J. P. van Buijtenen

Performance Modeling of a Modern Gas Turbine for Dispatch Optimization

As electricity demand from individual power plants is expected to fluctuate increasingly due to the growing share of renewables, operators of large Combined Cycle Gas Turbine power plants will have to deal with increasing load variations and rapid load changes. To keep up reliability and availability of the plants, it is useful to accurately keep track of plant performance by comparing actual cycle data with a steady state base case model. This paper presents various aspects of the performance modeling of Alstom’s GT26 gas turbine as recently installed in the Netherlands. The modeling environment is GSP, a component based zero-dimensional software tool. Firstly, the modeling strategy is presented, taking into account the specific features of this sequential combustion gas turbine. Secondly, the method of processing field measurements to model inputs is shown and furthermore, the influence of measurement uncertainty on model parameter estimation is assessed. Procedures will be proposed to use this model in daily operation, to keep track of actual component loading. Later on, the recorded performance data can be used to evaluate maintenance as a function of actual operational history, as a basis for future strategies.Copyright

Performance Analysis of a Microturbine Centrifugal Compressor From a Manufacturing Perspective

Gasturbine part manufacturers are often not involved in the design process. This means opportunities to optimize the design including manufacturing issues are missed. This paper presents a performance analysis of a microturbine centrifugal compressor from a manufacturer’s perspective. A one-dimensional (1D) performance modeling tool has been devised to predict the design and off-design performance by sequentially calculating the processes in the impeller, vaneless diffuser and scroll. Part drawings have been used to obtain the geometric information. Comprehensive two-zone modeling has been applied along with a set of meanline empirical loss models integrated in the secondary zone to estimate the entropy gain. This novel methodology has allowed the calculation of individual impeller loss mechanisms instead of predicting them as bulk. Computational Fluid Dynamics (CFD) has also been used to quantify the secondary flow properties and improve the 1D model. The results have been validated through a comparison with the microturbine test data. A sensitivity analysis has been performed to investigate the influence of geometric changes upon compressor performance. The study is important to develop design for manufacturing capability and optimize the designs for cost-effective manufacturing.Copyright

Conceptual Study of a Hybrid Turbofan Engine With Inter Turbine Burner

Most of the improvement in aviation during the last 7 decades has been mainly due to the advancement in the propulsion systems and technologies. The Advisory Council for Aeronautics Research in Europe (ACARE) has set ambitious objectives to be completed by 2020 and beyond; the major being reduction of CO2 emissions by more than 50%, for which significant improvement of the propulsion systems is required. However, it appears that a technological plateau has been reached with conventional engine architecture. The paper presents a novel hybrid engine architecture with inter turbine burner (ITB). The hybrid engine with two combustion chambers offers the possibility of operating on hydrocarbon fuels as well as liquid hydrogen, enabling the aimed reduction of CO2 emissions by 50% without encountering the storage problems related to pure hydrogen powered aircraft.Copyright

Experimental and Numerical Spray Characterization of a Gas Turbine Fuel Atomizer in Cross Flow

An experimental and numerical characterization of a macrolaminate pressure atomizer, placed perpendicularly to a high-velocity, turbulent air stream, is presented in this work. The purpose of the study was to compare detailed spray measurements with computations using a commercial CFD code. This study was part of the development of the premixing section of a midsize gas turbine, redesigned to meet low emissions and dual fuel market requirements. First, the spray characteristics were determined by injecting into a quiescent environment at ambient conditions. This data provided input for CFD calculations. Then the fuel injector was placed in a test section, at ambient conditions as well, that simulated the cross flow position of the atomizer in the prototype combustor. Droplet size and velocity were measured downstream of the injector nozzle, using a one-dimensional Phase Doppler Particle Analyzer. Measurements were done in two measuring planes. Flow field measurements were made to establish a common base for the computations. 2D computations were made of these experiments, using a k-e turbulence model. The droplet trajectories were calculated with a Lagrangian ‘random walk’ technique, including drop break-up. The computed droplet size and velocity show agreement with the measurements. Drop break-up was also well represented by the model. The computed dispersion of the injected mass is not in agreement with the measured profile. This discrepancy in droplet dispersion is possibly due to high turbulence levels in the flow field, which were not well captured in the model.Copyright

Optimization of a Centrifugal Compressor Impeller for Robustness to Manufacturing Uncertainties

Compressor impellers for mass-market turbochargers are die-casted and machined with an aim to achieve high dimensional accuracy and acquire specific performance. However, manufacturing uncertainties result in dimensional deviations causing incompatible operational performance and assembly errors. Process capability limitations of the manufacturer can cause an increase in part rejections, resulting in high production cost. This paper presents a study on a centrifugal impeller with focus on the conceptual design phase to obtain a turbomachine that is robust to manufacturing uncertainties. The impeller has been parameterized and evaluated using a commercial computational fluid dynamics (CFDs) solver. Considering the computational cost of CFD, a surrogate model has been prepared for the impeller by response surface methodology (RSM) using space-filling Latin hypercube designs. A sensitivity analysis has been performed initially to identify the critical geometric parameters which influence the performance mainly. Sensitivity analysis is followed by the uncertainty propagation and quantification using the surrogate model based Monte Carlo simulation. Finally, a robust design optimization has been carried out using a stochastic optimization algorithm leading to a robust impeller design for which the performance is relatively insensitive to variability in geometry without reducing the sources of inherent variation, i.e., the manufacturing noise.

