In recent years, research on gas turbine rim seals has shown that the sealing performance is strongly influenced by the inherent unsteadiness of the problem, making it clear that a steady analysis is not sufficient to fully understand the complex behavior of rim seal flows. In particular, the presence of unsteady large-scale flow structures rotating within the wheel-space has been identified. Previous research suggested that this phenomenon may originate from Kelvin-Helmholtz instabilities, which supposedly arise due to the tangential shear between the egress and the annulus flows. Although a few numerical studies have highlighted the direct influence of these instabilities on the sealing effectiveness, there is still a lack of experimental evidence. To fill this gap, the rotating cavity rig developed at the University of Florence was employed to perform a detailed investigation on the role of unsteadiness. First, the presence of large-scale flow structures was verified using a high-frequency pressure probe. Then, the fast pressure-sensitive paint technique was employed to capture 2D effectiveness contours on the stator wall at two distinct values of rotational Reynolds number ( R e (Phi) = 3.00 & times; 10 (5) - 1.20 & times; 10( 6) ) and at different levels of purge flow. The analysis of the time-resolved effectiveness maps highlighted the presence of large-scale rotating structures, which cause effectiveness deterioration especially at higher radius. The structures are then dispersed at a lower radius in a diffusion-like mechanism influenced by the disk rotation. Although these instabilities appear to be characterized by a high level of randomness, a statistical analysis of the contours showed that, as the sealing level of the cavity increases, the rotational speed of the structures remains relatively constant, while the average number of occurrences per revolution progressively decreases. Interestingly, the results appeared to be completely independent of the rotational speed of the rotor disk. In the end, the time-resolved description of the sealing effectiveness allows drawing general conclusions about the flow behavior, which, in turn, are expected to have a long-term impact on cavity flow modeling, from low-order methods to advanced CFD methodologies.

The chapter “The Department of Industrial Engineering: Today” outlines the current structure of DIEF within its regional, national, and international context, highlighting its organization, scientific sections, laboratories, and infrastructure. It presents the main research lines, collaborations with industry and institutions, participation in European programs and the PNRR, as well as its commitment to teaching and internationalization. The chapter portrays a dynamic, multidisciplinary department strongly focused on innovation, technology transfer, and sustainable development.

The chapter “From Knowledge to Innovation: The Role of DIEF in Technology Transfer” explores the activities through which the Department transforms scientific research into value for industry and society. Through patents, spin-offs, joint laboratories, and collaborative projects with companies, DIEF promotes innovation and industrial competitiveness, fostering strong links between academia and the local community and contributing to sustainable economic development.

Reliable and sustainable electricity supply remains a major challenge for remote off-grid communities, which often rely on costly and carbon-intensive diesel generators. Decarbonizing these areas requires the integration of renewable energy technologies with storage solutions to mitigate the variability and intermittency of renewable power production. This study aims to investigate the potential of micro-scale Compressed Air Energy Storage (micro-CAES) to improve the environmental and economic performance of hybrid photovoltaic (PV)-diesel systems under realistic operating conditions. A dynamic, system-level thermodynamic model is coupled with an optimization framework to determine the optimal sizing of photovoltaic and storage components according to alternative objective functions. A key aspect of this work lies in the integration of this optimization with a parametric cradle-to-grave Life Cycle Assessment, enabling the consistent evaluation of environmental impacts as a function of system size. Environmental performance is assessed using Global Warming Potential (GWP), while economic viability is evaluated through the Levelized Cost of Energy (LCOE). Three system configurations, namely diesel-only, PV-diesel, and PV-diesel-CAES, are analyzed for seven representative off-grid locations with differing solar resource availability and diesel price levels. Results show that replacing diesel generation with photovoltaic systems reduces greenhouse gas emissions from 0.996 to approximately 0.598 kgCO2eq/kWh. The integration of micro-CAES enables further reductions, reaching 0.144-0.247 kgCO2eq/kWh depending on site conditions. From an economic perspective, the results indicate that the viability of PV-diesel-CAES systems is primarily driven by system size, diesel fuel price, and site-specific photovoltaic potential. In general, limited round-trip efficiency leads to photovoltaic oversizing and increased capital costs, which tend to outweigh fuel savings. As a result, storage integration becomes advantageous only in scenarios characterized by high diesel prices, where reduced generator operation compensates for the relatively low round-trip efficiency and the capital cost of the storage system. Overall, this work provides a comprehensive techno-economic and environmental assessment of micro-CAES-based hybrid systems for off-grid applications, highlighting their potential for substantial emission reductions while clearly identifying the conditions under which economic competitiveness can be achieved.

