bluuebunny/crossref_metadata_2025 huggingface dataset:
Riblet Application in Compressors: Towards Efficient Blade Design?
Authors: Hergt A. , Hage W. , Grund S. , Steinert W. , Terhorst M. , Schongen F. , Wilke Y.
Published: September 2014

Nowadays, modern axial compressors have already reached a very high level of development. The current study is focused on the question, if the application of riblets on the surfaces of a highly efficient modern compressor blade can be a further step towards more efficient blade design. Therefore, a highly loaded compressor cascade has been designed and optimized specifically for low Reynolds number conditions, as encountered at high altitudes and under consideration of the application of riblets. The optimization was performed at a Mach number of 0.6 and a Reynolds number of 1.5×105. Two objective functions were used. The aim of the first objective function was to minimize the cascade losses at the design point and at incidence angles of +5 and −5 degrees. The intention of the second objective function was to achieve a smooth distribution of the skin friction coefficient on the suction side of the blade by influencing the blade curvature in order to apply riblets. The MISES flow solver as well as the DLR optimizer “AutoOpti” were used for the optimization process.

The developed compressor cascade was investigated in the transonic cascade wind tunnel of DLR in Cologne, where the Reynolds number was varied in the range of 1.5×105 to 9.0×105. Furthermore, the measurements were carried out at a low turbulence level of 0.8 percent and at a high turbulence level of 4 percent, representative for high pressure compressor stages. The measurement program was divided into two parts. The first part consisted of the investigation of the reference cascade. In the second part of the study riblets were applied on suction and pressure side of the cascade blades; two different manufacturing techniques, a rolling and a coating technique were applied. The rolling technique provides riblets with a width of 70 μm and the coated riblets have a width of 50 μm.

The wake measurements were performed using a 3-hole probe at midspan of the cascade in order to determine the resulting losses of the reference blade and the blades with applied riblets. The detailed analysis of the measurements shows, that the riblets have only a slight influence on the viscous losses in the case of the compressor application in this study. Finally, these results are discussed and assessed against the background of feasibility and effort of riblet applications within the industrial design and manufacturing process.
Zonal Detached Eddy Simulation of Tip Leakage Flow Control in an Axial High Pressure Compressor
Authors: Marty Julien , Riéra William , Castillon Lionel
Published: September 2014

In the present study, several control devices have been investigated in the framework of a high pressure compressor rotor using RANS simulations. The analysis of performance maps and of flow predictions leads to select the injection device located up-stream of the rotor tip, at the shroud in order to control the tip leakage flow. The high loss levels are reduced and the radial and azimuthal extension of the high loss area is smaller. Then the chosen flow control technique has been simulated using URANS and ZDES with the IGV passing wakes. The injection technique reduces the loss area and level, energizing and stabilizing the tip leakage vortex thanks to high momentum. So the vortex disruption is removed or at least delayed. Moreover, the influence of IGV passing wakes is reduced.
Thermo-Economic Evaluation of ORC System in Off-Shore Applications
Authors: Bhargava R. K. , Bianchi M. , Branchini L. , De Pascale A. , Melino F. , Peretto A. , Valentini E.
Published: September 2014

This paper presents a study related with off-shore oil & gas production and processing facilities, where required energy, for electric power, mechanical power and process heat, is mostly produced using gas turbines, as the fuel source (natural gas) is available onsite. Since size and weight of all equipment on an offshore facility are critical, it becomes necessary for the facility engineering team to ensure that all equipment are sized and selected appropriately to obtain better return on the investment. Therefore, any approach which could help in utilizing energy resources effectively will influence the bottom-line of the project, namely reduced capital cost and/or increased return on investment. In this paper, one such approach of recovering power and thermal energy through the use of Organic Rankine Cycle system is discussed. A detailed thermo-economic analysis, conducted considering a system with four gas turbines operating, shows that power recovery equivalent to one topping gas turbine is achievable with a suitable working fluid. The presented thermo-economic analysis clearly shows that use of the Organic Rankine Cycle system for waste heat recovery is a technically viable and economically attractive solution for the offshore applications.
Methodology to Characterize Heat Transfer Phenomena in Small Automotive Turbochargers: Experiments and Modelling Based Analysis
Authors: Serrano J. R. , Olmeda P. , Arnau F. J. , Dombrovsky A. , Smith L.
Published: September 2014

These days great effort is devoted to the study of turbocharging in order to minimize fuel consumption and pollutant emissions of turbocharged reciprocating engines. Among all the processes taking place in small automotive turbochargers, the heat transfer phenomenon is one of the least analysed in a systematic way. However turbocharger heat transfer phenomena are very important at low engine loads. An accurate prediction of gas temperatures at turbine and compressor outlet and fluid temperatures at the water and oil outlet ports is not possible without considering heat transfer phenomena in the turbocharger.

In the present work a comprehensive study of these phenomena is presented, showing their relevance compared to gas enthalpy variations through the turbomachinery. The study provides an experimental methodology to consider the different heat fluxes in the turbocharger and modelling them by means of a lumped capacitance heat transfer model.

