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Radial impulse turbine for wave energy conversion. A new geometry

Profile image of Bruno PereirasBruno Pereiras

2008, Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE Volume 6, Pages 841-850

https://doi.org/10.1115/OMAE2008-57951
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Abstract

The Oscillating Water Column system (OWC) is an interesting concept for ocean wave energy extraction. Several kinds of air turbines have been used for pneumatic energy conversion to mechanical energy. The Wells turbine has been used widely in OWC plants. However, as an alternative the self-rectifying turbine called Impulse turbine has been studied during the last years.

FAQs

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What improvements does the new radial impulse turbine geometry offer?add

The new turbine geometry aims to enhance performance beyond the original design by optimizing torque and input coefficients, potentially achieving superior efficiency metrics.

How does the radial impulse turbine compare to Wells turbines?add

Research indicates that the radial impulse turbine exhibits reduced oscillating axial thrust and simpler manufacturing compared to Wells turbines, addressing significant operational disadvantages.

What numerical modeling techniques were utilized for performance prediction?add

The study employed CFD simulations using FLUENT® to develop and validate a 3D model of the radial impulse turbine's airflow characteristics against experimental data.

What are the key advantages of the Oscillating Water Column system?add

The OWC system offers low installation and maintenance costs due to its shoreline placement and effective corrosion resistance, as there is no direct contact with seawater.

What challenges do existing pneumatic turbines face in wave energy conversion?add

Inherent issues include narrow flow rate ranges for optimal efficiency, severe aerodynamic stalling, and high operational noise levels linked to high rotational speeds.

