harmonic motion using panel methods


I am trying to simulate the flow over a wing undergoing harmonic motion using the panel solver.
But so far I haven't been able the setup the case, I wonder if there is a tutorial or example similar to my problem. I already took a look at the tutorials available on the site, but I am still not able to setup a proper case.

Thanks for your help,


Pitching Wing

For an example try "Screencast of Transient Air Flow Over a Pitching Wing." Be sure to read the notes.

To produce cyclic motion, you'll need to setup multiple key frames (set the time - use the Next and Previous buttons on the toolbar - and then apply a transform relative to the previous key frame position or rotation) for the peak movements (max. and min. positions or angles). To produce harmonic motion you'll need to select your volume, then in the Properties Panel click the motion tab (middle tab), visit each key frame transform and set Time-><Transform>->Transition = Smooth

How to set the rotational velocity?


Ok I followed the screencast but I find it a little bit confusing. My main question is, when did I setup the rotational velocity?, 'cause the wing is rotating but I never input a rotational velocity value. In the same order of ideas, how do I input the maximum pitching angle and the rotational velocity?. Let's say for instance that I want the wing to rotate aroung the leading edge with a max velocity of 5 rad/s and a maximum angle of attack of 30.

Regarding to the BCs, how do I erase a BC, let's say that I assigned the wake BC to the wrong edge, how do I erase it? and most important, how do I know where this BC is in use (i think I already asked something similar).



Erase or Delete Boundary Condition

To erase a BC, select the entity (e.g., edge) with the BC, then in the Properties Panel select the entity tab (first tab, e.g., Edge tab), select the Physics property you want to erase (pink properties can be deleted, e.g., Physics:Wake) and then right-click the same property and select Delete Physics in the popup context menu.

There is currently no indicator in the 3D view as to what BCs are in use. I suggest as soon as you assign a BC you change the color of the entity as the best means to currently see your BCs.

Visualize Mesh and Apply Accuracy?


I am working in some tutorials and I think I am starting to understand better symscape.
My question now is how do I see the mesh used in the potential solver?. Also I wonder how can I control the quality and type of elements used (triangles vs. quads)?. So far I am using accuracy control but there i just have 3 options, I wonder if I can have a better control over the mesh.


Mesh and Accuracy

To see the mesh set the face view properties:

  • Style = Flat
  • Transparent = off

For more details try "View a Mesh."

Whether a mesh is created using triangles or quads is governed by the topology of your geometry and the Accuracy constraints. Quads are limited to 4-edged geometry faces, and where opposing Accuracy constraints don't conflict.

For more details on the Accuracy tool try "Accuracy Tool."

Export the solution?

hi thanks for your promptly reply. How can export the solution into another format? Lets say for instance that I want to export a potential flow solution into tecplot format or csv format, is it possible?

Export Formats for Panel Flow

You can export your Panel Flow mesh and 3D results to POV-Ray, Renderman, and VRML formats (with either the Professional or Viz Export add-ons activated). The Tecplot, EnSight, and FieldView formats are only available for RANS Flow results.

Plots and monitors can be exported to CSV formats.

To see the available formats for a particular window (i.e., 3D View, Plot, or Monitor), click in the window to give it focus and then launch the export dialog using File->Export.

Is there a theory manual of the panel solver?

is there a theory manual of the panel solver? I am interested in getting more info on the solver and wake parameters.

Solver Property Tool Tips

Each property under Substance->Solver:Panel Flow has a tool tip that you might find useful. Click a property and then read the tool tip in the status bar at the bottom left of the Caedium application window.

For the theory behind the panel method I suggest you consider the book Low-Speed Aerodynamics, by Joseph Katz and Allen Plotkin.

How to report integrated forces?


So far it seems that the panel solver fits our needs but I still have some other question. How do I compute lift and drag?. I can plot the contours of Fx, Fy and Fz but I dont see any tool to integrate the values over the surface.

It would be possible to output the data from the panel solver to tecplot or vtk format or ascii format?

Before trying it, it is possible to simulate multiple bodies?

Can I plot the induced velocity, circulation or strength of each panel on the wake?



Integrated Forces and More

For the integrated forces on a surface or group, you would use Vector Variables->F from the Results Tool Palette to create a monitor.

As I mentioned earlier, you can export CSV data from plots and monitors. The Panel Flow add-on does not currently export to Tecplot or VTK formats.

It is possible to simulate multiple bodies, as an example see "NLR 7301 Multi-Element Airfoil Calculation."

You can not plot anything on the wake mesh. Though, you can view the the doublets on the geometry faces.

A few more questions


Before taking a short break until next week, I have a few questions.

Does the panel solver runs in parallel?
Can I run caediun in a cluster?, for the rans solver, the dynamic mesh solvers are suported?

