I've been playing with some different simulation techniques and found these images quite interesting.
Obviously less turbulence with the square, but what about drag?
I am no fluid dynamics expert. But it looks like less turbulence with the elliptical foil -- no trailing vortices.
I thought one of the advantages of the elliptical wing on the British WWII Supermarine Spitfire was less induced drag.
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Hans, I was going to ask if you could use your Finfoil expertise towards developing a Hydrofoil ?
Technically a fin is a hydrofoil.
Hydrofoils (as the term is used in surfing) and fis are both low Mach and high Froude number lifting bodies with similar Reynolds numbers.
- Low Mach: means flow can be considered incompressible
- High Froude: gravitation forces on fluid can be ignored
- Similar Reynolds: similar turbulence properties.
The high Froude number and similar Reynolds numbers mean that the flow around horizontal hydrofoils and vertical fins behaves similar.
Therefore, learnings from fins apply to hydrofoils too.
@phebus & stoneburner
The voriticity you see in the images is not real turbulence.
But you are correct in assuming this high vorticity leads to higher turbulence.
Induced drag is drag resulting from energy dissipated in the turbulent wake, so higher turbulence in the wake leads to higher drag.
The total drag is the sum of the induced drag (form drag) and skin friction drag.
Beware, these images do not prove anything, I've just been experimenting with different flow calculation techniques that make different assumptions and simplifications about the flow field.
But I thought these images were interesting enough to share and start a discussion.
finFoil: free fin designing software
Hans , I've gotten really good results with longitudinal or Linear foils, are you able to do images with aspect ratios of <1 ?
So you mean a picture of a square low AR foil?
Like the first one, but with AR < 1 ?
Yes Hans, exactly that, if the first one has an AR of 10 then I would be interested in seeing an image of potential flow would look for a foil with an AR of . 1
10 times the chord length for the width please if it's possible ?
That looks very interesting, Hans.
Can you run this program on any of the finFoil files in the index?
If so, could you program a 'bot' to use spare processor time to mill through all the files made by the users of finFoil, to find the interesting ones?
And, could you compare the effects of winglets vs tubercles on otherwise identical wings/fins with this software?
I could try to concoct some wing shapes if you are happy to run them through this.
Here is a low aspect ratio foil span/chord = 1/5, the first pic was 5/1.
Why do you assume these to be potential flow solutions?
I could run this on all fins indeed.
However, there is no best fin criterium.
Please understand that I don't claim these simulations to be accurate flow solutions!
I'm just experimenting with different simulation techniques and models to figure out which ones would be interesting enough to integrate in finfoil.
While doing so, I came across the interesting images I posted and couldn't resist sharing them.
Thank you Hans, I think we all enjoy seeing a representation of the flow.