Marine current turbines (MCTs) are a promising technology for predictable renewable energy generation, but their long-term performance is significantly affected by the harsh marine environment. Among the various degradation mechanisms, biofouling is one of the most critical, as it increases surface roughness, modifies hydrodynamic loads, reduces energy conversion efficiency, and raises operation and maintenance costs. This review critically examines the effects of biofouling on MCT performance by integrating hydrodynamic, biological, operational, and techno-economic perspectives. Existing experimental, numerical, and field studies indicate that moderate biofouling typically reduces the power coefficient by 10–20%, while severe natural colonisation may lead to power losses exceeding 40%, with the magnitude of degradation depending on fouling morphology, turbine configuration, installation conditions, and operating strategy. The effectiveness and limitations of current mitigation approaches, including antifouling and foul-release coatings, adaptive tip-speed-ratio control, cleaning schedules, and component-specific maintenance strategies, are systematically discussed. A key contribution of this review is the identification of the gap between site-specific biofouling observations, predictive growth modelling, and turbine performance assessment. To address this limitation, an integrated framework is proposed that combines local biofouling monitoring, hydrodynamic modelling, and techno-economic indicators to support lifecycle performance assessment. The analysis highlights that biofouling should be considered not only as a surface degradation phenomenon but also as a key lifecycle driver influencing turbine design, maintenance planning, annual energy production, and the economic viability of tidal energy systems.

Storing hydrogen in solid state is gaining attention enabling for overcoming simultaneously two specific limits of conventional hydrogen storage technologies: storage capacity and safety. Currently, hydrogen is stored as compressed gas (usually, at either 350 or at 700 bar), reaching densities ranging from 24.5 to 41.4 kg/m(3), but requiring a significant compression work and determining several safety issues; otherwise, it can be stored in liquid state under cryogenic conditions (70.8 kg/m(3) at 1 bar and 20 K), but requiring a great amount of energy for lique-faction (about 12.5 kWh/kg) and costs to keep it liquid. In solid state context, physisorption (also said adsorption) mechanism has been recognized as an attractive technique for its capability of storing hydrogen in a porous structure, with weaker bonds, differently from chemisorption mechanism where hydrogen molecules chemically bonds to the absorbing material forming, for instance, metal hydrides. During adsorption, heat is released and thermal management can become an issue when the tank volume is increased. This work aims to numerically investigate the effect of increasing the tank volume on the solid-state hydrogen storage capacity. Moreover, the effect of the tank aspect-ratio is considered. The investigation has been carried out through Computational Fluid Dynamic analyses. The modified Dubinin-Astakhov isotherm model has been taken into account to describe the isotherm sorption during charge, dormancy, and discharge processes. Initially, the model has been validated on a 2.5 dm(3) tank, against experimental results available in the literature; then, the geometry has been scaled by a factor of 10, and several aspect ratio considered. The numerical study was conducted considering three different aspect ratios (i.e., 5, 8.5, and 15), whilst keeping the internal volume constant. In this work, it is shown that larger aspect ratios can lead to improved adsorbed mass and decreased maximum temperatures in the system.

This work deals with a comprehensive 1-D numerical analysis to assess ozone-assisted combustion of Toluene Reference Fuel/air flames. Ozone, O3, represents a promising oxidizer that enhances the laminar flame speed of alkanes through its decomposition into atomic oxygen. Simulations have been carried out by using two different chemical kinetic mechanisms with the addition of an ozone sub-mechanism. Results show that ozone increases the laminar flame speed across all thermodynamic conditions for ozone concentrations ranging from 0 to 7000 ppm. At a reactants temperature of 358 K and ambient pressure, the highest enhancement occurred under lean conditions with a lower enhancement near stoichiometric conditions. Above 500 K, a cool flame occurred under both lean and stoichiometric conditions, as fast ozone decomposition favors both OH production and a sharp increase in temperature. Moreover, with an increase of the reactants pressure, the hydrogen diffusivity becomes less important leading to an enhancement of the laminar flame speed under stoichiometric mixture condition. Sensitivity analysis has shown that at high pressure and in the presence of ozone, the reaction pathway is drastically modified. This suggests that reactions involving OH radicals prevail and lead to the formation of cool flames.

