Divergence issue with SST Turb Model

jehanz · May 12, 2015, 19:29

I am analyzing a propeller of an UAV. I have static thrust measurements such that when I used Euler results I got 3.5 lbf thrust as compared to the measured 6 lbs. My next step was to perform an NS equation with SA turb model. I got 7 times over predicted results such that the mesh has a Y+ of less than 1. Then I thought of doing an SST but was not long enough that it gave me error with divergence. I have been setting up my SST case as per the tutorial example of NACA0012. However, I do not happen to see any entry with regards to eddy frequency etc. (usually required by SST) in the config file. Any guidance will be great.

awendorff · May 19, 2015, 16:46

You can instead try specifying the FREESTREAM_TURBULENCEINTENSITY, which is set to 0.05 by default, and FREESTREAM_TURB2LAMVISCRATIO, which is set to 10 by default. Both of these options can be set in the config file.

jehanz · May 19, 2015, 16:48

Thanks

Let me try and will post my results.

Regards,

jehanz · May 19, 2015, 18:01

Hi,
I tried with:
FREESTREAM_TURBULENCEINTENSITY=0.001
FREESTREAM_TURB2LAMVISCRATIO = 100.0

but I am not sure if these are suitable as I got the following:
Free-stream viscosity (non-dim): 3.61984e-007
Free-stream turb. kinetic energy (non-dim): 0
Free-stream specific dissipation (non-dim): 0

Initialize Jacobian structure (Navier-Stokes). MG level: 0.
Initialize Jacobian structure (SST model).

----------------- Integration and Numerics Preprocessing ----------------
Integration Preprocessing.
Numerics Preprocessing.
Setting dynamic mesh structure.

------------------------------ Begin Solver -----------------------------

Setting rotating frame grid velocities.
Rotational origin (x,y,z): ( 0, 0, 0 )
Angular velocity about x, y, z axes: ( 0, 0, 628.318 ) rad/s

Maximum residual: -4.8402, located at point 57638.

Iter Time(s) Res[Rho] Res[kine] Res[omega] CThrust(Total) C
Torque(Total)
0 149.877000 -6.044197 1.#QNAN0 1.#QNAN0 1.196632e-003 1.77
8442e-003
1 142.350000 -6.044205 -16.000000 -10.059252 1.512296e+000 2.61
1483e+000
2 139.579000 -6.084640 -16.000000 -10.085875 2.813472e+000 4.90
3540e+000
3 138.195750 -6.131297 -15.946917 -9.946917 3.895072e+000 6.87
1384e+000
4 136.817200 -6.180195 -14.692565 -8.692565 4.754986e+000 8.50
6734e+000
5 135.953000 -6.225935 -13.091395 -7.091395 5.397893e+000 9.80
3564e+000
6 135.258000 -6.260035 -11.293994 -5.293994 5.833925e+000 1.07
6124e+001
7 134.779750 -6.273887 -9.338135 -3.338135 6.081352e+000 1.13
9192e+001
8 134.426667 -6.265993 -7.271303 -1.271303 6.164761e+000 1.17
1971e+001
9 134.119100 -6.243379 -5.132733 0.867267 6.115658e+000 1.17
8181e+001
10 134.201455 -6.214587 -2.937581 3.062423 5.966512e+000 1.16
2132e+001

!!! Error: NaNs detected in solution. Now exiting... !!!

It appears I am not seeting the Free stream turb. KE and free stream specific dissipation terms.
Thanks for your help.

May 12, 2015, 19:29	Divergence issue with SST Turb Model	#1
jehanz New Member Jehan Khan Join Date: Jun 2014 Location: Lisle, IL Posts: 6 Rep Power: 11	I am analyzing a propeller of an UAV. I have static thrust measurements such that when I used Euler results I got 3.5 lbf thrust as compared to the measured 6 lbs. My next step was to perform an NS equation with SA turb model. I got 7 times over predicted results such that the mesh has a Y+ of less than 1. Then I thought of doing an SST but was not long enough that it gave me error with divergence. I have been setting up my SST case as per the tutorial example of NACA0012. However, I do not happen to see any entry with regards to eddy frequency etc. (usually required by SST) in the config file. Any guidance will be great.

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May 19, 2015, 16:46		#2
awendorff New Member Andrw Wendorff Join Date: Apr 2014 Posts: 28 Rep Power: 12	You can instead try specifying the FREESTREAM_TURBULENCEINTENSITY, which is set to 0.05 by default, and FREESTREAM_TURB2LAMVISCRATIO, which is set to 10 by default. Both of these options can be set in the config file.

May 19, 2015, 16:48		#3
jehanz New Member Jehan Khan Join Date: Jun 2014 Location: Lisle, IL Posts: 6 Rep Power: 11	Thanks Let me try and will post my results. Regards,

May 19, 2015, 18:01		#4
jehanz New Member Jehan Khan Join Date: Jun 2014 Location: Lisle, IL Posts: 6 Rep Power: 11	Hi, I tried with: FREESTREAM_TURBULENCEINTENSITY=0.001 FREESTREAM_TURB2LAMVISCRATIO = 100.0 but I am not sure if these are suitable as I got the following: Free-stream viscosity (non-dim): 3.61984e-007 Free-stream turb. kinetic energy (non-dim): 0 Free-stream specific dissipation (non-dim): 0 Initialize Jacobian structure (Navier-Stokes). MG level: 0. Initialize Jacobian structure (SST model). ----------------- Integration and Numerics Preprocessing ---------------- Integration Preprocessing. Numerics Preprocessing. Setting dynamic mesh structure. ------------------------------ Begin Solver ----------------------------- Setting rotating frame grid velocities. Rotational origin (x,y,z): ( 0, 0, 0 ) Angular velocity about x, y, z axes: ( 0, 0, 628.318 ) rad/s Maximum residual: -4.8402, located at point 57638. Iter Time(s) Res[Rho] Res[kine] Res[omega] CThrust(Total) C Torque(Total) 0 149.877000 -6.044197 1.#QNAN0 1.#QNAN0 1.196632e-003 1.77 8442e-003 1 142.350000 -6.044205 -16.000000 -10.059252 1.512296e+000 2.61 1483e+000 2 139.579000 -6.084640 -16.000000 -10.085875 2.813472e+000 4.90 3540e+000 3 138.195750 -6.131297 -15.946917 -9.946917 3.895072e+000 6.87 1384e+000 4 136.817200 -6.180195 -14.692565 -8.692565 4.754986e+000 8.50 6734e+000 5 135.953000 -6.225935 -13.091395 -7.091395 5.397893e+000 9.80 3564e+000 6 135.258000 -6.260035 -11.293994 -5.293994 5.833925e+000 1.07 6124e+001 7 134.779750 -6.273887 -9.338135 -3.338135 6.081352e+000 1.13 9192e+001 8 134.426667 -6.265993 -7.271303 -1.271303 6.164761e+000 1.17 1971e+001 9 134.119100 -6.243379 -5.132733 0.867267 6.115658e+000 1.17 8181e+001 10 134.201455 -6.214587 -2.937581 3.062423 5.966512e+000 1.16 2132e+001 !!! Error: NaNs detected in solution. Now exiting... !!! It appears I am not seeting the Free stream turb. KE and free stream specific dissipation terms. Thanks for your help.