bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Combustion Noise Generation in a Realistic Turbine Stage Configuration
Authors: Becerril C. , Moreau S. , Gicquel L. Y. M.
Published: August 2018

Generation of combustion noise is here studied in a realistic turbine stage configuration, where the temperature fluctuations generated by an aeronautical burner (responsible of the direct combustion noise generation, often neglected in most of the studies) are modelled using a cylindrical fluctuating energy source term placed upstream of the inlet guide vanes. This modelling not only better accounts for the actual physical combustion noise generation phenomena, but also for the actual stratification of temperature at the combustor exit and covers a broader range of exciting frequencies as in actual engines. The temperature fluctuations generated by this realistic fluctuating energy source term are then convected through the turbine stage and the resulting noise is analyzed and compared with previous LES results with ideal monochromatic entropy forcing and analytical compact methods. New physical insight on the various noise generation mechanisms and mode conversion is also provided.
Experimental Determination of Lean Flammability Limits of Renewable and Process Gas Mixtures at Elevated Temperature and Pressure Conditions
Authors: Jaimes Daniel , McDonell Vincent , Samuelsen Scott
Published: August 2018

Elevated pressure and temperature conditions are widely encountered during gas turbine operation. To avoid unexpected ignition and explosion of mixtures of fuel and air under these conditions, it is imperative to identify the flammability limits of relevant fuel mixtures. Common fuels include process gases such as natural gas, coke oven gas and IGCC syngas fuel. The flammability limits of pure fuels and common gas/air mixtures have been widely reported, however a significant lack of flammability data for fuel mixtures relevant for use in gas turbines as well as data at elevated pressure and temperature conditions is available. The objective of this study is to characterize the flammability limits of fuel/air mixtures and their dependence on initial temperature and pressure. Experimental studies of lean flammability limits (LFLs) for methane, hydrogen, and carbon monoxide, in addition to mixtures of these gases (i.e. CH4/H2, H2/CO, and CH4/CO2) were performed at temperatures up to 200 °C and pressures up to 9 bar. ASTM Standard E918 (1983) provided the framework for tests using a one-liter pressure-rated test cylinder in which the fuel-air mixtures were prepared and then ignited. Flammability is determined using a 7% and 5% pressure rise criterion per the ASTM E918 and European EN 1839 standards, respectively. The LFLs for each gas and gas mixture are found to decrease linearly with increasing temperature for the temperature range tested. The LFLs of hydrogen and mixtures containing hydrogen are observed to increase with an increase in the initial pressure, whereas the LFLs of all other mixtures exhibit a negligible dependence on pressure. For mixtures, predicted LFL values obtained using Le Chatelier’s mixing rule (LC) are fairly consistent with the experimentally determined values near ambient conditions, however it is not recommended for use at elevated pressure and/or temperature. Finally, the experimental data presented in this study are compared with previous experimental studies, flammability limits calculated using numerical methods, and past studies of predicted LFL values for similar fuel/air mixtures. The purpose for characterizing the flammability limits for these gaseous mixtures is to extend the results to developing appropriate procedures for the safe industrial use of renewable gases, such as bio-derived methane, biogas composed mainly of methane and carbon dioxide, and renewably derived syngas which contains large quantities of hydrogen and carbon monoxide gas.
The Effect of Turbulent Scales on Low-Pressure Turbine Aerodynamics: Part B — Scale Resolving Simulations
Authors: Schwarzbach Felix , Müller-Schindewolffs Christoph , Bode Christoph , Herbst Florian
Published: August 2018

Turbulence contains a wide range of scales which form the turbulent spectrum. In low-pressure turbines (LPT) these scales of the turbulent free-stream influence large-scale mixing, the decay of turbulence kinetic energy and the transition of boundary layers through their reception of the small scales. Although these mechanisms are known in principle, the effect of turbulent scales on LPT aerodynamics has not been quantified and analyzed in detail yet.

By means of Large Eddy Simulations (LES) applying the Incompressible Divergence-Free Synthetic Eddy Method (I-DFSEM) — introduced in Part A of this two-part paper — at the domain inlet to impose any desired turbulent boundary condition, the MTU-T161 LPT cascade is investigated under low-speed conditions. The simulations are successfully validated by the experimental results of the turbulent spectrum. In order to separate the effect of turbulence intensity and length scale on the cascade aerodynamics, the turbulent length scale is systematically varied while ensuring similar turbulence intensity at the profile’s leading edge.

