Browsing by Author "Malan, Arnaud"

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    A CFD framework for aeroelastic gust load calculations
    (2018) Man, William Liw Tat; Malan, Arnaud
    A Computational Fluid Dynamics (CFD) framework for the simulation of the aeroelastic response of aircraft flying under gust loading was developed. The multiphysics, Finite Volume, VertexCentered code Elementaltextsuperscript{textregistered} was employed and calculations were performed for the transonic flow regime. In the structural domain, the fuselage was treated as rigid and the wing was considered for aeroelastic calculations. The latter was represented by a beam stick model using Timoshenko beam theory in Elementaltextsuperscript{textregistered}'s structural module. The case under consideration was the NASA Common Research Model (CRM) flying at Ma = 0.86 with a 30 ft gust applied over the aircraft. Key contributions of this work included implementation of a computationally efficient gust model as well as the development of a fluidstructure interface. The latter was to transfer forces from a deforming wing skin to the wing-beam in a conservative manner while reflecting the resulting displacements on the wing surface. An interface library was developed for this purpose and 3rd order accurate Bezier curves used to recover a smooth deformed wing. The various sub-components of the aeroelastic model were rigorously validated. Following this, the developed framework was applied to the CRM under gust load conditions.
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    A Volume of Fluid (VoF) based all-mach HLLC Solver for Multi-Phase Compressible Flow with Surface-Tension
    (2021) Oomar, Muhammad Yusufali; Malan, Arnaud; Langdon, Genevieve
    This work presents an all-Mach method for two-phase inviscid flow in the presence of surface tension. A modified version of the Hartens, Lax, Leer and Contact (HLLC) approximate Riemann solver based on Garrick et al. [1] is developed and combined with the popular Volume of Fluid (VoF) method: Compressive Interface Capturing Scheme for Arbitrary Meshes (CICSAM). This novel combination yields a scheme with both HLLC shock capturing as well as accurate liquid-gas interface tracking characteristics. To ensure compatibility with VoF, the Monotone Upstream-centred Scheme for Conservation Laws (MUSCL) [2] is applied to non-conservative (primitive) variables, which yields both robustness and accuracy. Liquid-gas interface curvature is computed via both height functions [3, 4] and the convolution method [5]. This is in the interest of applicability to both cartesian and arbitrary meshes. The author emphasizes the use of VoF in the interest of surface tension modelling accuracy. The method is validated using a range of test-cases available in literature. The results show flow features that are in agreement with experimental and benchmark data. In particular, the use of the HLLC-VoF combination leads to a sharp volume fraction and energy field with improved accuracy (up to secondorder).
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    Elastic Mesh Deformation for Internal Flows with Moving Boundaries
    (2023) Mohammed, Ali Alaa Abdelkareem Awad; Malan, Arnaud
    This project aims to study elastic-based mesh deformation for internal flow problems with obstructions. As such a tank with a flexible internal beam serves as the tested case employed in this work. As such a computer code was developed and the elastic deformation was implemented via the Finite Element Galerkin method with two methods to control the element's distortion near the moving boundaries, Jacobian-based stiffening modification and the distance criterion method. Verification of the scheme was performed by conducting the same test as described in a journal and comparing the obtained results. The project focused on mesh deformation resulting from prescribing the displacements to the inner boundaries of the beam. The results were validated by assessing mesh quality using aspect ratio as a metric, for the 2D unstructured triangular mesh, the element mesh quality showed improvement when the Jacobian-based stiffening method was applied, which involved excluding the determinant of the Jacobian from the stiffness matrix formulation. Similarly, for the 3D unstructured mesh, the aspect ratio improved from elements collapsing to a value close to 1. In both cases, optimal mesh quality was achieved using the distance criterion method for 2D and 3D structured meshes. Specifically, for the 2D structured mesh, the aspect ratio demonstrated improvement, while for the 3D structured mesh, a further enhancement was also observed.
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    Optimisation of feedwater heaters and geothermal preheater in fossil-geothermal hybrid power plant
    (2019) Nsanzubuhoro, Christa; Bello-Ochende, Tunde; Malan, Arnaud
    Sufficient energy supply is a fundamental necessity for the stimulation of socio-economic advancement. However, the current rapid rise in urbanisation has resulted in the significant increase in energy demands. Consequently, the current conventional energy supply systems are facing numerous challenges in meeting the world's growing demand for energy sustainably. Thus, there is an urgent and compelling need to develop innovative, more effective ways to integrate sustainable renewable energy solutions into the already existing systems or better yet, create new systems that all together make use of renewable energy. This research aims to investigate and establish the optimum working conditions of a feedwater heater and geothermal preheater in a power plant that makes use of both renewable and non-renewable energy resources, where renewable energy (geothermal energy) is used to boost the power output in an environmentally sustainable way. Henceforth, a simplified model of a Rankine cycle with single reheat and regeneration and another model with a geothermal preheater substituting the low-pressure feedwater heater were designed. The Engineering Equations Solver (EES) software was used to perform an analysis of the thermodynamic performance of the two models designed. The models were used to analyse the energetic and exergetic effects of replacing a low-pressure feedwater heater with a geothermal preheater sourcing heat from a low temperature geothermal resource (temperature generally < 150°C). The results of this research work reveal that the replacement of the low-pressure feedwater heater with a geothermal preheater increases the power generated since less heat is bled from the low-pressure turbine (allowing more heat energy from the steam to be converted into mechanical energy in the turbine). Applying the principle of the Second Law of thermodynamics analysis, the Number of Entropy Generation Units (EGU) and Entropy Generation Minimisation (EGM) analysis were employed to optimise the designed hybrid system. The feedwater heaters and geothermal preheater were modelled as counter-flow heat exchangers and a downhole co-axial heat exchanger, respectively. The feedwater heaters were optimised by means of the method of Number of Entropy Generation Units whereas the geothermal preheater was optimised by means of the Entropy Generation Minimisation analysis method. Owing to the optimisation of these components, the operating conditions of the boiler and turbines were secondarily improved. Overall, this research emphasises the impact renewable energy has on major power plant systems that are in operation and run on non-renewables.
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    The effect of steam generator tube plugging on its overall thermal performance - A Systems CFD-Based Study
    (2019) Ntuli, Japhet Mkhipheni Ali; Malan, Arnaud
    The steam generator in a pressurized water reactor power plant acts as a fission product barrier between primary and secondary system. Material failure of the tube bundle barrier could therefore lead to a release of radioactive product into the secondary side. Several repair methods have been used to address tube leakage, with the most popular being tube plugging. The objective of this study was to quantify the effect of tube plugging on the thermal performance of a steam generator. For this purpose, the systems computational fluid dynamics (CFD) software Flownex® was used. First, a Flownex® model of the steam generator was developed and validated via comparison of the results to a validated model from the literature. Following this, a hydro-thermal analysis was performed to determine the effect of the tube plugging on the thermal performance under normal operational conditions (excluding the possibility of a tube rupture). Tube plugging of up to 20% was investigated. The model predicted the following effects: decrease in heat transfer, primary coolant mass flowrate and primary outlet pressure. Further, primary flow velocity, pressure drop and outlet temperature increase with increasing tube plugging. On the secondary side, tube plugging lowers the mixture quality in the boiling region and steam production while the re-circulation ratio was increased. Lastly, the model predicted a plugging ratio limit of 17.3%. Beyond this point, the steam generator does not extract sufficient heat from the reactor at 100% power.