Ducted Turbines Research Papers - Academia.edu (original) (raw)

Due to their potential to beat the Betz-Joukowsky limit for power extraction, diffuser-augmented wind-turbines have experienced a great research interest, especially in the last two decades. This paper presents a thorough critical-analysis and review of the most important theoretical models conceived for the performance analysis and design of this wind-concentrator system. The models are classified and compared between each other, and their main analogies and differences are highlighted and explained. New bridging relations between several models are also laid down. All methods are verified and validated using new and/or existing numerical and experimental data. For the first time, the impact of the simplifying assumptions, typically used in these models, is evaluated and discussed on a quantitative basis. Attention is also paid to the optimization procedures aimed at evaluating the maximum power-coefficient attainable by a diffuser-augmented wind-turbine. It is revealed that none of these procedures is valid for a given duct geometry, whereas they still offer some usefulness from a design point of view. Finally, the review points out the main limitations, shortcomings and open-issues associated with theoretical models, paving the way for future research lines and improvements of this kind of models.

- by and +1
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- Mechanical Engineering, Aerospace Engineering, Fluid Mechanics, Renewable Energy

Advances in ramjet technology over the past century have been remarkable, involving dramatic advances in flight-demonstrated technologies. The path discovery has not been without its distractions, which include world events, Initial motivation began with the will for propelling advanced aircraft, followed by missile technology, and now encouraged by the event of reusable Earth-to-orbit vehicles that employ air breathing engines for at least some of, if not the whole, flight envelope. Solid Fuel Ducted Ramjet is a propulsion technique that is used very frequently in present Air to Air missiles, by modifying the design of duct and mechanism it can available with more powerful output during lifting. The classification and the analytical study of the solid fuel ducted ramjet is given in this literature.

- by IJRASET Publication
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- Solid Oxide Fuel Cells, Article Review, Ducted Turbines

A numerical modelling is proposed to efficiently
compute the power produced by a row of Vertical Axis Water
Turbines (VAWT) deployed in parallel within various types of
water flows. As the computational cost of the unsteady Reynolds Averaged Navier Stokes (URANS) approach is high, a coupled Blade Element Momentum (BEM) / (steady) Reynolds Averaged Navier-Stokes (RANS) approach is developed, restricted to a 2D approximation. More specifically, the HARVEST hydrokinetic devices considered in this study are made of twin contra-rotating VAWTs of ducted H-Darrieus type rotors. Momentum source terms are derived for such rotors from URANS simulations taking into account the presence of fairings. The source terms included in the BEM-RANS model are derived by also incorporating the optimal tip speed ratio (TSR), using a procedure based on the mass flow through each rotor and on local flow conditions upstream of the rotor path. When compared with reference URANS results, the BEM-RANS model yields an accurate prediction for a cost reduced by orders of magnitude.
This model is then applied to the targeted analysis of the power produced by a row of VAWTs through a river or a channel with various blockage ratios.

- by Favio Dominguez and +1
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- Renewable Energy (Marine hydrokinetics), Vertical Axis Wind Turbine (VAWT), Marine Turbines, Hydrokinetic Turbines

In this paper the analysis of the aerodynamic performance of ducted wind turbines is carried out by means of a nonlinear and semi-analytical actuator disk model. It returns the exact solution in an implicit formulation as superposition of ring vortices properly arranged along the duct surface and the wake region. In comparison with similar and previously developed models, the method can deal with ducts of general shape, wake rotation and rotors characterised by radially varying load distributions. Moreover, the nonlinear mutual interaction between the duct and the turbine, and the divergence of the slipstream, which is particularly relevant for heavily loaded rotors, are naturally accounted for. Present results clearly show that a properly ducted wind turbine can swallow a higher mass flow rate than an open turbine with the same rotor load. Consequently, the ducted turbine achieves a higher value of the extracted power. The paper also presents a detailed comparison between the aforementioned nonlinear and semi-analytical actuator disk method and the widely diffused CFD actuator disk method. The latter is based on the introduction of an actuator disk model in a CFD package describing the effects of the rotor through radial profiles of blade forces distributed over a disk surface. A set of reference numerical data, providing the inviscid axisymmetric velocity and pressure field distributions, are generated with controlled accuracy. Owing to an in-depth analysis of the error generated by the semi-analytical method and to the exactness of the solution in its implicit form, the collected data are well-suited for code-to-code validation of existing or newly developed computational methods.

- by Marcello Manna and +1
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- Fluid Mechanics, Wind Energy, Fluid Dynamics, Wind Power

The paper presents an extension to ducted rotors of the nonlinear actuator disk theory of Conway (J. Fluid Mech., vol. 365, 1998, pp. 235–267) and it is exact for incompressible, axisymmetric and inviscid flows. The solution for the velocities and the Stokes stream function results from the superposition of ring vortices properly arranged along the duct surface and the wake region. Using a general analytical procedure the flow fields are given as a combination of one-dimensional integrals of expressions involving complete as well as incomplete elliptic integrals. The solution being exact, the proper shape of the slipstream whether converging or diverging is naturally accounted for, even for heavy loads. A semi-analytical method has been developed that enables the flow induced by an actuator disk housed in a contoured duct to be solved duly accounting for the nonlinear mutual interaction between the duct and the rotor. Non-uniform load distributions, rotor wake rotation and ducts of general shapes and thickness distribution can be dealt with. Thanks to its reduced numerical cost, the method is well suited for the design and/or analysis of ducted rotors for marine, wind and aeronautical applications.

