Present study employed the large eddy simulation technique
to simulate the turbulent Couette-Poiseuille flow inside a square duct which are among the very few reported literatures. A semi-implicit, fractional step method proposed by Choi and Moin(1994) and the finite volume method are employed to solve the filtered incompressible Navier-Stokes equations. In order to meet the intensive computational demand by the large eddy simulation, the
SPMD and MPI library have been employed for realizing the parallel processing.

Four turbulent flows were simulated in the same square
duct, including one Poiseuille flow and three Couette-Poiseuille flows where the bulk Reynolds number is kept around 9700. The present numerical procedure was validated by computing the Poiseuille flow, which was then used as base to explore influences of the moving wall on Couette-Poiseuille duct flows. The turbulence generated secondary flow is modified by the presence of the top moving wall, where the symmetric vortex pattern vanishes. The angle
between two top vortices is found to correlate with the ratio of moving wall velocity to duct bulk velocity.

Turbulence level is reduced near the moving wall due to
the insufficient mean shear rates. However, the damping of
turbulence near the moving wall is non-isotropic with maximum damping presented in the streamwise direction. The dominant Reynolds normal and shear stress component near the moving wall is <u'u'> and <u'w'>, respectively. The resulting transverse turbulence intensities distribution is found to be beneficial for vertical than horizontal mean motion along the top corner bisector which can
explain the distortion of symmetric vortex pair near the moving wall. The spatial correlation between the structure parameter and <u'w'>/2k further demonstrates that the
turbulence extracting energy from mean fields primarily through the shear stress component <u'w'> near the moving wall.

The turbulence anisotropy invariant map (AIM) shows that
along the wall bisector at the top half of the duct, turbulence structure gradually moves towards a rod-like axi-symmetric state as the moving wall velocity increases. The relative increase of <u'u'> to <w'w'> is responsible for this tendency towards the rod-like state near the moving wall. In general, turbulence anisotropy level is reduced along the wall-bisector near the moving wall.

The generation of mean secondary flow in the square duct
is examined by the streamwise vorticity transport equation. For the Couette-Poiseuille flow, the moving wall reduces the level of the shear stress contribution, while the levels of the normal stress are only slightly affected. For case CP3, the maximum shear stress contribution is only two third of the normal stress contribution. For the generation of the larger vortex near the top corners, the
normal stress contribution is the primary production mechanism where the viscous diffusion and shear stress contribution are acted as transport mechanisms.

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