bluuebunny/crossref_metadata_2025 huggingface dataset:
Large Eddy Simulations of Separated Shear Layer Behaviors in a High-Lift LP Turbine
Authors: Zhang Weihao , Zou Zhengping , Ye Jian
Published: August 2015

Separated shear layer behaviors under the conditions without and with elevated inlet freestream turbulence intensity (FSTI=2.5%) are investigated by using large eddy simulations (LES) in this paper. The study is performed on a low-Re high-lift LP turbine blade (T106D-EIZ) at Reynolds number (Re) of 60,154 (based on the chord and outflow velocity) and isentropic exit Mach number of 0.402. A number of detection points are set along the dividing streamlines and long time series of data are gathered. The time-mean flow and the transient vortex structures are discussed, which indicated the FSTI can suppress the open separation and thus improve the aeroperformance. Power spectra and wavelet analysis are applied to axial velocity and pressure signals of the detection points. The results show that although the vortices pairing are missed, the subharmonic of the roll-up frequency is still observable under the elevated FSTI condition. It is also found that both of the locations and power of the vortices roll-up, as well as vortices pairing, vary with time in large scales and these phenomena are weakened under the elevated FSTI condition.
Comparison of Gas System Analysis Code GAMMA+ to S-CO2 Compressor Test Data
Authors: Bae Seong Jun , Ahn Yoonhan , Lim Hong-Sik , Cha Jae Eun , Lee Jeong Ik
Published: August 2015

The CO2 compressor control is one of the most important issues to operate a Supercritical CO2 (S-CO2) Brayton cycle with a high thermal efficiency because it is operated near the critical point to reduce the compressing work. Therefore, our research team has accumulated the CO2 compressor data from the S-CO2 compressor test facility called SCO2PE (Supercritical CO2 Pressurizing Experiment). The data can be obtained under various compressor inlet conditions, especially near the critical point of CO2.

Despite the growing interest in the S-CO2 Brayton cycle, research on the cycle transient analysis, especially in case of CO2 compressor inlet condition variation, is still in its early stage. So, in this study, the validation and verification of the gas system transient analysis code GAMMA+ is carried out by utilizing the experimental data of SCO2PE. To simulate the SCO2PE by the GAMMA+ code, the code was revised to reflect the compressor performance and add an expansion valve option. Moreover, the NIST database was connected to the GAMMA+ code for more accurate CO2 properties near the critical point. Prior to the transient analysis with the whole SCO2PE loop, major components such as a compressor and a heat exchanger were separately tested with the steady state data of SCO2PE. The loss of cooling water accident was assumed as the transient situation by observing the operating condition variations of the SCO2PE while the mass flow rate of water loop was decreased. Thus, the experimental data of SCO2PE was compared with the revised GAMMA+ code under the planned transient.
Experimental Investigation of a FLOX®-Based Combustor for a Small-Scale Gas Turbine Based CHP System Under Atmospheric Conditions
Authors: Seliger Hannah , Huber Andreas , Aigner Manfred
Published: August 2015

This paper presents a comprehensive experimental investigation of a newly designed single-stage combustion system based on the flameless oxidation (FLOX®) technology for a small scale micro gas turbine (MGT). It is used for a combined heat and power plant (CHP) with an electrical power output of 3 kW, using natural gas as fuel. Flameless oxidation is characterized by a flame distributed over a large volume and a high internal recirculation of flue gas. Considering the high combustor inlet temperatures up to 1000 K as required for this application, the FLOX®-combustion concept offers various advantages compared to swirl-stabilized combustion systems in terms of flashback risk and exhaust gas emissions.

This paper describes the detailed characterization of the jet-stabilized combustor. Two versions of the combustor were tested, one generic and one modified version suitable for the integration into the micro gas turbine at an atmospheric test rig with optical access. The stable operating range, including lean blow out (LBO) limits, was determined for varying equivalence ratios, thermal powers and preheat temperatures. The influence of these parameters on the combustion characteristics is discussed. Furthermore, the shape and location of the heat release zone is investigated with OH*-chemiluminescence (OH* CL). The exhaust gas emissions NOx, CO and unburned hydrocarbon (UHC) were also measured.

