Gaps and Scope of Turbulence Study Near Piano Key Weir (PKW) (original) (raw)
Related papers
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.
This research paper focuses on the need of turbulence, instruments reliable to capture turbulence, different turbulence parameters and some advance methodology which can decompose various turbulence structures at different levels near hydraulic structures. Small-scale turbulence research has valid prospects in open channel flow. The relevance of the study is amplified as we introduce any hydraulic structure in the channel which disturbs the natural flow and creates discontinuity. To recover this discontinuity, the piano key weir (PKW) might be used with sloped keys. Constraints of empirical results in the vicinity of PKW necessitate extensive laboratory experiments with fair and reliable instrumentation techniques. Acoustic Doppler velocimeter was established to be best suited within range of some limitations using principal component analysis. Wavelet analysis is proposed to decompose the underlying turbulence structure in a better way.
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.
Hydraulic Behavior Of Piano Key Weir Type B Under Free Flow Conditions
2016
In this study, laboratory experiments were performed to evaluate the effects of the weir geometry of a Piano Key Weir (PKW) type B on the discharge coefficient under free flow conditions. Experiments were conducted in a 15m long, 0.3m wide and 0.45m deep rectangular glass-walled flume. The experimental work includes testing of fourteen PKW models which results 290 tests to cover the effects of weir length and height, up-and downstream key widths, upstream apex overhangs length, dam height and noses length on the weir flow discharge coefficient as well PKW with outlet stepped key were considered in the analysis. Considering the experimental data, the dimensional analysis allowed the development of relations between discharge coefficient and the shape of the PKW and gave a good agreement. Experimental results showed that the most influential parameters for the tested PKW models are the Relative length L/W, Key widths W W ⁄ , PKW Height B/P, and Overhangs length B B ⁄ . The effectivene...
International Journal of Energy and Environment, Vol. 10, Issue 1, 2019
Inlet and outlet keys are the main two components of piano key weir. Understanding the phenomena of flow over these two components is an important factor in the design of this structure. In this article, 2D investigation into the velocity and pressure distributions of the flow over individual inlet and outlet keys under different discharges has been performed using CFD technique. Analysis of the results provided information about the critical areas that should be taken into account when designing the PKW structure.
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.
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...
Hydrodynamics and Free-Flow Characteristics of Piano Key Weirs with Different Plan Shapes
Water, 2021
This paper focuses on Piano Key Weirs (PKWs) as an effective solution for improving the discharge capacity of spillway systems. The flow behavior in inlet and outlet keys is experimentally studied to analyze the discharge capacity of PKWs with different plan shapes (i.e., rectangular, trapezoidal, and triangular). The results show that in outlet keys, the flow aeration regimes extend to higher values of headwater ratios (Ho/P) by increasing the length magnification ratio (B/w) and apex width ratio (A/w). In addition, the local submergence length is a decreasing function of A/w, especially in high flow heads. While the total interference length enlarges by reducing A/w in lower Ho/P values (Ho/P < 0.5), a reverse trend is observed in higher headwater ratios. PKW performance may also be impacted by the flow contraction and recirculation zone in inlet keys, which intensify in higher values of Ho/P, B/w, and A/w. According to the obtained results, while the discharge coefficient is a...
Experimental study on vertical velocity and submergence depth near Piano Key weir
Insufficient spillway capacity has been the cause of one-third of all dam failures. An innovative and effective way of increasing the spillway capacity is to use a Labyrinth weir in the modified form of PKW having range of specific flow from 3 to 1000m3/s/m. As the flow approaches towards the PKWeir, it was observed that the Z-component of the velocity of water in lower levels increases which enhances the flushing capacity. One of the important observations is that with decrease in discharge from higher flow to medium flow; Z component velocity is getting lowered by about 14 percent. Increase in discharge from lower to medium flow Z component velocity is getting increased by about 40 percent. It indicates that at lower discharge, upward velocity component is appreciably more which may be helpful for significant amount of sediment suspension at lower discharge also. For flood flow, it was found that there has been reduction of around 25–30% of submergence depth with respect to ogee spillway. Induced flow characteristics near PKW and tractive stress exertion by flowing water in the inlet cell are capable to flush out even the coarser sand particles.
In this research, the flow and scour patterns downstream of a rectangular Piano Key Weir (PKW) were studied experimentally and simulated by using the Flow-3D numerical model and with RNG turbulence model. It was found that the Flow-3D model simulates the scour downstream of a PKW with acceptable accuracy. Variations of the bed topographical downstream of type-A PKWs with different crest shape (i.e. standard crest and with zigzag indentations in various geometries, including: triangulate, half circular, sinusoidal, rectangular and fort crest) were investigated. The results demonstrate that the zigzag indentations of the lateral crest walls substantially influenced the geometrical characteristics of the scour hole including: scour depth at the weir toe, maximum scour depth, scour hole area and scour hole volume. The lowest value of maximum scour depth was occurred downstream of the PKW with the triangulation indentations, in this case a decrease of 10.5 and 17% in the longitudinal and...