Description AC6-15: Difference between revisions
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Computer simulations have been seen as a potential tool for capturing the subtleties of the development of instabilities and associated vortical and turbulence structures. Such information can be obtained by direct and large-eddy simulations (DNS, LES) over a range of important scales, but the accuracy of DNS and LES depends much on the numerical resolution. For complex configurations the Reynolds-averaged Navier-Stokes (RANS) approach, being computationally less demanding, has been considered as a more rational option for industrial purposes. | Computer simulations have been seen as a potential tool for capturing the subtleties of the development of instabilities and associated vortical and turbulence structures. Such information can be obtained by direct and large-eddy simulations (DNS, LES) over a range of important scales, but the accuracy of DNS and LES depends much on the numerical resolution. For complex configurations the Reynolds-averaged Navier-Stokes (RANS) approach, being computationally less demanding, has been considered as a more rational option for industrial purposes. | ||
However, because of its empirical nature, the RANS approach in general has not been regarded as a trustful research tool, recognizing that its credibility depends much on the choice of the turbulence model to close the time- or ensemble-averaged conservation equations. Hybrid LES/RANS schemes (including detached eddy-simulations, DES), where LES is used in the flow bulk and a RANS model for the wall-adjacent, or complete wall-attached flow regions, are becoming popular and, by some in the community, are seen as the future industrial standard (Slotnick et al., 2014). | However, because of its empirical nature, the RANS approach in general has not been regarded as a trustful research tool, recognizing that its credibility depends much on the choice of the turbulence model to close the time- or ensemble-averaged conservation equations. Hybrid LES/RANS schemes (including detached eddy-simulations, DES), where LES is used in the flow bulk and a RANS model for the wall-adjacent, or complete wall-attached flow regions, are becoming popular and, by some in the community, are seen as the future industrial standard | ||
([[Best_Practice_Advice_AC6-15#15|Slotnick ''et al.'', 2014]]). | |||
Using the here reported experimental data and a fine-grid LES as the reference, we analyzed the performance of two levels of RANS models representing the LEVM and RSM families, the basic DES and LES with WALE sub-grid scale viscosity in reproducing not only the time-averaged basic flow and turbulence properties in the turbine draft tube, but also the flow patterns, vortical structures and their relation with the, industrially most critical, frequencies and amplitudes of pressure pulsations, all in the range of off-design conditions. The material presented here is based on the work published in [[Best_Practice_Advice_AC6-15#10|Minakov ''et al.'' (2017)]]. | Using the here reported experimental data and a fine-grid LES as the reference, we analyzed the performance of two levels of RANS models representing the LEVM and RSM families, the basic DES and LES with WALE sub-grid scale viscosity in reproducing not only the time-averaged basic flow and turbulence properties in the turbine draft tube, but also the flow patterns, vortical structures and their relation with the, industrially most critical, frequencies and amplitudes of pressure pulsations, all in the range of off-design conditions. The material presented here is based on the work published in [[Best_Practice_Advice_AC6-15#10|Minakov ''et al.'' (2017)]]. | ||
Revision as of 12:30, 26 November 2018
Vortex ropes in draft tube of a laboratory Kaplan hydro turbine at low load
Application Area 6: Turbomachinery Internal Flow
Application Challenge AC6-15
Description
Introduction
Computer simulations have been seen as a potential tool for capturing the subtleties of the development of instabilities and associated vortical and turbulence structures. Such information can be obtained by direct and large-eddy simulations (DNS, LES) over a range of important scales, but the accuracy of DNS and LES depends much on the numerical resolution. For complex configurations the Reynolds-averaged Navier-Stokes (RANS) approach, being computationally less demanding, has been considered as a more rational option for industrial purposes.
However, because of its empirical nature, the RANS approach in general has not been regarded as a trustful research tool, recognizing that its credibility depends much on the choice of the turbulence model to close the time- or ensemble-averaged conservation equations. Hybrid LES/RANS schemes (including detached eddy-simulations, DES), where LES is used in the flow bulk and a RANS model for the wall-adjacent, or complete wall-attached flow regions, are becoming popular and, by some in the community, are seen as the future industrial standard (Slotnick et al., 2014).
Using the here reported experimental data and a fine-grid LES as the reference, we analyzed the performance of two levels of RANS models representing the LEVM and RSM families, the basic DES and LES with WALE sub-grid scale viscosity in reproducing not only the time-averaged basic flow and turbulence properties in the turbine draft tube, but also the flow patterns, vortical structures and their relation with the, industrially most critical, frequencies and amplitudes of pressure pulsations, all in the range of off-design conditions. The material presented here is based on the work published in Minakov et al. (2017).
Contributed by: A. Minakov [1,2], D. Platonov [1,2], I. Litvinov [2], S. Shtork [2], K. Hanjalić [3] —
[1] Institute of Thermophysics SB RAS, Novosibirsk, Russia,
[2] Siberian Federal University, Krasnoyarsk, Russia,
[3] Delft University of Technology, Chem. Eng. Dept., Holland.