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Inadequate lubrication might lead to high friction and wear and can ultimately translate in a higher dissipation of energy, initiation and propagation of fracture and material fatigue. These occurrences are avoided or delayed thanks to an efficient lubricating system. The core of a reliable system is the hydraulic pump which, in the automotive field, is also responsible for power transmission and cooling. Given the importance of such components, improving reliability and performance of the pumps is a topic that is greatly pursued by manufacturers. A machine that is infrequently addressed in the open literature of the fluid power field is the pendulum slider pump. This kind of machine has the makings of high durability performance, short response time, and significant ability to withstand flow contamination by solid particles. Considering the available literature, no Computational Fluid Dynamics (CFD) studies have been presented so far. Among the complexities that hindered the application of CFD to this machine, motion complexity and narrow gaps make the development of a numerical algorithm for its modelling non-straightforward. In this work, the authors present the development and the application of a CFD model for the simulation of pendulum slider pumps. The structured mesh generation process has been successfully applied to a state-of-the-art pendulum slider pump for automotive applications, and the outcome of the numerical investigation has been validated against an on-purpose built test bench. The results both in terms of variable displacement and fixed displacement behaviour are shown. This work proofs the suitability of the developed model for the analysis of hydraulic pendulum slider pumps.

Engineering systems continuously interact with nano-sized particles coming from natural or artificial sources. Considering nano-sized contaminants the detrimental effects are known as soiling and fouling phenomena. The objective of the present work is to gather morphological and three-dimensional quantitative information of discontinuities such as voids and pores within the nano-sized particle layer and in correspondence to the substrate/layer interface using microtomography. Deposits are obtained through impact tests using fine powder (soil and soot), and there are realized on a low-density material substrate characterized by different surface roughness values. The packing process and the discontinuities at the substrate-to-layer interfaces explain macroscopic effects as detachment and spallation but at the same time, give the possibility to understand more in detail the process related to the deposition mechanisms involved in this type of test defining general guidelines to predict the fouling phenomenon and to improve the capability of the removal process.

Nanoparticle surface interaction is a common phenomenon, even if a general explanation of nanoparticle deposit growth is still unknown. For several applications, the adhesion of such nanoparticles is detrimental, generating safety and performance issues. The present work shows an interpretation of deposit growth due to nanoparticle deposition, capable of predicting particle adhesion and layer accretion. The nanoparticle deposits grow analogously to a typical autonomous population settlement in a virgin area following statistical rule, which includes the initial growth, the successive stable condition (development), and catastrophic events able to destroy the deposited layer. This statistical population model allows the generalization of the nanoparticle adhesion/deposition behavior, and it could be used for improving the prediction capability of nanoparticle deposition to common engineering applications.

This paper addresses the topic of balanced vane pump simulations for pressure ripple optimization by means of metering grooves at the leading edge of delivery ports. It presents a computational fluid dynamics case study based on a transient three-dimensional model developed using an up-to-date commercial software tool. Special attention is dedicated to gaseous cavitation and the impact of the related modeling choices on predictions. The effect of groove dimensions and interaction with the precompression features of the cam ring of the pump are addressed. Experimental data obtained using a dedicated test rig are presented for comparison with numerical results in terms of delivery pressure ripple and volumetric flowrate. A validation strategy based on tuning of the dynamic cavitation model adopted for simulations is proposed. The results demonstrate the critical importance of gas release modeling for the simulation of porting details in the case of significant aeration effects.

Heavy-duty centrifugal fans are employed for the transport of dust-laden flows in industrial plants, for cement or steel production, or in energy production of plants and mine ventilation systems. These applications require the disposal of huge amounts of suspended particles, which can lead to a gradual erosion of the machine parts where impacts take place. The wear of the fan components can lead to premature failure of the machine, threatening human safety and reliability of the whole plant. The assessment of the wear severity of the machine, according to the process parameters, can aid the plant owner in scheduling overhaul operations along with the operative life of the machine. Moreover, through a reliable estimation of the wear severity, fan manufacturers can optimize the whole machine design process, from the material selection to the warranty time assessment. This work aims to develop a semi-empirical method capable of estimating the erosion severity of centrifugal fans employed for heavy-duty operations. A mechanistic model which accounts for the erosion on the blade leading edge is proposed. The model is derived by means of an analytical approach and accounts for a number of operating parameters (i.e.,, fan geometry, fan operating point, particle concentration in the flow, fluid properties, and material erosion resistance). A comparison of the theoretical model to the computational fluid dynamic (CFD) simulation results obtained through the use of multiphase particle tracking is also provided to assess the reliability of the present method.

