Flow visualization movies of flow through a cascade of compressor blades showed propagating stall at stagger angles of 36.5 and 45 degrees for angles of attack of 20 degrees and higher. At a stagger angle of 25 degrees, the development of a steady, separated boundary layer occurred with no propagation. The observed propagating stall process was the development of a vortex in the boundary layer and its subsequent shedding. The shedding mechanism was observed to be the interference by the reverse flow from the previously stalled passage with the vortex flow in the stalled passage. This dissipated the vortex in the blade passage and the incoming flow then flushed the stagnated vortex out of the passage. Measurements of propagation speeds showed that the propagation speed is related to the blockage of the passage, that stagger angle has an insignificant effect on propagation speed, and that propagation speed is proportional to the relative velocity. Based on the observations, a geometric model was developed to predict the onset of propagating stall. This model showed that increased solidity, decreased stagger angles, and operation at low angles of attack make a cascade more resistant to propagating stall inception. The model shows the relation of the operating point of a compressor to the stall inception point. When expanded to include all significant aspects of blade geometry, the model may provide a basis for controlling propagating, and hence, rotating, stall inception based on the blade row·geometry. / Master of Science

Pressure signals were taken on a rotor blade surface of a single-stage, low-speed axial flow compressor. The data showed unsteady, stationary pressure perturbations that correlated with the locations of five large downstream support struts. In the present work, these data are thoroughly analysed. Strut-induced pressure amplitudes as measured on the rotor are presented as a function of the downstream strut locations. Unsteady lift and moment are calculated by integrating the pressures measured by the blade-mounted transducers. In addition, a sequence of instantaneous pressure distributions on the blade surfaces presented over time shows how the rotor is influenced by the potential effect of the struts. The strut is shown to produce a significant effect on rotor flow. This effect exceeds the unsteady stator effect at design rotor-stator-strut spacing, but falls off rapidly as the struts are moved downstream. / M.S.

The oil-film surface flow visualization technique was applied to circular arc compressor blades in a solid wall, high aspect ratio cascade for the purpose of describing the transition from corner stall to full blade stall, and the blade surface flow under fully stalled conditions. Photos of the visualizations for three stagger angles are presented and analyzed. A map quantitatively describing the observed boundary layer development at midspan is presented. The most interesting discovery of the work showed the suction surface flow to be essentially two-dimensional, in the geometric sense, preceding and following the transition to a fully separated flow at the leading edge. Corner stall was the observed three-dimensional mechanism prior to full stall. For fully-stalled conditions, the three-dimensional mechanism took the form of recirculating flow regions at the blade ends. Complete separation at the leading edge occurred at lower angles of attack for the higher stagger angles. Special blade oil-flow tests were conducted to evaluate Reynolds number and tip clearance effects on boundary layer development. The experimental work was done as part of a larger research program aimed at measuring and predicting the stalled performance of a compressor cascade. / Master of Science

The design of a cascade wind tunnel for testing of compressor blades at high angle of attack is described. Methods to insure uniform velocity profiles and control of inlet turbulence are discussed. The problem of maintaining two-dimensional flows at high angle of attack was addressed. A tunnel capable of testing cascades of compressor blades at angles of attack up to seventy-five degrees was constructed. Performance of the tunnel was evaluated and data were acquired for flow over double-circular-arc blades with angles of attack extending into the fully-stalled region. Comparisons were made with available data in the installed flow regime. Results showed that the tunnel had adequately uniform inlet velocities and low turbulence levels, and that two-dimensional flow was maintained over the center two-thirds of the high-aspect ratio blades. / Master of Science

Stator current spectral analysis techniques are usually used to detect rotor faults in induction machines. Magnetic field anomalies in the airgap due to the rotor faults result in characteristic side-band harmonic components in the stator current spectrum, which can be measured as rotor fault signatures. A position-varying load torque oscillation at multiples of the rotational speed, however, has exactly the same effect. Stator current harmonics due to a load torque oscillation often obscure and even overwhelm rotor eccentricity fault detection since the magnitude of load oscillation induced harmonics is usually much larger. Although previous research has suggested some methods to differentiate between these two effects, most of them rely heavily on the accurate estimation of motor parameters. The objective of this research is to develop a far more practical and computationally efficient method to detect rotor faults effectively in the presence of a load torque oscillation. A significant advantage of the proposed scheme is that it does not need any knowledge of motor parameters. The normalized negative sequence information induced by a mixed rotor eccentricity in the stator current or terminal voltage space vector spectra, serves as a reliable rotor fault indicator to eliminate load oscillation effects. Detailed airgap magnetic field analysis for an eccentric motor is performed and all machine inductance matrices as well as their derivatives are reformulated accordingly. Careful observation of these inductance matrices provides a fundamental understanding of motor operation characteristics under a fault condition. Simulation results based on both induction motor dynamic model and Maxwell 2D Finite Element Model demonstrate clearly the existence of the predicted rotor fault indicator. Extensive experimental results also validate the effectiveness and feasibility of the proposed detection scheme.