Abstr:Unsteady near-field plume: Difference between revisions
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This document examines the Underlying Flow Regime of a turbulent, | This document examines the Underlying Flow Regime of a turbulent, | ||
non | non-reacting plume flowing into a quiescent and unstratified | ||
environment. Only the unsteady flow behaviour in the near | environment. Only the unsteady flow behaviour in the near-field is | ||
considered, within the region extending up to around five diameters | considered, within the region extending up to around five diameters | ||
downstream from the source. Figure 1 shows a CFD simulation of such a | downstream from the source. Figure 1 shows a CFD simulation of such a | ||
plume. The fully | plume. The fully-developed, far-field behaviour of turbulent plumes | ||
is examined in a related UFR. | is examined in a [[Axisymmetric_buoyant_far-field_plume|related UFR]] (UFR 1-06). | ||
Turbulent buoyant plumes are a feature of many important scientific and | Turbulent buoyant plumes are a feature of many important scientific and | ||
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Medium to large scale plumes are characterised by the repetitive | Medium to large scale plumes are characterised by the repetitive | ||
shedding of coherent vortical structures at a well | shedding of coherent vortical structures at a well-defined frequency, | ||
a phenomenon known as | a phenomenon known as “puffing”. A number of empirical | ||
correlations for the puffing frequency of plumes have been developed, | correlations for the puffing frequency of plumes have been developed, | ||
based on the Richardson number, which are described in this UFR. | based on the Richardson number, which are described in this UFR. | ||
A brief review is provided of near | A brief review is provided of near-field plume experiments and CFD | ||
studies. Three CFD studies are examined in greater detail, those by | studies. Three CFD studies are examined in greater detail, those by | ||
DesJardin | DesJardin ''et al.'' [[UFR_1-07_References#1|[1]]], | ||
Tieszen ''et al.'' [[UFR_1-07_References#2|[2]]] and Xin [[UFR_1-07_References#3|[3]]]. | |||
These have all simulated the recent helium plume experiments of | These have all simulated the recent helium plume experiments of | ||
O | O‘Hern ''et al.'' [[UFR_1-07_References#4|[4]]]. The studies have each used | ||
slightly different numerical modelling approaches, although all are | slightly different numerical modelling approaches, although all are | ||
based on Large | based on Large-Eddy Simulation (LES). The plume experiments | ||
O | O‘Hern ''et al.'' [[UFR_1-07_References#4|[4]]] are particularly | ||
well | well-suited for model evaluation as they involved simultaneous | ||
measurement of velocities and mass fraction, allowing both Reynolds and | measurement of velocities and mass fraction, allowing both Reynolds and | ||
Favre | Favre-averaged quantities to be determined. | ||
Based on the three CFD studies, best practice advice is provided for | Based on the three CFD studies, best practice advice is provided for | ||
| Line 62: | Line 63: | ||
<center>'''Figure 1 ''' CFD Simulation of the near-field of a buoyant helium plume. | <center>'''Figure 1 ''' CFD Simulation of the near-field of a buoyant helium plume. | ||
The vorticity isosurface is coloured with the magnitude of the gravitational torque. From DesJardin ''et al.'' [[UFR_1-07_References|[1]]] </center> | The vorticity isosurface is coloured with the magnitude of the gravitational torque. From DesJardin ''et al.'' [[UFR_1-07_References#1|[1]]] </center> | ||
====Acknowledgements==== | |||
The author would like to thank Sheldon Tieszen (Sandia), Paul DesJardin | |||
(University at Buffalo, NY), Yibing Xin (FM Global), Wolfgang Rodi | |||
(Karlsruhe) and Chris Lea (Lea CFD) for their help and assistance in | |||
preparing this review. | |||
{{ACContribs | {{ACContribs | ||
Latest revision as of 11:44, 14 January 2022
Free Flows
Underlying Flow Regime 1-07
Abstract
This document examines the Underlying Flow Regime of a turbulent, non-reacting plume flowing into a quiescent and unstratified environment. Only the unsteady flow behaviour in the near-field is considered, within the region extending up to around five diameters downstream from the source. Figure 1 shows a CFD simulation of such a plume. The fully-developed, far-field behaviour of turbulent plumes is examined in a related UFR (UFR 1-06).
Turbulent buoyant plumes are a feature of many important scientific and engineering applications including flows generated by fires, smokestacks, cooling towers, and large geothermal events, such as volcanoes. The source of the buoyancy may be provided by temperature differences in the fluid or can be related to two fluids of different density mixing together.
Medium to large scale plumes are characterised by the repetitive shedding of coherent vortical structures at a well-defined frequency, a phenomenon known as “puffing”. A number of empirical correlations for the puffing frequency of plumes have been developed, based on the Richardson number, which are described in this UFR.
A brief review is provided of near-field plume experiments and CFD studies. Three CFD studies are examined in greater detail, those by DesJardin et al. [1], Tieszen et al. [2] and Xin [3]. These have all simulated the recent helium plume experiments of O‘Hern et al. [4]. The studies have each used slightly different numerical modelling approaches, although all are based on Large-Eddy Simulation (LES). The plume experiments O‘Hern et al. [4] are particularly well-suited for model evaluation as they involved simultaneous measurement of velocities and mass fraction, allowing both Reynolds and Favre-averaged quantities to be determined.
Based on the three CFD studies, best practice advice is provided for industrial CFD practitioners on some key modelling issues involved in simulating unsteady buoyant plumes.
LES is less mature than RANS turbulence modelling and a number of uncertainties remain when using LES for industrial flow predictions, such as the appropriate grid resolution and the choice of numerical schemes. Some guidance is given on these issues and suggestions are provided for where future work could contribute to providing improved quality and trust in the simulation of plumes.
Acknowledgements
The author would like to thank Sheldon Tieszen (Sandia), Paul DesJardin (University at Buffalo, NY), Yibing Xin (FM Global), Wolfgang Rodi (Karlsruhe) and Chris Lea (Lea CFD) for their help and assistance in preparing this review.
Contributed by: Simon Gant — UK Health & Safety Laboratory
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