The objective of this work is to provide experimental validation of the graph theory approach for predicting the thermal history in additively manufactured parts that was recently published in the ASME transactions. In the present paper the graph theory approach is validated with in-situ infrared thermography data in the context of the laser powder bed fusion (LPBF) additive manufacturing process. We realize this objective through the following three tasks. First, two types of test parts (stainless steel) are made in two corresponding build cycles on a Renishaw AM250 LPBF machine. The intent of both builds is to influence the thermal history of the part by changing the cooling time between melting of successive layers, called interlayer cooling time. Second, layer-wise thermal images of the top surface of the part are acquired using an in-situ a priori calibrated infrared camera. Third, the thermal imaging data obtained during the two builds were used to validate the graph theory-predicted surface temperature trends. Furthermore, the surface temperature trends predicted using graph theory are compared with results from finite element analysis. As an example, for one the builds, the graph theory approach accurately predicted the surface temperature trends to within 6% mean absolute percentage error, and approximately 14 Kelvin root mean squared error of the experimental data. Moreover, using the graph theory approach the temperature trends were predicted in less than 26 minutes which is well within the actual build time of 171 minutes.

This paper reports on the latest phase of the development of a new rotating machinery sealing technology, which was a successful seal test in a high temperature steam test facility at TU Brauschweig in Germany. The “Aerostatic Seal” is a dynamic clearance seal that is capable of maintaining very small clearances with a rotor and has the potential for a wide range of rotating machinery applications. It has been developed in recent years at Durham University, UK, in collaboration with a major OEM, with a focus on steam turbine sealing, and has previously been reported on in a number of ASME Turbo Expo papers. Previous work has reported on the design tool, and two air test facilities; testing in steam addressed the effect of high temperature components and the working fluid, and was an opportunity to verify the design system. The seal is a development of a retractable gland seal and so in a low load condition it is retracted from the rotor with a large rotor clearance and then when the pressure ratio is sufficient moves to an operational small clearance. At its operational clearance the seal is capable of moving with rotor vibrations which means the design clearance can be smaller than any expected rotor movement. The benefits include a significant reduction in leakage when compared to conventional sealing technologies and also the ability to react to large transients or thermal growths caused by rapid changes in machine loads and speeds. The seal is shown to operate well in this environment and this work moves the technology closer to deployment in industry.

Selective laser melting (SLM) is a relatively new manufacturing technique which offers many benefits. However the utilisation of SLM manufactured components depends on the assurance of their integrity during operation. Fracture toughness testing ( J IC ) has been performed on as-built compact tension fracture mechanics samples manufactured in three orthogonal directions. When the crack growth plane was transverse to the interface of the build layers, the fracture toughness values were found to be similar to those manufactured using conventional techniques. However, the fracture toughness is significantly reduced when the crack plane is parallel to the interface of the build layers. Simple heat treatments have been performed on Charpy fracture samples and the resulting impact energy values indicate that the fracture toughness of a component may be improved by heat treatment.

The successful demonstration of the “Aerostatic Seal” in a half scale rotating facility is described in this paper. The Aerostatic seal is a novel dynamic clearance seal specifically designed for steam turbine secondary gas path applications. The seal responds to radial rotor excursions, so a reduced clearance can be maintained compared to conventional labyrinth seal without damage to the seal. This enables increased turbine performance through reduced leakage and increased tolerance of turbine transient events typically found during start up. The seal is an extension of the existing retractable seal design already deployed in commercial steam turbines. The seal was tested in the Durham Rotating Seals Rig, which was developed specifically to test this device. The rig featured a rotor designed to run with large eccentricities to model high speed radial rotor excursions, and the seal was instrumented to measure the real time seal response to the rotor. The experimental campaign has conclusively demonstrated the ability of the seal to dynamically respond to the rotor position. The key result is that the seal is able to track the rotor position at high speed, and hence maintain a mean seal clearance that is lower than the rotor eccentricity. Overall this work marks a key milestone in the development of the Aerostatic Seal, and leads the way to testing in a steam environment and application in steam turbine plant.

