As the demand for renewable energy grows, the use of small wind turbines becomes increasingly attractive. Turbines using vertical-axis geometries are particularly suited to the urban environment by virtue of their operation being independent of wind direction. However, such designs have received much less attention than the more common ‘propeller type’ designs and the understanding of some aspects of their operation remains weak. This is particularly true of their starting characteristics. Indeed, some authors maintain that they cannot start without external assistance. In this investigation a numerical model is used to simulate the starting of an H-rotor Darrieus turbine under steady wind conditions. Experimental wind-tunnel data for a small prototype is presented, demonstrating unaided start-up of a three-bladed Darrieus in a steady wind. Discrepancy between the modelled and experimental results demonstrate that modelling remains constrained by the quality of data on aerofoil characteristics.

Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Abstract-Real-Time Thermal Rating is a smart grid technology that allows the rating of electrical conductors to be increased based on local weather conditions. Overhead lines are conventionally given a conservative, constant seasonal rating based on seasonal and regional worst case scenarios rather than actual, say, local hourly weather predictions. This paper provides a report of two pioneering schemes-one in the United States of America and one in the United Kingdom-in which Real-Time Thermal Ratings have been applied. Thereby, we demonstrate that observing the local weather conditions in real time leads to additional capacity and safer operation. Secondly, we critically compare both approaches and discuss their limitations. In doing so, we arrive at novel insights which will inform and improve future Real-Time Thermal Rating projects.

Full-scale fatigue testing is part of the certification process for large wind turbine blades. That testing is usually performed about the flapwise and edgewise axes independently but a new method for resonant fatigue testing has been developed in which the flapwise and edgewise directions are tested simultaneously, thus also allowing the interactions between the two mutually perpendicular loads to be investigated. The method has been evaluated by comparing the Palmgren-Miner damage sum around the cross-section at selected points along the blade length that results from a simulated service life, as specified in the design standards, and testing. Bending moments at each point were generated using wind turbine simulation software and the test loads were designed to cause the same amount of damage as the true service life. The mode shape of the blade was tuned by optimising the position of the excitation equipment, so that the bending moment distribution was as close as possible to the target loads. The loads were converted to strain-time histories using strength of materials approach, and fatigue analysis was performed. The results show that if the bending moment distribution is correct along the length of the blade, then dual-axis resonant testing tests the blade much more thoroughly than sequential tests in the flapwise and edgewise directions. This approach is shown to be more representative of the loading seen in service and can thus contribute to a potential reduction in the weight of wind turbine blades and the duration of fatigue tests leading to reduced cost.

Durham University have embarked on a new research initiative in low pressure (LP) steam turbine exhaust hoods. An extensive literature review has highlighted the importance of applying representative conditions at inlet to the exhaust diffuser, specifically accurate total pressure and swirl angle distributions, in numerical simulations to generate flow fields within the hood in line with field data. With commercial sensitivity surrounding industrial designs for exhaust hoods and last stage blades, Durham University have developed a generic, research-level exhaust diffuser geometry and accompanying last stage blade to encourage the expansion of academic research in the field. Preliminary CFD calculations on the LP exhaust has shown the design produces a representative flow structure, capturing the primary sources of loss; the separation along the bearing cone and at the tip of the flow guide.

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As turbine manufacturers strive to develop machines that are more efficient, one area of focus has been the control of secondary flows. To a large extent these methods have been developed through the use of computational fluid dynamics and detailed measurements in linear and annular cascades and proven in full scale engine tests. This study utilises 5-hole probe measurements in a low speed, model turbine in conjunction with computational fluid dynamics to gain a more detailed understanding of the influence of a generic endwall design on the structure of secondary flows within the rotor. This work is aimed at understanding the influence of such endwalls on the structure of secondary flows in the presence of inlet skew, unsteadiness and rotational forces. Results indicate a 0.4% improvement in rotor efficiency as a result of the application of the generic non-axisymmetric endwall contouring. CFD results indicate a clear weakening of the cross passage pressure gradient, but there are also indications that custom endwalls could further improve the gains. Evidence of the influence of endwall contouring on tip clearance flows is also presented.

The potential for loss reduction by using non-axisymmetric end-wall profiling has been demonstrated in the so called “Durham” cascade (Hartland et al [1]) and in a turbine representative rig (Brennan et al [2] and Rose et al [3]). This paper aim to enhance the understanding of end-wall profiling. It describes detailed measurements from upstream to downstream through the Durham cascade. The measurements cover the profiled end-wall used by Hartland, a second generation end-wall design (Gregory-Smith et. al. [4]) and the planar reference case. Considerable effort has gone into refining the measurement technique used in the cascade and new results are presented for traverses downstream which capture more accurately the flow near the end-wall. These measurements show the development of loss and secondary flow throughout the blade row. It is shown that end-wall profiling has a dramatic effect on the flow patterns in the early part of the blade row which then translates to a loss reduction later in the blade row. Comparison with CFD results aids the understanding of the role of the reduced horseshoe vortex in this process.