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-   -   Need some help to change the world! :-) (http://www.cfd-online.com/Forums/main/82097-need-some-help-change-world.html)

todayican2 November 16, 2010 15:41

Need some help to change the world! :-)
 
I represent a small group of regular guys building a (hopefully) 150mpg road going vehicle. Three wheeler, 2 in front, one in back.

We are looking for someone to help with 3d modelling and virtual wind tunnel analysis, can pay a bit, Id really love to move the project forward with your guys help.

Any takers?
Thanks
Tom

todayican2 November 17, 2010 10:52

1 Attachment(s)
Here is a sketch of one of the versions so far.

todayican2 November 17, 2010 23:36

I think I may have the 3d modeling and renders taken care of, now in need of a virtual wind tunnel test person :-)
Thanks!

siri November 18, 2010 07:20

changing the wheels
 
hey,

some innovative idea coming up for testing in CFD ! surprised not to see anyone taking a shot . .

i have a doubt: what is the intent of this design ? a SUV or F1 or flying car ? !

other than needing flow analysis, what stability or safety problems do you foresee for the wheeler and rider in this scenario. have u addressed them?

todayican2 November 18, 2010 11:21

The intent of the car is an open source car design people can build that will cost 5k or less to build and carry 2 people at highway speeds (70 mph plus) and get over 100 mpg.

The stability and safety problems are being addressed, essentially this is to be a very safe motorcycle, or a marginally safe car. rollover stability will be a touch less then a 4 wheel car as well as side impact protection (a price to be paid for 3 wheels and weighing 600 to 700 pounds)

The main thing we are looking for with the flow analysis is overall drag ratio and body lift / down force, how much of it there is and over which axles.

This way we can build something with a very low drag ratio and stick to the road better the faster it goes :-)

Tom

gerritgroot November 18, 2010 11:53

You don't need to spend a lot of time with CFD on this (sorry to say this on a CFD forum).

In spite of what people will try to sell you here, you'd better use tables or empirical values from for example Hoerner's drag book or from other drag tables on car or zeppelin configurations.

For saving fuel, apart from better aerodynamics, you may use electrical brakes that store the energy for accelerating later on.

It seems an interesting project! :)

todayican2 November 18, 2010 12:01

I dunno GerritGroot, theres a lot of weird airflow interaction between the vertical planes of the body and the horizontal, theres a lot of question (in my mind anyway) about potential lift vs downforce at different approach angles.

siri November 19, 2010 01:22

open source car design !
 
Tom

This idea sounds coolest.. just imagine .. smart engineers ending the monopolies of them all - (read 'the billionaires') once again .. and this time, only it would not be a Microsoft fella .. but falling of his Auto clones of the 21st Century

Now if u r being serious about this, itself can be a great motivation for anyone to work on this. however, perhaps u r posted on the wrong sub-forum -

Since you sound new to CFD forum, let me spell one gospel truth for you now. "Of all the members from CFD community who have climbed the ladder using commerical softwares, almost every third person you will meet is today a part of another OPEN SOURCE initiative .. (reasons obvious)"

- and that's where you will probably get the right help ... welcome to OpenFOAM .. the CFD terrain of liberation

-post there and you will be liberated too !

siri November 19, 2010 01:33

technically speaking
 
Quote:

Originally Posted by todayican2 (Post 283924)
I dunno GerritGroot, theres a lot of weird airflow interaction between the vertical planes of the body and the horizontal, theres a lot of question (in my mind anyway) about potential lift vs downforce at different approach angles.

philosophy aside, your observations are quite natural to the flow over the design - here you may have physically swapped the airplane rear-to-front, but overlooked (or forgot) to swap the physics upside down ! After all, you still intend to deliver a speeding roadie and not a flyer as I can see .

todayican2 November 19, 2010 01:41

you mean up for down right? the design is a series of tradeoffs, between great aero and the need to have space for the rear riders knees for example.

Ive been growing grey hair tonight reviewing torque curves for small engines as well as reviewing an efi unit for a 200cc engine! (Very cool!) I will post on the other forum as well, thanks for the advice!

