Correction Technique of Inertial Force and Moment in Direct Force Measuring Test of Dynamic Aerodynamic Performance of Airfoils

The research on both direct force measuring test technique of dynamic aerodynamic performance of oscillating airfoils in low-speed flow and inertial force and pitching moment correction technique is carried out in the two-dimensional test section of the NF-3 low-speed wind tunnel of Northwestern Polytechnical University. The influence of the inertial force and pitching moment of the airfoil model on wind tunnel experimental data of dynamic aerodynamic performance is studied, the signal interference of the experimental data is analyzed, and the digital filtering method of the data, and the correction method for inertial force and pitching moment of airfoil models are proposed. The analysis of the results shows that the experimental data have obvious interference signal components within frequency interval between 16 and 60 Hz. When the oscillation frequency of the airfoil increases, the frequency band of the interference component becomes wider. Low-pass digital filtering in which the lift and drag data are subjected to a cutoff frequency of 16 Hz and the pitching moment data to a cut-off frequency of 8 Hz can eliminate the signal interference. The direct force measuring result of dynamic aerodynamic performance in the wind-off state contains a certain amount of aerodynamic forces, and there is a larger error in the method in which the influence of inertial force and pitching moment on the direct force measuring result is corrected by subtracting the wind-off data in the dynamic test. It is correct and feasible to use designed model motion law to fit the change of the angle of attack, to calculate and correct the inertial force and pitching moment. As the reduced frequency increases, the dynamic stall of the pitching oscillating airfoil is further delayed and the hysteresis loop of lift and pitching moment becomes larger.