TR-PIV experiment
The TR-PIV system consists of a continuous solid Nd:YAG laser system
(Kingder KSPL-05), a high-speed CMOS camera (CAMMC 1362), an image
acquisition card and an image post-processing system.
The resolution of the camera is
1280*1024 pixels, and the highest recording frequency is 506 frames per
second. The TR-PIV system is equipped with 850 MB/s image acquisition
card and the computer memory is 32GB. The images collected by the
high-speed camera
are
transmitted to the image acquisition card with a speed of 850 MB/s.
The
continuous semiconductor laser has a power of 5.27 W with the wavelength
of 532 nm. The thickness of the laser sheet is less than 1mm. The planer
laser sheet is located on the plane of P45. Fluorescent
particles of 6µm in diameter are used as the seeding particles.
Three typical planes, i.e. 10˚ before the baffle (P10),
the middle plane between two
adjacent baffles (P45), and 10˚ after the baffle
(P-10) in the direction of rotation, as shown in Figures
2b and 2c, are chosen as the sampling planes. About 6000 images were
captured in each experiment, corresponding to the data acquisition of
about 12 s. Cross-correlation analysis was performed on two adjacent
images to obtain the transient velocity distribution. The images were
analyzed with the fast Fourier transformation (FFT) in 2 passes using
interrogation area (IA)12. The first pass was
64*64 pixels, and the second pass was 32*32 pixels (each pass with 50%
overlap between the neighboring
interrogation
areas).
The
camera frequency was fixed at 500 Hz (∆t =2 ms),
which
can ensure that the maximum in-plane and out-of-plane displacements of
seeding particles are less than one-quarter of the size of IA and
the diameter of the light sheet13. PIVlab in the
commercial software of MATLAB tool is used to analyze the particle flow
fields quantitatively14.