Hao-lin DING, Xin-hai ZHAO, Yang-zhu ZHU, et al. Investigation on coherent structure of supersonic film aero-optics based on wavelet packet[J]. Optics and precision engineering, 2018, 26(6): 1299-1305.
DOI:
Hao-lin DING, Xin-hai ZHAO, Yang-zhu ZHU, et al. Investigation on coherent structure of supersonic film aero-optics based on wavelet packet[J]. Optics and precision engineering, 2018, 26(6): 1299-1305. DOI: 10.3788/OPE.20182606.1299.
Investigation on coherent structure of supersonic film aero-optics based on wavelet packet
While a high-speed aircraft is flying in the atmosphere
its optical hood is subjected to severe aerodynamic heating. Supersonic film cooling method can effectively isolate external heating
but the flow structures formed by the supersonic film cooling can cause beam degradation and affect the imaging quality. To investigate the aero-optics of supersonic film cooling
an experimental model was adopted in this paper
with its mainstream Mach number 3.4
designed jet Mach number 2.5
and measured jet Mach number 2.45. High-resolution images of flow were acquired by the nano-based planar laser scattering (NPLS) technique
by reconstructing the density field of supersonic film cooling
and then
the optical path difference (OPD) was acquired by the ray-tracing method. Depending on the comparison between the K-H vortex and OPD distribution
the valleys of OPD correspond to the vortex 'rollers' and the peaks to the 'braids'. However
the corresponding relationship becomes quite irregular for the flow field with developed vortices
and cannot be summarized in this manner. According to the NPLS result of the supersonic film flow field
based on the fractal dimension results obtained by the fractal principle
the flow field is divided into three regions along the direction of flow
and the coherent structures of the corresponding OPD are calculated respectively. The corresponding flatness is 3.4
2.9
and 3.6
which verifies that Zone 2 is more suitable for coherent structure extraction.
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references
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