[en] Measuring of flow velocities in aerated flows is known to be difficult in physical models. Application of classical anemometers or ADV probes is limited to low air concentration. Thus, highly aerated flows are commonly investigated by use of intrusive needle probes (conductivity or optical fiber) which allow determination of both, air concentration and velocity, as well as related parameters (e.g. bubble chord lengths and turbulence). In the recent past, non-intrusive image processing techniques have gained more attraction. In the present paper, Bubble Image Velocimetry and Optical Flow methods are applied to aerated stepped spillway flows using high-speed cameras with different resolution to highlight capabilities and limitations of both methods.
Results show that Optical Flow is capable to give results of at least the same accuracy as Bubble Image Velocimetry. A higher image resolution enhances the quality of the results. The dense velocity information being obtained by Optical Flow may help to carry out investigations on turbulence in future.
Research center :
UEE - Urban and Environmental Engineering - ULiège
Adelson, E., Anderson, C. H., Bergen, J. R., Burt, P. J. & Ogden, J. M. 1984. Pyramid methods in image processing. RCA Engineer, 29(6), 33-41.
Amador, A., Sánchez-Juny, M. & Dolz, J. 2006. Characterization of the nonaerated flow region in a stepped spillway by PIV. Journal of fluids engineering, 128(6), 1266-1273.
Boes, R.M. 2000b. Zweiphasenströmung und Energieumsetzung an Großkaskaden. PhD thesis, ETH Zurich (in German).
Bruhn, A., Weickert, J. & Schnörr, C. 2005. Lucas/Kanade meets Horn/Schunck: Combining local and global optic flow methods. International Journal of Computer Vision, 61(3), 211-231.
Bung, D.B. 2009. Zur selbstbelüfteten Gerinneströmung auf Kaskaden mit gemäßigter Neigung.PhDthesis, University ofWuppertal (in German)
Bung,D.B. 2011a. Developing flowin skimming flowregime on embankment stepped spillways. Journal of Hydraulic Research, 49(5), 639-648.
Bung, D.B. 2011b. Non-intrusive measuring of air-water flow properties in self-aerated stepped spillway flow. 34th IAHRWorld Congress, Brisbane, 2380-2387.
Bung, D.B. & Valero, D. 2015. Image processing for Bubble ImageVelocimetry in self-aerated flows, 36th IAHRWorld Congress, Den Haag.
Bung, D.B. & Valero, D. 2016a. Optical flow estimation in aerated flows, Journal of Hydraulic Research (in re-review).
Bung, D.B. & Valero, D. 2016b. Application of the optical flow method to velocity determination in hydraulic structure models, 6th Int. Symposium on Hydraulic Structures (IAHR), Portland.
Burt, P. J., & Adelson, E. H. 1983. The Laplacian pyramid as a compact image code. IEEE Transactions on Communications, 31(4), 532-540.
Chanson, H. (2002). Air-water measurements with intrusive phase-detection probes: Can we improve their interpretation? Journal of Hydraulic Engineering, 128(3), 252-255.
Corpetti, T., Heitz, D.,Arroyo, G., Memin, E. & Santa-Cruz, A. 2006. Fluid experimental flow estimation based on an optical-flowscheme. Experiments in Fluids, 40(1), 80-97.
Felder, S. & Chanson, H. 2015. Phase-detection probe measurements in high-velocity free-surface flows including a discussion of key sampling parameters. Experimental Thermal and Fluid Science, 61, 66-78.
Fortun, D., Bouthemy, P. & Kervrann, C. 2015. Optical flow modeling and computation: A survey. Computer Vision and Image Understanding, 134, 1-21.
Leandro, J., Bung, D.B. & Carvalho, R. 2014. Measuring void fraction and velocity fields of a stepped spillway for skimming flowusing non-intrusive methods. Experiments in Fluids, 55(5).
Liu, T., Merat, A., Makhmalbaf, M.H.M., Fajardo, C., & Merati, P. 2015. Comparison between optical flow and cross-correlation methods for extraction of velocity fields from particle images. Experiments in Fluids, 56(8).
Liu, T., and Shen, L. (2008). Fluid flow and optical flow. Journal of Fluid Mechanics, 614, 253-291.
Lucas, B.D. & Kanade, T. 1981. An iterative image registration technique with an application to stereo vision. Proceedings of imaging understanding workshop, 121-130.
Matos, J., Frizell, K.H.,André, S.&Frizell,K.W. 2002. Onthe performance of velocity measurement techniques in airwater flows. Hydraulic Measurements and Experimental Methods, 1-11.
Ryu,Y., Chang, K.-A.&Lim, H.-J. 2005. Use of bubble image velocimetry for measurement of plunging wave impinging on structure and associated greenwater, Meas. Sci. Technol 16 (10), 1945-1953.
Sveen, J.K. 2004. An introduction to MatPIV v.1.6.1, Department of Mathematics, Mechanics and applied Mathematics, University of Oslo.