Experimental studies of non-stationary aerodynamic characteristics of a helicopter airfoil oscillating in the pitch

Abstract

The article presents the results of experimental studies of non-stationary integral and distributed aerodynamic characteristics one of the helicopter airfoil in stationary and non-stationary modes. The stationary mode is a fixed airfoil in a uniform steady airflow. The non-stationary mode is an airfoil oscillating in the pitch in a uniform steady airflow. The investigations were carried out in the vertical, closed-circuit TsAGI wind tunnel with an open test section. The tests were carried out at Reynolds numbers Re = 270,000 and 540,000; at reduced frequencies from 0.06 to 0.26. A particular feature of the research was the use of two methods for determining aerodynamic characteristics, namely: a direct method of measuring forces using balance and calculating forces by integrating the pressure distribution along the chord. The obtained results are compared with each other, their satisfactory agreement in the stationary mode is shown. Another feature of the research was the analysis of pulsations of forces and pressures on the airfoil surface. In particular, using the wavelet analysis, a phenomenon called "frequency explosion", specific of dynamic stall of the flow, is demonstrated.