Roughness effects on a laminar separation bubble, formed on a flat plate boundary layer due to a strong adverse pressure gradient similar to those encountered on the suction side of typical low-pressure turbine blades, are studied by direct numerical simulation. The discrete roughness elements that have a uniform height in the spanwise direction and ones that have a height that is a function of the spanwise coordinate are modeled using the immersed boundary method. The location and the size of the roughness element are varied in order to study the effects on boundary development and turbulent transition; it was found that the size of the separation bubble can be controlled by positioning the roughness element away from the separation bubble. Roughnesses that have a height that varies in a periodic manner in the spanwise direction have a great influence on the separation bubble. The separation point is moved downstream due to the accelerated flow in the openings in the roughness element, which also prevents the formation of the recirculation region after the roughness element. The reattachment point is moved upstream, while the height of the separation bubble is reduced. These numerical experiments indicate that laminar separation and turbulent transition are mainly affected by the type, height, and location of the roughness element. Finally, a comparison between the individual influence of wakes and roughness on the separation is made. It is found that the transition of the separated boundary layer with wakes occurs at almost the same streamwise location as that induced by the three-dimensional roughness element.

References

References
1.
Pauley
,
L.
,
Moin
,
P.
, and
Reynolds
,
W.
,
1990
, “
The Structure of Two-Dimensional Separation
,”
J. Fluid Mech.
,
220
, pp.
397
411
.10.1017/S0022112090003317
2.
Wu
,
X.
,
Jacobs
,
R.
,
Hunt
,
J.
, and
Durbin
,
P.
,
1999
, “
Simulation of Boundary Layer Transition Induced by Periodically Passing Wakes
,”
J. Fluid Mech.
,
398
, pp.
109
153
.10.1017/S0022112099006205
3.
Wissink
,
J.
, and
Rodi
,
W.
,
2006
, “
Direct Numerical Simulation of Flow and Heat Transfer in a Turbine Cascade With Incoming Wakes
,”
J. Fluid Mech.
,
569
, pp.
209
247
.10.1017/S002211200600262X
4.
Gungor
,
A.
,
Simens
,
M.
, and
Jiménez
,
J.
,
2012
. “
Direct Numerical Simulations of Wake-Perturbed Separated Boundary Layers
,”
ASME J. Turbomach.
,
134
, p.
061024
.10.1115/1.4004882
5.
Hodson
,
H.
, and
Howell
,
R.
,
2005
, “
Blade Row Interactions, Transition, and High-Lift Aerofoils in Low-Pressure Turbines
,”
Annu. Rev. Fluid Mech.
,
37
, pp.
71
98
.10.1146/annurev.fluid.37.061903.175511
6.
Bons
,
J.
,
2010
, “
A Review of Surface Roughness Effects in Gas Turbines
,”
ASME J. Turbomach.
,
132
, pp.
1
16
.10.1115/1.3066315
7.
Vera
,
M.
,
Zhang
,
X.
,
Hodson
,
H.
, and
Harvey
,
N.
,
2007
, “
Separation and Transition Control on an Aft-Loaded Ultra-High-Lift LP Turbine Blade at Low Reynolds Numbers: High-Speed Validation
,”
ASME J. Turbomach.
,
129
, pp.
340
347
.10.1115/1.2437220
8.
Vera
,
M.
,
Hodson
,
H.
, and
Vazquez
,
R.
,
2005
, “
The Effects of a Trip Wire and Unsteadiness on a High-Speed Highly Loaded Low-Pressure Turbine Blade
,”
ASME J. Turbomach.
,
127
, pp.
747
757
.10.1115/1.1934446
9.
Zhang
,
X.
, and
Hodson
,
H.
,
2005
, “
Combined Effects of Surface Trips and Unsteady Wakes on the Boundary Layer Development of an Ultra-High-Lift LP Turbine Blade
,”
ASME J. Turbomach.
,
127
, pp.
479
488
.10.1115/1.1860571
10.
Lorenz
,
M.
,
Schulz
,
A.
, and
Bauer
,
H.-J.
,
2012
, “
Experimental Study of Surface Roughness Effects on a Turbine Airfoil in a Linear Cascade—Part II: Aerodynamic Losses
,”
ASME J. Turbomach.
,
134
, pp.
1
10
.10.1115/1.4003656
11.
Roberts
,
S.
and
Yaras
,
M.
,
2006
, “
Effects of Surface-Roughness Geometry on Separation-Bubble Transition
,”
ASME J. Turbomach.
