Flow field analysis of partially porous coated cylinders on the
leeward side
Katharina Klausmann, Bodo Ruck, January 10, 2017
Laboratory of Building- and Environmental Aerodynamics, Institute for Hydromechanics.
Flows around circular cylinders are ubiquitous in the natural and built environment. For instance, flows around
towers, bridge cables, bridge piers or pipelines are some examples concerning the field of building
aerodynamics. Also in many other fields like technical or chemical applications, the flow around cylinders
plays an important role. The fluid mechanics of the flow around smooth circular cylinders is best known and
for a wide range of Reynolds numbers detailed information about flow separation, near and far wake and
pressure distribution is available. There exist also investigations of active or passive flow control methods
which lead to a reduction of drag. Typical passive control devices are based on surface modification for
example by roughness, textures, patterns, longitudinal grooves or dimples (Achenbach 1971, Shih et al. 1993,
Bechert & Hoppe 1985, Frohnapfel et al. 2007, Bearman & Harvey 1993, Choi et al. 2006).
The motivation of our previous work was to find out whether or not partial coating of cylinders on the leeward
side with porous foam material can be applied for drag reduction of cylinders submersed in a flow.
Systematic force and pressure measurements of partially porous coated cylinders on the leeward side were
carried out and the study showed that the effect of leeward porous coating clearly exists. The results of the
measurements indicated that a leeward porous coating leads to a drag reduction of up to 13.2 %.
For a better understanding of the phenomenology of the flow around such porous coated cylinders a flow field
analysis was performed by 2D TR-PIV-measurements in the present study.
Compared to a smooth cylinder the results indicate that a porous layer leads to a decrease in strength of the
normal stress patterns and the lateral normal stress is shifted further downstream. The turbulent kinetic
energy in the near wake is reduced due to the leeward porous layer and, therefore, less fluctuations exist in
the near wake. An inflow into the porous layer takes place at the rear side of the cylinder which could be
shown by the instantaneous streamwise velocity component at centerline position.
Streamwise normal stress.
Turbulent kinetic energy.