Force Outputs in a single moving-reference frame

    • Patrick Kozlowski

      Problem with drag and lift outputs for analysis of FSAE car in a corner. Domain setup:

      Inlet on left side, zero-gauge pressure outlet on right. The fluid region is created using an enclosure around the car (connected to ground), and this fluid region is rotating at 1.25 rad/s, about 20 m/s at the cars location. The ground is moving at the same speed from the same axis origin. The car and ground are no-slip walls, while the enclsure walls are free shear. 

      When creating report files for drag and lift, are there any considerations for referance frames in terms of calculating forces that need to be changed? Or does using an enclosure as the moving fluid region not work for this setup?

      For the straigt-line simulation, the car showed around 500 N of downforce. In the curved domain, we get an output of only 13 N. Below are some example output plots of the corner domain simulations. The mesh has no problems.

    • Sunil Lilhare
      Ansys Employee


      For this simulation I think no special consideration for force calculation is required just be sure about the values of x, y and z force vectors for force calculation. For more accuracy the fluid zone should be rotated by using frame motion in the Cell Zone Conditions of the solver if not done already. To know more on different options available for setting frame motion to cell zones, please refer to the link of Ansys Fluent User Guide given below
      7.2. Cell Zone Conditions (ansys.com)
      Velocity contour would help in resolving the issue.


      • Patrick Kozlowski

        Thank you for the reply.

        The flow was set using the frame motion, and the force outputs are in the correct directions. Below are additional outputs including velocity contour. The pathlines show less interaction than expected, and forces are too low.

        The second approach was to use a stationary frame and rotate  the flow around the domain. This resulted in better forces, although the flow was only ideal around  the car. The pathlines and contours sohw turbulence not seen with the frame motion.

        Based on the results and the  fact that only the fluid zone was changed from moving to stationary, I think the problem stems from the enclosure + moving frame pairing. The car seems to be present when flow first makes contact in  moving frame, but then pathlines look like they stop, and force values are far too low.

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