The input data required for the model is obtained experimentally by a proper combination of both steady and transient tests. These tests are performed in different test benches, in which compressible fluids (gas) and incompressible fluids (oil) are used in a given sequence. The experimental data allows developing heat transfer correlations for the different turbocharger elements. These correlations take into account all the possible heat fluxes, discriminating between internal and external heat transfer.

In order to analyse the relative importance of heat transfer phenomena in the predictability of the turbocharger performance and the different related variables; model results, in hot and cold conditions, have been compared with those provided by the standard technique, consisting on using look up maps of the turbocharger.

The analysis of these results evidences the highly diabatic operative areas of the turbocharger and it provides clearly ground rules for using hot or cold maps. In addition, paper conclusions advise about using or not a heat transfer model, depending on the turbocharger variables and the operative conditions that one desires to predict.
Effects of Tip Injection on Tip Clearance Flow in a Low-Pressure Turbine Stator Cascade
Authors: Chen Shaowen , Zhou Zhihua , Cui Tao , Wang Jinsheng , Wang Songtao
Published: September 2014

Taking into account the tip leakage flow will cause the loss of a substantial increase, how to effectively control the tip clearance flow has become a current research focus. In this paper, the effects of tip injection in a low pressure turbine cascade with different injection locations, number of injection holes and mass flow rate are investigated in detail. The SST k-ω turbulence model on the basis of the Gamma-Re transition model is adopted to compute the three-dimensional flow in the cascade of a turbine cascade with tip clearance. The feasibility of a commercial computational fluid dynamic code was validated and the computed data showed a good agreement with experimental data. The effect of the tip injection locations at camber line is better than that of close to the suction side or the pressure side. The total pressure loss decreased significantly by about 22% by increasing the injection flow rate to 6g/s. The main purpose of tip injection for the control of tip clearance flow is not simple to decrease the mass flow rate of leakage flow. There needs to be a more reasonable tip injection scheme which must consider the unfavorable effects of flow blockage in the clearance, and the losses due to the mixing of injection flow with tip clearance flow and leakage flow with main flow are reduced in order to achieve the optimal effect of clearance flow control.
Use of Pressure Measurements to Determine Effectiveness of Turbine Rim Seals
Authors: Owen J. Michael , Wu Kang , Scobie James A. , Sangan Carl M. , Cho GeonHwan , Lock Gary D.
Published: September 2014

The ingress of hot gas through the rim seal of a gas turbine depends on the pressure difference between the mainstream flow in the turbine annulus and that in the wheel-space radially inward of the rim seal. In this paper, a previously published orifice model is modified so that the sealing effectiveness εc determined from concentration measurements in a rig could be used to determine εp the effectiveness determined from pressure measurements in an engine. It is assumed that there is a hypothetical ‘sweet spot’ on the vane platform where the measured pressures would ensure that the calculated value of εp equals εc, the value determined from concentration measurements. Experimental measurements for a radial-clearance seal show that, as predicted, the hypothetical pressure difference at the sweet spot is linearly related to the pressure difference measured at an arbitrary location on the vane platform. There is good agreement between the values of εp determined using the theoretical model and values of εc determined from concentration measurements. Supporting computations, using a 3D steady CFD code, show that the axial location of the sweet spot is very close to the upstream edge of the seal clearance. It is shown how parameters obtained from measurements of pressure and concentration in a rig could, in principle, be used to calculate the sealing effectiveness in an engine.
Analysis of the Flame Structure in a Trapped Vortex Combustor Using Low and High-Speed OH-PLIF
Authors: Xavier Pradip , Vandel Alexis , Godard Gilles , Renou Bruno , Grisch Frederic , Cabot Gilles , Boukhalfa Mourad A. , Cazalens Michel
Published: September 2014

Operating with lean combustion has led to more efficient “Low-NOx” burners but has also brought several technological issues. The burner design geometry is among the most important element as it controls, in a general way, the whole combustion process, the pollutant emissions and the flame stability. Investigation of new geometry concepts associating lean combustion is still under development, and new solutions have to meet the future pollutant regulations. This paper reports the experimental investigation of an innovative staged lean premixed burner. The retained annular geometry follows the Trapped Vortex Combustor concept (TVC) which operates with a two stage combustion chamber: a main lean flame (1) is stabilized by passing past a vortex shape rich-pilot flame (2) located within a cavity. This concept, presented in GT2012-68451 and GT2013-94704, seems to be promising but exhibits combustion instabilities in certain cases, then leading to undesirable level of pollutant emissions and could possibly conduct to serious material damages. No precise information have been reported in the literature about the chain of reasons leading to such an operation. The aim of this paper is to have insights about the main parameters controlling the combustion in this geometry. The flame structure dynamics is examined and compared for two specific operating conditions, producing an acoustically self-excited and a stable burner. Low and high-speed OH-PLIF laser diagnostics (up to 10 kHz) are used to have access to the flame curvature and to time-resolved events. Results show that the cavity jets location can lead to flow-field oscillations and a non-constant flame’s heat release. The associated flame structure, naturally influenced by turbulence is also affected by hot gases thermal expansion. Achieving a good and rapid mixing at the interface between the cavity and the main channel leads to a stable flame.
Exploiting Waste Heat in Small and Medium-Sized Combined Heat and Power Plants Using Steam Injection
Authors: Arnold Stephan , Schatz Markus
Published: September 2014

