4.3.4. Modeling Considerations¶

KiteAeroDyn was designed as an extremely flexible tool for modeling a wide-range of aerodynamic conditions and kite configurations. This section provides some general guidance to help you construct models that are compatible with KiteAeroDyn.

4.3.4.1. Standalone KiteAeroDyn Driver¶

The standalone KiteAeroDyn driver code is very useful for computing kite aerodynamics under prescribed motion of the kite independent of aero-elastic coupling. The standalone KiteAeroDyn driver code uses a time-series of rigid-body flight kinematics and control signals (the inputs to the aerodynamic calculations). The full suite of KiteAeroDyn output channels are available for these simulations.

4.3.4.2. Environmental Conditions¶

For air, typical values for AirDens, KinVisc, and SpdSound are around 1.225 kg/m³, 1.460E-5 m²/s, and 340.3 m/s, respectively.

4.3.4.3. Lifting Line Vortex-step Method¶

We recommend setting VSMToler to 2 when simulating an operational kite to enable the lifting line vortex-step method. We recommend initially setting VSMToler, VSMMaxIter, and VSMPerturb to DEFAULT. If this simulation issues errors regarding convergence of the VSM solution, then you may need to alter these default values. First, try increasing the value of VSMMaxIter beyond the default value of 40. Then you may need to change either or both of the VSMToler or VSMPerturb values.

4.3.4.4. Temporal and Spatial Discretization¶

For accuracy and numerical stability, we recommend that DTAero be set to 0.01 seconds when KiteAeroDyn is coupled to KiteFAST.

For the kite aerodynamic surfaces spatial discretization, using higher number of analysis nodes will result in a more accurate solution at the expense of longer computational time. We recommend a node spacing of roughly 1 meters (e.g., 10-20 nodes per wing). The vortex step method theory is not meant for discretizations finer than this. When KiteAeroDyn is coupled to KiteFAST, the aerodynamic surfaces analysis node discretization may be independent from the discretization of the nodes in the structural module (MBDyn).

4.3.4.5. Pylon and Rotor Ordering¶

The pylon node list in the Pylon Properties section of the primary KiteAeroDyn input file must be structured such that all starboard pylon nodes appear first, starting with the inner-most pylon and ending with the outer-most pylon. Then the port pylon nodes are listed, again starting with the inner-most pylon and ending with the outer-most pylon.

Additionally, the list of rotor properties in the primary KiteAeroDyn input file must be structured such that all starboard pylon rotors appear first, starting with the inner-most pylon and ending with the outer-most pylon. Then the port pylon rotors are listed, again starting with the inner-most pylon and ending with the outer-most pylon. Each pylon must contain a line for the top rotor followed by the bottom rotor. Therefore, the list will contain a total of four times NumPylons lines.

Likewise, the plyon reference point node list in the Energy Kite Reference Configuration section of the KiteAeroDyn driver input file must be structured such that all starboard pylon nodes appear first, starting with the inner-most pylon and ending with the outer-most pylon. Then the port pylon nodes are listed, again starting with the inner-most pylon and ending with the outer-most pylon.

Likewise, the rotor reference point node list in the Energy Kite Reference Configuration section of the KiteAeroDyn driver input file must be structured such that all starboard pylon rotors appear first, starting with the inner-most pylon and ending with the outer-most pylon. Then the port pylon rotors are listed, again starting with the inner-most pylon and ending with the outer-most pylon. Each pylon must contain a line for the top rotor followed by the bottom rotor. Therefore, the list will contain a total of four times NumPylons lines.

4.3.4.6. Units of the User-supplied Control Settings¶

The units used for the Ctrl values in the multi-dimensional airfoil tables must match the units of the control signals generated by the user-supplied KiteFAST controller.