Alessio Suman

Experimental Investigation of Stall and Surge in a Multistage Compressor

Flow instability conditions, in particular during surge and stall phenomena, have always influenced the operational reliability of turbo-compressors and have attracted significant interest resulting in extensive literature. Nowadays, this subject is still one of the most investigated because of its high relevance on centrifugal and axial compressor operating flow range, performance and efficiency. Many researchers approach this important issue by developing numerical models, whereas others approach it through experimental studies specifically carried out in order to better comprehend this phenomenon. The aim of this paper is to experimentally analyze the stable and unstable operating conditions of an aeronautic turbo-shaft gas turbine axial-centrifugal compressor installed on a brand new test-rig properly designed for this purpose.The test facility is set up in order to obtain i) the compressor performance maps at rotational speeds up to 25,000 rpm and ii) the compressor transient behavior during surge. By using two different test rig layouts, instabilities occurring in the compressor, beyond the peak of the characteristic curve, are identified and investigated.These two types of analysis are carried out thanks to pressure, temperature and mass flow sensors located in strategic positions along the circuit. These measurement sensors are part of a proper control and acquisition system, characterized by an adjustable sampling frequency. Thus, the desired operating conditions of the compressor, in terms of mass flow and rotational speed and transient of these two parameters are regulated by this dedicated control system.© 2016 ASME

A Shape Memory Alloy-Based Morphing Axial Fan Blade—Part I: Blade Structure Design and Functional Characterization

The possibility to realize adaptive structures is of great interest in turbomachinery design, owing to the benefits related to enhanced performance and efficiency. To accomplish this, a challenging approach is the employment of Shape Memory Alloys (SMAs), which can recover seemingly permanent strains by solid phase transformations whereby the so-called Shape Memory Effect (SME) takes place.This paper presents the development of a heavy-duty automotive cooling axial fan with morphing blades activated by SMA strips that works as actuator elements in the polymeric blade structure. Concerning the fan performance, this new concept differs from a conventional viscous fan clutch solution especially during the non-stationary operating condition. The blade design was performed in order to achieve the thermal activation of the strips by means of air stream flow. Two polymeric matrices were chosen to be tested in conjunction with a commercially available NiTi binary alloy, whose phase transformation temperatures were experimentally evaluated by imposing the actual operating thermal gradient.The SMA strips were then thermo-mechanically treated to memorize a bent shape and embedded in the polymeric blade. In a specifically designed wind tunnel, the different polymeric matrices equipped with the SMA strips were tested to assess the fluid temperature and surface pattern behavior of the blade. Upon heating they tend to recover the memorized shape and the blade is forced to bend, leading to a camber variation and a trailing edge displacement. The recovery behavior of each composite structure (polymeric matrix with SMA strips) was evaluated through digital image analysis techniques. The differences between the blade shape at the initial condition and at the maximum bending deformation were considered.According to these results, the best coupling of SMA strips and polymeric structure is assessed and its time-wise behavior is compared to the traditional time-wise behavior of a viscous fan clutch.Copyright

A Shape Memory Alloy-Based Morphing Axial Fan Blade—Part II: Blade Shape and Computational Fluid Dynamics Analyses

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.

A Shape Memory Alloy-Based Morphing Axial Fan Blade: Part II — Blade Shape and CFD Analyses

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.© 2015 ASME

Eco-design of a small size industrial fan for ceramic tile cooling

In this paper, the one-dimensional design and the three-dimensional numerical analysis through computational fluid dynamics simulations of a small size fan are carried out. The fan in consideration provides the airflow used for controlling the surface thermal gradient of ceramic tiles between the dryer and the digital printing stage. An experimental campaign performed on a backward-curved centrifugal fan prototype with an optimized air blowing device demonstrates that fan performances (efficiency and air flow rate) meet the eco-design demands and the air velocity field at the blowing device outlet is suitable to obtain the expected heat exchange. The new cooling system can also reduce acoustic emissions up to 3 dB(A) with respect to the existing one.

