ReFRESCO related MSc and Phd Theses

@mastersthesis{2014-Msc_Thesis_MichelMake,
title = {Predicting scale effects on floating offshore wind turbines},
author = {Michel Make},
url = { http://www.refresco.org/?wpdmpro=2014-msc_thesis_michelmake-pdf},
year = {2014},
date = {2014-04-28},
school = {Technical University of Delft, the Netherlands},
abstract = {Floating wind turbines are becoming fashionable within the Renewable Energy world. In the last years MARIN has been involved in an increasing number of projects for the offshore wind industry. Model tests are often used for validating and optimizing the floater design before
construction starts. A key point of model testing floating wind turbines is that wind and waves are presented simultaneously in the basin. This makes it possible to study the complex motions and interactions between the rotating turbine and the moving platform. However the experiments are done using smaller scaled models. While for the underwater loads Froude scaling laws are used successfully in the Offshore industry, the same should
not be done for the aerodynamic loads. Due to the strong Reynolds scale effects, the flow regime on the blades is critical or even sub-critical, and therefore laminar-turbulent transition and flow-separation effects play an important role. The traditional potential-flow based tools used for design and analysis of turbines (Blade-Element-Momentum-Theory BEMT) were not intended to work in these regimes, nor the inviscid-viscous (Boundary-Element-Method BEM) tools, like XFOIL, used to obtain the turbine sections Cl/Cd/Cm input for the BEMT calculations.
The complete simulation of a full-scale free-floating wind turbine under waves and winds using viscous-flow (Unsteady-Reynolds-Averaged-Navier-Stokes URANS) CFD codes is still nowadays very costly, if not impossible. However these CFD theoretically more accurate methods, can be used in an efficient way for aerodynamic analysis. And they can be used rather to generate 2D input for the BEMT design tools or for the real complete analysis of the wind turbine. In the present work CFD URANS code ReFRESCO is used for both purposes, having in mind the design of the new MARIN Stock (not Floating) Wind Turbine (MSWT), based on the 5MW NREL full-scale turbine. Only open-water constant wind, fixed platform conditions are considered here. The objectives of the work presented are therefore threefold: 1) the NREL 5MW baseline turbine is calculated using ReFRESCO both in full-scale and model-scale (Froude-scaling) conditions and the scale-effects studied and quantified; 2) the MSWT designed for thrust and performance-scaling is analyzed using CFD and validation against available MARIN experimental data is done; 3) in order to possibly further improve the MSWT design, the
aerodynamic characteristics of its sections/foils are scrutinized by means of a full numerical study using ReFRESCO.
The poor performance of the NREL 5MW turbine is due to a fully separated flow over the full range of tip speed ratios. Additionally decambering laminar separation bubbles are observed at the pressures side of the blades, further decreasing the aerodynamic performance of the turbine. Although laminar separation bubbles are not observed for the model-scale MSWT, separation does occur over the full span of the suction side of the blades. For the performance-scaled MSWT, however, an attached flow region is observed at the blade tips for the higher tip speed ratios, resulting in increased CP /CT values and performance. Flow separation at full-scale conditions is present only for the heavily loaded operating conditions. These separated regions show large radial velocity components, which contradict the assumed 2D flow in BEMT models. The separated flow is also observed for the flow over the 2D airfoil sections of the MSWT. Even for small angles of attack at model-scale Reynolds numbers, separation occurs and URANS computations are necessary for larger angles of attack. For the full-scale Reynolds number regime the flow remains attached up to larger angles of attack and URANS computations are needed only for the extreme angles of attack (AoA > 14deg). The 2D flow phenomena at model- and full-scale are in line with those observed for the flow over the 3D turbine. Although the MSWT has already greatly improved model-scale performance characteristics, the present research indicate that more improvements are perhaps possible. An alternative pitch angle distribution can be considered in order to reduce flow separation for even lower TSRs. Furthermore the present work showed the challenge of obtaining accurate numerical solutions for the complex unsteady flow over a wind turbine at these critical Reynolds numbers, which requires: domain studies, grid and time-step studies, good iterative convergence and an adequate turbulence model. All of these aspects were studied in this thesis.},
