Calibration Process
Professional calibration of a probe is essential to achieve reliable measurement results. A calibration defines the relationship between the pressure at the probe head holes and the measured velocity and flow angle. To perform this task, the probe is held in a known flowfield generated by our calibration wind tunnel. We measure the pressures for a matrix of points by changing the angle-of-attack of the probe in the air flow. With these results we calculate the calibration factors for the probe. When the probe is later used to characterize an unknown flow field, the measured pressures and calibration factors are used to compute the flow angle and velocity.
The basis of every calibration is a clean free jet – a constant, homogenous air flow with low turbulence. Our 90kW asynchronous motor drives 2 centrifugal compressors. The compressed air flows into a settling chamber and then through multiple screens and a honeycomb flow straightener to reduce turbulence, thus generating a clean, homogenous air flow. The flow then exits through specially designed nozzles optimized for minimum pressure loss. With a selection of nozzle exit diameters, we are able to reach velocities between 1 m/s and Mach 1.2. Probes are positioned by a 2-axis traverse (roll and pitch angle) at a total accuracy of 0.05°, to enable an exact calibration for the required angle and velocity range.
Performance parameters of the calibration wind tunnel
| Angle range | ± 165° (yaw), ± 180° (pitch) |
| Maximum power | 90 kW |
| Velocity range | 1 m/s up to Mach 1.2 (3 ft/s up to Mach 1.2) |
| Parameters | Mach Number, Airspeed, Reynolds number |
| Time Variance in Velocity | ± 0.25% (at Ma 0.1) |
