Verification of numerical lidars in HAWC2: Analysis of nacelle- and hub-mounted lidars

This report provides a comprehensive assessment of the nacelle and hub-lidar sensors implemented as of HAWC2 13.1. The study originated as part of the CONTINUE project, which led to the implementation of the numerical hub lidar. The main objective of this investigation is to ensure accurate code implementation for both the hub- and nacelle-lidar sensors by verifying that their output aligns with theoretical expectations. Rigorous verifications were performed on various aspects, including the global coordinate positions of the beam focal point, the nominal and weighted line-of-sight wind speed, and the numerical integration for the hub lidar’s weighting function.

During the study, several discrepancies were identified in the pre-existing nacelle-lidar implementation. The sensor has thus been updated in HAWC2 13.1 such that it both translates and rotates with the nacelle, as opposed to just translation. Furthermore, the nacelle lidar was corrected to sample the relative velocity observed by the lidar, which is impacted by tower motion, as opposed to the absolute wind velocity.

A convergence study on the numerical integration parameters of the hub lidar is also presented using the NREL 5 MW. The study demonstrates that, for the examined conditions, excellent convergence is found for 200 integration points and a half-width of the integration volume equal to 3 times the full width at half-maximum of the lidar. It is recommended that a user conducts their own convergence study using the inflow/lidar parameters relevant for their study.