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Forced Pitch Oscillation of Wing with pisoFoam/uniformFixedValue inlet 

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January 21, 2019, 23:50 
Forced Pitch Oscillation of Wing with pisoFoam/uniformFixedValue inlet

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Ben
Join Date: Oct 2016
Posts: 25
Rep Power: 10 
I would really appreciate it if anyone could shed some information on this problem that I'm facing where I encounter nonphysical behavior at the boundaries of my domain due to sinusoidal oscillation at the inlet.
Context: I'm trying to perform a forced pitch oscillation of a wing where the angle of attack is sinusoidal at the inlet resulting in the wing undergoing pitch oscillation. Here is my grid (polyMesh file here) and its checkMesh details: The mesh is relatively coarse, but of good quality as I'm trying to get something running first. Here is my checkMesh output: Code:
/**\ =========  \\ / F ield  OpenFOAM: The Open Source CFD Toolbox \\ / O peration  Website: https://openfoam.org \\ / A nd  Version: 6 \\/ M anipulation  \**/ Build : 66257b17a4cf8 Exec : checkMesh Date : Jan 22 2019 Time : 11:02:10 Host : "bentkj" PID : 12927 I/O : uncollated Case : /home/bentkj/Desktop/FPO_Re1.8M_10deg_NACA0012_6x36ft_SqTips_SharpTE_VeryCoarse nProcs : 1 sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE). fileModificationChecking : Monitoring runtime modified files using timeStampMaster (fileModificationSkew 10) allowSystemOperations : Allowing usersupplied system call operations // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // Create time Create polyMesh for time = 0 Time = 0 Mesh stats points: 485178 faces: 1421163 internal faces: 1387026 cells: 468075 faces per cell: 5.99944 boundary patches: 5 point zones: 0 face zones: 1 cell zones: 1 Overall number of cells of each type: hexahedra: 467814 prisms: 261 wedges: 0 pyramids: 0 tet wedges: 0 tetrahedra: 0 polyhedra: 0 Checking topology... Boundary definition OK. Cell to face addressing OK. Point usage OK. Upper triangular ordering OK. Face vertices OK. Number of regions: 1 (OK). Checking patch topology for multiply connected surfaces... Patch Faces Points Surface topology NACA0012 1695 1725 ok (nonclosed singly connected) SYM 8784 8957 ok (nonclosed singly connected) FARFIELD 8871 9007 ok (nonclosed singly connected) OUTLET 5088 5238 ok (nonclosed singly connected) INLET 9699 9936 ok (nonclosed singly connected) Checking geometry... Overall domain bounding box (26.8371 27.4 27.4) (36.5 0 27.4) Mesh has 3 geometric (nonempty/wedge) directions (1 1 1) Mesh has 3 solution (nonempty) directions (1 1 1) Boundary openness (2.27861e15 3.89001e16 7.70399e17) OK. Max cell openness = 4.17414e16 OK. Max aspect ratio = 136.035 OK. Minimum face area = 0.000160401. Maximum face area = 4.88289. Face area magnitudes OK. Min volume = 4.54879e05. Max volume = 3.68761. Total volume = 86323.4. Cell volumes OK. Mesh nonorthogonality Max: 48.1605 average: 9.37349 Nonorthogonality check OK. Face pyramids OK. Max skewness = 0.935538 OK. Coupled point location match (average 0) OK. Mesh OK. End Therefore, I have written a python script to output u and v velocity components as a function of time for my inlet as a .csv file to be read. An example of the first few lines of my .csv file: Code:
time,u,v,w 0.0,14.155626641797479,2.496018905784457,0 0.00025,14.15542130460082,2.4971831509229037,0 0.0005,14.155215871695166,2.4983473789105717,0 (the comments contained are other options I've tried but I'm faced with the same problem). Code:
INLET { type uniformFixedValue; uniformValue { type csvFile; nHeaderLine 1; // number of header lines refColumn 0; // time column index componentColumns (1 3 2); // data column index separator ","; // optional (defaults to ",") mergeSeparators no; // merge multiple separators file "$FOAM_CASE/0/sineAlpha.csv"; } } An example of my log.pisoFoam output is typical, and is as such: Code:
Time = 0.9275 Courant Number mean: 0.00723135 max: 0.569428 smoothSolver: Solving for Ux, Initial residual = 0.000446676, Final residual = 5.48794e11, No Iterations 2 smoothSolver: Solving for Uy, Initial residual = 9.264e05, Final residual = 4.35567e08, No Iterations 1 smoothSolver: Solving for Uz, Initial residual = 0.000602655, Final residual = 3.40641e11, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00192879, Final residual = 9.81297e07, No Iterations 17 time step continuity errors : sum local = 3.18157e13, global = 3.5438e14, cumulative = 9.26395e10 GAMG: Solving for p, Initial residual = 3.12659e05, Final residual = 8.22712e07, No Iterations 7 time step continuity errors : sum local = 2.66708e13, global = 4.71905e14, cumulative = 9.26348e10 GAMG: Solving for p, Initial residual = 7.78922e06, Final residual = 7.65518e07, No Iterations 3 Problem: Monitoring the solution shows nonphysical results occurring at both the upper and lower boundaries of the domain, and the solution sometimes diverges if it's run long enough (about 4 pitch cycles) As pictured: The contours seem incorrect and are not representative of freestream conditions. The upper and lower patches are also of the inlet type (polyMesh file linked above) and from my understanding, I do not see any reason why this would not work. From my own experimenting, this nonphysical behavior does not seem to occur when a fixedValue inlet boundary condition is used! Could someone please enlighten me on why this is occurring and what is wrong with my methodology? I would greatly appreciate it if I could get hints, or an alternative approach to overcome this problem. I have been stuck on this for weeks now and conducting this forced pitching simulation is vital progressing in my work. Thank you. Last edited by bentkj; January 22, 2019 at 03:51. 

March 23, 2022, 11:49 

#2  
New Member
Sandro Brad Martinez Sardon
Join Date: Sep 2021
Posts: 17
Rep Power: 5 
Quote:
First of all I have to say that I've followed the same strategy and I got the same results. As a result I have the same issue. So , did you eventually get physical results using this strategy ? If not, how did you get physical results ? using dynamic meshes? Currently I am stuck in this point and I don't know if I rely on my cl, alpha results or switch to the dynamic mesh strategy. Thats all for the moment. Thank you in advance and I'm so eager to see what you've done eventually. Cheers 

Tags 
pisofoam, pitching oscillation, sinusoidal oscillating, uniformfixedvalue, wing motion 
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