Browse Publications Technical Papers 2019-01-2037
2019-06-10

UAV Icing: Ice Accretion Experiments and Validation 2019-01-2037

Atmospheric icing on UAVs is a key challenge to their operational envelope. Today, several numeric icing codes exist, that all have been developed mainly for general aviation applications. UAVs typically operate at Reynolds numbers an order of magnitude lower than commercial and military aircraft. Therefore, the question arises to what extent these codes can be applied for low-Reynolds UAV applications. To answer this question, experimental validation data is required. This paper describes an experimental campaign at the Cranfield icing wind tunnel on a RG-15 airfoil at low velocities (25-40m/s). Three meteorological icing conditions have been selected to represent the main ice typologies: rime, glaze, and mixed. Manual ice shape tracings have been taken from three spanwise locations for each icing case. Furthermore, each case has been run at least two times in order to assess the repeatability of the test. A key issue has been identified related to the calibration of the liquid water contents. The initial calibration was performed according to ARP5905 with an icing blade. The tests have shown significantly higher water contents that anticipated, which could be attributed to dimensional differences of the icing blade as well as the low flow velocities. After adjusting the water contents, the results show good repeatability and moderate spanwise variability. In addition to manual tracings, photogrammetry and a handheld laser-scanner were used to attempt to capture the ice shapes. The results indicate that manual tracings are still the most efficient method. Furthermore, numerical simulations with two icing codes, LEWICE and FENSAP-ICE are performed for validation purposes for a rime, glaze, and mixed case. Comparison with the experiments shows that the icing conditions play an important role in the ability of the codes to accurately predict the ice shapes.

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