Further Development of a High-Speed Three-Dimensional Flow Visualization System

Abstract

Further development of a high-speed three-dimensional flow visualization system is explored. The technique is based on the high-speed scanning and imaging of a laser sheet produced by a pulse burst laser capable of operating in excess of 1 MHz. The focus of this study is on the characteristics of a galvanometric scanning mirror and its subsequent use within a 3-D imaging system. The maximum angular velocity of the mirror is in excess of 100,000 degrees/second over a 150 microsecond period with the mirror capable of accessing over 18 resolvable spots every 1 µsec. Preliminary three-dimensional images of rising incense smoke were acquired by operating the system in a “low-speed” mode with a 15 mW HeNe laser and a high-speed camera operating at 1,000 fps. In this configuration, each 3-D image (220 x 220 x 68 voxel resolution) took 67 msec to acquire. Sample 3-D images are presented that demonstrate the technique’s capability to visualize complex, threedimensional flow structures, such as those associated with the transition to turbulence in rising smoke. Future work will concentrate on incorporating the pulse burst laser into the imaging system and should increase the speed by 2-3 orders of magnitude making the technique suitable for higher speed flows.