Abstract
In 2D molecular tagging velocimetry (MTV), tags are written into a fluid flow with a laser grid and imaged at discrete times. These images are analyzed to calculate Lagrangian displacement vectors, often by direct cross correlation. The cross correlation method is inherited from particle imaging velocimetry, where the correlated images contain a random pattern of particles. A template matching method is presented here which takes advantage of the known geometry of laser written tag grids in MTV to achieve better accuracy. Grid intersections are explicitly located in each image by correlation with a template with several linear and rotational degrees of freedom. The template is a continuous mathematical function, so the correlation may be optimized at arbitrary sub-pixel resolution. The template is smooth at the spatial scale of the image noise, so random error is substantially suppressed. Under typical experimental conditions at low imaging resolution, displacement uncertainty is reduced by a factor of 5 compared to the direct cross correlation method. Due to the rotational degrees of freedom, displacement uncertainty is insensitive to highly deformed grids, thus permitting longer delay times and increasing the relative accuracy and dynamic range of the measurement. In addition, measured rotational displacements yield velocity gradients which improve the fidelity of interpolated velocity maps.
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Notes
The a priori image normalization described here works well for uniformly illuminated grid images and simplifies the mathematical presentation. If the image is not uniformly illuminated, the windowed images may be normalized within Eq. 1 as described in Gendrich and Koochesfahani (1996) and elsewhere.
References
Adrian RJ (1991) Particle-imaging techniques for experimental fluid mechanics. Annu Rev Fluid Mech 23:261–304
Drain LE (1980) The laser Doppler technique. Wiley, New York
Gendrich CP, Koochesfahani MM (1996) A spatial correlation technique for estimating velocity fields using molecular tagging velocimetry (MTV). Exp Fluids 22:67–77
Gendrich CP, Koochesfahani MM, Nocera DG (1997) Molecular tagging velocimetry and other novel applications of a new phosphorescent supramolecule. Exp Fluids 23:361–372
Grady NR, Friedlander T, Pitz RW, Carter CD, Hsu K-Y (2010) Hydroxyl tagging velocimetry in a supersonic flow over a piloted cavity. AIAA Aerospace Sciences Meeting, AIAA Paper 2010-1405, AIAA, Orlando, FL
Hill RB, Klewicki JC (1996) Data reduction methods for flow tagging velocity measurements. Exp Fluids 20:142–152
Hsu AG, Srinivasan R, Bowersox RDW, North SW (2009) Two-component molecular tagging velocimetry utilizing NO fluorescence lifetime and NO2 photodissociation techniques in an underexpanded jet flowfield. Appl Opt 48:4414–4423
Huang HT, Fiedler HE, Wang JJ (1993) Limitation and improvement of PIV. Part II: Particle image distortion, a novel technique. Exp Fluids 15:263–273
Keane RD, Adrian RJ (1992) Theory of cross-correlation analysis of PIV images. Appl Sci Res 49:191–215
Lahr MD, Pitz RW, Douglas ZW, Carter CD (2010) Hydroxyl tagging velocimetry measurements of a supersonic flow over a cavity. J Propuls Power 26:790–797. doi:10.2514/1.47264
Lai MJ, Schumaker LL (2007) Spline functions on triangulations. Cambridge University Press, Cambridge
Park H, Moore JA, Trass O, Ojha M (1999) Laser photochromic velocimetry estimation of the vorticity and pressure field—two-dimensional flow in a curved vessel. Exp Fluids 26:55–62
Prasad AK, Adrian RJ, Landreth CC, Offutt PW (1992) Effect of resolution on the speed and accuracy of particle image velocimetry interrogation. Exp Fluids 13:105–116
Ribarov LA, Wehrmeyer JA, Hu S, Pitz RW (2004) Multiline hydroxyl tagging velocimetry measurements in reacting and nonreacting experimental flows. Exp Fluids 37:65–74. doi:10.1007/s00348-004-0785-3
Stier B, Koochesfahani MM (1999) Molecular tagging velocimetry (MTV) measurements in gas phase flows. Exp Fluids 26:297–304
Tokumaru PT, Dimotakis PE (1995) Image correlation velocimetry. Exp Fluids 19:1–15
Acknowledgments
M.C. Ramsey was supported by a National Science Foundation Graduate Research Fellowship. R. W. Pitz acknowledges support by the U. S. Air Force Office of Scientific Research (AFOSR) Combustion and Diagnostics Program. The authors wish to thank Dr. Larry Schumaker at Vanderbilt for direction regarding the spline interpolation technique, Dr. Thomas Yu at Drexel for the use of interpolation code, and Dr. Manooch Koochesfahani at Michigan State University for the use of image correlation software.
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Ramsey, M.C., Pitz, R.W. Template matching for improved accuracy in molecular tagging velocimetry. Exp Fluids 51, 811–819 (2011). https://doi.org/10.1007/s00348-011-1098-y
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DOI: https://doi.org/10.1007/s00348-011-1098-y