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To understand the influences of blade positive and negative bowing on flowfields of turbine stator cascades with low aspect ratio, six sets of cascades with different bowed angles of the blades were designed and tested. A five-hole pitot microprobe, which was located upstream and downstream of the cascades, was used to survey the flowfields in detail. The results were different from other published results with a different kind of turbine stator blade profile. When a blade has positive or negative bowing, the passage vortices do not change, whereas the characteristics of the trailing vortices, such as the intensity, locations, size, and structure, do change distinctly. In the case of blade positive bowing, the local spanwise distribution of the yaw flow angle at the cascade exit is significantly affected, with very little changes in the cascade overall loss.

If the sensors of gas turbine fail during operations, and the measurement deviation would seriously affect the accuracy of gas path diagnosis results. In order to solve the above problems, a gas path and sensor coupling fault diagnosis model for gas turbines was proposed. In this model, the measurement variations caused by the changes of working conditions were used instead of the conventional measurements, to reduce the interferences of sensor bias faults. Then, the unscented Kalman filter was adopted to estimate the gas path health parameters by tracking the residual errors between the measured variation and predicted variation caused by different working conditions. Each filter in the sensor diagnosis systems was updated, and the sensor faults were isolated according to the weighted square sum of the residual sequence of the filters. Finally, a simulation example of a typical three-shaft gas turbine was carried out, which shows that the proposed model may reduce the coupling effects between gas path faults and sensor faults, and may realize accurate diagnosis of gas path fault and sensor fault. [ABSTRACT FROM AUTHOR]

To understand the effects of the origination and development of centralized vortices on the aerodynamic characteristics of turbine rectangular cascades with high turning angles, experiments with five-hole microspherical probes, accompanied by color helium bubble flow displays, were carried out. The measurement planes are arranged as three before, six in, and one after the cascade. The experiments reveal that the origination and development of horseshoe vortices and passage vortices as well as the interaction of the latters almost dominate the whole flow field of traditional linear cascades. Lean linear cascades favor the horseshoe vortices and passage vortices in the acute angle zone, and impede those in the obtuse angle zone. So it is a logical result to adopt the negatively curved blades, whose pressure surfaces and both endwalls compose both obtuse angles, respectively, to improve the cascade aerodynamic characteristics.

Two one-dimensional models are established for the tip leakage vortex trajectory and rotating stall-onset point prediction respectively for subsonic centrifugal impellers. The goal of modeling is to supply an effective estimation strategy of the stall-onset point for use in the one-dimensional performance prediction stage. The tip leakage vortex trajectory prediction is a critical part of the stall-onset prediction. The proposed one-dimensional model (one-dimensional tip leakage vortex trajectory model) to predict the tip leakage vortex trajectory is based on blade loading, i.e. the velocity difference between the pressure and suction surfaces. The loading function considers the effect of radial rotation, blade turning, and passage width variation. Compared with the computational fluid dynamics results, the current model shows reasonable accuracy, with an average relative error below 12.35%. The one-dimensional prediction model (Model II) is developed to determine the stall-onset point, where the interface between the tip leakage flow and the main flow spills from the blade leading edge. In this model, the momentum balance analysis is applied to identify the position of the interface. The parameter of the tip leakage vortex trajectory in Model II is determined by one-dimensional tip leakage vortex trajectory model. The effective origin of the tip leakage flow is correlated with the rotational speed and tip clearance. The effectiveness of Model II is validated with the experimental and computational fluid dynamics results using three impellers. Compared with the conventional model (Model I), Model II shows better accuracy, with a maximum error of about 7.42%. [ABSTRACT FROM AUTHOR]