The Experts below are selected from a list of 201 Experts worldwide ranked by ideXlab platform

David Wood - One of the best experts on this subject based on the ideXlab platform.

  • Effect of the Diffuser Efficiency on wind turbine performance
    Renewable Energy, 2018
    Co-Authors: Jerson Rogério Pinheiro Vaz, David Wood
    Abstract:

    Abstract A Diffuser surrounding a rotor is able to increase the power coefficient of a wind turbine above the Betz-Joukowsky limit (16/27), and so has attracted great attention for many years. This work presents a novel analysis of the performance of Diffuser-augmented wind turbines (DAWTs) taking into account the influence of the Diffuser Efficiency and thrust, in which a new formulation for the far-wake velocity is proposed. The mathematical model extends Blade Element Theory to include the Diffuser Efficiency in the axial velocity formulation, which in turn, modifies the thrust and power. Additionally, a correction for high rotor thrust is presented, where a quadratic equation is used to incorporate the losses within the Diffuser that are associated with the Efficiency being less than 100%. An algorithm to assess DAWT performance was developed and implemented. The new model was validated by comparison with experimental data match and shows good agreement when a Diffuser Efficiency of 80% is assumed. The impact of the Diffuser is assessed by the augmentation factor, the ratio of turbine Efficiency to the Betz-Joukowsky limit. It is shown, for example, that the augmentation factor exceeds unity only for Efficiency greater than 74% when the Diffuser thrust is 0.2 of the total thrust and ratio of the rotor area to Diffuser exit area is 0.54.

  • Aerodynamic optimization of the blades of Diffuser-augmented wind turbines
    Energy Conversion and Management, 2016
    Co-Authors: Jerson Rogério Pinheiro Vaz, David Wood
    Abstract:

    Abstract Adding an exit Diffuser is known to allow wind turbines to exceed the classical Betz–Joukowsky limit for a bare turbine. It is not clear, however, if there is a limit for Diffuser-augmented turbines or whether the structural and other costs of the Diffuser outweigh any gain in power. This work presents a new approach to the aerodynamic optimization of a wind turbine with a Diffuser. It is based on an extension of the well-known Blade Element Theory and a simple model for Diffuser Efficiency. It is assumed that the same conditions for the axial velocity in the wake of an ordinary wind turbine can be applied on the flow far downwind of the Diffuser outlet. An algorithm to optimize the blade chord and twist angle distributions in the presence of a Diffuser was developed and implemented. As a result, an aerodynamic improvement of the turbine rotor geometry was achieved with the blade shape sensitive to the Diffuser speed-up ratio. In order to evaluate the proposed approach, a comparison with the classical Glauert optimization was performed for a flanged Diffuser, which increased the Efficiency. In addition, a comparative assessment was made with experimental results available in the literature, suggesting better performance for the rotor designed with the proposed optimization procedure.

Jerson Rogério Pinheiro Vaz - One of the best experts on this subject based on the ideXlab platform.

  • A new approach for the design of Diffuser-augmented hydro turbines using the blade element momentum
    Energy Conversion and Management, 2018
    Co-Authors: Paulo A.s.f. Silva, Déborah Aline Tavares Dias Do Rio Vaz, Vinicius De Sousa Britto, Taygoara Felamingo De Oliveira, Jerson Rogério Pinheiro Vaz, Antonio Cesar Pinho Brasil Junior
    Abstract:

    Abstract It is known surrounding a turbine with a Diffuser may significantly increase its power. This effect has attained considerable attention as it shows theoretically the possibility of achieving a power coefficient about 2 times greater than an ordinary turbine. However, the effect of the Diffuser Efficiency has not been implemented into blade element momentum yet. Hence, this paper presents a novel approach to design Diffuser-augmented hydro turbines considering the Diffuser Efficiency. Based on the blade element momentum, new expressions for the axial induction factor and thrust are obtained. To assess the proposed model, a comparative evaluation of two different Diffusers (flanged conical Diffuser and flanged lens Diffuser) is performed. A numerical modeling investigation using computational fluid dynamics is carried out based on the Reynolds Averaged Navier-Stokes formulation, using the κ - ω shear-stress transport turbulence model. Evaluations for both turbine and Diffuser are performed using experimental data available in the literature. Numerical and theoretical results are compared for a shrouded turbine equipped with a 83% Efficiency Diffuser. The relative difference observed for the maximum power coefficient between the proposed model and an actuator disk model with Diffuser is about 5.3%. For the hydro turbine with flanged conical Diffuser, the mass flow rate is about 20 % higher than for a bare turbine, while for the turbine with flanged lens Diffuser the increase is only 2.4 % . Also, for the flanged conical Diffuser the power is increased by 53 % . Furthermore, it is observed that the proposed blade element momentum with Diffuser achieved good agreement with the numerical model, providing improved results compared to other models available in the literature.

