Analysis of high subsonic sweeping jet external flow characteristics and velocity using schlieren visualization and schlieren image velocimetry method

Abstract

A significant research gap exists in understanding the external flow mechanisms of sweeping jets (SWJs) in high subsonic condition and their application in active flow control (AFC). This study aims to address this gap by investigating the external flow characteristics and velocity of high subsonic SWJs using schlieren visualization and schlieren image velocimetry (SIV). Schlieren visualization of SWJs under subsonic condition is achieved by heating the air, using two proportionally scaled sweeping jet actuators (SJAs) with throat widths of $T$ = 2 mm and 3 mm. The results revealed that increasing the throat width led to more pronounced flow structures and stronger acoustic waves. Additionally, the sweeping angle (SA) was observed to initially increases and then decreases with inlet pressure ($P$, 0–0.2 MPa) and outlet Mach number (${\mathrm{Ma}}_{\text{outlet}}$ < 1). Frequency analysis showed a rapid increase followed by a gradual increase in the oscillation frequency of SWJ with increasing $P$ and ${\mathrm{Ma}}_{\text{outlet}}$. The external velocity field of SWJs from an SJA with a throat width of $T$ = 3 mm was calculated using the SIV method. Instantaneous velocity field analysis demonstrated that the SIV method effectively captured the SWJ velocity. The trends in SA and oscillation frequency extracted from the velocity field were consistent with those obtained from schlieren images. Higher outlet temperature ($T_{outlet}$) led to a higher oscillation frequency. Additionally, it was conjectured that increased SA and oscillation frequency led to greater energy loss, resulting in reduced outflow velocity.