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%.

<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>