Flying Fifteen CFD – Update 1

After a couple of further attempts I have now got a smoother version of the hull into a 3D CAD package.  I had to dispense with the lines from the drawing and just use the Offset Table.  As you can see below my third version is smooth along the length but I am still not sure I have the flat section either side of the centreline quite correct.

First model

Second Model (surface lofts over original curves)

Third Model (Surface Lofts over new Spline Curves)

All three of these images are of models run at 10 knots with the Centre of Gravity set to be 3 metres in front of the Transom Datum point.  Looking at the effective power calculated by Simerics for the three models they are 2015, 1995 and 2045 Watts respectively.  This is the amount of power you would need to drag the hull through the water.  The pitch angles are 2.45, 2.39 and 2.52 degrees.

Below is an animation of the new hull showing the bow wave at 10 knots.

The next step is finding the geometry of the Keel and Rudder.

Flying Fifteen Sailboat CFD

At the recent RYA Dinghy Show I was reminded that last year I had discussed trying out Simerics’ new Marine-CFD template on a Flying Fifteen hull.  The idea of this was more to see whether it could illustrate the importance of keeping the boat flat, etc. rather than to try improve the design within the limits of strict one design rules.

At the show Keith Jamieson found some old measurement diagrams on his laptop which he e-mailed on to me.  I have tried to make these into a 3D geometry, but currently this probably doesn’t pass the “batten test”.  Anyway I tried running a free surface CFD simulation on this last night and here are some initial results.  These are equivalent to a tow tank test on flat water with a speed of 10 knots.

This second image is probably indicating that the model is currently sailing in a very bow down attitude.  This is because I set the Centre of Gravity as being 3.75 m in front of the transom which in hindsight is probably far too far forward.  Has anyone ever calculated where it would be in a Flying Fifteen with two people on board?

This image shows the poor quality of my geometry and how it is  inducing additional drag.  Back to the drawing board!

So the next steps are to tidy up this hull geometry and then find some decent drawings of the keel and rudder so I can add those to the model.  Of course, this shape is based on the 1993 measurement diagrams so they will not illustrate any differences between the Mark 9 and 10 designs.  To do this I would need to obtain some scanned geometry from somewhere.

By the way, if anyone ever wondered what it would be like being towed in a Flying Fifteen at 15 m/sec (30 knots) I did run the simulation at that speed by mistake …

Choosing the Right CFD Simulation Tool

We continue to be surprised with decisions we see being made where companies are buying simulation software to suit the needs of individual’s career aspirations as opposed to what is right for the given application and intended users. What is the point of a company investing in some form of CFD software to be used by an individual who in all likelihood will leave once they’ve learnt how to use tool or whose real agenda is to become or remain the only one able to use the software? Shouldn’t companies invest in CFD software that can be used by the whole engineering or design team so that the investment is then protected for the long term?

CFD Simulation Versus Physical Testing

When is CFD Simulation better than Physical Testing? With the advent of rapid prototyping its now possible to physically test a new design of a part or product within a day or two of the change being made to the CAD geometry. However, CFD Simulation still delivers enormous value when an improvement in product performance is sought. Making design changes without really understanding what is happening is not efficient and can simply move a problem somewhere else as opposed to eliminating the issue. Also, physical testing is normally quite restrictive and the conditions or environments a product can have to deal with in reality often cannot be tested for.

 

Sean Horgan, Director at 80/20 Engineering

We felt it important to start to reach out using a communication method that many people have come to expect so we’ve started an 80/20 Blog to compliment our existing http://www.8020engineering.com web-site. CFD Simulation is what we do and we would like to share more of the success we have had helping our clients over the years and the knowledge we have of using CFD Software.

NAFEMS UK Conference

15th / 16th June 2016

NAFEMS UK Conference – Telford. 80/20 Engineering will present a paper entitled ‘Advances in CFD Simulation of Positive Displacement Machinery’

Come and visit us within the exhibition at booth no. 10