With the growing need to reduce carbon emissions, renewable energy sources (e.g., solar and wind power) have gained significant attention in modern energy applications. In particular, thermal solar energy allows for the generation of high power but has the disadvantage of not being continuously available for a period of 24 hours. The deployment of advanced and efficient energy storage systems is critical in solar power plants to support grid stability and ensure an uninterrupted energy supply. Among the different storage strategies, Latent Heat Thermal Energy Storage (LHTES) stands out for its high energy density, which makes it particularly suitable for integration into Concentrated Solar Power (CSP) plants where energy continuity is essential. LHTES systems provide a simple, cost-effective, and environmentally friendly method of storing large amounts of thermal energy, with significant weight and volume reductions compared to other thermal storage solutions. An interesting research challenge is identifying the number and geometry of fins that improve heat exchange within LHTESs. In this study, different fin configurations are evaluated using numerical simulations to identify the best one. The first step was to validate the developed numerical model by comparing the results in terms of PCM melting time and temperature trends with the experimental results. A comparative analysis is then performed to identify which of the studied configurations leads the LHTES to charge in the shortest time, comparing the total melting times of the PCM with those of a reference case without fins. This study focused on improving heat transfer by varying the geometry of the annular fins through CFD analysis. Numerical simulations showed that increasing the height and number of fins improved heat transfer and, consequently, the thermal power absorbed by the LHTES, reducing the total PCM melting time. However, the performance improvement appears to be limited by the overall size of the system. Therefore, cost and manufacturing considerations should be taken into account in the design process.

The need to reduce pollutant emissions has pushed the automotive industry towards sustainable mobility promoting new technological solutions, among which the use of hybrid powertrains stands out. The development of a hybrid architecture is very complex and demands proper components sizing and the determination of optimized power-split strategies among different power sources, for example: Internal Combustion Engine (ICE), electric generator/motor and batteries. Moreover, the experimental analysis regarding performance and emissions requires that the whole propulsive system must be set up on the test bench, hence, negatively affecting the cost of the entire design phase. In this scenario, an optimum design and sizing approach for a series-hybrid electric vehicle (S-HEV) is proposed aiming at a design cost reduction. The presented procedure relies on numerical modelling of the hybrid powertrain and on the optimization of the fuel consumption and the driving range. The series-hybrid architecture model is referred to a front-wheel-drive vehicle. It is developed by modelling the longitudinal dynamics, the tyre grip control, the driveline and the power generation system. An Energy Management System (EMS) is adopted to manage the power fluxes among the on-board power devices, according to the imposed mission requirements. The model also includes a braking energy recovery mode allowing the battery to be partially recharged during the mission. The application of a Genetic Algorithm for optimization leads to an improvement in the overall efficiency of the powertrain. A commercially available series-hybrid vehicle is analysed as a representative case study, considering the use of a diesel engine rather than a petrol engine. The simulations were performed by using the New European Driving Cycle (NEDC). From this design stage, the evaluation of emissions and the performance optimization for the hybrid configuration can be conducted through experimental measurements on engine test benches, providing a more cost-effective and simpler assessment method.

This paper presents the design of a scale model of a kite-like tidal converter, GEMSTAR, intended for long-term deployment at sea. The main objective of this experiment is to develop a digital twin with integrated fault detection and isolation capabilities to improve the reliability and performance of the system. A fully functional 1:10 scale model of GEMSTAR was designed based on extensive measurements of tidal currents at the planned deployment site. Several locations were investigated to determine the most suitable flow profiles for energy generation. This study outlines the key challenges for operational functionality and describes the selection of critical physical parameters to be monitored during deployment using onboard sensors.

Abstract The transition to sustainable energy raises many issues that need to be addressed in order to develop reliable energy production infrastructures. Among these challenges, the mismatch between primary energy sources and energy loads stands out as a significant barrier to the widespread adoption of renewable technologies. Efficient energy storage solutions are crucial to mitigate this mismatch and facilitate the integration of renewable energy sources into existing grids. In this study, to evaluate the performance of this component within any plant, we focus on developing a simple yet effective model for predicting the behavior of shell-and-tube latent heat thermal energy storage (LHTES) systems limiting the analysis to the melting phase. LHTES systems offer promising potential due to their high energy density and ability to store thermal energy at a slightly constant temperature. However, their performance depends on various factors such as material properties, geometry and operating conditions, which require accurate predictive models for optimization and design purposes. Our proposed model uses fundamental principles of heat transfer and phase change phenomena to simulate the behavior of LHTES systems during the melting phase. By considering factors such as heat transfer coefficients, phase change kinetics and thermal properties of the storage medium, our model aims to provide insight into the thermal performance and efficiency of shell-and-tube LHTES configurations. Through validation against experimental data and numerical simulations, we demonstrate the effectiveness of our model in accurately predicting key performance metrics such as charge rates, temperature distribution within the storage medium, and overall energy storage efficiency. Its simplicity and computational efficiency make it suitable for practical applications, enabling engineers and designers to optimize LHTES systems for specific operating conditions and integration scenarios.