Combined heat and power generation (CHP) is a way of providing both electric power and thermal heat for industrial and domestic facilities at high fuel efficiencies. Often small and medium sized gas powered internal combustion (IC) engines, rated at electric power outputs of 50–600 kW, are used for such applications. During the time when the available thermal heat is used, the fuel efficiency of such CHP plants is very high, but it drops to the efficiencies of simple power generation when there is no heat demand, e.g. during summer. In these cases, the exhaust heat is blown off, especially as CHP units are mainly heat-lead, i.e. designed to cover the heat demand rather than the demand for electrical power. Moreover, as the cooling water heat rejection is also more difficult at elevated ambient temperatures, these units are then operated at part load or even switched off, hence having a lower degree of capacity utilization.

The approach of the work presented here is to replace the turbocharger system commonly used for IC engines and to use an electric driven compression device instead, while the turbine serves to generate additional electric power from the exhaust gas.

Furthermore, for periods with low thermal heat demand, steam is generated from the turbine exhaust heat. The steam is injected in front of the turbine in order to increase the turbine work output further. Thus, at least part of the exhaust heat available is used and the power output as well as the electric efficiency is increased. In the present work, two configurations of the described setup using a medium sized gas powered IC engine CHP unit are modeled in order to assess the impact on plant performance and the characteristics of such a facility. In both cases the engine cooling circuit is integrated. Depending on the configuration used, the plant power output increases by up to 7% only because of the power turbine. Additional steam injection to use the waste heat increases the power output further. The relative electric efficiency increase with steam injection is in the range of 3–5%. Apart from the higher output of electric power, this approach allows longer operating hours to be achieved, as the exhaust heat available is utilized and the heat load for the cooling water circuit is reduced.
Characterization of Aviation Soot Emissions With a High-Pressure Gas Turbine Combustor Rig
Authors: Liscinsky David S. , Yu Zhenhong , Jennings Archer , Peck Jay , True Bruce , Freedman Andrew , Herndon Scott C. , Miake-Lye Richard C.
Published: September 2014

Characterization of particulate matter (PM) emissions from commercial and military aircraft engines is a costly procedure, usually influenced by a number of uncontrollable technical issues such as ambient conditions. In this study we demonstrated that a research sector rig representing an aircraft engine combustor can be used to evaluate PM emissions, such as carbonaceous soot, in a well-controlled manner. PM emissions in terms of mass and number, as well as particle size distribution and optical properties, were characterized and quantified with a variety of state-of-the-art measurement instruments. Compared to previously published measurements on advanced commercial aircraft engines (CFM56-7B22), the measured emission index of black carbon soot was 58±3 mg/kg-fuel at simulated higher power conditions, consistent within 25% of field measurements. Measurements of number emission index were within a factor of 2 and geometric mean diameter was between 25 and 35nm again similar to field measurements on engines. Based on the measurements on particle mass and size, the mass mobility exponent of the soot particles had a lower limit of 2.4 indicating near-sphericity and an average density near 1 g/cm3.
Influence of Nonlinear Effects on the Limit Cycle in a Combustion Chamber Equipped With Helmholtz Resonator
Authors: Campa Giovanni , Camporeale Sergio Mario
Published: September 2014

The influence of the introduction of a Helmholtz resonator as a passive damper in a gas turbine combustion chamber on the bifurcation mechanism that characterizes the transition to instability is investigated. Bifurcation diagrams are tracked in order to identify the conditions for which the machine works in a stable zone and which are the operative parameters that bring the machine to unstable conditions. This work shows that a properly designed passive damper system increases the stable zone, moving the unstable zone and the bistable zone (in the case of a subcritical bifurcation) to higher values of the operative parameters, while have a limited influence on the amplitude of limit cycle. In order to examine the effect of the damper, a gas turbine combustion chamber is first modeled as a simple cylindrical duct, where the flame is concentrated in a narrow area at around one quarter of the duct. Heat release fluctuations are coupled to the velocity fluctuations at the entrance of the combustion chamber by means of a nonlinear correlation. This correlation is a polynomial function in which each term is an odd-powered term. The corresponding bifurcation diagrams are tracked and the passive damper is designed in order to increase the stability zone, so reducing the risk to have an unstable condition. Then both plenum and combustion chamber are modeled with annular shape and the influence of Helmholtz resonators on the bifurcation is examined.
A Harmonic Balance Technique for Multistage Turbomachinery Applications
Authors: Frey Christian , Ashcroft Graham , Kersken Hans-Peter , Voigt Christian
Published: September 2014

This article describes a nonlinear frequency domain method for the simulation of unsteady blade row interaction problems across several blade rows in turbomachinery. The capability to efficiently simulate such interactions is crucial for the improvement of the prediction of blade vibrations, tonal noise, and the impact of unsteadiness on aerodynamic performance.

