Left: the Judel-Vrolijk TP52 Platoon is typical of the lighter, full-stern hull form that the SYRF is working to assess more accurately as the old narrower and heavier hull model becomes less relevant – especially at the top level. The tank model from Judel-Vrolijk (above) was chosen to protect the company’s current intellectual property; looks very like the original Rán 72/Jethou to us… before those aft topside hollows were all filled in
the methods were accelerated to more quickly generate results. An invitation was extended to practitioners active in the racing yacht field, and many well-known figures were able to give their support. Fortunately, the final list of stake - holders represented most parts of the CFD community, ranging from commercial RANS codes, through open source RANS codes, to the computationally less inten- sive panel codes.
more equitable racing, and also to inform the scientific community of what might be seen as current best practice. This is also valuable for academics as it will allow students, researchers and lecturers to frame new research projects most effectively. The project speaks to the SYRF objec- tives by focusing on the following aspects: a. Publishing an assessment of alternative methodologies to specify and analyse sailing yacht hydrodynamic resistance using computational tools. b. Making the data available for researchers and students as an accessible experimental data set for a contemporary sailing yacht. c. Demonstrating how this type of study can inform the handicapping process.
Methods
The procedures for comparing CFD data with experimental data are well estab- lished in ship hydrodynamics. Unlike in typical commercial and military studies where there are numerous tight controls on the process, for the Wide Light Project
The towing tank model for the project was provided by Judel-Vrolijk, with a slight modification to protect their own intellectual property. It was the availability of this model that was one of the main reasons this project could proceed at all. A test matrix was then developed on the basis of a typical evaluation programme for a sailing yacht. This included tests of the bare canoe body and the appended hull over a range of speeds, heel and leeway angles. Traditionally towing tank tests have been conducted using an assumed sail centre of effort height so that an appropri- ate bow-down trimming moment from the sail thrust can be applied to the model. In order to do this an estimate of the hull resistance is required. In this study each test run has been at a predetermined longi- tudinal centre of gravity (LCG) to avoid each contributor applying a slightly differ- ent sail trim moment. The specified LCG position for each test does broadly simu- late the effect of the sail trim moment based on an assumed hull resistance curve and appropriate sail plan.
This matrix was delivered to the CFD stakeholders who used their usual proce- dures to generate data for each point in the matrix. It was agreed that the data compar- ison would be made at model scale and tow tank conditions to avoid conflating the uncertainties of the scaling procedure with the CFD comparison. This was a blind test in the sense that the CFD calculations were completed before the tank test. The tank testing was then carried out by the Wolfson
Unit in the QinetiQ #2 towing tank at Haslar in Gosport, England.
The test matrix for the project was developed with the computational work in mind. However, for the experimental work the process is somewhat more com- plicated, and there are several steps between gathering the raw experimental results and being able to make a direct comparison with the CFD results. For example, there is usually some difference in the side force for a given lee- way on the two tacks, and at higher speeds and heel angles a difference of drag tack to tack at the same side force (not the same leeway) of 1-2% is acceptable. Greater dif- ferences than this indicate a misalignment of the centre planes between the hull and keel and rudder. Therefore, heeled and yawed tests were conducted on both port and starboard tacks to mitigate any effects from possible model asymmetry.
Results and analysis
The complete set of computational and experimental results can be found in the final published report. In addition, the hull and appendage geometry will shortly be made available as a validation source for CFD users, code developers and acade- mics. All files will go on the SYRF website. In comparing model test results with computational results, there are two fundamental questions: 1. Do the absolute values of the forces and moments agree? 2. Are the trends, how the data varies, in agreement?
It would, of course, be nice to have close agreement on the values of forces and moments. But if both CFD and model test have similar predictions for the changes (trends) in forces and moments between models or between different runs of the same model then a correlation can be established between the two sources of data. That correlation provides a degree of confidence in using either method.
SEAHORSE 47
INGRID ABERY
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