Accepted Manuscripts

Artur Figueiredo, Robin Jones, Oliver J Pountney, James Scobie, Gary Lock, Carl Sangan and David Cleaver
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041206
This paper presents Volumetric Velocimetry (VV) measurements for a jet in crossflow that is representative of film cooling. Volumetric velocimetry employs particle tracking to non-intrusively extract all three components of velocity in a three-dimensional volume. This is its first use in a film-cooling context. The primary research objective was to develop this novel measurement technique for turbomachinery applications, whilst collecting a high-quality data set that can improve the understanding of the flow structure of the cooling jet. A new facility was designed and manufactured for this study with emphasis on optical access and controlled boundary conditions. For a range of momentum flux ratios from 0.65 to 6.5 the measurements clearly show the penetration of the cooling jet into the freestream, the formation of kidney-shaped vortices and entrainment of main flow into the jet. The results are compared to published studies using different experimental techniques, with good agreement. Further quantitative analysis of the location of the kidney vortices demonstrates their lift off from the wall and increasing lateral separation with increasing momentum flux ratio. The lateral divergence correlates very well with the self-induced velocity created by the wall-vortex interaction. Circulation measurements quantify the initial roll up and decay of the kidney vortices and show that the point of maximum circulation moves downstream with increasing momentum flux ratio. The potential for non-intrusive volumetric velocimetry measurements in turbomachinery flow has been clearly demonstrated.
TOPICS: Jets, Film cooling, Vortices, Kidney, Momentum, Flow (Dynamics), Cooling, Turbomachinery, Boundary-value problems, Separation (Technology), Particulate matter
Eric Kurstak, Ryan Wilber and Kiran D'Souza
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041204
A considerable amount of research has been conducted to develop reduced order models of bladed disks that can be constructed using single sector calculations when there is mistuning present. A variety of methods have been developed to efficiently handle different types of mistuning ranging from small frequency mistuning, which can be modeled using a variety of methods including component mode mistuning (CMM), to large geometric mistuning, which can be modeled using multiple techniques including pristine rogue interface modal expansion (PRIME). Research has also been conducted on developing reduced order models that can accommodate the variation of specific parameters in the reduced space; these models are referred to as parametric reduced order models (PROMs). This work introduces a PROM for bladed disks that allows for the variation of rotational speed in the reduced space. These PROMs are created by extracting information from sector models at three rotational speeds, and then the appropriate reduced order model is efficiently constructed in the reduced space at any other desired speed. This work integrates these new PROMs for bladed disks with two existing mistuning methods, CMM and PRIME, to illustrate how the method can be readily applied for a variety of mistuning methods. Frequencies and forced response calculations using these new PROMs are compared to the full order finite element calculations to demonstrate the effectiveness of the method.
TOPICS: Disks, Coordinate measuring machines, Finite element analysis
Oliver Schulz and Nicolas Noiray
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041205
This numerical study deals with a premixed ethylene-air jet at 300 K injected into a hot vitiated crossflow at 1500 K and atmospheric pressure. The reactive jet in crossflow (RJICF) was simulated with compressible 3-D large eddy simulations (LES) with an analytically reduced chemistry (ARC) mechanism and the dynamic thickened flame (DTF) model. ARC enables simulations of mixed combustion modes, such as autoignition and flame propagation, that are both present in this RJICF. 0-D and 1-D simulations provide a comparison with excellent agreement between ARC and detailed chemistry in terms of autoignition time and laminar flame speed. The effect of the DTF model on autoignition was investigated for varying species compositions and mesh sizes. Comparisons between LES and experiments are in good agreement for average velocity distributions and jet trajectories; LES remarkably capture experimentally observed flame dynamics. An analysis of the simulated RJICF shows that the leeward propagating flame has a stable flame root close to the jet exit. The lifted windward flame, on the contrary, is anchored in an intermittent fashion due to autoignition flame stabilization. The windward flame base convects downstream and is "brought back" by autoignition alternately. These autoignition events occur close to a thin layer that is associated with radical build-up and that stretches down to the jet exit.
TOPICS: Chemistry, Flames, Large eddy simulation, Simulation, Engineering simulation, Dynamics (Mechanics), Combustion, Atmospheric pressure
fushui Liu, Zhongjie Shi, Yang Hua, Ning Kang, Yikai Li and Zheng Zhang
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041169
Since the intake valve close timing (IVC) directly determines the amount of displacement backflow and the amount of fresh charge trapped in the cylinder, optimizing the IVC is important to improve the performance of the diesel engine. In this paper, the relationship between the IVC and the displacement backflow of the cylinder at the high-speed condition was studied by establishing a one-dimensional (1D) gas dynamic model of a single-cylinder diesel engine. The results show that the forward airflow mass of intake and the backflow increase as the IVC retards, and the airflow mass trapped in cylinder increases at first and then decreases. It is interesting to find that the backflow does not equal zero when the air mass trapped in cylinder is the largest, which is different from the traditional optimizing strategy on the IVC. That is to say, there exists a misalignment between the maximum-volume-efficiency IVC and the none-backflow IVC. To further verify this interesting misalignment, the airflow characteristics at the optimized IVC condition are studied by establishing a three-dimensional (3D) simulation. It is found that the appearance of backflow is a gradual process and there exists an overall backflow when the engine volume efficiency reaches its maximum value. In addition, the misalignment is reduced as the mean valve-closing velocity increases. The misalignment equals to 0 only if the mean valve-closing velocity approaches infinity.
