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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.

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.

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.

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.

In this paper, a three-dimensional computational fluid dynamics (CFD) simulation is carried out to investigate the performance of a single screw expander by linking its behavior with the dynamic features of the flow field. To study this aspect and other phenomena that can affect expander operation in an actual Organic Rankine Cycle (ORC) system, in this work an approach based on the dynamic analysis of the machine operation with the use of both the overset mesh strategy and real gas modeling is showed. The expansion process is investigated to analyze both flow characteristics and machine performance during on-design operating conditions. The model aims to investigate the SSE operation without the effects of the sealing process of the lubricant oil to highlight the effects of the fluid expansion on the SSE operation. Pressure and flow patterns which resulted from this analysis depend on the design characteristics of the machine, operating conditions, and working fluid properties. The resulting output torque and isentropic efficiency are coherent with the simulated operating conditions.

In this work, the authors present a robust and integrated procedure for the design of multi-stage gear pumps to be used in dry sump system applications. Based on the target delivery flow rate, rotational speed and fluid properties, the developed iterative method enables to directly obtain the geometrical features and the working parameters of the pump components, such as gearpair specifics, shaft and journal bearing dimensions, clearance values. The methodology is then applied to a case study in order to highlight its features and detail the achievable outcomes. Quality of the results is assessed by means of a CFD analysis, demonstrating the capability to obtain the expected volumetric efficiency.

This paper addresses the problem of computational fluid dynamics (CFD) modeling of gaseous cavitation (GC) in lubricating positive-displacement pumps (PDPs). It is important for designers and analysts to predict the dynamic features of air release/dissolution processes which characterize this phenomenon, along with their effects on filling capability and noise-vibration-harshness behavior of the machine. The focus is on the empirical tuning of the commercial homogeneous-flow cavitation model known as dissolved gas model (DGM). Considering an automotive case study of a balanced vane pump (BVP), the effects of air modeling on numerical predictions of discharge flow/pressure ripple and volumetric efficiency have been studied. The tuning time parameters of the model have been correlated to the machine Reynolds number as part of a simplified theoretical background based on dimensional analysis. Considering experimental data at different operating conditions, the tuned model has shown a good capacity in predicting the pressure ripple and the flowrate at the discharge of the pump.

Positive displacement machines (e.g. scroll, twin screw, reciprocating, etc.) are proven to be suitable as expanders for organic Rankine cycle (ORC) applications, especially in the medium to low power range. However, in order to increase their performance, detailed simulation models are required to optimize the design and reduce the internal losses. 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 expansion (or compression) process and deforming working chambers. The majority of the studies reported in literature focused on scroll, twin screw and reciprocating machines. Furthermore, the limitation of such methodologies to be applied directly to complex multi-rotor machines has been highlighted in literature. In this paper, a single screw expander (SSE) is used as benchmark to evaluate the applicability of different grid generation methodologies (dynamic remeshing and Chimera strategy overlapping grid), in terms of computational resources required, accuracy of the results and limitations. Although, the low-order models have been applied to single screw machines, there is still a lack of CFD analyses due to the particular complexity of the machine geometry and of its working principle. The calculations have been performed with air to reduce the complexity of the problem. to the main results are two folds: (i) the assessment of a numerical strategy with respect to the most critical parameters of a dynamic mesh-based simulation and (ii) the comparison of the pressure field and internal flow features obtained by using different numerical approaches.

Nowadays, the evaluation of the transport and thermodynamic properties in computational fluid dynamics (CFD) analysis is based on common real gas equations (such as Redlich–Kwong and Peng–Robinson equations of state) and polynomial models. Such quantities are not always accurate: very large pressure ranges, working conditions close to the critical point or phase change could introduce an error during the computation of the thermophysical properties of interest. Moreover, the computational effort of numerical simulations is strongly affected by the evaluation of such properties. In light of these considerations, and to extend the modeling capabilities of CFD software suites, a fluid thermophysical property library can be included in the computation of the quantities required for the solution of the flow field. The focus of this work is the coupling of an open source CFD tool (OpenFOAM) with the open source CoolProp library. The proposed wrapper is intended to provide a connection between the most popular open-source thermophysical library and one of the most used open-source CFD software. CoolFOAM extends the thermophysical modeling possibilities of OpenFOAM. The formal implementation of this library follows the coding standards of the CFD suite.

