UFR 2-12 Evaluation: Difference between revisions
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(''L<sub>z</sub>/ D'' = 3) and the widest of the considered domains (''L<sub>z</sub>/ D'' = 16) | (''L<sub>z</sub>/ D'' = 3) and the widest of the considered domains (''L<sub>z</sub>/ D'' = 16) | ||
in the form of instantaneous isosurface of the magnitude of the second eigenvalue of the velocity gradient tensor or | in the form of instantaneous isosurface of the magnitude of the second eigenvalue of the velocity gradient tensor or | ||
"swirl" quantity, &lambda<sub>2</sub>. | "swirl" quantity, λ<sub>2</sub>. | ||
The figure is reassuring in the sense that it visibly displays that the narrow-domain simulation resolves not only | The figure is reassuring in the sense that it visibly displays that the narrow-domain simulation resolves not only | ||
fine-grained turbulent eddies but also large, nearly coherent, structures and exhibits all the complex flow features | fine-grained turbulent eddies but also large, nearly coherent, structures and exhibits all the complex flow features | ||
Revision as of 12:38, 27 October 2012
Turbulent Flow Past Two-Body Configurations
Flows Around Bodies
Underlying Flow Regime 2-12
Evaluation
Comparison of CFD Calculations with Experiments
This section is organized as follows. First (Section 6.1), results of some sensitivity studies are presented and briefly discussed. These include evaluation of such effects as span-size of the domain, compressibility, time sample used for computing the mean flow and turbulent statistics, and numerical dissipation of the method used. Then, in Section 6.2, a comparison with the experimental data is shown for the main body of simulations carried out within the ATAAC project with the use of the physical and computational problem setups outlined in Section 5.
RESULTS OF SENSITIVITY STUDIES
Effect of span size of domain
As mentioned in Section 4, the aspect ratio of the CT configuration Lz/ D in the BART facility is equal to 12.4. Strictly speaking this demands carrying out simulations exactly at this value of Lz/ D and imposing no-slip boundary conditions on the floor and ceiling of the test section (see Figure 2). However such simulations would be very expensive. Considering this and, also, recommendations of the BANC-I Workshop based on simulations at different Lz/ D with periodic boundary conditions in the spanwise directions, most of the simulations in the ATAAC project were performed at Lz/ D = 3 assuming spanwise periodicity. In order to get an idea on how strong the effect of such a simplification could be, NTS conducted a series of simulations at different Lz/ D. Some results of these simulations are presented below [3].
Figure 4 compares flow visualisations from the SA DDES carried out in the "mandatory"
(Lz/ D = 3) and the widest of the considered domains (Lz/ D = 16)
in the form of instantaneous isosurface of the magnitude of the second eigenvalue of the velocity gradient tensor or
"swirl" quantity, λ2.
The figure is reassuring in the sense that it visibly displays that the narrow-domain simulation resolves not only
fine-grained turbulent eddies but also large, nearly coherent, structures and exhibits all the complex flow features
observed in the visualization of the wide-domain simulation, except for the initial region of the free shear-layer
separated from the upstream cylinder, where a noticeable difference between the two flow-visualizations is observed.
Contributed by: A. Garbaruk, M. Shur and M. Strelets — New Technologies and Services LLC (NTS) and St.-Petersburg State Polytechnic University
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