Optical Flow Technique for Supersonic Jet Measurements
This paper outlines the development of an experimental technique in quantifying supersonic jet flows, in an attempt to avoid seeding particle problems frequently associated with particle-image velocimetry (PIV) techniques at high Mach numbers. Based on optical flow algorithms, the idea behind the technique involves using high speed cameras to capture Schlieren images of the supersonic jet shear layers, before they are subjected to an adapted optical flow algorithm based on the Horn-Schnuck method to determine the associated flow fields. The proposed method is capable of offering full-field unsteady flow information with potentially higher accuracy and resolution than existing point-measurements or PIV techniques. Preliminary study via numerical simulations of a circular de Laval jet nozzle successfully reveals flow and shock structures typically associated with supersonic jet flows, which serve as useful data for subsequent validation of the optical flow based experimental results. For experimental technique, a Z-type Schlieren setup is proposed with supersonic jet operated in cold mode, stagnation pressure of 4 bar and exit Mach of 1.5. High-speed singleframe or double-frame cameras are used to capture successive Schlieren images. As implementation of optical flow technique to supersonic flows remains rare, the current focus revolves around methodology validation through synthetic images. The results of validation test offers valuable insight into how the optical flow algorithm can be further improved to improve robustness and accuracy. Despite these challenges however, this supersonic flow measurement technique may potentially offer a simpler way to identify and quantify the fine spatial structures within the shock shear layer.
Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1110940Procedia APA BibTeX Chicago EndNote Harvard JSON MLA RIS XML ISO 690 PDF Downloads 1465
 Horn, B.K. and B.G. Schunck. Determining optical flow. in 1981 Technical symposium east. 1981. International Society for Optics and Photonics.
 Quénot, G.M., J. Pakleza, and T.A. Kowalewski, Particle image velocimetry with optical flow. Experiments in fluids, 1998. 25(3): p. 177-189.
 Liu, T. and L. Shen, Fluid flow and optical flow. Journal of Fluid Mechanics, 2008. 614: p. 253-291.
 Atcheson, B., W. Heidrich, and I. Ihrke, An evaluation of optical flow algorithms for background oriented schlieren imaging. Experiments in fluids, 2009. 46(3): p. 467-476.
 Liu, T., A. Merat, H. Makhmalbaf, C. Fajardo, P. Merati, Comparison between optical flow and cross-correlation methods for extraction of velocity fields from particle images. Experiments in Fluids, 2015. 56(8): p. 1-23.
 Wang, B., Z. Cai, L. Shen, T. Liu, An analysis of physics-based optical flow. Journal of Computational and Applied Mathematics, 2015. 276: p. 62-80.
 Zang, B. and T.H. New, On the wake-like vortical arrangement and behaviour associated with twin jets in close proximity. Experimental Thermal and Fluid Science, 2015. 69: p. 127-140.
 New, T.H. and J. Long, Dynamics of laminar circular jet impingement upon convex cylinders. Physics of Fluids (1994-present), 2015. 27(2): p. 024109.
 New, T.H. and E. Tsioli, Effects of area-ratio on the near-field flow characteristics and deflection of circular inclined coaxial jets. Experimental Thermal and Fluid Science, 2014. 54: p. 225-236.
 Shi, S. and T.H. New, Some observations in the vortex-turning behaviour of noncircular inclined jets. Experiments in fluids, 2013. 54(11): p. 1-11.
 New, T.H. and D. Tsovolos, On the flow characteristics of minor-plane inclined elliptic jets. Experimental Thermal and Fluid Science, 2012. 38: p. 94-106.
 New, T.H. and D. Tsovolos, On the vortical structures and behaviour of inclined elliptic jets. European Journal of Mechanics-B/Fluids, 2011. 30(4): p. 437-450.
 New, T.H. and D. Tsovolos, Influence of nozzle sharpness on the flow fields of V-notched nozzle jets. Physics of Fluids (1994-present), 2009. 21(8): p. 084107.
 New, T.H., K.S. Tan, and H.M. Tsai, Effects of noncircular collars on an axisymmetric jet. Physics of Fluids (1994-present), 2007. 19(8): p. 084104.
 New, T.H. and H.M. Tsai, Experimental investigations on indeterminate-origin V-and A-notched jets. AIAA journal, 2007. 45(4): p. 828-839.
 Lim, T.T., T.H. New, and S.C. Luo, Scaling of trajectories of elliptic jets in crossflow. AIAA journal, 2006. 44(12): p. 3157-3160.
 New, T.H. and W.L. Tay, Effects of cross-stream radial injections on a round jet. Journal of Turbulence, 2006(7): p. N57.
 Corpetti, T., É. Mémin, and P. Pérez, Dense estimation of fluid flows. Pattern Analysis and Machine Intelligence, IEEE Transactions on, 2002. 24(3): p. 365-380.
 Corpetti, T., D. Heitz, G. Arroyo, E. Memin, A. Santa-Cruz, Fluid experimental flow estimation based on an optical-flow scheme. Experiments in fluids, 2006. 40(1): p. 80-97.