There is a growing interest in organic Rankine cycle (ORC) turbogenerators because they are suitable as sustainable energy converters. ORC turbogenerators can efficiently utilize external heat sources at low to medium temperature in the small to medium power range. ORC turbines typically operate at very high pressure ratio and expand the organic working fluid in the dense-gas thermodynamic region, thus requiring computational fluid dynamics (CFD) solvers coupled with accurate thermodynamic models for their performance assessment and design. This article presents a comparative numerical study on the simulated flow field generated by a stator nozzle of an existing high-expansion ratio radial ORC turbine with toluene as working fluid. The analysis covers the influence on the simulated flow fields of the real-gas flow solvers: FLUENT, FINFLO, and ZFLOW, of two turbulence models and of two accurate thermodynamic models of the fluid. The results show that FLUENT is by far the most dissipative flow solver, resulting in large differences in all flow quantities and appreciably lower predictions of the isentropic nozzle efficiency. If the combination of the k−ω turbulence model and FINFLO solver is adopted, a shock-induced separation bubble appears in the calculated results. The bubble affects, in particular, the variation in the flow velocity and angle along the stator outlet. The accurate thermodynamic models by Lemmon and Span (2006, “Short Fundamental Equations of State for 20 Industrial Fluids,” J. Chem. Eng. Data, 51(3), pp. 785–850) and Goodwin (1989, “Toluene Thermophysical Properties From 178 to 800 K at Pressures to 1000 Bar,” J. Phys. Chem. Ref. Data, 18(4), pp. 1565–1636) lead to small differences in the flow field, especially if compared with the large deviations that would be present if the flow were simulated based on the ideal gas law. However, the older and less accurate thermodynamic model by Goodwin does differ significantly from the more accurate Lemmon–Span thermodynamic model in its prediction of the specific enthalpy difference, which leads to a considerably different value for the specific work and stator isentropic efficiency. The above differences point to a need for experimental validation of flow solvers in real-gas conditions, if CFD tools are to be applied for performance improvements of high-expansion ratio turbines operating partly in the real-gas regime.

New promising applications of organic Rankine cycle (ORC) technology, e.g., concentrated solar power, automotive heat recovery and off-grid distributed electricity generation, demand for more dynamic operation of ORC systems. Accurate physically-based dynamic modeling plays an important role in the development of such systems, both during the preliminary design as an aid for configuration and equipment selection, and for control design and optimization purposes. A software library of modular reusable dynamic models of ORC components has been developed in the MODELICA language and is documented in the paper. The model of an exemplary ORC system, namely the 150 kW e Tri-O-Gen ORC turbogenerator is validated using few carefully conceived experiments. The simulations are able to reproduce steady-state and dynamic measurements of key variables, both in nominal and in off-design operating conditions. The validation of the library opens doors to control-related studies, and to the development of more challenging dynamic applications of ORC power plants

There is a growing interest in organic Rankine cycle turbogenerators because of their ability to efficiently utilize external heat sources at low-to-medium temperature in the small-to-medium power range. High-temperature organic Rankine cycle turbines typically operate at very high pressure ratio and expand the organic working fluid in the dense-vapour thermodynamic region, thus requiring computational fluid dynamics solvers coupled with accurate thermodynamic models for their performance assessment and design. In this article we present a steady-state three-dimensional viscous computational fluid dynamics study of the Tri-O-Gen organic Rankine cycle radial turbine, including the radial nozzle, the rotor and the diffuser. The turbine operates with toluene as the working fluid, whose accurate thermophysical properties are obtained with a look-up table approach. Based on the three-dimensional simulation results, together with a two-dimensional fluid dynamic optimisation procedure documented elsewhere, an improved nozzle geometry is designed, manufactured and experimentally tested. Measurements show it delivers 5 kWe or 4% more net power output, as well as improved off-design performance.