The simulation technique presented here is based on the harmonic balance approach and has been integrated into an existing flow solver. A nontrivial issue in the application of harmonic balance methods to turbomachinery flows is the fact that various fundamental frequencies may occur simultaneously in one relative system, each one being due to the interaction of two blade rows. It is shown that, considering the disturbances corresponding to different fundamental frequencies as mutually uncoupled, one can develop an unsteady simulation method which from a practial view point turns out to be highly attractive. On the one hand, it is possible to take into account arbitrarily many nonlinear interaction terms. On the other, the computational efficiency can be increased considerably once it is known that the nonlinear coupling between certain subsets of the harmonics plays only a minor role.

To validate the method and demonstrate its accuracy and efficiency a multistage compressor configuration is simulated using both the method described in this article and a conventional time-domain solver.
Whole Engine Interaction in a Bladed Rotor-to-Stator Contact
Authors: Parent Marie-Océane , Thouverez Fabrice , Chevillot Fabrice
Published: September 2014

Reducing the clearances between rotating and fixed parts is an important factor in increasing the performances of turbomachines. The physical counterpart however is an evolution in possible rotor-stator contacts capable of causing unstable dynamic behavior. A proper prediction of the rotor-stator contact occurrences and associated induced phenomena, has therefore become of a great interest for aero-engine mechanical engineers. Most numerical simulations involving rotor-stator contact can be divided into two types of physical behavior. The first focuses on contact induced blade/casing interactions, in only taking into account the blades and casing flexibility. The second type of behavior takes into account the shaft dynamic while neglecting blade flexibility. Future designs of aircraft engines will however raise the need to combine these two types of models. Since, the structural components are more flexible, the dynamic coupling between engine modules is increased. This paper proposes a study based on a structure representative of the whole aircraft engine, including the contacts that may arise between the fan-blade tips and fan casing. We have introduced a fully-coupled phenomenological model with flexible blades, shaft and casing. Furthermore, this model includes an elastic link between shaft and casing to simulate the fan frame behavior. We begin by explaining the linear results, which highlight the dynamic couplings between these various model components. During a second step, this paper presents the nonlinear results obtained by introducing a contact law. These results demonstrate the influence of the whole engine dynamic on contact-related behavior with special focus on the system dynamic stability.
High Efficiency Cavity Winglets for High Pressure Turbines
Authors: Coull John D. , Atkins Nicholas R. , Hodson Howard P.
Published: September 2014

The flow leaking over the tip of a high pressure turbine blade generates significant aerodynamic losses as it mixes with the freestream flow. This paper examines the potential for reducing these losses using winglets with recessed cavities on the tip. These features combine the loss-reduction mechanisms of cavity tips, which reduce the discharge coefficient, and winglet overhangs, which reduce the mixing Mach number, leakage flow angle mismatch, and the driving pressure ratio. RANS calculations are performed for an un-cooled HP rotor blade to explore the cavity-winglet design space and examine the impact on the aerothermal performance of the blade.

Relative to a plain-tip design, a cavity tip can reduce the sensitivity to clearance by around 30%. Similar performance can be achieved using a flat-tip winglet with an overhang around the whole blade perimeter. However, by adding a cavity to this winglet it is possible to out-perform the cavity tip at all clearances, and reduce the sensitivity to clearance by 46% relative to the plain tip. This sensitivity is equivalent to a two-fin attached shroud, but the winglet blade will exhibit lower stress and require less coolant flow. Furthermore this cavity-winglet may offer some cooling advantages over the cavity tip.
Conjugate Heat Transfer CFD Predictions of Impingement Heat Transfer: Influence of the Number of Holes for a Constant Pitch-to-Diameter Ratio X/D
Authors: El-Jummah Abubakar M. , Abdul Hussain Reyad A. A. , Andrews Gordon E. , Staggs John E. J.
Published: September 2014

