Browsing by Author "Konozsy, Laszlo Z."
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Item Open Access Advanced numerical methods for dissipative and non-dissipative relativistic hydrodynamics(Cranfield University, 2020-05) Townsend, Jamie F.; Konozsy, Laszlo Z.; Jenkins, Karl W.High-energy physical phenomena such as astrophysical events and heavy-ion collisions contain a hydrodynamic aspect in which a branch of fluid dynamics called relativistic hydrodynamics (RHD) is required for its mathematical description. The resulting equations must be, more often than not, solved numerically for scientists to ascertain useful information regarding the fluid system in question. This thesis describes and presents a twodimensional computational fluid dynamics (CFD) solver for dissipative and non-dissipative relativistic hydrodynamics, i.e. in the presence and absence of physically resolved viscosity and heat conduction. The solver is based on a finite volume, Godunov-type, HighResolution Shock-Capturing (HRSC) framework, containing a plethora of numerical implementations such as high-order Weighted-Essentially Non-Oscillatory (WENO) spatial reconstruction, approximate Riemann solvers and a third-order Total Variation Diminishing (TVD) Runge–Kutta method. The base numerical solver for the solution of non-dissipative RHD is extensively tested using a series of one-dimensional test cases, namely, a smooth flow problem and shock-tube configurations as well as the two-dimensional vortex sheet and Riemann problem test cases. For the case of non-dissipative relativistic hydrodynamics the relativistic CFD solver is found to perform well in terms of the orders of accuracy achieved and its ability to resolve shock wave patterns. Numerical pathologies have been identified when the relativistic HLLC Riemann solver is used in multi-dimensions for problems exhibiting strong shock waves. This is attributed to the so-called Carbuncle problem which is shown to occur because of pressure differencing within the process of restoring the missing contact discontinuity of its predecessor, the HLL Riemann solver. To avoid this numerical pathology and improve the robustness of numerical solutions that make use of the HLLC Riemann solver, the development of a rotated-hybrid Riemann solver arising from the hybridisation of the HLL and HLLC (or Rusanov and HLLC) approximate Riemann solvers is presented. A standalone application of the HLLC Riemann solver can produce spurious numerical artefacts when it is employed in conjunction with Godunov-type high-order methods in the presence of discontinuities. It has been found that a rotated-hybrid Riemann solver with the proposed HLL/HLLC (Rusanov/HLLC) scheme could overcome the difficulty of the spurious numerical artefacts and presents a robust solution for the Carbuncle problem. The proposed rotated-hybrid Riemann solver provides sufficient numerical dissipation to capture the behaviour of strong shock waves for relativistic hydrodynamics. Therefore, focus is placed on two benchmark test cases (odd-even decoupling and double-Mach reflection problems) and the investigation of two astrophysical phenomena, the relativistic Richtmyer– Meshkov instability and the propagation of a relativistic jet. In all presented test cases, the Carbuncle problem is shown to be eliminated by employing the proposed rotated-hybrid Riemann solver. This strategy is problem-independent, straightforward to implement and provides a consistent robust numerical solution when combined with Godunov-type highorder schemes for relativistic hydrodynamics...[cont.]Item Open Access Aeroelastic analysis on a multi-element composite wing in ground effect using fluid-structure interaction.(Cranfield University, 2021-08) Bang, Chris Sungkyun; Temple, Chris; Konozsy, Laszlo Z.The present research focuses on an advanced coupling of computational fluid dynamics (CFD) and structural analysis (FEA) on the aeroelastic behaviour of a multi-element inverted composite wing with the novelty of including the ground effect. Due to the elastic properties of composite materials, Formula One (F1) car’s front wing may become flexible under fluid loading, modifying the flow field and eventually affecting overall aerodynamics. This research investigates the influence of elastic behaviour of the wing in ground proximity on the aerodynamic and structural performance by setting up an accurate the Fluid-Structure Interaction (FSI) modelling framework. A steady-state two-way coupling method is exploited to run the FSI simulations using ANSYS, which enables simultaneous calculation by coupling CFD with FEA. A grid sensitivity study and turbulence model study are preferentially performed to enhance confidence of the numerical approach. The FSI study encompasses everything from basic examination and measurement of the interaction phenomena using a single and double element inverted wing to the creation of a multi-objective wing design optimisation procedure. The computational results obtained from FSI simulations are assessed and compared with the experimentation with respect to surface pressure distribution, aerodynamic associated forces, and wake profiles. Concerning structure layups, ply orientation and core materials, the effect of various composite structure configurations on the wing performance is extensively studied. An efficient and unique decomposition-based optimisation framework utilising the response surface model is provided based on the aero-structural coupled analysis in order to enhance the wing design process' accuracy and efficiency while tackling aeroelastic phenomena.Item Open Access CFD modelling of carbon capture in large-scale for structured packed bed column.(Cranfield University, 2021-05) Hossain, Mohammad Ashraf; Manovic, Vasilije; Konozsy, Laszlo Z.; Navabi, Syed AliIn this Ph.D. thesis, a novel 3D numerical model is developed to solve multiphase flow problem for carbon capture. The model solves the Navier-Stokes equations with commercial solver Ansys Fluent with higher accuracy and much better prediction. The proposed model was at first developed to solve the hydrodynamics problem inside the structured packed bed. In the hydrodynamic part, viscous resistance and inertia resistance for both gas and liquid were taken into account and were implemented by the User Defined Function (UDF). The structured mesh was done using ICEM-CFD. In this part, dispersion forces were also included by UDF. Hydrodynamics of the structured packed bed was validated in terms of liquid volume fraction and, a higher degree of accuracy was achieved. This achievement was done by implementing drag law in a novel way. Dispersion of the liquid inside the packed bed was modelled both by mechanical dispersion and by spread tensor. Pressure drop is a very important part of designing structured packing and, it has to be kept to a minimum. In the hydrodynamics study, this pressure drop was kept minimum, and a good distribution of gas and liquid was achieved. The second part of the model is the chemical reactions. In this case, all the five reactions that occur in carbon capture were taken into account along with the hydrodynamics. Few studies like the effect of solvent concentration, the effect of pressure were studied by using this part of the model. Another novel aspect of the model is that it can predict gas-liquid interfacial area and enhancement factor for chemical reactions. As a result, it has become much easier to understand chemical reactions and calculate carbon removal easily. The third part of the model is the heat transfer effect. Heat transfer effect was included by changing gas and liquid temperature and it was found that liquid temperature has a wider impact on carbon capture. All the contributions to the knowledge were summarized in Chapter 7.