Statistical analysis on the effect of reduced frequency on the aerodynamic behavior of an airfoil in dynamic physical motions

Abstract

In this paper, an extensive experimental tests were performed to determine the aerodynamic characteristics of an airfoil undergoing static, dynamic pitch, dynamic plunge and dynamic combined pitch and plunge motions for various cases. This paper, however, focuses on the effects of reduced frequencies and mean angles of attack on the surface pressure distribution and on the corresponding lift of the airfoil oscillating in either pure pitch or in combined pitch–plunge motions. The angles of attack variations were set such that the model motion would be ceased lower than the static stall, near the static stall and beyond the static stall angles of attack. All tests were conducted at a constant Reynolds number and at various reduced frequency. The plunging motion which is created by the vertical displacement of the model inside the test section, is transformed to the equivalent angle of attack and is added to the pitch angle of attack for the case of the combined pitch and plunge motion. The differences in the pressure distribution and the corresponding aerodynamic loads as a function of the equivalent angle of attack, represent an extreme dependence of the pitch–plunge motion on the reduced frequency. Pitch oscillation seems to have dominant role in the pitch–plunge oscillation case. For the same situation, same frequency and mean angles of attack, the corresponding aerodynamic lift of the pitch–plunge motion was seen to be much higher than the pitch alone oscillation case.