The results show an influence of the turbulent spectrum on separation-induced boundary layer transition. It is shown that the separated shear layer is amplified by integral length scales corresponding to frequencies close to the Kelvin-Helmholtz instability. Consequently it affects the turbulent mixing such that the transition point and lengths differ.
Film Cooling Effectiveness From Two-Row of Compound Angled Cylindrical Holes Using PSP Technique
Authors: Wang Nian , Zhang Mingjie , Shiau Chao-Cheng , Han Je-Chin
Published: August 2018

This study investigates the combined effects of blowing ratio and density ratio on flat plate film cooling effectiveness from two-row of compound angled cylindrical holes. Two arrangements of two-row compound angled cylindrical holes are tested: the first row and second row are oriented in staggered but same compound angled direction (β = +45° for the first row, +45° for the second row); the first row and second row are oriented in inline but opposite direction (β = +45° for the first row, −45° for the second row). Each cooling hole is 4 mm in diameter with an inclined angle 30°. The streamwise distance between the two rows is fixed at 4d and the spanwise pitch between the two holes (p) is 4d, 6d, and 8d, respectively. The experiments are performed at four blowing ratios (M = 0.5, 1.0, 1.5, 2.0) and three density ratios (DR = 1.0, 1.5, 2.0). The free stream turbulence intensity is kept at 6%. Detailed film cooling effectiveness distributions are obtained using the steady state pressure-sensitive paint (PSP) technique. The detailed film cooling effectiveness contours are presented and the spanwise averaged film effectiveness results are compared over the range of flow parameters. Film cooling effectiveness correlations are developed for both inline and staggered compound angled cylindrical holes. The results provide baseline information for the flat plate film cooling analysis with two-row of compound angled cylindrical holes.
Design Optimization of Splitter Blades for Rocket Engine Turbopump
Authors: Torre Francesco , Konno Shinichi , Lettieri Claudio , Pini Matteo , Kawata Yutaka
Published: August 2018

In this paper we present and validate a shape optimization framework for the design of splitter blades that extends the operative range under cavitation while maintaining the wetted performance of rocket engine turbopumps. For a target turbopump application, the optimization framework allows for independent changes to the blade angle distributions across the span and to the pitchwise position of the splitter blades while preserving the thickness distributions.

The optimization is conducted with a surrogate-based gradient method. The geometry is optimized at a fixed cavitation number corresponding to a 5% head coefficient dropoff, while constraints are imposed on the wet pump performance. It is found that this approach, coupled with the optimal design points distribution provided by the Design of Experiment method, reduces the computational cost of the optimization process by minimizing the number of multiphase calculations.

The numerical results suggest that the optimized splitter blades successfully increase the pump operative range by 2.2% and increase the head coefficient by 5.3% compared to the baseline case with non-optimized splitters. These results are corroborated by experiments conducted in a closed-loop water test facility. Several pump geometries are tested through rapid prototyping using additive manufacturing. The experimental data validate the optimization framework, demonstrating a 4.7% increase of pump operative range and a 7.6% increase in head coefficient. The calculations are used to gain insight in the physical mechanisms for the performance improvement. The analysis of the results indicates that the improved performance is due to the optimized position and shape of the splitter blades which increase the pump slip factor.
Power to Ice: A Novel Approach to Stabilize Non-Programmable Renewable by Means of Gas Turbine IACC
Authors: Ancona M. A. , Bianchi M. , Branchini L. , Brilloni A. , De Pascale A. , Melino F. , Peretto A.
Published: August 2018

Large penetration of non-programmable energy sources, such as wind, is a challenging issue for grid operators and quick ramping fossil fuel generators. Indeed, the variability and fluctuation of renewables (i.e. rapid change in generation over relatively short time periods) is increasing the need for regulating power. In this context and according to Authors knowledge, the innovative approach proposed in this study is to use a gas turbine equipped with continuous cooling in order to stabilize the power output generation of renewable generators. The gas turbine power boost, obtained thanks to inlet air cooling, will compensate for renewable generators underproduction. On the opposite, in case of renewable generators power output surplus, the excess of power is driven to a compressor chiller device for cold water storage, then used to chill gas turbine inlet air whenever needed.

A detailed performance evaluation on the proposed system is carried out showing the influence of most important parameters (i.e. additional pressure losses introduced with the cooling device, gas turbine models and assumed derating coefficients, etc.).

A feasibility analysis of the investigated system is presented for several case studies in case of wind generators (two different gas turbine models, different wind farm nameplate capacity, different power output set points), investigating the volume of tanks necessary to stabilize wind fluctuations.
A Proposal for Shaft Power Prediction of Centrifugal Compressor Under Wet Gas Conditions
Authors: Kawaguchi Daisuke , Kobayashi Katsutoshi , Bakken Lars Eirik
Published: August 2018

In this study, the influence of wet gas on the fluid performance of a centrifugal compressor was evaluated using a test facility in the Norwegian University of Science and Technology, NTNU. The experimental results indicated that the polytropic efficiency decreased with increases in LMF. One factor of decrease of the polytropic efficiency was an increase in the shaft power. Moreover, we hypothesized that the liquid film on the inner wall of the impeller was discharged from the trailing edge at a circumferential speed by a centrifugal force. Then an expression to predict the shaft power under wet gas conditions on the basis of the hypothesis was built and it was verified that the ratio of the predicted and experimental shaft power agreed well.
The Effects of Combustor Cooling Features on Nozzle Guide Vane Film Cooling Experiments
Authors: Holgate Nicholas E. , Ireland Peter T. , Romero Eduardo
Published: August 2018

