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Charles Meneveau - One of the best experts on this subject based on the ideXlab platform.

  • filtered Lifting Line Theory and application to the actuator Line model
    Journal of Fluid Mechanics, 2019
    Co-Authors: Luis A Martineztossas, Charles Meneveau
    Abstract:

    Lifting Line Theory describes the cumulative effect of shed vorticity from finite span Lifting surfaces. In this work, the Theory is reformulated to improve the accuracy of the actuator Line model (ALM). This model is a computational tool used to represent Lifting surfaces, such as wind-turbine blades in computational fluid dynamics. In ALM, blade segments are represented by means of a Gaussian body force distribution with a prescribed kernel size. Prior analysis has shown that a representation of the blade using an optimal kernel width of approximately one quarter of the chord size results in accurate predictions of the velocity field and loads along the blades. Also, simulations have shown that use of the optimal kernel size yields accurate representation of the tip-vortex size and the associated downwash resulting in accurate predictions of the tip losses. In this work, we address the issue of how to represent the effects of finite span wings and tip vortices when using Gaussian body forces with a kernel size larger than the optimal value. This question is relevant in the context of coarse-scale large-eddy simulations that cannot afford the fine resolutions required to resolve the optimal kernel size. For this purpose, we present a filtered Lifting Line Theory for a Gaussian force distribution. Based on the streamwise component of the vorticity transport equation, we develop an analytical model for the induced velocity resulting from the spanwise changes in lift force for an arbitrary kernel scale. The results are used to derive a subfilter-scale velocity model that is used to correct the velocity along the blade when using kernel sizes larger than . Tests are performed in large-eddy simulation of flow over fixed wings with constant and elliptic chord distributions using various kernel sizes. Results show that by using the proposed subfilter velocity model, kernel-size independent predictions of lift coefficient and total lift forces agree with those obtained with the optimal kernel size.

  • filtered Lifting Line Theory and application to the actuator Line model
    Journal of Fluid Mechanics, 2019
    Co-Authors: Luis A Martineztossas, Charles Meneveau
    Abstract:

    Lifting Line Theory describes the cumulative effect of shed vorticity from finite span Lifting surfaces. In this work, the Theory is reformulated to improve the accuracy of the actuator Line model (ALM). This model is a computational tool used to represent Lifting surfaces, such as wind-turbine blades in computational fluid dynamics. In ALM, blade segments are represented by means of a Gaussian body force distribution with a prescribed kernel size. Prior analysis has shown that a representation of the blade using an optimal kernel width . Tests are performed in large-eddy simulation of flow over fixed wings with constant and elliptic chord distributions using various kernel sizes. Results show that by using the proposed subfilter velocity model, kernel-size independent predictions of lift coefficient and total lift forces agree with those obtained with the optimal kernel size.

Luis A Martineztossas - One of the best experts on this subject based on the ideXlab platform.

  • filtered Lifting Line Theory and application to the actuator Line model
    Journal of Fluid Mechanics, 2019
    Co-Authors: Luis A Martineztossas, Charles Meneveau
    Abstract:

    Lifting Line Theory describes the cumulative effect of shed vorticity from finite span Lifting surfaces. In this work, the Theory is reformulated to improve the accuracy of the actuator Line model (ALM). This model is a computational tool used to represent Lifting surfaces, such as wind-turbine blades in computational fluid dynamics. In ALM, blade segments are represented by means of a Gaussian body force distribution with a prescribed kernel size. Prior analysis has shown that a representation of the blade using an optimal kernel width of approximately one quarter of the chord size results in accurate predictions of the velocity field and loads along the blades. Also, simulations have shown that use of the optimal kernel size yields accurate representation of the tip-vortex size and the associated downwash resulting in accurate predictions of the tip losses. In this work, we address the issue of how to represent the effects of finite span wings and tip vortices when using Gaussian body forces with a kernel size larger than the optimal value. This question is relevant in the context of coarse-scale large-eddy simulations that cannot afford the fine resolutions required to resolve the optimal kernel size. For this purpose, we present a filtered Lifting Line Theory for a Gaussian force distribution. Based on the streamwise component of the vorticity transport equation, we develop an analytical model for the induced velocity resulting from the spanwise changes in lift force for an arbitrary kernel scale. The results are used to derive a subfilter-scale velocity model that is used to correct the velocity along the blade when using kernel sizes larger than . Tests are performed in large-eddy simulation of flow over fixed wings with constant and elliptic chord distributions using various kernel sizes. Results show that by using the proposed subfilter velocity model, kernel-size independent predictions of lift coefficient and total lift forces agree with those obtained with the optimal kernel size.

