| Resumo : |
This study presents the investigation of horn ice accretion on propeller performance. A small-scale propeller was designed with the aid of an analytical Blade-Element Momentum method, to operate within the wind tunnel envelope. Simulated horn ice shapes were applied to the blade surface, and the effects of horn geometry were assessed through a parametric variation of its main geometric features, such as height, surface position and spanwise/radial distribution. Reynolds and Mach numbers effects on performance were also studied by varying the propeller rotation speed. The clean and iced propeller performance was investigated via wind tunnel tests and simulated computationally by a CFD RANS method in order to obtain a second source of data, besides providing an auxiliary tool for the comprehension of results. Experimental results revealed that ice shapes located at leading-edge to lower surface positions showed unexpected results presenting a greater thrust and comparable, or even lower, torque than the clean propeller. A leading-edge flap effect and an effective chord increase effect were identified as responsible for such outcomes. The ice shapes located at the upper surface caused the greatest performance degradation. The further downstream the icing, the greater the thrust and torque penalties, due to the lengthening of the separation bubble aft of the ice shape. The effects of ice surface position were observed to be directly proportional to the ice shape height. CFD results supported the main tendencies of the experimental results and had good agreement with experimental data regarding thrust. Propeller three-dimensional flow characteristics, such as the stall-delay effect, were found to have a substantial effect on the performance degradation level. Maximum thrust penalties lied in about 13\%, while, the literature has reported up to a 75\% reduction in airfoil lift coefficient. Both clean and iced configurations shown considerable variation with rotation speed, since the reference Reynolds numbers are quite low. |