CFD Struggles :)

Spondon Saha — Mon, 27 Jul 2026 22:16:45 +0000

CFD without prior knowledge is painful.

In order to progress in my Comparative Aerodynamic Analysis project, I have started to try and run the CFD solver on my CAD model of a rectangular wing, which has a 200 mm chord, 600 mm span and follows the standard NACA 2412 profile. Insane underestimation of how difficult OpenFOAM would be, for sure.

Only OpenFOAM knows how I ended up with this mesh:

I mean in a way it's impressive how I turned a square computational domain into something way more complex, right?

Here is my .stl in ParaView:

Here is my mesh in ParaView after running the solver:

So I exported a refined mesh from OnShape, five times before I got a somewhat usable result. The pressure contours this time made sense:

Then I decided I wanted to turn addLayers to true in snappyHexMeshDict. Evidently, not a good idea:

Why? Yet to be figured out.

I removed addLayers and then colored by velocity to see the velocity contours.

At least my Stream Tracers look sensible?

Yes. Trying to solve a self directed CFD case before properly learning CFD is clearly NOT a good idea. So naturally, I've decided to learn Fluid Dynamics & OpenFOAM in intricate detail before my next attempt. This might take a while but I don't see another path forward that will lead to the success of this project.

That was one hell of a week-long learning experience, though.

.DAT to .DXF Converter

Spondon Saha — Mon, 20 Jul 2026 23:23:46 +0000

NACA 2412 Airfoil Databases are in .dat file. The problem? There are no clean .dat -> .dxf converters. The solution? I built one.

This post is directly linked to my ongoing project at the time of writing: Comparative Aerodynamic Analysis Of Wing Planforms.

I needed to model a NACA 2412 wing which had .dat coordinate files available. But OnShape needed .dxf in order to import the coordinates. I couldn't find a clean converter online, so I decided to build one for the sake of this project. I wanted to share the script:

#plot_airfoil.py
# Desired chord length (mm)
CHORD = 200
# import necessary libraries for dxf conversion
import ezdxf
# Path to airfoil data file
import os
script_dir = os.path.dirname(os.path.abspath(__file__))
filename = os.path.join(script_dir, "..", "airfoil", "naca2412.dat")
#Open the file
with open(filename, 'r') as file:
    lines = file.readlines()
#Print every line
#for line in lines:
 #   print(line)
import matplotlib.pyplot as plt
x = []
y = []
with open(filename, 'r') as file:
    lines = file.readlines()
for line in lines[1:]: #Skip the NACA 2412 header line
    values = line.split()
    if len(values) == 2:
        x_coord = float(values[0]) * CHORD
        y_coord = float(values[1]) * CHORD
        x.append(float(x_coord))
        y.append(float(y_coord))
plt.figure(figsize=(8, 3))
plt.plot(x, y)

plt.axis("equal")
plt.grid(True)

plt.xlabel("x")
plt.ylabel("y")
plt.title("NACA 2412 Airfoil")

#plt.show()
# Remove the hashtag from the line above to plot the airfoil. The line is commented out to avoid opening a plot window when running the script in a non-interactive environment.
# ---
# Export airfoil to dxf file
CHORD = 200.0 #mm
#Scale coordinates to desired chord length
scaled_x = x
scaled_y = y

doc = ezdxf.new()
msp = doc.modelspace()
#Add polyline
msp.add_lwpolyline(list(zip(scaled_x, scaled_y)), close=True)
#Save file
script_dir = os.path.dirname(os.path.abspath(__file__))
output_file = os.path.join(script_dir, "..", "cad", "naca2412_200mm.dxf")

doc.saveas(output_file)

print(f"Saved to: {output_file}")

The paths & directories in the code was based on my own folder structure, so do feel free to change it as per your requirement if you do plan on using it! It is also available on the GitHub repository mentioned above.

DEV Community: Spondon Saha

CFD Struggles :)

CFD without prior knowledge is painful.

.DAT to .DXF Converter

NACA 2412 Airfoil Databases are in .dat file. The problem? There are no clean .dat -> .dxf converters. The solution? I built one.

This post is directly linked to my ongoing project at the time of writing: Comparative Aerodynamic Analysis Of Wing Planforms.