<div class="section abstract"><div class="htmlview paragraph">With the aim of decarbonizing the vehicles fleet, the use of hydrogen is promising solution. Hydrogen is an energy carrier, carbon-free, with high calorific value and with no CO₂ and HC emissions burning in ICE. Hydrogen use in spark ignition engines has already been extensively investigated and optimized. On the other hand, its use in compression ignition engines has been little developed and, therefore, there is a lack of information regarding the combustion in ultra-lean conditions, typical of diesel engines.</div><div class="htmlview paragraph">Several applications employ dual fuel combustion for the easy management of the PFI injection system to be applied in addition to the DI Common Rail system. However, this mode suffers from several problems regarding the management of the maximum flow rate of hydrogen into the intake. In particular, to avoid throwing hydrogen into the exhaust, injection must be started after the valve crossing. Furthermore, it is not possible to introduce gaseous fuel into the engine when the compression phase begins. In fact, the hydrogen can find favorable autoignition conditions, giving rise to unwanted combustion processes in the manifold.</div><div class="htmlview paragraph">For these reasons, a direct hydrogen injection system that could be easily applied to the head of the production engine has been designed and realized. In the head of 1.9l GM engine mounted on a single cylinder research engine, the adapter in place of the pre-heating glow plug has been modified to accommodate a commercial injector for the hydrogen direct injection up to 100 bar. Hydrogen is provided by a bottle at 200 bar via a secured line and a rail prior to reach the injector.</div><div class="htmlview paragraph">In the design stage, attention has been paid to the correct assessment of the optimum diameter of the injection system. A 1D Fanno flow based model has been developed to determine in a quick way the mass flow rate and total pressure losses for several possible diameters. In particular, in order to have the desired hydrogen quantity entering into the cylinder a probe featured by a diameter of 2 mm and length of 137 mm has been identified. To confirm the validity of the 1D result, the CAD model of injection system has been designed and analyzed by means of computational fluid-dynamic simulations, which have shown a good agreement with the 1D outcomes. Thus, the 1D Fanno model can be considered a fast and reliable tool for the preliminary design of injection systems for gaseous fuels.</div></div>

In this contribution the authors investigated by means of an analytical approach the performance of a latent heat thermal energy storage varying the internal HTF tube distribution and other design parameters of the device. The work is based on a simplified prediction model of the discharging phase in order to span several configurations. The effects of the physical parameters of the phase change material and the geometrical dimensions of the device have been studied in order to suggest the optimal configuration. Indeed, the maximisation of the capacity together with the maximisation of the heat transfer rate are often competing and need a multi objective approach in the optimisation procedure. Here, the authors showed several optimal solutions proposing an efficient procedure that can be used in the selection of the most interesting cases to investigate by means of an experimental campaign or detailed numerical simulations. The approach proposed is general and it can be used also to minimise the cost of the device with respect to the maximisation of the performance due to the particular application. Several phase change materials were considered and a preliminary capital cost minimisation was proposed.

Abstract Model scale testing is vital for developing technologies like tidal turbines. Reduced-scale tests follow numerical design and are cost-effective in controlled environments, allowing parameter adjustments. However, controlled tests face drawbacks, such as blockage effects and the inability to replicate real sea conditions. Sea trials, conducted in actual marine environments, offer realistic data and continuous collection, potentially being cost-effective despite environmental variability and complex data processing. This work aims to measure real sea effects, such as marine growth and stream turbulence, on fixed and moving parts, of a scaled model of GEMSTAR tidal stream energy converter, a twin rotors submerged tethered device, designed to tap tidal current energy. The planned model installation site is at the Renewable Marine Energy Laboratory, a natural facility located on the East coast of the Strait of Messina (southern Italy), characterized by tidal currents with a maximum speed of about 1.25 m/s. Due to the low stream speed, in order to get significant data, an up-scaling of the existing model rotor diameter has been necessary, and a specific new blade design has been performed, in order to lower the cut-in speed, increasing in this way the useful power production time of the model. The paper illustrates the different phases of model scale design.

