Browsing by Author "Zachos, Pavlos K."
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Item Open Access 2D3C measurement of velocity, pressure and temperature fields in a intake flow of an air turbine by Filtered Rayleigh Sattering (FRS) and validation with LDV and PIV(International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics, 2024-07-08) Dues, Michael; Dues, Fritz; Melnikov, Sergey; Steinbock, Jonas Johannes; Doll, Ulrich; Röhle, Ingo; Migliorini, Matteo; Zachos, Pavlos K.A Filtered Rayleigh Scattering Technique is implemented in two different experimental setups and compared to the established velocity measurement techniques Laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PIV). The Frequency Scanning Filtered Rayleigh Scattering Method employed uses an imagefiber bundle which allows for the simultaneous observation of the flow situation from six independent perspectives, utilizing only one sCMOS camera. A testrig with a nominal diameter of 80 mm was implemented by ILA R&D GmbH. Here measurements with straight pipe flow and a swirl generator were realised, as well as comparisions with LDA. A second experiment utilized Cranfields University’s Complex Intake Facility (CCITF), enabling the simulation of the flow field for an engine intake as observed behind an S-Duct diffuser. The diameter in the measuring plane was 160 mm. Measurements up to a mach number of 0.4 were performed and compared with HighSpeed Stereo-PIV (S-PIV) measurements. Good agreement was achieved in respect to both the absolute magnitude of the velocity measurements as well as to the resolution of complex flow structures. The developed FRS multi-view Setup is able to simultaneously determine the 3D velocity components, the pressure and the temperature on a measurement plane with high resolution and without seeding. After calibration the FRS system yields the pressure and temperature within 3 percent respectively 0.8 percent of the reference values. The measured velocity was within 1-2 m/s of the reference.Item Open Access Advancements on the use of Filtered Rayleigh Scattering (FRS) with machine learning methods for flow distortion in aero-engine intakes(Elsevier, 2025-01-01) Migliorini, Matteo; Doll, Ulrich; Lawson, Nicholas J.; Melnikov, Sergey M.; Steinbock, Jonas; Dues, Michael; Zachos, Pavlos K.; Röhle, Ingo; MacManus, David G.In-flight measurements of aerodynamic quantities are a requirement to ensure the correct scaling of Reynolds and Mach number and for the airworthiness certification of an aircraft. The ability to obtain such measurement is subject to several challenges such as instrument installation, environment, type of measurand, and spatial and temporal resolution. Given expected, more frequent use of embedded propulsion systems in the near future, the measurement technology needs to adapt for the characterization of multi-type flow distortion in complex flow, to assess the operability of air-breathing propulsion systems. To meet this increasing demand for high-fidelity experimental data, the Filtered Rayleigh Scattering (FRS) method is identified as a promising technology, as it can provide measurements of pressure, temperature and 3D velocities simultaneously, across a full Aerodynamic Interface Plane (AIP). Τhis work demonstrates the application of a novel FRS instrument, to assess the flow distortion in an S-duct diffuser, in a ground testing facility. A comparison of FRS results with Stereo-Particle Image Velocimetry (S-PIV) measurements reveals good agreement of the out of plane velocities, within 3.3 % at the AIP. Furthermore, the introduction of machine learning methods significantly accelerates the processing of the FRS data by up to 200 times, offering a substantial prospect towards real time data analysis. This study demonstrates the further development of the FRS technique, with the ultimate goal of inlet flow distortion measurements for in-flight environments.Item Open Access Aerodynamic design of a high-speed intake test rig for propulsion integration research(AIAA, 2025-01-06) Migliorini, Matteo; Zachos, Pavlos K.; MacManus, David G.; Martin, Peter G.Inlet flow distortion is a critical factor in supersonic air induction systems, primarily due to its complex spatial variations and significant temporal unsteadiness. These characteristics can have a substantial impact on the performance and reliability of propulsion systems. Conducting experiments at an early stage of technology readiness can help mitigate risks associated with industrial testing and certification processes. This paper is part of a broader programme aimed at advancing experimental capabilities for high-speed propulsion system integration. The research focuses on incorporating advanced, non-intrusive measurement techniques alongside current industry-standard methods to better characterize engine compatibility. The paper details the optimization process for designing a fixed-throat supersonic nozzle that delivers high-quality flow at Mach 1.8, the structural and functional design of the working section. The integration of an intake test article is described, together with instrumentation for measuring synchronous total pressure and swirl distortion at the aerodynamic interface plane of the intake. Preliminary computational work is also presented, evaluating the flow quality within the working section and investigating the distribution of bypass flow in the radial exhaust.Item Open Access Aerodynamic instabilities in high-speed air intakes and their role in propulsion system integration(MDPI, 