[yuwen zhang]

Hello there,

I am currently trying to use gmsh's boundary layer size field to refine the mesh near a 2d NACA0012 airfoil. It looks really nice everywhere except at the trailing edge when zoomed in. There are lines crossing over from other parts of the airfoil and connect to the same node of the first cell behind the trailing edge.
I can get around of this issue if I increase the first cell thickness a little higher. However, I need this small cell thickness for me to set a y plus value less than 1.
Please see attached photos below for the described mesh.

Thanks a lot you guys help in advance !!!


Screen Shot 2019-02-10 at 8.38.53 pm.png
Screen Shot 2019-02-10 at 8.42.39 pm.png




Here are my geo files that create this mesh.

parameters.geo:
XX = 12 ; // As in NACA00XX.
aoa = 0 ; // Angle of attack, in degrees.
lc1 = 50.00000; //characteristic lengths of elements at outer domain
lc2 = 0.00100; //characteristic lengths of elements at airfoil
lc3 = 0.10000; //characteristic lengths of elements at intermediate domain
t_firstcell = 4.6035e-06; //Cell size of the first cell coming out from the airfoil
t_total = 0.0163; //Total thickness of the boundary layer
t_r = 1.2; //Expansion ratio of the cell within the boundary layer

main.geo:
Include "parameters.geo";

Li = 500.0; Lo = 500.0; // distance of inflow and outflow boundary from origin
Li1 = 4.0; Lo1 = 4.0; // distance of intermediate inflow and outflow from origin

n = 400; // points on upper/lower surface of airfoil used to define airfoil
// These points may not appear in the mesh.


m = 2*n - 2; // total number of points on airfoil without repetition
// LE and TE points are common to upper/lower surface

nle = n; // point number of LE = no. of points on upper surface
// Point(1) is trailing edge

// NACA0012 profile: formula taken from http://turbmodels.larc.nasa.gov/naca0012_val.html

Macro NACA0012
x2 = x * x;
x3 = x * x2;
x4 = x * x3;
y = 0.594689181*(0.298222773*Sqrt(x)
- 0.127125232*x - 0.357907906*x2 + 0.291984971*x3 - 0.105174606*x4);
Return

Macro RotateAirfoilPoint
// rotates pointId about quarter-chord.
// aoa is the angle of attack in degrees.
Rotate {{0, 0, 1}, {0.25, 0, 0}, -aoa * Pi / 180.0}
{
Point{i};
}
Return

// put points on upper surface of airfoil
For i In {1:n}
theta = Pi * (i-1) / (n-1);
x = 0.5 * (Cos(theta) + 1.0);
Call NACA0012;
Point(i) = {x, y, 0.0, lc2};
Call RotateAirfoilPoint;
xx[i] = x;
yy[i] = y;
EndFor

// put points on lower surface of airfoil, use upper surface points and reflect
For i In {n+1:m}
Point(i) = {xx[2*n-i], -yy[2*n-i], 0.0, lc2};
Call RotateAirfoilPoint;
EndFor

Spline(1) = {1:n}; Spline(2) = {n:m,1};

Transfinite Line{1,2} = n ;


//Farfield domain
Point(1001) = { 0.0, Li, 0.0,lc1};
Point(1002) = { 0.0, -Li, 0.0, lc1};
Point(1003) = {Lo, -Li, 0.0, lc1};
Point(1004) = {Lo, Li, 0.0, lc1};
Point(1005) = {0,0,0};
origin = 1005;

Line(3) = {1004, 1001};
Circle(4) = {1001, origin, 1002};
Line(5) = {1002, 1003};
Line(6) = {1003, 1004};

Line Loop(1) = {1,2}; // airfoil line loop
Line Loop(2) = {3,4,5,6}; // far field line loop


//Intermediate Domain
Point(2001) = { 0.0, Li1, 0.0,lc3};
Point(2002) = { 0.0, -Li1, 0.0, lc3};
Point(2003) = {Lo1, -Li1, 0.0, lc3};
Point(2004) = {Lo1, Li1, 0.0, lc3};

Line(13) = {2004, 2001};
Circle(14) = {2001, origin, 2002};
Line(15) = {2002, 2003};
Line(16) = {2003, 2004};

Line Loop(3) = {13,14,15,16};


Plane Surface(201) = {3,1}; //intermediate and airfoil surface
Plane Surface(202) = {3,2}; //farfield and intermediate surface


Extrude {0,0,0.1} { Surface{201,202}; Layers{1}; Recombine;}

//Define Boundary Layer
Field[1] = BoundaryLayer;
Field[1].EdgesList = {1,2};
Field[1].AnisoMax = 1000000;
Field[1].FanNodesList = {1};
Field[1].hfar = 0.3;
Field[1].hwall_n = t_firstcell;
Field[1].thickness = t_total;
Field[1].ratio = t_r;
Field[1].Quads = 1;
Field[1].IntersectMetrics = 0;
BoundaryLayer Field = 1;

Physical Surface("frontAndBack") = {201,202,234,276}; //FrontAndBack
Physical Surface("Farfield") = {271, 275, 263, 267}; //Farfield
Physical Surface("Airfoil") = {233,229}; //Airfoil
Physical Volume("Volume") = {1, 2};

//+
Field[2] = Cylinder;
//+
Field[2].Radius = 0.3;
//+
Field[2].VIn = 0.01;
//+
Field[2].VOut = 20;
//+
Field[2].XAxis = 4;
//+
Field[2].XCenter = 5;
//+
Field[2].ZAxis = 0;
//+
Background Field = 2;

[chandra shekhar pant]

Hello,

It's been a very old post, but I am also facing a similar issue, have you found the solution to this problem?