Conjugate heat transfer CFD studies were undertaken on the influence of the number of impingement holes/unit surface area or hole density n (m−2) for n from 1076 to 26910m−2 at a constant X/D of 4.7, with n varied by varying the hole diameter D from 1.31 to 6.54mm and pitch X varied from 6.1mm to 30.5mm. Square array impingement cooling geometries for the jet holes were used with a 152.4 × 152.4mm experimental wall area. The impingement gap had a single sided exit which generated a cross-flow in the gap. The number of impingement holes N in the cross-flow direction was 5, 10, 15 and 25. A coolant mass flux G of 1.93kg/sm2bar was investigated at a constant impingement gap Z of 10mm (Z/D 1.53–7.65 as n was varied). This high coolant mass flow simulated the coolant flow for regeneratively cooled combustors using all the combustor air flow to cool the combustor wall prior to entering the low NOx flame stabiliser. The predictions were compared with experimental results for the heat transfer coefficient h, that used the lumped capacitance method. The predictions of the surface averaged h and pressure loss ΔP/P were in good agreement with the measured results. The predictions showed that increasing the number of impingement jet holes resulted in lower h, due to the impact of cross-flow for large numbers of holes. At the other extreme, a very small number of holes were predicted to have high thermal gradients. The maximum heat transfer was found experimentally and computationally to be 4306 holes per m2 for an X/D of 4.7, with acceptable thermal gradients.
Design of an Axial Impulse Turbine for Enthalpy Drop Recovery
Authors: Morgese Gaetano , Torresi Marco , Fortunato Bernardo , Camporeale Sergio Mario
Published: September 2014

In industrial process plants, often there is the need to reduce the pressure of the operating flow. Generally this is performed by means of valves which expand the flow without any work done. The same operation could be performed by replacing these valves with turbines, with the advantage of energy recovery, hence improving the overall efficiency of the system.

In this work, a simple and rapid method is shown in order to design a single stage, straight bladed, axial impulse turbine for enthalpy recovery. Assigned the desired flow rate and the minimum power output, the turbine design is performed according to a one-dimensional study into which loss effects are considered by means of appropriate coefficients. From the one-dimensional analysis the heights, the pitch angle, the inlet and outlet angles of both rotor and stator blades are obtained. Actually, the rotor and stator blade profiles are defined by means of several analytical functions. The blade design is then validated by means of CFD simulations. The definition of loss coefficients and blade geometrical parameters is clearly an iterative process, which needs to be repeated until convergence is reached. Furthermore, by means of fully 3D simulations, the effect of the rotor-stator distance is investigated in order to maximize the turbine performance.
Game-Theoretic Models for Cooperative Equilibrium Solutions of Interacting Engineering Sub-Systems
Authors: Shankaran Sriram , Vandeputte Tom
Published: September 2014

Although game-theoretical models to study social and economic problems have existed for a long time, they have been sparsely used for the design of engineering systems. This is due to the significant theoretical hurdles posed by game formulations for real engineering environments /problems. In this study we show our first attempt at adapting the frame-work of game-theoretical models for engineering problems, in particular the aero-mechanical optimization of a notional turbine blade. We pose the design problem as a series of games, starting with the determination of the Pareto front, the non-cooperative (disagreement) point and the optimal solution as the tangent intersection of the Pareto front and contours of the overall system objective. We present gradient-based algorithms that determine the Pareto front, the non-cooperative solution and the tangent solution. The solution to this series of games provides the basis of a new equilibrium concept namely, System Optimal Cooperative Solution (SOCS), which is the central theme of this paper. Finally we compare the SOCS solution against other cooperative solutions like Nash-Bargaining [1]. The results of this study show that in engineering environments previously known cooperative solutions like Nash-Bargaining and Kalai-Smordinsky [2] are not that important while the notion of a System Optimal Cooperative Solution, SOCS, is the equilibrium solution of relevance. For the particular example we consider, the SOCS is shown to be more favoring the aerodynamic performance when compared against the Nash-Bargaining equilibrium solution.
Numerical Investigations on the Leakage and Rotordynamic Characteristics of Pocket Damper Seals: Part I — Effects of Pressure Ratio, Rotational Speed and Inlet Preswirl
Authors: Li Zhigang , Li Jun , Feng Zhenping
Published: September 2014

Effects of pressure ratio, rotational speed and inlet preswirl on the leakage and rotordynamic characteristics of a eight-bladed fully-partitioned pocket damper seal (FPDS) were numerically investigated using proposed 3D transient CFD methods based on the multi-frequency elliptical whirling orbit model. The accuracy and availability of the multi-frequency elliptical whirling orbit model and the transient CFD numerical methods were demonstrated with the experimental data of frequency-dependent rotordynamic coefficients of the FPDS at two rotational speeds with high preswirl conditions. The frequency-dependent rotordynamic coefficients of the FPDS at three pressure ratios (three inlet pressures and three outlet pressures), three rotational speeds, three inlet preswirls were computed. The numerical results show that changes in outlet pressure have only weak effects on most rotordynamic coefficients. The direct damping and effective damping slightly increase in magnitude with decreasing outlet pressure at the frequency range of 20–200Hz. The effect of inlet pressure is most prominent, and increasing inlet pressure for the FPDS results in a significant increase in the magnitudes of all rotordynamic coefficients. The magnitudes of the seal response force and effective damping are proportional to pressure drop through the seal. Increasing rotational speed and increasing inlet preswirl velocity both result in a significant decrease in the effective damping term due to the obvious increase in the magnitude of the destabilizing cross-coupling stiffness with increasing rotational speed or increasing preswirl velocity. The crossover frequency of effective damping significantly increases and the peak magnitude of effective damping decreases with increasing rotational speed or increasing preswirl velocity. The destabilizing cross-coupling stiffness is mainly caused by the circumferential swirl velocity generating from high rotational speed and inlet preswirl. Reducing swirl velocity (such as swirl brake) can greatly enhance the stabilizing capacity of the FPDS.
Application of Gas Path Analysis to Compressor Diagnosis of an Industrial Gas Turbine Using Field Data
Authors: Blinstrub J. , Li Y. G. , Newby M. , Zhou Q. , Stigant G. , Pilidis P. , Hönen H.
Published: September 2014

