Ahmet Ozbay

Effects of incoming surface wind conditions on the wake characteristics and dynamic wind loads acting on a wind turbine model

An experimental investigation was conducted to examine the effects of incoming surface wind conditions on the wake characteristics and dynamic wind loads acting on a wind turbine model. The experimental study was performed in a large-scale wind tunnel with a scaled three-blade Horizontal Axial Wind Turbine model placed in two different types of Atmospheric Boundary Layer (ABL) winds with distinct mean and turbulence characteristics. In addition to measuring dynamic wind loads acting on the model turbine by using a force-moment sensor, a high-resolution Particle Image Velocimetry system was used to achieve detailed flow field measurements to characterize the turbulent wake flows behind the model turbine. The measurement results reveal clearly that the discrepancies in the incoming surface winds would affect the wake characteristics and dynamic wind loads acting on the model turbine dramatically. The dynamic wind loads acting on the model turbine were found to fluctuate much more significantly, thereby, muc...

Experimental Investigation on the Wake Characteristics and Aeromechanics of Dual-Rotor Wind Turbines

An experimental study was carried out to investigate the aeromechanics and wake characteristics of dual-rotor wind turbines (DRWTs ) in either co-rotating or counter-rotating configuration, in comparison to those of a conventional single-rotor wind turbine (SRWT). The experiments were performed in a large-scale Aerodynamic/Atmospheric Boundary Layer (AABL) wind tunnel available at Iowa State University with the oncoming Atmospheric Boundary Layer (ABL) airflows under neutral stability conditions. In addition to measuring the power output performance of DRWT and SRWT models, static and dynamic wind loads acting on those turbine models were also investigated. Furthermore, a high resolution digital particle image velocimetry (PIV) system was used to quantify the flow characteristics in the near wakes of the DRWT and SRWT models. The detailed wake flow measurements were correlated with the power outputs and wind load measurement results of the wind turbine models to elucidate the underlying physics to explore/optimize design of wind turbines for higher power yield and better durability.Copyright

An Experimental Study on the Performances of Wind Turbines over Complex Terrain

An experimental study was conducted to investigate the performance of wind turbines sited over hilly terrains in order to elucidate the underlying physics to explore/optimize design of wind turbines sitting over complex terrains for higher power yield and better durability. The experiments were conducted in an atmospheric boundary layer wind tunnel with wind turbines sited over a two-dimensional hill. In addition to measuring dynamic wind loads and the power outputs of the wind turbines, detailed flow field measurements were also made to quantify the flow characteristics of the surface wind and the wake interference among multiple wind turbines over hilly terrain. The detailed flow field measurements were correlated with the wind load and power output measurements of the wind turbine models to explicate the physical mechanisms associated with power generation and fatigue loads acting on the wind turbines for the optimal design of the wind turbine layout over complex terrain.

An Experimental Investigation on the Aeromechanics and Near Wake Characteristics of Dual-Rotor Wind Turbines (DRWTs)

An experimental study was conducted to investigate the aeromechanic performance and near wake characterstics of dual-rotor wind turbine (DRWT) models with co-rotating or counter-rotating configurations in comparison to a conventional single rotor wind turbine (SRWT) model in order to elucidate the underlying physics to explore/optimize design of wind turbines for higher power yield and better durability. The experiments were performed in a large-scale Aerodynamic/Atmospheric Boundary Layer (AABL) wind tunnel under neutral stability conditions. In addition to measuring the power output performance of the SRWT and DRWT models, static and dynamic wind loads acting on the test models were also investigated. Furthermore, a high resolution PIV system was used for detailed near wake flow field measurements ( free-run and phase-locked ) to quantify the characteristics of the near wake flows and to reveal the transient behavior of the unsteady vortex structures in the wakes of SRWT and DRWT models. In the light of the promising experimental results on DRWTs, this study can be extended further to investigate the turbulent flow in the far wake of DRWTs and utilize multiple DRWTs in different wind farm operations.

An Experimental Investigation on the Wake Interference of Multiple Wind Turbines in Atmospheric Boundary Layer Winds

In this study, an investigation was carried out in an atmospheric boundary layer (ABL) wind tunnel to investigate the wake interferences of multiple wind turbines sited over a flat terrain in order to elucidate the underlying physics to optimize the design of wind turbines layout in wind farm for higher power yield and better durability. Firstly, the effects of the turbine spacing and the wind farm layout on the wake interferences were investigated among multiple wind turbines sited over a flat terrain. The characteristics of the surface winds (both mean velocity and turbulence profiles) were quantified to elucidate the interaction between atmospheric boundary layer and wind farms. The detailed flow field measurements were correlated with the dynamic wind loads as well as the power outputs of the wind turbine models in both aligned and staggered wind farms. In addition, the effects of different characteristics of the incoming atmospheric boundary layer on the performance of the individual wind turbines and on the array efficiency of different wind farm layouts were also investigated. The results obtained from the present study shed light on how complex aerodynamics and efficiency of different wind farms could be affected by different factors such as the wind farm configuration, turbine spacing, as well as incoming flow turbulence level.

