David B. Goldstein1, Tai-Chang Tuan2
1Department of Aerospace Engineering and Engineering Mechanics, The University of Texas at Austin, Austin, TX 78712 USA
2University of Texas at Austin#TAB#
Tóm tắt
The effects of riblets on one wall of a channel bounding fully
developed turbulent
flow are investigated. Various perturbation elements including wires, fins
and slots are
modelled in order to understand the effects of riblets. It is found that
widely spaced
riblets, fins and wires create a substantial increase in turbulent activity
just above the
element. These elements are also found to produce a remarkable pattern
of secondary
mean flows consisting of matched pairs of streamwise vortices. The secondary
flows
occur only if the bulk flow is turbulent and their characteristics depend
on element
geometry. It is suggested that these secondary flows are strongly linked
with the
increase in drag experienced by widely spaced riblets in experimental studies.
The
secondary flows are probably caused by two-dimensional spanwise sloshing
of the flow,
inherent in a turbulent boundary layer, interacting with the stream-aligned
element.
This two-dimensional mechanism is investigated with a series of two-dimensional
simulations of sloshing flow over isolated elements. Grid resolution and
domain size
checks are made throughout the investigation.
