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Experiments on flow-induced vibrations using a close-packed
triangular rod array with a pitch-to-diameter ratio of 1.1
in water cross-flow was carried out and data analysis performed.
The bundle consists of 21 rows with
five rods in each. One flexibly mounted test rod (TR) is located in the
fourth row in an otherwise fixed array. The rod can freely
move in the transverse and in-line direction.
Two accelerometer sensors were attached at the both ends of
the TR to measure the rod response on the fluid flow. Kalman type
filters was used in order to restore TR kinematics from simultaneous
measurements of accelerometers and less sensitive laser extensometers.
The effect of Reynolds number on the stability of the flexibly mounted
TR has been analyzed. Flow history (different flow increasing and
decreasing scenarios) impact on the stability of TR oscillating motion
was studied as well.
Obtained experimental results was used for validation of
2-dimensional Computational Fluid Dynamics (CFD)
model. In the model rods are represented with the
cylindrical surfaces. Spring-mounted TR
was modeled in the fourth row, as in experimental installation.
Due to developed turbulence system of
Unsteady Reynolds-Averaged Navier-Stokes (URANS)
equations was used for fluid flow description.
Unsteady pressure and viscous forces acting on the TR then are
given by URANS solution. Open sourced CFD toolkit
OpenFOAM was used for coupled solution of both -
systems of RANS PDE's and ODE's of solid body dynamics with
the built-in six degree-of-freedom solver. In order to reduce
computational time several array size reduction techniques was applied.