EXPERIMENTAL STUDY OF PIANO KEY WEIR FOR SAND AND GRAVEL BED FLUVIAL CONDITIONS

Abstract

The natural fluvial hydraulic conditions are fraught with infinite complexities. Out of which few were chosen for investigating experimentally to assess the interventions of man-made structure piano key weir (PKW) in a stream. PKW is non-conventional in the sense that its geometric parameters are characteristically different from usual weirs or spillways. The features are unusual compared to traditional flow structures. The sloping inlet ramps starts much below the crest level giving rise to intricate manifestation and expenditure of turbulent kinetic energy. The flume studies were carried out in River Engineering Laboratory of the Department of Water Resources Development and Management, IIT Roorkee. The experiment was conducted in three distinct conditions with more or less constant discharge. Three-dimensional velocity was observed using Sontek Micro ADV. 140 data points were observed for each condition. The study accomplished spatial velocity distribution and vector studies, shear stress, Reynold’s stress, Turbulent Kinetic Energy, Quadrant and Octant analysis. In spite of this, the computer-based numerical technique was employed for simulation of fluvial hydraulics for one of the conditions by using computational fluid dynamics routine of ANSYS CFD. The study highlights the essence of smooth transition below the overhang key for better performance of the structure. A wide variation in estimation of shear stress was observed by different approaches but it has been neutralized near the structure. Shields parameter estimate shows that observed shear stress is much less than that required for bed movement. Variation of Reynolds stress was found to be more in case of rough bed than in smooth bed. For all experimental condition, the turbulence kinetic energy was found to be maximum near the half the depth of flow. Quadrant analysis with consideration of hole size revealed the strong presence of ejection and sweep phenomenon with an increase in hole size for all experimental conditions. The turbulence ratio for rough bed in presence of structure shows dramatic increment with an increase in hole size. The octant distribution of bursting phenomenon shows some needle shape in radar plot of near-bed data. It shows that some particular axis shows the sharp rise of octant events that are visible in octant analysis which can’t explain through quadrant analysis. Gravel bed in presence of piano key weir structure was simulated using CFX algorithm of ANSYS software. The boundary condition of the model was extracted from the experiment. As model output was tested for mesh independence, simulated results are compared with the observed flow velocity