Direct Numerical Simulation of a Spatially Advancing Turbulent Flow in a Two-Dimensional Curved Channel

Abstract

Direct numerical simulation was performed for a spatially advancing turbulent flow in a two-dimensional curved channel. Fully developed turbulence generated by straight channel simulation was used as the inlet value of curved part simulation. The radius ratio of the curved part, α, was set 0.92, the same as Kobayashi et al.'s experiment. However, the frictional Reynolds number, Reτ0, was assigned 150, which was roughly quarter the experiment and allowed direct simulation of all the essential scale of turbulence. Computation was made for three cases changing domain size, and mainly discussed was the results from the computational volume extending 150° with spanwise length of 7.2 times channel half width. In this case, total number of 512×61×128 grid points was allocated. Numerically solved mean velocity showed trends consistent with the experiment in spite of the Reynolds number difference. Mean velocity normalized by the local frictional velocity indicated upward and downward offset of the logarithmic region, respectively, in the inner and outer side of the channel, but simulation showed stronger laminarization near the inner wall due to the low Reynolds number effect. Numerical data of mean velocity field illustrated that characteristic behavior of ejection from the outer wall and streamwise vortices appeared with advancement of large scale vortices. Power spectrum analysis implied that coherent structures near the outer wall were related to the birth and formation of large scale vortices.