Despiking of Turbulent Flow Data in Gravel Bed Stream
Authors: Ratul Das
The present experimental study insights the decontamination of instantaneous velocity fluctuations captured by Acoustic Doppler Velocimeter (ADV) in gravel-bed streams to ascertain near-bed turbulence for low Reynolds number. The interference between incidental and reflected pulses produce spikes in the ADV data especially in the near-bed flow zone and therefore filtering the data are very essential. Nortek’s Vectrino four-receiver ADV probe was used to capture the instantaneous three-dimensional velocity fluctuations over a non-cohesive bed. A spike removal algorithm based on the acceleration threshold method was applied to note the bed roughness and its influence on velocity fluctuations and velocity power spectra in the carrier fluid. The velocity power spectra of despiked signals with a best combination of velocity threshold (VT) and acceleration threshold (AT) are proposed which ascertained velocity power spectra a satisfactory fit with the Kolmogorov “–5/3 scaling-law” in the inertial sub-range. Also, velocity distributions below the roughness crest level fairly follows a third-degree polynomial series.
Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1124657Procedia APA BibTeX Chicago EndNote Harvard JSON MLA RIS XML ISO 690 PDF Downloads 852
 Dey, S., and Das, R. “Gravel-bed hydrodynamics: a double averaging approach.” J. Hydraul. Eng., 2012, 138(8), 707-725.
 Franca, M. J., Ferreira, R. M. L, and Lemmin, U. “Parameterization of the logarithmic layer of double-averaged streamwise velocity profiles in gravel-bed river flows.” Adv. Water Resour., 2008, 31, 915-925.
 Goring, D. G., and Nikora, V. I. “Despiking acoustic Doppler velocimeter data.” J. Hydraul. Eng., 2002,128(1), 117-126.
 Lacey, R. W. J., and Roy, A. G. “Fine-scale characterization of the turbulent shear layer of an instream pebble cluster.” J. Hydraul. Eng., 2008,134(7), 925-936.
 Manes, C., Pokrajac, D., and McEwan, I. “Double-averaged open-channel flows with small relative submergence.” J. Hydraul. Eng., 2007, 133(8), 896-904.
 Mignot, E., Barthelemy, E., and Hurther, D. “Double-averaging analysis and local flow characterization of near-bed turbulence in gravel-bed channel flows.” J. Fluid Mech., 2009, 618, 279-303.
 Monin, A. S., and Yaglom, A. M. Statistical fluid mechanics, volume II: Mechanics of turbulence. Dover Publications, New York, USA.(2007.
 Nezu, I., and Nakagawa, H. Turbulence in open-channel flows. Balkema, Rotterdam, Netherlands. 1993.
 Nikora, V. I., Goring, D. G., and Biggs, B. J. F. “Some observations of the effects of microorganisms growing on the bed of an open channel on the turbulence properties.” J. Fluid Mech., 2002. 250, 317-341.
 Nikora, V., Goring, D., McEwan, I., and Griffiths, G. “Spatially averaged open-channel flow over rough bed.” J. Hydraul. Eng., 2001,127(2), 123-133.
 Nikora, V., and Rowiński, P. M. “Rough-bed flows in geophysical, environmental and engineering systems: double averaging approach and its applications.” Acta Geophysica, Special Issue, 2008, 56(3), 529-934.
 Pokrajac, D., Campbell, L. J., Nikora, V. L., McEwan, I. K., and Manes, C. “Quadrant analysis of persistent spatial velocity perturbations over square-bar roughness.” Exp. Fluids, 2007, 42(3), 413-423.
 Pope, S. B.. Turbulent flows. Cambridge University Press, U.K. 2001.
 Sarkar, S., and Dey, S. “Double-averaging turbulence characteristics in flows over a gravel-bed.” J. Hydraul. Res., 2010, 48(6), 801-809.