Abstracts - KTH Mechanics

20
Large eddy simulation of the turbulent field in a channel with
oscillating walls
D. Tordella ∗ , P.R.Bailey † ,M.Iovieno ∗
Large eddy simulation of the incompressible Navier-Stokes field are employed to
study the turbulent stresses in a channel flow forced by longitudinal sinusoidal oscillations
of the walls, which is a kind of flow forcing not yet considered in literature. The
two walls move in phase. The aim is the production of a friction reduction database
which can be associated to the spanwise wall oscillation data base, which gathers numerical
and laboratory results 1 . The calculations are performed at a Reynolds number
Reτ = 590, based on the friction velocity uτ of the unforced case, and on h, halfthe
channel width. In this condition, we compute a maximum drag reduction of 12% for
a dimensionless oscillation period of about half viscous units, T + = Tuτ/h ≈ 0.5, and
an amplitude equal to the friction velocity.
The instantaneous wall boundary conditions we recently proposed for resolved
large scale simulations that extend inside the viscous sublayer are used 2 . These conditions
transfer the physical no-slip and impermeability conditions, which can only be
rigorously applied to the unfiltered variables, to the filtered variables. Since the filter
scale close to the wall is increasing with the distance from the wall, this bondaury
condition is used together with the explicit noncommutation procedure 3 . The subgrid
turbulence model employed is the differential Intrinsic Angular Momentum model 4 ,
which, being based on the representation of the turbulent viscosity through a vectorial
quantity – the moment of momentum vector – may reproduce the anisotropic
non-equilibrium near wall turbulence. The wall function model is not employed. A
comparison with both experimental and numerical spanwise oscillation results will be
given.
∗Politecnico di Torino, DIASP, Cso Duca Abruzzi 24, 10129 Torino, Italy.
† Politecnico di Torino, Scuola di Dottorato, Cso Duca Abruzzi 24, 10129 Torino, Italy.
1see e.g. Iuso et al., Phys. Fluids 15, 9 (2003), Quadrio and Ricco, J. Fluid Mech. 521, 251
(2004)
2Iovieno et al., Phys. Fluids 16, 10 (2004)
3Iovieno and Tordella, Phys. Fluids 15, 7 (2003)
4Iovieno and Tordella, Phys. Fluids 14, 2673 (2002)
Stress reduction (%)
10
5
T +
0
0 0.2 0.4 0.6 0.8 1
Figure 1: Stress reduction (L ∞ norm) as function of the dimensionless period.