geoff birds new trike

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   Geoff,Bit of a curiosity question, 
When you use your cfd package to determine the flow over the shape how do you know that your predictions are close to real world(tm)? The speeds are much slower than with automotive design and with that the error factor will be larger no? 
The reason for asking is in any kind of cfd you need to calibrate your model other wise its dare I say bullsh*t in bullsh*t out? As we found with flow optimisation in a previous life playing with water treatment equipment. 

Will you expand a little.

But other wise a very sleek and lovely looking machine.. I am jealous :-)

Karl

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Karl Members Profile Send Private Message Find Members Posts Add to Buddy List Visitor (new) Joined: 11 June 2013 Location: Preston Status: Offline Points: 189	Post Options Post Reply Quote Karl Report Post Thanks(0) Quote Reply Posted: 05 April 2015 at 8:22pm
	Geoff, Bit of a curiosity question, When you use your cfd package to determine the flow over the shape how do you know that your predictions are close to real world(tm)? The speeds are much slower than with automotive design and with that the error factor will be larger no? The reason for asking is in any kind of cfd you need to calibrate your model other wise its dare I say bullsht in bullsht out? As we found with flow optimisation in a previous life playing with water treatment equipment. Will you expand a little. But other wise a very sleek and lovely looking machine.. I am jealous :-) Karl

GeoffBird Members Profile Send Private Message Find Members Posts Add to Buddy List BHPC Member Joined: 20 September 2005 Status: Offline Points: 2396	Post Options Post Reply Quote GeoffBird Report Post Thanks(0) Quote Reply Posted: 05 April 2015 at 9:08pm
	Hi Karl, As I said in the article, CFD is only a comparative tool at this level, so all you can do is do a baseline run and try changing things to see the effect I haven't got past the baseline yet, but do have a comparison with another shape (similar to Bubble & Squeak) using the same settings. Speed shouldn't be so much of an issue as CFD should correct for Reynolds Number, whereas this can be a problem for scale models of cars and aeroplanes in wind tunnels. So yes you're right, you have to correct against real world data to get a realistic figure (this is true for wind tunnels too). As an illustration of the problem, Miles is getting less than half the drag force with his CFD package at the same speed for a very similar shape (not mine) on the system I used (or was used for me). We're just shining a torch into the vast darkness - we can't afford floodlights! Edited by GeoffBird - 05 April 2015 at 9:10pm
	Right Time - Right Place - Wrong Speed

robh24 Members Profile Send Private Message Find Members Posts Add to Buddy List BHPC Member Joined: 01 April 2015 Status: Offline Points: 15	Post Options Post Reply Quote robh24 Report Post Thanks(0) Quote Reply Posted: 06 April 2015 at 2:20pm
	What's the advantage of those wheels. Lighter, stronger?

GeoffBird Members Profile Send Private Message Find Members Posts Add to Buddy List BHPC Member Joined: 20 September 2005 Status: Offline Points: 2396	Post Options Post Reply Quote GeoffBird Report Post Thanks(0) Quote Reply Posted: 06 April 2015 at 2:24pm
	Neither of those things Rob! They are a bit heavier and probably no stronger. However, they give a small amount of 'dish' which allows you to get the brake disc and therefore the suspension upright/steering axis much nearer tyre centreline. And they look cool IMHO Edited by GeoffBird - 06 April 2015 at 10:26pm
	Right Time - Right Place - Wrong Speed

russellbridge Members Profile Send Private Message Find Members Posts Add to Buddy List BHPC Member Joined: 21 October 2013 Location: Manchester Status: Offline Points: 843	Post Options Post Reply Quote russellbridge Report Post Thanks(1) Quote Reply Posted: 07 April 2015 at 4:28pm
	It's a great article in the magazine re the new machine - I was re-reading it over breakfast this morning - many thanks Geoff Russ

GeoffBird Members Profile Send Private Message Find Members Posts Add to Buddy List BHPC Member Joined: 20 September 2005 Status: Offline Points: 2396	Post Options Post Reply Quote GeoffBird Report Post Thanks(0) Quote Reply Posted: 07 April 2015 at 9:16pm
	Thanks Russ. Gratuitous shininess (it's easier than building things...):
	Right Time - Right Place - Wrong Speed

GeoffBird Members Profile Send Private Message Find Members Posts Add to Buddy List BHPC Member Joined: 20 September 2005 Status: Offline Points: 2396	Post Options Post Reply Quote GeoffBird Report Post Thanks(0) Quote Reply Posted: 18 April 2015 at 3:18pm
	The initial CFD results on the new shape are just in. Big improvement! About 22%, making the drag about the same as a Bubble & Squeak type machine. A couple of images from the CFD below. I don't understand the total pressure map - thought total pressure was constant (and equal to static plus dynamic pressure) - can someone explain? Looks dramatic anyway . Edited by GeoffBird - 18 April 2015 at 3:21pm
	Right Time - Right Place - Wrong Speed

Yanto Members Profile Send Private Message Find Members Posts Add to Buddy List Moderator Group Joined: 11 July 2005 Status: Offline Points: 1521	Post Options Post Reply Quote Yanto Report Post Thanks(0) Quote Reply Posted: 18 April 2015 at 9:53pm
	Geoff I can't help you unfortunately, however where do i put my name down to buy one?

GeoffBird Members Profile Send Private Message Find Members Posts Add to Buddy List BHPC Member Joined: 20 September 2005 Status: Offline Points: 2396	Post Options Post Reply Quote GeoffBird Report Post Thanks(0) Quote Reply Posted: 19 April 2015 at 12:08am
	Thanks for the implied compliment Ian. I think building one is going to be enough of a struggle! If you're serious, then I'm already discussing with someone else about getting a third party to take another set of mouldings off the moulds. But I'd wait until you see how it comes out before committing to anything One step at a time...
	Right Time - Right Place - Wrong Speed

GeoffBird Members Profile Send Private Message Find Members Posts Add to Buddy List BHPC Member Joined: 20 September 2005 Status: Offline Points: 2396	Post Options Post Reply Quote GeoffBird Report Post Thanks(0) Quote Reply Posted: 19 April 2015 at 10:39pm
	Edited by GeoffBird - 19 April 2015 at 10:41pm
	Right Time - Right Place - Wrong Speed