Browsing by Author "Al-Akam, Aws A."

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    Computational fluid dynamics-based approach for low-order models of propelling nozzle performance
    (Institution of Mechanical Engineers, 2019-03-14) Al-Akam, Aws A.; Nikolaidis, Theoklis; MacManus, David G.
    At the preliminary design stage for an aero-engine, the evaluation of the nozzle performance is an important aspect as it affects the overall engine cycle behaviour. Currently, there is a lack of systematic, extensive data on the nozzle performance and its dependence on the geometric and aerodynamic aspects. This paper presents a method that can be used to build characteristic maps for a nozzle as a function of a number of geometric and aerodynamic parameters. The proposed method encompasses the design of a nozzle configuration, a parameterisation of the nozzle pressure ratio, nozzle contraction ratio, plug half-angle (β), mesh generation, and an aerodynamic assessment using the Favre-averaged Navier–Stokes method. The method has been validated against experimental performance data of a plug nozzle configuration and then used for the aerodynamic assessment. The derived nozzle maps show that the thrust coefficient (Cfg) for this type of nozzle is significantly sensitive to the combined effect of the variation of the proposed parameters on the nozzle performance. These maps were used to build low-order models to predict Cfg, using response surface methods. The performance was assessed, and the results show that these low-order methods are capable of providing Cfg estimates with sufficient accuracy for use in preliminary design assessments.
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    A numerical model for predicting the aerodynamic characteristics of propelling nozzles
    (International Society for Air Breathing Engines, 2019-12-31) Al-Akam, Aws A.; Nikolaidis, Theoklis; MacManus, David G.; Goulos, Ioannis
    It is essential to predict the exhaust-system performance of the aero-engine during the design stages as it plays a critical role in the engine components matching. In addition to this, it has an impact on the overall engine performance. Consequently, it is important to model the complex flow features around the exhaust system accurately in order to capture the flow characteristics. Computational Fluid Dynamics (CFD) alongside with low-order models can play a central role in the design and performance assessment of the propulsion system. This paper aims to explore the suitability of a numerical model, boundary conditions, and the employed mesh topology in computing a propelling nozzle performance. The current work is a first step towards building a module to assess a wide range of nozzle configurations at the preliminary design stages. A single-stream and plug-nozzle propelling nozzle were simulated for this purpose. For the single-stream nozzle, the simulations were run at various flight conditions and different geometrical features. For both nozzle configurations, a comparison between the effectiveness of six turbulence models to capture the nozzle flow features is presented. The validated module is then used to assess the impact of the bypass flow and the plug half-angle on the performance of the core nozzle for a dual-stream nozzle configuration. The calculated nozzle efficiencies are lower than the experimental data for both nozzle types, with a maximum difference of single-stream nozzle efficiency ≈ - 3.29% at NPR = 1.83 and by -0.84% at NPR = 3.88 and for the plug nozzle with -1.05% at NPR 2.64 and across a range from -0.46% to -0.68% between NPR = 3.14 to 5.3. The application of RANS k-ω SST turbulence model showed the best results as compared with the standard k-ε, RNG k-ε, realizable k-ε, and Spalart-Allmaras models in simulating the propelling nozzles aerodynamics. Generally, the results show the strength and the weakness of the numerical module in simulating the nozzle flow features and predicting its performance. Moreover, the Fan Nozzle Pressure Ratio (FNPR) and the plug half-angle (ω) has a noticeable impact on the overall and core nozzle performance. Moreover, the combined impact of both parameters has a noticeable impact on the propelling nozzle performance.
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    The use of enhanced nozzle maps for gas-turbine performance modelling
    (American Society of Mechanical Engineers, 2021-09-16) Al-Akam, Aws A.; Nikolaidis, Theoklis; MacManus, David G.; Pellegrini, Alvise
    The use of a simulation tool to predict the aero-engine performance before committing to a final engine design has become one of the most cost-saving approaches in this field. However, most of these tools are based on low fidelity thermodynamic models, which are incapable of fully capturing the impact of three-dimensional flow characteristics. An aero-engine exhaust-system is one of the essential components that affect the engine performance. Currently, engine performance models tend to utilize simplified nozzle performance maps. These maps typically provide information over a very limited range of nozzle geometries, which may not apply to the wide range of architectures and designs of aeroengines. The current paper presents a methodology for the development of nozzle performance maps, which takes into account the aerodynamic and the geometric parameters of the nozzle design. The methodology is based on the reduced-order models. These models are integrated into a zero-dimensional engine performance code to improve the accuracy of its thrust calculation. The impact of the new thrust model on the overall engine performance and the operating point is analysed and discussed. The results showed that the implementation of the modified maps, which take into account the flow characteristics and the geometry of the nozzle, affects the thrust calculation. In a typical case of a turbofan operating at cruise conditions, the net thrust estimation with the modified nozzle maps showed a difference of 0.2%, compared with the simple nozzle maps. The new thrust calculation method has the advantage in capturing the multidimensional impact of the flow of the nozzle as compared with the conventional one. Furthermore, the implementation of the new method reduces the uncertainties introduced by a simplified nozzle model and, consequently, it can support the decision-making process in the design of the engine.