Current criteria used to determine whether rough surfaces affect skin friction typically rely on a single amplitude parameter to characterize the roughness. The most commonly used criteria relate the centerline averaged roughness, Ra, to an equivalent sandgrain roughness size, ks. This paper shows that such criteria are oversimplified and that Ra/ks is dependent on the roughness topography, namely, the roughness slope defined as the roughness amplitude normalized by the distance between roughness peaks, Ra/λ. To demonstrate the relationship, wake traverses were undertaken downstream of an aerofoil with various polished surfaces. The admissible roughness Reynolds number (ρ1u1Ra1) at which the drag rose above the smooth blade case was determined. The results were used to demonstrate a 400% variation in Ra/ks over the roughness topographies tested. The relationship found held for all cases tested, except those where the roughness first initiated premature transition at the leading edge. In these cases, where the roughness was more typical of eroded aerofoils, the drag was found to rise earlier.

References

References
1.
Bons
,
J. P.
,
2010
, “
A Review of Surface Roughness Effects in Gas Turbines
,”
ASME J. Turbomach.
,
132
(
2
), p.
021004
.
2.
Schlichting
,
H.
,
1962
,
Boundary Layer Theory
,
3rd ed.
,
McGraw-Hill
,
New York
.
3.
Goodhand
,
M. N.
,
2015
, “
Admissible Roughness in Turbomachines
,”
ASME
Paper No. GT2015-43326.
4.
Feindt
,
E. G.
,
1957
, “
Untersuchungen uber die Abhangigkeit des Umschlages laminar-turbulent von der Oberflachenrauhigkeit und der Druckverteilung
,” Diss. Braunschweig, Jb. 1956 Schiffbautechn. Gessellschaft 50, pp.
180
203
.
5.
Brinich
,
P. F.
,
1954
, “
Boundary Layer Transition at Mach 3.12 With and Without Single Roughness Element
,” Report No. NACA TN-3267.
6.
Küsters
,
B.
,
Schreiber
,
H. A.
,
Köller
,
U.
, and
Mönig
,
R.
,
2000
, “
Development of Advanced Compressor Airfoils for Heavy-Duty Gas Turbines, Part II: Experimental and Theoretical Analysis
,”
ASME J. Turbomach.
,
122
(
3
), pp.
406
415
.
7.
Henderson
,
A.
,
Walker
,
G. J.
, and
Hughes
,
J.
,
2008
, “
Unsteady Transition Phenomena at a Compressor Blade Leading Edge
,”
ASME J. Turbomach.
,
130
(
2
), p.
021013
.
8.
Tropea
,
C.
,
Yarin
,
A. L.
, and
Foss
,
J. F. F.
,
Springer Handbook of Experimental Fluid Dynamics
,
Springer-Verlag
,
Berlin
.
9.
Baals
,
D. D.
, and
Mourhess
,
M. J.
,
1945
, “
Numerical Evaluation of the Wake Survey Equations for Subsonic Flow Including the Effect of Energy Addition
,” NACA Report No. ARRL5H27.
10.
Walton
,
K.
,
2016
, “
High Fidelity Replication of Surface Texture and Geometric Form of a High Aspect Ratio Aerodynamic Test Component
,”
Surf. Topogr.: Metrol. Prop.
,
4
(
2
), p.
025003
.
You do not currently have access to this content.