The influence of fluid–structure interaction on cloud cavitation about a flexible hydrofoil. Part 2
Smith, SM and Venning, JA and Pearce, BW and Young, YL and Brandner, PA, The influence of fluid-structure interaction on cloud cavitation about a flexible hydrofoil. Part 2, Journal of Fluid Mechanics, 897 pp. A28-1-A28-39. ISSN 0022-1120 (2020) [Refereed Article]
The influence of fluid–structure interaction on cloud cavitation about a hydrofoil
is investigated by comparing results from a relatively stiff reference hydrofoil,
presented in Part 1, with those obtained on a geometrically identical flexible hydrofoil.
Measurements were conducted with a chord-based Reynolds number Re = 0.8 × 106
for cavitation numbers, σ, ranging from 0.2 to 1.2 while the hydrofoil was mounted at
an incidence, α, of 6◦
to the oncoming flow. Tip deformations and cavitation behaviour
were recorded with synchronised force measurements utilising two high-speed cameras.
The flexible composite hydrofoil was manufactured as a carbon/glass-epoxy hybrid
structure with a lay-up sequence selected principally to consider spanwise bending
deformations with no material-induced bend–twist coupling. Hydrodynamic bend–twist
coupling is seen to result in nose-up twist deformations causing frequency modulation
from the increase in cavity length. The lock-in phenomenon driven by re-entrant jet
shedding observed on the stiff hydrofoil is also evident on the flexible hydrofoil
at 0.70 ≤σ ≤ 0.75, but occurs between different modes. Flexibility is observed to
accelerate cavitation regime transition with reducing σ. This is seen with the rapid
growth and influence the shockwave instability has on the forces, deflections and
cavitation behaviour on the flexible hydrofoil, suggesting structural behaviour plays a
significant role in modifying cavity physics. The reduced stiffness causes secondary
lock-in of the flexible hydrofoil’s one-quarter sub-harmonic, fn/4, at σ = 0.4. This
leads to the most severe deflections observed in the conditions tested along with a
shift in phase between normal force and tip deflection.