[Marwa_Shaaban]

Hello every body !
Is there a way similar to dynamic mesh (6-DOF flunet solver) to obtain angular velocity every time step based on inertia of body at CFX ?

[ghorrocks]

Are you talking about a rigid body simulation? You can get the orientation of the body at any time using variable Euler Angle X/Y/Z

[Marwa_Shaaban]

Is rigid body valid to use for rotating domain like vertical axial turbine ?

[ghorrocks]

Yes, it can be done that way. Rotating frames of reference is much more efficient if that approach is valid. It depends on what you are trying to do and why you are doing it.

[Marwa_Shaaban]

I want to rotate rotor blades for vertical axial turbine around center of mass whith variable angular velocity depends on inertia by using cfx

[ghorrocks]

Yes, this can be done by rigid bodies. But if you search the forum you will find some people who have done a similar thing using rotating frames of reference - this will be many times faster if it works for you. The problem is that rotating frames of reference is designed for constant rotational speed, so have a look at the discussions on this for the available options.

Another option is if you can run the rotor at different speeds at steady state you can get a torque versus speed curve. Then you can write a simple ODE solver which uses this performance curve and the rotor inertia to model the dynamics of the system. This will be by far the quickest way of modelling this, but whether it is applicable to what you are trying to do will depend on exactly what dynamics you are trying to model.

[Opaque]

You can do non-constant angular speed in Ansys CFX. The equations are formulated to include angular acceleration. What you cannot do is a variable axis of rotation.

Recall w_vector = angular_speed * AxisRotation_vector

its derivative (a derivative of a product) includes the time variation of angular speed and the "time derivative of the motion of the axis". The latter is not part of the Ansys CFX formulation as far as I understand.

[Marwa_Shaaban]

I used rigid body but solution stoped whith that error "The solver exited abnormally, but reached the final synchronization point.
Continuing."

[ghorrocks]

That error can mean anything. You would have to post your output file so we can read it in context.

[Marwa_Shaaban]

+--------------------------------------------------------------------+
| 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. |
| Volume : -0.7638E-13 |
| Location : ( -0.19033E+00, 0.26402E+00, -0.34940E-02) |
+--------------------------------------------------------------------+

I can't upload out file due to file size limitation

[Marwa_Shaaban]

================================================== ====================
Wall Force and Moment Summary
================================================== ====================

Notes:
1. Pressure integrals exclude the reference pressure. To include
it, set the expert parameter 'include pref in forces = t'.


+--------------------------------------------------------------------+
| Pressure Force On Walls |
+--------------------------------------------------------------------+
X-Comp. Y-Comp. Z-Comp.

Domain Group: rotor

RotorWall 1.5668E+01 -8.8360E+00 -7.0890E-03
----------- ----------- -----------
Domain Group Totals : 1.5668E+01 -8.8360E+00 -7.0890E-03


+--------------------------------------------------------------------+
| Viscous Force On Walls |
+--------------------------------------------------------------------+
X-Comp. Y-Comp. Z-Comp.

Domain Group: rotor

RotorWall 7.4660E-01 1.1013E-01 -3.5926E-03
----------- ----------- -----------
Domain Group Totals : 7.4660E-01 1.1013E-01 -3.5926E-03


+--------------------------------------------------------------------+
| Pressure Moment On Walls |
+--------------------------------------------------------------------+
X-Comp. Y-Comp. Z-Comp.

Domain Group: rotor

RotorWall 3.0673E+00 5.4587E+00 6.7274E-01
----------- ----------- -----------
Domain Group Totals : 3.0673E+00 5.4587E+00 6.7274E-01


+--------------------------------------------------------------------+
| Viscous Moment On Walls |
+--------------------------------------------------------------------+
X-Comp. Y-Comp. Z-Comp.

Domain Group: rotor

RotorWall -3.8996E-02 2.6041E-01 6.4614E-02
----------- ----------- -----------
Domain Group Totals : -3.8996E-02 2.6041E-01 6.4614E-02

+--------------------------------------------------------------------+
| Average Scale Information |
+--------------------------------------------------------------------+

Domain Name : rotor
Global Length = 1.1324E+00
Minimum Extent = 1.2000E+00
Maximum Extent = 1.3000E+00
Density = 1.1850E+00
Dynamic Viscosity = 1.8310E-05
Velocity = 9.0333E+00
Advection Time = 1.2535E-01
RMS Courant Number = 2.3200E+01
Maximum Courant Number = 2.7195E+02
Reynolds Number = 6.6200E+05
Thermal Conductivity = 2.6100E-02
Specific Heat Capacity at Constant Pressure = 1.0044E+03
Prandtl Number = 7.0462E-01
Temperature Range = 8.2489E-01

Domain Name : stator
Global Length = 3.2821E+00
Minimum Extent = 2.0000E+00
Maximum Extent = 8.0000E+00
Density = 1.1850E+00
Dynamic Viscosity = 1.8310E-05
Velocity = 1.1866E+01
Advection Time = 2.7660E-01
RMS Courant Number = 9.1303E-01
Maximum Courant Number = 1.6787E+00
Reynolds Number = 2.5205E+06
Thermal Conductivity = 2.6100E-02
Specific Heat Capacity at Constant Pressure = 1.0044E+03
Prandtl Number = 7.0462E-01
Temperature Range = 6.3293E-02