Recent advances in experimental methods have allowed researchers to study nozzle guide vane film cooling in the presence of combustor dilution ports and endwall films. The dilution injection creates nonuniformities in temperature, velocity, and turbulence, and an understanding of the vane film cooling performance is complicated by competing influences. In this study, dilution port temperature profiles have been measured in the absence of vane film cooling and compared to film effectiveness measurements in the presence of both films and dilution, illustrating the effects of the dilution port turbulence on film cooling performance. It is found that dilution port injection can create significant effectiveness benefits at the difficult-to-cool vane stagnation region, due to the more turbulent hot mainstream enhancing the mixing of film coolant jets that have left the airfoil surface.

Also explored are the implications of endwall film cooling for infrared vane surface temperature measurements. The reduced endwall temperatures reduce the thermal emissions from this surface, so reducing the amount of extraneous radiation reflected from the vane surface where measurements are being made. The results of a detailed calibration show that the maximum local film effectiveness measurement error could be up to 0.05 if this effect were to go unaccounted for.
Numerical Investigation on the Differences Between Temperature Ratio and Density Ratio in Film-Cooled Endwall
Authors: Yao Ran , Wang Jianhua , Wang Ming , Song Wei
Published: August 2018

This paper presents a numerical investigation on the rationality and reliability of film cooling experiments, in which the realistic temperature ratio (TR) of mainstream to cooling air are substituted by the density ratio (DR) of ambient air to a foreign gas with high density. Today, advanced gas turbines operate at much higher temperatures than the allowable temperature of turbine component materials, which makes it very difficult to achieve real TR in the most of laboratory environments, because the real TRs are usually larger than 2.0. Therefore, the foreign gas (for example CO2) with high density was widely used to obtain a proper density ratio for simulating the mixing process of cooling air with high temperature mainstream thereby. However, the TR effect on film cooling is not completely replaced by DR, because the influence factors of film cooling performances are not only DR, but also the thermal properties of cooling gas and mainstream, such as specific heat capacity, viscosity and conductivity. In this work, a film-cooled endwall is used as specimen, and DRs are controlled by two ways, i.e. changing mainstream temperatures, and using a foreign gas, respectively. The numerical results of film cooling performances at the same DR obtained by the two ways are analyzed and compared. The analysis reveals the difference of film cooling performances between TR and DR on the film-cooled endwall, and the comparison indicated that the errors caused by the substitution of foreign gas are acceptable, only when BR, DR, Re∞ and T∞ are all small, but when BR, DR or Re∞ increases, the relative error cannot be neglected, and it may reach 30% in real running conditions.
Determination of Aerodynamic Damping at High Reduced Frequencies
Authors: Pan Minghao , Petrie-Repar Paul , Mårtensson Hans , Sun Tianrui , Gezork Tobias
Published: August 2018

In turbomachines, forced response of blades is blade vibrations due to external aerodynamic excitations and it can lead to blade failures which can have fatal or severe economic consequences. The estimation of the level of vibration due to forced response is dependent on the determination of aerodynamic damping. The most critical cases for forced response occur at high reduced frequencies. This paper investigates the determination of aerodynamic damping at high reduced frequencies. The aerodynamic damping was calculated by a linearized Navier-Stokes flow solver with exact 3D non-reflecting boundary conditions.

The method was validated using Standard Configuration 8, a two-dimensional flat plate. Good agreement with the reference data at reduced frequency 2.0 was achieved and grid converged solutions with reduced frequency up to 16.0 were obtained. It was concluded that at least 20 cells per wavelength is required. A 3D profile was also investigated: an aeroelastic turbine rig (AETR) which is a subsonic turbine case. In the AETR case, the first bending mode with reduced frequency 2.0 was studied. The 3D acoustic modes were calculated at the far-fields and the propagating amplitude was plotted as a function of circumferential mode index and radial order. This plot identified six acoustic resonance points which included two points corresponding to the first radial modes. The aerodynamic damping as a function of nodal diameter was also calculated and plotted. There were six distinct peaks which occurred in the damping curve and these peaks correspond to the six resonance points. This demonstrates for the first time that acoustic resonances due to higher order radial acoustic modes can affect the aerodynamic damping at high reduced frequencies.
CFD-Led Designs of Pre-Filming Injectors for Gas-Turbine Combustors
Authors: Ajmani Kumud , Mongia Hukam , Lee Phil , Tacina Kathleen
Published: August 2018

