Unsteady Performance Prediction of a Single Entry Mixed Flow Turbine Using 1-D Gas Dynamic Code Extended With Meanline Model

Turbochargers are widely regarded as one of the most promising enabling technology for engine downsizing, in the aim to achieve better specific fuel consumption, thermal efficiency and most importantly carbon reduction. The increasing demand for higher quality engine-turbocharger matching, leads to the development of computational models capable of predicting the unsteady behaviour of a turbocharger turbine when subjected to pulsating inlet flow. Due to the wide range of engine loads and speed variations, an automotive turbocharger turbine model must be able to render all the frequency range of a typical exhaust pulse flow. A purely one-dimensional (1-D) turbine model is capable of good unsteady swallowing capacity prediction, provided it is accurately validated. However, the unsteady turbine power evaluation still heavily relies on the quasi-steady assumption. On the other hand, meanline model is capable of resolving the turbine work output but it is limited to steady state flow due to its zero dimensional nature. This paper explores an alternative methodology to realize turbine unsteady power prediction in 1-D by integrating these two independent modelling methods. A single entry mixed-flow turbine is first modelled using 1-D gas dynamic method to solve the unsteady flow propagation in turbine volute while the instantaneous turbine power is subsequently evaluated using a mean-line model. The key in the effectiveness of this methodology relies on the synchronization of the flow information with different time-scales. In addition to the turbine performance parameters, the common level of unsteadiness was also compared based on the Strouhal number evaluations. Comparison of the quasi-steady assumption using the experiment results was made in order to further understand the strength and weaknesses of corresponding method in unsteady turbine performance prediction. The outcomes of the simulation showed a good agreement in the shape and trend profile for the instantaneous turbine power. Meanwhile the predicted cycle-averaged value indicates a positive potential of the current turbine model to be expanded to a whole engine simulation after few minor improvements.

Optimization of Advanced Liquid Natural Gas-Fuelled Combined Cycle Machinery Systems for a High-Speed Ferry

This paper is aimed at designing and optimizing combined cycles for marine applications. For this purpose, an in-house numerical simulation tool called DNA (Dynamic Network Analysis) and a genetic algorithm-based optimization routine are used. The top cycle is modeled as the aero-derivative gas turbine LM2500, while four options for bottoming cycles are modeled. Firstly, a single pressure steam cycle, secondly a dual-pressure steam cycle, thirdly an ORC using toluene as the working fluid and an intermediate oil loop as the heat carrier, and lastly an ABC with inter-cooling are modeled. Furthermore, practical and operational aspects of using these three machinery systems for a high-speed ferry are discussed. Two scenarios are evaluated. The first scenario evaluates the combined cycles with a given power requirement, optimizing the combined cycle while operating the gas turbine at part load. The second scenario evaluates the combined cycle with the gas turbine operated at full load. For the first scenario, the results suggest that the thermal efficiencies of the combined gas and steam cycles are 46.3% and 48.2% for the single pressure and dual pressure steam cycles, respectively. The gas ORC and gas ABC combined cycles obtained thermal efficiencies of 45.6% and 41.9%, respectively. For the second scenario, the results suggest that the thermal efficiencies of the combined gas and steam cycles are 53.5% and 55.3% for the single pressure and dual pressure steam cycles, respectively. The gas ORC and gas ABC combined cycles obtained thermal efficiencies of 51.0% and 47.8%, respectively.

Pressure Gain Combustion Application to Marine and Industrial Gas Turbines

Renewed interest in pressure gain combustion applied as a replacement of conventional combustors within gas turbine engines creates the potential for greatly increased capability engines in the marine power market segment. A limited analysis has been conducted to estimate the degree of improvements possible in engine thermal efficiency and specific work for a type of wave rotor device utilizing these principles. The analysis considers a realistic level of component losses. The features of this innovative technology are compared with those of more common incremental improvement types of technology for the purpose of assessing potentials for initial market entry within the marine gas turbine market. Both recuperation and non-recuperation cycles are analyzed. Specific fuel consumption improvements in excess of 35% over those of a Brayton cycle are indicated. The technology exhibits the greatest percentage potential in improving efficiency for engines utilizing relatively low or moderate mechanical compression pressure ratios. Specific work increases are indicated to be of an equally dramatic magnitude. The advantages of the pressure gain combustion approach are reviewed as well as its technology development status.

