Radial Impulse Turbine Research Articles

Influence of the blade leaning angle on the performance of a radial impulse turbine for OWC converters

Abstract Oscillating Water Column systems (OWC) have been in the spotlight in the last 20 years since these devices are considered one of the most promising devices among wave energy technology. These systems produce electricity by means a generator driven by a turbine, which takes advantage of the bidirectional flow created by the OWC itself. Among these turbines suitable for bidirectional flows, it is possible to find radial impulse turbines, which are the focus of this work. Traditionally, the radial impulse turbines have shown lower efficiencies than their competitors. However, the radial turbines present interesting mechanical features and, recently, some research show that the difference has been reduced. Following this thread, this work deals with another modification in the radial impulse turbine looking for a further improvement. By using a validated CFD model, it has been analysed the influence of the lean angle of the blade. Until now, all the turbines present in the literature are leaned zero degrees, leading to a strong interaction between the guide vanes and the blades. This work shows results of the same turbine, equipped with blades leaning from -5deg to 25deg, in order to determine the influence such a modification on the maximum total-to-static efficiency. Results have revealed a slight improvement in the maximum efficiency for positive leaning angles, whereas negative angles drive the turbine to worse performance.

Analysis of an optimized radial impulse turbine for an OWC wave energy converter

Abstract OWC concept is one of the most spread technologies among wave energy converters due to several reasons. However, this technology has always deal with the problem of the inherent bidirectional flow. Many solutions have been adopted such as a flow rectification system combined with a unidirectional turbine, several types of bidirectional turbines such as Wells turbine or impulse turbine. In this work, it is shown the performance of an optimized geometry for a radial impulse turbine, which improvement is based on the re-designing of the blades and settling angles of the vanes. A CFD model, validated against results from the bibliography, has been used to simulate both a new and a previous geometry taken as reference. The results of both turbines have been analysed in terms of the loss coefficients for each element in order to analyse the advantages of the new geometry. It has been found that the new geometry exceeds the efficiency of the previous geometry by 5%, being this gain based on the fact that sacrificing the rotor’s efficiency could lead to a great improvement in the performance of the guide vanes, reducing their loss and, in turn, lifting the turbine’s efficiency despite reducing the rotor’s one.

Optimized geometry design of a radial impulse turbine for OWC wave energy converters

Opposite to other types of turbines for OWC wave energy converters, like the axial impulse or the Wells turbine, there is scarce information about radial impulse turbines. The interest in radial impulse turbine for wave energy is low because the available research on it shows lower efficiencies than the competitors. On the other hand, radial turbines present several advantageous features that make it a worthy option if the efficiency is improved. The purpose of the present work is to propose a new geometry, not focused on improving the rotor efficiency, but on reducing losses downstream of the rotor. This new design, taking previous geometries as a reference, was based on the classical 2-D angle computations optimizing the flow and blade angles for both inflow and outflow modes. After setting a balanced agreement between both modes, a numerical model with the new design was mounted on ANSYS Workbench which has allowed to speed up the whole process by using the specific tools set for turbomachines. Taking advantage of the simulation speed provided by the use of this model. A solidity optimization process was performed out on the new geometry to decide the required number of blades and vanes of the proposed turbine. Once, the turbine was well-defined, it has been compared concerning the previous turbine under both, steady and non-steady flow. The improvement has been remarkable, reaching a 10 % in steady efficiency and 6.7 % in non-steady efficiency with respect to the previous geometries.

Optimization of Radial Impulse Turbine for Oscillating Water Column Wave Renewable Energy

An oscillating water column (OWC) extracts the power of waves by trapping air above a water column. This trapped air is compressed and decompressed by the wave action flow inside a turbine power to the mechanical power during process, and it is important as the turbines are expected to operate in oscillating and reversing flows over a wide range of conditions. The objectives of this study are to determine and analyze the type of radial impulse turbine of OWC and to optimize the performance of a radial impulse turbine for OWC by using Computational Fluid Dynamics (CFD). This requires a comprehensive investigation on turbine configuration, turbine efficiency, OWC integration, and turbine operation with respect to climate condition. The outcome of this study to settle the main drawbacks of radial turbine namely lower peak efficiency and damping on OWC can be considered. Later, these problems will be further study to identify the behavior of the airflow through the machine, sources of energy loss, and impact of different parameters on the turbine performance.

Efficiency improvement of a self-rectifying radial impulse turbine for wave energy conversion

This paper aims to improve the performances of a self-rectifying radial impulse turbine used in wave energy conversion. The turbine design involves blades of circular profiles. The Design of Experiments method has been implemented for the efficiency optimization. The objective function aims to maximize the average turbine efficiency between the inhalation and the exhalation modes. A 3D viscous flow modelling has been performed with the ANSYS Fluent code. Simulations allow the turbine efficiency computation accordingly to the changes in the turbine geometry. Influence of ten geometrical parameters has been considered in the optimization process. According to a confidence degree of 95%, it has been found that only four of them have significant influence on the turbine efficiency. The rotor geometry admits the highest influence, particularly the blade angle. Additional analysis has been conducted by considering the rotor blade stagger angle. It has been found that the efficiency can be kept high in the both modes with a stagger angle of 4°. Efficiencies more than 50% have been reached. The present turbine efficiency has been compared to that of a turbine of elliptical profiles. An increase of about 19% in the efficiency has been reached with the present turbine.

Possibility of using a bi-directional impulse turbine in a thermo-acoustic engine

The paper is devoted to one of engine types with external heating a thermoacoustic engine. Ways of transforming the energy of a shock wave of oscillating gas flow into electric energy are discussed. The authors suggest using a bidirectional impulse turbine as an energy converter. The distinctive feature of this kind of turbine is that the shock wave of oscillating gas flow passing through the turbine is reflected and passes through the turbine again in the opposite direction. The direction of turbine rotation does not change in the process. Different types of bidirectional impulse turbines for thermoacoustic engines are analyzed. The Wells turbine is the simplest and least efficient of them. A radial impulse turbine has more complicated design and is more efficient than the Wells turbine. The most appropriate type of impulse turbine was chosen. This type is an axial impulse turbine which has a simpler design than that of a radial turbine and similar efficiency. The peculiarities of the method of calculating an impulse turbine are discussed. They include changes in gas pressure and velocity as functions of time during the generation of gas oscillating flow shock waves in a thermoacoustic system.

Design and evaluation of a high-speed and precision microspindle

This study presents the design and evaluation of a high-speed and precision microspindle used for micromechanical machining. A radial impulse turbine with two rows of nozzles was designed to realize the high-speed performance. A monolithic flexible coupling was used to decouple the turbine shaft and the tool, and then, the tool shank was directly supported by aerostatic bearings, which can minimize the run-out of the tool at high speeds. Additionally, a shape memory alloy (SMA)-based clamp was designed for tool clamping. It can avoid the assembly error caused by stack-up tolerances. The microspindle has simple configuration and compact design with a 30-mm outer diameter and a 95-mm length. The prototype microspindle has a maximum speed of over 240,000 rpm and a tool radial run-out of 2.79 μm. The evaluation results show the feasibility and potential application of the new design concept of the microspindle proposed in this study.

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 et al. (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.