Validation of urban airflow measurements through a combined field test and wind tunnel study

A combined field test and wind-tunnel study was conducted to support the ongoing development of operator guidance and recommendations for Remotely Piloted Aircraft Systems (RPAS) operations in urban airflows. The goal of the overall study was to acquire urban-airflow data in a real environment in order to validate equivalent airflow characteristics from model-scale testing. The field test was designed to measure urban airflow characteristics using anemometers mounted on a small RPAS. The RPAS was flown along various flight paths in downtown Montréal in 2023. Following the field test, airflow measurements were taken at the equivalent spatial locations in a wind tunnel using a 1:300-scale model of the same test site. Data-processing routines for the RPAS airflow measurements included accounting for the body-motion of the vehicle and applying custom calibration equations for the RPAS-mounted sonic anemometers. Comparing the RPAS and wind-tunnel measurements required a common coordinate system, a digital model of the city, and identification of compatible reference conditions. The distribution of mean flow speed and turbulence intensity from the field test compared well with the wind-tunnel results, including the shape of the distribution and location of the maxima. Additionally, the variation in flow characteristics along a flight path, such as mean flow speed and turbulence intensity, compared favourably with wind-tunnel results acquired at the same relative locations. This work demonstrates the suitability of model-scale testing for studying urban flow fields.