Maintenance cost is one of the major life cycle costs of gas turbine engines. To reduce the maintenance costs, the maintenance should be changed from preventive (or scheduled) maintenance to predictive (or condition-based) maintenance where condition monitoring and diagnostics become crucially important.

This paper represents the application of a gas path diagnostic technique, Gas Path Analysis, to the diagnostic analysis of an aero-derivative gas turbine (GE LM2500+) operated by Manx Electricity Authority in the Isle of Man, UK. In the application, an engine thermodynamic model is created and adapted to the performance of the engine using field data obtained at different operating conditions. Different data pre-processing methods are presented and compared in the diagnostic analysis. The uncertainty of measurement data is analysed and the most suitable measurements are identified in the prediction of key gas path component degradation. A non-linear GPA diagnostic analysis provides promising results for the prediction of compressor degradation and the performance improvement due to a compressor water washing. Such diagnostic information would be very useful for maintenance engineers to optimise their maintenance activities including overhauls and compressor washing.
Influence of the Turbulence Length Scale and Intensity on Spark Ignition of Kerosene Jet-A1–Air Mixtures at High Altitude Relight Conditions
Authors: Majcherczyk Michał , Zarzalis Nikolaos , Turrini Fabio
Published: September 2014

In recent years Avio Aero and the Karlsruhe Institute of Technology (KIT) have significantly enhanced their available experimental technology level in order to consolidate and deepen the investigation of some critical phenomena in aero-engine gas turbine combustion. A key parameter in the development of a lean-burn combustor is the design of the ignition system. The increase in the amount of air that flows through the primary zone to approximately 60% of the overall air proves to be beneficial for emissions reduction. In return it causes shorter residence times in the primary zone and makes the flame kernel generation and propagation a real challenge.

With the scope to enhance the fundamental understanding of the ignition process at altitude conditions, the ISCRA rig (Ignition in Subatmospheric Conditions – Rig for Altitude Relight Investigation) has been designed and manufactured at the KIT. The design of the rig allows the generation of altitude conditions at variable flow velocities and turbulence characteristics. An optical access for ignition recording by a CCD camera is also provided.

The paper presents the results of a fundamental investigation at the KIT using a generic setup. It consists of a pressure atomizer with known atomization properties mounted in a test rig which allows the variation of several parameters that influence ignition, namely: air pressure; air temperature; velocity; Fuel-Air-Ratio (FAR); Sauter Mean Diameter (SMD); spark energy; turbulence intensity and length scale. Two grey spots that exist in the knowledge map of the ignition process are addressed in this paper. These are data on kerosene spray ignition at temperatures below 293 K, where data is scarce and the relationship between flame kernel generation and propagation, which has not been broadly investigated nor is well understood. The ignition probabilities of kerosene sprays as a function of ignition energy in the temperature range from 253 K to 293 K, pressure of 0.7 bar, flow velocities up to 6 m/s at different turbulence intensities and length scales are measured. Furthermore, the influence of the above mentioned parameters on the kernel generation and propagation is presented and discussed.

Results show that the energy required for flame kernel propagation is higher than for flame kernel generation. This difference increases at lower temperature and higher turbulence intensity. The paper gives an insight in magnitude of this difference in energy and compares the tendencies with an earlier model. The absolute values need to and will be corrected by future in situ measurements.
Non-Axisymmetric Turbine Endwall Aerodynamic Optimization Design: Part I — Turbine Cascade Design and Experimental Validations
Authors: Sun Hao , Li Jun , Song Liming , Feng Zhenping
Published: September 2014

