naca design

Discussion in 'Sailboats' started by akira88, Jun 5, 2010.

  1. akira88
    Joined: Jun 2010
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    akira88 Junior Member

    Good day everyone:)
    I am trying to design an airfoil for marine turbine, and I have decided to use NACA 63-010. So I went to this website http://www.pdas.com/avd.html to look for the ordinate for the airfoil, however there is no lower surface ordinate given for NACA 63-010, so how do i get the ordinate for lower surface?

    Thanks for helping:eek:

    ---edit---
    I am still not very familiar with these things so please forgive me if i did any silly mistake.
    After searching through the forum, i noticed a software known as javafoil, and it helped me alot. But I still have some doubts within me:

    1)Is this actually means NACA 63-010 is having same ordinate for both upper and lower surface? What would people use such airfoil for, since it wont generate any lift(maybe it will with some attack angle, but still inefficient imho)

    2)If this is the case, then what is the mean line for? I though it is suppose to be the mean of upper and lower ordinate. http://www.pdas.com/meanlines.html If both side are having same shape, the mean line should be always zero.

    A million thanks!!
     
  2. tspeer
    Joined: Feb 2002
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    tspeer Senior Member

    1) The 63-010 is a symmetric section. The lower surface is the negative of the upper surface.

    Are you sure you were looking at a table of ordinates? You may have been looking at the thickness distribution. You can tell because the maximum value will be 0.1 if it is the thickness distribution, and 0.05 if they truly are the ordinates. If you have the thickness distribution, you need to divide the thicknesses by 2 to get one side, and take the negative to get the other side.

    If I were designing a marine turbine, I probably wouldn't be planning to use the NACA 63-010 section. What are the requirements for your section?

    2) Before the advent of computers, thin airfoil theory was used to design sections. This was based on linear superposition. The lift and pitching moment could be approximated by a thin vortex sheet having the same shape as the mean (camber) line of the section, and zero angle of attack. The velocities for a symmetric thickness distribution were then added to the velocities from the vortex sheet and the effect of angle of attack on a flat plate to get the velocities on top and bottom.

    The 63-010 was a thickness distribution that was designed to have a constant pressure over the first 30% of the chord and then a linearly increasing pressure to the trailing edge. A NACA m camber line was then added to the thickness distribution. The NACA m camber line had a constant load back to m, and then a linearly decreasing load to the trailing edge. A NACA m=1 camber line resulted in a constant load over the entire chord.

    This is all explained in Abbott & von Doenhoff's "Theory of Wing Sections" available from Dover Books.
     
  3. akira88
    Joined: Jun 2010
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    akira88 Junior Member

    Thanks for the reply!!

    Before this I intended to use NACA 63-8xx series, however I wasnt able to find any ordinates for it, so I picked NACA 63-010 without noticing it is a symmetric section, and it wasn't ideal when I tried to run the simulation, the lift force produced was too low.

    However I found this program when I search through the forum yesterday night, http://www.mh-aerotools.de/airfoils/javafoil.htm
    and it enables me to find the ordinates for NACA 63-8xx series, so I guess I am going to forget NACA 63-010.

    A NACA 63-8xx series should be doing a good job for marine turbine right?
     
  4. tspeer
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    tspeer Senior Member

  5. akira88
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    akira88 Junior Member

    I see, I will consider the pro and cons about these designs.
    Thanks alot for spending time and efforts answering my doubts.:)
     
  6. tspeer
    Joined: Feb 2002
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    tspeer Senior Member

    Instead of considering what sections might be suitable, I think you should define what your requirements are and then design a section to meet them. For example, a high-lift section sounds good, but you can get as much lift as you want from a section, even a symmetrical one - you just have to make the chord large enough. The difference is the drag and weight. A high lift section will allow you to reduce the chord, but it will also have a narrow operating range. So it is critical that you define the operating range first.

    You can use momentum theory to define the operating conditions and overall performance of your turbine. You should have some idea of the end performance you want to reach, and that should tell you what section lift/drag ratio you need to reach the system performance.

    Only once you've defined these requirements does it make any sense to start working on the section shape.
     
  7. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Hi Tom,
    I would just like to point out one thing regarding airfoils "FX 74-CL5-140", "S1210" and "Strand". Those thin trailing edges can be difficult to manufacture and to make sufficiently structurally rigid and resistant. I would rather opt for airfoils with thicker T.E., like the remaining models in your list.
    Cheers!
     