The adoption of positive displacement machines as expanders in Organic Rankine Cycles (ORCs) is increasingly common, especially in the low to medium power range. At the same time, these devices often serve as compressor in Vapor-Compression Refrigeration Systems. In both cases, the application of Computation Fluid Dynamics (CFD) to optimize such machines has become an integrated tool in the design process. As a consequence, several challenges associated with the numerical simulation have to be taken into account. For example, the modeling of the gap represents a challenge for the stability of the numerical analysis. The dynamic of the process, combined with deformations of the clearances and of the working chamber has to be considered with extra care. To raise the efficiency of the machine, oil is typically injected. Its numerical modeling imply an extra challenge in the simulation of the actual operation of the machine. The present work is mainly focused on the multi-phase nature of the flow, with a particular analysis of the lubricant oil injected. In this work, a two-lobe Roots blower operated as expander has been simulated with the open-source software OpenFOAM-v1812, using the SCORG-V5.2.2. This analysis highlights the areas that are affected the most by the oil presence in order to highlight the sealing effect it provides

The development of a zero-dimensional model for analysing pressure phenomena in multiple stage external gear pumps is addressed in the present work. The tandem pump is composed of two coaxial stages: the high pressure one, made by spur gears, and the low pressure one, made by helical gears. The two stages have common shafts and a common case. The oil pressure course around the gearpair, as well as the suction/delivery pressure ripple, is estimated for both stages. Attention is focused on the description of the modelling approach: an original method is developed to model the helical gears and their effects on the determination of the geometrical parameters. The lumped parameter (LP) model takes advantage of a Computational Fluid Dynamic (CFD) model applied to different pump regions in order to estimate several internal flow features. Measured delivery pressure ripple and volumetric efficiency are used to evaluate the model reliability under different working conditions.

Several production processes involve the use of turbomachinery for the transport of gases with high concentrations of solid particles. Centrifugal fans employed in clinker production operate under severe erosive conditions. To limit the erosive wear of specific fan zones, wear-resistant plates are used. This paper presents a numerical investigation of the erosion behavior of a large-sized centrifugal fan operating in a cement factory. A contaminant characterization is carried out to define particle shape, size distribution and physical characteristics (i.e. density) on which the particle model is based. In addition, the surface analysis and microstructural characterization of the weld-deposited hardfacing alloy provide the wear-resistant coating features. Particles are tracked with a Lagrangian approach on the instantaneous flow fields corresponding to different relative impeller-to-volute positions. The particle impact angle is found to have a significant influence on the erosion of fan surfaces. CFD predictions are in close agreement with on-field erosion detections.

Micro-ORC systems are usually equipped with positive displacement machines such as expanders and pumps. The pumping system has to guarantee the mass flow rate and allows a pressure rise from the condensation to the evaporation pressure values. In addition, the pumping system supplies the organic fluid, characterized by pressure and temperature very close to the saturation. In this work, a CFD approach is developed to analyze from a novel point of view the behavior of the pumping system of a regenerative lab-scale micro-ORC system. In fact, starting from the liquid receiver, the entire flow path, up to the inlet section of the evaporator, has been numerically simulated (including the Coriolis flow meter installed between the receiver and the gear pump). A fluid dynamic analysis has been carried out by means of a transient simulation with a mesh morphing strategy in order to analyze the transient phenomena and the effects of pump operation. The analysis has shown how the accuracy of the mass flow rate measurement could be affected by the pump operation being installed in the same circuit branch. In addition, the results have shown how the cavitation phenomenon affects the pump and the ORC system operation compared to control system actions.

Centrifugal pumps change their performance with respect to water when processing non-Newtonian fluids. Many aspects about pumping of non-Newtonian fluids remain to be clarified due to complexity of the matter and the scarcity of investigations. In addition to experimental tests, in recent years some CFD fluid dynamics simulations have been realized to analyze the performance of centrifugal pumps with non-Newtonian fluids. Knowledge of rheology is required to correctly simulate the fluid inside the pump and predict the performance. The aim of this work is to emphasize the criticalities in the simulation of centrifugal pumps with non-Newtonian fluids, since, starting from the same rheological data, can be deduced different rheological laws, however reliable, that produce different effects on the simulations. In this paper, the performances of a model pump were measured experimentally with pear juice and accompanied by the rheological characterization of the fluid. Subsequently, the pump was simulated using five different rheology laws, all fitted to the same experimental rheogram, that differ from each other in predicting viscosity out of shear rate range experimentally measured. The pump performances were affected by the different rheology implemented. The simulations showed that the shear rates developed inside the pump are much higher than those measured with the rheometer. Consequently is necessary to achieve higher shear rates in the experimental rheogram to make sure to correctly model the rheology for shear rates values typically present in the pump.

The push for having more reliable and efficient positive displacement machines (both compressors and expanders) for vapor compression and power generation (e.g., ORCs) applications has moved researchers to an always more spread employment of computational fluid dynamics (CFD). In particular, twin screw compressors, because of their high efficiency compared to other compressor types, have received interest over the last years. The numerical analysis of such machines is challenging: the deforming working chambers are very difficult to be correctly replicated. The relative motion of the rotors and the variation of the gaps during machine operation are few of the major difficulties in implementing reliable CFD models. A custom mesh generation algorithm is therefore often required for sumulating the machine operation.\ud \ud In this work, SCORG-V5.2.2 was used to generate the meshes of the deforming domain around rotating parts of the machines. The open-source software OpenFOAM-v1606+ is then employed to compute the flow field associated with the operation of the twin screw. The coupling of the two tools has been carried out in this work, applying the methodology to a twin screw machine.

