Affordable schlieren visualization methods for understanding three-dimensional supersonic flows
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R E G UL A R P A P E R
S. Vaisakh
•
T. M. Muruganandam
Affordable schlieren visualization methods for understanding three-dimensional supersonic flows
Received: 11 January 2019 / Revised: 10 April 2020 / Accepted: 15 May 2020 Ó The Visualization Society of Japan 2020
Abstract This article discusses affordable schlieren methods which can visualize hidden details in threedimensional high-speed flow. Mainly, two schlieren methods are brought to light, namely inclined schlieren and focusing schlieren. These two methods have been applied to visualize three-dimensional flow fields like normal shock boundary layer interaction in ducts and flows with shock–shock interactions. The paper explains the possibility of measuring normal shock oscillation in spanwise/transverse direction. Shock height variation across the duct span is also illustrated, using inclined schlieren. Scanning of the focusing schlieren setup can give planar views of three-dimensional shock–shock interactions. It is also shown that the two methods can be merged to give the inclined focusing schlieren method which can also be used to understand three-dimensional flow fields. Further, the possibilities and limitations of these flow visualization methods have been discussed. Keywords Focusing schlieren Inclined schlieren Supersonic flow Three-dimensional shock wave
1 Introduction Schlieren is one of the oldest, yet most powerful, tools used in high-speed flow visualization. Even though different types of schlieren methods and arrangements exist (Settles 2001), conventional Z-type schlieren is the most commonly used one. Background-oriented schlieren is also popular in the recent years due to its simplicity. The line of sight integration of schlieren imaging limits its applicability in extracting threedimensional data. Other newer methods like laser-based velocimetry and fluorescence were resorted to understand three-dimensional flows (Settles 2001; Handa et al. 2014). The current focus in the research community is toward tomographic reconstructions from a large number of cameras to understand the threedimensional flows (Ota et al. 2015; Ishino et al. 2016; Nicolas et al. 2016; Grauer et al. 2018), which is exorbitant, and also requires higher effort in terms of alignment and post-processing. This paper lays out affordable ways by which one can understand three-dimensional flows through two non-conventional schlieren visualization methods, viz., focusing schlieren and inclined schlieren. These methods also require less optical access, are easier to setup and require simpler post-processing compared to the tomographic setups. The intent is to enable the large number of researchers using these methods to obtain threedimensional density fields in various flows.
S. Vaisakh (&) T. M. Muruganandam Department of Aerospace Engineering, Indian Institute of Technology Madras, Chennai 600 036, India E-mail: [email protected] T. M. Muruganandam E-mail: [email protected]
S. Vaisakh, T. M. Muruganandam
Focusing schlieren (Kantrowitz and Trimpi 1950
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