+--------------------------------------------------------------------+
| Variable Range Information |
+--------------------------------------------------------------------+

Domain Name : rotor
+--------------------------------------------------------------------+
| Variable Name | min | max |
+--------------------------------------------------------------------+
| Mesh Coordinates x | -6.00E-01 | 6.00E-01 |
| Mesh Coordinates y | -6.00E-01 | 6.00E-01 |
| Mesh Coordinates z | -3.00E-01 | 1.00E+00 |
| Mesh Displacement X | 0.00E+00 | 0.00E+00 |
| Mesh Displacement Y | 0.00E+00 | 0.00E+00 |
| Mesh Displacement Z | 0.00E+00 | 0.00E+00 |
| Density | 1.18E+00 | 1.18E+00 |
| Specific Heat Capacity at Constant Pressure| 1.00E+03 | 1.00E+03 |
| Dynamic Viscosity | 1.83E-05 | 1.83E-05 |
| Thermal Conductivity | 2.61E-02 | 2.61E-02 |
| Static Entropy | -1.48E+00 | 1.30E+00 |
| Velocity u | -6.49E+00 | 2.16E+01 |
| Velocity v | -1.37E+01 | 1.21E+01 |
| Velocity w | -1.53E+01 | 1.57E+01 |
| Pressure | 1.01E+05 | 1.01E+05 |
| Turbulence Kinetic Energy | 2.08E-04 | 1.38E+01 |
| Turbulence Eddy Dissipation | 2.94E-03 | 9.47E+03 |
| Eddy Viscosity | 1.64E-07 | 4.44E-02 |
| Temperature | 2.98E+02 | 2.99E+02 |
| Static Enthalpy | -4.42E+02 | 3.87E+02 |
| Total Enthalpy | -3.94E+02 | 4.41E+02 |
+--------------------------------------------------------------------+

Domain Name : stator
+--------------------------------------------------------------------+
| Variable Name | min | max |
+--------------------------------------------------------------------+
| Density | 1.18E+00 | 1.18E+00 |
| Specific Heat Capacity at Constant Pressure| 1.00E+03 | 1.00E+03 |
| Dynamic Viscosity | 1.83E-05 | 1.83E-05 |
| Thermal Conductivity | 2.61E-02 | 2.61E-02 |
| Static Entropy | -9.77E-03 | 2.04E-01 |
| Velocity u | 4.16E+00 | 1.23E+01 |
| Velocity v | -1.36E+00 | 2.13E+00 |
| Velocity w | -1.45E+00 | 1.82E+00 |
| Pressure | 1.01E+05 | 1.01E+05 |
| Turbulence Kinetic Energy | 1.07E-04 | 2.29E+00 |
| Turbulence Eddy Dissipation | 2.04E-03 | 3.85E+01 |
| Eddy Viscosity | 1.16E-07 | 1.53E-02 |
| Temperature | 2.98E+02 | 2.98E+02 |
| Static Enthalpy | -3.00E+00 | 6.06E+01 |
| Total Enthalpy | 7.10E+01 | 7.30E+01 |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| CPU Requirements of Numerical Solution - Total |
+--------------------------------------------------------------------+

Subsystem Name Discretization Linear Solution
(secs. %total) (secs. %total)
----------------------------------------------------------------------
Mesh Displacement 1.26E+03 3.2 % 2.00E+03 5.1 %
Momentum and Mass 1.22E+04 31.0 % 4.39E+03 11.2 %
Heat Transfer 3.00E+03 7.6 % 2.59E+03 6.6 %
TurbKE and Diss.K 2.39E+03 6.1 % 4.31E+03 11.0 %
-------- ------- -------- ------
Subsystem Summary 1.89E+04 48.0 % 1.33E+04 33.8 %

GGI Intersection 2.60E+02 0.7 %
File Reading 3.63E+00 0.0 %
Search Calculations 3.20E-01 0.0 %
Variable Updates 3.76E+03 9.6 %
File Writing 4.41E+02 1.1 %
Miscellaneous 2.71E+03 6.9 %
--------
Total 3.93E+04

[ghorrocks]

The most important bits of the output file are the initial lines listing the CCL, the progress of the convergence iterations and if there is an error the last bit of the output file from the convergence history to the end of the file.

But I see you report a negative volume element error - this is going to be the cause of the problem. Your mesh is turning inside out. If you just put the rotor in the middle of a domain and used moving mesh to do the motion you are going to get this error as the mesh will twist itself up until it fails. You need to either put the rotor in a cylindrical mesh region and join it to the rest of the mesh with a GGI so the mesh can slide around without distortion, or use rotating frames of reference (where you will also need a sliding GGI).

[Marwa_Shaaban]

I aready put Rotor at cylinderical domain which has 2 interfaces with rotor and statar.
but i confused which type of Rigid body motion i shouid use whith cylinderical domain (rotor and stator interface)

[ghorrocks]

If you look at the FAQ this error: https://www.cfd-online.com/Wiki/Ansy..._went_wrong.3F

If you do the visualisation it suggests you will see what is not working.