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[Other] is it possible to bump on boundary layer?

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Old   March 3, 2017, 07:35
Default is it possible to bump on boundary layer?
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Emma Cooke
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Hi,

I have a 2D mesh of an aerofoil and have added a boundary layer. I would really like to refine the elements around the leading edge of the geometry without making the whole boundary layer fine. I have tried to find how to add a progression or a bump to the surface but have come across nothing.

If anyone has any suggestions it would be greatly appreciated.

Thanks!
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Old   March 6, 2017, 16:56
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I have dealt with airfoils before. Can you please attach a picture to you grid?

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Old   March 7, 2017, 05:11
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Images now added, I hope this is a bit clearer now.

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Old   March 9, 2017, 09:10
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Hi Cookie,

Quote:
I would really like to refine the elements around the leading edge of the geometry without making the whole boundary layer fine.
Would it make a difference if you just refine the mesh around the leading edge in your case? What is the significance of that? In my experience, to just refine the leading edge only, you need to split the leading edge area using plane surface. Secondly, I see that you have hybrid grid any reason why?

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Old   March 14, 2017, 07:53
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Hi Tareqkh,

I have a hybrid mesh as I am trying to reduce the number of elements, this is also the reason I want to refine points around the leading edge but don't want to refinement further down stream. When I try with a structured mesh the generation doesn't work properly due to the sharp leading edge curvature. What do you mean by split the leading edge with plane surface?

Heres my code if it helps:

//points are defined from lower surface trailing edge, clockwise to upper surface trailing edge 225 points for complete geometry.

LE_index = 113; // (leading edge) last point with negative y on the lower surface

lc_begin = 0.0003;
lf = 0.1;
prog = 1.015;
startPoint = 90;
endPoint = 190;
numPoints = endPoint-startPoint;
attachment_point = startPoint + 37;

Ry = 0.3;
Rx = -0.4;
adjustment = 0.04;

pi = 3.141592653589793;

/* This section does not work to make fine leading edge
// Points definition airfoil
lc = lc_begin*prog^(attachment_point-startPoint);
For i In {startPoint:attachment_point}
Point(i-startPoint) = {x[i], y[i], 0.0, lc};
lc = lc/prog;
EndFor

lc = lc_begin*prog;
For i In {attachment_point+1:endPoint}
Point(i-startPoint) = {x[i], y[i], 0.0, lc};
lc = lc*prog;
EndFor
*/


lc = lc_begin;
For i In {startPoint:endPoint}
Point(i-startPoint) = {x[i], y[i], 0.0, lc};
//lc = lc*prog;
EndFor


//define aerofoil spline of geometry
BSpline(1) = {0:numPoints};


// Calculating the outer boundary based on the airfoil
For i In {startPoint:endPoint}
t[i] = (y[i+1]-y[i-1])/(x[i+1]-x[i-1]);
n[i] = -t[i];

theta_n[i] = (Atan((n[i])));

If (i > LE_index)
xExt[i] = x[i] + Ry*Sin(theta_n[i]);
yExt[i] = y[i] + Ry*Cos(theta_n[i]);
EndIf
If (i <= LE_index)
xExt[i] = x[i] - Ry*Sin(theta_n[i]);
yExt[i] = y[i] - Ry*Cos(theta_n[i]);
EndIf

Point(i-startPoint+numPoints+1) = {xExt[i], yExt[i], 0.0,lf};

EndFor

//Define outer boundary spline
BSpline(2) = {numPoints+1:numPoints*2+1};

nLine = 2;

// Join Splines

Line(nLine+1) = {numPoints, numPoints*2+1};
nLine = nLine+1;

Line(nLine+1) = {0 , numPoints+1};
nLine = nLine+1;


//define the boundary
Line Loop(100) = {2,4,-1,-3};

//define unstructured mesh
Plane Surface(200) = {100};

Physical Surface(500) = {200};

//Define Boundary Layer
Field[1] = BoundaryLayer;
Field[1].EdgesList = {1}; //(lines) of aerofoil on both planes
Field[1].NodesList = {0,100}; //(points) at which symmetry planes align
Field[1].FacesList = {1}; //(surface)loop of both surfaces
Field[1].hfar = 0.05; //element size far from the wall
Field[1].hwall_n = 0.0000095; //element size at wall
Field[1].thickness = 0.01; //BL thickness
Field[1].ratio = 1.1; //ratio between two successive layers
Field[1].AnisoMax = 0.0001; //maximum anisotropy of mesh
Field[1].Quads = 1; //generate recombined elements in BL
Field[1].IntersectMetrics = 0; //Intersect metrics of all faces
BoundaryLayer Field = 1;
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