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Homework Help: Wind Car, energy losses and model

  1. Dec 1, 2004 #1
    I am a student in Malmö, Sweden currently preparing for the IYPT (international young physicists tournament) 2005 in Switzerland.
    We are supposed to do a 10 minute presentation, solving the following problem:
    Construct a car which is propelled solely by wind energy. The car should be able to drive straight into the wind. Determine the efficiency of your car.

    As I interpret this, the problem is not about constructing the most efficient car, it is rather to construct a car which has a calculatable efficiency.

    We have chosen to utilize an anemnometer (wind measurer) as the engine. Mounted horisontally on a pillar above the chassis. The rotational force from this (horizontal windmill) can be converted to a vertical rotational force using, insert random english word for 'kugghjul' which i don't know here. Some kind of wheel anyway

    To determine the efficency experimentally we construct a mathematical model (not including energy losses) and then compare it to the real-life results we get, we will have access to a windtunnel I think and hope.

    The mathematical model without energy losses shouldn't be to hard to create I think but the goal of this project is to also include calculations for friction and air resistance to get a value as close to the experimental value as possible.

    To do this we will need components that are easy to calculate. Example: it is easier to calculate friction for a uniform wheel than it is for a "spiked" wheel (which would have a better grip though) ;)

    Is this a good approach? Any suggestions, criticism on the model or the interpretation of the problem? Is it doable?
    Which components would be helpful for calculations? Is it possible to do calculations on the air drag or resistance?

    If know of any proffessors that might help me further with this problem be sure to give me an e-mail adress.

    Thanks in advance,
  2. jcsd
  3. Dec 1, 2004 #2

    Andrew Mason

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    Kugghjul must refer to a gear wheel of some kind.

    One problem you have will be to determine the total amount of work that you can extract from the wind. This similar to the thermodynamic problem of extracting work from heat. You have to let some of the heat energy dissipate out of the system. Similarly, you cannot capture all of the wind energy - the wind has to flow through your anemometer.

    Another problem will be that when you use the wind power to generate vehicle speed, you create another wind. In sailing, this is referred to as the apparent wind. You have to take this apparent wind, due to the motion of the car through the air, into account. This will reduce the speed of the real wind by the speed of the car where the car is moving in the direction of the wind. It will create greatest drag when moving directly into the wind.

    I suspect that you will learn alot by trying to work out all the reasons that this car won't work very well. Good luck.

  4. Dec 1, 2004 #3


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    A suggestion:

    You may come up with a nice calculation learning something about Turbomachinery. Take a look at some Turbomachinery design book. In particular see something about Pelton Turbines. They are kinda similar to your anemometer, and maybe you can do some more accurate calculations about the torque avaliable on the shaft. As a cautionary note, I would say it can be a bit difficult to understand turbomachinery flows for a high school alumn, but it is worth of having a look at it.
  5. Dec 1, 2004 #4
    Thank you very much clausius2 I will have a look at the litterature, it's no problem if we can not fully grasp it we will have teachers to aid us and we don't need to completely understand it when presenting, although it would help =)

    But will it work well enough, as in go into the wind?
    And do you think these reasons can be calculatable as this is the point of the problem.

    What I really want to know with this thread is wether 1st: the car will go into the wind or not, 2nd if the effect losses on the vehicle will be relatively easily calculatable or if there is another option that will also work that is easier to calculate...
  6. Dec 1, 2004 #5

    Andrew Mason

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    There is no reason in principle why the wind energy cannot be captured and used to move the car in any direction. But you are going to have trouble, obviously, moving with much speed into the wind.

    I don't know. I would have to identify and estimate all the factors, which I suppose is the purpose of your assignment.

    For the 1st question, as I say, there is no reason in principle why the car cannot move into the wind. As to the 2nd, you will have to identify all of the factors and try to quantify them.

  7. Dec 2, 2004 #6
    Well I will obviously have to do that but it would be good to choose a model which I know will be fairly easy to work with so I don't build something only to realize I won't be able to do any calculations on it. That's why I'm asking people, that might have expierience, whether a model like mine is good enough to work with or there is an easier option. As a K-12 student I do not believe that I myself am able to learn the concepts of all the options good enough to quantify them, I'm not sure I can fully quantify even one of the options...
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