[hr4dx]

Hi all.
Im trying to calculate Blade Flutter using Fourier Transformation.
I read most of the threads I found, but it didnt help me.
I have errors with negative volumes and skewed elements.

ERROR #002100027 has occurred in subroutine cNWDIST_GEOM.
Message:
At least one highly skewed element has been detected on a wall
boundary, leading to an unreliable near-wall distance calculation
for the turbulent wall functions. The solver will continue
to execute, but convergence and/or accuracy may be affected.
Please consider improving the mesh quality. The coordinates of
the element face are ( 0.4659E-01, 0.3635E-02, 0.3427E-01)

ERROR #002100012 has occurred in subroutine Out_NegVol.
Message: |
A negative ELEMENT volume has been detected. This is a fatal
error and execution will be terminated. The location of the first
negative volume is reported below.

I think i made a mistake when export csv file from modal solution.
Maximum Displacement = 27.718890 [m].
To export from mechanical used this command line:

num_mode=arg1
!exun,surf,disp,comm,si
set,1,num_mode,,REAL
cmsel,,Mode1
expr,surf,mode,,Mode1,Mode1,csv,
cmsel,,all,

Import to CFX using expansion.
Physical timescale = 1/15*frequency.

Try meshdisp diffusin scheme and stiffness 1[m^2s^-1]*(1.0E-6[m^3]/Volume of Finite Volumes)^2, but no results.

Mesh in turbogrid. Model - SST.

Can some1 give me an advice?

[Opaque]

The Maximum Displacement reported in the exported file may be correct. Are you familiar with the modal analysis normalization in ANSYS?

Q: How are you setting up the mode shape to move the blade?
Q: Which option are you using for mesh motion boundary condition? Normalized Displacement?
Q: What amplitude are you using for the mesh motion? what fraction of the cord or thickness of the blade?

[hr4dx]

Originally Posted by Opaque

The Maximum Displacement reported in the exported file may be correct. Are you familiar with the modal analysis normalization in ANSYS?

Q: How are you setting up the mode shape to move the blade?
Q: Which option are you using for mesh motion boundary condition? Normalized Displacement?
Q: What amplitude are you using for the mesh motion? what fraction of the cord or thickness of the blade?

Ty for replay.
If you mean that only the shape om modal solution has real meaning, but not displacement/stresses, yeah.
1. I think mode shape goes from .csv file from modal analyses. I use edit profile data then initialize profile data.
2. For periodic and internal bounrady conditions i use stationary option, for other (shroud tip for 2 blades) conservative interface flux.
3. I dont understand what amplitude do u mean. Thickness of the balde for about 3mm.

[Opaque]

Could you post the boundary condition panel for the blade mesh motion section?

[hr4dx]

Originally Posted by Opaque

Could you post the boundary condition panel for the blade mesh motion section?

Sure. Here it is.

[Opaque]

The entry Amplitude cannot be 27[m]. What size is your machine?

For a blade flutter analysis (aerodamping calculation), the vibration amplitude is usually very small. A fraction of the thickness of the blade or the blade cord. Say 2% of the blade cord.

Once you get a solution for such value, you can increase it to twice/half as much, and verify your normalized aerodamping is still the same. Recall the aerodamping value scale with the square of the vibration amplitude.

[hr4dx]

Originally Posted by Opaque

The entry Amplitude cannot be 27[m]. What size is your machine?

For a blade flutter analysis (aerodamping calculation), the vibration amplitude is usually very small. A fraction of the thickness of the blade or the blade cord. Say 2% of the blade cord.

Once you get a solution for such value, you can increase it to twice/half as much, and verify your normalized aerodamping is still the same. Recall the aerodamping value scale with the square of the vibration amplitude.

But in my .csv file maximum displacement is 27 [m]. I understand that it is from modal solution and not physical, but In youtube tutorials people take it as entry amplitude.
Size of machine for about 200 mm.
I tryed take 0.00027 [m] as amplitude, but got same errors.
Will try to find files from CFX tutorial №37.
In different guides i saw, that they use different .csv files ( with imaginary part and without) and nodal diameter and "from file". What the difference?
Will try 2% as u say.
Thank you for your advices.

[hr4dx]

Hello again. I did for about 20 calculations with different options:
1) Different mass flow rates;
2) Different mesh (from 500k to 2kk elements);
3) SST and k-e models;
4) Time transformation and harmonic balance;
5) Amplitude from 1,5% to 5% blade coord.
I got solution for several flow rates and only for 500k mesh.
For other options as shown.

Originally Posted by Opaque

Recall the aerodamping value scale with the square of the vibration amplitude.

I don't understand the moment. Couldn't explain.
Will try FEMAP with SOL 145 and maybe MSC Flight Loads.

[hr4dx]

And when use Time Transformation method always get this graph.