Browsing by Author "McKenzie, A. B."
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Item Open Access Application of recess vaned casing treatment to axial flow compressors(Cranfield University, 1987-12) Azimian, A. R.; Elder, R. L.; McKenzie, A. B.In axial flow compressors and fans, the stable working range is restricted by the so called stall line where operation may become unstable and simultaneously a short fall in compressor performance appears. Stall margin improvement has been a major task and experimental observations over the last two decades have shown that modifying the shape of the outer annulus wall, above the tips of rotor blades, is effective in delaying the onset of stall to lower mass flow rates. A wide variety of wall modifications or casing treatments have been tried with a range of stall flow improvement which can amount to about 20% .(of the stalled flow) An alternative technique for stall margin improvement in a single stage axial flow machine has been studied and results will be described in the present thesis. The technique for delaying stall involves a large scale treatment to the outer casing of the compressor which extends partly over and mainly upstream of the rotor. The operating principle appears to be that as the flow is reduced towards the stall point some radially unbalanced cells are transported from the blade tips where they are collected in the treatment , turned by the treatment vanes , and re-introduced to the main flow upstream of the rotor. A rotor with and without outlet stators has been tested ( and also with and without casing treatment) over a range of speeds and flow conditions. Also the flow condition inside the recessed casing has been simulated by means of an existing computer code known as PHOENICS.Item Open Access End-wall flows and blading design for axial flow compressors(Cranfield University, 1991-05) Robinson, Christopher J.; McKenzie, A. B.The flow in multistage axial flow compressors is particularly complex in nature because of the proximity of moving bladerows, the growth of end-wall boundary layers and the presence of tip and seal leakages and secondary flow. The problems associated with these phenomena are at their most acute in the latter, subsonic stages of the core compressor, where Reynolds numbers are modest and the blading has low aspect ratio. Indeed, much of the inefficiency of axial stages is believed to be associated with the interaction between blading and end-wall flows. The fact that the end-wall flow phenomena result in conditions local to the blade which are quite different from those over the major part of the annulus was appreciated by many of the earliest workers in the axial turbomachinery field. However, experiments on blading designs aimed specifically at attacking the end-loss have been sparse. This thesis includes results from tests of conventional and end-bent blading in a four-stage, low-speed, axial compressor, built specifically for the task, at a scale where high spatial measurement resolution could be readily achieved within the flowpath. Two basic design styles are considered: a zero a0 stage with DCA aerofoils and a low-reaction controlled-diffusion design with cantilevered stators. The data gives insight into the flow phenomena present in 'buried' stages and has resulted in a much clearer understanding of the behaviour of end-bent blading. A 3D Navier-Stokes solver was calibrated on the two low-reaction stators and was found to give good agreement with most aspects of the experimental results. An improved design procedure is suggested based on the incorporation of end-bends into the throughflow and iterative use of the 3D Navier-Stokes solver.Item Open Access Vaned recess anti-stall for axial-flow fans and compressors(Cranfield University, 1996) Kang, Chang; McKenzie, A. B.; Elder, R. L.The study of anti-stall techniques for fans and compressors has never been more significant, since the potential applications were recognised in gas turbines, tunnel ventilation (jet fans) and industrial process where fans/compressors would benefit from the devices. This thesis will discuss the techniques achieving competitiveness by modifying the conventional casing design of the fan and compressor, which is referred to as casing treatments, taking into account the change of maximum efficiency and flow range. An experimental investigation to examine the influence of the vaned recess casing treatment on stall margin, operating efficiency and flow field of a low speed axial flow fan with aerospace type blade loading is presented. Different geometrical designs of the vaned passages were examined and more than 65% of stall margin improvements and over twice pressure rise with insignificant peak efficiency change were obtained. Experiments to examine the effect of casing treatments on the flow field were carried out using the same fan rig with a tip clearance of 1.2% of the blade height. A high frequency data acquisition system including both hardware and software was developed and the 3-D flow measurements with a slanted hot-wire were undertaken. The first detailed results of flow measurements associated with the vaned recess casing treatment are presented, including both time-averaged and ensemble-averaged measurement results. The flow features in both the solid casing and treated casing builds are captured and comparison between the builds presented. The results revealed that the stall margin improvement due to the casing treatment was not achieved by reducing the incidence nor by increasing the total pressure in the tip region. It appeared that the combined functions of elimination of the whirling flow, the removal of the randomness of the inlet flow and modification of the tip clearance flow are salient features associated with the mechanism of the treatment. The steady flow field of the test fan with various tip clearances has also been simulated in the rotating frame with computational fluid dynamics (CFD) to investigate the clearance effect on the end-wall flow development and to elucidate the behaviour of the tip leakage flow, and hopefully shed more light onto the flow phenomena involved.