Turbulence study in the vicinity of piano key weir: relevance, instrumentation, parameters and methods (original) (raw)
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Gaps and Scope of Turbulence Study Near Piano Key Weir (PKW)
Turbulence by its handiwork immeasurably enriches the lives of even those who cannot comprehend its mysteries. In turbulent flow the speed of the fluid at a point is continuously undergoing changes in both magnitude and direction. Flow parameters are complicated to envisage near any hydraulic structures like Piano Key Weir until small scale time fluctuating turbulent nature of flows is clearly understood. Theoretical analysis and prediction of turbulence has been problem of fluid dynamics due to random or chaotic nature of turbulence phenomena. Without the recognition of turbulence structure near any hydraulic structures like Piano Key Weir, it is impossible to properly understand the processes happening during the flow of water. Important issues regarding turbulence, development, methodology, gaps and scope for Piano Key Weir has been discussed in this paper.
Statistical Study of Turbulence Near Piano Key Weir: A Review
Piano Key Weirs are more efficient than the traditional Labyrinth weir and Piano Key Weirs can be an interesting solution for increasing the active storage of reservoir or for improving the safety of dam during extreme flood. This technology helps to reduce the reservoir sedimentation. It will also help in minimizing the sub-mergence effect. Flushing is vital for the preservation of long-term storage in reservoirs. However, downstream impacts such as turbidity act as a constraint in the planning and operation of sediment flushing. Physics especially about turbulence phenomena will be helpful to decide the design criteria. Turbulent mixing is an important process controlling the descent rate, water mass modification and volume transport. Under stable conditions dissipation essentially balances shear production, while turbulent transport and buoyant production are of secondary importance. Under unstable conditions, dissipation slightly exceeds the total production, and energy is also lost at a substantial rate due to upward export by the turbulence. Theoretical analysis and prediction of turbulence has been problem of fluid dynamics due to random or chaotic nature of turbulence phenomena. Because of this unpredictability, it has been usual to work with the time averaged forms of the governing equations, which inevitably results in terms involving higher order correlations of fluctuating quantities of flow variables. Turbulence is a very complex phenomenon so near PKW occurrence need extensive laboratory experiment and analysis of these results through some statistics will be reliable. This paper deals with issues, gaps and scope of statistical turbulence study near PKW.
Noise in the velocity measurements and boundaries effect in an open channel with Piano Key Weir
ISH Journal of Hydraulic Engineering, 2018
An Acoustic Doppler Velocimeter (ADV) system, with digital signal processing has been used to measure the longitudinal, transverse, and vertical velocity components in three-dimensional, fully developed open-channel flow with transversely placed Piano Key Weir (PKW). Simple experiments were conducted to deduce the influence of boundaries on noise occurrence. Both the longitudinal boundary (PKW) and vertical boundary (channel bed) affect noise. Magnitude of noise has been found to be increasing near both the boundaries. Consequences of noise on the first-and second-order velocity parameters have also been estimated. Results show that there is existence of higher correlation between noise and second-order velocity (turbulence) than first-order velocity. After the noise removal from the datasets, the reduction in the magnitude for the second-order velocity is found up to 80%. Magnitude of reduction is also dependent on the distance from the hydraulic structure. Analyses of data-sets in the horizontal plane indicate presence of noise (i.e. higher uncertainty) below the relative depth 0.3. Where, relative depth is defined as the ratio of point depth of measurement to total flow depth.
Flow hydrodynamics near inlet key of Piano Key Weir (PKW)
Sadhana, 2015
This paper presents fundamental outcomes from an experimental study on the hydrodynamic performance near inlet key of Piano Key Weir (PKW). Hydrodynamic performance was tested in a circulated open channel that comprised of PKW and sand bed (d 50 = 0.25 mm). Instantaneous velocities were measured at 20 cross sections using Laser Doppler Velocimeter (LDV) with constant discharge and depth. Average velocity and turbulence intensities in both directions were investigated. Average longitudinal velocities are found very much consistent at every point and maximum around the midway of inlet key. In transverse direction, flow is bifurcating in two directions which are also confirmed by average transverse velocity estimation. Variation of turbulence intensity presents average 10 times higher transverse turbulence than longitudinal turbulence near inlet key of PKW.
