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DIRECT NUMERICAL SIMULATIONS OF VARIABLE-ASPECT-RATIO TURBULENT DUCT FLOWS AT LOW TO MODERATE REYNOLDS NUMBERS

Ricardo Vinuesa
MMAE Department Illinois Institute of Technology Chicago, IL 60616, USA; Linne FLOW Centre, KTH Mechanics SE-100 44 Stockholm, Sweden

Azad Noorani
Swedish e-Science Research Centre (SeRC) Linne FLOW Centre, KTH Mechanics SE-100 44 Stockholm, Sweden

Adrian Lozano-Duran
School of Aeronautics Universidad Politecnica de Madrid 28040 Madrid, Spain

George K. El Khoury
Department of Marine Technology, The Norwegian University of Science and Technology NO-7491 Trondheim, Norway; Linne FLOW Centre KTH, Sweden

Phillipp Schlatter
Linne FLOW Centre and Swedish e-Science Research Centre (SeRC) KTH Mechanics, Royal Institute of Technology SE-100 44 Stockholm, Sweden

Paul F. Fischer
Mathematics and Computer Science Division, Argonne National Laboratory Argonne, IL 60439, USA

Hassan M. Nagib
MMAE, Illinois Institute of Technology, Chicago, IL 60616, USA

Abstract

Three-dimensional effects in turbulent duct flows, i.e., side-wall boundary layers and secondary motions, are studied by means of direct numerical simulations (DNS). The spectral element code Nek5000 is used to compute turbulent duct flows with aspect ratios 1 to 7 (at Rebc = 2800, Reτ ~ 180) and 1 (at Rebc = 5600, Reτ ~ 330) in streamwise-periodic boxes of length 25h. The total number of grid points ranges from 28 to 145 million, and the fluid kinematic viscosity ν was adjusted iteratively in order to keep the same bulk Reynolds number at the centerplane with changing aspect ratio. Spanwise variations in wall shear, mean-flow profiles and turbulence statistics are analyzed with aspect ratio, and also compared with the 2D channel. These computations show good agreement with experimental measurements carried out at IIT in parallel, and reinforces one important conclusion: the conditions obtained in the core region of a high-aspect-ratio duct cannot exactly be reproduced by spanwise-periodic DNSs of turbulent channel flows.