An Experimental Investigation on the Effects of Turbine Rotation Directions on the Wake Interference of Wind Turbines

An experimental study was conducted to investigate on the effects of the relative rotation directions of two tandwm wind turbines on the power production performance and flow characteristics in the wakes of two wind turbines in tandem. The experimental study was performed in a large-scale Aerodynamics/tmospheric Boundary Layer (AABL) Wind Tunnel located at the Aerospace Engineering Department of Iowa State University. While the oncoming Atmospheric Boundary Layer (ABL) wind was kept in constant during the experiments, the turbine power outputs, the dynamic wind loads (i.e., aerodynamic forces) acting on the wind turbines, and the flow characteristics in the wakes the wind turbines were measured and compared quantitatively with the turbines operating in either co-rotating (i.e., the downstream wind turbine has the same rotation direction as the upstream turbine) and counter-rotating configurations (i.e., the downstream wind turbine has an opposite rotation direction in relation to the upstream wind turbine). It was found that an obvious azimuthal flow velocity component, i.e., so-called “pre-rotating” effect, would be generated in the wake flow of the upstream turbine. When the downstream turbine operates in the co-rotating configuration, due to the effects of the “pre-rotating” azimuthal flow velocity, the effective angle of attack of the oncoming ABL wind approaching to the second wind turbine would be decreased, thereby, a smaller lift to drive the rotor of the downstream turbine. However, when the downstream turbine operated in the counter-rotating configuration, the “prerotating” azimuthal flow velocity would result in a greater effective angle of attack for the oncoming wind to approach the second wind turbine, thereby a larger lift to drive the rotor of the downstream turbine. As a result, the downstream wind turbine was found to be able to harvest more wind energy when it was operated in counter-rotating configuration (up to 17% more power output were achieved based according to the measurement results of the present study), compared with that in counter-rotating configuration. The benefits of the counter-rotating configuration in power production were found to decrease gradually as the distance between the two wind turbines increases.

An Experimental Investigation on the Wake Characteristics behind a Novel Twin-Rotor Wind Turbine

An experimental study was performed to examine the wake characteristics and aeromechanic performance of an innovative twin-rotor wind turbine (TRWT) in comparison with those of a conventional single-rotor wind turbine (SRWT). The comparative study was conducted in a large-scale Aerodynamic/Atmospheric Boundary Layer (AABL) wind tunnel with the TRWT and SRWT model sited in simulated atmospheric boundary layer (ABL) winds under neutral stability conditions. In addition to measuring the power outputs of the TRWT and SRWT models, dynamic wind loads acting on the wind turbine models were also investigated in detail. Furthermore, a high-resolution PIV system was used for detailed wake flow field measurements (free-run and phase-locked) in order to quantify the characteristics of the turbulent turbine wake flows and to quantitatively visualize the transient behavior of the unsteady vortex structures behind the wind turbine models. The detailed flow field measurements are correlated with the dynamic wind loads and power output measurements to elucidate the underlying physics for higher total power generation and better durability of the wind turbines.

An Experimental Investigation on the Wake Interference of Wind Turbines Sited Over Complex Terrains

() An experimental study was conducted to investigate the interferences of wind turbines sited over hilly terrains in order to elucidate underlying physics to explore/optimize design paradigms of wind turbines sited over complex terrains for higher power yield and better durability. The experiments were conducted in a large wind tunnel with of wind turbine models sited over a flat terrain (baseline case) and a 2D-ridge with non-homogenous atomospheric boundary layer winds. In addition to measuring dynamic wind loads (both forces and moments) and the power outputs of the wind turbine models, a high-resolution digital Particle Image Velocimetry (PIV) system was used to conduct detailed flow field measurements to quantify the flow characteristics of the surface winds and wake interferences among multiple wind turbines over flat (baseline case) and complex terrains. The detailed flow field measurements were correlated with the wind load measurements and power outputs of the wind turbine models to elucidate the underlying physics associated with turbine power generation and fatigue loads acting on the wind turbines.

An Experimental Investigation on Dynamic Wind Loads Acting on a Wind Turbine Model in Atomspheric Boundary Layer Winds

An experimental study was conducted to investigate the dynamic wind loads acting on a wind turbine model sited in atmospheric boundary layer winds. The experimental studies are conducted in a large-scale Aerodynamic/Atmospheric Boundary Layer (AABL) Wind Tunnel available at Iowa State University. A three-blade Horizontal Axial Wind Turbine (HAWT) model was placed in atmospheric boundary layer winds with different mean and turbulence characteristics to simulate the situations in onshore and offshore wind farms. In addition to measuring dynamic wind loads (both forces and moments) acting on the HAWT model, a high-resolution Particle Image Velocity (PIV) system is used to conduct detailed flow field measurements to quantify the characteristics of the turbulent vortex flow in the near wake of the wind turbine model. The detailed flow field measurements were correlated with the dynamic wind loads measurements to elucidate underlying physics in order to gain further insight into the characteristics of the dynamic wind loads for for better durability of the wind turbines in atmospheric boundary layer (ABL) winds.

An Experimental Investigation on the Wake Characteristics and Aeromechanics of Dual-Rotor Wind Turbines

An experimental study was carried out to investigate the aeromechanics and wake characteristics of dual-rotor wind turbines (DRWTs ) in either co-rotating or counter-rotating configuration, in comparison to those of a conventional single-rotor wind turbine (SRWT). The experiments were performed in a large-scale Aerodynamic/Atmospheric Boundary Layer (AABL) wind tunnel available at Iowa State University with the oncoming Atmospheric Boundary Layer (ABL) airflows under neutral stability conditions. In addition to measuring the power output performance of DRWT and SRWT models, static and dynamic wind loads acting on those turbine models were also investigated. Furthermore, a high resolution digital particle image velocimetry (PIV) system was used to quantify the flow characteristics in the near wakes of the DRWT and SRWT models. The detailed wake flow measurements were correlated with the power outputs and wind load measurement results of the wind turbine models to elucidate the underlying physics to explore/optimize design of wind turbines for higher power yield and better durability.Copyright