Browsing by Author "Tsoutsanis, Panagiotis"
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Item Open Access Adaptive mesh refinement techniques for high-order finite-volume WENO schemes(European Congress on Computational Methods in Applied Sciences and Engineering, 2016-06-30) Srinivasan, Harshavardhana; Tsoutsanis, PanagiotisThis paper demonstrates the capabilities of Adaptive Mesh Refinement Techniques (AMR) on 2D hybrid unstructured meshes, for high order finite volume WENO methods. The AMR technique developed is a conformal adapting unstructured hybrid quadrilaterals and triangles (quads & tris) technique for resolving sharp flow features in accurate manner for steady-state and time dependent flow problems. In this method, the mesh can be refined or coarsened which depends on an error estimator, making decision at the parent level whilst maintaining a conformal mesh, the unstructured hybrid mesh refinement is done hierarchically.When a numerical method can work on a fixed conformal mesh this can be applied to do dynamic mesh adaptation. Two Refinement strategies have been devised both following a H-P refinement technique, which can be applied for providing better resolution to strong gradient dominated problems. The AMR algorithm has been tested on cylindrical explosion test and forward facing step problems.Item Open Access Addressing the challenges of implementation of high-order finite volume schemes for atmospheric dynamics of unstructured meshes(European Congress on Computational Methods in Applied Sciences and Engineering, 2016-06-30) Tsoutsanis, Panagiotis; Drikakis, DimitrisThe solution of the non-hydrostatic compressible Euler equations using Weighted Essentially Non-Oscillatory (WENO) schemes in two and three-dimensional unstructured meshes, is presented. Their key characteristics are their simplicity; accuracy; robustness; non-oscillatory properties; versatility in handling any type of grid topology; computational and parallel efficiency. Their defining characteristic is a non-linear combination of a series of high-order reconstruction polynomials arising from a series of reconstruction stencils. In the present study an explicit TVD Runge-Kutta 3rd -order method is employed due to its lower computational resources requirement compared to implicit type time advancement methods. The WENO schemes (up to 5th -order) are applied to the two dimensional and three dimensional test cases: a 2D rising.Item Open Access Aerodynamic analysis of large wind farms using two-scale coupled modelling approaches.(2021-08) Ma, Lun; Tsoutsanis, Panagiotis; Antoniadis, AntoniosThe effects of turbine aerodynamics and response characteristics of the atmospheric boundary layer on the overall wind farm efficiency are investigated in this research. Various wind farm modelling strategies, which include a theoretical and several CFD models, are presented. This study consists of three main parts: (i) improve and validate an existing theoretical wind farm model, (ii) infinitely large wind farm modelling with actuator-disc and fully-resolved turbine models, and (iii) finite-size wind farm modelling with a numerical weather prediction model. In the first part, an extended theoretical model based on a two-scale coupled momentum balance method is proposed to estimate aerodynamic effects of wind turbine towers on the performance of large wind farms. The modified theoretical model predicts that the optimal turbine spacing should increase with the value of normalised support-structure drag, as well as additional parameters describing the response characteristics of the atmospheric boundary layer to the total farm drag. The Detached-Eddy simulations of a periodic array of fully staggered actuator discs (AD) show a reasonably good agreement (within 10% in the prediction of power) with the modified theoretical model. In the second part, a fully resolved (FR) NREL 5MW turbine model is employed in two URANS simulations (with and without the turbine tower) of a fully developed wind farm boundary layer. The FR-URANS results show stronger tower effects than both AD-RANS and theoretical model predictions, which is a strong indication of the necessity of considering turbine support structure within large wind farm models. The possibility of performing DDES is also investigated with the same FR turbine model and periodic domain setup. The results show complex turbulent flow characteristics within a large wind farm, where typical hairpin and hub vortices have been clearly captured. In addition, the computational cost of DDES has been found to be similar to URANS (for a given number of rotations), which is a positive sign for conducting DDES in future studies. In the third part, a numerical weather prediction model is used as a realistic farm-scale flow model to investigate how the streamwise pressure gradient, Coriolis force and acceleration/deceleration terms in the farm-scale momentum balance equation tend to change in time. The results