- by Marcello Manna and +1
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- Marine Engineering, Fluid Dynamics, Wind Power, Wind turbine

This work investigates the performance of ducted wind turbines (DWTs) through the axial momentum theory (AMT) as well as through a semi-analytical approach. Although the AMT points out that the duct thrust plays a key role in the enhancement of the power extraction, it does not allow for the evaluation of the flow field around the duct. For this reason, a semi-analytical model is also used to investigate the local and global features of the flow through a DWT. In comparison to the AMT, the proposed semi-analytical method can properly evaluate the performance of the device for each prescribed rotor load distribution and duct geometry. Moreover, in comparison to other linearised methods, this approach fully takes into account the wake rotation and divergence, and the mutual interaction between the turbine and the shroud. The analysis shows the opportunity to significantly increase the power output by enclosing the turbine in a duct and that the growth in the duct thrust has a beneficial effect onto the device performance. Finally, some insights on the changes occurring to the performance coefficients with the rotor thrust and the duct camber are obtained through a close inspection of the local features of the flow field.

- by Marcello Manna and +1
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- Wind Energy, Tidal Stream Energy, Wind Engineering, Wind Energy (Engineering)

The paper presents the validation of a generalised semi-analytical actuator disk model as applied to the study of the flow around ducted propellers. The method, which returns the exact solution as a superposition of ring vortex, duly accounts for the rotation of the wake, the convergence of the slipstream, and the nonlinear mutual interaction between the duct and the propeller. Furthermore, it can deal with an arbitrary radial distribution of the load and ducts of general shape. In order to validate the previously mentioned actuator disk model, results obtained through it are compared with those provided by the so-called " CFD actuator disk method ". The latter is a widely diffused tool for the analysis of the flow around open and ducted propellers which models the rotor by means of radial profiles of blade forces distributed over a disk surface. In this paper, evidence has been given of the excellent agreement between the results of the two methods. Thanks to its extremely reduced computational cost the semi-analytical method is well suited to be integrated into design systems based on the repeated analysis scheme of hierarchical type.

- by Rodolfo Bontempo and +1
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- Hydrodynamics (Physics), Fluid Mechanics, Wind Energy, Wind Engineering

Diffuser-augmented wind-turbines are drawing increasing attention since they can beat the Betz-limit referred to the rotor-area. However, their diffusion is still prevented by some issues including: 1) the attainable power has not yet been shown to be larger than that of an open-turbine with the same frontal-area, 2) the classical analysis methods rely on the one-dimensional-flow and no-tip-gap assumptions whose impact has never been quantified. The paper addresses these two items investigating the potential of ideal diffuser-augmented wind-turbines using a newly-developed Axial-Momentum-Theory approach, and an extended version of a free-wake ring-vortex actuator-disk model. In comparison with similar methods, the novelty of the first approach is that it accounts for the two-dimensional effects and the tip-gap presence. Since this approach cannot evaluate the performance of a turbine for a given duct-geometry, a ring-vortex method is also developed. This is the first low-computational-cost method relying on the exact solution of the inviscid-flow through a uniformly-loaded ducted-turbine with a finite-size tip-gap. It strongly couples the flow induced by the duct and the wake which are modelled as the superposition of ring-vortices. The combined use of axial-momentum and ring-vortex methods leads to the following results. Firstly, it is clearly shown that an ideal diffuser-augmented turbine can extract more power than a Betz disk with the same frontal-area. To strengthen this statement, a new duct geometry with a remarkable value of the exit-area power-coefficient equal to 0.6098 is presented. This value is significantly higher than that of a base-line NACA5415 duct profile, i.e. 0.4800. Secondly, the impact of the one-dimensional-flow and no-tip-gap assumptions is evaluated. It is also shown that the tip-gap has negligible effects. Moreover, the one-dimensional-flow hypothesis has a low impact for high values of the rotor load, while the errors grow up decreasing the rotor thrust.

- by Rodolfo Bontempo and +1
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- Wind Energy, Tidal Stream Energy, Wind Engineering, Tidal Stream Turbine Modelling

VI International Conference on Computational Methods in Marine Engineering. Marine 2015, Rome, Italy.

- by Marcello Manna
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- Mathematics, Wind Energy, Tidal Stream Energy, Wind Engineering

This paper presents the validation of a generalised semi-analytical actuator disk model as applied to the study of the flow around ducted propellers. The method, which returns the exact solution as a superposition of ring vortex, duly accounts for the rotation of the wake, the convergence of the slipstream, and the nonlinear mutual interaction between the duct and the propeller. Furthermore, it can deal with an arbitrary radial distribution of the load and ducts of general shape. In order to validate the previously mentioned actuator disk model, results obtained through it are compared with those provided by the so-called “CFD actuator disk method”. The latter is a widely diffused tool for the analysis of the flow around open and ducted propellers which models the rotor by means of radial profiles of blade forces distributed over a disk surface. In this paper, evidence has been given of the excellent agreement between the results of the two methods. Thanks to its extremely reduced c...

- by Marcello Manna
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- Engineering, Mechanical Engineering, Fluid Mechanics, Wind Energy