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L. Azzini

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6 records found

Semi-analytical model for the prediction of the Wilson point for homogeneously condensing steam flows

Journal article - L. Azzini, M. Pini, Piero Colonna

An investigation on non-equilibrium condensing steam flow is conducted to attain a semi-analytical model for the prediction of the Wilson point up to the critical point. The database for the analysis includes experimental observations in various nozzles and conditions (ranging fr ...

Numerical investigation of dense condensing flows for next-generation power units

Doctoral thesis - L. Azzini

Metastable condensation is the phase transition from vapor to liquid that occurs in a fluid subjected to rapid temperature variations. Under these conditions, the nucleation process is triggered when the fluid is in a supersaturated thermodynamic state. The dispersed phase forming during the process of condensation is not in stable thermodynamic equilibrium with the surrounding vapor. As a consequence, models suitable for condensing flows under large temperature gradients, which are relevant to many scientific studies and industrial applications, are rather complex as they must correctly treat metastable thermodynamic states. Applications of metastable condensation flowmodels include improved climate models [1], biomedical treatments [2], heat transfer enhancement for industrial purposes [3], natural gas separation [4], power conversion [5] and many others. The scope of the research documented in this dissertation is the numerical investigation of metastable condensing flows in turbomachinery for propulsion and power applications. The flow inside turbomachinery components is highly compressible, with absolute temperature gradients that can reach values of the order of 1e6 K/s[6], in the case of supersonic expansions. In such extreme conditions, metastable phenomena impact severely on the component performance in terms of both thermodynamic and fluid dynamic losses and lifetime. The number of technologies for propulsion and power characterised by the presence of condensing mixtures in turbomachinery is increasing. Considerable research and development efforts are currently concerned with components of next-generation thermal power and refrigeration systems, in which the flow undergoes metastable condensation. The characterization of metastable condensing flows and the development of advanced fluid dynamic design tools capable of treating these complex flow phenomena are fundamental steps towards the commercial application fo such promising technologies. @en

A Discrete Adjoint Method for Two-Phase Condensing Flows Applied to the Shape Optimization of Turbine Cascades

Journal article - M. Pini, L. Azzini, S. Vitale, Piero Colonna

This paper presents a fully turbulent two-phase discrete adjoint method for metastable condensing flows targeted to turbomachinery applications. The method is based on a duality preserving algorithm and implemented in the open-source CFD tool SU2. The optimization framework is ap ...

Numerical investigation of metastable condensing flows with an implicit upwind method

Conference paper - L. Azzini, T.P. van der Stelt, M. Pini

This work proposes and assesses two numerical models for solving high-speed condensing flows in metastable conditions. Each model involves a set of governing equations (mass, momentum, and energy) for the mixture or the continuum phase, i.e. the vapor, and two additional transpor ...

Numerical investigation of high pressure condensing flows in supersonic nozzles

Journal article - L. Azzini, M. Pini

High-pressure non-equilibrium condensing flows are investigated in this paper through a quasi-1D Euler model coupled to the method of moments for the physical characterization of the dispersed phase. Two different numerical approaches, namely the so-called (a) the mixture and (b) ...

Exploratory assessment of a combined-cycle engine concept for aircraft propulsion

Conference paper - C.M. de Servi, L. Azzini, M. Pini, Piero Colonna

This preliminary study considers a combined cycle configuration for aeroengines, whereby thermal energy from the exhaust of the gas turbine is partly recovered in order to obtain additional mechanical power. The waste heat recovery system is based on a closed thermodynamic botto ...

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Preliminary design optimization of the combined cycle engine

Master thesis - P.B. Jahn, A. Gangoli Rao, L. Azzini

Aviation has to reduce its emission. In the past the improvements of aero engine technology have been achieved by higher turbine inlet temperatures, higher overall pressure ratios, higher bypass ratios and more efficient components. However, these methods hold only limited potential for further improvements. Therefore, research into alternative cycle concepts started. No best solution for future aircraft engines has been identified yet and thus this research continues. As part of this research, the combined cycle engine has been proposed as a new solution. It has been realised that the thermal energy of the exhaust gases is the biggest energy loss in a turbofan engine. The combined cycle engine uses a combination of a conventional turbofan engine and an additional supercritical Brayton cycle to use this exhaust gas heat to produce additional thrust power. A heat exchanger uses the exhaust gases of the main engine as the heat source for the supercritical cycle. Initial investigations showed many difficulties in the application of this cycle and limited potential for fuel burn reduction. This study aims at investigating the behaviour of different combined cycle engine designs to find an optimal design and to be able to estimate the potential of the concept based on this optimal design. To predict the behaviour of the combined cycle engine, a simulation framework has been created and the results have been compared to similar investigations in literature. In addition to this, a gradient based optimization routine has been implemented to be able to optimize the system for the maximum range. With this methodology, the effect of the supercritical cycle operating conditions, the configuration of the main engine, the supercritical working fluid, the supercritical cycle configuration and the heat exchanger design have been investigated. It was found that the behaviour of the system is very non linear. The optimum performance becomes a trade off between the specific fuel consumption and the weight. The operating parameters of the supercritical cycle and the heat exchanger design have the biggest impact on the system performance. The heat exchanger technology plays an important role in enabling good heat exchanger designs in that it limits the minimum size and wall thickness of the heat exchanger tubes. The addition of an inter turbine burner to the main engine was found to be beneficial to the performance of the supercritical cycle and the combined cycle engine as a whole. While a turboshaft configuration of the main engine brings thermodynamic benefits for the combined cycle engine, it causes a higher weight of the heater. Therefore, a turbofan engine is the superior main engine for the combined cycle engine. The combination of a turbofan engine with an inter turbine burner and a simple recuperated supercritical carbon dioxide cycle has been identified as the best configuration of the combined cycle engine. In this configuration, the cooler is placed downstream of the fan of the main engine. The application of this cycle on a Boeing 777ER could increase the range of the aircraft by 0.46 %. With more advanced production techniques for the heat exchangers, a range increase of 2.15 % becomes possible. However, more in depth research has to be performed, to confirm these results.