suggest that the streamwise pressure gradient may be enhanced substantially by the resistance caused by the wind farm, whereas its influence on the other two terms appears to be relatively minor. These results suggest the importance of modelling the farm-induced pressure gradient accurately for various weather conditions in future studies of large wind farmsItem Open Access Application of central-weighted essentially non-oscillatory finite-volume interface-capturing schemes for modeling cavitation induced by an underwater explosion(MDPI, 2024-01-29) Adebayo, Ebenezer Mayowa; Tsoutsanis, Panagiotis; Jenkins, Karl W.Cavitation resulting from underwater explosions in compressible multiphase or multicomponent flows presents significant challenges due to the dynamic nature of shock–cavitation–structure interactions, as well as the complex and discontinuous nature of the involved interfaces. Achieving accurate resolution of interfaces between different phases or components, in the presence of shocks, cavitating regions, and structural interactions, is crucial for modeling such problems. Furthermore, pressure convergence in simulations involving shock–cavitation–structure interactions requires accurate algorithms. In this research paper, we employ the diffuse interface method, also known as the interface-capturing scheme, to investigate cavitation in various underwater explosion test cases near different surfaces: a free surface and a rigid surface. The simulations are conducted using the unstructured compressible Navier–Stokes (UCNS3D) finite-volume framework employing central-weighted essentially non-oscillatory (CWENO) reconstruction schemes, utilizing the five-equation diffuse interface family of methods. Quantitative comparisons are made between the performance of both models. Additionally, we examine the effects of cavitation as a secondary loading source on structures, and evaluate the ability of the CWENO schemes to accurately capture and resolve material interfaces between fluids with minimal numerical dissipation or smearing. The results are compared with existing high-order methods and experimental data, where possible, to demonstrate the robustness of the CWENO schemes in simulating cavitation bubble dynamics, as well as their limitations within the current implementation of interface capturing.Item Open Access Assessment of high-order finite volume methods on unstructured meshes for RANS solutions of aeronautical configurations.(Elsevier, 2017-01-03) Antoniadis, Antonis F.; Tsoutsanis, Panagiotis; Drikakis, DimitrisThis paper is concerned with the application of k-exact finite volume methods for compressible Reynolds-Averaged Navier-Stokes computations of flows around aeronautical configurations including the NACA0012, RAE2822, MDA30P30N, ONERA-M6, CRM and DLR-F11. High-order spatial discretisation is obtained with the Weighted Essentially Non-Oscillatory and the Monotone-Upstream Central Scheme for Conservation Laws methods on hybrid unstructured grids in two- and three- dimensions. Schemes of fifth, third and second order comprise the foundation of the analysis, with main findings suggesting that enhanced accuracy can be obtained with at least a third-order scheme. Steady state solutions are achieved with the implicit approximately factored Lower-Upper Symmetric Gauss-Seidel time advancing technique, convergence properties of each scheme are discussed. The Spalart-Allmaras turbulence model is employed where its discretisation with respect to the high-order framework is assessed. A low-Mach number treatment technique is studied, where recovery of accuracy in low speed regions is exemplified. Results are compared with referenced data and discussed in terms of accuracy, grid dependence and computational budget.Item Open Access Blade-resolved CFD simulations of a periodic array of NREL 5 MW rotors with and without towers(MDPI, 2022-01-14) Ma, Lun; Delafin, Pierre-Luc; Tsoutsanis, Panagiotis; Antoniadis, Antonis F.; Nishino, TakafumiA fully resolved (FR) NREL 5 MW turbine model is employed in two unsteady Reynolds-averaged Navier–Stokes (URANS) simulations (one with and one without the turbine tower) of a periodic atmospheric boundary layer (ABL) to study the performance of an infinitely large wind farm. The results show that the power reduction due to the tower drag is about 5% under the assumption that the driving force of the ABL is unchanged. Two additional simulations using an actuator disc (AD) model are also conducted. The AD and FR results show nearly identical tower-induced reductions of the wind speed above the wind farm, supporting the argument that the AD model is sufficient to predict the wind farm blockage effect. We also investigate the feasibility of performing delayed-detached-eddy simulations (DDES) using the same FR turbine model and periodic domain setup. The results show complex turbulent flow characteristics within the farm, such as the interaction of large-scale hairpin-like vortices