4; comparison of results with plug flow and experimentally determined inlet conditions.

Figure 18

rms velocity magnitude at (a) z/L=0.875 and (b) z/L=0.9375; comparison of results with plug flow and experimentally determined inlet conditions

Figure 19

Mean velocity magnitude at (a) z/L=−0.4 and (b) z/L=0.0; comparison of results using constant-coefficient and dynamic Smagorinsky models

Figure 20

Mean velocity magnitude at (a) z/L=0.875 and (b) z/L=0.9375; comparison of results using constant-coefficient and dynamic Smagorinsky models

Figure 21

rms velocity magnitude at (a) z/L=−0.4 and (b) z/L=0.0; comparison of results using constant-coefficient and dynamic Smagorinsky models

Figure 22

rms velocity magnitude at (a) z/L=0.875 and (b) z/L=0.9375; comparison of results using constant-coefficient and dynamic Smagorinsky models

Figure 23

Mean velocity magnitude from k-ϵ model at (a) z/L=−0.6 and (b) z/L=0.875

Figure 24

Turbulent kinetic energy from k-ϵ model at (a) z/L=−0.6 and (b) z/L=0.875

Figure 25

Mean velocity magnitude from k-ϵ and LES models at z/L=−0.8: (a) 0% and (b) 13% inlet turbulence intensities

Figure 26

Mean velocity magnitude from k-ϵ and LES models at z/L=0.75: (a) 0% and (b) 13% inlet turbulence intensities

Figure 27

Turbulent kinetic energy from k-ϵ and LES models at z/L=−0.8: (a) 0% and (b) 13% inlet turbulence intensities

Figure 28

Turbulent kinetic energy from k-ϵ and LES models at z/L=0.75: (a) 0% and (b) 13% inlet turbulence intensities

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