Effects of the length of frozen rivulets on the flow field structures and the aerodynamic performance of an airfoil

Runback ice can lead to significant aerodynamic deterioration and affects aircraft flight safety. The frozen rivulets can form during the aircraft icing process as a part of the runback ice. So far, the effect of frozen rivulets on the aerodynamic performance of airfoils has not been fully studied. The present study experimentally investigated the effects of the length of frozen rivulets on the flow field structures and aerodynamic performance of an airfoil. Detailed measurements were performed in a low-speed reflux wind tunnel by utilizing the particle Image Velocimetry technique and a high-sensitivity six-component balance. The results showed that the length of frozen rivulets had minor effects on lift and drag coefficients. The presence of the frozen rivulets delayed the trend of decreasing pitching moment and reduced the maximum lift-drag ratios of airfoils. Moreover, the frozen rivulets affected the separation bubble length. The separation of the airflow became more pronounced as the length of frozen rivulets increased. The spanwise vorticity distributions were more continuous and smoother with the increase of the length of frozen rivulets. In addition, the transition onset positions showed a strong dependence on the frozen rivulets. Besides, the length of frozen rivulets had limited influences on the turbulent kinetic energy and Reynolds stress distributions.