keywords = {BEMT, Foils, MSWT, NREL 5MW, RANS, Scale-Effects, Scaling, Spalart-Allmaras, SST, Transition, Turbines, URANS, XFOIL},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{2011-Stage_NicoKamphuis,
title = {ANALYSIS OF REFRESCO COMPUTATIONS APPLIED TO A TIP VORTEX OF A WING},
author = {Nico Kamphuis},
url = {http://www.refresco.org/?wpdmpro=2011-stage_nicokamphuis-pdf},
year = {2012},
date = {2012-12-01},
school = {University of Twente, Enschede, the Netherlands},
keywords = {Chow Wing, EARSM, RANS, Spalart-Allmaras, SST, Tip-vortex, Turbulence Models},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{2011-Msc_Thesis_PierreCrepier,
title = {Validation of URANS CFD Code ReFRESCO Roll Damping Simulations},
author = {Pierre Crepier},
url = {http://www.refresco.org/?wpdmpro=2011-msc_thesis_pierrecrepier-pdf},
year = {2011},
date = {2011-03-31},
school = {ENSTA, Brest, Bretagne, France},
abstract = {Unsteady calculations of the flow around rolling hull sections have been carried out. Two cases have been considered : a rectangular hull with sharp bilges and a rectangular hull fitted with triangular-shaped bilge keels. The double-body approach has been used for the computations. Sensitivity studies have been carried out on the grid refinement, the time-step size and the iterative convergence. It shows that the dependence on the grid is larger than on the time-step and the convergence threshold. Indeed, in order to have a grid converged, fine meshes have to be used. Results show that the viscous damping coefficient decreases when refining all the parameters. Results have been compared with existing data published by Ikeda and Yeung. Calculations for the case with sharp bilges appear to be in very good agreement with experimental results reported by Ikeda. They
confirm the linear behavior of the damping coefficient with the amplitude. Regarding the case with bilge keels, results show a linear behavior of the damping coefficient with the frequency which is a behavior confirmed by Ikeda. For this case, a fairly good agreement is found for non-dimensional frequencies lower than 0:7. For these values a deviation lower than 10% is obtained. However we observe larger deviations at high frequencies. Those deviations are believed to be due to free-surface effects and wave making. So, computations involving the free surface leading to a damping coefficient taking the wave damping into account have to be carried out. Preliminary studies on turbulence modeling and scale effects have also been done. Changing the turbulence model from SST to Spalart-Allmaras leads to a damping higher by 4:5% explained by a higher pressure
on the hull. Generated vortices are observed to be rounder and closer to each other than with SST. For the study on scale effects, a geometrical scale factor of 1=50 have been used and the viscosity have been tuned to reach the full scale conditions. The results obtained do not show large deviation with the model-scale computation. Indeed a damping higher by 1:5% is obtained due to a pressure slightly higher on the hull but the vorticity do not change much between the model-scale and the full-scale calculations},
keywords = {Bilge-keels, Roll-damping, Scale-Effects, Spalart-Allmaras, SST, URANS, Validation, Verification},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{2009-Msc_Thesis_SimonDelvoye,
title = {Simulation and analysis of the flow around an underwater exhaust with FreSCo},
author = {Delvoye, Simon},
url = {http://www.refresco.org/?wpdmpro=2009-msc_thesis_simondelvoye-pdf },
year = {2009},
date = {2009-08-07},
school = {ISITV, Toulon, France},
keywords = {Design, Multi-phase, RANS, Scoops, Spalart-Allmaras, SST, URANS, Verification},
pubstate = {published},
tppubtype = {mastersthesis}
}

@mastersthesis{2007-Stage_ManuelManzke,
title = {Using FreSCo for the Determination of Frictional Forces},
author = {Manuel Manzke},
url = {http://www.refresco.org/?wpdmpro=2007-stage_manuelmanzke-pdf},
year = {2007},
date = {2007-05-04},
school = {TUHH, Hamburg, Germany},
keywords = {1-eq Menter, Drag, Flat-plate, k-epsilon, k-omega, Spalart-Allmaras, SST, Turbulence Models, Validation, Verification, Wall-functions},
pubstate = {published},
tppubtype = {mastersthesis}
}