  The importance of fluid-elastic forces in tube bundle vibrations can hardly
be over-emphasized, in view of their damaging potential. In the last decades,
advanced models for representing fluid-elastic coupling have therefore been
developed by the community of the domain. Those models are nowadays embedded in
the methodologies that are used on a regular basis by both steam generators
providers and operators, in order to prevent the risk of a tube failure with
adequate safety margins. From an R&D point of view however, the need still
remains for more advanced models of fluid-elastic coupling, in order to fully
decipher the physics underlying the observed phenomena. As a consequence, new
experimental flow-coupling coefficients are also required to specifically feed
and validate those more sophisticated models. Recent experiments performed at
CEA-Saclay suggest that the fluid stiffness and damping coefficients depend on
further dimensionless parameters beyond the reduced velocity.
  In this work, the problem of data reduction is first revisited, in the light
of dimensional analysis. For single-phase flows, it is underlined that the
flow-coupling coefficients depend at least on two dimensionless parameters,
namely the Reynolds number $Re$ and the Stokes number $Sk$. Therefore, reducing
the experimental data in terms of the compound dimensionless quantity
$V_r=Re/Sk$ necessarily leads to impoverish results, hence the data dispersion.
In a second step, experimental data are presented using the dimensionless
numbers $Re$ and $Sk$. We report experiments, for a 3x5 square tube bundle
subjected to water transverse flow. The bundle is rigid, except for the central
tube which is mounted on a flexible suspension allowing for translation motions
in the lift direction.
