Pilot study: Experimental study of blockage effect using larger ultrasonic weather stations in wind tunnels

A study is conducted researching blockage effects when calibrating weather stations in different types of wind tunnels.

Method: A transfer standard type (Vaisala WXT536 weather station and Thies 2D ultrasonic) is calibrated in various wind tunnels of different sizes and using different setups of the reference standards to observe the blockage effect on the different setups. The equipment is calibrated at 10 calibration points: 1 m/s, 2 m/s, 3 m/s, 4 m/s, 5 m/s, 6 m/s, 8 m/s, 10 m/s, 12 m/s, and 14 m/s. All in different angles: 0 deg, 30 deg, 60 deg, 90 deg, 120 deg, 150 deg and 180 deg. For the Vaisala all angles will be researched while for the Theis ultrasonic will only include 0 deg to 90 deg.

The calibration of the ultrasonic meters is carried out using the participants normal procedures. All data as well as any corrections for blockage effect applied is made available for the coordinator for analysis and comparison.

The wind tunnels used in this project can both be open and closed but is recommended to be large enough to accommodate the sensors sizes without coming closer than 75 mm to the walls. However smaller setups are also welcomed as extreme cases.

If the participants are not able to calibrate in the full measurement range specified, they may calibrate the meter over a part of the flow range. Each laboratory will be responsible for transferring the equipment to the next laboratory.

Test conditions:
Test pressure: near atmospheric
Test temperature: (21±3) °C
Relative humidity: less than 70%