The recent interest in the use of renewable energy source for power plants has led to a paradigm shift in the design of steam turbines. In particular, due to the intermitted nature of such energy sources, steam turbines are driven to operate in off-design conditions and are subject to increasingly frequent startups and shutdowns. During the startup phase, if superheated steam comes into contact with the internal walls of the machine's ducts, which, before reaching steady-state thermal conditions, may be at a temperature lower than the saturation level corresponding to the operating pressure, the phenomenon of wall condensation occurs. From the literature on evaporative cooling techniques, it is well known that heat transfer involving phase change due to latent heat leads to a large amount of heat flux, causing significant thermal gradients in the machine that can compromise its structural integrity. During the design phase, it is also necessary to estimate the condensate flowrate for the sizing of appropriate drainage channels to prevent accumulation. From a numerical point of view, although multiphysics and multiphase models have been developed to address these needs, the three-dimensional computational fluid dynamics simulation of the entire thermal transient would result in high computational costs, unsuitable for a preliminary design phase. For this reason, the aim of this work is to propose a tool for estimating the steam turbine casing thermal transient and condensate flowrate in transient thermal conditions. The code has been validated with stationary and transient experimental data, as well as a reference analytical solution, showing excellent agreement with an extremely low computational cost.

One of the most critical challenges in gas turbine design is preventing the ingestion of hot mainstream gases into the disk space between the stator and rotor disks. Rim seals and superposed sealant flows are commonly used to mitigate the risk of component overheating. However, leakage paths inevitably form between the mating interfaces of adjacent components due to the complex architecture of the engine. Therefore, the interaction between the different flows present within the disk space complicates the accurate determination of the optimal sealing flow quantity. For this reason, this study experimentally investigates fluid dynamics inside a stator–rotor cavity, with a particular focus on leakage flows. In particular, this work examines the impact of multiple parameters, including injection radius position, number of leakage holes, and injection angle, on the sealing effectiveness values measured on the stator side of the cavity through CO2 gas sampling measurements. By comparing the effectiveness values with the swirl measurements derived from static and total pressure readings, the development of flow structures and the impact of leakage injection on sealing performance were finally evaluated. The results indicate that leakage injection has a minimal effect on the sealing effectiveness above the injection point, but significantly improves the performance at a lower radius. Moreover, it was observed that for a given mass flow rate, using a lower number of holes results in worse sealing performance due to a higher jet momentum, which causes the leakage flow to penetrate through the cavity toward the rotor side. In the end, employing two distinct injection angles—both aligned with the rotor’s direction of rotation—showed no substantial impact on sealing effectiveness.