  • Effect of the Diffuser Efficiency on wind turbine performance
    Renewable Energy, 2018
    Co-Authors: Jerson Rogério Pinheiro Vaz, David Wood
    Abstract:

    Abstract A Diffuser surrounding a rotor is able to increase the power coefficient of a wind turbine above the Betz-Joukowsky limit (16/27), and so has attracted great attention for many years. This work presents a novel analysis of the performance of Diffuser-augmented wind turbines (DAWTs) taking into account the influence of the Diffuser Efficiency and thrust, in which a new formulation for the far-wake velocity is proposed. The mathematical model extends Blade Element Theory to include the Diffuser Efficiency in the axial velocity formulation, which in turn, modifies the thrust and power. Additionally, a correction for high rotor thrust is presented, where a quadratic equation is used to incorporate the losses within the Diffuser that are associated with the Efficiency being less than 100%. An algorithm to assess DAWT performance was developed and implemented. The new model was validated by comparison with experimental data match and shows good agreement when a Diffuser Efficiency of 80% is assumed. The impact of the Diffuser is assessed by the augmentation factor, the ratio of turbine Efficiency to the Betz-Joukowsky limit. It is shown, for example, that the augmentation factor exceeds unity only for Efficiency greater than 74% when the Diffuser thrust is 0.2 of the total thrust and ratio of the rotor area to Diffuser exit area is 0.54.

  • Aerodynamic optimization of the blades of Diffuser-augmented wind turbines
    Energy Conversion and Management, 2016
    Co-Authors: Jerson Rogério Pinheiro Vaz, David Wood
    Abstract:

    Abstract Adding an exit Diffuser is known to allow wind turbines to exceed the classical Betz–Joukowsky limit for a bare turbine. It is not clear, however, if there is a limit for Diffuser-augmented turbines or whether the structural and other costs of the Diffuser outweigh any gain in power. This work presents a new approach to the aerodynamic optimization of a wind turbine with a Diffuser. It is based on an extension of the well-known Blade Element Theory and a simple model for Diffuser Efficiency. It is assumed that the same conditions for the axial velocity in the wake of an ordinary wind turbine can be applied on the flow far downwind of the Diffuser outlet. An algorithm to optimize the blade chord and twist angle distributions in the presence of a Diffuser was developed and implemented. As a result, an aerodynamic improvement of the turbine rotor geometry was achieved with the blade shape sensitive to the Diffuser speed-up ratio. In order to evaluate the proposed approach, a comparison with the classical Glauert optimization was performed for a flanged Diffuser, which increased the Efficiency. In addition, a comparative assessment was made with experimental results available in the literature, suggesting better performance for the rotor designed with the proposed optimization procedure.

François Guibault - One of the best experts on this subject based on the ideXlab platform.

  • Numerical Analysis of the Turbine 99 Draft Tube Flow Field Provoked by Redesigned Inlet Velocity Profiles.
    IOP Conference Series: Earth and Environmental Science, 2014
    Co-Authors: Sergio Galván, François Guibault, Marcelo Reggio, L. Castro
    Abstract:

    In recent years, several investigations on hydraulic turbine draft tube performance have shown that the hydrodynamic flow field at the runner outlet determines the Diffuser Efficiency affecting the overall performance of the turbine. This flow field, for which the principal characteristics are the flow rate and the inlet swirling flow intensity, is mostly developed on turbines designed for low head (high specific velocity) and operated away from their best Efficiency point. To identify factors of the flow field responsible for loosing draft- tube Efficiency, the correlations between the flow pattern along the Diffuser and both swirl intensity and flow rate have been examined. An analytical representation of inlet flow field has been manipulated by a Multi Island Genetic Algorithm through the automatic coupling of multidisciplinary commercial software systems in order to obtain redesigned inlet velocity profiles. This loop allowed determining the profile for which the minimum energy loss factor was reached. With different flow field patterns obtained during the optimization process it was possible to undertake a qualitative and quantitative analysis which has helped to understand how to suppress or at least mitigate undesirable draft tube flow characteristics. The direct correlation between the runner blade design and the kinematics of the swirl at the draft tube inlet should suppose the perfect coupling at the runner-draft tube interface without compromising the overall flow stability of the machine.