The results demonstrate that the developed combustor design ensures stable and reliable performance. It also offers a high operational flexibility and low pressure loss with NOx, CO and UHC emissions far below regulation limits for all relevant engine conditions.
Numerical Simulations on Flow Separation Within an Axial Turbine at Very Low Reynolds Number
Authors: Wang Xiaodong , Liang Liping , Kang Shun
Published: August 2015

Reynolds number has significant impact on the aerodynamic performance of axial turbines. The internal flow within the stator of a low pressure turbine could be all laminar when the inlet Reynolds number is very low, and large flow separation may occur on the suction surface of the blade. The separated laminar boundary layer and the wake have strong unsteady interactions with the main flow in rotor passages. In order to investigate the laminar flow separation and the interaction, both laminar flow simulation and detached eddy simulation (DES) have been performed on a low speed axial turbine under a very low Reynolds number condition in this paper. For comparison, fully laminar modeling, transitional modeling and fully turbulent modeling are performed, also. The comparison between the computational results and the experimental results shows that both the laminar modeling and transition modeling can capture the laminar separation on the suction side of the stator blade accurately. The separation region locates in a thin zone strengthening from the blade tip to the hub, which is induced by the tip passage vortex. The separation generates a high turbulence intensity zone at the stator outlet. However, this zone in laminar simulation is smaller than that in the experimental due to the absence of turbulence disturbances. Fully turbulent modeling predicts a delayed separation and a smaller separation region. Detached eddy simulation is performed for single stator row, which gives better predictions for both the flow separation and high turbulent zone. The detailed flow structures of the secondary vortices of the stator, the rotor passage vortex and the tip leakage vortex are illustrated. The simulation results show that the laminar separation has obvious three dimensional behaviour. The radial movement of the horse shoe vortex is the main disturbance to the flow separation.
Analysis of Mistuned Blade Vibrations Based on Normally Distributed Blade Individual Natural Frequencies
Authors: Figaschewsky Felix , Kühhorn Arnold
Published: August 2015

With increasing demands for reliability of modern turbomachinery blades the quantification of uncertainty and its impact on the designed product has become an important part of the development process. This paper aims to contribute to an improved approximation of expected vibration amplitudes of a mistuned rotor assembly under certain assumptions on the probability distribution of the blade’s natural frequencies. A previously widely used lumped mass model is employed to represent the vibrational behavior of a cyclic symmetric structure. Aerodynamic coupling of the blades is considered based on the concept of influence coefficients leading to individual damping of the traveling wave modes. The natural frequencies of individual rotor blades are assumed to be normal distributed and the required variance could be estimated due to experiences with the applied manufacturing process. Under these conditions it is possible to derive the probability distribution of the off-diagonal terms in the mistuned equations of motions, that are responsible for the coupling of different circumferential modes. Knowing these distributions recent limits on the maximum attainable mistuned vibration amplitude are improved. The improvement is achieved due to the fact, that the maximum amplification depends on the mistuning strength. This improved limit can be used in the development process, as it could partly replace probabilistic studies with surrogate models of reduced order. The obtained results are verified with numerical simulations of the underlying structural model with random mistuning patterns based on a normal distribution of individual blade frequencies.
Some Experiences About the Impact of Unsteadiness in Turbine Flows
Authors: Bellucci Juri , Rubechini Filippo , Arnone Andrea
Published: August 2015

This paper describes some experiences about impact of unsteadiness in turbine flows, with a special focus on the effects of potential interaction on aerodynamic performance. The main motivation consists in trying to identify some design areas in which some further margins of improvement could be found, provided the designer chooses the proper computational framework. The underlying idea is that the approximations associated with the steady-state picture of a turbine stage might prevent the designer from unlocking the full potential of the stage, especially when the design requirements imply a challenging aerodynamics. To this end, three common design topics are presented in which the step from the classical steady-state approach to the time-accurate one unveils relevant issues, which in turn have an impact on aerodynamic performance: stator/rotor interaction in transonic stages, the choice of the axial gap between stator and rotor, and the choice of the blade count ratio. In all reported cases, significant departures are found between steady and time-averaged results, and the basic fluid mechanisms responsible for them are examined. In particular, an attempt is made to emphasize limitations deriving from of the steady-state picture of the turbine flow field, in order to warn the designer about the possible traps of the steady-state assumption.
Aerodynamic Analysis of Film Cooling Jet Under Different Main Stream Pressure Gradient
Authors: Qin Yanmin , Yin Hong , Ren Jing , Jiang Hongde
Published: August 2015

Streamwise pressure gradient is an important characteristic of the turbine flow and compound angle film cooling is a sufficient way to improve cooling performance. Both experimental and numerical studies are carried out to investigate the effect of streamwise pressure gradient and film cooling hole compound angle on aerodynamic loss of film cooling. Stronger mainstream favorable pressure gradient leads to a larger discharge coefficient. The effect of momentum supplement of the coolant jet with large blowing ratios is significant when pressure loss coefficient is investigated. Kinetic loss coefficient considering the kinetic energy of the coolant jet is used to investigate the overall aerodynamic loss of film cooling. The kinetic loss coefficient increases with blowing ratio. Favorable pressure gradient decreases the loss coefficient. The boundary layer is quite thick for adverse and moderate favorable pressure gradient case that the coolant jet remains within the boundary layer which increases the mixing loss. The kinetic loss coefficient of compound angle film cooling is about 40% higher than the axial hole. This is due to the dissipation of the momentum component in the spanwise direction and the stronger shearing between the single large vortex formed by the compound angle injection with the main flow.
Stability Criteria for Standing and Spinning Waves in Annular Combustors
Authors: Ghirardo Giulio , Juniper Matthew P. , Moeck Jonas P.
Published: August 2015