  • filtered Lifting Line Theory and application to the actuator Line model
    Journal of Fluid Mechanics, 2019
    Co-Authors: Luis A Martineztossas, Charles Meneveau
    Abstract:

    Lifting Line Theory describes the cumulative effect of shed vorticity from finite span Lifting surfaces. In this work, the Theory is reformulated to improve the accuracy of the actuator Line model (ALM). This model is a computational tool used to represent Lifting surfaces, such as wind-turbine blades in computational fluid dynamics. In ALM, blade segments are represented by means of a Gaussian body force distribution with a prescribed kernel size. Prior analysis has shown that a representation of the blade using an optimal kernel width . Tests are performed in large-eddy simulation of flow over fixed wings with constant and elliptic chord distributions using various kernel sizes. Results show that by using the proposed subfilter velocity model, kernel-size independent predictions of lift coefficient and total lift forces agree with those obtained with the optimal kernel size.

Koichi Koyama - One of the best experts on this subject based on the ideXlab platform.

  • Relation between the Lifting surface Theory and the Lifting Line Theory in the design of an optimum screw propeller
    Journal of Marine Science and Technology, 2013
    Co-Authors: Koichi Koyama
    Abstract:

    A Theory on an optimum screw propeller is described. The optimum means optimum efficiency of a propeller, that is, maximizing thrust horse power for a given shaft horse power. The Theory is based on the propeller Lifting surface Theory. Circulation density (lift density) of the blade is determined by the Lifting surface Theory on a specified condition in general. However, it is shown that, in the case of optimum condition, the circulation density is not determined by the Lifting surface Theory, although the circulation distribution which is the chordwise integral of the circulation density is determined. The reason is that the governing equation of the optimization by the Lifting surface Theory is reduced to that by the Lifting Line Theory. This theoretical deduction is the main part of this paper. The importance of the Lifting Line Theory in the design of the optimum propeller is made clear. Numerical calculations support the conclusion from the deduction. This is shown in the case of freely running propellers and in the case of wake adapted propellers.

Hua Wang - One of the best experts on this subject based on the ideXlab platform.

  • prediction of lift coefficient for tandem wing configuration or multiple Lifting surface system using prandtl s Lifting Line Theory
    International Journal of Aerospace Engineering, 2018
    Co-Authors: Hao Cheng, Hua Wang
    Abstract:

    In tandem airfoil configuration or multiple-Lifting-surface layouts, due to the flow interaction among their Lifting surfaces, the aerodynamic characteristics can be affected by each other. In accordance with Prandtl’s classical Lifting-Line Theory, a method to calculate the section lift coefficient for the tandem wing configuration or multiple-Lifting-surface system is presented. In that method, the form of Fourier sine series is used to express the variation of the section circulation which changes continuously along the wingspan. The accuracy of the numerical solutions obtained by the method has been validated by the data obtained from computational fluid dynamics and tunnel experiment. By varying the design parameters, such as the gap, the stagger, the incidence angle, the wingspan, the taper ratio as well as the aspect ratio, a series of tandem wing configurations are tested to analyze the lift coefficient and the induced drag of each Lifting surface. From the results, it can be seen that the bigger negative gap and stagger can produce better lift characteristic for tandem wing configuration. Besides, it will also be beneficial for the lift characteristic when the incidence angle and the wingspan of fore wing are appropriately decLined or if the incidence angle and the wingspan of hind wing are appropriately increased.

  • Prediction of Lift Coefficient for Tandem Wing Configuration or Multiple-Lifting-Surface System Using Prandtl’s Lifting-Line Theory
    Hindawi Limited, 2018
    Co-Authors: Hao Cheng, Hua Wang
    Abstract:

