Browsing by Author "Ferrer-Vidal, Luis E."

Now showing 1 - 6 of 6
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    Characterization of axial compressor performance at locked rotor and torque-free windmill conditions
    (Elsevier, 2020-04-28) Ferrer-Vidal, Luis E.; Iglesias-Pérez, Alejandro; Pachidis, Vassilios
    Prediction of aero-engine performance in the sub-idle regime is becoming increasingly important. Performance prediction tools rely on component maps to enable system-level simulations. Methods to obtain compressor sub-idle maps have traditionally relied on low-order extrapolations, but the continued development of robust turbomachinery numerical methods suggest that these tools may be sufficiently robust to allow improved performance predictions at these challenging off-design conditions. In this work, an axial compressor rig is used to obtain locked rotor and windmill performance characteristics which are then compared against results from Computational Fluid Dynamics (CFD) simulations. This paper assesses the capability of steady state RANS CFD as a tool for the prediction of sub-idle compressor performance and helps delineate the minimal modelling fidelity required to obtain sufficiently accurate performance models. The multi-stage performance of axial compressors at locked rotor and at the zero-torque windmilling condition are discussed. Windmilling multi-stage compressors are found to operate with the front stages compressing the flow and the last stages expanding to satisfy the power balance. The torque-free windmilling behavior of axial compressors can be described non-dimensionally, allowing limited numerical simulations to be used to build sub-idle performance models.
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    Considerations on axial compressor bleed for sub-idle performance models
    (American Society of Mechanical Engineers, 2021-01-11) Roig Tió, Ferran; Ferrer-Vidal, Luis E.; Azamar Aguirre, Hasani; Pachidis, Vassilios
    The trend towards increased bypass ratio and reduced core size in civil aero-engines puts a strain on ground-start and relight capability, prompting renewed interest in sub-idle performance modelling. While a number of studies have looked at some of the broad performance modelling issues prevalent in this regime, the effects that bleed can have on sub-idle performance have not been addressed in the literature. During start-up and relight, the unknown variation in bleed flows through open handling bleed valves can have a considerable impact on the compressor’s operating line. This paper combines experimental, numerical and analytical approaches to look at the effect that sub-idle bleed flows have on predicted start-up operating lines, along with their effect on compressor characteristics. Experimental whole-engine data along with a purpose-built core-flow analysis tool are used to assess the effect of bleed model uncertainty on engine performance models. An experimental rig is used to assess the effects of reverse bleed on compressor characteristics and measurements are compared against numerical results. Several strategies for the generation of sub-idle maps including bleed effects are investigated.
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    An enhanced compressor sub-idle map generation method
    (Global Power and Propulsion Society, 2018-01-13) Ferrer-Vidal, Luis E.; Pachidis, Vassilios; Tunstall, Richard J.
    Several techniques have come about for the mathematical extrapolation of compressor maps from the idle region down to zero speed. Relatively little work has been done on methods which attempt to extract compressor sub - idle performance from physical grounds. This paper focuses on the design of an axial compressor rig to obtain sub - idle data in the form of locked rotor and windmill characteristics. The rig design is presented and the results obtained discussed. The data gathered is used to generate physics - based sub - idle compressor maps which are then compared to existing method s for sub - idle map generation. Interpolation from the locked rotor characteristic is shown to improve map generation over extrapolation methodologies, while the windmilling characteristic is shown to be an important addition to the interpolation process.
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    Generating axial compressor maps to zero speed
    (SAGE, 2020-12-06) Ferrer-Vidal, Luis E.; Pachidis, Vassilios; Tunstall, Richard J.
    Gas turbine performance models typically rely on component maps to characterize engine component performance throughout the operational regime. For the sub-idle case, the lack of reliable rig test data or inability to run design codes far from design conditions entails that component maps have to be generated from the extrapolation of existing data at higher speeds. This undermines the accuracy of whole-engine sub-idle performance models, at times impacting engine development and certification of aviation engines and the accuracy of start-up performance prediction in industrial gas turbines. One of the main components driving this issue is the core compression system, which can present operability concerns during light-up and which also sets the combustor airflow required for ignition. This paper presents, discusses, and draws on previous approaches to describe a method enabling the creation of sub-idle compressor maps from analytical and physical grounds. The method relies on the calculation of zero-speed and torque-free lines to generate a map down to zero speed along with analytical interpolation. A method for the interpolation process is described. A sensitivity study is carried out to assess the effects that different elements of the map generation process may have on the accuracy of the resulting performance calculation. Overall, a method for the generation of accurate, consistent maps from limited geometry data is identified.
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    Low-order models for the calculation of compressor sub-idle characteristics
    (ISABE, 2019-09-27) Righi, Mauro; Ferrer-Vidal, Luis E.; Allegretti, Alessandro; Pachidis, Vassilios
    This paper focuses on the development of low-order models for the generation of compressor sub-idle characteristics via numerical simulation of an axial-flow compressor at sub-idle conditions. A through-flow code using body forces developed by Cranfield University is used as a framework to test three new methods to model blade row performance under sub-idle conditions. The first method is a simplified analytical model of a separated blade passage, originally developed to model reverse flow through the passage. The method consists of a modification to the body forces employed by the code and can be easily adapted to model the sub-idle operating condition. The second method is a set of pressure loss and deviation angle correlations developed at Cranfield University specifically for sub-idle conditions. A third approach makes use of the deviation angle correlations along with the modified body-force method, resulting in a hybrid approach. These three methods are implemented in the through-flow code to obtain low-order models that are then used to generate compressor characteristics under locked rotor and windmilling conditions. The code created is able to generate compressor characteristics throughout the sub-idle operating regime in a few minutes. The low-order model results are compared against experimental data from a sub-idle compressor rig and CFD RANS simulations of the same compressor. The generated characteristics show promising results, with only minor calibration required for the numerically calculated characteristics to match those generated via experiment.
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    Numerical modeling of core compressor discharge for a windmilling aero engine
    (Elsevier, 2020-11-30) Ferrer-Vidal, Luis E.; Pachidis, Vassilios
    A gas turbine engine’s ability to relight in flight depends heavily on the combustion chamber’s inlet conditions. These conditions are dictated by the core compression system located immediately upstream of the combustor, but such conditions during windmill have not been thoroughly investigated and are not commonly available in the literature. In this paper, an entire high pressure ratio axial compressor is modelled using scale adaptive simulation. Real windmilling inlet conditions extracted from altitude test facility data are used as boundary conditions. The implications of steady vs. unsteady modelling and the use of different interface modelling approaches are investigated. A description of the discharge flow-field is given in terms of flow statistics, turbulent quantities, and dominant dynamic modes. The discharge flow-field is dominated by small scale structures resulting from leading edge separation in the last stator (OGV), with little influence of the upstream stages on the stator flow-field dynamics. The study has shown that, while an unsteady analysis is required, reduced order models allowing for a decoupled analysis of the last stage flow dynamics may be sufficient in future studies seeking to characterize combustor inlet conditions for inflight relight