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Old   May 16, 2011, 14:21
Default Pressure distribution irregularities
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Hi Iím running a case on an RAE 2822 airfoil (M=0.729and Re=6.5E6) on a structured mesh. The mesh was created in ICEM CFD and FLUENT was used as the solver. In solving my case (I set my convergence criteria to <1E-5 and set y+=10 which is valid my the S-A turbulence model im using) I discovered irregularities on my pressure plot. I included a copy of my pressure plot below.

Firstly, when plotting my xy pressure plot I found that there were oscillations along the plot. I took this to indicate the nodes in the BL were skewed so I used global smoothing in ICEM targeting the skew and I was able to alleviate some of the oscillations. However some are still present. I was wondering what else could be the cause these small oscillations?

Additionally, at the nose of the airfoil on the top side the initial pressure drop is steeper than that found in the experimental data. The plot should not reach -1.25 at this location. As well the oscillations in this area seem to be severe and the smoothing didnít really help. Iím not sure what could cause this and am hoping someone could help me find a reason for this.

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Old   May 19, 2011, 21:16
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Hi, so in further trying to figure out this problem of oscillations i examined the mass imbalance residuals along the curve and noticed that they started to act up at a location of 0.03c along the airfoil. So I further refined the mesh in the longitudinal direction placing at one point 250 nodes along the airfoil which reduced my aspect ratio a fair bit along the wall (smething i thought could be the problem). However this did little to help the problem. Again I check the sckew of the mesh and it seems to be close to 1 in all places dipping to 0.65 in some and the overall quality of the mesh seemed was not lower than 0.9. I was wondering if anyone had any idea what could be causeing these oscillations along the pressure curve. I've concidered that my far-field boundaries may be too close but they are at a distance to 20 chord lengths in the front to the top and bottom and 30 chord lengths to the exit. So i dont feel the problem is there. Interestingly the code is predicitng the shock to be in the correct location just after the mid-chord point (something for which leading edge pressure resolution is critical for) even though the pressure values seem to oscillate and a larger than normal pressure drop is recorded a the leading edge of the airfoil. Please if anyone has any ideas whatsoever with how to deal with this, comments or anything please leave them. (on a side note im using ICEM to build the mesh and fluent to solve the case)

Thank you
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