Blade repair is often economically more attractive than the replacement of damaged blades by spare parts. Such regenerated turbine blades, however, can introduce non-uniform flow conditions which lead to additional forced response excitation of blades. A forced response excitation due to a typical geometric variation, introduced through current repair methods applied in an upstream stage, is investigated using a fluid-structure interaction (FSI) model previously experimentally validated in a five-stage axial turbine. In this study, geometrical variations are applied to the stator vane of the fourth stage of the five-stage axial turbine. The reference configuration, without variations, is compared with experimental data. The focus of the analysis is the determination of the aerodynamic excitation in a multi-stage setup. For both configurations, with and without variations, the stage loading coefficient of the last turbine stage remains constant. In contrast, the aerodynamic work acting on the last rotor blade increases by a factor of 4 dependent on the operating point. The vibration amplitude of the downstream blade is determined using a unidirectional fluid-structure interaction approach. The impact of the variations on the vibration amplitude decreases by a factor of 10 with increasing number of blade rows between the modified vane row and the analyzed blade row. However, the geometric variations induce vibration amplitudes 4 times higher than the reference case. Based on the methodology used, a linear correlation between the excitation of the blade by the aerodynamic work and the vibration amplitude is shown to exist.

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This paper shows the effect of local surface roughness on the aerodynamic loss behavior of a turbine blade. Non-contact measurements of the surface roughness of turbine blades of a jet engine are conducted. The roughness is quantitatively characterised using a shape and density parameter to parametrise the topology and the average roughness height. An experimental investigation in a linear cascade wind tunnel is conducted in order to identify the contributions of pressure- and friction-losses of the measured surfaces to the overall profile loss increase due to local surface roughness. The results show that the change of profile losses due to local surface roughness is significant. The change in losses is dependent on the roughness height, as well as of the position on the blade of the roughness and the condition of the boundary layer behind. The local pressure gradient at and downstream of the surface roughness is identified as the main influencing parameter besides the roughness height.

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Increase in ambient atmospheric temperature significantly reduces the thermal output of gas turbines. Inlet fogging is one of the power augmentation technique which is used to increase the power output of gas turbines. In this study, experimental work on the characteristics of a liquid film on to the surface of cascade blade is reported. Shadowgraph images of different regimes of the thin liquid film formed on the cascade blade were taken at different air flow conditions. It was observed that air flow velocity on the blade’s surface significantly affects the instability and thickness of the liquid’s surface, while blade’s angle of attack was found to enhance the instability pattern due to the flow separation on the blade’s surface. From the experimental results, it is concluded that the height to width ratio of liquid film thickness remains constant at a particular angle of attack and air flow velocity, and remained unchanged with the change in the mass flow rate of the liquid.

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Inlet fogging of gas turbines has been commonly adopted for the power augmentation of gas turbines. The major benefits of this method are; increase in power output and reduction of NOx levels. This paper covers the results of extensive visualization and experimental studies conducted to understand the phenomena of droplets breakup at different flow conditions. Experimental study of the behaviour of ligament breakup and droplets size distribution is addressed from 0-degree to 10-degree angle of attack. Image processing method was utilized for the measurements of droplets size distribution after the trailing edge of the blade. It is found that the droplets size distribution is governed by the dominance effects of aerodynamics and surface tension forces, and remains the same at a specific position after the trailing edge region. Also, droplets size increases with an increase in blade’s angle of attack and a decrease in air momentum.

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