Figures (19)
- We are interested in the radial version of the Impulse turbine, work aimed to improve the knowledge of the local flow behaviour an has been carried out using CFD (FLUENT®). The objectives of that wo: 3D model for air flow simulation in a radial Impulse turbine. Model v available experimental results. was conducted through a comparison with Lin
- We are interested in the radial version of the Impulse turbine, work aimed to improve the knowledge of the local flow behaviour an has been carried out using CFD (FLUENT®). The objectives of that wo: 3D model for air flow simulation in a radial Impulse turbine. Model v available experimental results. was conducted through a comparison with Lin
We are interested in the radial version of the Impulse turbine, which was initially proposed by McCormick [5]. A research work [9] aimed to improve the understanding of the local flow behaviour and the prediction of the performances for this kind of turbine has been carried out using CFD (FLUENT v6.3). The objectives of that work were connected mainly to the elaboration of a 3D flow model. The model simulates the flow in a radial Impulse turbine. Model validation was conducted through a comparison with available experimental results [6].
We are interested in the radial version of the Impulse turbine, which was initially proposed by McCormick [5]. A research work [9] aimed to improve the understanding of the local flow behaviour and the prediction of the performances for this kind of turbine has been carried out using CFD (FLUENT v6.3). The objectives of that work were connected mainly to the elaboration of a 3D flow model. The model simulates the flow in a radial Impulse turbine. Model validation was conducted through a comparison with available experimental results [6].
The flow model solwes the incompressible fluid conservation equations by using a segregated solver. The realizable k-¢ turbulence model was used with standard wall function. The time dependent term is approximated with a first order implicit scheme. The pressure-velocity coupling is performed through the SIMPLE algorithm. The highest order MUSCL scheme has been used for convection terms discretization and the classical central differences approximations for diffusion terms. Proceedings of the ASME 27th International Conference on Offshore Mechanics and Arctic Engineering OMAE 2008 J une 15-20, 2008, Estoril, Portugal
The flow model solwes the incompressible fluid conservation equations by using a segregated solver. The realizable k-¢ turbulence model was used with standard wall function. The time dependent term is approximated with a first order implicit scheme. The pressure-velocity coupling is performed through the SIMPLE algorithm. The highest order MUSCL scheme has been used for convection terms discretization and the classical central differences approximations for diffusion terms. Proceedings of the ASME 27th International Conference on Offshore Mechanics and Arctic Engineering OMAE 2008 J une 15-20, 2008, Estoril, Portugal
Table 3 Mesh influence In [9] the characteristics of the air flow within the M8 turbine are studied. It concludes that important losses of energy exist in the elbow and in the guide vanes, mainly during the exhalation. Therefore, the modifications made in the M8 turbine geometry are directed to diminish these losses. In this new geometry, from now on the M12 turbine, the inner guide vanes angles have been modified, the inner guide vanes length has been increased and the relative position of the rotor blades has been modified. The figure 4 shows the differences en the two geometries. The outer guide vanes is the same and is not represented in M1 of inner guide vanes has c er and the outer angle is 35. The i respect M8 is the rotor. The position is different, the he inner and outer angles
Table 3 Mesh influence In [9] the characteristics of the air flow within the M8 turbine are studied. It concludes that important losses of energy exist in the elbow and in the guide vanes, mainly during the exhalation. Therefore, the modifications made in the M8 turbine geometry are directed to diminish these losses. In this new geometry, from now on the M12 turbine, the inner guide vanes angles have been modified, the inner guide vanes length has been increased and the relative position of the rotor blades has been modified. The figure 4 shows the differences en the two geometries. The outer guide vanes is the same and is not represented in M1 of inner guide vanes has c er and the outer angle is 35. The i respect M8 is the rotor. The position is different, the he inner and outer angles
the numerical accuracy, we have reduced the 3D calculation domain to a small angular sector with periodic boundaries as depicted in figure 3. The real operation of the turbine is unsteady, the magnitude and the direction of air flow varies in the time. Nevertheless, the time scale of the waves is much greater han the residence time through the turbine and a i steady behaviour of the turbine can be supposed. Ther: he boundary conditions will remain constant in simulation, although the model is unsteady since the relati position between the rotor and the guide vanes varies wit ime. The boundary conditions are those indicated in the able 2. The flow rate is adjusted b ing the chamber pressure value. Proceedings of the ASME 27th International Conference on Offshore Mechanics and Arctic Engineering OMAE 2008 J une 15-20, 2008, Estoril, Portugal
the numerical accuracy, we have reduced the 3D calculation domain to a small angular sector with periodic boundaries as depicted in figure 3. The real operation of the turbine is unsteady, the magnitude and the direction of air flow varies in the time. Nevertheless, the time scale of the waves is much greater han the residence time through the turbine and a i steady behaviour of the turbine can be supposed. Ther: he boundary conditions will remain constant in simulation, although the model is unsteady since the relati position between the rotor and the guide vanes varies wit ime. The boundary conditions are those indicated in the able 2. The flow rate is adjusted b ing the chamber pressure value. Proceedings of the ASME 27th International Conference on Offshore Mechanics and Arctic Engineering OMAE 2008 J une 15-20, 2008, Estoril, Portugal