Premixing Air and LCV Gas in a Gas Turbine Compressor

When a gas turbine is operated on low calorific value (LCV) gas instead of natural gas, the operating point of the compressor will shift towards the surge line. The compressor pressure ratio can rise to a level where stall or surge can occur. Premixing LCV gas with air inside the compressor of a gas turbine can solve this problem. With all fuel premixed, no fuel needs to be injected through the normal fuel inlet. The mass flow balance between turbine and compressor is restored and matching problems will not occur. From calculations with two LCV gases it could be concluded that all LCV gas could be premixed with compressor air when a low percentage of hydrogen gas was present in the LCV gas. The LCV gas could not be fully premixed in case of a high amount of hydrogen. The calculations show that an OPRA OD 500 gas turbine operated on premixed LCV gas with a low amount of hydrogen can maintain its original efficiency and a loss of 14 efficiency points can be prevented.Copyright

Optimization of a Centrifugal Compressor Impeller Design for Robustness to Manufacturing Uncertainties

Compressor impellers for mass-market turbochargers are die-casted and machined with an aim to achieve high dimensional accuracy and acquire specific performance. However, manufacturing uncertainties result in dimensional deviations causing incompatible operational performance and assembly errors. Process capability limitations of the manufacturer can cause an increase in part rejections, resulting in high production cost. This paper presents a study on a centrifugal impeller with focus on the conceptual design phase to obtain a turbomachine that is robust to manufacturing uncertainties. The impeller has been parameterized and evaluated using a commercial computational fluid dynamics (CFD) solver. Considering the computational cost of CFD, a surrogate model has been prepared for the impeller by response surface methodology (RSM) using space-filling Latin hypercube designs. A sensitivity analysis has been performed initially to identify the critical geometric parameters which influence the performance mainly. Sensitivity analysis is followed by the uncertainty propagation and quantification using the surrogate model based Monte Carlo simulation. Finally a robust design optimization has been carried out using a stochastic optimization algorithm leading to a robust impeller design for which the performance is relatively insensitive to variability in geometry without reducing the sources of inherent variation i.e. the manufacturing noise.Copyright

Thermal Stability Fuel Additives for Civil Aviation Applications

Next generation aircraft propulsion systems inevitably place higher thermal loads on jet fuel since it is used as primary heat sink for engine, hydraulics, avionics and other on-board systems. Increased fuel temperatures prior to combustion may lead to deposit formation in fuel systems and combustion sections. This limits engine performance, puts a burden on maintenance personnel and increases operational costs. U.S. Air Force, industry and academia therefore decided to team up and start the development of thermally stable fuels in the late eighties. This initiative eventually led to the formulation of an additive package capable of improving fuel thermal stability with 100°F (56°C). Although significant experience has been gained with the additive in military applications, the potential in the much larger civil market is yet untapped. Recent evidence however indicates the ability of the additive to reduce particulate emissions and component wear as well. This paper describes the experiments that were undertaken with a stationary gas turbine located at Delft University of Technology (DUT). The proprietary additive in question, provided by Shell Aviation (SAV), was added to commercial Jet A-1 kerosene. Repeatable tests were conducted to characterize the exhaust aerosol and combustor deterioration of the test-rig with standard and dosed fuel. The outcome of the experiments indeed suggests a role of the stability additive in soot (precursor) formation processes. Short-term cleaning effects inside the combustor were not observed however.Copyright

A Simplified Method to Evaluate the Impact of Component Design on Engine Performance

This paper presents a simplified and fast method to evaluate the impact of a single engine component design on the overall performance. It consists of three steps. In the first step, an engine system model is developed using available data on existing engines. Alongside the cycle reference point, a sweep of operating points within the flight envelop is simulated. The engine model is tuned to match a wide range of conditions. In the second step, the module that contains the engine component of interest is analyzed. Different correlations between the component design and the module efficiency are investigated. In the third step, the deviations in efficiency related to different component configurations are implemented in the engine baseline model. Eventually, the effects on the performances are evaluated. The procedure is demonstrated for the case of a two-spool turbofan. The effects of tip leakage in the low pressure turbine on the overall engine performance are analyzed. In today’s collaborative engine development programs, the OEMs facilitate the design process by using advanced simulation software, in-house available technical correlations and experience. Suppliers of parts have a limited influence on the design of the components they are responsible for. This can be rectified by the proposed methodology and give subcontractors a deeper insight into the design process. It is based on commercially available PC engine simulation tools and provides a general understanding of the relations between component design and engine performance. These relations may also take into account of aspects like production technology and materials in component optimization.Copyright

Operational Experience With Internal Coatings in Aero- and Industrial Gas Turbine Airfoils

The internal surfaces of air cooled gas turbine airfoils will oxidize severely during service depending upon operational conditions, chosen design, substrate alloy and the presence of an internal coating. Contradictory experiences by Dutch operators about the need and the performance of internal coatings lead to a research project within the Dutch Gas Turbine Association (VGT). The work focussed on internally coated and non-coated airfoils of civil and military aero engines and industrial gas turbines. Cross-sections from airfoils for metallographic evaluation were selected from the civil aero engines, GE CF6-50 and -80C2 and PW4000, from military engines, PW F100-200 and -220, and from industrial engines, GE Frames 6 and 9. Coating thickness distributions, oxidation resistance and blockage of drilled film cooling holes were reviewed. Particularly the field experiences on the gas turbine airfoils are highlighted in this paper.Copyright