Using organic matter as the working fluid in small Rankine cycle power plants is beneficial. However, high molecular weight of the fluid and the single-stage design of the turbine lead to a supersonic flow in the turbine. An Organic Rankine Cycle (ORC) plant was designed and tested. Toluene was used as the working fluid and as lubricant. The turbine and the feed pump were placed on the same shaft as the high-speed generator in the designed 175 kW unit. CFD simulations were used in the design process. Toluene is behaving as a real gas in the nozzle. To ensure an accurate simulation, a real gas model of toluene was implemented in an existing Navier-Stokes flow solver. Polynomial and rational regression were used to achieve the functions for the gas properties. The pressure and temperature were measured at the nozzle inlet and outlet. In the CFD simulations the nozzle ring was modelled with and without a temperature probe in order to model the effect of the probe to the flow field and compare the simulated pressure and temperature values against the measurements. The nozzle geometry was also modelled in 2D and 3D in order to see the effect of the 3D in the flow field. There was quite a good agreement between the measured and simulated data. The agreement in the temperature was better than in the pressure. The effect of 3D on the simulation results was minor, which was expected. The simulated flow field revealed that the shock waves developing in the trailing edge of the nozzle were seen in the turbine rotor inlet.

The dramatic growth that air traffic has experienced in the last years is not likely to slow down in the future. The situation for the airlines has however been critical due to the large share of the operating costs corresponding to fuel. On the other hand, the society demands quieter aircraft which is then translated into stricter regulations. The Advisory Council for Aeronautics Research in Europe (ACARE) has set an ambitious array of objectives to be accomplished by 2020. It is often claimed that complying with those targets will not require evolution but, rather, revolution. One of the potential future engine configurations being considered is the counter-rotating turbofan (CRTF) concept. This paper addresses the possibilities of improvement that the CRTF can offer with respect to the specific fuel consumption, emissions and noise as compared to the baseline engine, the GE90. Semi-empirical correlations and methodologies have been used for the study. First a Blade Element Method (BEM) is developed to estimate the performance of the fan and to build confidence upon the applied loss and deviation angle models. Next, the design methodology is applied to three cases: a single-stage fan featuring the reference properties of the GE90 engine; a counter-rotating fan (CRF) fan with similar properties as a GE90 fan, but with a lower rotational speed; and a CRF with higher fan pressure ratio (FPR) for lower specific fuel consumption. Finally, noise emission by all the three configurations are estimated by noise models available in the literature. Reductions of equivalent perceived noise level (EPNL) were found to be possible if a CRF is used instead of the baseline single-stage arrangement. Other noise descriptors are also reduced by a similar amount. Approximately equal noise levels are expected if the CRF is of higher pressure than the baseline.

The soaring fuel price and the burgeoning environmental concerns have compelled global research towards cleaner engines, aimed at substantial reduction in emission, noise and fuel consumption. In this context, the present research investigates the feasibility of some novel engine concepts, namely Geared Turbofan and Intercooled Recuperated Turbofan concepts, by hypothetically applying them into an existing state-of-the-art high bypass ratio engine. This paper made an effort to estimate the effects on the baseline engine performances due to the introduction of these two concepts into it. By performing steady state simulations, it was found that the incorporation of the Geared Turbofan concept into the existing Turbofan engine caused a significant reduction in thrust specific fuel consumption, engine weight, and fan blade tip speed. However, when simulations were also carried out by incorporating the Intercooler and Recuperator concept in the baseline turbofan engine, it did not demonstrate any substantial improvement in fuel consumption. It was observed that the fuel flow rate was influenced to a large extent by heat exchanger’s effectiveness and the pressure drop within it. The overall engine weight was also found to get increased due to the inclusion of massive heat exchangers necessary for the system.

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The propulsion system provides the required force/power to propel forward an aircraft/rocket or any other object moving in air or space. The propelling force is the most important aspect in the design and operation of aircraft/spacecraft mission. Every major technological breakthrough in propulsion and associated system has redefined the frontiers of aerospace sciences. The urge to improve propulsion systems keeps engineers and scientist busy alike till this day and will continue to do so in the future. When the atmospheric air is used as a working medium in a propulsion system, it is often known as air‐breathing propulsion. This section explains the basics of air‐breathing propulsion through simple analogies. The evolution of various types of propulsion systems in the history of aviation is traced, with special emphasis on the jet engines. The developments and advancements in jet engines over the years, and the main challenges which aircraft propulsion will be facing in the future are also discussed. Finally, new engine concepts and their viability are presented.