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Mitigation of Pressure Pulsations in Francis Turbine Draft Tube with a GuideVane System : A Numerical InvestigationJoy, Jesline January 2021 (has links)
The use of renewable energy such as water and wind to produce electricity has been proven extremely effective in Sweden. The ability of these renewable resources to produce clean output energy counters the adversities caused by non-renewable resources. The use of hydraulic turbines is a good example of favoured technique for energy and power production using renewable resources. The hydro-turbines are designed to operate at best efficiency point (BEP). Varying energy demands in recent years implies on the need of flexible operation of hydraulic turbines. The issue of pressure pulsations in the draft tube of hydro-turbines, observed at lower operating conditions has been unresolved for many years. These pressure pulsations are related to the ‘rotating vortex rope’ (RVR) observed at part load operation and, affects the lifespan and performance of the hydro-turbine adversely. Several techniques have been investigated in the past to reduce the pressure pulsations in the draft tube at part load operation and enhance the flexibility of the turbine. During the present research study, a passive flow control technique was investigated numerically by implementing a guide vane system in the draft tube of the Francis-99model turbine. Guide vanes are mechanical devices that can direct the flow in a desired direction. The current study presents the possibility of reducing the pressure pulsations in the draft tube by mitigating the RVR using a guide vane system in the draft tube. At the initial stages of the research study, a reduced numerical model of the Francis model turbine was developed by only considering the draft tube domain. The motive was to develop a reduced model to perform the parametric analysis for the guide vane system in the draft tube with reduced computational time, power, and storage. The results obtained from the numerical study were found to be in good agreement with theFrancis-99 semi-model with passage domains. A parametric study was performed to achieve a guide vane system design that could mitigate RVR with minimum losses. During this study, the number of guide vanes, the chord and the span of the guide vanes were investigated. It was found that a set of three guide vane system with chord of 86% of runner radius and leading-edge span of 30% of runner radius is an ideal design that mitigates RVR above 95%.
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Development of a Reduced Computational Model to Replicate Inlet Distortion in an APU-Style Inlet of a Centrifugal CompressorEvan Henry Bond (12455190) 25 April 2022 (has links)
<p>The purpose of this research was to determine what components of a complex centrifugal compression system inlet needed to be modelled to accurately predict the swirl and total pressure distortions at the compressor face. Two computational models were developed. A full-fidelity case where all the inlet geometry was modelled and a reduced model where a small portion of the inlet was considered. Both the numerical cases were compared with experimental data from a research compressor rig developed by Honeywell Aerospace. The test apparatus was designed with a modular inlet system to develop swirl distortion patterns. The modular inlet system utilized transposable baffles within the radial-to-axial section of the inlet and blockage plates of varying sizes and geometries at the inlet to this section. Discerning the dominant inlet component that dictates distortion behavior at the compressor face would allow the reduced modelling of inlet components for compression systems and would allow coupling with more tortuous systems. Furthermore, it would reduce the design iteration and simulation time of the inlet systems. Several investigations utilizing a reduced model only considering a radial-to-axial inlet are available in literature, but no comprehensive justification has been presented as to the impact this has on the distortion behavior. Experimental surveys of flow conditions just upstream of the inducer of the centrifugal compressor were conducted at several operating conditions. The highest and lowest mass flow rates of these operating points were simulated using ANSYS CFX 2020R1 for both the computational models. Multiple inlet configurations were simulated to test the robustness of the reduced model in comparison to the full fidelity. The numerical simulations highlighted shortcomings of the instrumentation used to characterize the experimental flow field at the inducer, particularly with respect to total pressure distortion. Furthermore, transient pressure data were measured in experiment and indicated unsteady fluctuations in the inlet that would not be captured by steady computational fluid dynamic simulations. These data matched locations of disagreement with swirl distortion behavior at high mass flow rates. This suggested that transient vortex movement occured at the aerodynamic interface plane in certain configurations. The total pressure distortion metrics between the two models were remarkably comparable. Furthermore, the simplified model accurately predicted the mixing losses associated with the blockage plates at the inlet to the radial-to-axial inlet using a simple inlet extension. Swirl 18 distortion was dictated by the radial-to-axial inlet. The reduced model data trends were comparable with experiment for both the baffle and blocker plate configurations. The swirl intensities for all configurations were comparable between the two models. The reduced model swirl directivity trends matched those of experiment. The most notable deviations between the full-fidelity model and the reduced model were observed with swirl directivity numerics. </p>
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