The National Combustion Code (OpenNCC) was used to perform parametric design and analysis for three iterations of pre-filming injector design for gas-turbine combustors. The CFD analysis had significant impact on the design, integration and fabrication of a third-generation Lean-Direct Injection (LDI-3) flame-tube assembly consisting of nineteen injection elements. The air passages of the three pilot elements and sixteen main injection elements consisted of CFD-optimized compound-angle discrete jets and dual axial-bladed swirl-venturi passages, respectively. The aerodynamic characteristics of the nineteen-element injection array were evaluated by performing non-reacting flow simulation using a Time-Filtered Navier-Stokes (TFNS) method. The pilot and main injection elements were fueled with conventional pressure-atomizers and newly designed pre-filming nozzles, respectively. Fuel-air mixing and combustion performance was evaluated with reacting-flow TFNS computations using a 14-species, 18-step reduced kinetics mechanism for Jet-A fuel, Lagrangian spray modeling and a PDF turbulent-chemistry interaction model. The TFNS reacting-flow simulations provided considerable insight into the correlation between aerodynamics, combustion and emissions performance of the newly-designed pilot and main injection elements for the LDI-3 combustor at simulated cruise conditions.
Experimental Evaluations of the Relative Contributions to Overall Effectiveness in Turbine Blade Leading Edge Cooling
Authors: Bryant Carol E. , Wiese Connor J. , Rutledge James L. , Polanka Marc D.
Published: August 2018

Gas turbine hot gas path components are protected through a combination of internal cooling and external film cooling. The coolant typically travels through internal passageways, which may involve impingement on the internal surface of a turbine component, before being ejected as film cooling. Internal cooling effects have been studied in facilities that allow measurement of heat transfer coefficients within models of the internal cooling paths, with large heat transfer coefficients generally desirable. External film cooling is typically evaluated through measurements of the adiabatic effectiveness and its effect on the external heat transfer coefficient.

Efforts aimed at improving cooling are often focused on either only the internal cooling or the film cooling; however, the common coolant flow means the internal and external cooling schemes are linked and the coolant holes themselves provide another convective path for heat transfer to the coolant. Recently, measurements of overall cooling effectiveness using matched Biot number turbine component models allow evaluation of the nondimensional wall temperature achieved for the fully cooled component. However, the relative contributions of internal cooling, external cooling, and convection within the film cooling holes is not well understood.

Large scale, matched Biot number experiments, complemented by CFD simulations, were performed on a fully film cooled cylindrical leading edge model to evaluate the effects of various alterations in the cooling design on the overall effectiveness. The relative influence of film cooling and cooling within the holes was evaluated by selectively disabling individual holes and quantifying how the overall effectiveness changed. Several internal impingement cooling schemes in addition to a baseline case without impingement cooling were also tested. In general, impingement cooling is shown to have a negligible influence on the overall effectiveness in the showerhead region. This indicates that the cost and pressure drop penalties for implementing impingement cooling may not be compensated by an increase in thermal performance. Instead, the internal cooling provided by convection within the holes themselves was shown, along with external film cooling, to be a dominant contribution to the overall cooling effectiveness. Indeed, the numerous holes within the showerhead region impede the ability of internal surface cooling schemes to influence the outside surface temperature. The results of this research may allow improved focus of future efforts on the forms of cooling with the greatest potential to improve cooling performance.
Small Scale Supercritical CO2 Radial Inflow Turbine Meanline Design Considerations
Authors: Unglaube Tina , Chiang Hsiao-Wei D.
Published: August 2018

In recent years closed loop supercritical carbon dioxide Brayton cycles have drawn the attention of many researchers as they are characterized by a higher theoretic efficiency and smaller turbomachinery size compared to the conventional steam Rankine cycle for power generation. Currently, first prototypes of this emerging technology are under development and thus small scale sCO2 turbomachinery needs to be developed. However, the design of sCO2 turbines faces several new challenges, such as the very high rotational speed and the high power density. Thus, the eligibility of well-established radial inflow gas turbine design principles has to be reviewed regarding their suitability for sCO2 turbines. Therefore, this work reviews different suggestion for optimum velocity ratios for gas turbines and aims to re-establish it for sCO2 turbines. A mean line design procedure is developed to obtain the geometric dimensions for small scale sCO2 radial inflow turbines. By varying the specific speed and the velocity ratio, different turbine configurations are set up. They are compared numerically by means of CFD analysis to conclude on optimum design parameters with regard to maximum total-to-static efficiency. Six sets of simulations with different specific speeds between 0.15 and 0.52 are set up. Higher specific speeds could not be analyzed, as they require very high rotational speeds (more than 140k RPM) for small scale sCO2 turbines (up to 150kWe). For each set of simulations, the velocity ratio that effectuates maximum efficiency is identified and compared to the optimum parameters recommended for radial inflow turbines using subcritical air as the working fluid. It is found that the values for optimum velocity ratios suggested by Rohlik (1968) are rather far away from the optimum values indicated by the conducted simulations. However, the optimum values suggested by Aungier (2005), although also established for subcritical gas turbines, show an approximate agreement with the simulation results for sCO2 turbines. Though, this agreement should be studied for a wider range of specific speeds and a finer resolution of velocity ratios. Furthermore, for high specific speeds in combination with high velocity ratios, the pressure drop of the designed turbines is too high, so that the outlet pressure is beyond the critical point. For low specific speeds in combination with low velocity ratios, the power output of the designed turbines becomes very small. Geometrically, turbines with low specific speeds and high velocity ratios are characterized by very small blade heights, turbines with high specific speeds and small velocity ratios by very small diameters.
Influence of Geometric Design Parameters Onto Vibratory Response and HCF Safety for Turbine Blades With Friction Damper
Authors: Hüls Matthias , Panning-von Scheidt Lars , Wallaschek Jörg
Published: August 2018

