brenerstuff

GUI - O Mesh Normal Distribution

In the section “Airfoil Coordinate Interpolator” I show how to use a code that interpolates between points to form an airfoil shape with a desired distribution. This can be viewed as “tangent coordinates”. 

If you are working with a O mesh, it might be useful to also specify how the grid should stretch in the normal direction y. In other words, how the grid should stretch when you “walk” from the airfoil wall towards the far field. 

Normal direction of airfoil

In my work with dynamic stall, I needed the distribution in the y direction to do the following: 
– Start with a very small spacing between points in the normal direction;
– Grow this spacing slowly so that the mesh would be refined at the airfoil wall and consequently would be able to capture shear layer phenomena;
– Freeze the spacing at some point for a while so that the mesh close do the airfoil would still be refined; That was needed because the dynamic stall vortex had about a size of about one airfoil chord.
– Far from the airfoil I would not be interested in what was happening so the spacing could start to grow again in order to make the far field as distant as possible. 

In order to accomplish that I wrote a simple GUI with some interactive controls. 

 
GUI for generating points in y direction.
The way I used this program followed this logic:
– Choose how many points are there in the normal direction (ny);
– Start from a dy0 (this is the distance between the point at the airfoil surface (y0) and the next normal point (y1) (if this is too small you will be wasting computational resources but if it is too big you will lose too much accuracy) and increase dy values until reaching a dyFreeze after nyUntilFreeze points;
– Then dy will be kept the same until there are only nyFarField points left (I did this because I needed to maintain a fine mesh on the surroundings of the airfoil to properly capture the dynamic stall vortex as already mentioned);
– The idea now is to grow dy until dyFarField with the remaining points (if this is too small the far field will be close to the airfoil and this could be a problem but if it is too big the stretching could be too much and cause some weird effects on the boundaries of the domain). The truncateFarField is just for fine tuning things around the far field but overall this probably will not be needed. 
 
You then can hit Export and a file called “y.csv” will be generated.