Tip Vortex Cavitation (TVC) is a major issue in design and operation of axial hydraulic machines. We investigate the capacity flexible trailing thread alleviating TVC by analyzing flow-induced motion. For this purpose, nylon with three diameters cut various lengths attached to tip an elliptical hydrofoil. The selected threads are enough become unstable start flutter under almost all tested flow conditions. Due vortical flow, oscillating forced spiral around vortex axis. resulting rotational...

Abstract Francis turbines with medium or high specific speeds may experience a particular type of instability in the upper part load which precessing vortex has an elliptical shape. The occurrence part-load (UPLI) is accompanied by large-amplitude pressure fluctuations at distinct frequency between 2 and 4 times runner rotational speed. This paper experimentally investigates UPLI for reduced-scale turbine. To investigate causal factors this instability, draft tube measurements, particle...

Abstract Operating hydro turbines in off-design conditions increases the risk of cavitation occurrence, which turn, leads to numerous problems such as performance degradations, structural vibrations, and most importantly, mechanical damage due erosion. It is therefore crucial develop a monitoring system that detects occurrence severity real time. For this purpose, detection methodology has been developed based on analysis acoustic emissions turbine with machine learning algorithms. In...

This paper analyses adiabatic gas bubble formation, growth, and detachment which are produced from a submerged needle in water with the aim of elucidating impact surface tension on properties.A simulation model is utilized to enable examination problem for mentioned parameter.The numerical results compared experimental observations validation purposes.The results, including changes properties during process, recorded comprehensive research different tensions applied understand effect this...

The appearance of gas-filled vortices at the tip hydraulic machines blades is usually associated with increase losses, vibrations, noise and erosion risk. understanding roll-up region, where boundary layer on pressure side crosses foil generates vortex suction side, primary importance to control behaviour. However, very strong gradients encountered in regions make numerical simulations experimental measurements particularly challenging. In present paper we study region a skewed-back blade,...

Abstract It is well known that the performance of turbomachinery (losses, vibrations, noise, and erosion) often affected by trailing vortex from blade tip (Tip Leakage Vortex; TLV) impeller or propeller, sometimes cavitation occurs in center core Vortex Cavitation; TVC). Many researches on characteristics isolated hydrofoil numerical simulations experiments have been done so far, however, research understanding mechanism control technique not enough, it important to mitigate effect TLV TVC,...

Abstract This paper presents preliminary results of an experimental study on the occurrence and development upper part-load instability in a reduced-scale Francis turbine. The includes draft tube pressure measurements, high-speed flow visualization, particle image velocimetry. Our reveal that for operating point within range (70 to 85 % nominal discharge), vortex rope has circular cross section non-cavitating conditions, which is preserved even after appearance cavitation core. It only below...

Purpose – The purpose of this paper is to determine the reason for discrepancy in estimated and observed damage caused by fragmenting charges closed environments. Design/methodology/approach A series carefully conducted physical numerical experiments was conducted. results were analyzed compared. Findings analysis shows that environments, dust plays a far larger role than previously thought, leading much lower pressures damage. Research limitations/implications In light these findings, many...

The omnipresent vortical structures in hydraulic machines are extremely prone to the occurrence of cavitation. It is well known that besides flow parameters, incipience, development, and disappearance cavitation within a vortex very sensitive gas content. also pressure threshold for desinence may be significantly higher than its incipience. This hysteresis, which not yet understood, scope current work. case study made an elliptical NACA 16020 hydrofoil, placed test section EPFL high-speed...