Numerical Analysis of Propeller-Induced Higher-Order Pressure Fluctuations on the Ship Hull
Produktform: Buch / Einband - flex.(Paperback)
Abstract
This thesis documents and explains the development and validation of a hybrid simulation method
for investigating higher-order hull pressure fluctuations induced by cavitating propellers. Two forms
of propeller cavitation are considered in this work:coherent structures of sheet cavitation on the
propeller blades and tip vortex cavitation.The interaction between sheet cavitation and developed tip
vortex cavitation can be responsible for notable higher-order pressure fluctuations.
The essential element of this novel simulation method is panMARE, the in-house panel code used
to calculate the propeller flow including effects of sheet cavitation.Furthermore, relevant parts of the
hull surface above the propeller are incorporated in the panel model in order to evaluate fluctuations
of pressure in the aft ship region.The propeller operates in the effective wakefield of the ship which
results from the viscous interaction between hull and propeller flow. It is calculated by the RANSE
solver ANSYS CFX in combination with panMARE. A body force coupling approach is used to
couple both methods.Here in, the viscous hull flow is determined by ANSYS CFX and the impact of
the propeller is approximated by a corresponding distribution of bodyforces applied to the viscous
flow which in return is calculated by means of panMARE.
In order to model tip vortex cavitation,the vortex cavity is divided into a large number of
cylindrical segments, where each of them are treated separately. This breaks down the formerly three-
dimensional problem into a two-dimensional one, which is much easier to handle.For each segment,
the momentum equations in cylindrical coordinates,leading to a Rayleigh-Plesset-like equation for
the dynamical behaviour of the cavitating core,are solved by means of the newly developed code
VoCav2D. Interaction with sheet cavitation is taken into account by correlating the initial cavitation
radius with the cavity thickness at the trailing edge of the blade in the tip region.This and other
tip vortex parameters are extracted from detailed RANS simulations of the blade tip flow made in
advance for a number of representative loading conditions.
For validation purposes,three vessels are investigated.The numerical results are compared to
those obtained from experiments and–if available–from full-scale measurements.Furthermore, two
types of scale effects due to the Reynolds number are investigated by the method: the wake scale
effect on sheetcavitation and the influence of the viscous core radius on moderate and tip vortex
cavitation in the stage of formation in an idealised manner.weiterlesen
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