Industrial energy demand in the EU is driven by the thermal energy share, which accounts for the most part of the total energy demand. A large part, about one-third, is at medium temperatures, between 100 and 200 degrees C, and it is still produced by fossil fuels, mainly natural gas. This energy demand could be met by solar thermal energy by using Concentrated Solar Thermal (CST) technologies, suitably combined with thermal energy storage systems. This paper presents a study of CST plant composed by Parabolic Trough Collectors (PTC) combined with Latent Heat Thermal Energy Storage (LHTES) system in shell-and-tubes configuration for the supply of heat for industrial processes. Firstly, the criteria adopted for the sizing and the quasi-static simulation of the system are described. Significant attention is given to evaluate the variation of the Solar Fraction (SF) with the typical parameters of thermal storage, such as the maximum capacity and exchange surface, given a specific location and the Solar Multiple (SM). The methodology has been applied to a dairy processing facility within the agri-food sector with a thermal load of 500 kWth. Then, an economic analysis has been carried out by evaluating the impact of the component's costs, such as the linear parabolic collectors, thermal storage materials and landscape preparation. Finally, the Levelized Cost of Heat (LCOH) has been computed for different thermal storage sizes in order to find the best combination that minimizes it. As a result, despite the overall increase of the SF with the thermal storage capacity, the proposed work shows how the minimum value of the LCOH (7.24 c(sic)/kWh) corresponds to low storage capacity (1 MWh).

Abstract Based on the experimental results, a 3-D Computational Fluid Dynamics investigation is carried out to evaluate the influence of ozone on the combustion process in spark ignition engine fueled with gasoline/air mixtures. Ozone (O3) is a chemically reactive species capable of improving the laminar flame speed, reducing the ignition delay time, and stabilizing combustion variability. With the aim of proposing a 3-D numerical model to simulate combustion of fuel mixtures under ultra-lean conditions, two numerical correlations are proposed to reproduce the chemical properties of gasoline/air/ozone mixtures in terms of laminar flame speed. A chemical kinetic mechanism for Toluene Reference Fuel oxidation (iso-octane, n-heptane, toluene, 63/20/17% by mol.) modified with an ozone sub-mechanism is used to perform several 1-D numerical simulations. The laminar flame speed correlation estimates an enhancement of 3.4% at 600 K and 10 bar under ultra-lean condition (ϕ = 0.6). For the 3-D numerical simulations, the G-Equation model is used to reproduce the premixed combustion process in internal combustion engines. The results suggest that the numerical correlations can predict the combustion properties of gasoline/air mixtures without and with ozone addition. The presence of ozone traduces in a higher laminar flame speed, leading to an increase in the in-cylinder pressure peak and the rate of fuel consumption. Furthermore, the numerical analysis reveals that the greatest improvement is observed for fluid regions within the cylinder characterized by low turbulent flame speed.

Abstract Prediction and control of thermoacoustic instabilities is a major challenge in the development of modern power generation gas turbines and aeroengines. Such instabilities arise from the coupling between flame dynamics and combustor acoustic modes, resulting in severe oscillations that can lead to premature aging of combustor components and structural damage. In many combustors, passive dampers are implemented to increase the acoustic energy dissipation of the system and prevent the onset of these harmful flame-acoustic interactions. In the present study, passive damping systems based on a cavity-backed perforated plate are experimentally analyzed, with a focus on studying the impact of bias flow on the reflection coefficient over a wide range of frequencies. Tests are carried out on two cavity-backed perforated plates characterized by the same porosity but a different number of holes 25 and 49, namely P25 and P49, respectively. It is observed that, for a given plate geometry, a higher bias flow leads to an increase in the plates absorption capacity over a wider range of frequency. This is more pronounced in the P 49 plate configuration. For both tested configurations, comparing the experimental results with Scarpato model proposed in the literature [1], a good match it is observed only for low values of bias flow. The model instead is not able to correctly capture the behavior of the damping systems when higher dissipation is reached.

