Computed-Tomographic Density Measurement of Supersonic Flow Field by Coloured Grid Background Oriented Schlieren (CGBOS) Technique

Masanori OTA1, Kenta HAMADA2, Hiroko KATO2, and Kazuo MAENO1

1 Graduate School & Faculty of Engineering, Chiba University, 1-33 Yayoi, Inage, Chiba #263-8522, Japan, ota@faculty.chiba-u.jp

2 Graduate student, Graduate School of Engineering, Chiba University, 1-33 Yayoi, Inage,

Chiba #263-8522, Japan

ABSTRACT

The background oriented schlieren (BOS) technique is one of the novel visualization techniques for the quantitative measurement of two-dimensional density information in the flow field with very simple experimental setup. In other previous reports the random dot pattern images have been commonly used in BOS technique, where local displacement of the dot pattern is calculated by image analysis between two images, i.e. without flow and with flow images. This displacement is caused by variation of the index of refraction related to the density gradient distribution. Thus the density information has been obtained by calculating the displacement of background image together with the same technique as commonly used in Particle Image Velocimetry (PIV). In this report we propose the coloured-grid background for BOS technique (CGBOS). Measurements of supersonic flow field around an asymmetric body were challenged at Mach number of 2.0. The distorted coloured-grid pattern is analyzed by the finite-fringe analysis technique, which has been developed in Laser Interferometric Computed Tomography (LICT) measurement. In CGBOS reference image is unnecessary, and the image analysis can be done from only one image through the flow. CGBOS technique has been also applied to CT measurement of supersonic flow field. The measurement result and prospect of CGBOS technique are discussed.

Keywords Background oriented schlieren, Tomography, Supersonic flow, Quantitative density measurement