Xfoil Ncrit

Discussion in 'Sailboats' started by Alvarogy, Jan 30, 2018.

  1. Alvarogy
    Joined: Jan 2018
    Posts: 1
    Likes: 0, Points: 1
    Location: Southampton

    Alvarogy New Member

    Hi, I am new to boatdesign.net and to XFoil.

    I am using XFoil to calculate the lift to drag coefficients of a NACA 4412 for a DSS system on a 50 footer.
    I've read that the Ncrit to be used for this cases ranges between 3 to 5, but the problem is that I don't know how to change the Ncrit in XFoil, and the default one is 9.
    Anybody knows the command to do this?

    Thank you very much,
    Alvaro
     
  2. Dolfiman
    Joined: Aug 2017
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    Location: NICE (France)

    Dolfiman Senior Member

  3. Dolfiman
    Joined: Aug 2017
    Posts: 421
    Likes: 203, Points: 43
    Location: NICE (France)

    Dolfiman Senior Member

    Doug Lord likes this.

  4. tspeer
    Joined: Feb 2002
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    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    Dolfiman has the commands correct. I would use even lower values of Ncrit, say 1<Ncrit<3. I also run cases with the boundary layer fully turbulent, by tripping the flow at 2.5% chord. This is done with the OPER->NPAR->X command. If you use a negative value (say, -0.025) transition will be referenced from the stagnation point rather than the leading edge.
     
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