2024-01-12) Philippou, Aristia L.; Zachos, Pavlos K.; MacManus, David G.High-speed air intakes often exhibit intricate flow patterns, with a specific type of flow instability known as ‘buzz’, characterized by unsteady shock oscillations at the inlet. This paper presents a comprehensive review of prior research, focused on unraveling the mechanisms that trigger buzz and its implications for engine stability and performance. The literature survey delves into studies concerning complex-shaped diffusers and isolators, offering a thorough examination of flow aerodynamics in unstable environments. Furthermore, this paper provides an overview of contemporary techniques for mitigating flow instability through both active and passive flow control methods. These techniques encompass boundary layer bleeding, the application of vortex generators, and strategies involving mass injection and energy deposition. The study concludes by discussing future prospects in the domain of engine-intake aerodynamic compatibility. This work serves as a valuable resource for researchers and engineers striving to address and understand the complexities of high-speed air induction systems.Item Open Access Assessment methods for unsteady flow distortion in aero-engine intakes(Elsevier, 2017-10-27) Gil-Prieto, Daniel; MacManus, David G.; Zachos, Pavlos K.; Bautista, AbianPeak events of unsteady total pressure and swirl distortion generated within S-duct intakes can affect the engine stability, even when within acceptable mean distortion levels. Even though the distortion descriptors have been evaluated in S-duct intakes, the associated flow field pattern has not been reported in detail. This is of importance since engine tolerance to distortion is usually tested with representative patterns from intake tests replicated with steady distortion generators. Despite its importance in intake/engine compatibility assessments, the spectral characteristics of the distortion descriptors and the relationship between peak unsteady swirl and both radial and circumferential total pressure distortion has not been assessed previously. The peak distortion data is typically low-pass filtered at a frequency associated with the minimum response time of the engine. However the engine design is not always known a priori in intakes investigations and a standard approach to reporting peak distortion data is needed. In addition, expensive and time-consuming tests are usually required to capture representative extreme distortion levels. This work presents a range of analyses based on Delayed Detached-Eddy Simulation and Stereo Particle Image Velocimetry data to assess these aspects of the unsteady flow distortion. The distorted pattern associated with different swirl distortion metrics is identified based on a conditional averaging technique, which indicates that the most intense swirl events are associated with a single rotating structure. . The main frequencies of the flow distortion descriptors in a representative S-duct intake are found to lie within the range in which the engine stability may be compromised. The peak total pressure and swirl distortion events are found to be not synchronous, which highlights the need to assess both types of distortion. Peak swirl and total-pressure distortion data is reported as a function of its associated time scale in a more general way that can be used in the assessment of intake unsteady flow distortion. Extreme Value Theory has been applied to predict peak distortion values beyond those measured in the available dataset, and whose measurement would otherwise require testing times two orders of magnitude longer than those typically considered.Item Open Access An assessment on the unsteady flow distortion generated by an S-duct intake(AIAA, 2019-08-16) Migliorini, Matteo; Zachos, Pavlos K.; MacManus, David G.Closer integration between the fuselage and the propulsion system is expected for futureaircraft toreducefuel consumption, emissions, weight and drag. The use of embedded or partially embedded propulsion systems may require the use of complex intakes. However, thiscanresult in unsteady flow distortion which can adversely affect the propulsion system efficiency and stability. This works assesses the characteristics of the unsteady flow with a view to the potential flow distortion presented to the compression system.Particle image velocimetry is used to measure the flow distortion generated by an S-shaped intake.The time-resolved tracking of the idealized relative incidence angle revealed that most frequent distortion events exhibited90°exposure sector and upto±5°meanrelativeincidence. The imposition of a thicker boundary at the S-duct inlet increased the probability of distortion events that are characterized by a longer exposure sector and higher relative incidence angles.Because of these characteristics, thedistortion caused by the S-duct intake could induce instabilities that are detrimental for the propulsion system performances and stability. Overall, this work proposes a new method to assess thepossible relativeincidence angle on the compressor rotor taking into account the intake flow unsteadiness.Item Open Access Characterization of unsteady distortion events for S-duct intakes under non-uniform inlet conditions(AIAA, 2023-01-19) Migliorini, Matteo; Zachos, Pavlos K.; MacManus, David G.The use of convoluted intakes is expected to grow in novel aircraft configurations as designers seek to integrate more closely the propulsion system with the airframe. Previous research highlighted