Rotationally symmetric annular combustors are of practical importance because they generically resemble combustion chambers in gas turbines and aeroengines, in which thermoacoustically driven oscillations are a major concern. We focus on thermoacoustic oscillations of azimuthal type, neglect the effect of the transverse acoustic velocity in the azimuthal direction, and model the heat release rate as being dependent only on the pressure in the combustion chamber. We study the dynamics of the annular combustor with a finite number of compact flames equi-spaced along the annulus, and characterise the flames’ response with a describing function. We discuss with broad generality the existence, amplitudes and the stability of standing and spinning waves, as a function of: 1) the number of the burners; 2) the damping in the chamber; 3) the flame describing function. These have implications on industrial applications, the future direction of investigations, and for what to look for in experimental data. We then present as an example of application the first theoretical study of triggering in annular combustors, and show that rotationally symmetric annular chambers can experience stable standing solutions.
On the Development of Strategies for an Efficient Semi-Automated Hex-Meshing Process of Complex Jet Engine Component Assemblies
Authors: Böhm H. , Hornig A. , Langkamp A. , Gude M. , Keskin A.
Published: August 2015

A significant proportion of the work effort for a whole engine analysis is spent for prep-processing tasks especially for component assemblies and complex structural components. With respect to the generation of a pure hexahedral mesh, the work effort increases due to the absence of an automatic method to generate high quality hexahedral meshes for an arbitrary geometry. In addition, the time-consuming hexahedral meshing process contains numerous, repetitive tasks for large and complex assemblies due to similar and identical components.

In this work a modular strategy for hexahedral meshing of large and complex assemblies was explored with the aim to reduce and to simplify the development process due to a prospective semi-automation of time-consuming routines. The procedure bases on an initial identification and classification of each component of the whole assembly regarding e.g. overall meshing complexity. Meshing relevant parameters were identified for geometry preparation and hexahedral meshing itself. Furthermore, for semi-automation the software package NX (Siemens NX Software), in particular the incorporated automation tool Product Template Studio (PTS) was investigated which enables an automated re-meshing of the geometry model in case of design changes.
Development Approach to the Combustor of Gas Turbine for Oxy-Fuel, Supercritical CO2 Cycle
Authors: Iwai Yasunori , Itoh Masao , Morisawa Yuichi , Suzuki Shinju , Cusano David , Harris Mark
Published: August 2015

As global demand for energy increases while environmental regulations tighten, novel power generation cycles are being developed to meet market needs while accommodating green requirements. The Allam cycle is an approach (with high pressure, low pressure ratios, oxygen-fuel combustion and CO2 as a working fluid) that efficiently produces power in a compact plant, avoids NOx emissions, makes efficient use of clean-burning methane (natural gas) and can generate high-pressure carbon dioxide for enhanced oil and gas recovery in the field. The cycle requires oxy-fuel-CO2 combustion at approximately 30MPa and 1150° C turbine inlet temperatures.

Due to its relatively compact size (owing to the high operating pressures), the Allam cycle technology can be implemented for a low cost in relative existing power plants, and given the current economic climate, natural gas is the most financially appealing application. Meeting environmental regulations for decades to come, the cycle can dramatically lower the cost of electricity.

The critical path for plant implementation lies in demonstrating efficient, stable combustion at 30MPa. Similar pressures have been demonstrated in rocket engine systems, where reusability typically means 3 to 4 hot fires and surviving 8 to 32 minutes lit. The technical challenge here lies in designing durable hardware capable of thousands of hours of continuous operation and efficient combustion over the range of conditions required in a power plant. Production of clean CO2 exhaust (ideally, free of O2 and CO) is another challenge that will drive plant viability.
Experimental Investigation of Steady State and Transient Heat Transfer in a Radial Turbine Wheel of a Turbocharger
Authors: Tadesse Hailu , Rakut Christian , Diefenthal Mathias , Wirsum Manfred , Heuer Tom
Published: August 2015

Turbochargers make an essential contribution to the development of efficient combustion engines by increasing the boost pressure. In recent years, there has been a trend towards enhanced turbine inlet temperatures, which cause heat fluxes within the turbocharger. Due to the high rotational speed, the centrifugal force and thermal stress of the turbine components rise inevitably. In addition to the enhanced temperature level, due to the variation of the load and speed of the engine in cold start, acceleration and deceleration periods, the turbine inlet temperature is changing permanently, which leads to higher thermal loads. The flow state and thus the heat transfer in the turbocharger are constantly changing within a single cycle. This induces an unsteady temperature profile, which is essential for the thermal stress and thus the prediction of the component life cycle.

