Large-eddy simulations of transitional flows over a flat plate have been performed for different sets of free-stream-turbulence conditions. Interest focuses, in particular, on the unsteady processes in the boundary layer before transition occurs and as it evolves, the practical context being the flow over low-pressure turbine blades. These considerations are motivated by the wish to study the realism of a RANS-type model designed to return the laminar fluctuation energy observed well upstream of the location at which transition sets in. The assumptions underlying the model are discussed in the light of turbulence-energy budgets deduced from the simulations. It is shown that the pretransitional field is characterized by elongated streaky structures which, notwithstanding their very different structural properties relative to fully established turbulence, lead to the amplification of fluctuations by conventional shear-stress/shear-strain interaction, rather than by pressure diffusion, the latter being the process underpinning the RANS-type transitional model being investigated.

1.
Lardeau
,
S.
,
Leschziner
,
M.
, and
Li
,
N.
, 2004, “
Modelling Bypass Transition With Low-Reynolds-Number Non-Linear Eddy-Viscosity Closure
,”
Flow, Turbul. Combust.
1386-6184,
73
, pp.
49
76
.
2.
Mayle
,
R.
, and
Schulz
,
A.
, 1997, “
The Path to Predicting Bypass Transition
,”
ASME J. Turbomach.
0889-504X,
119
, pp.
405
411
.
3.
Lardeau
,
S.
, and
Leschziner
,
M.
(2006). “
Unsteady RANS Modeling of Wake-Induced Transition in Linear LP-Turbine Cascades
,”
AIAA J.
0001-1452,
44
(
6
), pp.
1845
1865
.
4.
Matsubara
,
M.
, and
Alfredsson
,
P. H.
, 2001, “
Disturbance Growth in Boundary Layers Subjected to Freestream Turbulence
,”
J. Fluid Mech.
0022-1120,
430
, pp.
149
168
.
5.
Jacobs
,
R.
, and
Durbin
,
P.
, 2001, “
Simulations of Bypass Transition
,”
J. Fluid Mech.
0022-1120,
428
, pp.
185
212
.
6.
Brandt
,
L.
,
Schlatter
,
P.
, and
Henningson
,
D.
, 2004, “
Transition in Boundary Layers Subject to Free-Stream Turbulence
,”
J. Fluid Mech.
0022-1120,
517
, pp.
167
198
.
7.
Jonáš
,
P.
,
Mazur
,
O.
, and
Uruba
,
V.
, 2000, “
On the Receptivity of the By-Pass Transition Length Scale of the Outer Stream Turbulence
,”
Eur. J. Mech. B/Fluids
0997-7546,
19
, pp.
707
722
.
8.
Voke
,
P.
, and
Yang
,
Z.
, 1995, “
Numerical Study of Bypass Transition
,”
Phys. Fluids
1070-6631,
7
(
9
), pp.
2256
2264
.
9.
Meneveau
,
C.
,
Lund
,
T.
, and
Cabot
,
W.
, 1996, “
A Lagrangian Dynamic Subgrid-Scale Model of Turbulence
,”
J. Fluid Mech.
0022-1120,
319
, pp.
353
385
.
10.
Sarghini
,
F.
,
Piomelli
,
U.
, and
Balaras
,
E.
, 1999, “
Scale-Similar Models for Large-Eddy Simulations
,”
Phys. Fluids
1070-6631,
11
(
6
), pp.
1596
1607
.
11.
Rogallo
,
R.
, 1981, “
Numerical Experiments in Homogeneous Turbulence
,” Tech. Memo No. 81315,
NASA
, Washington, D.C.
12.
Pope
,
S. B.
, 2000,
Turbulent Flows
,
Cambridge University Press
,
Cambridge, UK
, pp.
160
161
.
13.
Hunt
,
J. C. R.
, and
Durbin
,
P.
, 1999, “
Perturbed Shear Layers
,”
Fluid Dyn. Res.
0169-5983,
24
, pp.
375
404
.
14.
Zaki
,
T. A.
, and
Durbin
,
P. A.
, 2005, “
Mode Interaction and the Bypass Route to Transition
,”
J. Fluid Mech.
0022-1120,
531
, pp.
85
111
.
This content is only available via PDF.
You do not currently have access to this content.