Turbulence Budgets in Buoyancy-affected Vertical Backward-facing Step Flow at Low Prandtl Number

Niemann, Martin; Fröhlich, Jochen

doi:10.1007/s10494-017-9862-6

Cited by 18 publications

(13 citation statements)

References 41 publications

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“…The temperature at the heated wall shows only slight variation in spanwise direction for the average value. This is, however, also observed for instantaneous temperature which showed notable variation in spanwise direction in the periodic cases also at this Reynolds number [3]. With side walls, the spanwise variation of (instantaneous) temperature is small and surpassed by variations in streamwise direction.…”

Section: Flow Behind a Sudden Expansionsupporting

confidence: 65%

“…Mech. 17 (2017) www.gamm-proceedings.com the shear layer are well resolved (see also [3]). The spanwise z-direction is discretized using 212 cells which are clustered towards the side walls to also resolve the boundary layers there.…”

Section: Flow Behind a Sudden Expansionmentioning

confidence: 92%

“…Two regimes of buoyancy impact are considered, namely the forced regime (Ri = 0) and the mixed convection regime at Ri = 0.2. The parameters and domain are chosen to allow comparison with the results reported for the spanwise periodic configuration in [3]. For both simulations, the grid in x-and y-direction is the same as in the periodic cases so that the boundary layers at the walls and PAMM · Proc.…”

Section: Flow Behind a Sudden Expansionmentioning

confidence: 99%

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Heated vertical duct flow of liquid metal with and without expansion

Niemann

Saini

Fröhlich

2017

Proc Appl Math and Mech

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The effects of buoyancy on vertical duct flows with one heated side wall are investigated by means of Direct Numerical Simulations. In particular, the flow through square ducts and behind the expansion of a backwardfacing step with side walls are presented for the forced and mixed convection regime. These configurations allow studying the interaction of buoyancy forces with secondary flow of second kind in the square duct and with the shear layer and recirculation zone in case of the expansion. In both configurations, buoyancy substantially alters the mean flow field, the turbulent stresses, and the heat transfer compared to the corresponding forced convection cases.

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Section: Flow Behind a Sudden Expansionsupporting

confidence: 65%

Section: Flow Behind a Sudden Expansionmentioning

confidence: 92%

Section: Flow Behind a Sudden Expansionmentioning

confidence: 99%

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Heated vertical duct flow of liquid metal with and without expansion

Niemann

Saini

Fröhlich

2017

Proc Appl Math and Mech

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“…Although it is most commonly used in simple geometries, 9 it is not limited to such and today's simulations are performed in different geometries. Among the recent examples is flow in the BFS geometry with natural convection, 10 and a complex DNS of pebble bed reactor by Fick et al 11 The largest DNS runs performed in the past years are by Lee and Moser: 12 channel flow DNS of at friction Reynolds number around 5200 with approximately 1.2 × 10 11 points. Similar DIRECT NUMERICAL SIMULATION AND WALL-RESOLVED LES · TISELJ et al 3…”

Section: Ie Brief History Of Nuclear-related Dns and Lesmentioning

confidence: 99%

“…38), while the most recent DNS of heat transfer in this geometry can be found in Ref. 10 where the buoyant flow pattern in the BFS geometry with the expansion ratio 2 at Reynolds number of 10 000 (based on step height and bulk velocity at inlet) and Prandtl number of sodium, Pr = 0.0088, was analyzed with one (spanwise) homogeneous dimension. Our research is focused on thermal fluctuations in the BFS geometry with solid walls.…”

Section: Dns In Nuclear Thermal Hydraulics: Some Examplesmentioning

confidence: 99%

Direct Numerical Simulation and Wall-Resolved Large Eddy Simulation in Nuclear Thermal Hydraulics

2019

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The critical review discusses the most accurate methods for description of turbulent flows: the computationally very expensive direct numerical simulation (DNS) and slightly less accurate and slightly less expensive large eddy simulation (LES) methods. Both methods have found their way into nuclear thermal hydraulics as tools for studies of the fundamental mechanisms of turbulence and turbulent heat transfer. In the first section of this critical review, both methods are briefly introduced in parallel with the basic properties of the turbulent flows. The focus is on the DNS method, the so-called quasi-DNS approach, and the coarsest turbulence modeling approach discussed in this work, which is still on the very small-scale, wall-resolved LES. Other, coarser turbulence modeling approaches (such as wall-modeled LES, Reynolds Averaged Navier-Stokes (RANS)/LES hybrids, or RANS) are beyond the scope of the present work. Section II answers the question: "How do the DNS and LES methods work?" A short discussion of the computational requirements, numerical approaches, and computational tools is included. Section III is about the interpretation of the DNS and LES results and statistical uncertainties. Sections IV and V give some examples of the DNS and wall-resolved LES results relevant for nuclear thermal hydraulics. The last section lists the conclusions and some of the challenges that might be tackled with the most accurate techniques like DNS and LES.

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