Solid particle ingestion is one of the main causes of gas turbine compressors degradation for both heavy-duty and aero-propulsion applications. Particles that enter the engine can stick to the internal surfaces and then form deposits. These, in turn, involve a change in the surface roughness and then performance deterioration. In the literature, several strategies have been proposed in order to account for the deposits effects on compressor numerical simulations. Among the others, the most used is the mesh-morphing strategy, which consists of the modification of the computational grid according to the particle deposition. Even though it is well suited for turbine fouling, the large computational costs and complexity of this strategy are not acceptable for compressor simulations. In this work, an innovative microscale-based approach has been proposed. An axial compressor deposition experiment from the literature has been considered as the reference case to test the reliability of the presented strategy. The main advantage of this approach consists of reducing both computational costs and numerical instability since it does not need the modification of the mesh. The deposition has been modelled by means of the OSU model and the roughness influence on the fluid flow has been accounted for by using the well-known sand-grain-roughness height (ks). Efforts have been made to find the ks correlation that best represents a fouled surface. The presented strategy enables the prediction of the fouling effects on axial flow compressors, and the prediction of the performance losses during the operation.

Gas turbines can operate in an environment dispersed with particles that, if ingested by the machine, may have a detrimental effect on the aerodynamic performances. Therefore, the aim of this work is to gather information about how particles adhesion is influenced by geometrical features of gradually growing complexity. At this scope, the particle deposition problem is investigated from the numerical standpoint. Specifically, the LS-89 transonic high pressure turbine (HPT) vane is simulated and an encounter with a volcanic ash cloud is modelled. Three simulations are carried out: a 2D simulation has been compared with the set of 3D simulations. Different levels of complexity of the geometry have been considered for the 3D case: the endwall effect has been assessed considering the presence of a variable radius fillet and comparing it with the prediction obtained by a cylindrical extrusion. The proposed analysis provides indications on the 2D and 3D prediction with regards to particle deposition problems. The sticking pattern of the particle has been investigated in relation to the different nature of secondary flows.

The detrimental effects generated by the gas turbine fouling phenomenon are well known. Due to soil and soot particles ingestion, gas turbines experience performance drops related to greater fuel consumption and even lower efficiency. These effects are related to the modification of the shape and surface roughness of relevant surfaces (compressor and turbine blades and vanes, especially) due to the presence of a thin layer generated by micro/nano-sized particle adhesion. Such contaminants are swallowed by the unit and, as a function of the operating conditions, adhere to the surface, causing a sort of dangerous coating to the surface. In this work, a microtomography analysis of the deposited layer is reported. The deposited layer has been generated using micro-sized soil and soot powders under specific impact conditions and substrate surface roughness similar to those in the cold section of a gas turbine compressor. The microtomography analysis has been carried out using the beamline at the ELETTRA Sincrotrone research center. Thanks to the resolution of the beamline, the detection of the three-dimensional internal structure of the soil and soot layers has revealed that within the layer, the structure is characterized by discontinuities. Soot and soil particles, even characterized by similar diameter distributions and test conditions, generate layer structures that differ by the magnitude, orientation, location of the internal discontinuities, and surface morphology (i.e., roughness). The comprehension of the packing process allows to understand the adhesion process and define general guidelines to predict the fouling phenomenon.

The increment of the industrialization processes led to even more release of carbonaceous particulate into the environment. These airborne contaminants are produced by endothermic machines, coal combustion, heating systems, and production plants. Soot particles suspended into the air can overpass the inlet filters (if present) of gas turbines and deposit onto the internal parts of the compressor. This phenomenon, leading to the modification of the aerodynamic surface of the airfoils, is the main responsible for the gas turbine performance losses over time. This detrimental effect can be partially recovered by washing the compressor unit, frequently. In this work, the assessment of the washing effectiveness against soot deposits of an on-purpose designed eco-friendly cleaner is provided. The removal effectiveness of this water-based cleaner is related to the capability to collect soot particles from surfaces, limiting redeposit phenomena over the stages. The experimental investigation has been carried out by injecting soot particles, under controlled conditions, into a multistage test axial compressor. Using image post-processing techniques, carried out over the entire compressor flow path, a quantitative evaluation of the washing capability has been assessed. Compared with demineralized water, the cleaner was found to be effective if high cleaning performances are expected.

Numerical simulations of particle-laden flows have received growing attention in the last decade, due to the broad spectrum of industrial applications in which discrete phases prediction is of interest. Among these, ingestion of particles by turbomachinery is an area that is seeing vivid research and studies. The most common technique to tackle this kind of problem is the Eulerian-Lagrangian method, in which individual particles are tracked inside the domain. At the same time, in multi-stage turbomachinery simulations interfaces are needed to couple the flow solution in adjacent domains in relative motion. In this work, an open-source extension for Lagrangian simulations in multistage rotating machines is presented in the foam-extend environment. Firstly, a thorough discussion of the implementation is presented, with particular emphasis on particle passage through General Grid Interfaces (GGI) and mixing planes. Moreover, a mass-conservative particle redistribution technique is described, as such a property is requested at interfaces between Multiple Reference Frame (MRF). The peculiarities of the algorithm are then shown on a relevant test-case. Eventually, three turbomachinery applications are presented, with growing complexity, to show the capabilities of the numerical code in real-life applications. Simulation results in terms of erosion and impacts on aerodynamic surfaces are also presented as examples of possible parameters of interest in particle-laden flow computations.