considerable unsteady flow distortions for S-duct configurations. However, most of the work was limited to the types of flow distortion inherently generated within the duct which reflects a relatively narrow range of aerodynamic conditions. In addition, the conditions of the flow distortion approaching the propulsion system is still not well understood due to the lack of experimental data and methods for unsteady distortion analysis. Recently, a novel analysis method was developed to consider the unsteady flow distortion from the perspective of an envisaged rotor blade through the exploitation of measurements with high-bandwidth Particle Image Velocimetry. In this study, and with this method, the aim is to provide a more advanced classification of unsteady distortion events based on the distribution of incidence on the envisaged rotor blades. This work can provide guidelines for methods to evaluate peak distortion levels under different inlet configurations for intake-engine integration assessments.Item Open Access Cluster-based tracking method for the identification and characterisation of vortices(Association Aéronautique et Astronautique de France (3AF), 2025-03-26) Ibanez, Claudia; Migliorini, Matteo; Giannouloudis, Alexandros; Tejero, Fernando; Zachos, Pavlos K.An unsupervised, flow-agnostic and automatic cluster-based tracking algorithm for the segmentation of vortex-dominated flows has been successfully developed. It combines the Rortex method and density-based clustering algorithms. The Rortex method differs shear from rotation and overcomes the sensitivity to user-defined thresholds that characterises current practice of vortex identification methods. The algorithm is demonstrated with experimental Stereoscopic Particle Image Velocimetry data from two cases; a high-Reynolds (≈ 106) vortex generated by a half-delta wing, and distorted flow in a scaled-model of a civil aero-engine intake under cross-wind conditions. The approach is a successful method for the segmentation of complex vortical flows under a wide range of conditions.Item Open Access Complex aero-engine intake ducts and dynamic distortion(AIAA, 2015-06-19) MacManus, David G.; Chiereghin, Nicola; Gil-Prieto, Daniel; Zachos, Pavlos K.For many embedded and partially-embedded engine systems, the complexity of the flow field associated with convoluted intakes presents an area of notable research challenges. The convolution of the intake duct introduces additional flow distortion and unsteadiness which must be understood and quantified when designing the turbo machinery components. The aim of the current work is to investigate the capabilities of modern computational methods for these types of complex flows, to study the unsteady characteristics of the flow field and to explore the use of proper orthogonal decomposition methods to understand the nature of the unsteady flow distortion. The unsteady flow field for a range of S-duct configurations has been simulated and assessed using a delayed detached eddy simulation method. The configurations encompass the effects of Mach number, Reynolds number and S-duct centre line offset distance. Analysis of the conventional distortion criteria highlights the main sensitivities to the S-duct configuration and quantifies the unsteady range of these parameters. These results illustrate the strongly dynamic nature of the flow field for both total pressure as well as swirl based distortion. Analysis of the unsteady flow field shows signature regions of unsteadiness which are postulated to be related to the classical secondary flows as well as to the stream wise flow separation. The more aggressive duct, with a larger centre line offset, shows some similar characteristics, but the unsteadiness is more broadband and the distinction between these two mechanisms is less clear. A proper orthogonal decomposition of the total pressure field at the duct exit identifies the underpinning flow modes which are associated with the overall total pressure unsteadiness distributions. For the more aggressive duct, the flow modes are notably different and highlight the reduced demarcation between the unsteady flow field mechanismsItem Open Access Complex aero-engine intake ducts and dynamic distortion(AIAA, 2017-03-29) MacManus, David G.; Chiereghin, Nicola; Gil-Prieto, Daniel; Zachos, Pavlos K.For many embedded engine systems, the intake duct geometry introduces flow distortion and unsteadiness, which must be understood when designing the turbomachinery components. The aim of this work is to investigate the capabilities of modern computational methods for these types of complex flows, to study the unsteady characteristics of the flowfield, and to explore the use of proper orthogonal decomposition methods to understand the nature of the unsteady flow distortion. The unsteady flows for a range of S-duct configurations have been simulated using a delayed detached-eddy simulation method. Analysis of the conventional distortion criteria highlights the main sensitivities to the S-duct configuration and quantifies the unsteady range of these parameters. The unsteady flowfield shows signature regions of unsteadiness, which are postulated to be related to the classical secondary flows as well as to the streamwise flow separation. A proper orthogonal decomposition of the total pressure field at the duct exit identifies the underpinning flow modes, which are associated with the overall total pressure unsteadiness distributions. Overall, the unsteady distortion metrics are not found to be solely linked