Reporting Lift and Drag Coefficients

Lift and drag coefficients are common measures in the design of aerodynamic bodies, such as airfoils or vehicles. You can also use these force coefficients to monitor solution convergence.

The calculation of force coefficients requires the specification of a reference area. For an airfoil, it is the planform area (that is, the area of the airfoil as if it were projected down onto the ground below). For vehicles and other objects, it is the projected frontal area.
To report lift and drag coefficients:
  1. Calculate the reference area:
    1. Right click the Reports node and select New Report > Frontal Area.
      A Frontal Area report allows you to calculate the combined projected area of all parts in the report onto a user-specified plane. Note that this report uses a rasterization technique in computing the area and so has some inherent uncertainty.
    2. Select the created report and set the following properties:
      Property Setting
      Coordinate System If the default Laboratory coordinate system is not aligned with the geometry, define a local coordinate system that is.
      Normal
      • For an airfoil, set the direction as the direction of lift.
      • For a vehicle or another object, set the direction normal to the frontal plane. For a vehicle travelling in a straight line, this is the direction of travel.
      View Up Set a direction orthogonal to the Normal vector.
      Parts Set the boundaries on which you want to calculate the force coefficient.
    3. Right-click the report and select Run Report.
  2. Create a report for the lift coefficient:
    1. Right-click the Reports node and select New Report > Force Coefficient.
    2. Rename the report to Lift Coefficient.
    3. Select the created report and set the following properties:
      Property Setting
      Reference Density Set the density of the free stream.
      Reference Velocity Set the velocity of the free stream.
      Reference Area Set the value of the reference area as calculated in Step 1c.
      Direction Set the direction of lift.
      Parts Set the boundaries on which you want to calculate the lift coefficient.
  3. Create a report for the drag coefficient:
    1. Copy the lift coefficient report and rename it to Drag Coefficient.
    2. Select the created report and set Direction to the direction of drag.
  4. To monitor the force coefficients while the simulation is running:
    1. Multi-select the Lift Coefficient and the Drag Coefficient nodes.
    2. Right-click an select Create Monitor and Plot from Report.
With advanced Java techniques, you can add flexibility in calculating the force coefficients by dividing the aerodynamic body into bands. For more information, see Using Bands with Force and Moment Reports.