Learning Forum

[Jack Spreadbury]

Hi,

I'm running a 2D Transient LES simulation of a NACA0012 aerofoil at 0 degrees AoA. As part of the validation, I'm comparing the outputted chordwise Cp data to experimental data collected by NASA. When plotting the Cp distribution, I've noticed a weird trend from around 65% chord to 100% chord (SHOWN AT BOTTOM OF POST)

Just wondering if anyone has come across this before and has any explanation as to what might be causing it? (I'm relatvively inexperienced at CFD so apologies if this is an obvious error/solution!)

[Rob]

Have a look at the pressure contours & velocity vectors too. Trying to diagnose anything from one graph is nearly impossible, and it may be clearer once you look at the flow. 

[Jack Spreadbury]

Hi,

I've analysed the velocity and pressure contours, and there are eddies forming on the aerofoil surface that coincide with the start of the Cp fluctuations. I'm assuming these eddies are cuasing the pressure fluctuations?

 

[Rob]

That's a fair assumption, posting images would be useful. Looking at your course notes, how well will the mesh handle separation in that region? 

[Jack Spreadbury]

I'm pretty confident in the mesh setup, it's a Structured C-Type mesh. I've reduced the cell size to ensure large eddies are capable of being captured. (max y+ is approximately 1, courant number is around 0.5).

Apologies for the poor photo (I'm away from my desk at the minute), but here's a velocity contour plot illustrating the vortex shedding and eddie formation towards the rear of the TE:

[Rob]

Check aspect ratio too - y+ is the measure away from the wall you also need to capture changes along the wall. 

Nice result.