Experimental study on detection of unsteady boundary layer transition on airfoil

To investigate the unsteady boundary layer transition characteristics of airfoils, fluctuating pressure signals on the airfoil surface were acquired. The phase averaging method and moving averaging method were used to calculate the standard deviation of the fluctuating pressure signals along the airfoil chord. The transition position was determined based on the peak value of the standard deviation.Infrared images of the airfoil surface were obtained using an infrared thermography camera. The differential infrared image processing method was applied to acquire the temperature distribution and temperature change rate along the airfoil chord. The transition position was also identified according to the peak value of the temperature change rate.These two measurement techniques were employed to conduct experimental studies on the unsteady transition characteristics of airfoils under pitching oscillation conditions. The study obtained the unsteady transition law during the airfoil's sinusoidal oscillation motion and the influence of different oscillation frequencies on transition detection. The results show that during the sinusoidal pitching oscillation of the airfoil, the transition position moves toward the leading edge of the model as the angle of attack increases, and toward the trailing edge as the angle of attack decreases. A hysteresis loop is formed in the boundary layer transition position during the increase and decrease of the angle of attack, and the higher the oscillation frequency, the larger the hysteresis loop. Meanwhile, the transition position laws measured by the two methods show good consistency, with an error of less than 0.04 (x/c) between them.