Ive been running some numbers and I beleive this car can be built for under $5000 and return (so the calculations say) 146mpg (100 would be a grand slam success)

If we can just safely keep it on the ground where it belongs :-)

siri November 19, 2010 02:23

// you mean up for down right? // YEP !

//the design is a series of tradeoffs, between great aero and the need to have space for the rear riders knees for example. //

As per my guess, the problem lies not at the rear. if you wish, you may have the way it is now or maybe want to improve it further later

//If we can just safely keep it on the ground where it belongs :-)//

I wont say, I am sure about this right away (unless I get to see some real stuff) - but perhaps your problem could be resolved (i) either from under the hood or (ii) from over the front. That's were real aerodynamics is at play (playing spoilsport eh?) THINK ABOUT IT FIRST!

Finally, going back where you started, virtual simulation can definitely help you in seeing things. But it may be too early to jump over it yet, as GerritGroot already pointed.

Beware ... CFD is not mature enough even of today.. i.e, maybe pictures can tell you something's wrong abt the flow but not what's wrong actually. this we may have to still figure it out in a more human way ....

So what are the torque data saying out anyway ?!?

todayican2 November 19, 2010 02:37

Actually, I was looking at the best torque rpm for the engine (A lifan 200cc) and sourcing drive sprockets for the lifan and electric motors turns out it makes its best torque, good for steady state cruising around 4000 rpm where its best horsepower is up around 7500.

All things considered, since I will be going with the efi in the near future, ill just gear it for best torque for the moment, once the efi unit is in I can get the curves programmed a little better.

siri November 19, 2010 04:45

Okay, now how is the final resultant of the torque oriented w.r.t the car as per your present analysis ? Does it tend to be lifting both the forewheels off the surface .. or ... swaying sidewards on one of the forewheels .. or something else happening?

For making sure the forewheels & hence the vertical forces honor equilibrium condition and stability against roll tendency, since you should estimate the effect of net (or aerodynamic) forces at some point, will it not suffice to develop a theoritical calculation (approximate and/or with some correction factored in) in so far as you are designing at one peak torque only ?

RameshK November 22, 2010 12:20

What exactly are u expecting and in what time
 
Hi

I have seen the discussion, I would like to give a trial, but before that I have few questions

1) exactly are u expecting from a CFD Simulation?
2) Time for the results..


since you are expecting a 3D simulation it may take some time so....


and can u give little more details so that I can make a feasibility study on this

todayican2 November 22, 2010 22:39

Siri, your language, im sorry to say is a bit beyond me, just being honest. As nearly as I can tell, Torque plays its role during accel / decel and matters little (outside of varying rolling resistance) at speed.

My main goal is to establish the overall drag ratio across a few body variations and measure potential lift / downforce at the 3 axles.

siri November 23, 2010 07:06

Tom

Hey apologize for the difficult jargon; it has nothing to do with cfd though. I will try to make it simpler. Let me know if this helped ..

Typically two possibilites may happen to the flow due to the present frontal design:
- either the front bottom portion is subject to upward lift (wing action) if the ground clearance is large (in which case the vehicle will tend to leave the ground) and has relatively higher pressure on the lower side
- or the front top portion gets bogged down due to excessive relative pressure over it (increasing traction and drag forces)

In earlier post, I mentioned it is premature to perform cfd for determining the aerodynamic effects; rather I recommend that you first estimate the net imbalance due to the present frontal design for the best value of torque/speed chosen by you somewhat as follows:

i) compute the horizontal and vertical forces theoretically (approximate but fair enough) and check the direction in which the resultant is acting
ii) evaluate force and moments balances analytically at each of the axles
iii) estimate the net imbalance (due to present frontal design and torque / speed chosen by you)
iv) check if the roll is severe
iv) revise the frontal shape to achieve maximum balance
v) test this improved & evaluated design virtually
vi) modify rear portion to streamline the flow in the region
vii) see how the design works at other torque ratings
viii) test your optimized model in wind tunnel


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