RESULTS AND DISCUSSION The global characteristics corresponding to M8 turbine and those of the new geometry are compared in the figure 5. The positive flow rate coefficients correspond to the exhalation while the negative ones to the inhalation.
RESULTS AND DISCUSSION The global characteristics corresponding to M8 turbine and those of the new geometry are compared in the figure 5. The positive flow rate coefficients correspond to the exhalation while the negative ones to the inhalation.
For exhalation, the tor ient i lar for both designs, but the input co in the case In the figure 6 the turbine efficiency is shown. It is observed that M12 yield a better efficiency than M8, except for inhalation at low flow rate. The turbine will work at non- steady flow, then the average efficiency is better for M12 in most of the sea states, as we will show later.
For exhalation, the tor ient i lar for both designs, but the input co in the case In the figure 6 the turbine efficiency is shown. It is observed that M12 yield a better efficiency than M8, except for inhalation at low flow rate. The turbine will work at non- steady flow, then the average efficiency is better for M12 in most of the sea states, as we will show later.
Energy loosed in fixed components and _ energy transferred to the rotor are showed in figure 7 a) and 7 b) for inhalation and exhalation operation respectively. Its percentages are displayed in figure 8. Proceedings of the ASME 27th International Conference on Offshore Mechanics and Arctic Engineering OMAE 2008 J une 15-20, 2008, Estoril, Portugal
Energy loosed in fixed components and _ energy transferred to the rotor are showed in figure 7 a) and 7 b) for inhalation and exhalation operation respectively. Its percentages are displayed in figure 8. Proceedings of the ASME 27th International Conference on Offshore Mechanics and Arctic Engineering OMAE 2008 J une 15-20, 2008, Estoril, Portugal
It is important to mention here that turbine efficiencies, reported in figure 6 and experimental studies [6, 7, 8] show maximum value of 40 %. This is enough low if it is compared to efficiency calculated only in the rotor. That means that important losses occur as well as in the other parts of the turbine such as the guide vanes (IGV and OGV) and the inlet and outlet regions. Therefore, more investigations and analysis are needed in order to minimize losses in these components. In the figure 10 both energy coefficients are compared. In both cases, inhalation and exhalation, the energy available to be extracted by the rotor, represented by the net coefficient, is higher in M8.
It is important to mention here that turbine efficiencies, reported in figure 6 and experimental studies [6, 7, 8] show maximum value of 40 %. This is enough low if it is compared to efficiency calculated only in the rotor. That means that important losses occur as well as in the other parts of the turbine such as the guide vanes (IGV and OGV) and the inlet and outlet regions. Therefore, more investigations and analysis are needed in order to minimize losses in these components. In the figure 10 both energy coefficients are compared. In both cases, inhalation and exhalation, the energy available to be extracted by the rotor, represented by the net coefficient, is higher in M8.
Figure 12: Flow angles (B, a)and geometry angles (B*, a*
Figure 12: Flow angles (B, a)and geometry angles (B*, a*
There are no differences between the M8 and M12 so the yehaviour of both turbines is. similar, figure 13c).
There are no differences between the M8 and M12 so the yehaviour of both turbines is. similar, figure 13c).
Proceedings of the ASME 27th International Conference on Offshore Mechanics and Arctic Engineering OMAE 2008 J une 15-20, 2008, Estoril, Portugal TURBINES CHARACTERISTICS IN SINUSOIDAL: ISCILLATING FLOW - —
Proceedings of the ASME 27th International Conference on Offshore Mechanics and Arctic Engineering OMAE 2008 J une 15-20, 2008, Estoril, Portugal TURBINES CHARACTERISTICS IN SINUSOIDAL: ISCILLATING FLOW - —
where V, is the amplitude and @ is the frequency. Mean efficiency, 7, in grasoidal oscillating flow is presented in figure 15 for the models M8 and M12. As can be seen, although the stationary efficiency of M12 is not always bigger (small values of © in inhalation), the efficiency of M12 is only lower in calmer sea states.
where V, is the amplitude and @ is the frequency. Mean efficiency, 7, in grasoidal oscillating flow is presented in figure 15 for the models M8 and M12. As can be seen, although the stationary efficiency of M12 is not always bigger (small values of © in inhalation), the efficiency of M12 is only lower in calmer sea states.
An getigetry for a impulse turbine has been studi metrical model dying the flow features en used. ha
An getigetry for a impulse turbine has been studi metrical model dying the flow features en used. ha

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References (6)

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  2. M. E. McCORMICK, J. G. REHAK, B. D. WILLIAMS : "An Experimental Study of a Bidirectional Radial Turbine for Pneumatic Wave Energy Conversion", Proceeding of Mastering the Oceans Through Technology ( OCEANS '92), Vol. 2, pp. 866-870, New Port, RI, USA, October 1992.
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  5. M. TAKAO, Y. FUJIOKA, H. HOMMA, T-W. KIM, T. SETOGUCHI : "Experimental Study of a Radial Turbine Using Pitch-Controlled Guide Vanes for Wave Power Conversion", Int. J. of Rotating Machinery, Vol. 2006, Article ID 1739, pp. 1-7.
  6. F. CASTRO, A. EL MARJANI, M.A. RODRIGUEZ, M.T. PARRA "Viscous Flow analysais in a radial impulse turbine for OWC wave energy system" 7th European Wave and Tidal Energy Conference, Porto 2007.

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