Again, so far I think the panel solver can fit part of our needs. So I wonder if we get access to the source code of the solver as we will like to add some extra features, such as boundary layer corrections and probably so transition models.

What about the feature of user defined kinematics? it can be added?, and this is very important for us as we are planing to use quite complex kinematics.

Regarding to the postprocesing, can it be possible to add the posibility to export the results of the panel solver to tecplot or vtk format?.



Some more answers

The Panel Flow solver runs in parallel on a multi-core computer using OpenMP, but it does not run in parallel on a cluster (i.e., multiple computers). Distributing a Panel Flow solver case across discrete computers (cluster) seems unnecessary in that the case sizes are typically small (1000-10,000 surface cells), such that communication overheads would negate any speedups.

The RANS Flow solvers can run in parallel on a Windows HPC Server cluster, for details see "Microsoft Windows HPC Server 2008 Cluster Configuration."

The RANS Flow solvers do not currently support dynamic (moving) mesh.

Our current policy is not to provide access to our source code, sorry.

User defined arbitrary motion (kinematics) could be added, but it is not currently a high priority.

Exporting Panel Flow solver results to the VTK format could also be added.

To add feature requests I suggest you post them in our Ideas Forum.

Accuracy dependent on distorted wake panels?


I have been able to run some simulations using an harmonic motion, but sometimes the wake's panels become to distorted, I dont know if this just a visual issue or a numerical issue, so I am wondering if this issue will affect the accuracy of the solution.

What kind of function is used when I set the transition to smooth?



Distorted Wake Elements

If the wake panels are intersecting either themselves or surfaces then there will be a negative effect on the accuracy of the solution. If self intersecting panels are relatively far away from your lifting surfaces then your solution accuracy may be OK.

To control the wake (some what) you have the option to increase or decrease your global time-step by selecting the simulation (sim in the Select dialog), then in the Properties Panel select the simulation tab (first tab) and adjust the Time->Increment property.

The smooth transition function is a cosine running from 0 to pi, i.e., half a revolution.

Is it possible to model internal flows with the panel solver?


I wonder if it will be possible to model internal flows (for instance models in wind tunnels) and ground effect using the panel solver.


Internal Flow Simulation with Caedium Panel Flow

Yes, internal flows are possible, for a tutorial see "Internal Flow".

To simulate an object inside a wind tunnel you'd need to either:

  • Create a single volume, i.e., subtract the object from the wind tunnel volume.
  • Create two (object and wind tunnel as separate volumes) or more separate volumes, group them and then apply a Substance to the group. After specifying the internal objects faces as Walls you'll also need to set the associated Physics:Wall->Reverse Normal property to on. The advantage of this multi-volume setup is that you can vary the angle of attack for the object in the wind tunnel by transforming it.

Yes simple ground affects can be simulated with the Panel Flow solver too, for an example see "Racing-Car Rear Diffusers."

Caedium will fit our needs


I think Caedium will fit our needs. For the moment we are only interested in the potential flow solver, so in order to run unsteady potential simulation and import stp files, what modules do we need to buy?

Regarding to the user defined motion and output files do you think those features can be added?



Caedium add-ons for unsteady potential flow simulations


So you'll need the following Caedium add-ons:

You should also consider the Builder add-on, so you can create geometry to serve as the:

  • Boundaries for a wind tunnel
  • Seeds and targets for streamlines

User defined motion is unlikely to make the next Caedium release. However, VTK export has a good chance of making it into the next release of the Viz Export add-on.

When is this new version due?


So I guess if we want to export files we will need viz export as well. When is this new version due?

One more question. I think that by using the keyframe editor to create the motion pretty much I can impose any kinematics, but I found that it is really cumbersome to setup a lot of steps, so I wonder if it is possible to read in an ascii file with the info of the timestep and the type of transformation and its respective value.



No definitive release date

I can't provide a definitive release date, but most likely it will be before the end of 2011.

The idea of importing a set of times and transformations to control geometry motion is really a variation on user defined motion, so I suggest you add a comment for this idea to your previous idea "user defined arbitrary motion...".


Btw, is it possible to use scripts?

No Scripts

No scripts I'm afraid. I'm sure this would be a popular item to add to the Ideas Forum.

Rotational Velocity is Implicit

The rotational velocity is implicit in your rotation and keyframe specification, e.g., for linear transition:

Rdot = R / (ti - ti-1)

where Rdot is the rotation velocity and R is the rotation transform at keyframe ti.

To perform a full pitching cycle, with max. angle of attack alpha and duration omega, then at keyframes:

  • t = 0, set R = alpha
  • t = omega / 2, set R = -alpha
  • t = omega, set R = alpha

To specify harmonic motion set the Transition property as outlined in my previous reply.