DYNAMIC MASKING TECHNIQUES FOR PARTICLE IMAGE VELOCIMETRY

Öz

Objects and surfaces often appear in Particle Image Velocimetry (PIV) images. Unless masked, the features on these contribute to the cross correlation function and introduce an error in the vectors as a result of the PIV analysis in the vicinity of the phase boundary. Digital masking of objects has appeared numerous times in the literature as part of the analysis chain, with a growing focus on isolating moving features using dynamic masks. One aim of this article is to provide a summary of milestones achieved in dynamic masking covering a wide range of applications. Another aim is to show the difference between image masking and vector masking. Finally, two different dynamic masking examples are described in detail and compared. The examples used are selected from swimming microorganisms in small channels. In the first example, a histogram thresholding-based dynamic masking is used, while, in the second example, a novel technique employing a feature tracking-based dynamic masking is used. Results show that histogram thresholding-based masking provides better results for swimmers which randomly change shape and direction; whereas, feature tracking-based masking provides better results for swimmers which do not change shape or direction significantly. In order to show the improvement due to dynamic masking, a comparison is made between PIV results a) with no masking, b) with just image masking and c) with both image and vector masking. Results show that the best approach is to use both image and vector masking.

Anahtar Kelimeler

• Dynamic masking,Image masking

Kaynakça

1. Carrier O, Ergin FG, Li HZ, Watz BB and Funfschilling D “Time-resolved mixing and flow-field measurements during droplet formation in a flow-focusing junction” J. Micromech. Microeng. (2015) 15 084014
2. M1 - Movie of the droplet break-up experiment performed by Carrier et al. http://www.dantecdynamics.com/microfluidics-category/time-resolved-velocity-measurements-of-droplet-formation-in-a-flow-focusing-junction
3. Coron X, Champion JL and Champion M: Simultaneous measurements of velocity field and flame front contour in stagnating turbulent premixed flame by means of PIV. In 12th International Symposium on Applications of Laser Techniques to Fluid Mechanics, 2004. Deen NG, et al. On image pre-processing for PIV of single-and two-phase flows over reflecting objects. Exp Fluids, 2010, 49.2: 525-530.
4. Ergin FG “Flow field measurements during microorganism locomotion using MicroPIV and dynamic masking” Proc. 11th Int. Symp. on PIV, Santa Barbara, California, September 14-16, 2015
5. Ergin FG, Watz BB and Wadhwa N “Pixel-accurate dynamic masking and flow measurements around small breaststroke-swimmers using long-distance MicroPIV” Proc. 11th Int. Symp. on PIV, Santa Barbara, California, September 14-16, (2015a)
6. Ergin FG, Watz BB, Erglis K and Cebers A “Time-resolved velocity measurements in a magnetic micromixer” Exp. Therm. Flu. Sci. (2015b) 67, pp. 6-13
7. Fritz HM, Hager WH and Minor HE ”Landslide generated impulse waves. 1. Instantaneous flow fields” Exp Fluids 35 (2003) 505-519
8. Gui L and Merzkirch W (1996) Phase-separation of PIV measurements in two-phase flow by applying a digital mask technique. ERCOFTAC Bulletin 30: 45-48

9. Hammad KJ. “Liquid jet impingement on a free liquid surface: PIV study of the turbulent bubbly two-phase flow.” In: ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2010. p. 2877-2885.
10. Honkanen M and Saarenrinne P “Multiphase PIV method with digital object separation methods” 5th International Symposium on PIV, Busan Korea, Sept 2003
11. Lindken R and Merzkirch W (2000) Velocity measurements of liquid and gaseous phase for a system of bubbles rising in water. Exp Fluids 29, 194-201
12. Lindken R and Merzkirch W (2002) A novel PIV technique for measurements in multiphase flows and its application to two-phase bubbly flows. Exp Fluids 33, 814-825
13. Sanchis A and Jensen A “Dynamic masking of PIV images using the Radon transform in free surface flows” Exp in Fluids 2011 51(4) 871-880
14. Seol DG and Socolofsky SA (2008) Vector post-processing algorithm for phase discrimination of two-phase PIV. Exp Fluids 45:223
15. Stevens EJ, Bray KNC and Lecordier B “Velocity and scalar statistics for premixed turbulent stagnation flames using PIV” Proc. 27th International Symposium on Combustion (1998) pp. 949-955. Sveen JK and Dalziel SB “A dynamic masking technique for combined measurements of PIV and synthetic schlieren applied to internal gravity waves” Measurement Science and Technology, (2005) 16, 1954-1960
16. Wadhwa N, Andersen A and Kiørboe T “Hydrodynamics and energetics of jumping copepod nauplii and copepodids” J. Exp. Biol. (2014) 217, pp.3085-3094
17. Westerweel, J. and & Scarano, F. (2005). Universal outlier detection for PIV data. Experiments in Fluids, 39(6), 1096-1100.
18. Wosnik, M., and Arndt, R. E. A., (2013), "Measurements in High Void-Fraction Bubbly Wakes Created by Ventilated Supercavitation," ASME J. Fluids Eng. 135(1), pp. 011304-011304-9