In this paper an integrated Reverse Engineering – Computational Fluid Dynamics (RE/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 analysis consists of the acquisition of a real scroll compressor geometry through an RE procedure, the transient numerical simulation of the scroll in compression and expansion mode and the analysis of the performance in terms of pressure and mass flow rate profiles and volumetric efficiency. In order to set up the numerical strategy, a literature test case is used to perform a sensitivity analysis. The results obtained are: (i) the assessment of a numerical strategy with respect to the most critical parameters of a dynamic mesh-based simulation; (ii) the set up and validation of a Reverse Engineering-based numerical procedure; (iii) the evidence of the different fluid dynamic behavior of the scroll machine in compressor mode compared to the expander mode and (iv) the strong relationship between the volumetric efficiency of the scroll machine and the magnitude of the flank gap.

Solid particle ingestion is one of the principal degradation mechanisms in the compressor and turbine sections of gas turbines. In particular, in industrial applications, the microparticles not captured by the air filtration system can cause deposits on blading and, consequently, result in a decrease in compressor performance. In the literature, there are some studies related to the fouling phenomena in transonic compressors, but in industrial applications (heavy-duty compressors, pump stations, etc.), the subsonic compressors are widespread. It is highly important for the manufacturer to gather information about the fouling phenomenon related to this type of compressor. This paper presents three-dimensional (3D) numerical simulations of the microparticle ingestion (0.15–1.50 μm) in a multistage (i.e., eight stage) subsonic axial compressor, carried out by means of a commercial computational fluid dynamic (CFD) code. Particles of this size can follow the main air flow with relatively little slip, while being impacted by flow turbulence. It is of great interest to the industry to determine which zones of the compressor blades are impacted by these small particles. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separately from the continuous phase. The adopted computational strategy allows the evaluation of particle deposition in a multistage axial compressor thanks to the use of a mixing plane approach to model the rotor/stator interaction. The compressor numerical model and the discrete phase model are set up and validated against the experimental and numerical data available in the literature. The number of particles and sizes is specified in order to perform a quantitative analysis of the particle impacts on the blade surface. The blade zones affected by particle impacts and the kinematic characteristics (velocity and angle) of the impact of micrometric and submicrometric particles with the blade surface are shown. Both blade zones affected by particle impact and deposition are analyzed. The particle deposition is established by using the quantity called sticking probability (SP), adopted from the literature. The SP links the kinematic characteristics of particle impact on the blade with the fouling phenomenon. The results show that microparticles tend to follow the flow by impacting on the compressor blades at full span. The suction side (SS) of the blade is only affected by the impacts of the smallest particles. Particular fluid dynamic phenomena, such as corner separations and clearance vortices, strongly influence the impact location of the particles. The impact and deposition trends decrease according to the stages. The front stages appear more affected by particle impact and deposition than the rear ones.

The concept of smart morphing blades, which can control themselves to reduce or eliminate the need for active control systems, is a highly attractive solution in blade technology. In this paper, an innovative passive control system based on Shape Memory Alloys (SMAs) is proposed. On the basis of previous thermal and shape characterization of a single morphing blade for a heavy-duty automotive cooling axial fan, this study deals with the numerical analysis of the aerodynamic loads acting on the fan. By coupling computational fluid dynamics and finite element method approaches, it is possible to analyze the actual blade shape resulting from both the aerodynamic and centrifugal loads. The numerical results indicate that the polymeric blade structure ensures proper resistance and enables shape variation due to the action of the SMA strips.

The spread of the organic rankine cycle applications has driven researchers and companies to focus on the improvement of their performance. In small to medium-sized plants, the expander is the component that has typically attracted the most attention. One of the most used types of machine in this scenario is the scroll. Among the other methods, numerical analyses have been increasingly exploited for the investigation of the machine’s behaviour. Nonetheless, there are major challenges for the successful application of computational fluid dynamics (CFD) to scrolls. Specifically, the dynamic mesh treatment required to capture the movement of working chambers and the nature of the expanding fluids require special care. In this work, a mesh generator for scroll machines is presented. Given few inputs, the software described provides the mesh and the nodal positions required for the evolution of the motion in a predefined mesh motion approach. The mesh generator is developed ad hoc for the coupling with the open-source CFD suite OpenFOAM. A full analysis is then carried out on a reverse-engineered commercial machine, including the refrigerant properties calculations via CoolProp. It is demonstrated that the proposed methodology allows for a fast simulation and achieves a good agreement with respect to former analyses.