Gas turbine particle ingestion may lead to the deposition of contaminants in the compressor section, inducing the performance losses of the whole engine. The economic losses derived from this issue push great interest in the investigation of such a phenomenon from a numerical and experimental standpoint. This article describes a quantitative approach to predict particle deposition on the vanes of an axial compressor starting from the flow field obtained employing computational fluid dynamic (CFD) simulations. The results are then compared to the experiments performed on the Allison 250 C18 compressor unit subject to particle ingestion under controlled conditions. The results derived from the experimental and numerical investigations are presented, providing insight into the mass deposited on the vanes and the corresponding zones most affected by the particle deposition issue. The methodology showed good agreement in the estimation of the predicted values of the deposited mass and the corresponding patterns through the compressor stages. The low-complexity approach proposed here could help the designer to predict the contamination of the stationary rows starting from a simple set of single-phase numerical results. Furthermore, with the implementation of this approach into the design path, the designer could reduce the impact of fouling, looking at the effects of their solutions under the fouling-reduction light.

High-chromium cast irons are frequently used in high-demanding applications, where low production costs and wear performance are key factors. The excellent abrasive resistance of these alloys results from the overall microstructural features, i.e., type, morphology, and distribution of hard primary and secondary carbides, along with the matrix constituents. Such a microstructure is the result of the chemical composition and solidification process, even though it could be further tuned by heat treatments. These latter are usually performed to destabilize the austenite and to induce the precipitation of secondary carbides. The present study investigates the combined effect of destabilization heat treatment route and erodent powder type on the erosive wear behavior of two commercial hypereutectic white cast irons. The as-received and the heat-treated materials were analyzed through optical and scanning electron microscopy, hardness tests, and X-ray diffraction to determine the relationship between microstructural variations and applied heat treatment. The erosive resistance was evaluated per the ASTM G76 standard in a purpose-built air blast test rig. Experiments were performed considering a raw meal powder, commonly used in cement factories, and Al2O3 as erodent powders. The adopted heat treatments were effective in increasing the overall hardness of the material, but this was not directly related to the erosion resistance. By contrast, the relative hardness ratio, i.e., erodent/target hardness, affects the erosion rate and different behaviors in relation to the softer/harder erodent particles were found.

Atmospheric particulate is one of the main causes of performance degradation in gas turbine engines, especially in the aeronautical field where filter barriers are absent. The ingested particles can stick to the blade surfaces of the engine, varying their shape and roughness. As a consequence, engine performance degradation takes place. The type and the amount of the particles ingested depend on the flight zones and altitude. During their missions, aircrafts follow a prescribed path defined in terms of altitude, longitude, and latitude. During its route, the aircraft engine encounters different environments characterized by different temperature, pressure, and air composition. Regarding the latter issue, the knowledge of this characteristic can be key information when these statistics are needed for obtaining data useful for engine degradation assessment or prediction. Many satellites, such as the environmental satellite CALIPSO, are employed to study the terrestrial aerosol and clouds profile by using a LIDAR (Laser Detection and Ranging). This technology is commonly used to determine the distance between a light emitter and an object and it is based on the light refraction phenomenon. Backscatter coefficients profiles data, which characterize the distribution of particles and aerosols in the atmosphere, are available in the open literature from the findings of CALIPSO. In this work, a new methodology to estimate the aerosol type and concentration encountered by an aircraft during a mission is proposed. To test the feasibility of this method, two aircraft missions for different length scales (medium and long haul) are analyzed and an estimate of the particulate encountered by the engines is provided. The mission analysis has been conducted by discretizing the altitude profile, longitude, and latitude coordinates of each flight and then cross-referencing them with the particulate concentration obtained from CALIPSO data.

Natural events and human activities are responsible for the generation and transport of large amounts of micro-sized particles, which could contaminate several engineering devices like solar panels, wind turbines, and aero-engines. In industrial processes, systems as heat exchangers, fans, and dust collectors are continuously affected by nanoparticles’ interaction. For several applications, the adhesion of such nanoparticles is detrimental, generating safety and performance issues. Particle-to-particle and particle-to-surface interactions are well known, even if a general explanation of nanoparticle deposit growth is still unknown. In the present paper, an interpretation of deposit growth due to nanoparticle deposition can predict particle adhesion, and layer accretion is proposed. A statistical model and a set of coefficients are used to generalize nanoparticle deposits’ growth by an S-shaped function. In particular, the nanoparticle deposits grow analogously to a typical autonomous population settlement in a virgin area following statistical rule, which includes the initial growth, the successive stable condition (development), and catastrophic events able to destroy the layer. This approach generalizes nanoparticle adhesion/deposition behavior, overpassing the constraints reported in common deposition models, mainly focused on the mechanical aspect of the nanoparticle impact event. The catastrophic events, such as layer detachment, are modeled with a Poisson’s distribution, related to material characteristics and impact conditions. This innovative approach, analogies, and coefficients applied to common engineering applications may be the starting point for improving the prediction capability of nanoparticle deposition.

