1.  Hawkes, James; Vaz, Guilherme; Turnock, Stephen; Cox, Simon; Philips, Alexander: Potential of Chaotic Iterative Solvers for CFD. NUTTS2014, September, Gothenburg, Sweden., 2014. (Type: Conference  Links  BibTeX) @conference{NUTTS2014_Hawkes_et_al_ChaoticSolvers, title = {Potential of Chaotic Iterative Solvers for CFD}, author = {James Hawkes and Guilherme Vaz and Stephen Turnock and Simon Cox and Alexander Philips}, url = {http://www.refresco.org/?wpdmpro=2014nutts_hawkesvaz_et_al_chaoticsolverspdf}, year = {2014}, date = {20140908}, booktitle = {NUTTS2014, September, Gothenburg, Sweden.}, keywords = {}, pubstate = {published}, tppubtype = {conference} } 
2.  Make, Michel: Predicting scale effects on floating offshore wind turbines. Technical University of Delft, the Netherlands, 2014. (Type: Masters Thesis  Abstract  Links  BibTeX) @mastersthesis{2014Msc_Thesis_MichelMake, title = {Predicting scale effects on floating offshore wind turbines}, author = {Michel Make}, url = { http://www.refresco.org/?wpdmpro=2014msc_thesis_michelmakepdf}, year = {2014}, date = {20140428}, 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 subcritical, and therefore laminarturbulent transition and flowseparation effects play an important role. The traditional potentialflow based tools used for design and analysis of turbines (BladeElementMomentumTheory BEMT) were not intended to work in these regimes, nor the inviscidviscous (BoundaryElementMethod BEM) tools, like XFOIL, used to obtain the turbine sections Cl/Cd/Cm input for the BEMT calculations. The complete simulation of a fullscale freefloating wind turbine under waves and winds using viscousflow (UnsteadyReynoldsAveragedNavierStokes 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 fullscale turbine. Only openwater 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 fullscale and modelscale (Froudescaling) conditions and the scaleeffects studied and quantified; 2) the MSWT designed for thrust and performancescaling 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 modelscale MSWT, separation does occur over the full span of the suction side of the blades. For the performancescaled 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 fullscale 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 modelscale Reynolds numbers, separation occurs and URANS computations are necessary for larger angles of attack. For the fullscale 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 fullscale are in line with those observed for the flow over the 3D turbine. Although the MSWT has already greatly improved modelscale 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 timestep studies, good iterative convergence and an adequate turbulence model. All of these aspects were studied in this thesis.}, keywords = {}, pubstate = {published}, tppubtype = {mastersthesis} } 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 subcritical, and therefore laminarturbulent transition and flowseparation effects play an important role. The traditional potentialflow based tools used for design and analysis of turbines (BladeElementMomentumTheory BEMT) were not intended to work in these regimes, nor the inviscidviscous (BoundaryElementMethod BEM) tools, like XFOIL, used to obtain the turbine sections Cl/Cd/Cm input for the BEMT calculations. The complete simulation of a fullscale freefloating wind turbine under waves and winds using viscousflow (UnsteadyReynoldsAveragedNavierStokes 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 fullscale turbine. Only openwater 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 fullscale and modelscale (Froudescaling) conditions and the scaleeffects studied and quantified; 2) the MSWT designed for thrust and performancescaling 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 modelscale MSWT, separation does occur over the full span of the suction side of the blades. For the performancescaled 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 fullscale 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 modelscale Reynolds numbers, separation occurs and URANS computations are necessary for larger angles of attack. For the fullscale 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 fullscale are in line with those observed for the flow over the 3D turbine. Although the MSWT has already greatly improved modelscale 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 timestep studies, good iterative convergence and an adequate turbulence model. All of these aspects were studied in this thesis. 