Over the last decade, Computational Fluid Dynamics (CFD) has been increasingly applied for the design and analysis of positive displacement machines employed in vapor compression and power generation applications. Particularly, single-screw and twin-screw machines have received attention from the researchers, leading to the development and application of increasingly efficient techniques for their numerical simulation. Modeling the operation of such machines including the dynamics of the compression (or expansion) process and the deforming working chambers is particularly challenging. The relative motion of the rotors and the variation of the gaps during machine operation are a few of the major numerical challenges towards the implementation of reliable CFD models. Moreover, evaluating the thermophysical properties of real gases represents an additional challenge to be addressed. Special care must be given to defining equation of states or generating tables and computing the thermodynamic properties. Among several CFD suite available, the open-source OpenFOAM tool OpenFOAM, is regarded as a reliable and accurate software for carrying out CFD analyses. In this paper, the dynamic meshing techniques available within the software as well as new libraries implemented for expanding the functionalities of the software are presented. The simulation of both a single-screw and a twin-screw machine is described and results are discussed. Specifically, for the single-screw expander case, the geometry will be released as open-access for the entire community. Besides, the real gas modeling possibilities implemented in the software will be described and the CoolProp thermophysical library integration will be presented.

In this paper, a numerical method for the design of free opening hoods in industrial and domestic applications is presented. The method is based on a CFD (Computational Fluid Dynamics) formulation for the capturing velocity assessment in capturing hoods which account for geometrical and viscous effects. Different hoods, which differ in shape (square and rectangular) and size, are created and their velocity field determined numerically. A comparison between the obtained numerical results and results obtained from empirical formula found in literature are presented and the discrepancy between them highlighted. Then, starting from the numerical results, a new equation, which takes into account viscous effects, is proposed, together with its range of applicability and its level of confidence. The suggested equation is simple in nature and it can be user friendly for the designer, in order to predict the air velocity in front of a capturing hood, and therefore to correctly and efficiently design the ventilation system.

In this paper, the most common and experienced source of loss for a gas turbine, i.e. compressor fouling, is modeled and analyzed by means of a three-dimensional numerical approach. In particular, CFD simulations of fouling affecting an axial compressor stage are carried out. To do this, the NASA Stage 37 is considered as compressor model for numerical investigation. The numerical model, validated against experimental data available from literature, is used to simulate the occurrence of fouling by imposing different combinations of added thickness and surface roughness. The results highlighted that the main effect of fouling is the decrease in the flow rate, even if a decrease in the stage compression ratio was also noticed. Therefore, different non-uniform combinations of surface roughness levels on rotor and stator blades were imposed. Simulations showed that the greatest effect on performance is attributable to the rotor, and in particular, by analyzing the effect of roughening pressure surface and suction surface separately, to its suction surface. Moreover, a rotor roughness non-uniformity is considered also in spanwise direction, which causes a significant work redistribution.

Centrifugal pumps are used in many applications in which non-Newtonian fluids are involved, such as food industry and oil&gas applications, producing the pump performance derating. In order to give an overview of pros, cons of the different analytical approaches for pump performance derating a literature review on the most significant advances in this topic will be carried out. Moreover to deepen the knowledge about the internal flow and rheological behavior inside the centrifugal pumps working with non-Newtonian fluids, a detailed CFD analysis of two different pumps will be carried out. The analysis will be focus on the apparent viscosity correction involved in the performance derating with analytical methods and the effects of different types of fluid. Moreover the comparison of the results with two pumps with very different typology, field of application, and dimensions will help to generalize the meaning of the analysis.

In this paper experimental and CFD numerical analyses of an air-forced convection rotary bread-baking oven are presented. A particular experimental methodology for the thermo-fluid dynamic characterization of the rotary oven has been adopted. The purpose-designed on-board experimental apparatus represents a useful industrial test bench and, at the same time, can be used to collect data for the final user. The experimental apparatus can operate in stand-alone mode and under the actual cavity conditions in terms of temperature and humidity. A fully 3D numerical CFD model of the rotary bread-baking oven is proposed. By using the numerical model, validated by the experimental results, it is possible to highlight the airflow pattern inside the oven cavity and understand how the loaves change the airflow pattern inside the cooking chamber. Through the data collected using the experimental tests and CFD numerical simulations, some improvements in terms of airflow management inside the cooking chamber can be made. Through these improvements, the final user (as for instance bakers, either industrial or artisanal) can exploit several advantages in terms of energy saving and reduction of non-conformal baked products in relation with the localization of the recirculation zones and zones with higher velocity inside the oven cavity.

