Direct numerical simulations of variable-aspect-ratio turbulent duct flows at low to moderate reynolds numbers

• 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 Reb, c = 2800, Reτ 180) and 1 (at Reb, c = 5600, Reτ 330) in streamwiseperiodic boxes of length 25h. The total number of grid points ranges from 28 to 145 million, and the fluid kinematic viscosity n 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.

Subject headings

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Strömningsmekanik och akustik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Fluid Mechanics and Acoustics (hsv//eng)

Keyword

Boundary layers

C (programming language)

Channel flow

Direct numerical simulation

Ducts

Numerical models

Reynolds number

Shear flow

Turbulence

Wall flow

High aspect ratio

Mean flow profiles

Moderate Reynolds numbers

Spanwise variations

Spectral element

Three dimensional effect

Turbulence statistics

Turbulent channel flows

Aspect ratio

Publication and Content Type

ref (subject category)

kon (subject category)