  8. akira88
    Joined: Jun 2010
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    akira88 Junior Member

    Hi tspeer,
    I think I will stick to naca 63-8xx series first. I am stilllearning how to design a marine turbine, and there were a lot of people used this series in their design before. After I am familiar with these hydrofoil stuffs, then I would be able to reconsider the pros and cons of other airfoil types, and see how can they improve my turbine. So for now I will limit myself to a series first.:D

    However I faced another problem. Now I am trying to find a suitable angle of attack for my twisted blade. I read that xfoil is reliable, but I don't know why my foil always fail to converge. I have tried different nodes numbers from 60-200, and also tried the PANE comment, nothing work out. Attached is my airfoil ordinates, is there any problem with it?

    This is my alfa 0 for OPERi, personally I think the graph looks really weird and messy..
    [​IMG]

    What I did after loading a file was, enter OPER, enter v 337000 , and from this point onwards when I enter other command, if it started to converge, it fails, saying CPCALC: Local speed too large. Compressibility correction invalid.

    Javafoil says that the AoA for my foil is around 10 degree, but I was expecting somewhere around 12-20 degree. So I want to try out xfoil too, which i heard is more reliable.

    Thanks!!:)
     

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  9. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    There appears to be a problem with your coordinates for the NACA 63815. I have tried to use your txt file as input but the calculation hangs.

    I use this this DOS software to generate coordinates file for NACA airfoils:
    http://tracfoil.free.fr/airfoils/downloads/nacalte.exe
    I have tested it on my PC, containes no viruses.

    Once you have generated the .dat file with that software, XFOIL should work smoothly. I'm enclosing some of the results obtained. Btw, my graphics is different because I use XFLR5. It is an Opensource GUI software which uses XFOIL engine for calculations, so the results should be identical to those obtained with plain XFOIL.

    Cheers!
     

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  10. markdrela
    Joined: Jun 2004
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    markdrela Senior Member

    The coordinates near the trailing edge appear to have serious problems. It's possible that the upper and lower surfaces cross over. Blow up the view close to the trailing edge in GDES using the BLOW command to see what's going on there.
    If there's a problem you will need to modify the shape locally, or maybe open up a tiny trailing edge gap, say 0.001 in height or less.

    EDIT: I just noticed that you posted the coordinates. The problem is that the cusped trailing edge together with the strong aft camber causes the solver to exceed the numerical precision of the computer. The simplest fix is to open up a tiny trailing edge gap. This will work:

    GDES
    TGAP 0 1
    TGAP 0.0004 1
    EXEC

    OPER
    etc.

    You might also want to SAVE the modified airfoil so you don't need to do the gap operation again.
     
  11. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Hello Mr Drella,
    do you perhaps know why sometimes the analysis doesn't converge at just one single alpha, while it runs smoothly for all the others in the sequence, even those very close (+\- 0.5 deg.) to the "problematic" one? What indicator should one check out, in order to understand which corrections should be done? :\
     
  12. Guest62110524

    Guest62110524 Previous Member

    Tom and Daiquirio
    \often I use 2205 ss for rudder stocks on my alloy yachts, I do this for A strength and B because I have been taught thinner sections are better and the sections would be very thick if I were to go al alloy stock
    what say you two?
     
  13. Guest625101138

    Guest625101138 Previous Member

    The angle of attack on a turbine is a function of how it is loaded. You have to select an operating point for the turbine and work backwards. Once you have a design for those conditions you check it across the range of conditions it will experience.

    Also you will get a better result if you optimise the AoA across the span so a constant AoA is not the best.

    What are your operating conditions eg The stream flow rate? The power you want to get out? What are the constraint - reaction force, swept area, efficiency and/or high energy recovery.

    Rick W
     
  14. Guest625101138

    Guest625101138 Previous Member

    Something else to note is that the Re# will change over the span of the blade as well as being a function of many other parameters such as stream flow rate, blade chord and speed of rotation. Using a single polar based on a single Re# may not produce very reliable results.

    Rick W
     

  15. tspeer
    Joined: Feb 2002
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    tspeer Senior Member

    I agree. I wasn't proposing using the sections as is, but as a starting point for his design.

    Without looking it up, I think Wortmann designed the FX 74-CL5-140 section for a human powered airplane that would have seen very low dynamic pressure, so the loading on the thin trailing edge would have been manageable.

    If I were to actually use any of those, I'd thicken the trailing edge by maybe half a percent chord, with a squared edge and faired in over the whole section. Basically a parabolic wedge inserted into the thickness distribution. That would probably have negligible effect on the fluid dynamics and would add a lot of stiffness to the trailing edge.
     
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