Large-scale liquid rocket engines require high-speed turbopumps to inject cryogenic propellants into the combustion chamber. Modeling the impact of secondary path and leakage flows on the performance and axial thrust of the pump is critical during the early design phase. Previous studies derived simplified models and empirical correlations to model leakage loss and determine the pressure distribution in the side gaps. The prediction capabilities of these models are subject to limitations and uncertainties mainly due to the interaction between impeller exit flow and sidewall gaps especially at partload operation. The effects of the leakage injection on the impeller flow are not fully understood and not captured by analytical correlations from literature. These can have destabilizing and detrimental effects on the hydraulic performance and the head curve, leading to a divergence betweenmodel predictions and experimental results. In this project a reduced order model is developed to capture the effects of the sidewall gaps on turbopump performance and determine the axial thrust on the rotor. High fidelity calculations of the pump and volute are performed to identify the key physical mechanisms associated with loss generation in leakage paths and improve upon existing analytical models found in literature. Axial thrust and leakage losses are modeled numerically with a single passage geometry to capture the interaction of impeller flow and leakage flow through the side gaps at multiple operating points. It is found that the recirculation of pressurized fluid, leakage mass flow, is the most impactful effect on the performance. The volumetric efficiency is captured within 16% with the analytical model and 6% with the single passage numerical calculations at nominal operation. At partload operation however, the accuracy of both models reduces. Disk friction is under predicted by the investigated analytical model and axial thrust is over predicted. For both effects the reduced numerical model shows promising results that improve the prediction capability around nominal operation and offer a higher flexibility required for the early design phase as compared with the high fidelity, full annulus calculations. For the investigated cases the leakage injection to the impeller flow does not show a destabilizing impact on the characteristic behavior.

For the past fifty years, there has been a constant increase in the pressure ratio of gas turbines motivated by the need to increase the cycle efficiency. This has moved the operating pressure of gas turbine combustor to be above the critical pressure of jet fuels. This increasing trend in pressure of combustor, places the next generation gas turbines in supercritical regime of majority of jet fuels, making Supercritical Combustion a significant topic of research in the field of gas turbine. Understanding the fluid behavior at and above the critical point provides opportunity for better and efficient combustor design. The complexity in numerical modelling of supercritical fluids, due to the dramatic property variations, solubility in gas and difficulty in tracking the vanishing interface, requires alternate modelling techniques that are well suited for treating multi-phase systems efficiently. Lattice Boltzmann Methods(LBM) is one such system gaining popularity in the recent decade due to the inherent capability to model complex multi-phase flows. LBM is a hybrid particle-continuum method based on the kinetic theory, which entails solution of the Boltzmann equation for the distribution function of particles properties on a lattice node. Despite the advantages of LBM, there is considerable gap in effective application of this method as a solution for engineering problems. This research work is aimed to address this issue by creating a single and multi-component solver using LBM and making quantitative comparison with commercial fluid dynamic flow solver, ANSYS FLUENT. The results form created single-phase LBM solver agrees with the results from FLUENT single-phase solution in addition to showing superiority in terms of computational time and resources. In case of the multi-component model, LBM provided accurate results with coarser mesh refinement. A detailed investigation of LBM application for two simple systems has been studied and reported,bthus laying a foundation for future numerical investigation of supercritical fluid modelling.

The threat of global warming made the increase of efficiency a crucial objective for future power plants and aero engines. As secondary flow is a major source of aerodynamic losses in turbines, its mitigation is critical to enable efficient designs. However, the suppression of secondary flow formation is challenging due to the complexity of the flow field and to the variability of its features according to each cascade characteristics. One solution is the use of three- dimensional endwall fence, to reduce secondary flow losses. Three-dimensional fences can reduce the secondary flow penetration, increase the pitch-wise uniformity of vorticity, reduce the kinetic energy of the crossflow and decrease the mixing out of the vortices downstream the blade passage. At the same time, the endwall fence entails an increment of wetted area and viscous losses, making the design of its shape a trade-off problem. The design of such devices must be tailored to the specific turbine and is usually obtained via lengthy and time-consuming experimental campaigns. Shape optimization can greatly enhance the design process of these components as it provides a way to investigate the fluid dynamic performance of a multitude of fence geometries at affordable computational cost. This paper presents a numerical methodology to automate the endwall fence design; a surrogate-based optimization is applied to minimize the total pressure losses of a steam turbine cascade. The results of the numerical analysis indicate a reduction of 48% of the secondary kinetic energy leading to a decrease of 1.96% in total pressure loss of the optimized design with respect to the baseline geometry without endwall fence. The partition of the passage vorticity led to a weakening of the secondary flow strength and consequently to reduced downstream mixing losses. A wind tunnel validation of the improvement has been finally carried out, confirming the success of the methodology.

This thesis presents the results of a design optimisation of an inducer for a rocket engine turbopump. Its main goal was to optimise a shape of the inducer blades to enlarge an operating range of the entire pump that is limited by cavitation. The blade was parameterised with four parameters: sweep angle, sweep radius, incidence angle and blade solidity at the tip. The performance of the given pump design is evaluated with a two-phase CFD simulation. The optimisation process is based on a surrogate model that interpolates the simulation results in the entire design space from a fixed number of samples. The results show 17% improvement of the suction performance, which is caused by reduced vapour volume in the flow channel and higher inducer head. Sweep radius proved to be the most important parameter as it increases the minimal pressure at the leading edge.

Turbopumps are used in large-scale liquid rockets to inject the cryogenic propellants into the combustor. The turbopumps operate at high rotational speed, which in turn leads to cavitation at the inlet of the impeller. Cavitation can cause performance issues, instabilities and mechanical damage of the blades. This thesis presents and validates a shape optimization framework for the design of splitter blades that extends the operative range under cavitation while maintaining the wetted performance. For a target turbopump application, the optimization framework allows for independent changes to the blade angle distributions across the span and to the pitchwise position of the splitter blades while preserving the thickness distributions. The optimization is conducted with a surrogate-based gradient method. The geometry is optimized at a fixed cavitation number corresponding to a 5% head coefficient drop-off, while constraints are imposed on the wet pump performance. It is found that this approach, coupled with the optimal design points distribution provided by the Design of Experiment method, reduces the computational cost of the optimization process by minimizing the number of multiphase calculations. The numerical results show that the optimized splitter blades successfully increase the pump operative range by 2.2% and increase the head coefficient by 5.3% compared to the baseline case with non-optimized splitters. These results are corroborated by experiments conducted in a closed-loop water test facility. Several pump geometries are tested through rapid prototyping using additive manufacturing. The experimental data validate the optimization framework, demonstrating a 4.7% increase of pump operative range and a 7.6% increase in head coefficient. The calculations are used to gain insight in the physical mechanisms for the performance improvement. The analysis of the results indicates that the improved performance is due to the optimized position and shape of the splitter blades which increase the pump slip factor.