Michael Togneri | Swansea University (original) (raw)

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Papers by Michael Togneri

3rd Oxford Tidal Energy Workshop, 2014

"This presentation examines methods of generating synthetic turbulence for use in blade element ... more "This presentation examines methods of generating synthetic turbulence for use in blade element
momentum theory simulations of tidal stream turbines. Two techniques are employed, both based on data
gathered from field measurements. The first is a 'single-point' method, which generates a spatially-uniform but
temporally-varying field, and the second is the synthetic eddy method (SEM) of Jarrin et al. [1,2], which
generates a flowfield that varies in both space and time. This work is intended to help determine the best way to
incorporate turbulence into BEMT models in order to capture its effects on turbine loads."

In this presentation we present and discuss various turbulence characteristics from selected high... more In this presentation we present and discuss various turbulence characteristics from selected high energy tidal sites, including turbulent kinetic energy density, Reynolds stress distributions and turbulent length scales. These characteristics are calculated using the variance method on data obtained using bed-mounted acoustic Doppler current profilers (ADCPs). We also perform some analysis of errors (i.e., bias and spread) in these quantities, and discuss the validity of the conventional techniques for quantifying these values. One site is found to have extremely intense turbulence on one phase of the tide, and we find that such circumstances appear to make the standard estimates of error less robust than is usually accepted.

Blade element momentum theory (BEMT) is a well-established method for evaluating the performance ... more Blade element momentum theory (BEMT) is a well-established method for evaluating the performance of turbines designed to extract energy from a flowing fluid. In this paper, we discuss a modified version of BEMT that allows for greater variation in the permissible inflow conditions, paying particular attention to inflow conditions that model turbulence in coastal waters in order to calculate the power output and other performance parameters of tidal stream turbines (TSTs). In the first part of the paper, we describe the modification we have made to standard BEMT analysis. In the second part, we describe how we create an appropriate representation of a turbulent tidal stream or marine current, and what parameters we can extract from measurements of a real current in order to create this representation. Some preliminary results are presented and their significance discussed.

Proceedings of the 9th European Wave and …, 2012

Blade element momentum theory (BEMT) allows much more rapid modelling of turbines than full Navie... more Blade element momentum theory (BEMT) allows much more rapid modelling of turbines than full Navier-Stokes simulations. Classical BEMT greatly simplifies flow conditions to make this rapidity possible; we can, however, modify BEMT to incorporate additional flow phenomena without sacrificing much in the way of calculation speed. Using an already-existing extended BEMT model, this paper explores how turbulent flows can be synthesised in order to predict their effects on turbine performance.

The Proceedings of the 21th, 2011

Blade element momentum theory (BEMT) is a well-established method for evaluating the performance ... more Blade element momentum theory (BEMT) is a well-established method for evaluating the performance of turbines designed to extract energy from a flowing fluid. In this paper, we discuss a modified version of BEMT that allows for greater variation in the permissible inflow conditions, paying particular attention to inflow conditions that model turbulence in coastal waters in order to calculate the power output and other performance parameters of tidal stream turbines (TSTs). In the first part of the paper, we describe the modification we have made to standard BEMT analysis. In the second part, we describe how we create an appropriate representation of a turbulent tidal stream or marine current, and what parameters we can extract from measurements of a real current in order to create this representation. Some preliminary results are presented and their significance discussed.

Computers & Fluids, 2011

This paper outlines a velocity-vorticity based numerical simulation method for modelling perturba... more This paper outlines a velocity-vorticity based numerical simulation method for modelling perturbation development in laminar and turbulent boundary layers at large Reynolds numbers. Particular attention is paid to the application of integral conditions for the vorticity. These provide constraints on the evolution of the vorticity that are fully equivalent to the usual no-slip conditions. The vorticity and velocity perturbation variables are divided into two distinct primary and secondary groups, allowing the number of governing equations and variables to be effectively halved. Compact finite differences are used to obtain a high-order spatial discretization of the equations. Some novel features of the discretization are highlighted: (i) the incorporation of the vorticity integral conditions and (ii) the related use of a co-ordinate transformation along the semi-infinite wall-normal direction. The viability of the numerical solution procedure is illustrated by a selection of test simulation results. We also indicate the intended application of the simulation code to parametric investigations of the effectiveness of spanwise-directed wall oscillations in inhibiting the growth of streaks within turbulent boundary layers.