2014 

Hawkes, James; Vaz, Guilherme; Turnock, Stephen; Cox, Simon; Philips, Alexander Potential of Chaotic Iterative Solvers for CFD Conference NUTTS2014, September, Gothenburg, Sweden., 2014. Links  BibTeX  Tags: Chaotic Solvers, MPI, Parallelization, RANS, Scaling, Solvers, URANS @conference{NUTTS2014_Hawkes_et_al_ChaoticSolvers, title = {Potential of Chaotic Iterative Solvers for CFD}, author = {James Hawkes and Guilherme Vaz and Stephen Turnock and Simon Cox and Alexander Philips}, url = {http://www.refresco.org/?wpdmpro=2014nutts_hawkesvaz_et_al_chaoticsolverspdf}, year = {2014}, date = {20140908}, booktitle = {NUTTS2014, September, Gothenburg, Sweden.}, keywords = {Chaotic Solvers, MPI, Parallelization, RANS, Scaling, Solvers, URANS}, pubstate = {published}, tppubtype = {conference} }  
Make, Michel Predicting scale effects on floating offshore wind turbines Masters Thesis Technical University of Delft, the Netherlands, 2014. Abstract  Links  BibTeX  Tags: BEMT, Foils, MSWT, NREL 5MW, RANS, ScaleEffects, Scaling, SpalartAllmaras, SST, Transition, Turbines, URANS, XFOIL @mastersthesis{2014Msc_Thesis_MichelMake, title = {Predicting scale effects on floating offshore wind turbines}, author = {Michel Make}, url = { http://www.refresco.org/?wpdmpro=2014msc_thesis_michelmakepdf}, year = {2014}, date = {20140428}, 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 subcritical, and therefore laminarturbulent transition and flowseparation effects play an important role. The traditional potentialflow based tools used for design and analysis of turbines (BladeElementMomentumTheory BEMT) were not intended to work in these regimes, nor the inviscidviscous (BoundaryElementMethod BEM) tools, like XFOIL, used to obtain the turbine sections Cl/Cd/Cm input for the BEMT calculations. The complete simulation of a fullscale freefloating wind turbine under waves and winds using viscousflow (UnsteadyReynoldsAveragedNavierStokes 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 fullscale turbine. Only openwater 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 fullscale and modelscale (Froudescaling) conditions and the scaleeffects studied and quantified; 2) the MSWT designed for thrust and performancescaling 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 modelscale MSWT, separation does occur over the full span of the suction side of the blades. For the performancescaled 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 fullscale 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 modelscale Reynolds numbers, separation occurs and URANS computations are necessary for larger angles of attack. For the fullscale 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 fullscale are in line with those observed for the flow over the 3D turbine. Although the MSWT has already greatly improved modelscale 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 timestep 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, ScaleEffects, Scaling, SpalartAllmaras, SST, Transition, Turbines, URANS, XFOIL}, pubstate = {published}, tppubtype = {mastersthesis} } 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 subcritical, and therefore laminarturbulent transition and flowseparation effects play an important role. The traditional potentialflow based tools used for design and analysis of turbines (BladeElementMomentumTheory BEMT) were not intended to work in these regimes, nor the inviscidviscous (BoundaryElementMethod BEM) tools, like XFOIL, used to obtain the turbine sections Cl/Cd/Cm input for the BEMT calculations. The complete simulation of a fullscale freefloating wind turbine under waves and winds using viscousflow (UnsteadyReynoldsAveragedNavierStokes 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 fullscale turbine. Only openwater 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 fullscale and modelscale (Froudescaling) conditions and the scaleeffects studied and quantified; 2) the MSWT designed for thrust and performancescaling 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 modelscale MSWT, separation does occur over the full span of the suction side of the blades. For the performancescaled 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 fullscale 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 modelscale Reynolds numbers, separation occurs and URANS computations are necessary for larger angles of attack. For the fullscale 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 fullscale are in line with those observed for the flow over the 3D turbine. Although the MSWT has already greatly improved modelscale 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 timestep studies, good iterative convergence and an adequate turbulence model. All of these aspects were studied in this thesis. 