In this thesis, secondary flow in a two stage, low aspect ratio turbine is investigated using CFD. A parameter study is carried out to investigate how the turbine performance is affected by the choice of aspect ratio. This is done in two steps, first by changing the blade height and then the blade size. The study shows that increasing the aspect ratio will lead to a significant increase of efficiency, but the effect diminishes for large aspect ratios, at which the efficiency moves towards an asymptotic value. Furthermore it is shown that increasing the aspect ratio to a certain value by changing the blade height results in a higher efficiency compared to changing the blade size, which is due to the difference in hub-to-tip ratio. An attempt to quantify the secondary losses is also made by looking at the radial kinetic energy at the outlet of a blade row. It turns out though, that the radial kinetic energy does not follow the same trend as the total pressure loss coefficient, which implies that it can not be used to quantify the secondary losses. Lastly, an effort to improve the method used for generating blade profiles is made, and the updated method is used to redesign rotor 2 to reduce losses.

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This thesis studies competence of simplified simulation methods for boosting simulation.  The most efficient propulsion unit has higher amount of power compared to less efficient propulsion units in boosting. Boosting is relevant subject to study due to new concept. New concept allows a larger diameter for the propeller which increases the efficiency of the propeller. New concept relies on the idea to have the propeller behind the hull.   The thesis is restricted to study displacement hulls from a point of view of propulsion efficiency. Large cruise ship model is utilized in this thesis to identify boosting related effects efficiently. Model tests reports of this concept are used as a baseline and a comparison material for two methods that are tested in this thesis. These methods are Matlab simulation code and OpenFOAM as the CFD software.   New propulsion arrangement concept is more efficient than current solutions for this hull type according to model tests. Trend of the CFD and Matlab simulation results matches well with model test results for boosting. Matlab simulation is evidently more time efficient solution than CFD simulation for boosting. Simplified CFD simulation is sufficiently accurate to study boosting concept with this research setup. Matlab and CFD simulations can be combined to obtain the most efficient solution to analyze the most effective load division for boosting.   Different types of hulls should be simulated and results should be verificated with model or full scale tests. In addition, ships with old two shaft arrangements could be converted to have two smaller pods and center line propeller in order to have better comparison with current methods. Scaling factors increases the uncertainty for new concepts; therefore full scale measurements are required. / Denna masteruppsats studerar möjligheterna med förenklade simuleringsmetoder i relation till nya framdrivningskoncept. Studerat koncept ger möjlighet till en större diameter för en boosterpropeller i centerlinjen, vilket ökar propellerns effektivitet. Konceptet bygger på tanken att få propellern bakom skrovet. Masteruppsatsen är begränsad till att studera deplacerande skrov i relation till framdrivningseffektiviteten. Studien appliceras på stora kryssningsfartyg. Resultat från modellförsök används som en referens och ett jämförelsematerial för de två beräkningsmetoder som testas i denna masteruppsats. Dessa metoder är Matlab-simuleringskod och OpenFOAM som CFD-programvara. Arbetet visar att det nya framdrivningskonceptet är effektivare än nuvarande lösningar för denna skrovtyp. Resultaten från CFD och simuleringsresultat från Matlab matchar väl med modellprovresultat. Matlab-simulering är en mer tidseffektiv lösning än CFD-simulering. Förenklad CFD-simulering är tillräckligt exakt för att studera boosterkoncept. Matlab- och CFD-simuleringar kan kombineras för att få den mest effektiva lösningen och för att analysera den mest effektiva belastningsfördelningen mellan propulsorer. Olika typer av skrov bör undersökas och resultaten ska verifieras med modell- eller fullskaletester. Skaleffekter ökar osäkerheten, därför krävs fullskalemätningar

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The objective of this thesis was to develop an experimental method to research circulation control wings using numerical analysis. Specifically, it is of interest to perform 3D wind tunnel testing on a circulation control wing in the Cal Poly Low Speed Wind Tunnel (CPLSWT). A circulation control wing was designed and analyzed to determine the feasibility of this testing. This study relied on computational fluid dynamics (CFD) simulations as a method to predict the flow conditions that would be seen in a wind tunnel test. A CFD simulation was created of a wing model in a wind tunnel domain. Due to high computational requirements, reliable 3D CFD results were not obtained. This led to utilizing 2D CFD models to make estimations about the flow conditions that would be encountered in an experimental environment. The 2D CFD model was validated with previous experimental data on circulation control wings and was shown to accurately capture the flow physics. These 2D CFD results were used to create a set of guidelines to help improve the effectiveness of a future wind tunnel test campaign and demonstrate where further design work needs to be done. The key finding is that it is feasible to perform circulation control testing in the CPLSWT with limitations on the maximum momentum coefficient. Due to internal plenum pressures reaching 66 psi at Cμ=0.35, a limitation should be placed on experimental testing below the choked condition of at Cμ=0.15. This provides a more feasible operating range for the equipment available. The main performance parameter of the airfoil was met with CLMAX=5.01 at Cμ=0.35 which required 0.9 lb/s/m mass flow rate for the 2D model.

