Abstract

PIV (Particle Image Velocimetry) plays an important role in the technology of flow field display and measurement. The traditional 2D PIV technique is well-developed, though limited by the performance of the system hardware, like lasers and cameras, its sampling rate is quite low. The time-resolved PIV works at KHz, which however is not quite fit for large test area or high spatial resolution due to the low laser energy per pulse and the low pixel resolution of cameras. In fact, it is not easy to make out a PIV system with high pixel resolution and high sampling rate at the same time. But people are still work on this research field. Here in, a four-pulse PIV system for achieving high resolution particle images at extremely short time intervals is proposed, which is arranged with a four-pulse laser, two double exposure CCD cameras and DG645 synchronizer. The laser emits a series of four laser sheets with a time interval from 400 ns to any long, the laser energy is 500 mJ per sheet, pulse width is 8 ns and the wavelength is 532 nm. The cameras and laser are exactly synchronized by DG645 to get four time-resolved particle images. In this paper, the four-pulse PIV system is optimized by the liquid crystal optical shutter that controls the light transmittance by an externally applied drive voltage. Besides, the system is applied in supersonic flows to measure the shock train flow structure. The time-resolved particle images with high spatial resolution (2K×2K@10ns, time interval=3 μs) are quite important for the study of unsteadiness and evident oscillation of the shock train, which corresponds to intensive shockwave/boundary layer interaction.

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