Spin-out simulation

General Discussion
1

As a follow up to Fin tip vortex

Ever wondered what spin-out looks like? (https://twitter.com/finfoil/status/631847638418259968)

k is the turbulence kinetic energy.

AoA = 45deg

Water velocity = 6m/s

enjoy!

2

That’s the coolest thing I’ve seen on here in a while!

3

Thanks, it’s an honor to hear that from an industry icon!

I love your work :wink:

4

Cool images!

What is the vertical AoA?

Also, do you think that in real life (in real surfing sitiuations) the flow actually moves up (actually down in reality, since fins point down when surfing) the fin like that?

Also, why is this considered a “spin out”?

Thanks!

5

The flow you see is a time averaged turbulent flow.

This flow regime is known as spin-out in windsurfing, I’m not sure it’s called like that in surfing, maybe someone can confirm? In aerodynamics it’s known as stall: https://en.wikipedia.org/wiki/Stall_(fluid_mechanics)

So it is not a regime that you want your fin to operate in, since it mostly results in a wipe-out. If you want to see a normal flow regime, I refer to the thread about the fin tip vortex

I’m not sure what you mean by vertical AoA? If you mean cant, this fin is simulated without cant.

6

Template is # 1 in avoiding spinout .

Foil is next .

7

CFD is ideal for testing small changes in fin template or foil, in relation to something measurable like stall. Keep other variables constant and just tweak the template and foil. 

There’s so many other things about surfboards that aren’t even close to being quantifiable… And given the nature of our flow media and forces involved, we’re still a long ways away from verifying theories about what’s going on down there overall. Which of course it what makes it fun.

 

8

Exactly!

And thats where it often goes wrong with CFD when people are trying to come to an “optimal” solution but end up being way off. It’s not a coincidence that it’s often called Colors For Directors :slight_smile:

So it’s my goal to support theories with data but not to claim optimal fin designs.

9

Is the simulated fin flat on the inside? 

It’d be a large effort to correlate a quantifier of any sort with how it actually feels in the water, as you guys are saying. But it’s still very interesting. I’m all for numbers. All this finfoil talk is making me want to make a set.