The International Maritime Organization (IMO) is making efforts on reducing pollutant emissions within port areas in order to achieve the ambitious goal of zero net carbon emissions by 2050. This work analyses the effects of the cell degradation on the performance and thermal management of a hydrogen fueled Proton Exchange Membrane Fuel Cell (PEMFC) power system for ferry electric propulsion. The manuscript firstly describes the proposed models, which simulate the fuel cell system and the battery. Then, the development of both an Energy Management strategy and the optimization framework are shown. In details, the zero-order model for the fuel cell and the methodology to estimate its time degradation are described. The accuracy of the model is established through calibration with the characteristic curves of the Ballard FCvelocity™ HD6 PEMFC (150 kW) and further validated against experimental data. The model also involves energy storage and converters that connect both the fuel cell and battery to the electrical grid. The proposed online strategy for the Energy Management System considers four different operating modes and takes into account the estimated fuel cell degradation. Furthermore, the optimization framework finds the solution to achieve the best performance in terms of stack degradation over one year of ship operation, based on a real mission duty cycle. Overall, the efficiency of the fuel cell system decreases by 5%. The degradation involves an increase in fuel consumption of 14.65%. Furthermore, after the last mission, the cooling efficiency achieved through the proposed thermal management strategy is 90%.

The exploitation of hydrogen-based technologies for on-board power generation is having a significant impact on the shipping industry due to their potential to support the decarbonization. This paper proposes the modeling and optimization of a fuel-cell (FC) hybrid power system for the case study ferry in order to achieve the best performance on stack degradation over the vessel experimental missions cycle. The FC system degradation has a significant impact on hydrogen consumption, energy efficiency and machinery operational cost. The research target is to build a prescriptive digital twin to provide an holistic design of the fuel cell system. The simulations will consider power distribution between components proposing an energy management strategy during the preliminary design phase. By sizing the components to meet the energy demand of a real mission, this work aims to propose a feasible powertrain solution for the ferry under investigation. The results of this study could be valuable for the further development of fuel cell technology for the maritime industry and provide an effective tool in the sizing of the power generation system on board full electric propulsion vessels.

A scale model of a kite-like converter of tidal energy, the GEMSTAR, is designed to be installed at sea for a long term deployment. The aim of the experiment is to develope a digital twin with fault detection and isolation capabilities. To this aim, a fully-functional 1:10 scale of GEMSTAR is designed, starting from measurements of tidal currents in the site of installation. Several spots were investigated searching for the most suitable current profile. The paper describes the principal issues concerning operational functions and the choice of the physical parameters to monitor during the deployment through several sensors placed on board. A scale model of a kite-like converter of tidal energy, the GEMSTAR, is designed to be installed at sea for a long term deployment. The aim of the experiment is to develope a digital twin with fault detection and isolation capabilities. To this aim, a fully-functional 1:10 scale of GEMSTAR is designed, starting from measurements of tidal currents in the site of installation. Several spots were investigated searching for the most suitable current profile. The paper describes the principal issues concerning operational functions and the choice of the physical parameters to monitor during the deployment through several sensors placed on board.

In the present paper a new multi-objective optimisation procedure for the design of a shell-and-tube Latent Heat Thermal Energy Storage (LHTES) is proposed. A simple arrangement of a cylindrical shell with multiple vertical tubes has been examined. The optimisation considers, as design variables, the number of tubes, the tube internal radius and the device height-to-diameter ratio, H/D, while the storage volume is kept constant. This analysis aims to detect the set of solutions which optimises the LHTES performances evaluated in terms of charging and discharging times and overall thermal energy capacity. To accomplish the multi-objectives optimal thermal storage design, a simplified mathematical model of the LHTES has been employed. This model can evaluate the prescribed performances for a given set of design variables. The proposed optimisation procedure evaluates new solutions along the most promising directions in the design variables domain, leading to a significant improvement in storage performances. The Design of the Experiment, together with the Pareto dominance relationship, gives a starting optimal solutions subset. The proposed optimisation procedure permits to enhance the starting optimal solutions subset letting approach the Pareto barrier. The paper shows that, at the end of the optimisation procedure, the designer can select the solutions on the Pareto barrier with the best performance and the corresponding design variables for each chosen solution. The proposed optimisation procedure will also allow for maintaining low computational costs due to the low number of the new design variables evaluated only in the promising directions.

