Calibration of the probes is performed either in an in-house dedicated calibration facility or in-situ in the wind tunnels. The calibration is traceable and repeated at regular intervals. The dedicated calibrator is versatile, so that straight, L-shaped, and other probes can be mounted. The calibration process is fully automated. Probe positioning is performed by servo-motors with high-resolution optical encoders. Probes are calibrated in a jet flow and achievable cone angles are up to 150° but a typical standard range is below 60°. A blockage correction from the probe blockage is applied. The resolution of the calibration matrices is down to 0.2° in pitch and yaw angles but are adjusted for each case. Probes are typically calibrated at velocities from 5 to 60 m/s, limited by the measurement range of the reference manometer FCO 510/560 (Furness Control) but higher velocities are possible as well. Commercial and in-house software is used for data reduction. In-house calibration method, data reduction, error analysis and measurement corrections are described in Hjärne (2007), Chernoray and Hjärne (2008), Axelsson (2009), Arroyo (2009) and Rojo (2017). Figure 4.8 shows the calibrator with a mounted straight 5-hp probe.
A stand-alone data reduction script from Aeroprobe Corporation and calibrations performed by Aeroprobe Corporation are available for the commercial probes. References
: Arroyo, C. (2009) Aerothermal Investigation of an Intermediate Turbine Duct, PhD thesis, Chalmers. Axelsson, L.-U. (2009) Experimental Investigation of the Flow Field in an Aggressive Intermediate Turbine Duct, PhD thesis, Chalmers. Chernoray, V. and Hjärne, J. (2008) Improving the Accuracy of Multihole Probe Measurements in Velocity Gradients, In Proc of ASME Turbo Expo 2008, Paper GT2008-50492. Hjärne, J. (2007) Turbine Outlet Guide Vane Flows, PhD thesis, Chalmers. Rojo, B. (2017) Aerothermal Experimental Investigation of LPT-OGVs, PhD thesis, Chalmers.
Figure 4.8. Calibration of a straight 5-hp probe and an example of calibration error analysis.