Among the major concerns for high aspect-ratio turbine blades are forced and self-excited (flutter) vibrations which can cause failure by high-cycle fatigue. The introduction of friction damping in turbine blades, such as by coupling of adjacent blades via under platform dampers, can lead to a significant reduction of resonance amplitudes at critical operational conditions. In this paper, the influence of basic geometric blade design parameters onto the damped system response will be investigated to link design parameters with functional parameters like damper normal load, frequently used in nonlinear dynamic analysis. The shape of a simplified large aspect-ratio turbine blade is parameterized along with the under platform damper configuration. The airfoil is explicitly included into the parameterization in order to account for changes in blade mode shapes. For evaluation of the damped system response under a typical excitation, a reduced order model for non-linear friction damping is included into an automated 3D FEA tool-chain. Based on a design of experiments approach, the design space will be sampled and a surrogate model is trained on the received dataset. Subsequently, the mean and interaction effects of the true geometric blade design parameters onto the resonance amplitude and safety against high-cycle fatigue will be outlined for a critical first bending type vibrational motion. Design parameters were mainly found to influence the resonance amplitude by their effect onto the tip-to-platform deflection ratio. The HCF safety was affected by those design parameters with large sensitivity onto static and resonant vibratory stress levels. Applying an evolutionary optimization algorithm, it is shown that the optimum blade design with respect to minimum vibratory response at a particular node can differ significantly from a blade designed toward maximum HCF safety.
Automated Condition Evaluation of Hot-Gas Path Components of Jet Engines Through Exhaust Jet Analysis
Authors: Hartmann Ulrich , Seume Joerg R.
Published: August 2018

This paper determines the influence of different defective components in the hot-gas path (HGP) of a civil aircraft engine on the density distribution in the exhaust. The intention is to automate the identification of defective components inside the HGP through an analysis of the density distribution in the exhaust jet. The defects include an increased radial gap of the blades in the high-pressure turbine (HPT), and a reduction of the film cooling air mass flow in the first stage of the HPT. In addition, several combinations of both defects are simulated. In the present paper the exhaust density distributions are generated numerically using CFD simulations of the HGP. The density distribution in the exhaust jet is reconstructed with synthetic Background-Oriented Schlieren (BOS) measurements and automatically analyzed. The methodology for the automated defect detection consists of two algorithms, a Support Vector Machine (SVM) algorithm to automatically classify each measurement into a corresponding defect or reference class and an outlier detection algorithm to detect variations from the reference state — without assignment.

It is shown that BOS provides a sufficient reconstruction quality to automatically detect defective HGP components with a SVM algorithm. It is possible to automatically detect both defects, even when they occur at the same time. For this purpose, different features were calculated to isolate the influence of each defect on the density distribution. The outlier detection algorithm allows for an automated detection of variations in the density distribution compared to the reference state without any previous knowledge of the influence of the defects on the density distributions during the training procedure. With this algorithm it is possible to detect unknown or new defects which have not been observed or regarded yet. These results strengthen the hypothesis, that an automated detection of defects in jet engines prior to the disassembly is possible.
Experimental Validation of Forced Response Methods in a Multi-Stage Axial Turbine
Authors: Hauptmann Thomas , Meinzer Christopher E. , Seume Joerg R.
Published: August 2018

Depending on the in service condition of jet engines, turbine blades may have to be replaced, refurbished, or repaired in the course of an engine overhaul. Thus, significant changes of the turbine blade geometry can be introduced due to regeneration and overhaul processes. Such geometric variances can affect the aerodynamic and aeroelastic behavior of turbine blades. One goal in the development of the regeneration process is to estimate the aerodynamic excitation of turbine blades depending on these geometric variances caused during the regeneration. Therefore, this study presents an experimentally validated comparison of two methods for the prediction of forced response in a multistage axial turbine. Two unidirectional fluid structure interaction (FSI) methods, a time-linearized and a time-accurate with a subsequent linear harmonic analysis, are employed and the results validated against experimental data. The results show that the vibration amplitude of the time-linearized method is in good agreement with the experimental data and, also requires lower computational time than the time-accurate FSI.