The quality and purity of the air entering a gas turbine is a significant factor influencing its performance and life. Foulants in the ppm range which are not captured by the air filtration system usually cause deposits on blading, which results in a severe drop in the performance of the compressor. Through the interdisciplinary approach proposed in this paper, it is possible to determine the evolution of the fouling phenomenon through the integration of studies in different research fields: (i) numerical simulation, (ii) power plant characteristics and (iii) particle-adhesion characteristics. In fact, the size of the particles, their concentrations and adhesion ability, and filtration efficiency represent the major contributors to performing a realistic quantitative analysis of fouling phenomena in an axial compressor. The aim of this work is the estimation of the actual deposits on the blade surface in terms of location and quantity. This study combines the impact/adhesion characteristic of the particles obtained through a CFD and the real size distribution of the contaminants in the air swallowed by the compressor. The blade zones affected by deposits are clearly reported by using easy-to-use contaminant maps realized on the blade surface, in terms of contaminant mass. The analysis has shown that particular fluid-dynamic phenomena and airfoil shape influence the pattern deposition. The use of a filtration system decreases the contamination of the blade and the charge level of the electrostatic seems to be less important than the air contaminant concentration. From these analyses, some guidelines for proper installation and management of the power plant (in terms of filtration systems and washing strategies) can be drawn up. Characterization of the air contaminants in the power plant location represents the most important step in improving the management of the gas turbine power plant.

Solid particle ingestion is one of the principal degradation mechanisms in the compressor and turbine sections of gas turbines. In particular, in industrial applications, the micro-particles not captured by the air filtration system can cause deposits on blading and, consequently, result in a performance drop of the compressor. This paper presents three-dimensional numerical simulations of the micro-particle ingestion (0.15 μm – 1.50 μm) in a transonic axial compressor stage, carried out by means of a commercial computational fluid dynamic code. Particles of this size can follow the main air flow with relatively little slip, while being impacted by flow turbulence. It is of great interest to the industry to determine which zones of the compressor blades are impacted by these small particles. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separately from the continuous phase. A particular computational strategy is adopted in order to take into account the presence of two subsequent annular cascades (rotor and stator) in the case of particle ingestion. The proposed strategy allows the evaluation of particle deposition in an axial compressor stage thanks to its capability of accounting for the rotor/stator interaction. NASA Stage 37 is considered as a case study for the numerical investigation. The compressor stage numerical model and the discrete phase model are set up and validated against the experimental and numerical data available in literature. The blade zones affected by particle impact and the kinematic characteristics of the impact of micrometric and sub-micrometric particles with the blade surface are shown. Both blade zones interested by particle impact and deposition are analyzed. The particle deposition is established by using the quantity called sticking probability, adopted from literature. The sticking probability links the kinematic characteristics of particle impact on the blade with fouling phenomenon. The results show that micro-particles tend to follow the flow by impacting at full span with a higher impact concentration on the pressure side of rotor blade and stator vane. Both rotor blade and stator vane suction side are affected only by the impact of smaller particles (up to 1 μm). Particular fluid dynamic phenomena, such as separation, shock waves and tip leakage vortex, strongly influence the impact location of the particles. The kinematic analysis shows a high tendency of particle adhesion on the suction side of the rotor blade, especially for particles with a diameter equal to 0.15 μm.

Biomass gasification is regarded as one of the most promising technology in the renewable energy field. The outcome of such operation, i.e. the synfuel, can be exploited in several ways, for example powering engines and turbines, and is considered more flexible than the biomass itself. For this reason, a careful analysis of the gasification performance is of paramount importance for the optimization of the process. One of the techniques that can be used for such a purpose, is the numerical analysis. CFD is indeed a tool that can be of great help in the design and study of the operation of the gasifier, allowing for an accurate prediction of the operating parameters. In this work, a downdraft gasifier is considered, and the biomass is made of wood chip. The present analysis is devoted to build the numerical model and simulate all the reactions that happen inside an actual gasifier, considering the drying of the wood chip, heating, pyrolysis, and combustion. Good match with experimental results is found, making the numerical model here presented a reliable virtual test bench where investigating the effects of variation in the working parameters.