Quantifying the cooling performance of real hardware, internally-cooled gas turbine parts is challenging due to their characteristic dimensions and thermal properties and to the limited instrumentation access to their internal, cooled surfaces. Inverse heat conduction analysis methods are used in this context to estimate the heat loads generated by an internal cooling system from measurements of the resulting external surface temperature distribution of the cooled part. Existing works in the turbine cooling literature rely on bench-top testing facilities that do not reproduce a relevant external aero-thermal load, thus limiting the types of cooled components that may be tested with realistic internal flow behavior. The objective of this study is to extend traditional inverse conduction analysis and to demonstrate experimental and numerical methods to estimate the internal cooling performance of a real hardware-like nozzle-guide vane operating with engine-representative internal and external thermal loads. Thermal transient tests conducted with the test article installed in a linear cascade wind tunnel generate the external surface temperature responses necessary for the proposed iterative post-processing procedure to estimate both the internal and external heat loads. In particular, this work focuses on the description of the experimental test procedures developed and of the numerical post-processing approach. Internal and external heat load estimates are presented for a series of test conditions defined by combinations of different cooling system Reynolds numbers and the tunnel’s mainstream turbulence intensity. The results demonstrated it was possible to reproduce reference results with an acceptable accuracy within an evaluated experimental uncertainty of approximately 20%, suggesting the possibility of studying more complex and realistic test cases.

The use of additive manufactured microchannels for gas turbine cooled components is considered a promising approach to enhance the internal cooling efficiency. On the other hand, the evaluation of heat transfer and pressure loss characteristics is complicated by the fact that several manufacturing choices can affect the as-built geometry and surface roughness, thus making it difficult to predict their performance with simple relations. Moreover, the evaluation of the channels characteristic dimension must be carried out through complex processes and the distinction between channel shape and its intrinsic roughness is in general a nonambiguous aspect. The possibility to adopt micro-channels with noncylindrical cross-sectional shapes introduces an additional degree-of-freedom. This article builds on a previous one, where a procedure to retrieve the characteristic dimension was developed and tested on cylindrical microchannels; the method was based on a differential flow check, allowing to by-pass the direct geometrical investigation. In this, the methodology is applied to microchannels with various cross-sectional shapes, to assess its capabilities. The results are discussed, especially in terms of performance scaling capabilities, and compared to the ones achieved from the conventional approach based on geometrical inspection. The results showed that the approaches returned slightly different values of the characteristic dimension and, in turn, of the quantitative values of the parameters of interest. Nevertheless, the same conclusions and performance were achieved, as far as the comparative analysis of different coupons and the scaling capability are concerned.

The capabilities and accuracy of additive manufacturing processes have experienced remarkable advancements in recent years, with no signs of slowing down. As a result, there is increasing interest from researchers in the gas turbine industry regarding its potential application in cooling system designs. This study presents a comparative analysis of the heat transfer capabilities of pin-fins and Kagome turbulators applied to the trailing edge of a turbine vane. A transient experimental measurement technique was employed to investigate the internal convective heat transfer performance of both cooling configurations. The experimental setup involved the use of surface temperature measurements during transient heat flux conditions, and the internal convective heat transfer coefficient was determined using a numerical procedure that ends with a linear regression method applied to the transient thermal response. Since the pressure drop across each array of turbulators is another important performance parameter, their friction factor was also estimated during a dedicated test campaign. The investigated flow Reynolds numbers range from 3000 to 14,000. These values allow the authors to provide a deeper understanding of the latticework structures' performances in Reynolds numbers range typical of applications in a gas turbine vane trailing edge. Experimental results indicate that Kagome turbulators provide a slight improvement (about 2%) of the thermal performance with respect to the pin-fin geometry, thanks to the increased wet area and a lower friction factor especially at higher Reynolds number conditions, with a reduction of approximately 8%.

The chapter “Fluid Machinery: Research at the Department of Industrial Engineering (DIEF)” presents scientific activities in the field of turbomachinery and positive displacement machines, with particular focus on energy conversion, propulsion, and environmental sustainability. Through experimental approaches and advanced numerical simulations, the Department develops innovative solutions for gas turbines, compressors, and energy systems, in collaboration with national and international industrial partners, contributing to technological progress in the energy and aerospace sectors.

