An experimental study on the effect of initial ice roughness on the water/ice run-back behavior over a NACA 23012 airfoil

In the present study, an experimental study was conducted to evaluate the effect of initial ice roughness on the transient water/ice run-back behavior during glaze icing process over a NACA 23012 airfoil. A digital image projection-correlation (DIPC) technique was applied to provide non-intrusive, temporally resolved, and full-field measurements of the dynamic water/ice thickness distributions over the airfoil surface. The instantaneous morphologies of the surface water/ice flow were reconstructed and quantified. Two typical surface morphologies were observed: wave-modulated-film (WMF) flow and stripe-molded-rivulets (SMR) flow. In the WMF flow, film with one primary wave and multiple secondary waves was presented; while in the SMR flow, upstream film flow with multiple downstream rivulets development was observed. The initial ice roughness was able to retard and shorten the primary wave formation in the WMF flow, while the wave velocity was not affected. The initial ice roughness was suggested to be able to trap and decelerate the water/ice film flow and decrease the inertia force in the film front, which essentially delayed the rivulets formation in the SMR flow. The roughness trapped SMR flow also presented a meandering behavior as the rivulets started to form, due to which, the initially formed narrow rivulets merged into wider rivulets. In this study, a new method in recognizing the film/rivulets boundary was proposed to quantify the dynamic process of rivulets formation, transition, and development. The characteristics of the steady-state rivulets flow were also extracted. The initial ice roughness was demonstrated to have a significant effect on the rivulet shape (e.g., rivulet width, spacing, and height).