The non-axisymmetric endwall profiling has been proven to be an effective tool to reduce the secondary flow loss in turbomachinery. In this work, the aerodynamic optimization for the non-axisymmetric endwall profile of the turbine cascade and stage was presented and the design results were validated by annular cascade experimental measurements and numerical simulations. The parametric method of the non-axisymmetric endwall profile was proposed based on the relation between the pressure field variation and the secondary flow intensity. The optimization system combines with the non-axisymmetric endwall parameterization method, global optimization method of the adaptive range differential evolution algorithm and the aerodynamic performance evaluation method using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) and k–ω SST turbulent with transition model solutions. In the part I, the optimization method is used to design the optimum non-axisymmetric endwall profile of the typical high loaded turbine stator. The design objective was selected for the maximum total pressure coefficient with constrains on the mass flow rate and outlet flow angle. Only five design variables are needed for one endwall to search the optimum non-axisymmetric endwall profile. The optimized non-axisymmetric endwall profile of turbine cascade demonstrated an improvement of total pressure coefficient of 0.21% absolutely, comparing with the referenced axisymmetric endwall design case. The reliability of the numerical calculation used in the aerodynamic performance evaluation method and the optimization result were validated by the annular vane experimental measurements. The static pressure distribution at midspan was measured while the cascade flow field was measured with the five-hole probe for both the referenced axisymmetric and optimized non-axisymmetric endwall profile cascades. Both the experimental measurements and numerical simulations demonstrated that both the secondary flow losses and the profile loss of the optimized non-axisymmetric endwall profile cascade were significantly reduced by comparison of the referenced axisymmetric case. The weakening of the secondary flow of the optimized non-axisymmetric endwall profile design was also proven by the secondary flow vector results in the experiment. The detailed flow mechanism of the secondary flow losses reduction in the non-axisymmetric endwall profile cascade was analyzed by investigating the relation between the change of the pressure gradient and the variation of the secondary flow intensity.
Effect of a Recirculation Device on the Performance of Transonic Mixed Flow Compressors
Authors: Numakura Ryusuke , Tamaki Hideaki , Hazby Hamid , Casey Michael
Published: September 2014

Two transonic mixed flow compressors with an extremely high flow coefficient of ϕ = 0.25 and pressure ratios of 2.5 and 2.65 have been designed and tested. CFD simulations indicated that both impellers operate with a suction surface relative Mach number of above 1.5 at their design conditions. Both compressors achieved a narrow stable operating range when tested without recirculation devices.

The effects of two different recirculation devices on the compressor performance maps were investigated both experimentally and numerically. The first type is a widely used recirculation device which consists of an upstream slot, bleed slot and an annular cavity which connects both slots. The other has vanes installed in the cavity which were designed to provide a recirculation flow with negative swirl at the impeller inlet. Measurement data demonstrated the effect of the recirculation devices on increasing the range of these two transonic mixed flow compressors and showed the superiority of the recirculation device with vanes.

The effects of the recirculation devices on the impeller flow field at near surge conditions are studied using steady state 3D CFD calculations. Both measurements and simulations showed that the stability enhancement is partly caused by a steeper pressure rise characteristic.
Test Results and Analytical Predictions for MIL-STD-167 Vibration Testing of a Direct Drive Compressor Supported on AMB
Authors: Hawkins Lawrence A. , Khatri Rasish K. , Nambiar Koman B.
Published: September 2014

External vibration testing was performed on a semi-hermetic, direct drive compressor on magnetic bearings intended for US Navy Shipboard use. The compressor was placed on a US Navy MIL-STD-167 shaker platform and driven at sinusoidal frequencies from 4 to 33 Hz at graduated displacements equal to a maximum of 1.5Gs. During the machine design phase, a linear forced response analysis of the coupled rotordynamic system model of the rotor, housing and magnetic bearings was performed to predict rotor/housing displacements and actuator loads. The results were used to guide bearing sizing and control algorithm design. The measured rotor motion and actuator currents correlated well with predictions at all tested frequencies, amplitudes and orientations. Analysis methodology, test results, and comparisons are reported here.
Burner Rig Testing of Thermal Barrier Coatings for Lifetime Prediction
Authors: Witz Grégoire , Staerk Klaus F. , Maggi Carlo M. , Krasselt Ulrich , Bossmann Hans-Peter
Published: September 2014

Thermal barrier coating lifetime prediction has been commonly performed using furnace cyclic test results. This testing method causes coating failures driven by the bondcoat oxidation. This allows definition of lifetime prediction models representative of the field experience for thin thermal barrier coating systems where the difference between the bondcoat temperature and the coating surface are limited to 100–200 °C. Thick thermal barrier coating systems can experience coating surface temperatures 500 °C higher than the bondcoat temperature. In such cases sintering and phase transformations in the ceramic layers can also affect the coating lifetime. For this reason cyclic test methods like thermal gradient burner rig and laser heat-flux tests have been developed. They allow to test a coating system with surface temperatures >1400 °C while keeping bondcoat temperature <900 °C. The main issue of such tests is the often limited samples statistic, the reproducibility of the test conditions, and the coating failure mode that is not representative of the field experience. In Alstom, a burner rig test has been developed to solve these issues. It allows to test in parallel 10 samples, with a closed loop control system allowing live adjustment of the heat and cooling air input to keep an individually controlled constant thermal gradient with a homogeneous temperature distribution on the sample surface. Modeling of the test has been performed to understand the coating failure mechanism and to adapt the testing conditions such to get a failure mechanism closer to the relevant degradation mechanisms experienced in the field. Testing of coatings coming from the same production batch in various test campaign shows a low scatter in test results confirming that the burner rig test design allowed solving the test reproducibility and samples statistics issues. Examples will be shown how this burner rig test can be used for the development of lifetime prediction rules for thermal barrier coating systems.
Development of a Liquid Fuel Combustion System for SGT-750
Authors: Lindman Olle , Andersson Mats , Persson Magnus , Munktell Erik
Published: September 2014