,
128
, pp.
349
355
.10.1115/1.2101852
12.
Dovgal
,
A.
,
Kozlov
,
V.
, and
Michalke
,
A.
,
1994
, “
“Laminar Boundary Layer Separation: Instability and Associated Phenomena
,”
Prog. Aerosp. Sci.
,
30
, pp.
61
94
.10.1016/0376-0421(94)90003-5
13.
Abdessemed
,
N.
,
Sherwin
,
S.
, and
Theofilis
,
V.
,
2009
, “
Linear Instability Analysis of Low Pressure Turbine Flows
,”
J. Fluid Mech.
,
628
, pp.
57
83
.10.1017/S0022112009006272
14.
Reed
,
H.
,
Saric
,
W.
, and
Arnal
,
D.
,
1996
, “
Linear Stability Theory Applied to Boundary Layers
,”
Annu. Rev. Fluid Mech.
,
28
, pp.
389
428
.10.1146/annurev.fl.28.010196.002133
15.
Marxen
,
O.
,
Lang
,
M.
,
Rist
,
U.
,
Levin
,
O.
, and
Henningson
,
D.
,
2009
, “
Mechanisms for Spatial Steady Three-Dimensional Disturbance Growth in a Non-Parallel and Separating Boundary Layer
,”
J. Fluid Mech.
,
634
, pp.
165
189
.10.1017/S0022112009007149
16.
Marxen
,
O.
, and
Henningson
,
D.
,
2011
, “
The Effect of Small-Amplitude Convective Disturbances on the Size and Bursting of a Laminar Separation Bubble
,”
J. Fluid Mech.
,
671
, pp.
1
33
.10.1017/S0022112010004957
17.
Marxen
,
O.
, and
Rist
,
U.
,
2010
, “
Mean Flow Deformation in a Laminar Separation Bubble: Separation and Stability Characteristics
,”
J. Fluid Mech.
,
660
, pp.
37
54
.10.1017/S0022112010001047
18.
Simens
,
M.
,
Jiménez
,
J.
,
Hoyas
,
S.
, and
Mizuno
,
Y.
,
2009
, “
A High-Resolution Code for Turbulent Boundary Layers
,”
J. Comput. Phys.
,
228
, pp.
4218
4231
.10.1016/j.jcp.2009.02.031
19.
Simens
,
M.
,
2009
, “
The Study and Control of Wall Bounded Flows
,” Ph.D. thesis, Universidad Politécnica de Madrid, Madrid.
20.
Fadlun
,
E.
,
Verzicco
,
R.
,
Orlandi
,
P.
, and
Mohd-Yusof
,
J.
,
2000
, “
Combined Immersed-Boundary Finite-Difference Methods for Three-Dimensional Complex Flow Simulations
,”
J. Comput. Phys.
,
161
, pp.
35
60
.10.1006/jcph.2000.6484
21.
Mittal
,
R.
and
Iaccarino
,
G.
,
2005
, “
Immersed Boundary Methods
,”
Annu. Rev. Fluid Mech.
,
37
, pp.
239
261
.10.1146/annurev.fluid.37.061903.175743
22.
Uhlmann
,
M.
,
2005
, “
An Immersed Boundary Method With Direct Forcing for the Simulation of Particulate Flow
,”
J. Comput. Phys.
,
209
, pp.
448
476
.10.1016/j.jcp.2005.03.017
23.
Pinelli
,
A.
,
Naqavi
,
I.
,
Piomelli
,
U.
, and
Favier
,
J.
,
2010
, “
Immersed-Boundary Methods for General Finite-Difference and Finite-Volume Navier–Stokes Solvers
,”
J. Comput. Phys.
,
229
, pp.
9073
9091
.10.1016/j.jcp.2010.08.021
24.
Vanella
,
M.
, and
Balaras
,
E.
,
2009
, “
A Moving-Least-Squares Reconstruction for Embedded-Boundary Formulations
,”
J. Comput. Phys.
,
228
, pp.
6617
6628
.10.1016/j.jcp.2009.06.003
25.
Thwaites
,
B.
,
1949
, “
Approximate Calculation of the Laminar Boundary Layer
,”
Aeronaut. Q.
,
1
, pp.
61
85
.
26.
Curle
,
N.
, and
Skan
,
S. W.
,
1957
, “
Approximate Methods for Predicting Separation Properties of Laminar Boundary Layers
,”
Aeronaut. Q.
,
8
, pp.
257
268
.
You do not currently have access to this content.