Density Acquisition and Aero-optics Measurement from BOS Images for a Hot Jet

Abstract

Acquiring density field of a flow is important to understand the flow structure, especially for studying aero-optics. Background-oriented schlieren (BOS) is one of a flow visualization technique which can obtain density field of the flow. Using BOS images density gradient can be acquired quantitatively and density field can be obtained when additional numerical method is applied. In this paper, density field of a hot jet is reconstructed from BOS images by assuming the jet as asymmetric flow and applying adaptive Fourier–Hankel Abel method. Reconstructed density field is evaluated by comparing with wavefront of the optical wave propagating through the hot jet. Optical path difference (OPD) is calculated from the reconstructed density field and compared with Shack–Hartmann (S–H) sensor measured OPD map. OPD obtained from the reconstructed density field and S–H sensor show similar tendency, especially when results are time averaged and turbulence characteristics are removed. Comparing RMS OPD of each time-averaged result show 8.8% error, which is within reasonable range. Thus, it seems that the density field acquisition using BOS technique is reliable for the hot jet flow.