The BAT probe senses turbulence by measuring the pressure distribution around a hemisphere. A potential-flow model of the pressure field is then used to calculate the incidence angles (angles of attack and sideslip) of the airstream relative to the probe. Static air pressure is also measured.
The probe was tested in the Wright Brothers Wind Tunnel at M.I.T. in Cambridge, MA. The wind tunnel provided a large test section, airspeeds equal to those of the DA-42 aircraft, and very low flow distortion. The probe was mounted on a support that allowed its orientation (pitch and yaw) to be varied systematically. Measurements of the probe's orientation angles were made to an accuracy of 0.1º. These orientation angles were then compared to the incidence angles measured by the probe. Since the airflow in the tunnel is parallel to the tunnel centerline, a direct comparison between these angles is valid.
Results show good agreement between the incidence angles measured by the probe and the orientation angles measured with respect to the wind tunnel's centerline. The static air pressure measured by the BAT probe also agrees well compared with the wind tunnel standard. The results yielded new insight into how the probe functions and allowed us to validate and verify the operation of the probe under flight conditions. These results confirm the utility of the BAT probe for eddy-correlation measurement of turbulence.