  • Inlet Velocity Profile Optimization of the Turbine 99 Draft Tube
    Volume 1A Symposia: Advances in Fluids Engineering Education; Advances in Numerical Modeling for Turbomachinery Flow Optimization; Applications in CFD, 2013
    Co-Authors: Sergio Galván, Marcelo Reggio, François Guibault
    Abstract:

    In recent years, several investigations on hydraulic turbine draft tube performance have shown that the hydrodynamic field at the runner’s outlet is a direct outcome of the runner design and the operating point. This has shown the dependence of the Diffuser Efficiency on the flow rate and the inlet swirling flow intensity, mostly on turbines that present low head (high specific velocity) and operate away from their best Efficiency point. The numerical optimization of the inlet velocity profile is presented as an attempt to control these two inlet flow characteristics. The goal is the improvement of the flow through the draft tube to allow for better turbine performance. This methodology is based on the automatic coupling of several commercial softwares and is used to manipulate the analytical representation of the swirling flow, which has led to the minimization of hydraulic losses. Also, a qualitative and quantitative analysis of the draft tube flow field provoked by a redesigned inlet velocity profiles, has helped to understand how it is possible to suppress or at least mitigate undesirable draft tube flow characteristics.

  • Inlet Velocity Profile Optimization of the Turbine 99 Draft Tube
    2010
    Co-Authors: Sergio Galván, Marcelo Reggio, François Guibault
    Abstract:

    In recent years, several investigations on hydraulic turbine draft tube performance have shown that the hydrodynamic field at the runner’s outlet is a direct outcome of the runner design and the operating point. This has shown the dependence of the Diffuser Efficiency on the flow rate and the inlet swirling flow intensity, mostly on turbines that present low head (high specific velocity) and operate away from their best Efficiency point. The numerical optimization of the inlet velocity profile is presented as an attempt to control these two inlet flow characteristics. The goal is the improvement of the flow through the draft tube to allow for better turbine performance. This methodology is based on the automatic coupling of several commercial softwares and is used to manipulate the analytical representation of the swirling flow, which has led to the minimization of hydraulic losses. Also, a qualitative and quantitative analysis of the draft tube flow field provoked by a redesigned inlet velocity profiles, has helped to understand how it is possible to suppress or at least mitigate undesirable draft tube flow characteristics.Copyright © 2013 by ASME

Sergio Galván - One of the best experts on this subject based on the ideXlab platform.

  • Numerical Analysis of the Turbine 99 Draft Tube Flow Field Provoked by Redesigned Inlet Velocity Profiles.
    IOP Conference Series: Earth and Environmental Science, 2014
    Co-Authors: Sergio Galván, François Guibault, Marcelo Reggio, L. Castro
    Abstract:

    In recent years, several investigations on hydraulic turbine draft tube performance have shown that the hydrodynamic flow field at the runner outlet determines the Diffuser Efficiency affecting the overall performance of the turbine. This flow field, for which the principal characteristics are the flow rate and the inlet swirling flow intensity, is mostly developed on turbines designed for low head (high specific velocity) and operated away from their best Efficiency point. To identify factors of the flow field responsible for loosing draft- tube Efficiency, the correlations between the flow pattern along the Diffuser and both swirl intensity and flow rate have been examined. An analytical representation of inlet flow field has been manipulated by a Multi Island Genetic Algorithm through the automatic coupling of multidisciplinary commercial software systems in order to obtain redesigned inlet velocity profiles. This loop allowed determining the profile for which the minimum energy loss factor was reached. With different flow field patterns obtained during the optimization process it was possible to undertake a qualitative and quantitative analysis which has helped to understand how to suppress or at least mitigate undesirable draft tube flow characteristics. The direct correlation between the runner blade design and the kinematics of the swirl at the draft tube inlet should suppose the perfect coupling at the runner-draft tube interface without compromising the overall flow stability of the machine.

  • Inlet Velocity Profile Optimization of the Turbine 99 Draft Tube
    Volume 1A Symposia: Advances in Fluids Engineering Education; Advances in Numerical Modeling for Turbomachinery Flow Optimization; Applications in CFD, 2013
    Co-Authors: Sergio Galván, Marcelo Reggio, François Guibault
    Abstract:

    In recent years, several investigations on hydraulic turbine draft tube performance have shown that the hydrodynamic field at the runner’s outlet is a direct outcome of the runner design and the operating point. This has shown the dependence of the Diffuser Efficiency on the flow rate and the inlet swirling flow intensity, mostly on turbines that present low head (high specific velocity) and operate away from their best Efficiency point. The numerical optimization of the inlet velocity profile is presented as an attempt to control these two inlet flow characteristics. The goal is the improvement of the flow through the draft tube to allow for better turbine performance. This methodology is based on the automatic coupling of several commercial softwares and is used to manipulate the analytical representation of the swirling flow, which has led to the minimization of hydraulic losses. Also, a qualitative and quantitative analysis of the draft tube flow field provoked by a redesigned inlet velocity profiles, has helped to understand how it is possible to suppress or at least mitigate undesirable draft tube flow characteristics.