Based on this result, the time-linearized method is used to perform a sensitivity study of the tip clearance size of the last rotor blade row of the five stage axial turbine. The results show that an increasing tip clearances size causes an up to 1.35 higher vibration amplitude compared to the reference case, due to increased forcing and decreased damping work.
Some Recent Advances in Engineering Fracture Modeling for Turbomachinery
Authors: McClung R. Craig , Lee Yi-Der , Sobotka James C. , Moody Jonathan P. , Bhamidipati Vikram , Enright Michael P. , Guseman D. Benjamin , Thomas Colin B.
Published: August 2018

Recent advances in practical engineering methods for fracture analysis of turbomachinery components are described. A comprehensive set of weight function stress intensity factor (SIF) solutions for elliptical and straight cracks under univariant and bivariant stress gradients has been developed and verified. Specialized SIF solutions have been derived for curved through cracks, cracks at chamfered and angled corners, and cracks under displacement control. Automated fracture models are available to construct fatigue crack growth life contours and critical initial crack size contours for all nodal locations in 2D or 3D finite element models.
Thermoacoustic Instability Model With Porous Media: Linear Stability Analysis and the Impact of Porous Media
Authors: Dowd Cody S. , Meadows Joseph W.
Published: August 2018

Lean premixed (LPM) combustion systems are susceptible to thermoacoustic instability, which occurs when acoustic pressure oscillations are in phase with the unsteady heat release rates. Porous media has inherent acoustic damping properties, and has been shown to mitigate thermoacoustic instability; however, theoretical models for predicting thermoacoustic instability with porous media do not exist. In the present study, a 1-D model has been developed for the linear stability analysis of the longitudinal modes for a series of constant cross-sectional area ducts with porous media using a n-Tau flame transfer function. By studying the linear regime, the prediction of acoustic growth rates and subsequently the stability of the system is possible. A transfer matrix approach is used to solve for acoustic perturbations of pressure and velocity, stability growth rate, and frequency shift without and with porous media. The Galerkin approximation is used to approximate the stability growth rate and frequency shift, and it is compared to the numerical solution of the governing equations. Porous media is modeled using the following properties: porosity, flow resistivity, effective bulk modulus, and structure factor. The properties of porous media are systematically varied to determine the impact on the eigenfrequencies and stability growth rates. Porous media is shown to increase the stability domain for a range of time delays (Tau) compared to similar cases without porous media.
High Pressure Ignition Delay Times Measurements and Comparison of the Performance of Several Oxy-Syngas Mechanisms Under High CO2 Dilution
Authors: Barak Samuel , Ninnemann Erik , Neupane Sneha , Barnes Frank , Kapat Jayanta , Vasu Subith
Published: August 2018

In this study, syngas combustion was investigated behind reflected shock waves in CO2 bath gas to measure ignition delay times and to probe the effects of CO2 dilution. New syngas data were taken between pressures of 34.58–45.50 atm and temperatures of 1113–1275K. This study provides experimental data for syngas combustion in CO2 diluted environments: ignition studies in a shock tube (59 data points in 10 datasets). In total, these mixtures covered a range of temperatures T, pressures P, equivalence ratios φ, H2/CO ratio θ, and CO2 diluent concentrations. Multiple syngas combustion mechanisms exist in the literature for modelling ignition delay times and their performance can be assessed against data collected here. In total, twelve mechanisms were tested and presented in this work. All mechanisms need improvements at higher pressures for accurately predicting the measured ignition delay times. At lower pressures, some of the models agreed relatively well with the data. Some mechanisms predicted ignition delay times which were 2 orders of magnitudes different from the measurements. This suggests there is behavior that has not been fully understood on the kinetic models and are inaccurate in predicting CO2 diluted environments for syngas combustion. To the best of our knowledge, current data are the first syngas ignition delay times measurements close to 50 atm under highly CO2 diluted (85% per vol.) conditions.
Guiding Actuator Designs for Active Flow Control of the Precessing Vortex Core by Adjoint Linear Stability Analysis
Authors: Müller Jens S. , Lückoff Finn , Oberleithner Kilian
Published: August 2018

The fundamental impact of the precessing vortex core (PVC) as a dominant coherent flow structure in the flow field of swirl-stabilized gas turbine combustors has still not been investigated in depth. In order to do so, the PVC needs to be actively controlled to be able to set its parameters independently to any other of the combustion system. In this work, open-loop actuation is applied in the mixing section between the swirler and the generic combustion chamber of a non-reacting swirling jet setup to investigate the receptivity of the PVC with regard to its lock-in behavior at different streamwise positions. The mean flow in the mixing section as well as in the combustion chamber is measured by stereoscopic particle image velocimetry and the PVC is extracted from the snapshots using proper orthogonal decomposition. The lock-in experiments reveal the axial position in the mixing section that is most suitable for actuation. Furthermore, a global linear stability analysis is conducted to determine the adjoint mode of the PVC which reveals the regions of highest receptivity to periodic actuation based on mean flow input only. This theoretical receptivity model is compared with the experimentally obtained receptivity data and the applicability of the adjoint-based model for the prediction of optimal actuator designs is discussed.
Comparison of Center Nozzle Staging to Outer Nozzle Staging in a Multi-Flame Combustor
Authors: Culler Wyatt , Chen Xiaoling , Peluso Stephen , Santavicca Domenic , O’Connor Jacqueline , Noble David
Published: August 2018

