Ft. Smith et Ag. Walton, FLOW PAST A 2-DIMENSIONAL OR 3-DIMENSIONAL STEEP-EDGED ROUGHNESS, Proceedings - Royal Society. Mathematical, physical and engineering sciences, 454(1968), 1998, pp. 31-69
Citations number
42
Categorie Soggetti
Multidisciplinary Sciences
Journal title
Proceedings - Royal Society. Mathematical, physical and engineering sciences
Flow past a single small planar or three-dimensional roughness mounted
on a smooth surface is investigated theoretically for various edge st
eepnesses, the oncoming planar motion being within a boundary layer or
other near-wall shear. Nonlinear edge properties at large Reynolds nu
mbers largely control the flow responses at the three-dimensional roug
hness wing-tips and the impacts of separation(s), among other features
. From analysis and computation, criteria are found for the generation
of nonlinear upstream influence, downstream influence and separations
, for two-and three-dimensional roughnesses, as well as wing-tip separ
ations. In particular, it is predicted that with a severe edge (e.g. a
90 degrees forward-facing step) the ratio of the upstream separation
distance over the roughness edge height is a constant times Re-W(1/4)
in two dimensions, the constant being approximately 0.142 and the Reyn
olds number Re-W being based on the roughness edge height and the inci
dent velocity slope at the surface. In three dimensions Re-W is multip
lied by sin psi, as expected physically, where psi is the tangent angl
e of the roughness planform. The ratio prediction above is very genera
l, applying not only for any incident shear flow, but also for any fro
nt-edge geometry. Other separation and reattachment properties, extens
ions and a comparison with an experiment, are also discussed.