    In tandem airfoil configuration or multiple-Lifting-surface layouts, due to the flow interaction among their Lifting surfaces, the aerodynamic characteristics can be affected by each other. In accordance with Prandtl’s classical Lifting-Line Theory, a method to calculate the section lift coefficient for the tandem wing configuration or multiple-Lifting-surface system is presented. In that method, the form of Fourier sine series is used to express the variation of the section circulation which changes continuously along the wingspan. The accuracy of the numerical solutions obtained by the method has been validated by the data obtained from computational fluid dynamics and tunnel experiment. By varying the design parameters, such as the gap, the stagger, the incidence angle, the wingspan, the taper ratio as well as the aspect ratio, a series of tandem wing configurations are tested to analyze the lift coefficient and the induced drag of each Lifting surface. From the results, it can be seen that the bigger negative gap and stagger can produce better lift characteristic for tandem wing configuration. Besides, it will also be beneficial for the lift characteristic when the incidence angle and the wingspan of fore wing are appropriately decLined or if the incidence angle and the wingspan of hind wing are appropriately increased

Dimitriadis Grigorios - One of the best experts on this subject based on the ideXlab platform.

  • Unsteady Lifting Line Theory Using theWagner Function for the Aerodynamic and Aeroelastic Modeling of 3D Wings
    2018
    Co-Authors: Boutet Johan, Dimitriadis Grigorios
    Abstract:

    A method is presented to model the incompressible, attached, unsteady lift and pitching moment acting on a thin three-dimensional wing in the time domain. The model is based on the combination of Wagner Theory and Lifting Line Theory through the unsteady Kutta–Joukowski theorem. The results are a set of closed-form Linear ordinary differential equations that can be solved analytically or using a Runge–Kutta–Fehlberg algorithm. The method is validated against numerical predictions from an unsteady vortex lattice method for rectangular and tapered wings undergoing step or oscillatory changes in plunge or pitch. Further validation is demonstrated on an aeroelastic test case of a rigid rectangular finite wing with pitch and plunge degrees of freedom.Peer reviewe

  • Unsteady Lifting Line Theory Using theWagner Function for the Aerodynamic and Aeroelastic Modeling of 3D Wings
    'MDPI AG', 2018
    Co-Authors: Boutet Johan, Dimitriadis Grigorios
    Abstract:

    peer reviewedaudience: researcher, professionalA method is presented to model the incompressible, attached, unsteady lift and pitching moment acting on a thin three-dimensional wing in the time domain. The model is based on the combination of Wagner Theory and Lifting Line Theory through the unsteady Kutta–Joukowski theorem. The results are a set of closed-form Linear ordinary differential equations that can be solved analytically or using a Runge–Kutta–Fehlberg algorithm. The method is validated against numerical predictions from an unsteady vortex lattice method for rectangular and tapered wings undergoing step or oscillatory changes in plunge or pitch. Further validation is demonstrated on an aeroelastic test case of a rigid rectangular finite wing with pitch and plunge degrees of freedom

  • Unsteady Lifting Line Theory using the Wagner function
    'American Institute of Aeronautics and Astronautics (AIAA)', 2017
    Co-Authors: Boutet Johan, Dimitriadis Grigorios
    Abstract:

    audience: researcher, professional, studentA method is presented to model the incompressible, attached, unsteady lift and moment acting on a thin three-dimensional wing in the time domain. The model is based on the combination of Wagner Theory and Lifting Line Theory trough the unsteady Kutta-Joukowsky theorem. The result is a set of closed form Linear ordinary di erential equations that can be solved analytically or using a Runge-Kutta-Fehlberg algorithm. The method is validated against numerical predictions from an unsteady Vortex Lattice method for rectangular and tapered wings undergoing step or oscillatory changes in plunge or pitch. As the aerodynamic loads are written in state space form in the proposed method, they can be easily included in aeroelastic and flight dynamic calculations

  • Unsteady Lifting Line Theory using the Wagner function
    'American Institute of Aeronautics and Astronautics (AIAA)', 2017
    Co-Authors: Boutet Johan, Dimitriadis Grigorios
    Abstract:

    A method is presented to model the incompressible, attached, unsteady lift and moment acting on a thin three-dimensional wing in the time domain. The model is based on the combination of Wagner Theory and Lifting Line Theory trough the unsteady Kutta-Joukowsky theorem. The result is a set of closed form Linear ordinary di erential equations that can be solved analytically or using a Runge-Kutta-Fehlberg algorithm. The method is validated against numerical predictions from an unsteady Vortex Lattice method for rectangular and tapered wings undergoing step or oscillatory changes in plunge or pitch. As the aerodynamic loads are written in state space form in the proposed method, they can be easily included in aeroelastic and flight dynamic calculations