Abstract Rotating detonation combustors (RDCs) have recently garnered significant attention in aero combustion research due to their potential efficiency advantages over conventional deflagration-based systems. Specifically, small-scale RDCs, such as Micro-RDCs, have proven to be promising alternatives as thrusters or auxiliary power generators. Moreover, their compact dimensions and simple design make Micro-RDCs ideal research platforms for detailed investigation of detonation dynamics and cooling strategies. However, integrating RDCs into gas turbine systems remains challenging, with thermal management emerging as a critical bottleneck due to the extreme heat flux generated during detonation. Heat transfer in RDCs is still an under-explored topic. This work presents a methodology based on an inverse approach to determine the heat transfer coefficient (HTC) distribution along an RDC annulus flow path using measured wall temperature maps on the external surface. An infrared (IR) camera was employed to capture the evolution of the outer wall temperature during detonation tests. The inverse method, in combination with finite element modeling (FEM) simulations, enabled the retrieval of the spatial distribution of the HTC within the combustion chamber, as well as the heat flux through the outer wall during the detonation transition process. A series of experiments were conducted under varying operating conditions, providing a detailed understanding of the heat flux distribution on the liner and revealing the system’s sensitivity to thermal loads. This approach allows for a thorough assessment of the thermal environment, offering key insights for optimizing RDC design and improving thermal management strategies in practical applications.

Additive Manufacturing has demonstrated significant potential to produce components with complex geometries and small dimensions. This capability has sparked growing interest in recent years, leading to substantial efforts aimed at applying Additive Manufacturing (AM) methods to enhance film cooling techniques in turbine blade cooling systems. This work investigates the performance and repeatability of film cooling holes fabricated using a Laser Powder Bed Fusion (LPBF) technique, focusing on their cooling effectiveness. The work analyses the performance of a novel hole developed in the Design-for-Additive-Manufacturing framework. The proposed hole has a strongly three-dimensional shape with a reduced length compared to traditional holes, in order to inject the coolant further upstream on the target surface, and an expanding section inspired by the traditional fan-shaped holes. Pressure Sensitive Paints (PSP) measurements were performed for multiple flat plates housing a single row of 11 holes. The adiabatic effectiveness contours downstream of each hole were found to exhibit a different variability at each tested blowing ratio ranging between 0.25 and 2.00, especially at high blowing ratio values. A statistical analysis is performed to quantify the variability of cooling effectiveness, relating thermal performances deviations to manufacturing failure in order to assess the hole robustness across different operating conditions. Results show that, while AM enables the production of complex geometry, repeatability remains a challenge, with even a slight variation in the hole geometry strongly jeopardizing cooling performance. Moreover, the robustness in terms of film effectiveness is not constant varying the coolant conditions and reduces at high blowing ratios.

Film cooling is widely implemented in highly thermally stressed gas turbine components. Its performance has been extensively investigated for several decades and many results are available in the literature. In conventional gas turbines, regions of supersonic flow are not prevalent and should generally be avoided. For this reason, results relative to film cooling in supersonic flow are limited. Nevertheless, a new interest related to Rotating Detonation Combustors (RDC) and supersonic turbines is growing. The implementation of those engine components in a gas turbine is likely to need film cooling for thermal protection. In this context, it becomes crucial to gain an understanding of how the film interacts with the freestream when operated in a supersonic flow. This paper investigates the effect caused by the injection of film cooling on the morphology of the supersonic flow field. Results obtained by means of schlieren imaging indicated that the coolant injection acts as a wedge inside the flow, determining the local formation of an oblique bow shock around each film cooling hole. The shape, inclination, and strength of the oblique shock showed a dependency on the fundamental dimensionless parameters considered for the characterization of the operating conditions of film cooling. Furthermore, as the amount of mass injected was increased, the inclination of the generated shocks increased and the impingement location of the reflected shock moved upstream along the injection plate. The fluid dynamics of this interaction affected the local pressure distribution on the injection plate, measured by means of Pressure Sensitive Paint (PSP). Different film cooling geometries and main flow conditions were tested at multiple operating conditions. The relative impact of the different parameters is presented, providing useful information for the design of a film cooled engine component exposed to a supersonic flow.