The present study reports about the results of the experimental steady state and transient heat transfer investigations of a turbocharger which are conducted at a hot gas test rig. The investigations are performed transiently between different steady state operating points. In order to simulate the real driving conditions, the turbine inlet temperature is changed between a high and low temperature level abruptly (thermal shock) or cyclically at an approximately constant mass flow. The flow parameters at the inlet and outlet of the turbine as well as material and surface temperatures of the turbine wheel and casing are recorded. Additionally the compressor as well as the bearing housing inlet and outlet conditions are measured. The heat flux between the components is analyzed by means of the measured data.
Feasibility Study on Dehydrogenation of LOHC Using Excess Exhaust Heat From a Hydrogen Fueled Micro Gas Turbine
Authors: Hampel Balbina , Bauer Stefan , Heublein Norbert , Hirsch Christoph , Sattelmayer Thomas
Published: August 2015

In recent years, renewable energy technologies have received increasing attention. However, the constant availability of renewable energies is not predictable, so that technologies for excess energy storage become increasingly important. One possibility for the technical implementation of such a storage technology is to bind hydrogen, produced using this excess energy, to liquid organic compounds, so-called Liquid Organic Hydrogen Carriers (LOHC), where hydrogen is bound to a H2-lean LOHC molecule in an exothermal hydrogenation reaction. The dehydrogenation process releases the stored hydrogen in an endothermal reaction. This technology offers advantages such as storage and transport safety, along with the high energy density. LOHC systems can assist in the realization of future distributed energy supply networks, as well. Micro gas turbines (MGT) play an important role in distributed energy supply, so that the coupling of a hydrogen fueled MGT with a reactor for the dehydrogenation process is a desirable achievement. In such a combined system, the excess exhaust enthalpy can be used to maintain the endothermal dehydrogenation reaction without affecting the overall efficiency of the gas turbine. This paper investigates the feasibility of a direct coupling between a hydrogen fueled recuperated micro gas turbine and the dehydrogenation process using the excess exhaust heat. For this purpose, a numerical simulation based on energy balances and thermodynamic equilibrium is implemented to model the process. Primary criteria for the evaluation of the process feasibility are the MGTs exhaust gas temperature, the exhaust gas mass flow rate, and the LOHC mass flow rate through the dehydrogenation unit. These three parameters specify the mass flow rate of LOHC, which can be dehydrogenated and thus, the mass flow rate of released hydrogen. Using the implemented numerical model, the suitability of two different LOHCs, N-Ethylcarbazole and an industrial heat transfer oil is investigated at two different pressure levels with respect to thermodynamic feasibility and process efficiency. The results show that the usable excess enthalpy in the exhaust gas of the investigated Turbec T100 MGT is sufficient to release enough hydrogen for re-use as fuel in the micro turbine process for three of the four investigated cases.
Automated Optimisation of T-Root Rotor Grooves With B-Splines and Finite Element Analysis
Authors: Henson Jonathan , Dolan Richard , Thomas Gareth , Georgakis Christos
Published: August 2015

An Alstom tool is described for the automated and simultaneous design optimisation of 2 and 4-hook T-root grooving of multiple steam turbine rotor stages in order to minimise the peak stress. The finite element axisymmetric thermal-stress calculation is performed with Abaqus in a few hours on modest hardware. The tool embeds Python scripting to facilitate the rotor groove model definition and meshing within Abaqus/CAE, with emphasis placed on minimising the effort for the initial setup. Rotor groove shapes are described with B-splines, maintained and modified within the in-house tool. Their shape is progressively refined as directed by a hybrid evolutionary-gradient based optimisation engine in order to achieve the minimum stress objective. In the region of highest stress, the groove boundary shape adjusts as the optimisation proceeds to conform to the local contours of stress. Application to a low pressure steam turbine rotor demonstrates comparable or lower stresses with this tool compared to those from manual expert optimisation. The method can be readily extended to other geometric entities on the rotor described with B-spline curves, e.g. cavities, seals.
Impact of a Cooled Cooling Air Installation on the External Aerodynamics of a Gas Turbine Combustion System
Authors: Walker A. D. , Guo L.
Published: August 2015