This paper describes the latest results from the development of a liquid fuel solution for the 4th generation DLE system for Siemens medium size gas turbines. Gaseous fuels are the dominating fuels for industrial gas turbines. However, many customers need to be able to run on liquid fuel as backup. The demand for dry low NOx emissions when operating on liquid fuel is increasing. The aim for the 4th generation DLE system incorporated in the recently released SGT-750 [1] is to have emission levels well below market demands on both gas and liquid fuel. This paper will highlight the technical challenges when adding liquid fuel operation to a combustion system optimized for gas operation. The stand-alone spray characteristics for a liquid fuel nozzle is quite easy to predict, but the final combustion performance in a hot air cross flow environment is all but easy to predict by numerical simulations or cold flow tests [2]. Due to the complexity of the challenge, the development program focused on a selection of concepts for which fuel/air mixing calculations were made. The investigation was completed by testing in a full scale, single burner high pressure combustion test rig.
Heat Transfer and Pressure Loss Measurements of Matrix Cooling Geometries for Gas Turbine Airfoils
Authors: Carcasci Carlo , Facchini Bruno , Pievaroli Marco , Tarchi Lorenzo , Ceccherini Alberto , Innocenti Luca
Published: September 2014

Matrix cooling systems are relatively unknown among gas turbines manufacturers of the western world. In comparison to conventional turbulated serpentines or pin-fin geometries, a lattice-matrix structure can potentially provide higher heat transfer enhancement levels with similar overall pressure losses. This experimental investigation provides heat transfer distribution and pressure drop of four different lattice-matrix geometries with crossing angle of 45 deg between ribs. The four geometries are characterized by two different values of rib height which span from a possible application in the mid chord region up to the trailing edge region of a gas turbine airfoil. For each rib height two different configurations have been studied: one having four entry channels and lower rib thickness (open area 84.5%), one having six entry channels and higher rib thickness (open area 53.5%). Experiments were performed varying the Reynolds number Res, based on the inlet sub-channel hydraulic diameter, from 2000 to 12000. Heat transfer coefficients were measured using steady state tests and applying a regional average method; test models have been divided into 20 stainless steel elements in order to have a Biot number similitude with real conditions. Elements are 10 per side, 5 in the main flow direction and 2 in the tangential one. Metal temperature was measured with embedded thermocouples and 20 thin-foil heaters were used to provide a constant heat flux during each test. A specific data reduction procedure has been developed so as to take into account the fin effectiveness and the increased heat transfer surface area provided by the ribs. Pressure drops were also evaluated measuring pressure along the test models. Uniform streamwise distributions of Nusselt number Nus have been obtained for each Reynolds number. Measurements show that the heat transfer enhancement level Nus/Nu0 decreases with Reynolds but is always higher than 2. Results have been compared with previous literature data on similar geometries and show a good agreement.
Improvement of Flow Conditions for the Stages Subsequent to Extraction Modules in Industrial Steam Turbines
Authors: Schramm Andreas , Müller Tim , Polklas Thomas , Brunn Oliver , Mailach Ronald
Published: September 2014

Industrial steam turbines are applied for power generation as well as drive for turbo-compressors. They combine a high level of operational flexibility with highest reliability. Especially in the field of process technology they provide process heat on a certain enthalpy level for other industrial applications. Modular design concepts are used to meet these various requirements like admission or extraction of large steam quantities. Extraction modules use valves to control the amount of steam extracted from the turbine expansion path at constant steam parameters.

While extraction steam is taken from the turbine through an outlet flange, the remaining steam passes valves and downstream diffusers, flows into an annular inner casing and finally escapes through the subsequent stages. Depending on the valve lift, different flow separations can occur around the valves, resulting in unsteady transonic jets. Due to the compact and asymmetric design of the inner casing the flow into the subsequent stages is strongly disturbed. Hence, strong unsteady mechanical blade loading can occur in addition to efficiency loss.

The current work focusses on the improvement of the flow conditions in the subsequent stage. Experimental results are applied to quantify the viability of the used 3D RANS CFD-solver (ANSYS CFX 14) for these numerical investigations. Compared with the experiment, the distribution of pressure, velocity and incidence angle are well predicted by the numerical code. It is evident that the unsteady transonic jets emerging around the valves have a major influence on the distribution of the parameters considered. Thus, to quantify the impact of a modified inlet chamber design, it is sufficient to simulate the domain starting from the valves.

The influence of different design modifications on the flow parameters in comparison with the base design is discussed in detail in an extensive study. The results clarify that horizontal and vertical valve positions, as well as thorough contouring of the radial-axial deflection have a strong influence on the distribution of pressure, mass flux and incidence angle. Hence, in this contribution combinations of the most beneficial modifications are investigated numerically and compared with the base design.