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Towards a fundamental understanding of key physical aspects of narrow-throat pre-chamber combustion, the current work utilizes three-dimensional computational fluid dynamics (CFD) simulations using the CONVERGETM CFD solver, to analyze the effect of pre-chamber geometry, piston design, combustion models, and flame speed correlations in an engine operated with methane. The simulations were performed at lean operating conditions whilst the pre-chamber was fuel enriched with a direct fuel supply. The modeling work was performed in conjunction with metal engine testing at identical conditions, which provided validation data for the model. The particular pre-chamber utilized in this work fits in the diesel injector pocket of the cylinder head, thus features a narrow throat, which requires marginal engine modification, hence lowering the technical and economic barriers to deployment of this technology in production vehicles. The combustion process is simulated with the G-Equation model for flame propagation and/or with the multi-zone well-stirred reactor (MZ-WSR) model to determine the post-flame composition and to predict possible auto-ignition of reactant mixture; MZ-WSR and G-Equation were also compared separately and showed the potential to match experimental data upon appropriate calibration. When used, the laminar flame speed was tabulated from a methane oxidation mechanism; the turbulent flame speed was computed using Peters' relation. While the narrow throat was found to have a major impact on the pre-chamber combustion, the jet-piston interaction was also identified as crucial if additional improvements on engine emissions and performance are desired. On the fundamental modeling aspect, the significance of laminar flame speed prediction in the simulation of ultra-lean engine combustion was assessed. For engineering applications, the correlations of flame speeds with physical variables involve empirical constants that are valid for a limited range of operating conditions. In all cases, the original formulation of Peters' turbulent flame speed correlation was used; the results confirm the importance of the accurate determination of the laminar flame speed, which overrules any ad hoc constant corrections for high Karlovitz regimes. Finally, the relevant turbulent combustion regimes encountered in pre-chamber combustion engine conditions were examined using the Borghi-Peters diagram, further confirming the findings.

Supersonic retro-propulsion (SRP) is defined as rocket propulsion used to decelerate aerospace vehicles at supersonic speed. SRP is often used as a method of high-speed deceleration on space vehicles. The main method of propulsion used in the application of SRP is rocket propulsion. Rocket engine thrust and performance changes with altitude and expansion ratio. Changing altitudes across the trajectory of a rocket affect how the exhaust plume shock waves expand. Being able to identify how different expansion ratios affect the exhaust plume flow fields would provide useful data on how SRP performance can be predicted. This research projects aims at developing a computational model for existing physical test data on SRP and extrapolating data from the model to assess how SRP would perform with different nozzle expansion ratios.

The stability and maneuverability of aircraft are some key factors for selecting the locations of wings or canards on the fuselage. Another important variable that is considered in the design of an aircraft is drag force which impacts fuel efficiency. This research investigates how drag force of a surrogate aircraft is affected by the placement of the wing or canard along the fuselage. Unique for this study is the placement of the canard in the fuselage nose region, with the leading edge upstream of the nose, resembling the shape of a hammerhead shark's head. When the leading edge of all considered wing configurations was located 20% or more from the fuselage nose, the platforms produced the least amount of drag force. When the wing was placed in the nose region of the fuselage, the wings with small chords produced less drag when their leading edge was ahead of the nose.

The noise generated by jet engines represents a significant environmental concern that still needs to be addressed. Accurate and efficient numerical predictions are a key step towards reducing jet noise. The current standard in highidelity prediction of jet noise is large eddy simulation (LES), which resolves the large turbulent scales responsible for the low and medium frequency noise and models the smallest turbulent scales that correspond to the high frequency noise. While LES requires significant computational resources to produce an accurate solution, it fails to resolve the noise in the high frequency range, which cannot be simply ignored. To circumvent this, in this dissertation the Coupled LES-Synthetic Turbulent method (CLST) was developed to model the missing frequencies that relate to un-resolved sub-grid scale fluctuations in the flow. The CLST method combines the resolved, large-scale turbulent fluctuations from very large eddy simulations (VLES) with modeled, small-scale fluctuations from a synthetic turbulence model. The noise field is predicted using a formulation of the linearized Euler equations (LEE), where the acoustic waves are generated by source terms from the combined fluctuations of the VLES and the synthetic fields. This research investigates both a Fourier mode-based stochastic turbulence model and a synthetic eddy-based turbulence model in the CLST framework. The Fourier mode-based method is computationally less expensive than the synthetic eddy method but does not account for sweeping. Sweeping and straining of the synthetic fluctuations by large flow scales from VLES are accounted for in the synthetic eddy method. The two models are tested on a Mach 0.9 jet at a moderately-high Reynolds number and at a low Reynolds number. The CLST method is an efficient and viable alternative to high resolution LES or DNS because it can resolve the high frequency range in the acoustic noise spectrum at a reasonable expense.