Experimental investigation of the accretion and shedding process on a heatable NACA0012 airfoil in ice crystal icing conditions

Abstract

Ice crystal icing can lead to damage and flame-outs in the combustion chamber of an aircraft engine due to accretion and shedding of ice blocks. The present work aims at a better understanding of accretion and shedding phenomena by quantitatively analysing experimental investigations conducted at the icing wind tunnels of Airbus CRT and TU Braunschweig. Particular focus is laid on ice accretion and shedding resulting from ice crystal icing on heated substrates. Heatable NACA0012 airfoils were designed and tested in a broad range of parametric conditions. Generally, large ice accretions and large shed areas were observed on non-heated surfaces at positive wet bulb temperatures. On surfaces heated with a low heat flux the accreted area was larger, while with large heat fluxes mostly run-back of liquid water was observed. For the examined experimental conditions an ice accretion threshold existed beyond which there was continuous accretion or complete shedding. The experimental findings of this study not only consolidated previous studies in similar conditions, but also help identify new findings for heated surfaces at negative wet bulb temperatures and unheated surfaces with mixed-phase conditions at positive wet bulb temperatures. They form a large collection of new data on ice accretion and shedding and provide a comprehensive experimental database quantitatively analyzed for validating future physics based and numerical models.