The performance evaluation of vapor compression and Organic Rankine Cycles relies on the employment of thermophysical libraries. The evaluation of enthalpy, for example, requires the prediction of specific heat. Thermophysical properties, in turn, depend on the state of the fluid, and thus the library is needed. The actual state of the fluid can be obtained by measuring two state properties. Typically, pressure and temperature are evaluated by means of thermocouples and pressure sensors. These measurements are affected by uncertainty, that propagates when the quantities are combined. A physical quantity calculated starting from temperature and pressure is affected by an uncertainty that is a function of the one related to the measurement of the two base quantities and of the thermophysical library employed. This can indeed propagate differently the two starting uncertainty magnifying the contribution of temperature rather than pressure. In this work the propagation of temperature and pressure uncertainty in relation to the enthalpy calculation through the CoolProp library is investigated. The procedure is applied to a number of pure refrigerants and a mixture of common use in the engineering practice. The database reported can be of help to estimate the propagation of the uncertainty in the most common engineering application.

Fouling in gas turbines is caused by airborne contaminants which, under certain conditions, adhere to aerodynamic surfaces upon impact. The growth of solid deposits causes geometric modifications of the blades in terms of both mean shape and roughness level. The consequences of particle deposition range from performance deterioration to life reduction to complete loss of power. Due to the importance of the phenomenon, several methods to model particle sticking have been proposed in literature. Most models are based on the idea of a sticking probability, defined as the likelihood a particle has to stick to a surface upon impact. Other models investigate the phenomenon from a deterministic point of view by calculating the energy available before and after the impact. The nature of the materials encountered within this environment does not lend itself to a very precise characterization, consequently, it is difficult to establish the limits of validity of sticking models based on field data or even laboratory scale experiments. As a result, predicting the growth of solid deposits in gas turbines is still a task fraught with difficulty. In this work, two non-dimensional parameters are defined to describe the interaction between incident particles and a substrate, with particular reference to sticking behavior in a gas turbine. In the first part of the work, historical experimental data on particle adhesion under gas turbine-like conditions are analyzed by means of relevant dimensional quantities (e.g. particle viscosity, surface tension, and kinetic energy). After a dimensional analysis, the data then are classified using non-dimensional groups and a universal threshold for the transition from erosion to deposition and from fragmentation to splashing based on particle properties and impact conditions is identified. The relation between particle kinetic energy/surface energy and the particle temperature normalized by the softening temperature represents the original non-dimensional groups able to represent a basis of a promising adhesion criterion.

Nowadays non-contact measurement methods have become widely used systems in several fields especially robotics, aerospace, architecture, and cultural heritage. Practical devices, taken from mass markets, are increasingly being used in scientific and engineering research fields thanks to their ability to combine good accuracy with to the low-cost and ready-to-use experimental setup. In the present paper, digital image analysis (based on digital camera devices) and three-dimensional scanning technique (based on Kinect I and Kinect II sensors) are compared to evaluate their performance in detecting a time-wise shape modification. Digital camera and Kinect sensors are used to the non-contact detection of a morphing blade able to modify its geometry according to airflow temperature variation. The comparison showed the capability of the digital image technique to provide quantitative information when a proper alignment is adopted, while the three-dimensional scanning process allows the continuous blade detection useful to quantify the shape modification. Two-dimensional and three-dimensional blade shape reconstruction processes are also discussed.

Computational fluid dynamics (CFD) is increasingly used during the design phase of turbomachinery. Reducing the cost of such computations is one of the major challenges in the industrial field. The multi-physics phenomena and the multidisciplinary interactions needed for the design of the engine components are difficult to be faced with the classical design methods. In addition, the interest of manufacturers and operators of turbomachines in the increase in performance when degradation processes occur is growing. In the aeronautical sector degradation is among the most critical issues, as it can lead to the in-flight shutdown of the engine. In a bid to tackle these big problems, new design methods based on approximation techniques have been developed. These techniques are called surrogate models and are currently the most used design methods for the aerodynamic design of aircraft engines. In this work, the assessment of a surrogate surface built for the purpose of optimizing an HPT vane in degrading conditions is performed. Using machine learning and statistical techniques, a sensitivity analysis is conducted in order to reduce the problem dimensions. The results of the sensitivity analysis are used for a study of the surrogate, with the purpose of obtaining design guidelines when deterioration effects are considered in the design phase. The main outcome of this study is a map, that outlines the best design zone defined by the combination of the most influential parameters.

The operability region of a centrifugal compressor is bounded by the low-flow (or high-pressure ratio) limit, commonly referred to as surge. The exact location of the surge line on the map can vary depending on the operating condition and, as a result, a typical Surge Avoidance Line is established at 10% to 15% above the stated flow for the theoretical surge line. The current state of the art of centrifugal compressor surge control is to utilize a global recycle valve to return flow from the discharge side of a centrifugal compressor to the suction side to increase the flow through the compressor and, thus, avoid entering the surge region. This is conventionally handled by defining a compressor surge control line that conservatively assumes that all stages must be kept out of surge at all the time. In compressors with multiple stages, the amount of energy loss is disproportion-ally large since the energy that was added in each stage is lost during system level (or global) recycling. This work proposes an internal stage-wise recycling that provides a much more controlled flow recycling to affect only those stages that may be on the verge of surge. The amount of flow needed for such a scheme will be much smaller than highly conservative global recycling approach. Also, the flow does not leave the compressor casing and therefore does not cross the pressure boundary. Compared to global recycling this inherently has less loss depending upon application and specific of control design.

