Transient aerodynamic characteristics of a two-dimensional airfoil during stepwise incidence variation

Abstract

The present paper discusses the transient aerodynamic characteristics of a two-dimensional low-speed airfoil whose angle of attack is varied impulsively. The study is mainly an experimental one with observations made of the three dynamic loads, the static pressure distribution, and flow on the airfoil surface, following the airfoil motion. The changes in the characteristics and their aerodynamic causes are investigated in terms of the ultimate angle of attack and the rise time. foil other than the two-dimensional motion to be discussed in this paper. For instance, Refs. 7-10 deal with the effects of variations in the flow velocity and in the angle of attack. There are other studies11'12 that have analytically pursued the rela- tionship between dynamic stall and the ambient flowfield. Furthermore, little is known about the effects of Reynolds number, Mach number, airfoil profile, and airfoil motion.13 At this stage of information it is natural that the technology should be based on experimentation. In the present paper, in- stead of a conventional study of an oscillating airfoil, which has been often undertaken, the relations between the transient aerodynamic characteristics of an airfoil with stepwise varied angle of attack and the state of the ambient airflow are ex- perimentally investigated as a basic study leading to applica- tion. Another reason for adopting a stepwise varied input is the desirability of obtaining a simple motion for understand- ing the phenomena in a flow with prominent nonlinearity and hysteresis.