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Aerospace Could people check this for me?

  1. May 18, 2009 #1
    Hi there,

    Im doing a small right up on general aerodynamic terms. Can people have a look the following and tell me if I have all my facts straight?

    "-Laminar flow is when a fluid flows in parallel layers with no disruption between the layers. Generally it has a Reynold’s number of less than 2300.

    -Turbulence is the violent or unsteady movement of air due to a rapid change in pressure. This results in pressure drag. Air flows must be eased back together behind a car to prevent turbulence.

    -The Boundary Layer is an area of slow moving air adjacent to the car body. If attention isn’t paid to this it can result in skin friction drag due to the extra shear force and it can also add a ‘displacement thickness’ hence increasing the pressure drag.

    -Front wing side should curve out to the sides to spilt the air evenly to all sides of the wing to prevent vortices from being formed along the sides of a car."

  2. jcsd
  3. May 20, 2009 #2


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    Flow through a circular duct where Reynolds number is based on diameter is typically laminar with Re<2300.

    How would you measure Reynolds over a car?
  4. May 20, 2009 #3
    Typically, you use a characteristic length.
  5. May 20, 2009 #4


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    Well it's always a characteristic length. The question was rhetorical in nature for the OP though.
  6. May 22, 2009 #5
    I dont understand the point of the question you posed to the OP. I'm not trying to give you a hard time, but it seemed to not serve any real purpose and can confuse the OP.
  7. May 26, 2009 #6


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    The point was only that Reynolds of 2300 is really only meaningful when analyzing pipe flows and the Reynolds number was calculated using diameter. Is it wrong to use radius? It's not common, but it's not incorrect. Can we use pipe circumference? They are all lengths that can be used, and the "magic" number for transition will chance based on that.

    The point is that people often take that 2300 and apply it to everything without first asking what the reference length or even the problem is.
  8. May 26, 2009 #7
    You are right about the Re number for pipe. It just didn't come across as that was the point you were making for your post. The way I read it was more of a 'how do you define reynolds number', rather than: "Re>2300 is strictly for the case of a pipe."

    I just thought the way you worded it gave it a totally different meaning to the question. Either way, now that that is cleared up I dont want to sit here trying to split hairs.
  9. May 27, 2009 #8
    yeh mate, they are all pretty good easy to understand simple explanations

    of course you could go into alot more detail, but that may not be necessary for this case

    All your statements are pretty concise, but if someone wants to be picky, u may need to further elaborate on what i have highlighted in bold

    All my comments are not from professional experience as I'm still learning myself...keep researching though, wiki has heaps of useful articles
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