Surface material loss due to erosive wear is responsible for the increased cost of maintenance and downtime in industries. Hence, hardfacing is one of the most valuable and effective techniques employed to improve the wear resistance of heavy-duty components. The present paper investigates the microstructural and erosive wear characteristics of a hypereutectic high-chromium cast iron, considering the erosion resistance, resulting from the impact of micro-sized particles, of both as-received and heat-treated conditions. Micro-sized particles involve the erosion-resistant characteristics of carbide and matrix, contemporary. Due to this, the enhancement of the matrix strength could improve the mechanical support to withstand cracking deformation and spalling. Accordingly, the effect of a destabilization heat treatment on the microstructure was firstly investigated by hardness tests, X-ray diffraction analyses, optical and scanning electron microscopy. Specifically designed erosive tests were carried out using a raw meal powder at an impingement angle of 90°. The resulting superior wear resistance of the heat-treated samples was relayed on the improved matrix microstructure: consistent with the observed eroded surfaces, the reduced matrix/carbides hardness difference of the heat-treated material is pivotal in enhancing the erosion resistance of the hardfacing. The present results contribute to a better understanding of the microstructure–property relationships concerning the erosive wear resistance.

Compressor fouling is one of the main causes of gas turbine performance degradation. Microsized particles adhere to the blade surfaces increasing the surface roughness and modifying the airfoil shape. In the present work, the contamination of the Allison 250 C18 multistage compressor engine with four sorts of micrometric dust has been provided. The tests were performed changing the relative humidity at the compressor inlet and the unit rotational speed. After each test, a photographic inspection of the internal fouled parts has been realized and the digital pictures have been analyzed employing an image processing package. The deposits build-up of stator vanes and rotor blades have been post-processed and the most affected regions of each compressor stage have been highlighted. Besides, a numerical simulation of the machine has been performed. The numerical flow field has been used to highlight the blade regions which show the most favorable conditions for particle deposition. A theoretical model has been applied to the flow field to simulate the particle deposition. The combination of the deposition model with the results of the CFD simulations gives the chance to better understand the experimentally-founded deposition patterns. Those results have been finally compared to the pictures of the patterns. The possibility to detect and measure the deposition patterns on a rotating test rig and the comparison with models and experiments gave the possibility to assess in detail the particle deposition phenomenon on a multistage axial compressor flow path.

The analysis of the performance losses of a multistage compressor concerning the air contaminant is not widespread in literature and, the mutual interactions of particle materials, air humidity, and compressor load are not well studied. The airborne micrometric particles that enter the compressor can deposit on the internal surfaces, causing the loss of performance of the machine. In this paper, several experimental tests have been carried out on a multistage compressor unit. A detailed analysis has been carried out considering soil and soot ingestion, as well as the air relative humidity (RH) (ranging from 50% RH to 80% RH) and compressor rotating velocity. Several combinations of particle diameter, material, and operating conditions have been considered. The amount of contaminant at the compressor outlet has been measured and the capture efficiency of the whole machine has been determined. Over the exposure time, the capture efficiency ranges from 0.2 to 0.6 according to the powder type and compressor inlet conditions. The capability of the compressor to collect particles changes over time as a function of the condition, even if several tested cases appear characterized by an almost constant capture efficiency trend. In addition, the performance degradation has been monitored over time and, with the reference of the particle concentration, the present experimental campaign covers about 500 operating hours of an actual installation. After a detailed evaluation of experimental uncertainty, the performance losses due to particle contamination have been assessed. The losses in the compressor performance have been estimated by means of the pressure ratio of the axial stages. The maximum degradation has been estimated equal to 0.53%/h for the compressor pressure ratio. Soot particles appear stickier, especially in the presence of higher humidity and represent the most detrimental operating conditions for the compressor unit.

Rotor-stator interaction in turbomachinery is one of the most challenging fields in Computational Fluid Dynamics (CFD) and, in this regard, several studies can be found in the literature, concerning unsteady coupling of successive blade rows. By the way, the use of mixing plane for steady multistage calculations has been common for many years and, even though this technique is at present consolidated, it still represents a challenge when one has to cope with multiphase flow problems. In recent years, the growing capabilities of open-source codes to deal with multistage simulations offer new opportunities in the research community, since direct access to implementation details is provided. Currently, only a few particle-interface interaction models are reported in the literature, hence strong limitations in particle-laden flow simulations in multistage turbomachinery arises. In order to fill up this lack of models, the authors propose a sensitivity analysis for particle-mixing plane interaction. To compare the new methodologies, efforts have been done to adapt foam-extend interface treatment to Lagrangian tracking. The component analysed in this work is the first high-pressure stage of the Energy-Efficient Engine axial turbine. The results of this sensitivity analysis is compared to high-fidelity results obtained by a transient simulation based on the sliding mesh approach. Four different averaging techniques have been proposed, based on different easiness of implementation and physical soundness, and their performance has been assessed.