Integrated Training Solutions: An Effective Tool to Synchronize People and Maintenance (U.S. Navy LCAC Case Study)

Maintenance, especially in a Marine environment, is continuous and costly. Life Cycle Management of a Marine Gas Turbine system encompasses many costs, of which repair parts, labor and equipment downtime associated with failures and maintenance are a significant portion. In fact, people (labor) make up the largest component of overall maintenance costs. Investing in people the largest cost driver to life cycle cost has a direct return in the long run, in terms of maintenance effectiveness and efficiencies. Applying and reinforcing knowledge and skills in a maintenance environment translates to improved reliability outcomes, longer operating time, fewer parts needs, and ultimately costs savings. However, given today’s constrained fiscal environment, the value of spending money for training rather than buying more parts or applying more maintenance, may not appear obvious. Such thinking is short sighted, and ultimately leads to reduced reliability and increased maintenance in the long run. This paper will explore these areas, and recommend how training programs can be effective predictive, proactive and responsive.

An Impact of Self-Recirculation Casing Treatment (SRCT) Configurations on Impeller Stall Margin and the Flow Field

The present paper describes an investigation of stall margin enhancement and a detailed analysis of the impeller flow field due to self-recirculation casing treatment (SRCT) configuration of a high-speed small-size centrifugal impeller. The influence of different SRCT configurations on the impeller flow field at near-stall condition has been analyzed, highlighting the improvement in stall flow ability. This paper also discusses the influence of the SRCT configurations on the inlet flow angle, inlet swirl velocity and loss distribution in the impeller passage to understand the mechanism of the SRCT configurations in enhancing the stall margin of the impeller. The variation of the bleed flow rate at different operating conditions is also presented in this paper. Finally, the time-averaged unsteady simulation results at near-stall point are presented and compared with steady-state solutions.

Development and Experimental Performance Verification of a Magneto-Aerostatic Bearing for Cartridge of Dental Handpieces

Bearings for high-speed rotors are the key component of dental handpieces. The friction induced by conventional ball bearings restricts its speed and reduces its efficiency. In order to significantly improve the efficiency of dental handpieces, a mini-type cartridge that integrates a turbine and a spindle with radial aerostatic bearings and axial passive magnetic bearings has been ingeniously designed and realized. Around the rotating spindle, there is a high-pressured air film built up by a pair of radial aerostatic bearings, and magnet rings are applied to create repulsive forces to axially support the rotating spindle. The high-pressured air film comes from the specifically designed separable orifice restrictors, which can be easily and precisely manufactured. Frictionless bearing effect can be achieved by aerostatic principle, and the magnetic principle is applied to create large repulsive force against the axial working force. A tri-directional air inlet is designed to reduce radial loading force of a spindle during working. The modularized form of the magneto-aerostatic bearing allows it to be easily assembled and replaced in the very compact space of a mini-type cartridge. Through analytical simulations with fluid-dynamics software (CFD) and experiments, the magneto-aerostatic bearing is optimized to bring out efficient performance in its limited space. The experiments have verified that its noise level is 15dB lower than the conventional cartridge with ball bearings, and its startup air pressure is reduced from 0.4 bar to 0.1 bar. Under the same operation conditions, the newly developed cartridge with magneto-aerostatic bearings creates twice higher speed than that of the conventional one.

