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lfiorio3-Newcomer
3-Newcomer
August 29, 2018
Question

Understand which parameters can be extracted from Flow Analysis

  • August 29, 2018
  • 3 replies
  • 18430 views

Currently we are running some external CFD analysis on parts of our robot to get the lift and drag coefficient and the center of pressure [1].

The simulations are performed using ANSYS Fluent [2].

 

Considering that the CAD model of the robot is designed using PTC Creo, and considering that recently PTC has introduced a module for flow analysis [3], we would like to run such simulations directly in Creo.

 

The only problem is that so far we didn't find a document or a video explaining how to get the lift and drag coefficient and the center of pressure.

 

Here the questions:

- Do you know if it is possible to get the lift and drag coefficient and the center of pressure for external CFD?

- Do you have a link to a document that explains how to run such simulations?

- Which package (basic, plus or premium) should we buy?

 

Thank you.

 

[1]:https://www.youtube.com/watch?v=jNnQeKuF7PI

[2]:https://www.ansys.com/it-it/products/fluids/ansys-fluent

[3]:https://www.ptc.com/-/media/Files/PDFs/CAD/Creo-5/Datasheet-Creo_Flow_Analysis-en.pdf

3 replies

skunks
skunks19-Tanzanite
19-Tanzanite
August 30, 2018

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C
cfdgeek13-Aquamarine
13-Aquamarine
September 7, 2018

Hi,

 

Yes, you can select the surface and create a xyplot to monitor pressure or shear force on that surface. 

To compute lift and drag coefficient, we can use expression to do that very easily. You can use expression to define equations and formula.  We also support user defined variable for xyplot.

 

Example of cl, cd calculation

-----------------------------------------------

den=1.16
area=1
aoa=15*pi/180
vmag=200
cx=cos(aoa)
cy=sin(aoa)
nx=-cy
ny=cx

 

drag=(flow.px@patch.surfname + flow.tx@patch.surfname)*cx
+(flow.py@patch.surfname+flow.ty@patch.surfname)*cy

 

lift=(flow.px@patch.surfname + flow.tx@patch.surfname)*nx
+(flow.py@patch.surfname+flow.ty@patch.surfname)*ny

 

plot.cd = drag/(0.5*den*vmag^2*area)
#plot.cd: Drag Coefficient []

 

plot.cl = lift/(0.5*den*vmag^2*area)
#plot.cl: Lift Coefficient []

 -----------------------------------------------------

here flow.px@surfname means pressure force x component from flow module at surfname patch

similarly, flow.tx means shear force x component.

 

For the center of pressure, we need to do an integration of x times pressure of x component on all external surfaces and it is straightforward to use expression to write it.

----------------------------------------------------------------------

cpx = integral(x*flow.pressure*normal.x, patch.surfname)/flow.px@surfname
plot.cpx = cpx
#plot.cpx: Center of Pressure x []

----------------------------------------------------------------------------

 

 

Please contact me if you got further questions!

 

ls@simerics.com

 

Thanks.

 

 

 

    C
    cfdgeek13-Aquamarine
    13-Aquamarine
    September 7, 2018

    Hi 

     

    For the package, if you only have external fluid dynamics problems. You only need the basic package, that includes flow, turbulence, heat transfer and all post processing tools. The setup is very straightforward. Most of external fluid problems,  we can get the converged solution in couple minutes. We can also show the results in the real time during the calculation.

     

    For the cl, cd and center of pressure calculation,  you can select the surface and create a xyplot to monitor pressure or shear force on that surface. 

    To compute lift and drag coefficient, we can use expression to do that very easily. You can use expression to define equations and formula.  We also support user defined variable for xyplot.

     

    Example of cl, cd calculation

    -----------------------------------------------

    den=1.16
    area=1
    aoa=15*pi/180
    vmag=200
    cx=cos(aoa)
    cy=sin(aoa)
    nx=-cy
    ny=cx

     

    drag=(flow.px@patch.surfname + flow.tx@patch.surfname)*cx
    +(flow.py@patch.surfname+flow.ty@patch.surfname)*cy

     

    lift=(flow.px@patch.surfname + flow.tx@patch.surfname)*nx
    +(flow.py@patch.surfname+flow.ty@patch.surfname)*ny

     

    plot.cd = drag/(0.5*den*vmag^2*area)
    #plot.cd: Drag Coefficient []

     

    plot.cl = lift/(0.5*den*vmag^2*area)
    #plot.cl: Lift Coefficient []

     -----------------------------------------------------

    here flow.px@surfname means pressure force x component from flow module at surfname patch

    similarly, flow.tx means shear force x component.

     

    For the center of pressure, we need to do an integration of x times pressure of x component on all external surfaces and it is straightforward to use expression to write it.

    ----------------------------------------------------------------------

    cpx = integral(x*flow.pressure*normal.x, patch.surfname)/flow.px@surfname
    plot.cpx = cpx
    #plot.cpx: Center of Pressure x []

    ----------------------------------------------------------------------------

     

     

    Please contact me if you got further questions!

     

     

     

    Thanks.

     

      R
      Ruben11-Visitor
      1-Visitor
      May 27, 2020

      Hello CFD Geek, 

       

      I really want to know the drag coefficiënt of a car I developed. (it's for school en for the shell ecomarathon) Could you help me? I have no clue what I need to do... 

       

      I put the body into flow analysis and everything works, I just don't understand what I need to do to get the drag coefficiënt...

       

      Please help 🙂 

       

      C
      cfdgeek13-Aquamarine
      13-Aquamarine
      June 2, 2020

      Hi,

       

      Do you mind mentioning which school team are you working for this project? We may help your team on that project for CFD and aerodynamics design questions. thanks.

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