Search

Search Results

• 1. [Article] Blade Number Effects in a Scaled Down Wind Farm

  Two 3 × 4 scaled down wind farms were analyzed to understand differences in wind turbine boundary layers when turbines operating at identical power coefficients have two or three blades. Mean streamwise ...

  Citation × Citation Citation Abstract Copy Title: Blade Number Effects in a Scaled Down Wind Farm Author: Newman, A. Jensen, Cal, Raúl Bayoán, Castillo, Luciano Year: 2015 Two 3 × 4 scaled down wind farms were analyzed to understand differences in wind turbine boundary layers when turbines operating at identical power coefficients have two or three blades. Mean streamwise velocities in two bladed turbine near wakes ranged between 10 and 100% larger than those in the three bladed case with large differences just behind the nacelle. In the rotor swept region of far wakes, mean velocity differences between the two arrays were about 10% (max) and became smaller with increasing streamwise direction. Contrary to these findings, regions above and below rotors become less similar deep in the array. Incoming flow to downstream turbines was shown to have greater Reynolds streamwise normal stress for three bladed rotors. Percentage differences ranged between about 30% for the second turbine down to 10% for the fourth turbine. Additionally, there is qualitative evidence that suggests incoming streamwise Reynolds normal stress becomes similar between the two types of turbines, indicating that asymptotically two and three bladed turbines could have similar fatigue loading properties. These results show that use of two bladed turbines would have the most impact when used in a wind farm's first two rows. Title: Blade Number Effects in a Scaled Down Wind Farm Author: Newman, A. Jensen, Cal, Raúl Bayoán, Castillo, Luciano Year: 2015 Two 3 × 4 scaled down wind farms were analyzed to understand differences in wind turbine boundary layers when turbines operating at identical power coefficients have two or three blades. Mean streamwise velocities in two bladed turbine near wakes ranged between 10 and 100% larger than those in the three bladed case with large differences just behind the nacelle. In the rotor swept region of far wakes, mean velocity differences between the two arrays were about 10% (max) and became smaller with increasing streamwise direction. Contrary to these findings, regions above and below rotors become less similar deep in the array. Incoming flow to downstream turbines was shown to have greater Reynolds streamwise normal stress for three bladed rotors. Percentage differences ranged between about 30% for the second turbine down to 10% for the fourth turbine. Additionally, there is qualitative evidence that suggests incoming streamwise Reynolds normal stress becomes similar between the two types of turbines, indicating that asymptotically two and three bladed turbines could have similar fatigue loading properties. These results show that use of two bladed turbines would have the most impact when used in a wind farm's first two rows. Close

• 2. [Article] Focused-Based Multifractal Analysis of the Wake in a Wind Turbine Array Utilizing Proper Orthogonal Decomposition

  Hot-wire anemometry measurements have been performed in a 3×3 wind turbine array to study the multifractality of the turbulent kinetic energy dissipation. A multifractal spectrum and Hurst exponents are ...

  Citation × Citation Citation Abstract Copy Title: Focused-Based Multifractal Analysis of the Wake in a Wind Turbine Array Utilizing Proper Orthogonal Decomposition Author: Ali, Naseem, Falih Kadum, Hawwa, Cal, Raúl Bayoán Year: 2016 Hot-wire anemometry measurements have been performed in a 3×3 wind turbine array to study the multifractality of the turbulent kinetic energy dissipation. A multifractal spectrum and Hurst exponents are determined at nine locations downstream of the hub height, bottom and top tips. Higher multifractality is found at 0.5D and 1D downstream of the bottom tip and hub height. The second order of the Hurst exponent and combination factor shows the ability to predict the flow state in terms of its development. Snapshot proper orthogonal decomposition (POD) is used to identify the coherent and incoherent structures and to reconstruct the stochastic velocity signal using a specific number of the POD eigenfunctions. The accumulation of the turbulence kinetic energy in the top tip location exhibits fast convergence compared with the bottom tip and hub height. The dissipation of the large and small scales is determined using the reconstructed stochastic velocities. The higher multifractality is shown in the dissipation of the large scale compared with small scale dissipation showing consistency with the behavior of the original signals. Multifractality of turbulent kinetic energy dissipation in the wind farm is examined and the effect of the reconstructed flow field via proper orthogonal decomposition on the multifractality behavior is investigated. Findings are relevant in wind energy as multifractal parameters identify the variation between the near- and far-wake regions. Title: Focused-Based Multifractal Analysis of the Wake in a Wind Turbine Array Utilizing Proper Orthogonal Decomposition Author: Ali, Naseem, Falih Kadum, Hawwa, Cal, Raúl Bayoán Year: 2016 Hot-wire anemometry measurements have been performed in a 3×3 wind turbine array to study the multifractality of the turbulent kinetic energy dissipation. A multifractal spectrum and Hurst exponents are determined at nine locations downstream of the hub height, bottom and top tips. Higher multifractality is found at 0.5D and 1D downstream of the bottom tip and hub height. The second order of the Hurst exponent and combination factor shows the ability to predict the flow state in terms of its development. Snapshot proper orthogonal decomposition (POD) is used to identify the coherent and incoherent structures and to reconstruct the stochastic velocity signal using a specific number of the POD eigenfunctions. The accumulation of the turbulence kinetic energy in the top tip location exhibits fast convergence compared with the bottom tip and hub height. The dissipation of the large and small scales is determined using the reconstructed stochastic velocities. The higher multifractality is shown in the dissipation of the large scale compared with small scale dissipation showing consistency with the behavior of the original signals. Multifractality of turbulent kinetic energy dissipation in the wind farm is examined and the effect of the reconstructed flow field via proper orthogonal decomposition on the multifractality behavior is investigated. Findings are relevant in wind energy as multifractal parameters identify the variation between the near- and far-wake regions. Close