Combustion instability in gas turbines is often mitigated using fuel staging, a strategy where the fuel is split unevenly between different nozzles of a multiple-nozzle combustor. This work examines the efficacy of different fuel staging configurations by comparing axisymmetric and non-axisymmetric fuel staging in a four-around-one model gas turbine combustor. Fuel staging is accomplished by increasing the equivalence ratio of the center nozzle (axisymmetric staging) or an outer nozzle (non-axisymmetric staging). When the global equivalence ratio is ϕ = 0.70 and all nozzles are fueled equally, the combustor undergoes longitudinal, self-excited oscillations. These oscillations are suppressed when the center nozzle equivalence ratio is increased above ϕStaging = 0.79. This bifurcation equivalence ratio varies between ϕStaging = 0.86 and ϕStaging = 0.76 for the outer nozzles, and is attributed to minor hardware differences between each nozzle. High speed CH* chemiluminescence images in combination with dynamic pressure measurements are used to determine the instantaneous phase difference between the heat release rate fluctuation and the combustor pressure fluctuation throughout the combustor. This analysis shows that the staged flame has similar phase relationships for all staging configurations. It is found that axisymmetric staging can be as effective as non-axisymmetric staging; however, the aforementioned hardware variations can impact both the bifurcation equivalence ratio and the effectiveness of staging.
Mechanical Properties in GTD-111 Alloy in Heavy Frame Gas Turbines
Authors: Scheibel John R. , Aluru Rajeev , van Esch Hans
Published: August 2018

Nickel-based superalloys are extensively used in manufacturing hot gas path components in industrial gas turbines used for power generation. Specifically, GTD-111 DS is one of the widely used alloys used in manufacturing the hot gas path rotating components. These components are subjected to extreme operating environments resulting in creep, oxidation, and fatigue of the components during operation. After continued operation, these damage modes need to be repaired and the components go through extensive repair processes, which include several heat treatments to recover the mechanical properties of the base material (GTD-111 DS) lost during operation. The heat treatments used during repair by the different repair vendors can vary widely in terms of temperature, time and the sequence as well. This study focuses on understanding the differences in the effects of the heat treatments (partial solution, full solution, HIP and full solution) to the base material in terms of microstructure-mechanical property relationships. Results indicate that HIP and full solution resulted in refined microstructures and improved mechanical properties compared to the heat treatments involving partial solution or full solution only. Microstructuremechanical property relationships suggest that components that need to be repaired beyond OEM recommended repair intervals benefit from the HIP and full solution heat treatments.
Experimental Investigation of Heat Transfer in Cavities of Steam Turbine Casings Under Generic Test Rig Conditions
Authors: Spura David , Gampe Uwe , Eschmann Gunter , Uffrecht Wieland
Published: August 2018

This paper presents the first experimental results of the systematic investigation of forced convection heat transfer in scaled generic models of steam turbine casing side spaces with varied geometric dimensions under fully turbulent air flow. Data were obtained by two redundant low-heat measuring methods. The results from the steady-state inverse method are in good agreement with the data from the local overtemperature method, which was applied via a novel miniaturized heat transfer coefficient (HTC) sensor concept. All experiments were conducted at the new Side Space Test Rig “SiSTeR” at TU Dresden. The dependencies of the HTC distributions on the axial widths of the cavity and its inlet and on the eccentricity between them were investigated for Reynolds numbers from Re = 40,000 to 115,000 in the annular main flow passage. The measured HTC distributions showed a maximum at the stagnation point where the induced jet impinges on the wall surface, and decreasing values towards the cavity corners. Local values scaled roughly with the main flow Reynolds number. The HTC distributions thereby differed considerably depending on the dimensions and the form of the cavity, ranging from symmetric T-shape to asymmetric L-shape, with upstream or downstream shifted sidewalls.
Effect of Tandem Blading in Contra-Rotating Axial Flow Fans
Authors: Madasseri Payyappalli Manas , Pradeep A. M.
Published: August 2018

With the ever-increasing demand for improved fuel efficiency and lower emissions, there is a significant emphasis on finding innovative design solutions that can replace or significantly improve the present-day turbomachinery designs. The concepts of contra-rotation and tandem blade configuration are two different methods of achieving better performance. Though several independent studies have been carried out on the concepts of contrarotation and tandem blade configuration, a combination of both these techniques to achieve better performance is a thought unexplored. Therefore, the present work explores the applicability of tandem blading in a low-speed contra-rotating fan. The idea is to replace the front rotor of the contra-rotating fan stage with tandem blades. Several combinations of percent pitch for the tandem arrangement are analyzed to obtain the best configuration suitable for the case. The performance of the baseline contra-rotating fan is established numerically. A detailed numerical investigation of the flow physics associated with the contrarotating stage reveals some interesting phenomena affecting its performance. A comparison of the performance of tandem configuration with that of the baseline is carried out. The interaction of gap flow and the wake of the front blade with the tip-leakage flow of the rear blade of the tandem configuration is analyzed in detail. The performance of the stage is evaluated through stage loading or pressure rise and the stability margin.
Aerodynamic Optimization of a Two-Part Variable Inlet Guide Vane in a Highly Loaded Low Pressure Compressor
Authors: Hemmert-Pottmann Stefan , Gouézou William , Nicke Eberhard
Published: August 2018