3rd Oxford Tidal Energy Workshop, 2014

"This presentation examines methods of generating synthetic turbulence for use in blade element ... more "This presentation examines methods of generating synthetic turbulence for use in blade element
momentum theory simulations of tidal stream turbines. Two techniques are employed, both based on data
gathered from field measurements. The first is a 'single-point' method, which generates a spatially-uniform but
temporally-varying field, and the second is the synthetic eddy method (SEM) of Jarrin et al. [1,2], which
generates a flowfield that varies in both space and time. This work is intended to help determine the best way to
incorporate turbulence into BEMT models in order to capture its effects on turbine loads."

In this presentation we present and discuss various turbulence characteristics from selected high... more In this presentation we present and discuss various turbulence characteristics from selected high energy tidal sites, including turbulent kinetic energy density, Reynolds stress distributions and turbulent length scales. These characteristics are calculated using the variance method on data obtained using bed-mounted acoustic Doppler current profilers (ADCPs). We also perform some analysis of errors (i.e., bias and spread) in these quantities, and discuss the validity of the conventional techniques for quantifying these values. One site is found to have extremely intense turbulence on one phase of the tide, and we find that such circumstances appear to make the standard estimates of error less robust than is usually accepted.

Blade element momentum theory (BEMT) is a well-established method for evaluating the performance ... more Blade element momentum theory (BEMT) is a well-established method for evaluating the performance of turbines designed to extract energy from a flowing fluid. In this paper, we discuss a modified version of BEMT that allows for greater variation in the permissible inflow conditions, paying particular attention to inflow conditions that model turbulence in coastal waters in order to calculate the power output and other performance parameters of tidal stream turbines (TSTs). In the first part of the paper, we describe the modification we have made to standard BEMT analysis. In the second part, we describe how we create an appropriate representation of a turbulent tidal stream or marine current, and what parameters we can extract from measurements of a real current in order to create this representation. Some preliminary results are presented and their significance discussed.

Proceedings of the 9th European Wave and …, 2012

Blade element momentum theory (BEMT) allows much more rapid modelling of turbines than full Navie... more Blade element momentum theory (BEMT) allows much more rapid modelling of turbines than full Navier-Stokes simulations. Classical BEMT greatly simplifies flow conditions to make this rapidity possible; we can, however, modify BEMT to incorporate additional flow phenomena without sacrificing much in the way of calculation speed. Using an already-existing extended BEMT model, this paper explores how turbulent flows can be synthesised in order to predict their effects on turbine performance.

The Proceedings of the 21th, 2011

Blade element momentum theory (BEMT) is a well-established method for evaluating the performance ... more Blade element momentum theory (BEMT) is a well-established method for evaluating the performance of turbines designed to extract energy from a flowing fluid. In this paper, we discuss a modified version of BEMT that allows for greater variation in the permissible inflow conditions, paying particular attention to inflow conditions that model turbulence in coastal waters in order to calculate the power output and other performance parameters of tidal stream turbines (TSTs). In the first part of the paper, we describe the modification we have made to standard BEMT analysis. In the second part, we describe how we create an appropriate representation of a turbulent tidal stream or marine current, and what parameters we can extract from measurements of a real current in order to create this representation. Some preliminary results are presented and their significance discussed.

Computers & Fluids, 2011

This paper outlines a velocity-vorticity based numerical simulation method for modelling perturba... more This paper outlines a velocity-vorticity based numerical simulation method for modelling perturbation development in laminar and turbulent boundary layers at large Reynolds numbers. Particular attention is paid to the application of integral conditions for the vorticity. These provide constraints on the evolution of the vorticity that are fully equivalent to the usual no-slip conditions. The vorticity and velocity perturbation variables are divided into two distinct primary and secondary groups, allowing the number of governing equations and variables to be effectively halved. Compact finite differences are used to obtain a high-order spatial discretization of the equations. Some novel features of the discretization are highlighted: (i) the incorporation of the vorticity integral conditions and (ii) the related use of a co-ordinate transformation along the semi-infinite wall-normal direction. The viability of the numerical solution procedure is illustrated by a selection of test simulation results. We also indicate the intended application of the simulation code to parametric investigations of the effectiveness of spanwise-directed wall oscillations in inhibiting the growth of streaks within turbulent boundary layers.