Flow-induced forces on cylinders in statistically-symmetric cross flow
Carassale, L.
(2009). Probabilistic Engineering Mechanics, 24(3), 323-339.
Abstract The
measurements carried out during aerodynamic tests are usually (if the Reynolds
number is large) interpreted as realisations of random processes. Typical tests
regards cylinder exposed to the flow in a nominally-symmetric configuration
(e.g. symmetric cylinders with zero angle-of-attack). In such a condition, the
pressure field and the fluid-induced loads (forces and torque) acting on the
cylinder are expected to fulfil some statistical symmetry condition, as it was documented
by several researchers. In particular, it was experimentally observed that the
cross-wind force and the torsional moment tend to have zero mean value and to
be substantially uncorrelated with respect to the along-wind force. Small (but
non-null) correlation or coherence values were often reported and it is not
clear whether or not they should be treated as experimental imperfections or
they are rather the trace of some physical phenomenon. With the objective of
clarifying the mentioned problem, the present paper introduces the concept of
statistically-symmetric random process proposing a definition in which the
symmetry constraint is imposed on the characteristic functional of the pressure
field. Consequent conditions on the statistical moments and on the covariance
eigenfunctions of the aerodynamic actions are derived accordingly. A numerical
procedure aimed at correcting measured data to impose a rigorous second-order
statistical symmetry is presented and applied on pressure measurements carried
out in a wind-tunnel test.
