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Yawing and Rolling Moment Instability

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Old   August 10, 2021, 12:51
Default Yawing and Rolling Moment Instability
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Tanay Nagar
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Hello everyone,
I am finding out yawing and rolling moments for my aircraft using Fluent. It fails to achieve a steady-state value as it did for lift and pitching moment. Since I'm not an aerodynamics expert, I don't know what to expect or if it is right or wrong. I've already checked for asymmetries in the CAD model and run it for 1000 iterations as well. Can anyone discern a probable cause?

Details
SST K-omega
inlet velocity 33m/s
domain 3.5m x 2.5m x 4.2m
geometry bounding box 1.5m x 0.5m x 1.4m
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Old   August 11, 2021, 01:18
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Kira
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What is your y+ value and have you checked you are using the correct y+ value for your conditions?
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Old   September 16, 2021, 02:31
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Tanay Nagar
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Hello, I read about y+ and how much it should be for my model, took me a while to rectify other possible errors. As I understand, y+ should be around 1 as I'm geometrically resolving the mesh using inflation (first layer height = 1e-5 m) with a low Re turbulence model (k-w SST). The solution converges at 125 iterations.
Here is the y+ histogram with y-axis = % of total elements; x-axis = y+ range. Below are the values. the problem is that I'm getting non-zero moments for a symmetrical geometry.

0 elements below 0 (0 %)
3798 elements between 0 and 0.26075032 (9.5026021 %)
16775 elements between 0.26075032 and 0.52150064 (41.971077 %)
15333 elements between 0.52150064 and 0.78225095 (38.363191 %)
4008 elements between 0.78225095 and 1.0430013 (10.028022 %)
49 elements between 1.0430013 and 1.3037516 (0.12259808 %)
2 elements between 1.3037516 and 1.5645019 (0.0050040032 %)
2 elements between 1.5645019 and 1.8252522 (0.0050040032 %)
0 elements between 1.8252522 and 2.0860025 (0 %)
0 elements between 2.0860025 and 2.3467529 (0 %)
1 element between 2.3467529 and 2.6075032 (0.0025020016 %)
0 elements above 2.6075032 (0 %)
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Last edited by tanay_nagar; September 17, 2021 at 03:25.
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Tags
aerodynamic coefficients, aerodynamic forces, instability, rolling moment, yawing moment

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