High temperature, high supersonic Mach number flows can be encountered in different innovative propulsion systems configurations such as Rotating Detonation Combustors (RDCs) and scramjets, requiring the use of film cooling for the thermal management. For this reason, a clear understanding of the performance of film cooling in supersonic flow is paramount. This experimental study investigated the performance of film cooling in a supersonic flow at Mach 1.65 comparing it with subsonic flow operations at Mach 0.3. Adiabatic effectiveness measurements were performed using Pressure Sensitive Paint. This technique also provided pressure field maps, useful to enhance the understanding of the physical phenomena under investigation. Additionally, time-averaged schlieren images enabled the visualization of the flow field morphology and understanding of the underlying physics. Cylindrical holes both aligned with the flow and with a 30 degrees compound angle and 7-7-7 fan-shaped holes aligned with the flow were considered. The results indicated performance improvements in both centerline and laterally averaged adiabatic effectiveness induced by the action of the oblique shock forming upstream of the hole. The same shock is responsible for modifying the shape of the adiabatic effectiveness contour, determining a higher peak along the centerline which linearly decreases outward instead of showing the more typical bell shape. The fan-shaped holes outperform the other holes at any blowing ratio (BR) over 0.8 for supersonic main flow operations. Performance of cylindrical holes in supersonic flow follow the trend typically encountered in subsonic flows while also bringing the peak in adiabatic effectiveness upstream and closer to the hole exit.

Among internal cooling techniques for gas turbines components, skin cooling is recognized as one of the most promising, especially thanks to the spread of additive manufacturing techniques. In this regard, several studies have tried to characterize heat transfer and pressure loss performance of additive manufactured micro-channels, as well as the impact of AM characteristic parameters, mainly in the form of building angle, and resulting surface roughness and channel shape. The open literature offers several correlations in terms of friction and heat transfer coefficient using a representative hydraulic diameter. Despite that, little attention is given on the importance of such characteristic length definition which may lead to under/over estimation of the cooling rates when correlations are used in the design In this work, coupons featuring circular micro-channels with diameters of 0.5 and 1 mm and different building angles have been tested, to retrieve pressure losses and an average heat transfer coefficient through a lumped approach. The coupons were additive manufactured using the Laser Powder Bed Fusion (L-PBF) technique. Exploiting the experimental survey, the impact of the considered hydraulic diameter was investigated, by comparing different approaches based on a direct measurement. An additional and new approach, aimed at the identification of an "effective" diameter, based on fluid-dynamic considerations, was also considered. The data correlation and the comparison with available correlations from different authors showed the newly proposed approach to provide superior scaling capabilities and, in turn, allowing for the development of more accurate prediction methods.

The flow field developing inside the stator-rotor cavities of gas turbines is characterized by a complex unsteady behavior which still requires expensive and time consuming computational fluid dynamics simulations to be accurately modeled. Hence, the experimental characterization of the rim sealing effectiveness by means of scaled down geometries that replicate the rim seals found in actual engines still represent a widely used approach in literature. However, the obtained results can greatly depend on the specific geometry of the tested rim seal. Moreover, different geometrical parameters can vary during the operation of the engine, especially under transient or off-design conditions, thus influencing the resulting effectiveness values. For this reason, the sealing performance of seven different configurations of radial rim seals has been investigated and the obtained dataset has been correlated by using the orifice model. Hence, a detailed comparison of the results allowed the evaluation of the impact of different values of axial overlap, different distances between the vanes trailing edge and the blades leading edge and different values of radial gap. In particular, a three times greater axial overlap and a modest increase in the distance between the trailing edge of the vanes and the leading edge of the blades were both found to provide a limited improvement in the sealing performance, with a respective average reduction in U min of approximately 5% and 6%. A radial gap 2.4 times greater was instead found to lead to an average increase in the required quantity of sealing flowrate of approximately 44%. Hence, the amount of purge flow required to fully seal a cavity was not found to exhibit a linear increase with the radial gap. [DOI: 10.1115/1.4066536]

