Miguel A. Rodriguez

Tip Clearance Effect on the Flow Pattern of a Radial Impulse Turbine for Wave Energy Conversion

Turbines for wave energy conversion have a special feature to be taken into account in the study of the tip leakage flow: These turbines are self-rectifying, which work inside a cyclically bidirectional flow alternatively as an inflow/outflow turbine. The phenomena at the blade tip will be different in these two situations. Moreover, it is necessary to take into account the tip clearance of the guide vanes because it has a significant influence on the rotor performance. A previously developed numerical model has been used for this study. The geometry proposed by Setoguchi (2002, “A Performance Study of a Radial Impulse Turbine for Wave Energy Conversion ,” Journal of Power and Energy, 216, pp. 15–22) is used in the model. Three different tip clearance sizes have been simulated to compare the influence of the tip clearance size on the performance. Results show that changing the size of the tip clearance from 0% to 4% of the blade span reduces the turbine maximum efficiency by up to 8%. However, the efficiency reduction is more pronounced when the turbine works as an inflow turbine because the tip clearance effect is more important in the inner part of the rotor, since flow velocities are higher and the relative casing motion is lower. This study achieves its main aim, which is to improve knowledge about the phenomena related to the tip clearance and its influence on the performance of radial impulse turbines.

Radial Impulse Turbine for Wave Energy Conversion: A New Geometry

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. We are interested in the radial version of the Impulse turbine, which was initially proposed by McCormick. A former research work aimed to improve the knowledge of the local flow behaviour and the prediction of the performances for this kind of turbine has been carried out using CFD (FLUENT®). The objectives of that work were connected mainly to the elaboration of a suitable 3D model for air flow simulation in a radial Impulse turbine. Model validation was conducted through a comparison with available experimental results. In the present, the objective is, using the numerical model, to develop a new radial impulse turbine geometry that gets better performances than the original one. This new turbine geometry will be exploited next in a project for an OWC of 250 kW. In this paper we describe the flow behaviour and the performances of this new turbine. For that, we study the Torque and Input coefficients, the losses and flow direction in the turbine elements.© 2008 ASME

Swirl influence on mixing and reactive flows

The interaction of two confined coaxial jets has been studied using Computational Fluid Dynamics. Annular jet flows over 8 flat blade swirl generator. Numerical simulation uses RNG k- ϵ turbulence model. These models are suitable for turbulent swirl dominated flows. Intermediate swirl injector has been simulated and the flow patterns for non-reactive and reactive cases are contrasted. Low swirling injectors do not promote the fluid to turn over near the center of the chamber, resulting larger mixing zones with weak gradients. Whereas large swirling flows promote the formation of an Inner Recirculation Zone that is a precursor of higher gradients. Probability Density Function is selected as combustion model. High swirl numbers let fix the location of the reactive zone.

Mixing and combustion of turbulent coaxial jets an application of Computational Fluid Dynamics to swirling flows

The aim of this research is gaining an insight into flow patterns in swirling burners. These are suitable for lean mixtures, because of procuring the fix position of the flame. The interaction of the two reactive confined swirling jets leads to the formation of complex patterns which are not well understood. In the present study, these flow patterns are numerically investigated using Reynolds Averaging Navier-Stokes (RANS) equations for the flow and a Probability Density Function is used for modelling the combustion. Two swirl numbers were characterised: 0.14 and 0.74. Strong swirling annular jets are responsible of an inner recirculation zone. Low swirling flows produce poorer mixture and wide flame fronts whereas strong swirling flows are precursors of mixing enhancement and thing flame fronts.

Numerical Modelling in Turbines for OWC Systems: Application to a Radial Impulse

This work is focused on radial impulse turbines for an Oscillating Water Column (OWC) which is one of the alternatives to the Wells turbines traditionally installed in the OWC systems. All self-rectifying turbines work under special conditions due to the bi-directional flow caused by OWC. But a radial impulse turbine has another special point: it works alternatively as an inflow/outflow turbine, so that its behavior is not symmetrical as is expected in axial turbines for OWC (Wells and axial impulse turbines). The complete CFD analysis we have made of a radial impulse turbine is described. The model was created for a specific turbine but can be adapted for any self-rectifying turbine. We have studied the turbine by means of a one-dimensional study and a 3-D model solved with FLUENT® software, and the results were validated with experimental data extracted from the bibliography. This model allowed us to analyse both the classical dimensionless parameters and the flow pattern. Moreover, we have introduced a special definition for the reaction degree in order to analyse the process of the energy conversion.© 2010 ASME