The trend for higher overall pressure ratios means that turbine entry temperatures are continually increasing. Furthermore, the development of lean, low-emission combustion systems reduces the availability of cooling air and is accompanied by new problems at the combustor/turbine interface. For example, the exit temperature traverse differs from that found in traditional rich-burn combustors with increased swirl and a much flatter profile. Effectively cooling the turbine components is becoming increasingly difficult. One solution is to employ cooled cooling air (CCA) where some of the compressor efflux is diverted for additional cooling in a heat exchanger located in the by-pass duct. An example CCA system is presented which includes an off-take within the dump cavity and the addition of radial struts within the pre-diffuser through which the cooled air is returned to the engine core. This paper addresses the impact this CCA system has on the combustion system external aerodynamics. This included the development of a fully annular, isothermal test facility which incorporated a bespoke 1.5 stage axial compressor, engine relevant outlet guide vanes, pre-diffuser and combustor geometry. A datum aerodynamic performance was established for a non-CCA configuration with a clean, un-strutted pre-diffuser. Results for this baseline CCA system demonstrated that inclusion of a bleed in the dump cavity had limited effect on the overall flow field. However, the inclusion of struts within the pre-diffuser caused a reduction in area ratio and a notable increase in system loss. Consequently an alternative pre-diffuser was designed (using CFD) with the aim of increasing the area ratio back to that of the un-strutted datum. A so-called hybrid diffuser was designed in which the CCA bleed was moved to the pre-diffuser outer wall. The bleed was then used to re-energize the boundary layer, preventing flow separation, enabling the area ratio to be increased close to the datum value. The mechanisms of the hybrid diffuser are complex; the geometry of the off-take and its location with respect to the OGV and strut leading edge were seen to be critical. Experimental evaluation of the final design demonstrated the effective operation the hybrid diffuser with the result that the system loss returned to a level close to that of the datum. Only small differences were seen in the overall flow field.
Accurate Blade Tip Timing Limits Through Geometry Mistuning Modeling
Authors: Kaszynski Alexander A. , Brown Jeffrey M.
Published: August 2015

Blade tip timing (BTT) is a commonly used non-intrusive stress measurement system to estimate the operational stresses within an engine’s rotors without the costly installation of strain gauges that can add additional stiffness to the rotor. BTT systems are now standard on many engine tests and ensure safe operations by avoiding running near maximum rotor stress limits. Since these systems measure blade time of arrival (TOA), processes are applied to first convert this data to displacement and then to stress. This effort focuses on the conversion of displacement to stress where the the classic approach utilizes nominal geometry obtained from an “as-designed” nominal model and creates computes the mode shapes using finite element analysis (FEA). The predicted mode shapes of the cyclic analysis reveal the relationship between maximal blade stress and tip displacement for a given nominally designed rotor. However, manufactured rotors deviate from nominal design due to inherent variability in the machining procedures. It is now possible through high fidelity optical geometry collection systems to obtain more accurate BTT limits using measured IBR geometry from as-manufactured rotors. It will be shown that due to the high variability of blade-to-blade geometry obtained from an optically scanned rotor that the BTT limits can vary significantly between blades. A method is also developed that allows comparisons between cyclic sector and full rotor FEA. This research suggests to optimize BTT probe placement not only to measure the maximum expected deflection given blade tip mode shapes, but also to account to for blade to blade geometric variation.
Transient Response of Control Stage Blade Disk due to Partial Admission by a Reduced Method
Authors: Kan Xuanen , Xu Zili , Zhao Yu , Dou Baitong , Zhao Wenbin
Published: August 2015

Partial admission can improve the thermal efficiency of steam turbines at low loads, but a non-uniform flow in circumference will be caused inevitably at the same time. That makes control stage blade subject to complex load, leading to the high cycle fatigue. Therefore, it is important to calculate and accurately analyze transient response of control stage blade disk due to partial admission. However, the large number of degrees of freedom of the practical control stage blade disk will lead to an extremely high computational cost when the finite element method is used. A strategy for reducing the number of degrees of freedom based on the component modal synthesis (CMS) method is presented. CMS method is used to generate a super-element of one group of 4 blades. The cyclic symmetric property is used to generate super-elements for other groups of blades through circumferential rotation and coordinate transformation. The total number of degrees of freedom is reduced to 1.21% of the original DOF. When the rotating blades enter and leave the arc of admission under partial admission conditions, they are subject to the effect of shock loading. The length of the effect of shock loading depends on the rotating blade pitch and the peak of effect of shock loading depends on stage pressure ratio. The displacement response of control stage blade disk under different shock coefficients (1.6, 2.5, 4) is calculated. This paper analyses the vibrations of blade disk under high frequency force caused by nozzles under partial admission conditions. The results show that compared to the shock coefficient of 1.6 the maximum displacement response increased by 27.3% and 72.6% for shock coefficients 2.5 and 4. In addition, a beat phenomenon is found in displacement response of blade disk under high frequency force. The FFT of the response and excitation and the ZZENF of blade disk indicate that the composite vibration of 6050Hz, 6000Hz and 4900Hz these 3 kinds of harmonic vibrations is the main reason of the beat phenomenon.
Determination of Criteria for Flame Stability in an Annular Trapped Vortex Combustor
Authors: Xavier Pradip , Pires Mickael , Vandel Alexis , Renou Bruno , Cabot Gilles , Boukhalfa Mourad A. , Cazalens Michel
Published: August 2015

Development of lean premixed (LP) combustion is still a challenge as it results in considerable constraints for the combustor design. Indeed, new combustors using LP combustion are more prone to flashback, blow-off, or even thermo-acoustic instabilities. A detailed understanding of mechanisms leading to such extreme conditions is then crucial to reduce pollutant emissions, widen the range of operating conditions, and reduce design time. This paper reports the experimental study of an innovative LP trapped vortex combustor (TVC). The TVC concept uses a recirculating rich flow trapped in a cavity to create a stable flame that continuously ignites a main lean mixture passing above the cavity. This concept gave promising performances but some workers highlighted the existence of combustion instabilities for some operating conditions. Detailed studies have therefore been carried out in order to understand the occurrence of these drastic operating conditions. Results showed that the cavity flow dynamics in conjunction with the location of the interfacial mixing zone (between the cavity and the mainstream) were the driving forces to obtain stable combustion regimes.

