The application of the Colored Background Oriented Schlieren technique (CBOS) to free-flight and in-flight measurements

The improved background oriented schlieren technique CBOS (Colored Background Oriented Schlieren) is presented in this paper. This technique measures the light deflection caused by density gradients in a compressible flow. For this purpose, the CBOS technique uses the distortion of a background image. In order to increase the performance of the conventional Background Oriented Schlieren technique (BOS) the monochromatic background is replaced by a colored dot pattern. The different colors are treated separately. Therefore the precision and the spatial resolution can be increased. The CBOS technique is applied in order to measure the flow around test models in a supersonic wind tunnel, during a free-flight and during a full-scale flight tests with a helicopter.