to a particular proper orthogonal decomposition mode, but are dependent on a wider range of modes.Item Open Access Computational design optimization for S-ducts(MDPI, 2018-10-12) D’Ambros, Alessio; Kipouros, Timoleon; Zachos, Pavlos K.; Savill, Mark; Benini, ErnestoIn this work, we investigate the computational design of a typical S-Duct that is found in the literature. We model the design problem as a shape optimization study. The design parameters describe the 3D geometrical changes to the shape of the S-Duct and we assess the improvements to the aerodynamic behavior by considering two objective functions: the pressure losses and the swirl. The geometry management is controlled with the Free-Form Deformation (FFD) technique, the analysis of the flow is performed using steady-state computational fluid dynamics (CFD), and the exploration of the design space is achieved using the heuristic optimization algorithm Tabu Search (MOTS). The results reveal potential improvements by 14% with respect to the pressure losses and by 71% with respect to the swirl of the flow. These findings exceed by a large margin the optimality level that was achieved by other approaches in the literature. Further investigation of a range of optimum geometries is performed and reported with a detailed discussion.Item Open Access Convoluted intake distortion measurements using stereo particle image velocimetry(2017-04-18) Gil-Prieto, Daniel; MacManus, David G.; Zachos, Pavlos K.; Tanguy, Geoffrey; Menzies, Kevin R.The unsteady distorted flowfields generated within convoluted aeroengine intakes can compromise the engine performance and operability. Therefore, there is a need for a better understanding of the complex characteristics of the distorted flow at the exit of S-shaped intakes. This work presents a detailed analysis of the unsteady swirl distortion based on synchronous, high-spatial-resolution measurements using stereoscopic particle image velocimetry. Two S-duct configurations with different centerline offsets are investigated. The high-offset duct shows greater levels of dynamic and steady swirl distortion and a notably greater tendency toward bulk swirl patterns associated with high swirl distortion. More discrete distortion patterns with locally high swirl levels and the potential to impact the engine operability are identified. The most energetic coherent structures of the flowfield are observed using proper orthogonal decomposition. A switching mode is identified that promotes the alternating swirl switching mechanism and is mostly associated with the occurrence of potent bulk swirl events. A vertical mode that characterizes a perturbation of the vertical velocity field promotes most of the twin swirl flow distortion topologies. It is postulated that it is associated with the unsteadiness of the centerline shear layer.Item Open Access Coupled fan-intake dynamic distortion characterization at crosswind conditions(AIAA, 2025-02) Piovesan, Tommaso; Zachos, Pavlos K.; MacManus, David G.; Kempaiah, Kushal; Michaelis, Dirk; van Rooijen, Bart; Vahdati, Mehdi; Sheaf, ChristopherItem Open Access Data for "SINATRA - Complex intake flow distortion measurements"(Cranfield University, 2024-09-01) Migliorini, Matteo; Doll, Ulrich; Lawson, Nicholas; Melnikov, Sergey M.; Steinbock, Jonas; Dues, Michael; Zachos, Pavlos K.; Roehle, Ingo; MacManus, David G.Item Open Access Delayed detached-eddy simulation and particle image velocimetry investigation of S-Duct flow distortion(AIAA, 2017-03-31) Gil-Prieto, Daniel; MacManus, David G.; Zachos, Pavlos K.; Tanguy, Geoffrey; Wilson, François; Chiereghin, NicolaThe dynamic flow distortion generated within convoluted aeroengine intakes can affect the performance and operability of the engine. There is a need for a better understanding of the main flow mechanisms that promote flow distortion at the exit of S-shaped intakes. This paper presents a detailed analysis of the main coherent structures in an S-duct flowfield based on a delayed detached-eddy simulation. The capability of this numerical approach to capture the characteristics of the highly unsteady flowfield is demonstrated against high-resolution, synchronous stereoscopic particle image velocimetry measurements at the aerodynamic interface plane. The flowfield mechanisms responsible for the main perturbations at the duct outlet are identified. Clockwise and counterclockwise streamwise vortices are alternately generated around the separation region at a frequency of St=0.53 St=0.53 , which promote the swirl switching at the duct outlet. Spanwise vortices are also shed from the separation region at a frequency of St=1.06 St=1.06 and convect downstream along the separated centerline shear layer. This results in a vertical modulation of the main loss region and a fluctuation of the velocity gradient between the high- and low-velocity flow at the aerodynamic interface plane.Item Open Access Design and optimisation of a Mach 2.5 wind tunnel nozzle(AIAA, 2023-01-19) Moreno, Miguel; Migliorini, Matteo; Zachos, Pavlos K.; Haslam, Anthony; MacManus, David G.The paper presents a methodology for the numerical design and optimization of a distortion-free two-dimensional Mach 2.5 nozzle based on a parametric model. The non-uniformities generated at the Mach wave reflections downstream of the nozzle throat that the Method of Characteristics only partially addresses are minimized. The spatial discretization of the domain is integrated with the boundary layer analysis for fast and robust data processing, especially in the