Liquid water content measurement with SEA multi-element sensor in CARDC icing wind tunnel: Calibration and performance

Abstract

The measurement of cloud liquid water content (LWC) plays a critical role in the development of icing airworthiness standards for aircraft and the calibration of icing wind tunnels. The SEA multi-element sensor, the modern hot-wire device for LWC measurement, still faces several challenges for performance calibration due to the effects of the baseline drift and droplet retention characteristics. To fully calibrate the performance of the sensor, two wind tunnel tests were conducted in the China Aerodynamics Research and Development Center (CARDC) icing wind tunnel including a dry air calibration test and an icing cloud measurement test. Using the in-situ dry power calibration method developed in this study, the compensation function and the empirical formula of dry air Nusselt number for each sense element are obtained, and present great linear characteristics in the range of the test section velocity VTS from 40 to 110 m/s. However, there is an abnormal peak area of total power for the W1 element at the VTS of 120 and 130 m/s, which may be associated with significant water vapor condensation. The consistency and discrepancy of four LWC calculation methods via the combinations of dry and wet power calculation methods are assessed. Further, the LWC response characteristics of the sense elements are examined and the correlations of the droplet retention efficiency for the W2 and W3 elements are acquired as functions of median volume diameter. Finally, the measurement accuracy of the SEA multi-element sensor is validated compared to the icing blade device. It demonstrates that the uncertainty of the W1 element for the sensor is about ±5% at the low LWC and the W1 element has a better ability in the measurement of the high LWC.