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ken_ichikawa

Engineers!

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Does anybody know of some software, which doesn't cost an arm and a leg (open source = better) which can simulate aerodynamics?

Currently a quick search has found http://web.mit.edu/drela/Public/web/xfoil/ xfoil. But this only allows wing shapes.

Thanks

I would have thought that aerodynamics is pretty complicated to model.. you have all sorts of density effects to consider on top of the usual non-compressible fluid dynamics.

Can't really help, but I will be interested to see if you find one.

Is it for motorbikes?

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google "open source computational fluid dynamics"

openfoam is the first result. Never used it or any others and these things tend to be heavy on cpu and memory and take a while to learn

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I've decided as a little project to build a super streamlined bike. Using a Honda C90 as the base. A dutch guy recently did this to a Honda Innova he added 40 kilos to the street weight but he averages out at 245mpg (real world conditions 55mph cruising) The aerodynamic shape was based on a guess. He also did not set out to use light weight parts using thick box section steel for internal supports.

If I can get a computer model use light weight fiberglass or ABS plastic as well as replacing much of the steel body of the C90 with alloy I think I can get maybe 300+ mpg.

This is what I want it for.

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Does anybody know of some software, which doesn't cost an arm and a leg (open source = better) which can simulate aerodynamics?

Currently a quick search has found http://web.mit.edu/d...blic/web/xfoil/ xfoil. But this only allows wing shapes.

Thanks

I have the answer (same as Rahhh found in Google) ------->>>>> OpenFoam http://www.openfoam.com/ it will run on Windows and Linux and I know quite a few big firms are using it..

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If you already have a Windows machine it may be worth quickly trying out the Windows version at sourceforge http://sourceforge.net/projects/openfoam-mswin/ in case the package provider has done a good job and it just works. That said, I saw some references to the Windows install that didn't look easy and apparently needed some work around to do with how Openfoam runs under Paraview in Windows - of course this may be fixed by now.

Otherwise if you have a Debian/Ubunt machine, then the instruction for the Ubuntu install are well tried and tested and by Linux standards are pretty easy: http://www.openfoam.com/download/ubuntu.php

So my suggestion would be to try the install for whatever platform (Windows / Debian-Ubuntu) you have available. If that is Windows hopefully it will just work, if it doesn't then you'll need to do an OS install for Ubuntu and thens tick Openfoam on that.

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I reckon if your fairing is a "bit fish shaped" it will go through the air well!

I didn't calculate anything today, even though I am an Engineer!

That's how fish work! :blink:

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Unless you know what you're doing I wouldn't bother with CFD. Go an an engineers forum and ask about the most aerodynamic shape.

It will resemble something teardrop shaped I think. Narrower at the back than at the front with a long trailing edge.

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Unless you know what you're doing I wouldn't bother with CFD. Go an an engineers forum and ask about the most aerodynamic shape.

It will resemble something teardrop shaped I think. Narrower at the back than at the front with a long trailing edge.

I'm envisaging a Kamm tail which is a cut off tear drop. As said I'll merely be guessing without any guidance.

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I'm envisaging a Kamm tail which is a cut off tear drop. As said I'll merely be guessing without any guidance.

Might be worth reading 'Low power laminar aircraft design' ny Alex Strojnik, if you can get hold of a copy. You won't see much laminar flow on a bike or a car but he really does a straightforward introduction to the basics of aerodynamics while keeping to simple maths. He manages to pretty much avoid calculus altogether.

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I'm envisaging a Kamm tail which is a cut off tear drop. As said I'll merely be guessing without any guidance.

I imagine that most racing bikes must be designed to be aerodynamic.. I would loosely copy them and try to avoid any unnecessary protrusions.

Unfortunately I suspect the most un-aerodynamic part of a motorbike is probably the rider.. I doubt there's a lot you can do about that apart from make up body panels to precisely mask your form.

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I imagine that most racing bikes must be designed to be aerodynamic.. I would loosely copy them and try to avoid any unnecessary protrusions.

Unfortunately I suspect the most un-aerodynamic part of a motorbike is probably the rider.. I doubt there's a lot you can do about that apart from make up body panels to precisely mask your form.

Nah the FIM banned dust bin fairing since 1958, citing they reduced steering and generated side yaw. Thus fairings must have rider fully visible and go no lower than the axles on the wheels. Moto GP compensated with rider humps to clean up the airflow a bit. But motorbikes today are still like house bricks in terms of aerodynamics. The zzr1400 and Hayabusa just add more power to compensate for lack of aerodynamics.

MotoGP fairings are actually aerodynamically poor and unstable which adds stability in corners. The CBR600RR changed to this in 2005 in a straight line it is worse than my older CBR600F as the fairing is for better cornering.

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cfd is way over the top for this - wouldn't give any decent results without spending months at it. Basically lower the frontal area as much as possible (no wing mirrors, low riding position) and keep everything pointy and as smooth as possible is the best bet. Try googling the fastest indian for some inspiration and as mentioned adding a kamm tail (sharply cut off tapering tail) for practicality, but any tail probably wouldn't make a big difference without a full fairing that covered the body. Weight will make very little difference to steady state mpg

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As regards steady speed fuel consumption gear ratios would be worth a look at. In general you would get the best fuel consumption at a given speed if the engine were at peak torque with the throttle wide open at that speed. Might be a bit difficult to get anywhere near that ideal with a bike as I would assume that the engines are fairly peaky. A biggish engine with a flattish torque curve and a lots of gears might be a line of thought.

I say a biggish engine as the frictional losses in the engine are proportional to RPM and I say lots gears as such a set up with a small number of gears would be severely overgeared.

Has anyone designed a practical infinitely variable transmission yet?

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Has anyone designed a practical infinitely variable transmission yet?

You can get them for push bikes. No idea if they make a version robust enough for a motorbike though.

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You can get them for push bikes. No idea if they make a version robust enough for a motorbike though.

This is what I had in mind

new_cvt_diag.gif

Here's a motorbike with a continuously variable transmission:

Honda DN-01

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I suppose for the engine we need a turbo compound diesel. I wonder has anyone ever built one of those? The only turbo compound engine I can think of was the Wright one use in the Boeing Stratocruiser. Marvellous SFC so how much better could a diesel one be? The 100cc one for a bike might be a bit fiddly to build though :rolleyes:

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  • 276 Brexit, House prices and Summer 2020

    1. 1. Including the effects Brexit, where do you think average UK house prices will be relative to now in June 2020?


      • down 5% +
      • down 2.5%
      • Even
      • up 2.5%
      • up 5%



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