final viscous sublayers in the transition regions within the bulk of the fluid. The flow patterns and corner flows of the supersonic nozzle are assessed via three-dimensional high-fidelity computational fluid dynamics. As a result, a fast workflow for nozzle design to meet prescribed flow quality requirements is herein illustrated.Item Open Access Design of a high-speed intake distortion simulator for propulsion integration research(AIAA, 2023-01-19) Migliorini, Matteo; Szymanski, Artur; Zachos, Pavlos K.; MacManus, David G.; Martin, Peter G.High levels of inlet flow distortion can be a critical aspect in supersonic air induction systems due to the complex spatial nature and notable temporal unsteadiness. This can affect the operability and performance of the propulsion system. Simulation of the intake shock system in a relatively less expensive, lower technology readiness level experimental facility can be an important element to mitigate a significant part of the risk that industrial and certification testing carries. The work described in this paper is part of a programme that aims to develop such a distortion simulation test rig where the capability of advanced non-intrusive measurement techniques would be applied in propulsion integration research. The paper describes the concept, preliminary design and sizing of the working section of the rig, the exhaust system design and the integration of the test model. A brief summary of the rig architecture is provided along with details of the high-pressure system that drives the supersonic flow. The work indicates that careful design of the working section is required to ensure sufficient operating range and representative aerodynamics of the test model. It is also shown that the working section wall interference on the test model is tightly linked with the type and size of the aircraft intake to be tested. Ways to mitigate this interference are herein explored.Item Open Access Design point performance and optimization of humid air turbine power plants(2017-04-20) Brighenti, Giovanni D.; Orts-Gonzalez, Pau Lluis; Sanchez-de-Leon, Luis; Zachos, Pavlos K.With the recent drive towards higher thermal efficiencies and lower emission levels in the power generation market, advanced cycle power plants have become an increasingly appealing option. Among these systems, humid air turbines have been previously identified as promising candidates to deliver high efficiency and power output with notably low overall system volume, weight and emissions footprint. This paper investigates the performance of an advanced humid air turbine power cycle and aims to identify the dependencies between key cycle design variables, thermal performance, weight and cost by means of a parametric design optimization approach. Designs of the main heat exchangers are generated, aiming to ascertain the relationship between their technology level and the total weight and acquisition cost of them. The research outcomes show that the recuperator and the intercooler are the two components with the largest influence on the thermal efficiency and the total cost. The total weight of the power system is driven by the technology level of the recuperator and the economizer. Finally, the effectiveness of the aftercooler seems to have the greatest impact in reducing the total acquisition cost of the system with minimum penalty on its thermal efficiency.Item Open Access Development of an experimental S-CO2 loop for bottoming cycle applications(Unknown, 2016-10-11) Anselmi Palma, Eduardo; Zachos, Pavlos K.; Collins, Robert; Hassan, MarkThis paper describes the design of a supercritical carbon dioxide [S-CO2] rig for bottoming power cycle applications. The final envisaged layout of the facility includes a fully coupled compressor-turbine system, a number of heat exchangers to enable heat management of the cycle and a control system for start-ups, shut-downs, inventory control and transient operation of the loop. The objective of the preliminary design phase is to experimentally de-risk the robustness of the closed loop system as well as prove the purpose of individual components and various measurement and control modules.Item Open Access Drag decomposition of a subsonic wing via a far-field, exergy-based method(SAGE, 2022-10-13) Logothetis, Dimitrios K.; Zachos, Pavlos K.; Rogero, Jean-MichelThis paper focuses on the aerodynamic analysis and drag decomposition of an unpowered, low aspect ratio wing, using a far-field, exergy-based method. As opposed to traditional drag accounting methods, exergy balance provides insights into the amount of energy that can be potentially recovered off the body’s wake, which further translates into potential efficiency gains of the integrated engine-wing system. In this study, a far-field exergy balance method was used to determine the total drag of a three-dimensional wing. The far-field drag prediction was verified against near-field calculations. In addition, drag decomposition using exergetic terms was conducted to identify drag components that contain possibly recoverable energy. Such analysis can be subsequently used to educate the integration of a propulsion system to exploit the potentially recoverable wake energy and deliver an integrated engine-wing system with enhanced installed efficiency. The present methodology is a major step ahead in the application of far-field methods on three-dimensional wake domains and can potentially become a major enabler for optimal propulsion integration for future, novel aircraft-engine configurations.