with smaller-scale blade-tip vortices. The computational cost of the DDES required for a given number of rotor revolutions is found to be similar to the corresponding URANS simulation, but the sampling period required to obtain meaningful time-averaged results seems much longer due to the existence of long-timescale fluctuations.Item Open Access CODE_MRF.zip(Cranfield University, 2023-10-11 09:00) Silva, Paulo; Tsoutsanis, Panagiotissource codeItem Open Access Complete body aerodynamic study of three vehicles(SAE International, 2017-03-28) Simmonds, Nicholas; Pitman, John; Tsoutsanis, Panagiotis; Jenkins, Karl W.; Gaylard, Adrian; Jansen, WilkoCooling drag has traditionally proven to be a difficult flow phenomenon to predict using computational fluid dynamics. With the advent of grille shutter systems, the need to accurately pre-dict this quantity during vehicle development has become more pressing. A comprehensive study is presented in the paper of three automotive models with different cool-ing drag deltas using the commercial CFD solver STARCCM+. The notchback DrivAer model with under-hood cooling provides a popular academic benchmark alongside two fully-engineered production cars; a large saloon (Jaguar XJ) and an SUV (Land Rover Range Rover). Previous studies detail the differences in the flow field; highlighting the interaction between the exiting under-hood cooling flow, and the wheel and base wakes for open and closed grilles. In this study three levels of spatial discretization were used for each vehicle in order to study the importance of accurately capturing the base wake on the absolute and cooling delta drag values and the cooling air mass flow rates. This study is performed using three steady-state RANS solvers (k-ɛ realizable, k-ω SST and Spalart-Allmaras), and the unsteady k-ω SST Detached-Eddy-Simulation. Results show that it is very important to capture both separation and large wake structures in order to recover physically realistic behavior. The RANS models perform well (within 0.005 Cd, 5 counts) on saloon based models, with the k-ɛ realizable model displaying mesh independence. For the SUV model the RANS models predict the correct cooling deltas; however, only the k-ω SST model gives accurate absolute values, with those for k-e realizable and Spalart-Allmaras 22 and 18 counts too high, respectively. The k-ω SST model on the finest mesh contains oscillations in the flow field, particularly in the wake, which are attributable to the unsteady nature of the flow. When averaging the steady-state simulations over 1000 iterations the resulting wake structure is shown to be in close agreement to the unsteady Detached-Eddy-Simulations. The DES model confirms that the variance in the residuals for the k-w SST was indicative of flow unsteadiness.Item Open Access Computational assessment of the hazardous release dispersion from a diesel pool fire in a complex building’s area(MDPI, 2018-12-13) Vasilopoulos, Konstantinos; Mentzos, Michalis; Sarris, Ioannis E.; Tsoutsanis, PanagiotisA hazardous release accident taking place within the complex morphology of an urban setting could cause grave damage both to the population’s safety and to the environment. An unpredicted accident constitutes a complicated physical phenomenon with unanticipated outcomes. This is because, in the event of an unforeseen accident, the dispersion of the hazardous materials exhausted in the environment is determined by unstable parameters such as the wind flow and the complex turbulent diffusion around urban blocks of buildings. Our case study focused on a diesel pool fire accident that occured between an array of nine cubical buildings. The accident was studied with a Large eddy Simulation model based on the Fire Dynamics Simulation method. This model was successfully compared against the nine cubes of the Silsoe experiment. The model’s results were used for the determination of the immediately dangerous to life or health smoke zones of the accident. It was found that the urban geometry defined the hazardous gasses dispersion, thus increasing the toxic mass concentration around the buildings.Item Open Access CWENO finite-volume interface capturing schemes for multicomponent flows using unstructured meshes(Springer, 2021-11-09) Tsoutsanis, Panagiotis; Adebayo, Ebenezer Mayowa; Carriba Merino, Adrian; Perez Arjona, Agustin; Skote, MartinIn this paper we extend the application of unstructured high-order finite-volume central-weighted essentially non-oscillatory (CWENO) schemes to multicomponent flows using the interface capturing paradigm. The developed method achieves high-order accurate solution in smooth regions, while providing oscillation free solutions at discontinuous regions. The schemes are inherently compact in the sense that the central stencils employed are as compact as possible, and that the directional stencils are reduced in size, therefore simplifying their implementation. Several parameters that influence the