Browsing by Author "Zachos, Pavlos"

Now showing 1 - 8 of 8
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    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
    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.
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    An assessment on the unsteady flow distortion generated by an S-duct intake
    (AIAA, 2019-08-16) Migliorini, Matteo; Zachos, Pavlos; 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.
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    Computational design optimization for S-ducts
    (MDPI, 2018-10-12) D’Ambros, Alessio; Kipouros, Timoleon; Zachos, Pavlos; Savill, Mark; Benini, Ernesto
    In 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.
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    Development of an experimental S-CO2 loop for bottoming cycle applications
    (Unknown, 2016-10-11) Anselmi Palma, Eduardo; Zachos, Pavlos; Collins, Robert; Hassan, Mark
    This 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.
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    The impact of inlet boundary layer thickness on the unsteady aerodynamics of S-duct intakes
    (AIAA, 2019-09-16) Migliorini, Matteo; Zachos, Pavlos; MacManus, David G.
    The need to reduce aero-engine emissions and direct operating costsis driving the civil aerospace sectortowards considering more integrated propulsion systems. Many of the proposed novel aircraft architectures employ convoluted intakes for either the aero-engine or propulsion system. These intakes are characterized by unsteady distortion that can hinder the performance and operability of the propulsion system. This work assessesthe impact of the inlet boundary layer on the unsteady aerodynamics of an S-duct intake using time-resolved particle image velocimetry at the aerodynamic interface plane.An increase in the boundary layer thickness at the intake inlet increasesthe flow unsteadiness on the swirl angle by up to 40% relativeto the baseline case. The azimuthal orientation of the inlet boundary layer modifies the intensity and topology of the most frequent swirl distortion pattern. For a relatively thick inlet boundary layer, the reduction of the dominant frequencies associated withthe unsteady swirl angle is postulated to be beneficial for the engine stability. Overall, this works gives guidelines for the integration between the intake and the engine across the range of potential inlet operating conditions.
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    An overview of the Rolls-Royce sCO2-test rig project at Cranfield University
    (Southwest Research Institute, 2018-04-08) Anselmi Palma, Eduardo; Bunce, Ian; Pachidis, Vassilios; Zachos, Pavlos; Johnston, Michael
    An experimental facility is currently under development at Cranfield University, aiming to explore supercritical carbon dioxide as a working fluid for future bottoming power cycle applications for Rolls- Royce. The initial objectives of this experimental program are to de-risk and demonstrate the robustness of a closed loop system, as well as to prove the function and performance of individual components and various measurement and control modules. This paper describes the planning and development phases of the test facility and summarises the lessons learnt from the component specification and component interface processes.
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    Parametric evaluation of S-CO2 Brayton cycles for bottoming applications
    (2016-10-11) Brighenti, Giovanni; Anselmi Palma, Eduardo; Zachos, Pavlos
    Parametric design studies for the preliminary assessment of physical footprint of Supercritical CO2 power plants are presented herein. The aim of the study is to quantify trade-offs between cycle efficiency and plant complexity for a range of S-CO2 cycle configurations.
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    Unsteady swirl distortion characteristics for S-ducts using Lattice Boltzmann and time-resolved, stereo PIV methods
    (AIAA, 2019-08-16) Guerrero-Hurtado, Manuel; Zachos, Pavlos; MacManus, David G.; Migliorini, Matteo; Trapani, Giuseppe
    The unsteady flowfields generated by convoluted aero engine intakes are major sources of instabilities that can compromise the performance of the downstream turbomachinery components. This highlights theneed for high spatial and temporal resolution measurements that will allow a greater understanding of the aerodynamics but also improvements in our current predictive capability for such complex flows. This paper presents the validation of a modern Lattice Boltzmann method (LBM)to predict the unsteady flow and swirl distortion characteristics within a representative S-duct intake.The numerical results are compared against high spatial and temporal resolutionParticle Image Velocimetry(PIV)data for the same S-duct configuration at an inlet Mach number of0.27.The work demonstrates that LBM is broadly able to capture the flow topologies and temporal characteristics with the exception of the magnitude of the unsteady fluctuations which were found to be notably under-predicted compared to the PIV data. Proper Orthogonal Decomposition analysis shows that LBM is able to provide the key flow modes and their spectral distributions which were found broadly in alignment with the PIV data. A statistical assessment of the unsteady distortionhistoryhighlights that LBM can also provide representative distributions of the main swirl distortion descriptors. Overall the work demonstrates that LBM shows promising potential for S-duct unsteady flow predictions which combined with the minimum computational grid requirements, robustness and fast convergence make it an attractive solution for wider use in thearea of unsteady propulsion system aerodynamics.