This paper presents a series of experiments on the Aerostatic Seal, a dynamic clearance seal for steam turbine application first described at the 2015 ASME Turbo Expo (Paper Number GT2015-43471). This dynamic clearance seal moves with rotor excursions and so has the potential to deliver a smaller clearance than traditional seals. The concept is an extension of the retractable seal design which is widely used in existing steam turbines. The experimental program was carried out in a low cost static test facility using an aerostatic seal design. The seal exhibited a dynamic clearance response and will therefore respond to rotor excursions. 3D CFD was also used to aid the understanding of flow features not captured by the analytical design tool. Adjustments to both the design process and to future seal designs are proposed in the body of the paper. This paper therefore describes an experimental proof of concept for the aerostatic seal and paves the way for future development in rotating facilities.

Effective sealing in turbomachinery reduces the leakage flow bypassing the turbine blades and also reduces the losses where the leakage flow mixes with the primary flow. In general the clearance should be as small as possible but is limited by thermal and mechanical effects which vary with load. In recent years intermittent energy sources, particularly wind and solar, have appeared in greater numbers on the power network. As a consequence conventional power plants need to become more flexible to accommodate renewable energy generation. A sealing technology which can accommodate rapid changes in load and maintain seal performance would be a valuable development. This paper presents a novel seal design for steam turbines. The seal is designed to be capable of maintaining a smaller clearance than that of conventional labyrinth seals whilst allowing for dynamic movement with the rotor. The paper describes the seal concept and the analytic al work undertaken to demonstrate the concept. The seal design has also been tested in test facilities at Durham and the initial experimental results are included. They show that the concept works as intended.

This paper presents a cost benefit analysis for wind turbine condition monitoring systems. It is widely acknowledged that performing proactive maintenance actions can reduce the number and severity of wind turbine failures. However, the use of condition monitoring systems to determine the health of the system is often viewed as costly and of little financial benefit. In this analysis the increased costs associated with condition monitoring were offset by the positive effect of early fault detection, with faults being detected before they reach a critical stage. The continual growth in turbine output and the emergence of far-offshore wind farm sites make the economic case for cost of energy reduction from timely and accurate fault detection ever stronger. An assessment of the capability of the monitoring system was undertaken through allowance for the true to false condition monitoring detection ratio and the ability of the system to detect the severity of a fault. The analysis also compared onshore and offshore assets where the access availability can severely influence the downtime. The results show a clear financial justification for wind turbine condition monitoring and indicate the successful detection ratio required before a condition monitoring system can offer a financial benefit.

Most large scale cascade experiments and the corresponding computational fluid dynamics are conducted on geometries without fillet radii, that is with sharp edges. Despite that the fact that all real machines have a fillet radii there has not so far been a detailed examination of the influence of fillet radii on the secondary flow structures in turbines. This paper presents detailed measurements on a large scale, low speed cascade with significant secondary flows. A series of detailed traverses inside the blade row were obtained allowing the influence of fillet radii on the formation of secondary flows to be examined. The experimental campaign is backed up by RANS computations. The fillets were found to increase loss by around 10% compared to the base case. This loss could not be accounted for by a simple model of boundary layer behaviour and an accounting of the complex secondary flow interactions is required to explain the observed changes in performance. The secondary flow interactions include a larger radial migration of secondary flows from the endwall and the elimination of the corner vortex. The potential to improve performance by varying the fillet radii around the blade was identified.

This paper considers the asset management of offshore wind farms and, in particular, how this will change as wind farms increase significantly in capacity and move to sites further offshore. Health monitoring, industrial operational structures, infrastructure, operations and maintenance and operational strategies are discussed based on the experiences and expectations of industry partners across the operational cycle of a wind farm. The exercise was undertaken through discussions with UK and European industrial companies and fellow academics to obtain their experiences to date, better define the challenges the industry expects to face in the coming years and establish the areas of significant research interest from an industrial point of view. This paper is of interest to both industrial and academic members of the offshore wind community who are interested in the challenges of future asset management strategy.

Large tip clearances in the region of six percent span exist in the high pressure stages of compressors of industrial gas turbines. The over tip clearance flow causes significant blockage and accounts for the largest proportion of loss in the high pressure compressor. This paper examines large tip clearances in two different compressor cascades. The first was a cascade of controlled-diffusion blades and the second cascade had geometry more representative of modern engine practise. The second cascade also featured realistic inlet boundary layer conditions delivered by an upstream injection system. Increasing the understanding of such flows will allow for improvements in the design of such compressors. The key conclusions of this paper are: a) At large tip clearances the tip clearance is the primary variable influencing the flow pattern, blade geometry is a secondary consideration; b) The blade geometry has a significant influence on loss generation through the cascade; c) With increasing tip clearance the loss generation through the cascade can diminish but the flow turning is much reduced; and d) The blade loading at the tip can increase at large tip clearances.