Fouling represents a major problem for Gas Turbines (GTs) in both heavy-duty and aero-propulsion applications. Solid particles entering the engine can stick to the internal surfaces and form deposits. Components' lifetime and performance can dramatically vary as a consequence of this phenomenon. These effects impact the whole engine in terms of residual life, operating stability, and maintenance costs. In the High-Pressure Turbine (HPT), in particular, the high temperatures soft the particles and promote their adhesion, especially in the short term. Unfortunately, predicting the GT response to this detrimental issue is still an open problem for scientists. Furthermore, the stochastic variations of the components operating conditions increase the uncertainty of the forecasting results. In this work, a strategy to predict the effects of turbine fouling on the whole engine is proposed. A stationary Gas Path Analysis (GPA) has been performed for this scope to predict the GT health parameters. Their alteration as a consequence of fouling has been evaluated by scaling the turbine map. The scaling factor has been found by performing Computational Fluid Dynamic (CFD) simulations of a HPT nozzle with particle injection. Being its operating conditions strongly uncertain, a stochastic analysis has been conducted. The uncertainty sources considered are the circumferential hot core location and the turbulence level at the inlet. The study enables to build of confidence intervals on the GT health parameters predictions and represents a step forward towards a robust forecasting tool.

The interaction between gas turbines and airborne particles determines detrimental effects on the performance, efficiency, and reliability of the power unit. When it is possible, the interaction is reduced by the use of inlet separators and filtration systems. In an aero engine, these barriers are difficult to implement, and only bigger particles (usually greater than 10 μm) are separated from the airflow. Small units, especially those equips helicopters, are usually affected by fouling issues, especially when the aircraft is employed in harsh environments such as firefighting and rescue activities. To recover this contamination, the unit is washed after the mission by ground operations to restore the unit performance by removing the deposits. This operation occurs during a sub-idle unit operation, and the washing process has to be effective when the engine operates in this off-design condition. In this paper, the evaluation of the washing performance during a sub-idle unit operation is carried out. The compressor unit is a multistage axial compressor that equips the Allison 250-C18 engine. The washing operation was performed by water, and a sensitivity analysis is carried out to discover the capability of water droplets to remove the contaminants. The experimental analysis involves the contamination of the unit by micro-sized soot particles and a washing operation by micro-sized water droplets. These experimental results are compared to numerical simulations to discover the effects of the washing operation on a small power unit during sub-idle operating conditions. The off-design regime imposes a specific evaluation of the proper setup of the washing strategy: flow separations involve wider regions in the compressor unit, and the removal capability is strongly related to the droplet path through the stages. The results show how in the off-design washing operation, the droplet diameter has greater importance than the water flow rate for reducing the deposits over the compressor stages.

Gas turbine particle ingestion may lead to the deposition of contaminants in the compressor section, inducing the performance losses of the whole engine. The economic losses derived from this issue push great interest in the investigation of such a phenomenon from a numerical and experimental standpoint. This paper describes a quantitative approach to predict particle deposition on the vanes of an axial compressor starting from the flow field obtained employing CFD simulations. The results are then compared to the experiments performed on the Allison 250 C18 compressor unit subject to particle ingestion under controlled conditions. The results derived from the experimental and numerical investigations are presented, providing insight into the mass deposited on the vanes and the corresponding zones most affected by the particle deposition issue. The numerical model showed good agreement in the estimation of the predicted values of the deposited mass and the corresponding patterns through the compressor stages. The low-complexity approach proposed here, helps the designer to predict the contamination of the stationary rows starting from a simple set of single-phase numerical results. Furthermore, with the implementation of this approach into the design path, the designer could reduce the impact of fouling, looking at the effects of their solutions under the fouling-reduction light.

Heavy-duty fans are frequently employed in industrial processes that involve the operation of contaminated gases. Particle-laden flows may cause erosion issues, generating several drawbacks such as unbalanced load, vibrations and structural damage responsible for performance degradation and early failure. In this paper, the erosion behavior of a large-sized centrifugal fan employed in clinker production is studied by numerical simulation. Based on preliminary numerical results for the undamaged fan configuration and on-field erosion detections, the geometry damage effects due to the erosion process are analyzed. The severe erosive conditions under which these machines operate determine a progressive reduction in wall thickness of specific fan zones, which may finally result in the formation of holes. This, in turn, makes the internal flow field changing, affecting contaminant trajectories and impact characteristics. CFD predictions show that erosion-induced damage on the fan inlet cone causes a distortion of the velocity profile immediately upstream of the impeller, which influences the impeller flow. Simultaneously, the erosion process changes, leading to a modification of particle impact areas, impact kinematic characteristics and erosion intensity. This investigation focuses on the importance of erosion predictions for maintenance planning and scheduling and demonstrates how localized damage could be responsible for larger damage, involving the structural integrity of the installation.

