This paper presents the results of the numerical simulations carried out to evaluate the performance of a high solidity Wells turbine designed for an oscillating water column wave energy conversion device. The Wells turbine has several favorable features (e.g., simplicity and high rotational speed) but is characterized by a relatively narrow operating range with high efficiency. The aim of this work is to investigate the flow-field through the turbine blades in order to offer a description of the complex flow mechanism that originates separation and, consequently, low efficiency at high flow-rates. Simulations have been performed by solving the Reynolds-averaged Navier–Stokes equations together with three turbulence models, namely, the Spalart–Allmaras, $k-ω$, and Reynolds-stress models. The capability of the three models to provide an accurate prediction of the complex flow through the Wells turbine has been assessed in two ways: the comparison of the computed results with the available experimental data and the analysis of the flow by means of the anisotropy invariant maps. Then, a detailed description of the flow at different flow-rates is provided, focusing on the interaction of the tip-leakage flow with the main stream and enlightening its role on the turbine performance.

The effects of climate change and global warming are arising a new awareness on the impact of our daily life. Power generation for transportation and mobility as well as in industry is the main responsible for the greenhouse gas emissions. Indeed, currently, 80% of the energy is still produced by combustion of fossil fuels; thus, great efforts need to be spent to make combustion greener and safer than in the past. For this reason, a review of the most recent gas turbines combustion strategy with a focus on fuels, combustion techniques, and burners is presented here. A new generation of fuels for gas turbines are currently under investigation by the academic community, with a specific concern about production and storage. Among them, biofuels represent a trustworthy and valuable solution in the next decades during the transition to zero carbon fuels (e.g., hydrogen and ammonia). Promising combustion techniques explored in the past, and then abandoned due to their technological complexity, are now receiving renewed attention (e.g., MILD, PVC), thanks to their effectiveness in improving the efficiency and reducing emissions of standard gas turbine cycles. Finally, many advances are illustrated in terms of new burners, developed for both aviation and power generation. This overview points out promising solutions for the next generation combustion and opens the way to a fast transition toward zero emissions power generation.

The focus of this paper is on the part load performance of a small scale (100 kWe) combined heat and power (CHP) plant fired by natural gas (NG) and solid biomass to serve a residential energy demand. The plant is based on a modified regenerative microgas turbine (MGT), where compressed air exiting from recuperator is externally heated by the hot gases produced in a biomass furnace; then the air is conveyed to combustion chamber where a conventional internal combustion with NG takes place, reaching the maximum cycle temperature allowed by the turbine blades. The hot gas expands in the turbine and then feeds the recuperator, while the biomass combustion flue gases are used for preheating the combustion air that feeds the furnace. The part load efficiency is examined considering a single shaft layout of the gas turbine and variable speed regulation. In this layout, the turbine shaft is connected to a high speed electric generator and a frequency converter is used to adjust the frequency of the produced electric power. The results show that the variable rotational speed operation allows high the part load efficiency, mainly due to maximum cycle temperature that can be kept about constant. Different biomass/NG energy input ratios are also modeled, in order to assess the trade-offs between: (i) lower energy conversion efficiency and higher investment cost when increasing the biomass input rate and (ii) higher primary energy savings (PESs) and revenues from feed-in tariff available for biomass electricity fed into the grid. The strategies of baseload (BL), heat driven (HD), and electricity driven (ED) plant operation are compared, for an aggregate of residential end-users in cold, average, and mild climate conditions.