Large tip clearances typically in the region of six percent exist in the high pressure stages of compressors of industrial gas turbines. Due to the relatively short annulus height and significant blockage, the tip clearance flow accounts for the largest proportion of loss in the HP. Therefore increasing the understanding of such flows will allow for improvements in design of such compressors, increasing efficiency, stability and the operating range. Experimental and computational techniques have been used to increase the physical understanding of the tip clearance flows through varying clearances in a linear cascade of controlled-diffusion blades. This paper shows two unexpected results. Firstly the loss does not increase with clearances greater than 4% and secondly there is an increase of blade loading towards the tip above 2% clearance. It appears that the loss production mechanisms of the pressure driven tip clearance jet do not increase as the clearance is increased to large values. The increase in blade force is attributed to the effect of the strong tip clearance vortex which does not move across the blade passage to the pressure surface, as is often observed for high stagger blading. These results may be significant for the design of HP compressors for industrial gas turbines.

During the third quarter of 2003, Eos Research & Consulting Ltd. conducted a two part study examining emerging standards for how energy companies manage climate change related risks. The first part was a survey of financial institutions in Canada, U.S. and internationally to determine their expectations for how energy companies should approach risks associated with climate change and policies to address it. In a parallel effort, using criteria which were based in part on the results from the financial sector survey, eleven leading energy companies were compared in a benchmarking study which examined response to climate change risks to date. The result provided two facets of the emerging standard for climate change risk management in the energy sector. This paper examines the results of the financial sector survey, drawing conclusions about the role that sector will play in setting expectations for how energy companies respond to climate change risks in the foreseeable future.

In today’s commercial environment, unplanned outages have a significant affect on revenues, and hence reliability, availability and maintainability of plant are key factors. Emergency Response Planning, combined with real time monitoring can have significant beneficial impacts on unplanned and planned outage duration’s. This paper details our company’s experience of Emergency Response Planning (ERP), giving detailed overview of how this is achieved and the benefits that can be obtained. The paper focuses on unit disaster recovery of large turbo-alternators and how the concept of Emergency Response planning can reduce unplanned outage duration’s, including the steps required to implement best practice. The paper uses a detailed a case study of a 1200MW, 4-pole generator with severe rotor winding inter-turn faults and associated vibration problems to demonstrate how a combination of condition monitoring, Emergency Response Planning, and a skilled repair team have been used to implement an effective maintenance strategy. The benefits to the customer have been detailed. The successful repair of all faults and the significant reduction in generator vibration levels without the requirement for any site balancing is illustrated on return of the unit to service. The paper details how Rotor Flux Monitoring (RFM) has been identified a series of winding faults and with ERP has mitigated areas of high risk within this turbo-generator.

The tip clearance flow of industrial axial compressor rotors has a significant impact on compressor performance. Most tip clearance flow research work has been undertaken in the earlier low-pressure transonic stages of compressors. The main differences between the earlier (low-pressure) and later (high-pressure) stages include blade profile, stagger angle, Mach number, blade length and tip clearance. The tip clearance in the later stages of an industrial axial compressor is relatively large due to mechanical constraints and short blading. The stagger angle is much lower and so the tip clearance flow is at a higher angle to the (negative) axial direction. In the present work, a computational method has been employed to investigate tip clearance flow from 1% span to 10% span for blading such as that found in the later stages. A pinch tip model is used to model the blade tip in a cascade with a stationary and moving end-wall. It has been found that the tip clearance flow rolls up into a vortex much later than in the earlier stages. The migration of the tip clearance vortex across the passage is much less than for the earlier stages and also the induced vortex is much weaker. Comparisons between a cascade with fixed and moving end-walls are made, the main difference being that the tip clearance flow is stronger with a moving end-wall. The 1% tip clearance flow structure with stationary end-wall is shown to be different from all other cases investigated.