performance of the schemes are investigated, such as reconstruction variables and their reconstruction order. The performance of the schemes is assessed under a series of stringent test problems consisting of various combinations of gases and liquids, and compared against analytical solutions, computational and experimental results available in the literature. The results obtained demonstrate the robustness of the new schemes for several applications, as well as their limitations within the present interface-capturing implementation.Item Open Access Data for Paper "Numerical Investigation of Orifice Nearfield Flow Development in Oleo-Pneumatic Shock Absorbers"(Cranfield University, 2022-02-18 09:57) Sheikh Al Shabab, Ahmed; Skote, Martin; Tsoutsanis, Panagiotis; Antoniadis, Antonios; Vitlaris, Dimitrios; Grenko, BojanData for the journal paper titled: Numerical Investigation of Orifice Nearfield Flow Development in Oleo-Pneumatic Shock AbsorbersItem Open Access Data for Paper "Unsteady Multiphase Simulation of Oleo-Pneumatic Shock Absorber Flow"(Cranfield University, 2024-02-21 18:05) Sheikh Al Shabab, Ahmed; Grenko, Bojan; Silva, Paulo; Antoniadis, Antonios; Tsoutsanis, Panagiotis; Skote, MartinDataset for the paper "Unsteady Multiphase Simulation of Oleo-Pneumatic Shock Absorber Flow"Item Open Access Data Supporting "Study of Orifice Design on Oleo-Pneumatic Shock Absorber"(Cranfield University, 2024-05-02 11:15) Silva, Paulo; Tsoutsanis, Panagiotis; Skote, Martin; Sheikh Al Shabab, AhmedThis data contain the results of the paper.Item Open Access Data supporting 'Numerical Investigation of full helicopter with and without the ground effect'(Cranfield University, 2022-02-09 18:11) Silva, Paulo; Tsoutsanis, PanagiotisIn the present work, the aerodynamic performance of the full helicopter PSP in hover flight is investigated using a simplified concept of multiple reference frame (MRF) technique in the context of high-order Monotone Upstream Centred Scheme for Conservation Laws (MUSCL) cell-centred finite volume method. The predictions were obtained for two ground distances and several collective pitch angle at tip Mach number of 0.585. The calculations were made for both out-of-ground-effect (OGE) and in-ground-effect (IGE) cases and compared with experimental data in terms of pressure distribution and integrated thrust and torque and vortex system.Item Open Access Data supporting: High-order hybrid DG-FV framework for compressible multi-fluid problems on unstructured meshes""(Cranfield University, 2024-02-12 17:07) Maltsev, Vadim; Skote, Martin; Tsoutsanis, PanagiotisThis dataset contains binary output in Tecplot format for the test problems analysed in the "High-order hybrid DG-FV framework for compressible multi-fluid problems on unstructured meshes" JCP paper. Test cases included are: - Gas-water isolated material interface advection - 2D and 3D helium bubble interaction with shock wave - 2D shock driven air bubble collapse in water - 2D and 3D shock driven air bubble array collapse in water - 2D underwater explosionItem Open Access Dynamic swirl distortion characteristics in S-shaped diffusers using UCNS3D and time-resolved, stereo PIV methods(AIAA, 2024-01-04) Piovesan, Tommaso; Migliorini, Matteo; Zachos, Pavlos K.; Tsoutsanis, PanagiotisEmbedded propulsion systems are key enablers of future aircraft configurations with expected benefits in reduced environmental impact and enhanced performance. Such propulsion systems are typically integrated with convoluted, complex air induction systems whose dynamic distortion characteristics previously found detrimental to the engine’s stability. Therefore, predictive capability for these complex flows is critical for the design of closely coupled engine – intake architectures. A new High-Order Delayed Detached Eddy Simulation (HODDES) is applied in this work to predict dynamic flow distortion within an S-shaped subsonic diffuser. The aim is to assess the ability of a new solver to predict unsteady and extreme distortion events. The HODDES results have been validated with Time-Resolved Stereo PIV (TR-PIV) data. The analysis shows that the HODDES captures the key mean and unsteady flow characteristics, the spectral content and unsteady distortion descriptor behavior across the Aerodynamic Interface Plane (AIP). Although the predicted mean velocity levels, flow field unsteadiness and range of predicted velocities are notably higher than the ones observed at the experiment by at least 40%, it is suggested that this is an artifact of a discrepancy between the axial planes where the CFD and test data were analyzed. The findings of the work suggest that the HODDES is broadly capturing the dynamic flow fields and with some further effort towards the calibration of its RANS models can be further used to study the integration of closely coupled fan system downstream of air induction systems.Item Open Access Extended bounds limiter for high-order finite-volume schemes on unstructured