In a traditional automotive cooling system, energy optimization could be achieved by controlling the engine temperature by means of several sensors placed inside the cooling circuit. Nevertheless, in some cases the increasing use of a great number of sensor devices makes the control system too bulky, expensive and not sufficiently robust for the intended application. This paper presents the development of a heavy-duty automotive cooling axial fan with morphing blades activated by Shape Memory Alloy (SMA) strips that work as actuator elements in the polymeric blade structure. The application of smart materials to compact, high-energy density devices as well as the development of modeling and control systems has been of great interest during the last decade. SMAs are frequently combined within monolithic or composite host materials to produce adaptive structures whose properties could be tuned in response to external stimuli. The blade was designed to achieve the activation of the strips (purposely thermo-mechanically treated) by means of an air stream flow. With the aim of studying the morphing capability of the adaptive structure together with the recovery behavior of the NiTi strips, four different polymeric compounds have been compared in a specifically-designed wind tunnel. Digital image analysis techniques have been performed to quantitatively analyze the blade deflections and to evaluate the most suitable polymeric matrix for the intended application. As the airstream flow increases in temperature, the strips recover the memorized bent shape, leading to a camber variation. To study the possibility of employing SMA strips as actuator elements, a comparison with common viscous clutch behavior is proposed. The time range actuator response indicates that the SMA strips provide a lower frequency control that fits well with the engine coolant thermal requirement. The experimental results demonstrate the capability of SMA materials to accommodate the lower power actuators in the automotive field. Finally, the blade tip airfoils, reconstructed using a CAD procedure, were used to study the fluid dynamic behavior of the blade tip airfoil. A CFD numerical simulation was carried out in order to highlight the differences in the airfoil performance due to the different shapes of the blade. The analyses showed that the activated blade tip airfoil led to an increase in the lift coefficient according to the stiffness provided by the polymeric compound. This innovative passive control system results from the selection of (i) the memorized shape of the SMA strips and (ii) the polymeric compound used for the blade structure.

The ability of a morphing blade to change its geometry according to the different operating conditions represents a challenging approach for the optimization of turbomachinery performance. In this paper, experimental and computational fluid dynamics (CFD) numerical analyses on a morphing blade for a heavy-duty automotive cooling axial fan are proposed. Starting from the experimental results proposed in the first part of this work, a morphing blade, made of shape memory alloy (SMA) strips embedded in a polymeric structure, was thoroughly tested. In order to assess the ability of the strips to reach a progressive and smooth shape changing evolution, several experiments were performed in a purpose-built wind tunnel. The morphing blade changed its shape as the strips were thermally activated by means of air stream flow. The bending deformation evolution with the increasing number of thermal cycles was evaluated by digital image analysis techniques. After the analyses in the wind tunnel, CFD numerical simulations of a partially shrouded fan composed of five morphing blades were performed in order to highlight the evolution of the fan performance according to air temperature conditions. In particular, the capability of the blade activation was evaluated by the comparison between the fan performance with nonactivated blades and with activated blades. The results show a progressive stabilization of the shape memory behavior after the first cycle. The blade deformation led to a significant improvement in the fan performance at a constant rotational velocity. The CFD numerical simulation points out the differences in the overall performance and of three-dimensional fluid dynamic behavior of the fan. This innovative concept is aimed at realizing a sensorless smart fan control, permitting (i) an energy saving that leads to fuel saving in the automotive application fields and (ii) an increase in engine life, thanks to a strong relationship between the engine thermal request and the cooling fan performance.

In literature, there are some studies related to the fouling phenomena in transonic compressors, but, in industrial applications (heavy-duty compressor, pumping stations, etc.) the subsonic compressors are widespread. It is of great interest to the manufacturer to discover the fouling phenomenon related to this type of compressor. This paper presents three-dimensional numerical simulations of the microparticle ingestion on a subsonic axial compressor rotor carried out by means of a commercial computational fluid dynamic code. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separate from the continuous phase. The number of particles, sizes, and concentrations are specified in order to perform a quantitative analysis of the particle impact on the blade surface. In this paper, the particle impact pattern and the kinematic characteristics (velocity and angle) of the impact are shown. Both of the blade zones affected by particle impact and the blade zones affected by particle deposition are analyzed. The particle deposition is established by using the quantity called sticking probability (SP). The SP links the kinematic characteristics of particle impact on the blade with fouling phenomenon. The results show that microparticles tend to follow the flow by impacting at full span with a higher impact concentration on the leading edge (LE). The suction side (SS) is affected only close to the LE and, at the hub, close to the trailing edge (TE). Particular fluid-dynamic phenomena such as separation, stagnation, and tip leakage vortex strongly influence the impact location of the particles. The kinematic analysis showed a high tendency of particle adhesion on the SS, especially for smaller particles for which the fluid dynamic phenomena play a key role regarding particle impact velocity and angle.

In literature there are some studies related to the fouling phenomena in transonic compressors, but, in industrial applications (heavy-duty compressor, pump stations, etc.) the subsonic compressors are widespread. It is of great interest to the manufacturer to discover the fouling phenomenon related to this type of compressor. This paper presents three-dimensional numerical simulations of the micro-particle ingestion on a subsonic axial compressor rotor carried out by means of a commercial computational fluid dynamic code. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separate from the continuous phase. The number of particles, sizes, and concentrations are specified in order to perform a quantitative analysis of the particle impact on the blade surface. In this paper the particle impact pattern and the kinematic characteristics (velocity and angle) of the impact are shown. Both of the blade zones affected by particle impact and the blade zones affected by particle deposition are analyzed. The particle deposition is established by using the quantity called sticking probability. The sticking probability links the kinematic characteristics of particle impact on the blade with fouling phenomenon. The results show that micro-particles tend to follow the flow by impacting at full span with a higher impact concentration on the leading edge. The suction side is affected only close to the leading edge and, at the hub, close to the trailing edge. Particular fluid-dynamic phenomena such as separation, stagnation and tip leakage vortex strongly influence the impact location of the particles. The kinematic analysis showed a high tendency of particle adhesion on the suction side, especially for smaller particles for which the fluid dynamic phenomena play a key role regarding particle impact velocity and angle.

