Advanced Search provides additional search options providing the ability to narrow your search by combining multiple search variables.
Note that by default, the Date Range set to 2017 will return all results from a text search. You can select both Date Range settings to narrow the returned results.
Over the past two decades, the numerical and experimental progresses made in the field of downwind sail aerodynamics have contributed to a new understanding of their behaviour and improved designs. Contemporary advances include the numerical and experimental evidence of the leading-edge vortex, as well as greater correlation between model and full-scale testing. Nevertheless, much remains to be understood on the aerodynamics of downwind sails and their flow structures. In this paper, a detailed review of the different flow features of downwind sails, including the effect of separation bubbles and leading-edge vortices will be discussed. New experimental measurements of the flow field around a highly cambered thin circular arc geometry, representative of a bi-dimensional section of a spinnaker, will also be presented here for the first time. These results allow to interpret some inconsistent data from past experiments and simulations, and to provide guidance for future model testing and sail design
Experimental and numerical trimming optimizations for a mainsail in upwind conditions
This paper investigates the use of meta-models for optimizing sails trimming. A Gaussian process is used to robustly approximate the dependence of the performance with the trimming parameters to be optimized. The Gaussian process construction uses a limited number of performance observations at carefully selected trimming points, potentially enabling the optimization of complex sail systems with multiple trimming parameters. We test the optimization procedure on the (two parameters) trimming of a scaled IMOCA mainsail in upwind conditions. To assess the robustness of the Gaussian process approach, in particular its sensitivity to error and noise in the performance estimation, we contrast the direct optimization of the physical system with the optimization of its numerical model. For the physical system, the optimization procedure was fed with wind tunnel measurements, while the numerical modeling relied on a fully non-linear Fluid-Structure Interaction solver. The results show a correct agreement of the optimized trimming parameters for the physical and numerical models, despite the inherent errors in the numerical model and the measurement uncertainties. In addition, the number of performance estimations was found to be affordable and comparable in the two cases, demonstrating the effectiveness of the approach.
In small sailboats, the bodyweight of the sailor is proportionately
large enough to induce significant unsteady dynamics
of the boat and sail. Sailors use a variety of techniques
to create sail dynamics which can provide an increment
in driving force, increasing the boatspeed. In this
study, we experimentally investigate the unsteady aerodynamics
associated with one such technique, called “sail
flicking”. We employ a two-part approach...
Pressure Measurements on Yacht Sails: Development of a New System for Wind Tunnel and Full Scale Testing
The paper presents an overview of a joint project
developed among Politecnico di Milano, CSEM and North
Sails, aiming at developing a new sail pressure measurement
system based on MEMS sensors (an excellent compromise
between size, performance, costs and operational
conditions) and pressure strips and pads technology. These
devices were designed and produced to give differential
measurement between the leeward and windward side of the
sails. The project has been developed within the Lecco
Innovation Hub Sailing Yacht Lab, a 10 m length sailing
dynamometer which intend to be the reference
contemporary full scale measurement device in the sailing
yacht engineering research field, to enhance the insight of
sail steady and unsteady aerodynamics [1].
The pressure system is described in details as well as the
data acquisition process and system metrological validation
is provided; furthermore, some results obtained during a
wind tunnel campaign carried out at Politecnico di Milano
Wind Tunnel, as a benchmark of the whole measuring
system for future full scale application, are reported and
discussed in details.
Moreover, the system configuration for full scale testing,
which is still under development, is also described.
Wind Tunnel Investigation of Dynamic Trimming on Upwind Sail Aerodynamics
An experiment was performed in the Yacht Research Unit’s
Twisted Flow Wind Tunnel (University of Auckland) to test
the effect of dynamic trimming on three IMOCA 60 inspired
mainsail models in an upwind (AWA = 60) unheeled configuration.
This study presents dynamic fluid structure interaction
results in well controlled conditions (wind, sheet
length) with a dynamic trimming system. Trimming oscillations
are done around an optimum value of CFobj previously
found with a steady trim. Different oscillation amplitudes
and frequencies of trimming are investigated. Measurements
are done with a 6 component force balance and
a load sensor giving access to the unsteady mainsail sheet
load. The driving CFx and optimization target CFobj coefficient
first decrease at low reduced frequency fr for quasisteady
state then increase, becoming higher than the steady
state situation. The driving force CFx and the optimization
target coefficient CFobj show an optimum for the three
different design sail shapes located at fr = 0:255. This optimum
is linked to the power transmitted to the rig and sail
system by the trimming device. The effect of the camber
of the design shape is also investigated. The flat mainsail
design benefits more than the other mainsail designs from
the dynamic trimming compared to their respective steady
situtation. This study presents dynamic results that cannot
be accurately predicted with a steady approach. These results
are therefore valuable for future FSI numerical tools
validations in unsteady conditions.