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Title: Time-domain and harmonic balance turbulent Navier-Stokes analysis of oscillating foil aerodynamics
Author: Piskopakis, Andreas
ISNI:       0000 0004 5360 8976
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2014
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The underlying thread of the research work presented in this thesis is the development of a robust, accurate and computationally efficient general-purpose Reynolds-Averaged Navier-Stokes code for the analysis of complex turbulent flow unsteady aerodynamics, ranging from low-speed applications such as hydrokinetic and wind turbine flows to high-speed applications such as vibrating transonic wings. The main novel algorithmic contribution of this work is the successful development of a fully-coupled multigrid solution method of the Reynolds-Averaged Navier-Stokes equations and the two-equation shear stress transport turbulence model of Menter. The new approach, which also includes the implementation of a high-order restriction operator and an effective limiter of the prolonged corrections, is implemented and successfully demonstrated in the existing steady, time-domain and harmonic balance solvers of a compressible Navier-Stokes research code. The harmonic balance solution of the Navier-Stokes equations is a fairly new technology which can substantially reduce the run-time required to compute nonlinear periodic flow fields with respect to the conventional time-domain approach. The thesis also features the investigation of one modelling and one numerical aspect often overlooked or not comprehensively analysed in turbulent computational fluid dynamics simulations of the type discussed in the thesis. The modelling aspect is the sensitivity of the turbulent flow solution to the, to a certain extent, arbitrary value of the scaling factor appearing in the solid wall boundary condition of the second turbulent variable of the Shear Stress Transport turbulence model. The results reported herein highlight that the solution variability associated with the typical choices of such a scaling factor can be similar or higher than the solution variability caused by the choices of different turbulence models. The numerical aspect is the sensitivity of the turbulent flow solution to the order of the discretisation of the turbulence model equations. The results reported herein highlight that the existence of significant solution differences between first and second order space-discretisation of the turbulence equations vary with the flow regime (e.g. fully subsonic or transonic), operating conditions that may or may not result in flow separation (e.g. angle of attack), and also the grid refinement. The newly developed turbulent flow capabilities are validated by considering a wide range of test cases with flow regime varying from low-speed subsonic to transonic. The solutions of the research code are compared with experimental data, theoretical solutions and also numerical solutions obtained with a state-of-the-art time-domain commercial code. The main computational results of this research regard a low-speed renewable energy application and an aeronautical engineering application. The former application is a thorough comparative analysis of a hydrokinetic turbine working in a low-speed laminar and a high-Reynolds number turbulent regime. The time-domain results obtained with the newly developed turbulent code are used to analyse and discusses in great detail the unsteady aerodynamic phenomena occurring in both regimes. The main motivation for analysing this problem is both to highlight the predictive capabilities and the numerical robustness of the developed turbulent time-domain flow solver for complex realistic problems, and to shed more light on the complex physics of this emerging renewable energy device. The latter application is the time-domain and harmonic balance turbulent flow analysis of a transonic wing section animated by pitching motion. The main motivation of these analyses is to assess the computational benefits achievable by using the harmonic balance solution of the Reynolds-Averaged Navier-Stokes and Shear Stress Transport equations rather than the conventional time-domain solution, and also to further demonstrate the predictive capabilities of the developed Computational Fluid Dynamics system. To this aim, the numerical solutions of this research code are compared to both available experimental data, and the time-domain results computed by a state-of-the-art commercial package regularly used by the industry and the Academia worldwide.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QA76 Computer software ; QC Physics ; TA Engineering (General). Civil engineering (General) ; TL Motor vehicles. Aeronautics. Astronautics