The ability of a morphing blade to change its geometry according to the different operating conditions represents a challenging approach for the optimization of turbomachinery performance. In this paper experimental and CFD numerical analyses on a morphing blade for a heavy-duty automotive cooling axial fan are proposed. Starting from the experimental results proposed in the first part of this work, a morphing blade, made of Shape Memory Alloy (SMA) strips embedded in a polymeric structure, was thoroughly tested. In order to assess the ability of the strips to reach a progressive and smooth shape changing evolution, several experiments were performed in a purpose-built wind tunnel. The morphing blade changed its shape as the strips were thermally activated by means of air stream flow. The bending deformation evolution with the increasing number of thermal cycles was evaluated by digital image analysis techniques. After the analyses in the wind tunnel CFD numerical simulations of a partially shrouded fan composed of five morphing blades were performed in order to highlight the evolution of the fan performance according to air temperature conditions. In particular, the capability of the blade activation was evaluated by the comparison between the fan performance with non-activated blades and with activated blades. The results show a progressive stabilization of the shape memory behavior after the first cycle. The blade deformation led to a significant improvement in fan performance at a constant rotational velocity. The CFD numerical simulation points out the differences in the overall performance and of three-dimensional fluid dynamic behavior of the fan. This innovative concept is aimed at realizing a sensorless smart fan control, permitting (i) an energy saving that leads to fuel saving in the automotive application fields and (ii) an increase in engine life thanks to a strong relationship between the engine thermal request and the cooling fan performance.

Solid particle ingestion is one of the principal degradation mechanisms in the turbine and compressor sections of gas turbines. In particular, in industrial applications, the microparticles that are not captured by the air filtration system cause fouling and, consequently, a performance drop of the compressor. This paper presents three-dimensional numerical simulations of the microparticle ingestion (0 μm–2 μm) on an axial compressor rotor carried out by means of a commercial computational fluid dynamic (CFD) code. Particles of this size can follow the main air flow with relatively little slip, while being impacted by flow turbulence. It is of great interest to the industry to determine which areas of the compressor airfoils are impacted by these small particles. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separate from the continuous phase. Then, the NASA Rotor 37 is considered as a case study for the numerical investigation. The compressor rotor numerical model and the discrete phase treatment have been validated against the experimental and numerical data available in literature. The number of particles, sizes, and concentrations are specified in order to perform a quantitative analysis of the particle impact on the blade surface. The results show that microparticles tend to follow the flow by impacting at full span with a higher impact concentration on the pressure side (PS). The suction side (SS) is affected only by the impact of the smaller particles (up to 1 μm). Particular fluid dynamic phenomena, such as separation, stagnation point, and tip leakage vortex, strongly influence the impact location of the particles.

The quality and purity of the air entering a gas turbine is a significant factor influencing its performance and life. Foulants in the ppm range which are not captured by the air filtration system usually cause deposits on blading, which results in a severe drop in the performance of the compressor.Through the interdisciplinary approach proposed in this paper, it is possible to determine the evolution of the fouling phenomenon through the integration of studies in different research fields: (i) numerical simulation, (ii) power plant characteristics and (iii) particle-adhesion characteristics. In fact, the size of the particles, their concentrations and adhesion ability, and filtration efficiency represent the major contributors to performing a realistic quantitative analysis of fouling phenomena in an axial compressor. The aim of this work is the estimation of the actual deposits on the blade surface in terms of location and quantity. This study combines the impact/adhesion characteristic of the particles obtained through a CFD and the real size distribution of the contaminants in the air swallowed by the compressor.The blade zones affected by deposits are clearly reported by using easy-to-use contaminant maps realized on the blade surface, in terms of contaminant mass.The analysis has shown that particular fluid-dynamic phenomena and airfoil shape influence the pattern deposition. The use of a filtration system decreases the contamination of the blade and the charge level of the electrostatic seems to be less important than the air contaminant concentration. From these analyses, some guidelines for proper installation and management of the power plant (in terms of filtration systems and washing strategies) can be drawn up. Characterization of the air contaminants in the power plant location represents the most important step in improving the management of the gas turbine power plant.© 2016 ASME

In recent years, a considerable effort has been devoted towards the application of advanced techniques for turbomachinery efficient fluid dynamic control during operations. A novel strategy to dynamically modify and optimize the performance during operations takes advantage of shape memory alloys properties. Experimental and numerical analyses on a morphing polymeric blade for an automotive axial fan are presented. The blade shape change was achieved by shape memory alloys strips, thermomechanically treated, embedded in the blade and thermally activated by hot air stream flow. Measurement of fluid temperature, blade surface temperature pattern and three-dimensional shape change of the blade during activation was performed by means of an innovative image analysis technique in a purpose-built wind tunnel. Computational fluid dynamics numerical simulations were performed to study performance variations and three-dimensional fluid dynamic behavior of the fan originated from the shape memory effect.

