BL meshing airfoil with gap
Hi,
I have a 2D airfoil that has a gap along the surface for blowing. Gambit is unable to create a boundary layer on the surface, stating it is not the correct entity when I tried to select the edge. I assumed this is due to the gap. Can I have some advice how I should create the BL or mesh this airfoil? Thank you. 
1 Attachment(s)
Quote:
Attachment 1467 
I think Chris's suggestion is the right way to do it. split the wall, assign inlet BC to the blowing part

sorry, but i do not quite understand the image. how do i actually split the wall?
my airfoil is 2D, and there is a gap at the top wetted surface of the airfoil, but no gap at the bottom of airfoil. and the blowing is tangential to the airfoil surface, not normal. 
2 Attachment(s)
Quote:
Attachment 1485Attachment 1486 
1 Attachment(s)
this is an image of the leading edge of the aerofoil. there is a gap where there will be blowing.
i would like to add BL along the surface of the aerofoil. 
3 Attachment(s)
Quote:
Start off with an airfoil without at gap. Split the edge of the airfoil with verticies to define the gap, but don't delete the new edge that is formed from the split. Next, offset the vertex at the origin some distance in the negative x direction and create an edge between this new vertex and the vertex at the origin. Then, under the face geometry toolbar, select "Sweep Edges" under "Form Faces", pick the edge you just created as the edge to be swept, pick the edge between the leading edge vertex of the airfoil and the start of the gap as the path edge, and under type select "Perpendicular", and click "Apply." Do this two more times, next using the edge that defines the gap as the path edge, and then using the edge after the end of the gap. After attaching a boundary layer to the edges that define the airfoil AND the edge that defines the gap, you should have something like this: Attachment 1495 Meshing the inside of the airfoil with a structured grid is tough due to the singularity at the edge of the gap, so I used an unstructured quad mesh as a first pass. Also, I made sure to cluster grid around the gap. This is what I got (the second image below is a closeup view of the gap): Attachment 1496Attachment 1497 For boundary conditions, I would set "Wall" for the airfoil and "Interior" for the edges in the interior of the domain and the gap edge. I'm not really sure what to set for the inlet to the interior of the airfoil (maybe "Mass Flow Inlet"?) I hope this helped! 
after creating an edge over the gap, and creating the BL, how do I remove the edge? it cannot be deleted since it is being referenced by the BL now.

Quote:

2 Attachment(s)
thanks for the help.
now i have another problem. the BL mesh does not attach to the surface of the aerofoil, n there is a small gap. may i know what is causing this? (first pic) also, what is the usual method of meshing the area around an aerofoil? i used a semi circle with a rectangle at the trailing edge. n now i have matching problem because the curve of the top quadrant is not the same as the curve of the aerofoil. if i used the sweeping edge method, the mesh will not be of similar sizes. the leading edge mesh will be larger than the trailing edge. 
Quote:
As far as meshing the domain around the airfoil, check out the grid in the FLUENT External Compressible Flow tutorial. In the tutorial, the airfoil is meshed with a C grid, which is one common way of meshing an airfoil. 
I successfully mesh the aerofoil and set the gap to a massflowinlet BC.
However when i read the mesh file in fluent, i got an "Error: massflowinlet zone 3 has two adjacent cell zones" during the grid check. I tried searching the forum n found that fluent cannot have blowing BC. Is that true? If so, how else can I set a blowing boundary condition, with fluid coming out of the gap? 
Quote:

It is exactly the same as the above when I asked how to model a gap with BL over it. The gap is supposed to be the fluid blowing hole.
And yes, there are two mesh regions on both sides of the gap, but they are of the same fluid, which is air. 
Quote:
If you want to solve for the flow inside the airfoil, which (I think) is the configuration that you described before, then define the gap as an interior boundary. In this case, the gap will be the "outlet" of the fluid zone inside the airfoil to the fluid zone outside of the airfoil. Use the mass flow inlet boundary condition for the inlet of the fluid zone inside of the airfoil. 
Quote:
for the second method, if the gap is set as interior, do u mean that the internal region of the airfoil BC be set as "mass flow inlet" instead of "wall"? is the total mass flow inlet now supposed to be equal to what i need at the gap? 
1 Attachment(s)
Quote:
Attachment 1633 The "internal region" is a fluid zone. In 2D, the edges that define the zone are where you apply boundary conditions. So you don't define the region as a mass flow inlet, you define it as a fluid zone. Define the edge marked in the picture as a mass flow inlet. To your question about the mass flow rate at the gap, if it's steady flow, then the mass flow rate at the inlet should be equal to the mass flow rate at the gap. 
2 Attachment(s)
thanks for the help. i used the second method n the grid check is successful.
but i have a question regarding meshing. below is a pic of my meshing. due to the shape of the aerofoil, the mesh is highly skewed. does it matter? the top n bottom half are not symmetrical because for the leading edge of the top half, i made it perpendicular to the contour of the aerofoil. n it becomes very sparse as it moves radially outwards. whereas for the bottom half, i just made it follow the contour of the quadrant, hence it becomes highly skewed. 
Quote:
If you have the resources, you should try your grid to see if it works. Ultimately, though, you'll probably need to play around with how you are blocking the domain and meshing the edges until you get a grid that is good enough. Beyond that, I'm sorry to say that I'm not really sure what else to do. Hopefully, someone can chime in and discuss how they have managed to solve a problem like this. Also, you'll probably want to increase the density of the grid at the gap inside the airfoil (the unstructured region.) As you have it, there is a large change in cell volume at that point, which might give you some problems. 
All times are GMT 4. The time now is 17:34. 