Hi everyone,
first, because this is my first message here, thank you for developing
this free software, it is very helpful for me.
Second I'm actually trying to build a mesh for an naca6412 airfoil and I
have trouble with it. I have written the script attached and it works
well when I ask for a relatively small number of points on the airfoil
(for example NACA4_npts = 100;).
But when I ask for a larger value of this variable (NACA4_npts = 500;),
I get the following error :
ala...@troll:~/Maillages/Naca_Eolienne$ gmsh-2.4.2 Naca.geo
-0
Info : Running 'gmsh-2.4.2 Naca.geo -0'
Info : Started on Sun Oct 18 22:42:55 2009
Info : Reading 'Naca.geo'
Error : Unknown curve -2000
Info : Adding edge points to compute mean plane of face 2007
** On entry to DGESVD parameter number 6 had an illegal value
Could someone help me please with this, I have googled it many different
ways and didn't get any relevant answer ? Is it a problem of distance between the two nearest points ?
Thank You,
Adam
// the following variables must be set on entry:
// NACA4_th thickness in percent of chord
// NACA4_ch aerofoil chord
// NACA4_le_x,y,z leading edge coordinates
// constants from NASA TM4741
NACA4_a0 = 0.2969 ;
NACA4_a1 = -0.1260 ;
NACA4_a2 = -0.3537 ; // 0.3516 on
http://www.aerospaceweb.org/question/airfoils/q0100.shtml but then the sum of
the corfficients is not 1.0 !
NACA4_a3 = 0.2843 ;
NACA4_a4 = -0.1015 ;
NACA4_npts = 500;
NACA4_ch = 1.0;
NACA4_le_x = 0.0 ;
NACA4_le_y = 0.0 ;
NACA4_le_z = 0.0 ;
NACA4_Points[] = {} ;
NACA4_Splines[] = {} ;
xu[] = {};
yu[] = {};
// Definition du Naca####
camber = 6/100; // First Digit : maximum camber in percentage of the
chord (m)
position = 4/10; // Second Digit : position of the maximum camber in tenths of
the chord (p)
Thickness = 12/100; // Two last Digits : thickness of the airfoil in
percentage of the chord (t)
// We here suppose that NACA4_npts is even...
// First half of the NACA starting from the trailing edge
For i In {0:NACA4_npts/2}
x = 0.5*(1+Cos(i/NACA4_npts*Pi));
x = x*((2-4*position)*x+4*position-1); // x[i=NACA4_npts/2] is now
situated at the maximum camber
yc = camber/(1-position)^2*(1-2*position+2*position*x-x^2);
yt =5.0*Thickness*(NACA4_a0*Sqrt(x) +
x*(NACA4_a1 + x*(NACA4_a2 + x*(NACA4_a3 + x*NACA4_a4)))) ;
theta = Atan(2*camber/(1-position)^2*(position-x));
xu[i] = x-yt*Sin(theta);
yu[i] = yc+yt*Cos(theta);
pt_oppose = 2*NACA4_npts-i;
xu[pt_oppose] = x+yt*Sin(theta);
yu[pt_oppose] = yc-yt*Cos(theta);
EndFor
// Second Half
For i In {NACA4_npts/2+1:NACA4_npts}
x = 0.5*(1+Cos(i/NACA4_npts*Pi));
x = x*((2-4*position)*x+4*position-1);
inter = x/position;
yc = camber*inter*(2-inter);
yt = 5.0*Thickness*(NACA4_a0*Sqrt(x) +
x*(NACA4_a1 + x*(NACA4_a2 + x*(NACA4_a3 + x*NACA4_a4)))) ;
theta = Atan(2*camber/position*(1-inter));
xu[i] = NACA4_ch*(x-yt*Sin(theta))+NACA4_le_x;
yu[i] = NACA4_ch*(yc+yt*Cos(theta))+NACA4_le_y;
pt_oppose = 2*NACA4_npts-i;
xu[pt_oppose] = NACA4_ch*(x+yt*Sin(theta))+NACA4_le_x;
yu[pt_oppose] = NACA4_ch*(yc-yt*Cos(theta))+NACA4_le_y;
EndFor
// Computation of the Characteristic Length such that the defined
// points and only them are on the boundary...
distance[0]= Sqrt((xu[1]-xu[0])^2 +(yu[1]-yu[0])^2);
For i In {1:NACA4_npts*2-1}
distance[i]= Sqrt((xu[i+1]-xu[i])^2 +(yu[i+1]-yu[i])^2);
length[i] = 0.5*(distance[i]+distance[i-1]);
EndFor
length[0] = 0.5*(distance[0]+distance[NACA4_npts*2-1]);
// Creation des Points
For i In {0:NACA4_npts*2-1}
Point(i+1) = {xu[i],yu[i],NACA4_le_z,length[i]};
EndFor
// Creation des lignes
j=NACA4_npts*2+1;
lNaca[0]=j;
For i In {0:NACA4_npts*2-2}
Line(j) = {i+1,i+2};
j++;
lNaca[i+1]=j;
EndFor
Line(j) = {NACA4_npts*2,1};
// Line Loop
ll = newll;
Line Loop(ll)={lNaca[]};
// FarField
i=0; ext = 1.0;
pCercle[i] = newp;Point(pCercle[i]) = {11,0,0,ext};
i++;pCercle[i] = newp;Point(pCercle[i]) = {1,0,0,ext};
i++;pCercle[i] = newp;Point(pCercle[i]) = {1,10,0,ext};
quartCercle = newl;
Circle(quartCercle) = {pCercle[]};
c1[] = Rotate{{0,0,1},{1,0,0},Pi/2} {Duplicata{Line{quartCercle};}};
c2[] = Rotate{{0,0,1},{1,0,0},Pi} {Duplicata{Line{quartCercle,c1[0]};}};
ligneExt[] = {quartCercle,c1[0],c2[0],c2[1]};
cercleExt = newll;
Line Loop(cercleExt) = {ligneExt[]};
Physical Line(2) = {ligneExt[]};
// Surface
surf = news;
/*
Printf("%g",surf);
Printf("%g %g",cercleExt,ll);
For i In {0:# ligneExt[]-1}
Printf("%g %g",i,ligneExt[i]);
EndFor
For i In {0:# lNaca[]-1}
Printf("%g %g %g",i,lNaca[i],length[i]);
EndFor
*/
Plane Surface(surf) = {cercleExt,ll};
Physical Surface(0) = surf;
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