The goal of this work has been to take advantage of these detailed recommendations to determine stability maps, trends, and dimensionless parameters which could be easily used as early-design rules. For this reason, the study introduced a simple and robust criterion, based on the global pressure fluctuation energy. The latter was used to distinguish stable and unstable modes. An aerodynamic momentum flux ratio and a chemical stratification ratio (taken between the cavity and the mainstream) were defined to scale all measurements. Results indicated that the mainstream velocity was critically important to confine the cavity and to prevent combustion instabilities. Remarkably, this trend was verified and even more pronounced for larger cavity powers. In addition, flame stabilization above the cavity resulted in the existence of specific stratification ratios, in order to obtain a soft gradient of gas composition between the rich and lean regions. Finally, a linear relation between the mainstream and cavity velocities became apparent, thereby making possible to simply predict the combustor stability.
Development and Aerothermal Investigation of Integrated Combustor Vane Concept
Authors: Jacobi Simon , Rosic Budimir
Published: August 2015

This paper presents the development and aerothermal investigation of the Integrated Combustor Vane concept for power generation gas turbines with individual can combustors. In this novel concept, first introduced in 2010 [1], the conventional Nozzle Guide Vanes (NGVs) are removed and flow turning is achieved by vanes that extend the combustor walls. The concept is developed using the inhouse CFD code TBLOCK. Aerothermal experiments are conducted using a modular high speed linear cascade, designed to model the flow at the combustor-vane interface. The facility comprises two can combustor transition ducts and either four Conventional Vanes (CVs) or two Integrated Vanes (IVs). The experimental study validates the linear CFD-simulations of the IV development. Annular full stage CFD-simulations, used to evaluate aerodynamics, heat transfer and stage efficiency, confirm the trends of the linear numerical and experimental results and thus demonstrate the concept’s potential for real gas turbine applications. Results show a reduction of the total pressure loss coefficient at the exit of the stator vanes by more than 25% due to a reduction in profile- and endwall-loss. Combined with an improved rotor performance these aerodynamic benefits result in a gain in stage efficiency of above 1%, illustrated by unsteady stage simulations. A distinct reduction in HTC levels on vane surfaces, in the order of 25%–50%, and endwalls is observed and attributed to an altered state of boundary layer thickness. The development of IV’s endwall- and LE-cooling geometry shows a superior surface coverage of cooling effectiveness, and the cooling requirements for the first vane are expected to be halved. Moreover, by halving the number of vanes, simplifying the design and eliminating the need for vane LE film cooling, manufacturing and development costs can be significantly reduced.
Design Consideration of Fogging and Wet Compression Systems as Function of Gas Turbine Inlet Duct Configurations
Authors: Chaker Mustapha , Mee Thomas R.
Published: August 2015

Ambient temperature strongly influences gas turbine performance with power output dropping between 0.5 to 0.9 % for every 1 °C of temperature rise. This is accompanied by a significant increase in the heat rate, resulting in increased operating costs. As an increase in power demand often coincides with high ambient temperatures, power augmentation during the hot part of the day is of value to gas turbine operators. This is true for both the utility industry, where peak-rate power payments often apply, and to the petrochemical and process industries, where throughput can be improved or held constant as ambient conditions change. Evaporative fogging and wet compression are relatively low-cost solutions for recovering reduced gas turbine output.

This paper addresses the important design considerations for fogging and wet compression systems for different sized gas turbines with different duct configurations. These design considerations include the selection of appropriate ambient psychrometric design conditions, selection of appropriate fog nozzles and the optimization of fog nozzle manifold locations in the inlet ducts. For this research, Computational Fluid Dynamics (CFD) software is used to analyze the interaction between the atomized water droplets and the airflow within the confined geometry of inlet air ducts. The location of the nozzle manifolds is simulated in the inlet ducts for four different inlet duct configurations. Experimentally obtained spray data is used to simulated water atomization in the inlet ducts. The effect of the duct geometry is analyzed in term of fog-spray cooling efficiency based on both nozzle manifold location and droplet size distribution.
Mechanical Design and Manufacturing of Improved GT24 SEV Burner
Authors: Tschuor Remigi , Fruechtel Gerhard , De Jonge Jeffrey , Meng Patrik , Graber Christof
Published: August 2015