Suspended micrometric particles are always present in the air swallowed by gas turbines. These solid particles can overpass the filters of heavy-duty gas turbines and deposit onto the internal surfaces of the compressor, leading to the overtime reduction of the machine performances, and, as a result, to the fuel consumption augmentation. A widely employed method to slow down the engine degradation is to wash the engine frequently. Over the years, the washing techniques have been continuously improved in order to reach the best compromise between low fluid consumption and high washing capabilities. In this work, an experimental campaign has been carried out to estimate the washing effectiveness on a multistage axial-flow compressor fouled with micrometric soot particles. The cleaning fluids tested in the present work were demineralized water and two cleaners provided by ZOK International Group ltd: a commercial cleaner available on the market (ZOK 27), and a new, under development, environmentally-sensitive formula. The fluids have been tested employing three droplet size distributions (with mean diameters of 20 μm, 50 μm, and 100 μm). The washing effectiveness has been assessed through image post-processing techniques by analyzing the pictures of the stator vanes and rotor blades taken in fouled and washed conditions. From the present investigation, two results arise. The finest droplets show a greater capability to remove soot deposits showing how, when the washing operation takes place during quasi-idle operating condition, the turbulent-driven motion spread smaller particles on a wider blade region. The second results is the demonstration how a environmentally-sensitive chemical formula allows the obtainment of good results in terms removal capability for the same amount of product. This finding could help the plant manager to operate the gas turbine with less constraints in terms of cost and rules.

Particle ingestion is a major concern for the operation of gas turbines. In the case of an aircraft, particle dispersed in the air ingested by the engine can threaten flight safety. Swallowed particles can erode or stick to aerodynamic surfaces. Both the occurrences translate in a reduction of performance due to variation in shape and in roughness of the aerodynamic surfaces. This work is devoted to the analysis of fouling, i.e. the deposition of particles over time. By observing that the deposition pattern is strongly influenced by the flow field in the nearby of the walls, the central idea of this work is to employ Active Flow Control (AFC) to mitigate fouling when emergency conditions are met by the aircraft. The proposed system will inject air bled from compressor discharge in front of the critical locations where fouling is supposed to occur. The present work aspires to lay the foundations for the development of such an AFC device, by focusing on the modified aerodynamics consequent to the introduction of the transverse jet. The potential of this device is evaluated quantitatively using CFD simulations. An energy-based sticking model, coupled with a mesh-morphing solver, is used to track the airfoil deposition thickness evolution in time. The work is two-fold: first, the dynamics of the interaction between flow structures and particle transport is addressed. Second, the attention is posed on correlating fouling pattern variation to the modified aerodynamics of the vane consequent to the introduction of the device. Three design concepts are investigated on the 3D test case geometry of an HPT NGV cascade. The counter-rotating vortex pair (CVP) is detected as the main responsible for jet-particle interaction. Finally, the jet impact on aerodynamic performance is also assessed.

Solid particles dispersed in the air represent a real hazard for gas turbines in both heavy-duty and aero-propulsion applications. Particles impacting the inner surfaces of the machine can stick to such surfaces or erode them. The geometry modifications related to such occurrences entail aerodynamic surface degradation. As the severity of the problem increases, the performance reduction can increase, demanding engine shut-down and off-line washing or refurbishing. Numerical modeling is one of the techniques employed for understanding and predicting the particle deposition problem. Multiple numerical studies investigated the influences of these phenomena. However, the basic challenge of modeling the particle wall-interaction with sufficient accuracy remains. In this work, a cascade exposed to a particle-laden flow is numerically investigated. The numerical analysis is devoted to investigate a test rig designed to be representative of aircraft engine compressor blading and exposed to an accelerated deposition process. Firstly, the relation between flow structures and particle trajectory is investigated. Then, a computational analysis is carried out considering different particle-wall interaction models of varying complexity levels (e.g. pure adhesion, presence of humidity or the influence of surface roughness) in order to identify advantages and disadvantages of each model and their ability to include different phenomena. The results are discussed by taking into account measurement data from a cascade test rig. The deviation between experimental data and the investigated model is evaluated, showing the increasing reliability that derives from successive model refinement. This work is proposed to be a test case for the numerical analyses of compressor fouling applications and a first step towards a general physical based particle-wall interaction model.

The soil layer is a common issue for energy systems as solar panels or prime mover and driven turbomachines. This phenomenon is usually known as fouling, and it consists of a microscopic layer (usually lower than 1 mm) that wraps the surface of these machines and devices. The presence of a deposited layer determines the modification of the surface characteristics as transparency or roughness with the consequent performance and efficiency reduction. In the present paper, a detailed investigation is carried out on seven measurement methods used for estimating the sand layer morphology and thickness. Each method has been applied for measuring similar soil layers, giving the possibility to compare the methodologies and show the capability of each method to obtain different information from the same specimen. Several guidelines and suggestions about technology, cost, and usefulness of each method are also included.

