Abstracts - KTH Mechanics

156
Direct numerical simulation of turbulent flow in a tilted
rotating duct
G. E. M˚artensson ∗ ,G.Brethouwer ∗ and A.V. Johansson ∗
Studying the effects of system rotation on turbulent flow is a most difficult and important
area of turbulence research. This area is of fundamental academic interest, as well
as of considerable industrial importance concerning applications such as centrifugal
separators and turbines. In centrifugal separator applications, the flow is subjected
to extremely high system rotation rates, the Rotation number being typically around
or above one. At these high Rotation numbers, the flow field in a plane channel is
strongly asymmetric and contains large zones of relaminarized flow on the stable side.
Recent experimental 1 and numerical studies 2 of the turbulent flow in rapidly rotating
square ducts have shown the importance of the specific geometric configuration.
In the present study, a direct numerical simulation of turbulent flow in a rotating
tilted square duct is carried out to further probe these geometric effects. The rotation
vector is in the (0,1,1) direction, see Figure 1. Simulations have been performed for
a set of Rotation numbers between 0 and 1, where the rotation number is defined as
Ro = Ω d/U, whereU is the mean flow velocity, Ω is the magnitude of the rotation
vector and d is a characteristic length of the duct. The Reynolds number, defined as
Re = (U d)/ν, whereν isthekinematicviscosityofthefluid,hasbeenchosentobe
4400. The change of the boundary layers owing to rotation has a pronounced effect
on the resistence in the duct, producing an increase compared to the non-tilted case.
The boundary layer configuration, as well as mean and turbulent quantities will be
presented, see for example Figure 1.
∗ KTH Mechanics, Osquarsbacke 18, S-100 44 Stockholm, Sweden.
1 M˚artensson, G.E., Gunnarsson, J., Johansson, A. V. and Moberg, H. 2002 ”Experimental investigation
of a rapidly rotating turbulent duct flow”, Exp. Fluids, 33, pp. 482–487.
2 M˚artensson, G.E., Brethouwer, G. and Johansson, A. V. 2005 ”Direct numerical simulation of
turbulent flow in a rotating duct”, Proceedings of TSFP-4, Williamsburg, VA, USA, 3, pp. 911–916.
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Figure 1: (a) Contour plot of the streamwise velocity u. (b) Combined contour and
vector plot of the secondary flow, v and w.
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