A shape memory alloy-based morphing axial fan blade, part I: Blade structure design and functional characterization

The possibility to realize adaptive structures is of great interest in turbomachinery design, owing to the benefits related to enhanced performance and efficiency. To accomplish this, a challenging approach is the employment of Shape Memory Alloys (SMAs), which can recover seemingly permanent strains by solid phase transformations whereby the so-called Shape Memory Effect (SME) takes place.This paper presents the development of a heavy-duty automotive cooling axial fan with morphing blades activated by SMA strips that works as actuator elements in the polymeric blade structure. Concerning the fan performance, this new concept differs from a conventional viscous fan clutch solution especially during the non-stationary operating condition. The blade design was performed in order to achieve the thermal activation of the strips by means of air stream flow. Two polymeric matrices were chosen to be tested in conjunction with a commercially available NiTi binary alloy, whose phase transformation temperatures were experimentally evaluated by imposing the actual operating thermal gradient.The SMA strips were then thermo-mechanically treated to memorize a bent shape and embedded in the polymeric blade. In a specifically designed wind tunnel, the different polymeric matrices equipped with the SMA strips were tested to assess the fluid temperature and surface pattern behavior of the blade. Upon heating they tend to recover the memorized shape and the blade is forced to bend, leading to a camber variation and a trailing edge displacement. The recovery behavior of each composite structure (polymeric matrix with SMA strips) was evaluated through digital image analysis techniques. The differences between the blade shape at the initial condition and at the maximum bending deformation were considered.According to these results, the best coupling of SMA strips and polymeric structure is assessed and its time-wise behavior is compared to the traditional time-wise behavior of a viscous fan clutch.Copyright

Centrifugal pumps performance estimation with non-Newtonian fluids: review and critical analysis

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.

AN ENERGY BASED FOULING MODEL FOR GAS TURBINES: EBFOG

Fouling is a major problem in gas turbines for aeropropulsion because the formation of aggregates on the wet surfaces of the machine affects aerodynamic and heat loads. The representation of fouling in CFD is based on the evaluation of the sticking probability, i.e. the probability a particle touching a solid surface has to stick to that surface. Two main models are currently available in literature for the evaluation of the sticking coefficient: one is based on a critical threshold for the viscosity, the other is based on the normal velocity to the surface. However, both models are application specific and lack generality. This work presents an innovative model for the estimation of the sticking probability. This quantitiy is evaluated by comparing the kinetic energy of the particle with an activation energy which describes the state of the particle. The sticking criterion takes the form of an Arrhenius-type equation. A general formulation for the sticking coefficient is obtained. The method, named EBFOG (Energy Based FOulinG), is the first ”energy” based model presented in the open literature able to account any common deposition effect in gas turbines. The EBFOG model is implemented into a Lagrangian tracking procedure, coupled to a fully three-dimensional CFD solver. Particles are tracked inside the domain and equations for the momentum and temperature of each particle are solved. The local geometry of the blade is modified accordingly to the deposition ∗Address all correspondence to this author, email: nicola.casari@unife.it, nicola.casari15@imperial.ac.uk rate. The mesh is modified and the CFD solver updates the flow field. The application of this model to particle deposition in high pressure turbine vanes is investigated, showing the flexibility of the proposed methodology. The model is particularly important in aircraft engines where the effect of fouling for the turbine, in particular the reduction of the HP nozzle throat area, influences heavily the performance by reducing the core capacity. The energy based approach is used to quantify the throat area reduction rate and estimate the variation in the compressor operating condition. The compressor operating point as a function of the time spent operating in a harsh environment can be in this way predicted to estimate, for example, the time that an engine can fly in a cloud of volcanic ashes. The impact of fouling on the throat area of the nozzle is quantified for different conditions.

Using shape memory alloys for improving automotive fan blade performance: experimental and computational fluid dynamics analysis

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.

Quantitative CFD Analyses of Particle Deposition on a Transonic Axial Compressor Blade: Part II — Impact Kinematics and Particle Sticking Analysis

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.Copyright