Continuous reduction of fuel consumption for a wide range of operating conditions leads to a high efficiency demand for all engine parts of modern jet engines and especially the compressor. To meet these requirements a two-part Variable Inlet Guide Vane (VIGV), composed of a fixed strut and a variable flap, can be used. Besides the aerodynamic aspects, the VIGV strut is a substantial part for the structural integrity of the compressor. The aerodynamic design optimization of such a VIGV, located upstream of the first rotor of a 2.5 stage low pressure compressor, under the conditions of three different operating points is presented in this paper.

In a previous study the shape of the axial gap between strut and flap was optimized without changing the envelope of both parts [1]. The new design tool SplitBlade, developed at the DLR, enables the creation of an axial gap and has been integrated in the design process of the in-house optimization tool AutoOpti. The target of the optimization was to decrease the total pressure loss coefficients for all three operating points.

The design optimization presented in this paper is more complex by allowing the VIGV blade geometry to change. The basic dimensions of the VIGV such as the axial chord and the maximum profile thickness are still frozen. In total, 88 parameters are free to change in the optimization process. Additionally to the main target of loss reduction, the circumferential outflow angles are restricted to maintain the deflection of the blade and therewith the required rotor inflow conditions to ensure the operability of the entire compressor in the whole working range.

The final result is a two-part VIGV with an axial gap, which is optimized in terms of total pressure losses in three operating points. Compared to a reference geometry without an axial gap, the losses are almost equal at nominal speed, and about one to two percentage points higher in the two part speed operating points.
Development of a Criterion for a Robust Identification of Diffuser Rotating Stall Onset in Industrial Centrifugal Compressors
Authors: Bianchini Alessandro , Andreini Giulia , Ferrara Giovanni , Ferrari Lorenzo , Rubino Dante Tommaso
Published: August 2018

Recent studies showed that a prompt detection of the stall inception, connected with a specific model to predict its associated aerodynamic force, could provide room for an extension of the left margin of the operating curve of high-pressure centrifugal compressors.

In industrial machines working in the field, however, robust procedures to detect and identify the phenomenon are still missing, i.e. the operating curve is almost ever cut preliminary by the manufacturer by a proper safety margin; moreover, no agreement is found in the literature about a well-defined threshold to define the onset of the stall. In particular, in some cases the intensity of the arising subsynchronous frequency is compared to the revolution frequency, while in many other ones it is compared to the blade passage frequency. A large experience in experimental stall analyses collected by the authors revealed that in some cases unexpected spikes could make this direct comparison not reliable for a robust automatic detection.

To this end, a new criterion was developed based on an integral analysis of the area subtended to the entire subsynchronous spectrum of the dynamic pressure signal of probes positioned just outside the impeller exit. A dimensionless parameter was then defined to account for the spectrum area increase in proximity to stall inception. This new parameter enabled the definition of a reference threshold to highlight the arising of stall conditions, whose validity and increased robustness was here verified based on a set of experimental analyses of different types of full-stage test cases of industrial centrifugal compressors at the test rig.
On the Transferability of Probabilistic Fracture Mechanics Results for Scaled 50Hz and 60Hz Heavy Duty Gas Turbine Rotor Disks
Authors: Amann Christian , Kadau Kai , Gumbsch Peter
Published: August 2018

In the development of heavy duty gas turbines for the energy sector oftentimes the majority of the design work is performed in either the 50 Hz or the 60 Hz size. Many aspects of the designed engine for one market (50 Hz as an example) can then be used to design with significantly reduced effort for the other market (i.e. 60 Hz). For example, most dimensions of rotor components can be geometrically scaled such that centrifugal forces in those massively rotating parts are conserved. This article investigates the transferability of probabilistic fracture mechanics results from one market to the other one. Or in other words: can we perform probabilistic fracture mechanics for the 50 Hz rotor design and deduce the risk of failure for the scaled 60 Hz design (or vice versa)? Multiple challenges must be considered in the transferability including the different volume, surface to volume ratio, as well as the different transient behavior for the smaller 60 Hz design. We address that challenge by building up complexity for a generic rotor design in order to separate the different effects and associated design features. We then discuss several Siemens rotor designs with respect to transferability of probabilistic fracture mechanics results and correlations to deterministic approaches. This work enables the creation of design rules to avoid unnecessary work for scaled 50 Hz/60 Hz market engines and therefore supports the reduction of product development costs.