Fluids processed by the machinery involved in ORC cycles undergo several transformations among which the expansion in positive displacement machines. The fluid path inside this component is very complicated and gaps play a crucial role. Due to the importance of this technical detail, gap design and optimization is a decisive step in achieving an high efficiency both of the expander and the whole cycle. In this work the fluid dynamics of several fluids commonly used in ORC cycles is investigated. Particularly, their behaviour during the expansion through the gap in operation is numerically investigated. The effects of the gap formation and its evolution on the processed fluid is studied thanks to a dynamic mesh approach. A typical application has been considered in this work: the variable gap between the fixed and mobile spirals of a scroll expander is analysed. The relative motion and in turn, the variation of the gaps during the machine operation, implies the use of particular numerical strategies able to well represent these localized geometrical features. On the top of that, the modelling of the processed fluids as a real gas determines an extra effort in the way of representing the actual behavior involved in the positive displacement machine operation. This analysis shows the local fluid dynamic phenomena due to the variable clearances. R134a and its replacements R152a and R1234ze(E), fluids widespread in the ORC cycles, are used in this work. The fluids are investigated under the same conditions and effects like separation and shock wave are highlighted. This analysis allows the comprehension of how local phenomena could affect the overall machine operation and efficiency. Gaps are the responsible of the volumetric efficiency of the machine and, coupled with (i) time-variable geometry modification, (ii) relative velocities and (iii) fluid characteristics characterize the global ORC system performance.

Micro-ORC systems are characterized by low efficiency values, but at the same time could be used as energy recovery systems in domestic applications for which reliability and low noise level represent the biggest challenges. In this paper, an integrated Reverse Engineering (RE)-Computational Fluid Dynamics (CFD) methodology is applied in order to study the adaptation of a commercial scroll compressor to be used as an expander in a micro-ORC system. The analyses reported in this paper consist of: (i) the acquisition of the 5-kW oil-free scroll expander through a RE procedure and its CAD reconstruction, (ii) the set-up of fully three-dimensional transient simulations with the Chimera strategy using the Siemens PLM software, (iii) the validation of the computational analysis by means of experimental tests and finally, (iv) the analysis of the geometry-flow features like flank and axial gaps, coupled with the analysis of the scroll volumetric efficiency and overall performance. Chimera strategy is able to move the computational grid at each time step in order to accommodate the shape and size changes of the gas pockets. The scroll characterization was carried out using both experimental and numerical tests. Six different rotational velocities in the range of (400 – 2400) rpm with a fixed pressure level (7.5 bar) were tested for validating the numerical model using air as a working fluid. The numerical model was then used to calculate the scroll expander performance operating in an existing ORC system with R134a as working fluid.

In recent years, computational fluid dynamics (CFD) has been applied for the design and analysis of positive displacement machines (both compressors and expanders) with numerous challenges due to the dynamics of the compression (or expansion) process and deforming working chambers. The relative motion and in turn, the variation of the gaps during machine operation implies several obstacles for the implementation of reliable CFD models. The majority of the studies reported in literature focused on scroll, twin screw and reciprocating machines. The limitation of the developed methodologies to be applied directly to positive displacement machines with more complex meshing such as that of single-screw has been highlighted in literature. In this paper, a single screw expander is studied by means of (i) a moving mesh technique (dynamic mesh in the Key Frame Remeshing approach) and (ii) a real gas model of a R134a (Peng-Robinson model) implemented in OpenFOAM. On the top of that, all the possible techniques that come with the software are investigated in their application to single screw. An useful review of the state of the art CFD with open-source software (OpenFOAM-v1606+ and foam-extend4.0) is therefore carried out. The reliability of CFD model represents indeed the first step on which the design process and further optimization will be based. (C) 2017 The Authors. Published by Elsevier Ltd.

Centrifugal pumps are used in many applications in which non-Newtonian fluids are involved: food processing industry, pharmaceutical and oil/gas applications. In addition to pressure and temperature, the viscosity of a non-Newtonian fluid depends on the shear rate and usually is several orders of magnitude higher than water. High values of viscosity cause a derating of pump performance with respect to water. Nowadays, pumping and mixing non-Newtonian fluids is a matter of increasing interest, but there is still lack of a detailed analysis of the fluid-dynamic phenomena occurring within these machines. A specific design process should take into account these effects in order to define the proper pump geometry, able to operate with non-Newtonian fluids with specific characteristics. Only few approaches are available for correcting the pump performance based on the Hydraulic Institute method. In this work, an experimental and numerical campaign is presented for a semi–open impeller centrifugal pump elaborating non-Newtonian fluids. An on-purpose test bench was built and used to investigate the influence on pump performance of three different non-Newtonian fluids. Each pump performance test was accompanied by the rheological characterization of the fluid, in order to detect modifications of the rheological phenomena and allow a proper Computation Fluid Dynamics (CFD) modeling. The performance of the machine handling both Newtonian and non-Newtonian fluids are highlighted in relation with the internal flow field.