Design Analysis of a Micro Gas Turbine Combustion Chamber Burning Natural Gas

Gas turbines are reliable energy conversion systems since they are able to operate with variable fuels and independently from seasonal natural changes. Within that reality, micro gas turbines have been increasing the importance of its usage on the onsite generation. Comparatively, less research has been done, leaving more room for improvements in this class of gas turbines. Focusing on the study of a flexible micro turbine set, this work is part of the development of a low cost electric generation micro turbine, which is capable of burning natural gas, LPG and ethanol. It is composed of an originally automotive turbocompressor, a combustion chamber specifically designed for this application, as well as a single stage axial power turbine. The combustion chamber is a reversed flow type and has a swirl stabilized combustor. This paper is dedicated to the diagnosis of the natural gas combustion in this chamber using computational fluid dynamics techniques compared to measured experimental data of temperature inside the combustion chamber. The study emphasizes the near inner wall temperature, turbine inlet temperature and dilution holes effectiveness. The calculation was conducted with the Reynolds Stress turbulence model coupled with the conventional β-PDF equilibrium along with mixture fraction transport combustion model. Thermal radiation was also considered. Reasonable agreement between experimental data and computational simulations was achieved, providing confidence on the phenomena observed on the simulations, which enabled the design improvement suggestions and analysis included in this work.

Uncontained Failure of a U.S. Navy Rolls-Royce 250-KS4, Root Cause Investigation and Subsequent Corrective Actions

In 2008, a US Navy DDG-51 Class destroyer experienced an uncontained failure of a Rolls Royce 250-KS4 turbine engine which serves as a starter for the Ship Service Gas Turbine Generator (SSGTG). This paper discusses the events that preceded the failure, the root cause and contributing factors. It also describes multiple corrective actions, including design improvements that have been implemented with the goal of preventing this type of failure in the future.

Arbitrary Surface Flank Milling and Flank SAM in the Design and Manufacturing of Jet Engine Fan and Compressor Airfoils

A pragmatic and versatile airfoil design and fabrication system, named the Arbitrary Surface Flank Milling (ASFM) system, has been continuously developed and applied to the design and manufacturing of fan and axial compressor airfoils — in the form of integrally bladed rotors (IBR) and centrifugal impeller blades — for jet engines at Pratt & Whitney over the past 28 years. In a previous paper 18 years ago, we gave an account of the general concept and methodology of the system, illustrated with a number of actual production engine applications. We have since then greatly expanded the domain of applicability of the system to successfully handle blades of unusual geometric complexity. We have made strides in the area of design for flank mill-ability with conventional cutters, and cutters shaped according to blade geometry. Based on the same concept and software methodology, we have also successfully demonstrated the superior quality and cost effectiveness of Flank Super Abrasive Machining (Flank SAM) of blades in nickel-based alloy IBRs.

Development US Navy Gas Turbine Vibration Analysis Expertise: LM2500 Vibration and Trim Balance

Although generally reliable in-service and with an ever increasing mean time between removal, it was identified in the mid to late 1980’s that the LM2500 gas turbine in US Navy service had a problem with self generated vibration; this was principally due to imbalance in the gas generator or power turbine rotor, however, other non-synchronous sources for vibration were discovered to be important as well. The initial method for resolving this problem was to remove and repair, at a depot, the engines that exceeded the in-service alarm level. This turned out to be a very expensive approach and it was found that most engines that had excessive vibration levels in other respects (performance, etc.) were perfectly acceptable for continued use without repair. Raising the vibration alarm level was tried for a time. However, it became clear that prolonged engine operation with higher levels of vibration were detrimental to the mechanical integrity of the engine. This paper discusses the systematic approach developed to reduce LM2500 self generated vibration levels. This included monitoring system improvements, engine design & hardware improvements and the development and implementation of in-place trim balance. This paper also discusses some of the analysis and practical difficulties encountered reducing and maintaining low LM2500 vibration levels through trim balance and by other means. Also discussed is the present implementation of remotely monitoring LM2500 operating parameters, in particular vibration, through the Integrated Performance Analysis Reports (IPAR) and the Maintenance Engineering Library Server (MELS).