The computation of flow and heat transfer through an orthogonally rotating square-ended U-bend, using low-Reynolds-number models

Nikas, KSP

dc.contributor.author	Nikas, KSP	en
dc.date.accessioned	2014-03-01T01:55:43Z
dc.date.available	2014-03-01T01:55:43Z
dc.date.issued	2006	en
dc.identifier.issn	0961-5539	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/27814
dc.subject	heat transfer	en
dc.subject	rotational motion	en
dc.subject	flow	en
dc.subject	turbulent flow	en
dc.subject.classification	Thermodynamics	en
dc.subject.classification	Mathematics, Interdisciplinary Applications	en
dc.subject.classification	Mechanics	en
dc.subject.other	TURBULENCE	en
dc.subject.other	PASSAGES	en
dc.subject.other	PREDICTION	en
dc.subject.other	PROGRESS	en
dc.title	The computation of flow and heat transfer through an orthogonally rotating square-ended U-bend, using low-Reynolds-number models	en
heal.type	journalArticle	en
heal.language	English	en
heal.publicationDate	2006	en
heal.abstract	Purpose - To assess how effectively two-layer and low-Reynolds-number models of turbulence at, effective viscosity and second-moment closure level, can predict the flow and thermal development through orthogonally rotating U-bends. Design/rnethodology/approach - Heat and fluid flow computations through a square-ended U-bend that rotates about an axis normal to both the main flow direction and also the axis of curvature have been carried out. Two-layer and low-Reynolds-number mathematical models of turbulence are used at effective viscosity (EM level and also at second-moment-closure (DSM) level. In the two-layer models the dissipation rate of turbulence in the new-wall regions is obtained from the wall distance, while in the low-Re models the transport equation for the dissipation rate is extended right up to the walls. Moreover, two length-scale correction terms to the dissipation rate of turbulence are used with the low-Re models, and original Yap term and a differential form that does not require the wall distance (NYap). The resulting predictions are compared with available flow measurements at a Reynolds number of 100,000 and a rotation number (Omega D/U-bl) of 0.2 and also with heat transfer measurements at a Reynolds number of 36,000, rotation number of 0.2 and Prandtl number of 5.9 (water). Findings - While the main flow features are well reproduced by all models, the development of the mean flow within the just after the bend in better reproduced by the low-Re models. Turbulence levels within the rotation U-bend are under-predicted, but DSM models produce a more realistic distribution. Along the leading side all models over-predict heat transfer levels just after the bend. Along the trailing side, the heat transfer predictions of the fully low-Re DSM with the differential length-scale correction term NYap are close to the measurements, with an average error of around 10 per cent, though at the bend exit it rises to 25 per cent. The introduction of a differential form of the length-scale correction term to improve the heat transfer predictions of both low-Re models. Research/limitations/implications - The numerical models assumed that the flow remains steady and is not affected by large-scale, low frequency fluctuations. Unsteady RANS computations or LES must also be tested in the future. Originality/value - This work has expanded the range of complex turbulent flow over which the effectiveness of RANS models has been tested, to internal cooling flows simultaneously affected by orthogonal rotation and strong curvature.	en
heal.publisher	EMERALD GROUP PUBLISHING LIMITED	en
heal.journalName	INTERNATIONAL JOURNAL OF NUMERICAL METHODS FOR HEAT & FLUID FLOW	en
dc.identifier.isi	ISI:000242460600004	en
dc.identifier.volume	16	en
dc.identifier.issue	7-8	en
dc.identifier.spage	827	en
dc.identifier.epage	844	en