Experimental Investigation on Relationship between Reynolds Number and Aero-Optics Produced by Supersonic Films

Nowadays, with development of relevant projects, it is becoming an important proposition how to study high Reynolds effects on the aero-optical distortions. Experiment unit Reynolds number can change from 7.2×10⁶~2.2×10⁸ m^-1 by designing a variable Reynolds number aero-optical experiment equipment. A wavefront measurement system based on BOS was assembled, and its temporal resolution can reach to 6 ns. With this system, the measurement results from the plano-convex lens wavefront show that:experimental measurement error compared to the theoretical calculation is within ±4%. The transient wavefronts of supersonic film in nine different Reynolds conditions were measured. The analysis shows that, in high Reynolds condition, Reynolds has obvious effects on the supersonic film aero-optical distortion. OPD_rms∝Re^0.88 was found by function fitting the experimental data, which is similar with the derivation result OPD_rms∝Re^0.9. The distribution features of aero-optical distortion along flow direction were studied by wavelet analysis methods in high Reynolds condition. Low-frequency portion (body signals) of OPD_rms decreased firstly then increased, but the volatility of its high frequency portion increased firstly and then decreased. The low-frequency part of OPD_rms is primarily affected by the overall structure of the flow field, and the high-frequency part is affected by the spatial distribution of the vortex.