Assessment of image processing methods to characterize the precise shape of the jet head in the hypersonic jet flows

Abstract

Image-based methods are going to be the best ones in fluid dynamics, especially where other techniques are not capable to detect the phenomena of the flows. One of these topics is hypersonic jet flow, while recently several laboratory experiments of the long-term hypersonic jet flows have been performed to explore different morphological aspects of the flow, such as asymmetric stability properties, cocoon and pumping phenomena. In this paper, to get a deeper insight in the phenomenology of the hypersonic jets, a set of image processing methods has been applied to the laboratory fluorescent images of hypersonic jets, which helps to recognize the precise shape of the jet head. The captured images are pre-processed through nonlinear diffusion that removes the noises, while as the time elapses, the image is segmented into the jet and ambient media. Then, the edge detection operator, coupling with curve fitting function, is applied to specify the jet flow boundary.Although the precise shape of the jet head is not recognizable through the original fluorescent images, the image processing techniques significantly help to specify the exact boundary of the bow shock, which demonstrate the beam pumping phenomena and the originality of non-symmetrical structures of the jet head. In addition, the results have been compared with the counterpart numerical simulations, which yield a fairly good agreement, in most of the comparisons.