3D numerical modeling of non-isotropic turbulent buoyant helicoidal flow and heat transfer in a curved open channel Yong-Ming Shen a, * , Chiu-On Ng b , Hao-Qing Ni a a State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116023, PR China b Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, PR China Received 29 September 2002 Abstract A3Dnon-isotropicalgebraicstress/fluxturbulencemodelisemployedtosimulateturbulentbuoyanthelicoidalflow andheattransferinarectangularcurvedopenchannel.Thepredictionshowsthat,unliketheisothermalflow,thereare two major and one minor secondary flow eddies in a cross section of thermally stratified turbulent buoyant helicoidal flow in a curved open channel. The results compare favorably with available experimental data. The thermocline in a curved channel is thicker than that in a straight channel. All of these is the result of complex interaction between the buoyantforce,thecentrifugalforceandtheReynoldsstresses.Theturbulentflowinacurvedchannelisobviouslynon- isotropic: the turbulence fluctuations in vertical and radial directions are lower in magnitude than that in the axial direction, which illustrates the suppression of turbulence due to buoyant and centrifugal forces. The results are of significantpracticalvaluetoengineeringworkssuchasthechoiceofsitesforintakeandpollutant-dischargestructures in a curved river. Ó 2003 Elsevier Science Ltd. All rights reserved. Keywords: Curved open channel; Non-isotropic turbulent flow; Stratification; Buoyancy; 3D numerical modeling 1. Introduction The disposal of waste heat into natural watercourses fromindustrialandpowergenerationprocessesposesan increasing threat to the worldÕs fresh water resources. It is important, on the part of environmental hydraulic engineers, to understand the hydrodynamics of the flow andheattransportincurvedchannelsinordertobeable to assess the impact caused by thermal pollution on a natural stream. Turbulent buoyant helicoidal flow in a curved channel can be considered as one of the most complex fluid-flow situations encountered in the envi- ronmentowingtothefactthattheflowisturbulentand stronglythreedimensional.Therearemarkedsecondary motions in cross sections normal to the streamwise di- rection. Induced by complex interactions between the buoyant force, the centrifugal force and the Reynolds stresses, the secondary motions can be organized to emerge in the form of three-dimensional helicoidal flow that may in return modify the characteristics of the primary flow, sediment transport and heat transfer in the channel. In particular, these secondary motions can significantly enhance the rate of lateral spreading of substances released to the channel. Knowledge of the hydrodynamic and heat transport processes in curved open-channel flow is of significant practical value, for such knowledge is required for the design of preventive measures against silting and for the choice of sites for intake and pollutant-discharge structures in a river. Despite the practical importance, the understanding of the hydrodynamics of turbulent buoyant helicoidal flow and heat transfer has been very limited. In the past two decades, various 3D numerical models have been used to simulate curved channel flow, which include notably the works by Leschziner and Rodi [1], De Vriend [2], Galmes and Lakshminarayana [3], Demuren and Rodi [4], Shimizu et al. [5], Demuren [6],Sinhaetal.[7],YeandMcCorquodale[8],Wuetal. * Corresponding author. Fax: +86-411-470-8526. E-mail address: ymshen@dlut.edu.cn (Y.-M. Shen). 0017-9310/03/$ - see front matter Ó 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0017-9310(02)00501-X International Journal of Heat and Mass Transfer 46 (2003) 2087–2093 www.elsevier.com/locate/ijhmt