This work details an integrative mechanical design process for combustion chambers. A major challenge in the development process of modern gas turbine combustors is to achieve low NOx emissions whilst ensuring the stability of the combustion process at all phases of the guaranteed operation regimes. The burner hardware plays a crucial role in determining emissions and maintaining a suitable aero- and thermo-acoustic performance of the combustion process. In addition, the burner hardware must be manufacturable at a reasonable cost. Efficient burner development requires a design process able to judge this behaviour at an early phase. This process must predict the combustor behaviour, the thermoacoustic mechanisms, the mechanical integrity as well as the life cycle of the burner. Based on the Alstom SEV (Sequential EnVironmental) burner for the reheat combustor of the GT24 gas turbine, this paper describes an exemplary process for the mechanical design, mechanical integrity, cooling and manufacturing. The acoustic aspects and the successful engine validation are addressed in separate papers.

The improved GT24 SEV burner has been developed with the following key features:

a) A Straight Mixing Zone aerodynamic design (SMZ) resulting in increased velocity and improved reactant pre-mixing

b) Multi-layered and braze constructed Front Panel design integrating combined and novel cooling and high frequency damping features

c) Optimised alloy selection for extended lifetime and improved manufacturability

In addition to the mechanical design and manufacturing process further details will be provided on aspects of cooling and mechanical integrity.
The Relative Performance of External Casing Impingement Cooling Arrangements for Thermal Control of Blade Tip Clearance
Authors: Choi Myeonggeun , Dyrda David M. , Gillespie David R. H. , Tapanlis Orpheas , Lewis Leo V.
Published: August 2015

As a key way of improving jet engine performance, a thermal tip clearance control system provides a robust means of manipulating the closure between the casing and the rotating blade tips, reducing undesirable tip leakage flows. This may be achieved using an impingement cooling scheme on the external casing. Such systems can be optimized to increase the contraction capability for a given casing cooling flow. Typically this is achieved by changing the cooled area, local casing features such as the external flanges, or the external cooling geometry. This paper reports the effectiveness of a range of impingement cooling arrangements in typical engine casing closure system. The effects of jet-to-jet pitch, number of jets, inline and staggered alignment of jets, on an engine representative casing geometry are assessed through comparison of the convective heat transfer coefficient distributions as well as the thermal closure at the point of the casing liner attachment. The investigation is primarily numerical, however, a baseline case has been validated experimentally in tests using a transient liquid crystal technique. Steady numerical simulations using the realizable k-ε, k-ω SST and EARSM turbulence models were conducted to understand the variation in the predicted local heat transfer coefficient distribution. Constant mass flow rate was used as a constraint at each engine condition, this approximately pertaining to a constant feed pressure when the manifold exit area is constant. Sets of local heat transfer coefficient data generated using a consistent modelling approach were then used to create reduced order distributions of the local cooling. These were used in a thermo-mechanical model to predict the casing closure at engine representative operating conditions.
Development of a New Titanium 54’’ LSB: Static and Dynamic Assessment
Authors: Hlous Jan , Misek Tomas , Kubin Zdenek , Mestanek Petr
Published: August 2015

Today’s power generation market requests high efficiency for steam turbines. One key factor in fulfilling these demands is the increase of exhaust area: efficiency is increased by reducing exhaust losses and lower costs are reached by a lower number of flows. The 54″ last stage blade for a steam turbine has been developed with the application of modern design features. It was designed with integral cover, mid-span tie-boss connection, and straight fir-tree dovetail. Blades are continuously coupled by the blade untwist due to the centrifugal force, so vibration control and increased structural damping are provided.

This paper describes in detail the design characteristics used in the development of the blade including non-linear structural analysis methods. The blade airfoil was optimized from point of view of minimization of its centrifugal force. The blade was well tuned in order to have natural frequencies safely away from possible excitation. Because of connection members, the number of the resonant vibration modes can be reduced by virtue of the vibration characteristics of the circumferentially continuous blades. Coupled rotor-blade frequencies were also analysed.

Extensive material tests were performed to check titanium properties, which showed lower erosion and low cycle fatigue properties. New procedures were developed to improve titanium characteristics, so the material behaviour is acceptable for last stage blade construction.

To validate the results, full scale rotational vibration test in vacuum chamber was carried out and suitable dynamic properties as well as mechanical integrity of the blade were confirmed.
Film Cooling Parameter Waveforms on a Turbine Blade Leading Edge Model With Oscillating Stagnation Line
Authors: Rutledge James L. , Rathsack Tylor C. , Van Voorhis Matthew T. , Polanka Marc D.
Published: August 2015

