Abstract
Sediment-laden flow measurement with Particle Tracking Velocimetry (PTV) introduces a series of finite-sized sampling bins along the vertical of the flow. Instantaneous velocities are collected at each bin and a significantly large sample is established to evaluate mean and root mean square (rms) velocities of the flow. Due to the presence of concentration gradient, the established sample for the solid phase involves more data from the lower part of the sampling bin than from the upper part. The concentration effect causes bias errors in the measured mean and rms velocities when velocity varies across the bin. These bias errors are analytically quantified in this study based on simplified linear velocity and concentration distributions. Typical bulk flow characteristics from sediment-laden flow measurements are used to demonstrate rough estimation of the error magnitude. Results indicate that the mean velocity is underestimated while the rms velocity is overestimated in the ensemble-averaged measurement. The extent of deviation is commensurate with the bin size and the rate of concentration gradient. Procedures are proposed to assist determining an appropriate sampling bin size in certain error limits.
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References
LIU Yong-hui, DU Guang-sheng and LIU Li-pin. et al. Experimental study of velocity distributions in the transition region of pipes [J]. Journal of Hydrodynamics, 2011, 23(5): 643–648.
TANG L. M., WANG X. K. Experimental study on three dimensional movements of particles (?) Effects of particle diameter on velocity and concentration distributions [J]. International Journal of Sediment Research, 2009, 24(2): 159–168.
TANG L. M., WANG X. K. Experimental study on three dimensional movements of particles (II) Effects of particle diameter on turbulence characteristics [J]. International Journal of Sediment Research, 2009, 24(2): 169–176.
CHENG Wen, LIU Wen-hong and HU Bao-we. et al. Experimental study on gas-liquid two-phase flows in an areation tank by using image treatment method [J]. Journal of Hydrodynamics, 2008, 20(5): 650–655.
NEZU I., SANJOU M. PIV and PTV measurements in hydro-sciences with focus on turbulent open-channel flows [J]. Journal of Hydro-Environment Research, 2011, 5(4): 215–230.
MUSTE M., YU K. and FUJITA I. et al. Two-phase versus mixed-flow perspective on suspended sediment transport in turbulent channel flows [J]. Water Resources Research, 2005, 41(10): W10402.
NEZU I., AZUMA R. Turbulence characteristics and interaction between particles and fluid in particle-laden open channel flows [J]. Journal of Hydraulic Engineering, ASCE, 2004, 130(10): 988–1001.
MEUNIER P., LEWEKE T. Analysis and treatment of errors due to high velocity gradients in particle image velocimetry [J]. Experiments in Fluids, 2003, 35(5): 408–421.
WESTERWEEL J., GEELHOED P. F. and LINDKEN R. Single-pixel resolution ensemble correlation for micro-PIV applications [J]. Experiments in Fluids, 2004, 37(3): 375–384.
THEUNISSEN R., SCARANO F. and RIETHMULLER M. L. An adaptive sampling and windowing interrogation method in PIV [J]. Measurement Science and Technology, 2007, 18(1): 275–287.
LI D. X., MUSTE M. and WANG X. K. Quantification of the bias error induced by velocity gradients [J]. Measurement Science and Technology, 2008, 19(1): 015402.
LHERMITTE R., LEMMIN U. Open channel flow and turbulence measurement by high-resolution Doppler sonar [J]. Journal of Atmosphere and Ocean Technology, 1994, 11(5): 1295–1308.
CHIEN N., WAN Z. H. Mechanics of sediment transport [M]. Reston, USA: USCE Press, 1999.
NEZU I., NAKAGAWA H. Turbulence in open-channel flows [M]. IAHR/AIRH Monograph Series, Rotterdam, The Netherlands: A. A. Balkema, 1993.
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Project supported by the National Natural Science Foundation of China (Grant No. 50779023).
Biography: LI Dan-xun (1970-), Male, Ph. D., Associate Professor
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Li, Dx., Lin, Qs., Zhong, Q. et al. Bias Errors Induced by Concentration Gradient in Sediment-Laden Flow Measurement with PTV. J Hydrodyn 24, 668–674 (2012). https://doi.org/10.1016/S1001-6058(11)60290-4
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DOI: https://doi.org/10.1016/S1001-6058(11)60290-4