Gas turbine operating state determination consists of the assessment of the modification, due to deterioration and fault, of performance and geometric data characterizing machine components. One of the main effects of deterioration and fault is the modification of compressor and turbine performance maps. In this paper, three-dimensional numerical simulations of a multistage axial compressor are carried out. As a case study, the axial sections (i.e. the first six stages) of the Allison 250-C18 axial-centrifugal compressor are considered for the numerical investigation. Simulations are performed by means of a commercial computational fluid dynamic code. A multistage numerical model is set up and validated against the experimental data, gathered from an in-house test rig. Computed performance maps and main flow field features show fairly good agreement with the experimental data. The model is then used to cross-validate the results of zero-dimensional stage-stacking procedures and the stage maps obtained by means of a multistage CFD calculation (i.e. to evaluate the mutual consistency of the two methods for the generation of multistage compressor maps). The stage-stacking procedure results adequately fit the behavior of the multistage compressor.Copyright © 2014 by ASME

Solid particle ingestion is one of the principal degradation mechanisms in the turbine and compressor sections of gas turbines. In particular, in industrial applications, the micro-particles not captured by the air filtration system cause fouling and, consequently, a performance drop of the compressor. This paper presents three-dimensional numerical simulations of the micro-particle ingestion (0–2 μm) on an axial compressor rotor carried out by means of a commercial computational fluid dynamic code. Particles of this size can follow the main air flow with relatively little slip, while being impacted by flow turbulence. It is of great interest to the industry to determine which areas of the compressor airfoils are impacted by these small particles. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separate from the continuous phase. Then, the NASA Rotor 37 is considered as a case study for the numerical investigation. The compressor rotor numerical model and the discrete phase treatment have been validated against the experimental and numerical data available in literature. The number of particles, sizes, and concentrations are specified in order to perform a quantitative analysis of the particle impact on the blade surface. The results show that micro-particles tend to follow the flow by impacting at full span with an higher impact concentration on the pressure side. The suction side is affected only by the impact of the smaller particles (up to 1 μm). Particular fluid-dynamic phenomena such as separation, stagnation point and tip leakage vortex strongly influence the impact location of the particles.

In heavy-duty gas turbines, the micro-particles not captured by the air filtration system can cause fouling and, consequently, a performance drop of the compressor. This paper presents three-dimensional numerical simulations of the micro-particle ingestion (0–2 μm) on an axial compressor rotor carried out by means of a commercial computational fluid dynamic code. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separately from the continuous phase. The NASA Rotor 37 is considered as a case study for the numerical investigation. The compressor rotor numerical model and the discrete phase model were previously validated by the authors in the first part of this work. The kinematic characteristics (velocity and angle) of the impact of micrometric and sub-micrometric particles with the blade surface of an axial transonic compressor are shown. The blade zones affected by particle impact were extensively analyzed and reported in the first part of this work, forming the starting point for the analyses shown in this paper. The kinematic analysis showed a high tendency of particle adhesion on the suction side, especially for the particles with a diameter equal to 0.25 μm. Fluid dynamic phenomena and airfoil shape play a key role regarding particle impact velocity and angle. This work has the goal of combining, for the first time, the kinematic characteristics of particle impact on the blade with fouling phenomenon by the use of a quantity called sticking probability adopted from literature. From these analyses, some guidelines for a proper management of the power plant (in terms of filtration and washing strategies) are highlighted.

In this paper, three-dimensional numerical simulations are carried out to evaluate the effect of fouling on an axial compressor stage. A numerical model of the NASA Stage 37, validated in previous papers of the same authors against experimental data available from literature, is used as a case study.The occurrence of fouling is simulated by imposing different spanwise distributions of surface roughness, in order to analyze its effect on compressor performance. To this aim, both the stage performance maps of the fouled compressor and the spanwise distribution of work and losses are analyzed and discussed. Moreover, the definition of an averaged roughness parameter is suggested, to characterize the different roughness distributions.The results show that the drop of overall performance can actually be predicted by means of the numerical model. Moreover, detailed information about fluid-dynamic phenomena can be analyzed on the basis of the actual distribution of surface roughness on rotor blades.Copyright © 2013 by ASME