Hydrogen can play a key role in the gradual transition towards a full decarbonization of the combustion sector, e.g., in power generation. Despite the advantages related to the use of this carbon-free fuel, there are still several challenging technical issues that must be addressed such as the thermoacoustic instability triggered by hydrogen. Given that burners are usually designed to work with methane or other fossil fuels, it is important to investigate their thermoacoustic behavior when fueled by hydrogen. In this framework, the present work aims to propose a methodology which combines Computational Fluid Dynamics CFD (3D Reynolds-Averaged Navier-Stokes (RANS)) and Finite Element Method (FEM) approaches in order to investigate the fluid dynamic and the thermoacoustic behavior introduced by hydrogen in a burner (a lab-scale bluff body stabilized burner) designed to work with methane. The case of CH4-air mixture was used for the validation against experimental results and benchmark CFD data available in the literature. Numerical results obtained from CFD simulations, namely thermofluidodynamic properties and flame characteristics (i.e., time delay and heat release rate) are used to evaluate the effects of the fuel change on the Flame Response Function to the acoustic perturbation by means of a FEM approach. As results, in the H2-air mixture case, the time delay decreases and heat release rate increases with respect to the CH4-air mixture. A study on the Rayleigh index was carried out in order to analyze the influence of H2-air mixture on thermoacoustic instability of the burner. Finally, an analysis of both frequency and growth rate (GR) on the first four modes was carried out by comparing the two mixtures. In the H2-air case the modes are prone to become more unstable with respect to the same modes of the case fueled by CH4-air, due to the change in flame topology and variation of the heat release rate and time delay fields.

Nowadays, mobility represents a key sector to achieve the goal of carbon neutrality. Indeed, the development of hybrid powertrains is contributing to a reduction in the environmental impact of vehicles. One of the most promising energy-saving solutions is regenerative braking, which enables deceleration while recovering energy, otherwise wasted. Even though much scientific community effort has been addressed to the optimization of this technology in the automotive field, the increase of energy storage systems efficiencies enables the overcoming of the constraints related to the reuse of electric energy in railway vehicles. This solution could be extremely useful for those railway vehicles which operate on non-electrified lines, where traction is usually provided by diesel engines. For this reason, the present work focuses on how regenerative braking technology could be exploited in diesel-powered rail applications. In further detail, a diagnostic train working on real railway lines has been considered as a case study. Given the real duty-cycle of the vehicle, a simulation model has been developed with the aim of evaluating the amount of energy recovered during braking phases and, consequently, the fuel saving and the avoided CO2 emissions. As a result, the analysis shows an improved energy efficiency of propulsion system. Compared with a pure diesel operation, it leads to fuel savings of 20%, a reduction of CO2 emissions of 22.3 kg with 23.25 kWh stored in the battery at the end of the route.

Marine energy still plays a marginal role in the current global energy scenario, despite the incessant effort by research for more than thirty years in the exploitation of the so-called blue energy. Among the wide range of marine technologies, wave energy harvesting can play a significant role in view of its potential and Oscillating Water Column (OWC) systems, coupled with Wells turbines, can be considered among the most mature wave energy technology. Due to the oscillating nature of the flow rate in this kind of applications, Wells turbines are affected by dynamic stall, which has significant effects in terms of performance, fatigue, noise and structural integrity of the turbine.Actually, during dynamic stall, the Wells turbine experiences evident high frequency torque fluctuations which overlay on the typical hysteresis loop, mainly during flow deceleration. The amplitudes of these fluctuations are damped as the flow rate decreases toward reattachment. Often these fluctuations are not evident because hysteresis loops are usually provided with phase-averaged data, which can significantly smoothen or even conceal them. Indeed, it is difficult to find in the literature high frequency torque measurements able to show these fluctuations. With the aim to better investigate how the stall triggers this phenomenon, a monoplane Wells turbine has been manufactured in 3D printing and tested in the open wind tunnel of the Polytechnic University of Bari, Italy. The interest of the experimental campaign has been mainly focused on the effects of main parameters of the oscillating inlet flow rate (mean flow rate, amplitude and period of the oscillations, modifying the controlling parameters of the inverter driving the squirrel cage blower) on the performance of the machine. The machine has been firstly investigated under steady state inlet flow conditions, then under dynamic stall conditions. As a result, unsteady torque fluctuations occur during the flow deceleration till the flow reattachment. After the stall, the investigated Wells turbine experiences a drastic reduction of the torque coefficient of about 90%. Moreover, the torque coefficient shows a number of peaks during deceleration phases ranging from 2 to 4. Specifically, the case with the maximum period of the flow rate under investigation (i.e., T = 20 s) shows a greater number of peaks (4) than those related to the other cases (3). Moreover, it has been found that this unsteady behavior is due neither to the mass flow rate crossing the turbine, nor to the stagnation pressure drop, nor to the rotational speed control, which is correctly performed keeping the rotational speed within 1% of the target value. Hence, detecting these oscillations can be relevant in the turbine design phase to enhance the structural strength of the turbine.