A novel optical diagnostic technique, namely, dual-hologram shearing interferometry with regulated sensitivity, is proposed for visualization and measuring of the density gradients of compressible flows in wind tunnels. It is superior to conventional shearing interferometry in both accuracy and sensitivity. The method is especially useful for strong turbulent or unsteady regions of the flows, including shock flows. The interferometer has proved to be insensitive to mechanical vibrations and has allowed us to record holograms during the noisy wind-tunnel run. The proposed approach is demonstrated by application to a supersonic flow over spherically blunted and sharp nose-cone-cylinder models. We believe that the technique will become an effective tool for receiving optical data in many flow facilities. (C) 1998 Optical Society of America. [References: 18]
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