Detailed thermal performance estimation of real-hardware internally cooled gas-turbine components is challenging due to the lack of optical and instrumentation access to the internal surfaces. In scaled, laboratory conditions, such estimates can be obtained by solving an inverse heat conduction problem that links the desired internal heat load distribution to a set of measured external temperatures through the solution of a partial differential equation. If sufficiently reliable, the results provide cooling system designers with valuable insights into the effects of the combinations of different cooling techniques, of secondary flows, and of manufacturing methods. Without some form of regularization, however, such inverse problems are ill-posed in that the estimates are not uniquely defined by the temperature measurements and are highly sensitive to measurement noise. In this study, an adjoint-based deterministic optimization method is used to estimate high-dimensional internal heat transfer coefficient distributions produced by a jet-array impingement system with local extraction of post-impingement flow. A method for determining the optimum amount of regularization to apply is also adopted and validated using the experimental results. Tests were performed by applying the impingement system in steady conditions to a heated metal plate and measuring the temperature response on the opposite side with a scientific grade infra-red camera. The particular cooling system was chosen because it produces high spatial gradients of heat transfer coefficients which are difficult to reconstruct from the external temperature measurements due to the three-dimensional conduction effects through the wall of the plate. Variations of plate thickness and Reynolds number were used to test the robustness of the method, and the resulting estimates for all conditions were compared to corresponding reference results obtained in a previous, dedicated test campaign.

Due to the rising interest in using renewable energy for environmental impact reduction, steam turbines are facing with a radical change in design practices and operability. In particular, the unpredictable and variable production of renewable plants drives to frequent shutdowns and fast start-ups of steam turbines, which have a huge impact on structural integrity. During start-up phases, the high temperature steam could face with a below-saturation wall temperature causing condensation and then high temperature gradients on solid components. Hence, the proper thermal gradient evolution and condensing mass prediction are quite relevant in steam turbine design. Nowadays, numerical Conjugate Heat Transfer (CHT) analysis is a good industrial practice to quantify the thermal distribution in turbomachinery components. On the other hand, the usual bottleneck of these analyses is the fluid timestep and the required temporal discretization that is one or two order of magnitude smaller than the solid one: therefore a fully coupled unsteady is still unaffordable in terms of computational costs. In this context, this work presents a low dimensional multiphysics approach which models the condensation phenomenon through correlations and the solid heat transfer through discrete 1D transient heat equation. Furthermore, a 3D CHT by employing the eulerian wall film multiphase approach is presented and compared with the developed algorithm. Finally, the numerical results obtained are compared with field data on a real unit where the inlet section, as usual, is subjected to the described condensation phenomenon.

Additive manufacturing (AM) is widely recognized as a prominent tool to maximize the potential of internal cooling systems for gas turbine applications. Several past studies have been undertaken in order to assess the effect of additive manufactured components peculiar characteristics, mainly in the form of surface roughness, on heat transfer and pressure losses. On the other hand, impingement constitutes one of the most adopted solutions for turbine vane internal cooling; also, its heat transfer performance has been shown to be potentially improved through the use of roughened target surfaces in several studies. In this work, the effect of AM-generated roughness on the performance of impingement systems has been experimentally investigated. A lumped approach was used to test additive manufactured coupons reproducing an impingement array in 1:1 scale and retrieve an average heat transfer assessment. The Laser Powder Bed Fusion (L-PBF) technique was used for the manufacturing process. As one of the main parameters affecting AM-generated roughness, the building direction of the target surface was varied in order to highlight its impact on the overall performance comparing four different building directions with a smooth reference target plate made by standard CNC machining.