scholarly journals The Computation of Flow and Heat Transfer through an Orthogonally Rotating Square-Ended U-Bend Using Low-Reynolds-Number Models

2005 ◽  
Vol 2005 (3) ◽  
pp. 232-243 ◽  
Author(s):  
Konstantinos-Stephen P. Nikas ◽  
Hector Iacovides
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Direction ◽  
Low Reynolds Number ◽  
Main Flow ◽  
Moment Closure ◽  
Mean Flow ◽  
Flow And Heat Transfer ◽  
Second Moment Closure ◽  
Low Reynolds

We present computations of heat and fluid flow through a square-ended U-bend that rotates about an axis normal to both the main flow direction and also the axis of curvature. Two-layer and low-Reynolds-number mathematical models of turbulence are used at effective-viscosity (EVM) level and also at second-moment-closure (DSM) level. Moreover, two length-scale correction terms to the dissipation rate of turbulence are used with the low-Re models, the original Yap term, and a differential form that does not require the wall distance (NYap). The resulting predictions are compared with available flow and heat transfer measurements of water. While the main flow features are well reproduced by all models, the development of the mean flow within and just after the bend is better reproduced by the low-Re models. Turbulence levels within the rotating U-bend are underpredicted, but DSM models produce a more realistic distribution. Along the leading side, all models overpredict heat transfer levels just after the bend. Along the trailing side, the heat transfer predictions of the low-Re DSM with the NYap, are close to the measurements.

scholarly journals Turbulent Flow Computations in Rotating Cavities Using Low-Reynolds-Number Models

1996 ◽  
Author(s):  
Hector Iacovides ◽  
Kostas S. Nikas ◽  
Marcel A. F. Te Braak
Keyword(s):  
Reynolds Number ◽  
Dissipation Rate ◽  
Correction Term ◽  
Low Reynolds Number ◽  
Moment Closure ◽  
Rotating Disc ◽  
Moment Coefficient ◽  
Second Moment Closure ◽  
Low Reynolds ◽  
Radial Outflow

This study is concerned with the use of low-Reynolds-number models of turbulence transport in the computation of flows through rotating cavities. The models tested are the Launder and Sharma low-Re k-ε (L-S) and a low-Re differential second-moment closure (DSM), first used by Iacovides and Toumpanakis, both with and without the Yap correction term to the dissipation rate equation. The cases examined include rotor-stator systems without throughflow, rotor-stator systems with radial outflow, contra-rotating disc systems without throughflow and also with radial outflow, co rotating discs with radial outflow and also rotor-stator systems with radial inflow. Earlier studies have shown that, when no throughflow or when radial outflow is involved, the L-S tends to over-estimate the size of the regions over which the boundary layers remain laminar, while the zonal k-ε/l-eqn model is unable to predict partially laminarized flows. A modification to the ε equation proposed here, which in regions of low turbulence reduces the dissipation rate when the fluid is in solid body rotation, provides a simple empirical way to significantly improve the L-S predictions of partially laminarized flows through rotating cavities, to acceptable levels. The DSM model used, in some cases led to some further predictive improvements and, for rotor-stator systems without throughflow, to a significant improvement in the predicted value of the moment coefficient. The Yap length scale correction term, while in most cases it has either a beneficial or a neutral effect on the flow predictions, in cases involving radial inflow it leads to poorer predictions. Models that do not rely on wall distance thus appear more likely to have a wider range of applicability.

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