In the current research work, a computational analysis of a high-speed centrifugal compressor stage for turbocharger applications is presented. A detailed investigation about the interactions between backswept impeller and downstream vaneless and vaned diffusers is carried out. ' A unshrouded backswept impeller with splitters was combined with a vaneless diffuser or a number of different designs of vaned diffusers. The CFD solver CFX-TASCow was used. The three-dimensional Reynolds- Averaged Navier-Stokes equations are solved and a pressure correction method is employed to solve the system of equations. A steady simulation and analysis of the interactions between the impeller and the vaneless diffuser is carried out, emphasis is focused on the comparisons of the different interactions at different conditions regarding the flow structures at different radius ratios, effect of rotational speed, mass flow rate and impeller tip clearance. The predicted results were also compared with the available experimental results in terms of radial Velocity, tangential Velocity and flow angle. In general, the predicted results show a reasonable agreement with the experimental data. A steady state simulation and analysis regarding the interaction between the impeller and various vaned diffusers is carried out. For the interface between the rotational impeller outlet and the stationary vaned diffuser inlet, the stage averaging condition is used. A detailed comparison between the predicted and the available experimental data is performed in terms of static pressure rise, total pressure ratio, choking mass flow and efficiency characteristics, and very good agreement is accomplished. In addition, detailed flow distributions are compared, assessed and critically analysed, regarding different number of diffuser vanes, rotational speed, gap between the leading edge of the vaned diffuser and impeller tip, mass flow rate. Emphasis is focused on the steady state study of the effect of the number of diffuser vanes on the stage operating range. Further more, unsteady simulation and analysis regarding the interactions between backswept impeller and downstream vaned diffusers is carried out. In the unsteady simulation, a geometry scaling method is used to modify the diffuser geometry to the nearest integer pitch ratio while keeping the throat area, flow direction and area ratio unchanged in order to deal with the unequal pitch ratio problems which exist in the unsteady simulation. The unsteady investigation was undertaken regarding different number of diffuser vanes, rotational speed, gap between the leading edge of the vaned diffuser and impeller tip, mass flow rate and impeller tip clearance. The detailed interactions at different conditions are compared, assessed and analysed. The studies focus on the analyses of the effect of the different interactions on the stage operating range, peak efficiency, total pressure ratio, level of unsteadiness, flow structures, flow angle or incidence angle, etc. In addition, the' predicted results are compared with available experimental data and a quite good agreement is achieved although the geometry is scaled. On the other hand, a detailed investigation on the differences between the time averaged unsteady simulation results and steady simulation results was performed at different conditions. The comparisons were carried out regarding static pressure, total pressure, speed, flow angle (or incidence angle) and isentropic efficiency. The investigation confirms that unsteady simulation is still quite important, since some of the steady state simulation results are still not similar to the time averaged ones. Designers should take into account the influence of the unsteadiness on the flow fields when they employ the steady state model in the design process.

abstract: In previous work, the effects of power extraction for onboard electrical equipment and flight control systems were studied to determine which turbine shaft (i.e. high power shaft vs low power shaft) is best suited for power extraction. This thesis will look into an alternative option, a three-spool design with a high-pressure turbine, low-pressure turbine, and a turbine dedicated to driving the fan. One of the three-spool turbines is designed to be a vaneless counter-rotating turbine. The off-design performance of this new design will be compared to the traditional two-spool design to determine if the additional spool is a practical alternative to current designs for high shaft horsepower extraction requirements. Upon analysis, this thesis has shown that a three-spool engine with a vaneless counter-rotating stage has worse performance characteristics than traditional two-spool designs for UAV systems. / Dissertation/Thesis / Masters Thesis Aerospace Engineering 2019

The effects of impeller-diffuser interaction are investigated through numerically simulating the modified wedge vane profiles. Steady and time-accurate, 3D- viscous RANSsolver is used to perform flow field computations. The original design is modified to obtain better aerodynamic performance. Five morechanges are made to the leading edge profile of the new design, in order to assess different degrees of unsteadiness. These changes show that their contribution on stageefficiency is rather minor, while they have a huge reduction on blade loadings. Moreover, it is shown that the shorter radial distance of vaneless space does not necessarilymean an increased loading thanks to the eliminating in-phase fluctuations on pressureand suction sides. It is found that the impeller reacts to the upstream static pressure disturbance, whichis caused by the applied geometry change and its resultant flow field in the wedge diffuser, but not to the radial location of a certain profile. In addition, the results indicatethat the wedge diffuser aerodynamic performance is driven by time-averaged flow fieldbehaviour.

This work will be focused on issue of a jet engine. The thesis will be divided into search retrieval part and computational part. In the search retrieval part it will focus on different configurations of jet engines as well as areas of their use. The main part of the thesis will however focus on a calculations where a turbine, compressor and an exhaust nozzle will be designed in order to give a thrust of approximately 1kN. Next step will be determination of an engine charcteristic that will give us a preview on how the engine performance will look like in off-design modes.