Browsing by Author "Templalexis, Ioannis"

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    Comparative assessment of fouling scenarios in an axial flow compressor
    (American Society of Mechanical Engineers, 2020-12-05) Templalexis, Ioannis; Pachidis, Vassilios; Azamar, Hasani
    It is commonly accepted that fouling degrades severely axial compressor performance. Deposits build up as operating hours sum up, causing a decrease in the compressor's delivery pressure, efficiency and flow capacity. Researchers have also concluded that compressor susceptibility to fouling depends on many factors, such as atmospheric conditions, air quality, filtration system, the size and design of the compressor, etc. The current study identifies four basic operating scenarios which refer to the same compressor, in order to put forward a comparative assessment as to how incoming air quality would affect compressor performance. SOCRATES, an in-house, streamline curvature-based through-flow tool, in conjunction with a detailed, fully customizable fouling empirical model, conceived based on flow physics and relevant experimental data, is used to qualify and quantify, compressor degradation with time.
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    Comparative assessment of fouling scenarios in an axial flow compressor (Conf)
    (American Society of Mechanical Engineers, 2021-01-11) Templalexis, Ioannis; Pachidis, Vassilios; Hasani, Azamar
    It is commonly accepted that fouling degrades severely axial compressor performance. Deposits build up throughout the compressor’s operating life, causing a decrease in its delivery pressure, efficiency and flow capacity. Researchers have also concluded that the presence of wet contaminants and/or high air humidity, plus the quality of air filtration systems, have a far greater impact on fouling rates, than engine specific fouling susceptibility factors [1]. The size of airborne particles ingested into the engine is primarily controlled by the presence of a filtration system. On the other hand, the particle deposition rate and the fouling patterns formed on the blade surfaces are greatly affected by the “stickiness” of the blade surfaces which in turn is affected by the moisture level of the incoming air. Compressor geometry, size and operating point would affect far less the rate of contaminants built up on the wetted surfaces and they would affect even less the exact location on compressor walls and blade surfaces. The current study identifies four basic operating scenarios which refer to the same compressor, in order to put forward a comparative assessment as to how the factors mentioned above, affect the compressor performance through the fouling mechanism. Scenarios were formed out of the possible combinations regarding the presence of a filtration system and the level of humidity. These were: i) Filtered - dry air, ii) Filtered - humid air, iii) Unfiltered - dry air, and iv) Unfiltered - humid air. These scenarios will eventually reproduce four completely different situations regarding the quality of the incoming air and subsequently, four different fouling regimes for the compressor operating downstream. Data to support the impact of each reported incoming air condition on compressor wetted surfaces, are based on experimental findings collected from a thorough literature review. A fixed operating period was set for all cases. Prescribed requirements of the computational tool selected to build the compressor model were; i) low computational power since several runs had to be performed in order to cover the assumed time period, and ii) ability to introduce the imprint of various fouling patterns on compressor blades, into the performance of the compressor. SOCRATES, an in-house two-dimensional, streamline curvature-based, through-flow computational tool, meets these requirements and it was used for this study. A fully customizable empirical model, recently introduced in the code, takes into account various aspects of fouling such as the surface roughness level, the flow blockage and the altered deviation angle at the exit of the blade row. A coverage factor was introduced which takes into account the location and the extent of fouling onto the blade surfaces.
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    Development of a streamline curvature axial-flow compressor performance simulator graphical-user-interface for design and research
    (International Society for Air Breathing Engines (ISABE), 2017-09-11) Azamar Aguirre, Hasani; Pachidis, Vassilios; Templalexis, Ioannis
    The all-time interest to increase turbomachinery efficiencies and pressure ratios has led to the progression of more robust and accurate simulation methods and tools. Even though 3-D CFD analyses are highly detailed and despite the computational power nowadays, they can be costly in terms of time and resources. Conversely, 2-D SLC methods provide acceptable performance and flow field results in short times. Because of economical and practical reasons, SLC still represents the cornerstone for turbomachinery design. In the present, the knowledge demand from the academia community in the airbreathing engine field has been expanding year after year. Nevertheless, there are very few open-source turbomachinery solvers that can be accessed, where user needs to know at least the basics of the programming language syntax and familiarize with it. For these reasons, a GUI was developed for an existing in-house 2-D SLC axial-flow compressor performance code, called SOCRATES. A GUI in this context supports as a teaching mechanism to explain not only the method itself, but also the compressor aerodynamic behaviour. The SOCRATES GUI consists in the axial-flow compressor model setup, solution and visualization for geometry and results. This paper outlines the main features of the 2-D SLC GUI, and uses a two-stage fan to show the flow field parameters and compressor/fan map, showing a consistent agreement against measured data.
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    An improved streamline curvature-based design approach for transonic axial-flow compressor blading
    (International Society for Air Breathing Engines (ISABE), 2017-09-11) Azamar Aguirre, Hasani; Pachidis, Vassilios; Templalexis, Ioannis
    The increasing demand to obtain more accurate turbomachinery blading performance in the design and analysis process has led to the development of higher fidelity flow field models. Despite extensive flow field information can be collected from threedimensional (3-D) Reynolds-averaged Navier-Stokes (RANS) numerical simulations; it comes at a high computational cost in terms of time and resources, particularly if a comprehensive design space is explored during optimization. In contrast, through-flow methods such as streamline curvature (SLC), provide a flow solution in minutes whilst offering acceptable results. Furthermore, if the SLC fidelity is improved, a more detailed component-blading study is expected. For this reason, a fully-detailed transonic flow framework was implemented and validated in an existing in-house two-dimensional (2-D) SLC compressor performance to improve the performance results fidelity in transonic conditions. The improvements consist of two sections: (1) blade-profile modelling; (2) flow field solution. The bladeprofile modelling considers a 3-D blade-element-layout method to correctly model the sweep and lean angle, which determine the shock structure. The essential part of the transonic flow framework is its solution, formed of two parts: (1) a physics-based shock-wave model to predict its structure, and associated losses; (2) and a novel choking model to define the choke level for future spanwise mass flow redistribution. To demonstrate the functionality of the full comprehensive transonicflow approach, the well-known NASA Rotor 67 compressor was used to prove that the inlet relative flow angle should be limited by the choking incidence at the required blade span locations. A 3-D RANS numerical simulation for the NASA Rotor 67 validated the transonic-flow model, showing minimum differences in the spanwise mass flow distribution for the choked off-design cases. The current improvements implemented in the 2-D SLC compressor/fan performance simulator enhance the fidelity not only in analysis mode, but also in design optimisation applications.