It is necessary to understand how film cooling influences the external convective boundary condition involving both the adiabatic wall temperature and the heat transfer coefficient in order to predict the thermal durability of a gas turbine hot gas path component. Most studies in the past have considered only steady flow, but studies of the unsteadiness naturally present in turbine flow have become more prevalent. One source of unsteadiness is wake passage from upstream components which can cause fluctuations in the stagnation location on turbine airfoils. This in turn causes unsteadiness in the behavior of the leading edge coolant jets and thus fluctuations in both the adiabatic effectiveness and heat transfer coefficient. The dynamics of h and η are now quantifiable with modern inverse heat transfer methods and non-intrusive infrared thermography. The present study involved the application of a novel inverse heat transfer methodology to determine time resolved adiabatic effectiveness and heat transfer coefficient waveforms on a simulated turbine blade leading edge with an oscillating stagnation position. The leading edge geometry was simulated with a circular cylinder with a coolant hole located 21.5° downstream from the leading edge stagnation line, angled 20° to the surface and 90° to the streamwise direction. The coolant plume is shown to shift in response to the stagnation line movement. These oscillations thus influence the film cooling coverage and the time-averaged benefit of film cooling is influenced by the oscillation.
Data Analytics Methods for Wind Energy Applications
Authors: Ding Yu , Tang Jiong , Huang Jianhua Z.
Published: August 2015

In the wind industry, it is important to assess a turbine systems response under different wind profiles. For instance, a wind-to-power relationship is crucial for wind power forecast, and a wind-to-stress relationship is important for selecting critical design parameters meeting the reliability requirement. Given the complexity involved in a turbine system, it is impossible to write a neat, analytical expression to underlie the above-mentioned relationships. Almost invariably does the wind industry resort to data driven methods for a solution, namely that wind data and the corresponding turbine response data (bending moments or power outputs) are used together to fit empirically the functional relationship of interest. This paper presents a couple of nonparametric data analytic methods relevant to wind energy applications with real life example for demonstration.
Investigation Into Coupling Techniques for a High Pressure Turbine Blade Tip
Authors: Caloni Stefano , Shahpar Shahrokh
Published: August 2015

In this paper the aero-thermal performance of a high pressure turbine rotor blade is investigated, making use of coupled and uncoupled simulations. The fluid domain is solved via Finite Volume analyses whilst Finite Elements are used in the solid domain. In the CFD model, a temperature distribution is imposed as a boundary condition at the interfaces between the fluid and the solid domain. In the corresponding FE model, a convective zone is applied. The parameters of the convective zone are computed from the CFD analysis. In the uncoupled simulations, the convective zone can make use of a two or three parameters model. In the first case, a linear relation between the heat flux and the wall temperature is assumed, whilst in the second model a parabolic relation is adopted. In the coupled simulation, an iterative process is used where the temperature distribution in the CFD model and the parameters of the convective zone in the FE model are updated at every iteration. The aforementioned three models are applied to a shroudless blade with and without an internal cooling system. When the blade is uncooled, all three methods offer a close prediction of the temperature reached by the component. However, when the blade is internally cooled the convective zone based on two parameters fails to provide a trustworthy prediction. The three-parameter convective zone, on the other hand, shows a closer agreement with the coupled simulation. The couple simulation is then applied to investigate the performance of three different tip configurations, a simple cavity, a novel contoured cavity and a tip with a small winglet. The small winglet shows a significant improvement in aerodynamic performance as well as a reduction in the operative temperature.
Open Rotor Design Strategy: From Wind Tunnel Tests to Full Scale Multi-Disciplinary Design
Authors: Vlastuin Jonathan , Dejeu Clément , Louet Anthony , Talbotec Jérôme , Lepot Ingrid , Lonfils Timothée , Leborgne Michaël
Published: August 2015

For several years, Safran has been involved in the design and optimization of contra rotating open rotors. This innovative architecture is known for allowing drastic reduction in fuel burn, but its development is facing complex technological challenges such as acoustics, aerodynamics, and weight penalty due to the mechanical complexity of an Open Rotor. Since 2010, Safran has been developing the experimental test bench HERA (1/5 mock-up scale) to improve the understanding of the complex aerodynamics and acoustics phenomena involved in the counter rotating propellers configuration. Isolated and installed low speed and high speed wind tunnel campaigns, including PIV measurements have been extremely helpful in defining design guidelines for full scale open rotor specification. These tests have been used as CFD feed-back among other purposes. An iterative process involving CFD optimization (in close collaboration with Cenaero) and wind tunnel test campaigns has been developed over the last 4 years and has led to the definition of an innovative design strategy, which has been successfully tested during the process of the full scale counter rotating propellers design for the SAGE2 ground test demonstrator engine. This phase has evidenced the absolute necessity of a multi-disciplinary design method when it comes to full scale and “rig-ready” design. Ensuring high propulsive efficiency and at the same time, minimizing the acoustic level, while maintaining severe mechanical constraints such as weight, inertia and proper dynamic positioning under control, requires a dedicated and integrated “all inclusive” design process.

The aim of this paper is to present the design methodology and some of the wind tunnel tests results carried out over the last 4 years, which have led to the definition of a novel multidisciplinary design methodology that involves CFD, FEM and acoustics.