Open-channel turbulence measurements with a three-component acoustic Doppler velocimeter
Publications of the Institute of Geophysics Polish …, 2007
The paper described some turbulence measurements carried out in an experimental compound channel with flood plains. The surface of the main channel bed was smooth and made of concrete, whereas the floodplains and sloping banks were covered by cement mortar composed with terrazzo. Instantaneous velocities were measured be means of a three-component acoustic Doppler velocity meter (ADV) manufactured by Sontek Inc. This article presents the results of measurements of primary velocity, the distribution of turbulent intensities, Reynolds stresses, autocorrelation functions, turbulent scales, as well as the energy spectra.
Experimental investigation of submerged flow over piano key weir
2018
Extensive experimental investigation has been performed to analyse the behaviour of piano key weir under submerged flow conditions. More than 2500 runs were performed on 14 physical models in an experimental rectangular flume, 15 m long and 0.3 m by 0.45 m cross-section. Effect of submergence phenomenon on the discharge capacity was studied for different discharge values. It was found that the discharge reduction factor Cs is mainly influenced by the submergence factor S. This effect starts when S is greater than the modular submergence limit which proved to be around 0.4 to 0.6. Models with different geometrical parameters were compared to each other and final conclusions about their effect on discharge capacity were achieved. However, the influence of all the geometrical parameters was small (less than 12%). Copyright © 2018 International Energy and Environment Foundation All rights reserved.
Measurement of Turbulent Velocity Fluctuations in Open Channel using Acoustic Doppler Velocimeter
Indian journal of applied research, 2011
Entrainment of sediment particles from channel beds into the channel ow is in uenced by the characteristics of the ow turbulence which produces stochastic shear stress uctuations at the bed. These uctuations can be measured in open channel bed by measuring the instantaneous velocity components. Present study deals with extraction of information related with measurement of instantaneous velocity components which helps in nding turbulence parameters in open channel bed. The experimental work was planned for collection of data related with 3-D instantaneous velocity over the depth in an open channel mobile bed using 3-D Acoustic Doppler Velocimeter (ADV). The instantaneous velocity components and normalized velocity pro le on uniform size (2.0-4.0 mm) sediment bed in an open channel ow over rough beds were also presented. The turbulence parameters such as turbulent kinetic energy and Reynolds shear stresses were quanti ed across the ow depth by measuring the time averaged velocity components.
2009
The capability of acoustic Doppler velocimeters to resolve flow turbulence is analyzed. Acoustic Doppler velocimeter performance curves APCs are introduced to define optimal flow and sampling conditions for measuring turbulence. To generate the APCs, a conceptual model is developed which simulates different flow conditions as well as the instrument operation. Different scenarios are simulated using the conceptual model to generate synthetic time series of water velocity and the corresponding sampled signals. Main turbulence statistics of the synthetically generated, sampled, and nonsampled time series are plotted in dimensionless form APCs . The relative importance of the Doppler noise on the total measured energy is also evaluated for different noise energy levels and flow conditions. The proposed methodology can be used for the design of experimental measurements, as well as for the interpretation of both field and laboratory observations using acoustic Doppler velocimeters. DOI: ...
Turbulence characteristics of the transition region from hydraulic jump to open channel flow
Journal of Hydraulic Research, 2010
This Technical Note presents experimental measurements on the turbulence characteristics in the transition region from the end of a hydraulic jump to open channel flow in a rectangular channel. An Acoustic Doppler Velocimeter was used to measure the mean velocities, turbulent intensities, Reynolds stress, and turbulent kinetic energy for the supercritical Froude number equal to 4 and 7. We have been able to develop general correlations for the variation of the normalized maximum values of the Reynolds normal stresses as well as the shear stress and the turbulent kinetic energy, using the present results and other results from the literature.
2021
Piano key weirs are being increasingly used for better flood passage downstream, both as a new structure or on top of hydraulic structures like a dam, to increase their discharging capacity as well as reservoir storage. Much research has been done on rectangular plan-form, while other plan-forms warrant attention. The present study focuses on two different plan geometries of PKW, i.e., rectangular (RPKW) and trapezoidal with angle α equal to 9 degrees (TPKW9) for their head-discharge relation in a wide channel of 0.984 m width under free-flow condition. Since the role of CFD is increasingly becoming prominent in present times, a numerical study using ANSYS-FLUENT was also carried out to ascertain its relevance in predicting flows around complex structures like PKW. Further, the tailgate was closed to render the PKW’s outlet from partial to fully submerged conditions. The effect of these submerged outlets was studied for any changes in the discharging capacity of the PKW. The study s...