Schlieren imaging is a highly sensitive and flexible technique widely used for flow visualization in high-speed fluid flow investigations.However,there is a lack of robust methods for extracting quantitative velocity ...Schlieren imaging is a highly sensitive and flexible technique widely used for flow visualization in high-speed fluid flow investigations.However,there is a lack of robust methods for extracting quantitative velocity from Schlieren images.In this study,a wavelet-based optical flow(WOF)algorithm incorporating a viscous regularization term is employed to compute velocity fields from Schlieren images under subsonic conditions.The method is applied to both a steady turbulent jet and an unsteady sweeping jet(SWJ).The estimated velocity and vorticity fields are compared with results obtained from an optimized optical flow(OF)method.The comparison demonstrates that the WOF method resolves more intricate flow details and exhibits greater resistance to noise.In experiments involving three different scenarios for both the turbulent jet and the SWJ,the measured velocities at lower speeds—where the flow can be considered incompressible—show good agreement with the theoretical values.However,under compressible conditions,the effects of compressibility and the internal flow oscillation mechanisms of the sweeping jet actuator(SJA)lead to energy dissipation,resulting in measured velocities lower than the theoretical values.These results confirm the effectiveness of the WOF method for velocity measurement in subsonic flows and represent the first validation of its application to high-subsonic SWJ flows.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.52306052,12072196,12227803,2022YFA1008200,92270001,12371511,12572382,12521002)the Foundation of National Key Laboratory of Aircraft Configuration Design(Grant No.ZYTS-202406)+2 种基金the Shanghai Municipal Science and Technology Major Project(Grant No.2021SHZDZX0102)the Shanghai Municipal Science and Technology Commission(Grant No.25ZR1401194)partially supported by the SJTU Kunpeng&Ascend Center of Excellence。
文摘Schlieren imaging is a highly sensitive and flexible technique widely used for flow visualization in high-speed fluid flow investigations.However,there is a lack of robust methods for extracting quantitative velocity from Schlieren images.In this study,a wavelet-based optical flow(WOF)algorithm incorporating a viscous regularization term is employed to compute velocity fields from Schlieren images under subsonic conditions.The method is applied to both a steady turbulent jet and an unsteady sweeping jet(SWJ).The estimated velocity and vorticity fields are compared with results obtained from an optimized optical flow(OF)method.The comparison demonstrates that the WOF method resolves more intricate flow details and exhibits greater resistance to noise.In experiments involving three different scenarios for both the turbulent jet and the SWJ,the measured velocities at lower speeds—where the flow can be considered incompressible—show good agreement with the theoretical values.However,under compressible conditions,the effects of compressibility and the internal flow oscillation mechanisms of the sweeping jet actuator(SJA)lead to energy dissipation,resulting in measured velocities lower than the theoretical values.These results confirm the effectiveness of the WOF method for velocity measurement in subsonic flows and represent the first validation of its application to high-subsonic SWJ flows.
