Search Results (5)

A damaged stator vane can disrupt the circumferential symmetry of the design flow for turbine assemblies, which can lead to a low-engine-order (LEO) forced response of rotor blades. To help engineers be able to better address sudden vane damage failures, this paper conducts a mechanism analysis of the LEO forced response of rotor blades induced by a single damaged vane using an in-house computational fluid dynamic code (Hybrid Grid Aeroelasticity Environment). Firstly, it is found that the damaged vane introduces a family of LEO aerodynamic excitations with high amplitudes by full-annulus unsteady aeroelastic simulations of a single-stage turbine. In particular, the LEO forced response of the rotor blades excited by 3EO is 2.01 times higher than the resonance response excited by vane passing frequency, and the LEO resonance risk of the rotor blades is greatly increased. Then, by analyzing the flow characteristics of the wake and potential field of the stator row with a damaged vane, the localized high transient pressure in the notch cavity and the radial redistribution of the secondary vortex at the stator exit are the main sources of the low-order harmonic components in the flow field. Importantly, the interaction mechanisms in two regions with high LEO excitation amplitude on the rotor blade surface are revealed separately. Finally, an evaluation and comparison of a single damaged vane in terms of aerodynamic performance and LEO forced response was carried out. The results of this paper provide a good theoretical basis for engineers to effectively control the resonance response of rotor blades caused by a damaged stator vane in turbine design. Full article

In gas turbines, the hot gas exiting the combustor can have temperatures as high as 2000 °C, and some of this hot gas enter into the space between the stator and rotor disks (wheelspace). Since the entering hot gas could damage the disks, its ingestion must be minimized. This is carried out by rim seals and by introducing a cooler flow from the compressor (sealing flow) into the wheelspace. Ingress and egress into rim seals are driven by the stator vanes, the rotor and its rotation, and the rotor blades. This study focuses on the ingress and egress driven by the rotor and its rotation. This is carried out by performing wall-resolved large eddy simulation (LES) around an axial seal in a rotor–stator configuration without vanes and blades. Results obtained show the mechanisms by which the rotor and its rotation induce ingress, egress, and flow trajectories. Kelvin–Helmholtz instability was found to create a wavy shear layer and displacement thickness that produces alternating regions of high and low pressures around the rotor side of the seal. Vortex shedding on the backward-facing side of the seal and its impingement on the rotor side of the seal also produces alternating regions of high and low pressures. The locations of the alternating regions of high and low pressures were found to be statistically stationary and to cause ingress to start on the rotor side of the seal. Vortex shedding and recirculating flow in the seal clearance also cause ingress by entrainment. With the effects of the rotor and its rotation on ingress and egress isolated, this study enables the effects of stator vanes and rotor blades to be assessed. Full article

In recent years, large-capacity, high-head pump–turbine units have been developed for pumped storage power plants to effectively utilise water energy and store large amounts of electricity. Compared with the traditional Francis turbine unit, the radial distance between the trailing edge of the guide vanes and the leading edge of runner blades of high-head pump–turbine unit is smaller, so the rotor–stator interaction and the corresponding pressure fluctuations in the vaneless space of pumped storage units are more intense. The pressure fluctuations with high amplitudes and high frequencies induced by rotor–stator interaction (RSI) become the main hydraulic excitation source for the structures of the unit and may cause violent vibration and fatigue damage to structural components, and seriously affect the safe operation of the units. In this paper, the RSI of a high-head pump–turbine in turbine mode of operation is studied in detail by means of site measurement and full three-dimensional unsteady simulations. The results of RSI-induced pressure fluctuations in turbine mode are analysed experimentally and numerically. The accuracy of the numerical calculations is verified by comparing with the measured results, and the variation law of RSI is deeply analysed. The results show that the pressure fluctuations in the vaneless space are affected by the wake of the guide vane, the rotating excitation of the runner, the low-frequency excitation of the draft tube, and the asymmetric characteristics of the incoming flow of the spiral case, and shows significant differences in spatial position. The findings of the investigation are an important and valuable reference for the design and safe operation of the pumped storage power station. It is recommended to design the runner with inclined inlets to reduce the amplitudes of RSI-induced pressure fluctuations and to avoid operating the pump–turbine units under partial load for long periods of time to reduce the risk of pressure fluctuation induced severe vibration on the structures. Full article

The instability of the no-load working condition of the pump turbine directly affects the grid connection of the unit, and will cause vibration and damage to the components of the unit in severe cases. In this paper, a three-dimensional full flow numerical model including the runner gap and the pressure-balance pipe was established. The method SST k-ω model was used to predict the internal flow characteristics of the pump turbine. The pressure pulsation of the runner under different operating conditions during the no-load process was compared. Because the rotation speed, flow rate, and guide vane opening of the unit change in a small range during the no-load process, the pressure pulsation characteristics of the runner are basically the same. Therefore, a working condition was selected to analyze the transient characteristics of the flow field, and it was found that there was a high-speed ring in the vaneless zone, and a stable channel vortex was generated in the runner flow passage. Analyzing the axial water thrust of each part of the runner, it was found that the axial water thrust of the runner gap was much larger than the axial water thrust of the runner blades, and it changed with time periodically. It was affected by rotor stator interaction. The main frequency was expressed as a multiple of the number of guide vanes, that is, vanes passing frequency, 22f_n. During the entire no-load process, the axial water thrust of the runner changed slowly with time and fluctuated slightly. Full article

In this study, an assessment of degradation and failure modes in the gas-path components of twin-shaft industrial gas turbines (IGTs) has been carried out through a model-based analysis. Measurements from twin-shaft IGTs operated in the field and denoting reduction in engine performance attributed to compressor fouling conditions, hot-end blade turbine damage, and failure in the variable stator guide vane (VSGV) mechanism of the compressor have been considered for the analysis. The measurements were compared with simulated data from a thermodynamic model constructed in a Simulink environment, which predicts the physical parameters (pressure and temperature) across the different stations of the IGT. The model predicts engine health parameters, e.g., component efficiencies and flow capacities, which are not available in the engine field data. The results show that it is possible to simulate the change in physical parameters across the IGT during degradation and failure in the components by varying component efficiencies and flow capacities during IGT simulation. The results also demonstrate that the model can predict the measured field data attributed to failure in the gas-path components of twin-shaft IGTs. The estimated health parameters during degradation or failure in the gas-path components can assist the development of health-index prognostic methods for operational engine performance prediction. Full article