S. Tullis et A. Pollard, MODELING THE TIME-DEPENDENT FLOW OVER RIBLETS IN THE VISCOUS WALL REGION, Applied scientific research, 50(3-4), 1993, pp. 299-314
The flow over riblets is examined computationally using a time depende
nt model of the viscous wall region. This ''21/2 D model'', developed
by Hatziavramidis and Hanratty (1979) and modified by Nikolaides (1984
) and Chapman and Kuhn (1981, 1986) assumes homogeneity in the streamw
ise direction so that the flow is solved only in the cross-sectional p
lane. The flow at the upper boundary of the computational domain (y+ c
ongruent-to 40) is described using a streamwise eddy model consisting
of two scales, one of the streak spacing (lambda+ congruent-to 100), w
hich dominates vertical momentum transport, and a larger scale that ac
counts for the influence of large outer flow eddies. The protrusion he
ight concept (Bechert and Bartenwerfer, 1989) is used to define a y+ =
0 location for surfaces with riblets. A control volume finite element
method utilizing triangular meshes is used to exactly fit the riblet
cross-sectional geometry. Results obtained using fairly large riblets
compare well with the limited experimental evidence available. Observa
tions of the transient flow suggest that the riblets interact with the
near-wall streamwise vortices, weakening them by the generation of in
termittent secondary vortices within the riblet valleys. The riblets a
lso appear to limit the lateral spread of inrushes towards the wall an
d retain low momentum fluid in the riblet valleys effectively isolatin
g much of the wall from such inrushes.