meshes(Elsevier, 2018-02-09) Tsoutsanis, PanagiotisThis paper explores the impact of the definition of the bounds of the limiter proposed by Michalak and Ollivier-Gooch in [Accuracy preserving limiter for the high-order accurate solution of the Euler equations, J. Comput. Phys. 228 (2009) 8693–8711], for higher-order Monotone-Upstream Central Scheme for Conservation Laws (MUSCL) numerical schemes on unstructured meshes in the finite-volume (FV) framework. A new modification of the limiter is proposed where the bounds are redefined by utilising all the spatial information provided by all the elements in the reconstruction stencil. Numerical results obtained on smooth and discontinuous test problems of the Euler equations on unstructured meshes, highlight that the newly proposed extended bounds limiter exhibits superior performance in terms of accuracy and mesh sensitivity compared to the cell-based or vertex-based bounds implementations.Item Open Access High-order hybrid DG-FV framework for compressible multi-fluid problems on unstructured meshes(Elsevier, 2024-02-06) Maltsev, Vadim; Skote, Martin; Tsoutsanis, PanagiotisIn this work we extend the hybrid Discontinuous Galerkin/ Finite Volume framework, introduced in V. Maltsev, D. Yuan, K. W. Jenkins, M. Skote, P. Tsoutsanis, “Hybrid discontinuous Galerkin-finite volume techniques for compressible flows on unstructured meshes, Journal of Computational Physics 473 (2023)” [1], to multi-species problems involving gas-gas and gas-liquid systems. The numerical scheme achieves high order accuracy in smooth flow regions thanks to the DG discretisation, yet avoiding oscillations at material interfaces and shocks thanks to a FV type reconstruction. This strategy, as typically represented in literature, makes use of the so-called troubled cell indicators for the detection of numerical oscillations generated by an unlimited high-order scheme in presence of discontinuities, and enables a more dissipative scheme in the troubled cells only in order to suppress the spurious oscillations. As will be shown in a series of increasingly challenging test-cases, when applied to multi-species flows in the context of diffuse-interface models, the hybrid framework is able to limit the excessive material interface dissipation, characteristic of these interface-capturing methods, allowing at the same time a control over the amount of dissipation necessary to solve stiffer problems.Item Open Access High-order methods for diffuse-interface models in compressible multi-medium flows: a review(AIP, 2022-02-03) Maltsev, Vadim; Skote, Martin; Tsoutsanis, PanagiotisThe diffuse interface models, part of the family of the front capturing methods, provide an efficient and robust framework for the simulation of multi-species flows. They allow the integration of additional physical phenomena of increasing complexity while ensuring discrete conservation of mass, momentum, and energy. The main drawback brought by the adoption of these models consists of the interface smearing, increasing with the simulation time, therefore, requiring a counteraction through the introduction of sharpening terms and a careful selection of the discretization level. In recent years, the diffuse interface models have been solved using several numerical frameworks including finite volume, discontinuous Galerkin, and hybrid lattice Boltzmann method, in conjunction with shock and contact wave capturing schemes. The present review aims to present the recent advancements of high-order accuracy schemes with the capability of solving discontinuities without the introduction of numerical instabilities and to put them in perspective for the solution of multi-species flows with the diffuse interface method.Item Open Access Hovering rotor solutions by high-order methods on unstructured grids(Elsevier, 2019-12-19) Ricci, Francesco; Silva, Paulo A. S. F.; Tsoutsanis, Panagiotis; Antoniadis, Antonis F.This paper concerns the implementation and evaluation of high-order reconstruction schemes for predicting three well established hovering rotor flows i.e. Caradonna and Tung, PSP and UH-60A. Monotone Upstream Centred Scheme for Conservation Laws (MUSCL) and Weighted Essentially Non-Oscillatory (WENO) spatial discretisation schemes, up to fourth-order, are employed to approximate the compressible Reynolds Averaged Navier-Stokes (RANS) equations in a rotating reference frame, on mixed-element unstructured grids. Various flow speed conditions are simulated including subsonic and transonic, with the latter stretching the discontinuities capturing abilities of the numerics. We consistently evaluate the accuracy, cost and robustness of the developed numerical framework by analysing the discretisation error with respect to the grid resolution. A thorough validation is conducted for all cases by comparing the obtained numerical solutions with experimental data points and relevant literature
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