  • Inlet Velocity Profile Optimization of the Turbine 99 Draft Tube
    2010
    Co-Authors: Sergio Galván, Marcelo Reggio, François Guibault
    Abstract:

    In recent years, several investigations on hydraulic turbine draft tube performance have shown that the hydrodynamic field at the runner’s outlet is a direct outcome of the runner design and the operating point. This has shown the dependence of the Diffuser Efficiency on the flow rate and the inlet swirling flow intensity, mostly on turbines that present low head (high specific velocity) and operate away from their best Efficiency point. The numerical optimization of the inlet velocity profile is presented as an attempt to control these two inlet flow characteristics. The goal is the improvement of the flow through the draft tube to allow for better turbine performance. This methodology is based on the automatic coupling of several commercial softwares and is used to manipulate the analytical representation of the swirling flow, which has led to the minimization of hydraulic losses. Also, a qualitative and quantitative analysis of the draft tube flow field provoked by a redesigned inlet velocity profiles, has helped to understand how it is possible to suppress or at least mitigate undesirable draft tube flow characteristics.Copyright © 2013 by ASME

Marcelo Reggio - One of the best experts on this subject based on the ideXlab platform.

  • Numerical Analysis of the Turbine 99 Draft Tube Flow Field Provoked by Redesigned Inlet Velocity Profiles.
    IOP Conference Series: Earth and Environmental Science, 2014
    Co-Authors: Sergio Galván, François Guibault, Marcelo Reggio, L. Castro
    Abstract:

    In recent years, several investigations on hydraulic turbine draft tube performance have shown that the hydrodynamic flow field at the runner outlet determines the Diffuser Efficiency affecting the overall performance of the turbine. This flow field, for which the principal characteristics are the flow rate and the inlet swirling flow intensity, is mostly developed on turbines designed for low head (high specific velocity) and operated away from their best Efficiency point. To identify factors of the flow field responsible for loosing draft- tube Efficiency, the correlations between the flow pattern along the Diffuser and both swirl intensity and flow rate have been examined. An analytical representation of inlet flow field has been manipulated by a Multi Island Genetic Algorithm through the automatic coupling of multidisciplinary commercial software systems in order to obtain redesigned inlet velocity profiles. This loop allowed determining the profile for which the minimum energy loss factor was reached. With different flow field patterns obtained during the optimization process it was possible to undertake a qualitative and quantitative analysis which has helped to understand how to suppress or at least mitigate undesirable draft tube flow characteristics. The direct correlation between the runner blade design and the kinematics of the swirl at the draft tube inlet should suppose the perfect coupling at the runner-draft tube interface without compromising the overall flow stability of the machine.

  • Inlet Velocity Profile Optimization of the Turbine 99 Draft Tube
    Volume 1A Symposia: Advances in Fluids Engineering Education; Advances in Numerical Modeling for Turbomachinery Flow Optimization; Applications in CFD, 2013
    Co-Authors: Sergio Galván, Marcelo Reggio, François Guibault
    Abstract:

    In recent years, several investigations on hydraulic turbine draft tube performance have shown that the hydrodynamic field at the runner’s outlet is a direct outcome of the runner design and the operating point. This has shown the dependence of the Diffuser Efficiency on the flow rate and the inlet swirling flow intensity, mostly on turbines that present low head (high specific velocity) and operate away from their best Efficiency point. The numerical optimization of the inlet velocity profile is presented as an attempt to control these two inlet flow characteristics. The goal is the improvement of the flow through the draft tube to allow for better turbine performance. This methodology is based on the automatic coupling of several commercial softwares and is used to manipulate the analytical representation of the swirling flow, which has led to the minimization of hydraulic losses. Also, a qualitative and quantitative analysis of the draft tube flow field provoked by a redesigned inlet velocity profiles, has helped to understand how it is possible to suppress or at least mitigate undesirable draft tube flow characteristics.

  • Inlet Velocity Profile Optimization of the Turbine 99 Draft Tube
    2010
    Co-Authors: Sergio Galván, Marcelo Reggio, François Guibault
    Abstract:

    In recent years, several investigations on hydraulic turbine draft tube performance have shown that the hydrodynamic field at the runner’s outlet is a direct outcome of the runner design and the operating point. This has shown the dependence of the Diffuser Efficiency on the flow rate and the inlet swirling flow intensity, mostly on turbines that present low head (high specific velocity) and operate away from their best Efficiency point. The numerical optimization of the inlet velocity profile is presented as an attempt to control these two inlet flow characteristics. The goal is the improvement of the flow through the draft tube to allow for better turbine performance. This methodology is based on the automatic coupling of several commercial softwares and is used to manipulate the analytical representation of the swirling flow, which has led to the minimization of hydraulic losses. Also, a qualitative and quantitative analysis of the draft tube flow field provoked by a redesigned inlet velocity profiles, has helped to understand how it is possible to suppress or at least mitigate undesirable draft tube flow characteristics.Copyright © 2013 by ASME