A. Orellano et H. Wengle, Numerical simulation (DNS and LES) of manipulated turbulent boundary layerflow over a surface-mounted fence, EUR J MEC B, 19(5), 2000, pp. 765-788
Results from numerical simulations are presented for manipulated turbulent
boundary layer flow over a surface-mounted fence, for a Reynolds number of
Re-h = 3000 (based on fence height, h, and maximum inflow velocity, U-infin
ity) First, a reference data set was provided from a Direct Numerical Simul
ation (DNS) using 51.6 million grid points to resolve all the relevant spat
ial scales of the flow. A Large-Eddy Simulation (LES), using 1.67 million g
rid points, was validated with this reference solution and compared with ex
perimental data for the same Reynolds number. Then, manipulated flow cases
were investigated applying time-periodic forcing through a narrow slot upst
ream of the Row obstacle. High-frequency forcing, with Str(1) = f(1)h/U-inf
inity = 0.60, leads to about 10% reduction of the mean re-attachment length
. A much stronger reduction of about 36% could be achieved by low-frequency
forcing with Str(2) = f(2)h/U-infinity = 0.08. In the latter case, large-s
cale coherent structures are created between the location of the disturbanc
e and the fence, they roll over the flow obstacle (nearly unaffected) and i
n rolling downstream they still grow in size until they fill out the entire
height of the separation zone behind the fence. In agreement with correspo
nding experiments of Siller and Fernholz in 1997 for a higher Reynolds numb
er (Re-h = 10500) the optimum forcing Strouhal number seems to be related t
o the low-frequency movement of the entire separation bubble and not to the
instability mode of the separating shear layer. (C) 2000 Editions scientif
iques et medicales Elsevier SAS (C) 2000 Editions scientifiques et medicale
s Elsevier SAS.