Experimental investigation on the influence of impact angle on ice crystal fragmentation

Ice crystal icing (ICI) poses a severe threat to aviation engine safety, wherein the impact and fragmentation behavior of ice crystals is the critical initial stage of the icing process. To investigate the influence of impact angle, the impact dynamics of ice crystals colliding with a rigid surface have been experimentally studied under various velocities (2–40 m/s) and angles using ultrasonic levitation and an ejecting impact surface. The results indicate that ice crystal impact exhibits three distinct regimes: rebound, minor fragmentation, and major fragmentation. The critical fragmentation velocity, which is governed by radial crack propagation, is proportional to the –1/2 power of the ice crystal diameter, exhibiting a significant increase with the impact angle. Furthermore, the experiments revealed that relying solely on the normal impact velocity fails to accurately predict fragmentation behavior under oblique impact conditions. The tangential component of the impact velocity induces ice crystal rotation, thereby altering the dispersion direction of secondary particles—an effect that is particularly significant when the impact angle exceeds 45°. As a result, a modified critical fragmentation velocity model incorporating the impact angle is proposed. This model provides a more physically consistent description of fragmentation thresholds over the impact angle range of 0° to 75°.