TOPICS: Cylinders, Diesel engines, Air flow, Valves, Displacement, Dynamic models, Engines, Simulation
Houman Hanachi, Jie Liu, Ping Ding, Il Yong Kim and Chris K Mechefske
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041168
Gas turbine engines are widely used for power generation, ranging from stationary power plants to airplane propulsion systems. Compressor fouling is the dominant degradation mode in gas turbines that leads to economic losses due to power deficit and extra fuel consumption. Washing of the compressor removes the fouling matter and retrieves the performance, while causing a variety of costs including loss of production during service time. In this paper the effect of fouling and washing on the revenue of the power plant is studied, and a general solution for the optimum time between washes of the compressor under variable fouling rates and demand power is presented and analyzed. The framework calculates the savings achievable with optimization of time between washes during a service period. The methodology is utilized to optimize total costs of fouling and washing and analyze the effects and sensitivities to different technical and economic factors. As a case study, it is applied to a sample set of cumulative gas turbine operating data for a time-between-overhauls and the potential saving has been estimated. The results show considerable saving potential through optimization of time between washes.
TOPICS: Gas turbines, Optimization, Compressors, Foundry coatings, Power stations, Fuel consumption, Aircraft propulsion, Energy generation, Matter
Andreas Hartung, Hans-Peter Hackenberg, Malte Krack, Johann Gross, Torsten Heinze and Lars Panning-von Scheidt
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041160
Since the first non-linear forced response validation of frictionally coupled bladed disks, more than 20 years have passed, and numerous incremental modeling and simulation refinements were proposed. With the present work, we intend to assess how much we have improved since then. To this end, we present findings of an exhaustive validation campaign designed to systematically validate the non-linear vibration prediction for the different friction joints at blade roots, interlocked shrouds and under-platform dampers. An original approach for the identification of crucial contact properties is developed. By using the Dynamic Lagrangian contact formulation and a refined spatial contact discretization, it is demonstrated that the delicate identification of contact stiffness properties can be circumvented. The friction coefficient is measured in a separate test, and determined as unique function of temperature, preload, wear state. Rotating rig and engine measurements are compared against simulations with the tool OrAgL, developed jointly by the Leibniz Universität Hannover and the University of Stuttgart, in which state of the art Component Mode Synthesis and Harmonic Balance methods are implemented.
TOPICS: Engines, Simulation, Friction, Wear, Temperature, Dampers, Modeling, Nonlinear vibration, Disks, Blades, Stiffness
Diogo Berta Pitz, Dr. John W. Chew and Olaf Marxen
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041113
Buoyancy-induced flows occur in the rotating cavities of gas turbine internal air systems, and are particularly challenging to model due to the inherently unsteadiness of these flows. While the global features of such flows are well documented, detailed analyses of the unsteady structure and turbulent quantities have not been reported. In this work we use a high-order numerical method to perform large-eddy simulation (LES) of buoyancy-induced flow in a sealed rotating cavity with either adiabatic or heated disks. New insight is given into long-standing questions regarding the flow characteristics and nature of the boundary layers. The analyses focus on showing time-averaged quantities, including temperature and velocity fluctuations, as well as on the effect of the centrifugal Rayleigh number on the flow structure. Using velocity and temperature data collected over several revolutions of the system, the shroud and disk boundary layers are analysed in detail. The instantaneous flow structure contains pairs of large, counter-rotating convection rolls, and it is shown that unsteady laminar Ekman boundary layers near the disks are driven by the interior flow structure. The shroud thermal boundary layer scales as approximately Ra^-1/3 , in agreement with observations for natural convection under gravity.
TOPICS: Flow (Dynamics), Buoyancy, Cavities, Large eddy simulation, Disks, Boundary layers, Temperature, Turbulence, Fluctuations (Physics), Rayleigh number, Convection, Gas turbines, Natural convection, Numerical analysis, Gravity (Force), Thermal boundary layers
Jan Zanger, Thomas Krummrein, Teresa Siebel and Jürgen Roth
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041119
Detailed information of the thermodynamic parameters, system performance and operating behavior of aircraft APU cycles is rarely available in literature. In order to set up numeric models and study cycle modifications, validation data with well defined boundary conditions is needed. Thus, the paper introduces an APU test rig based on a Garrett GTCP36-28 with detailed instrumentation which will be used in a further step as a demonstration platform for cycle modifications. The system is characterized in the complete feasible operating range by alternating bleed air load and electric power output. Furthermore, simulations of a validated numerical cycle model are utilized to predict the load points in the operating region which were unstable during measurements. The paper reports and discusses turbine shaft speed, compressor air mass flow, fuel mass flow, efficiencies, compressor outlet pressure and temperature, turbine inlet and outlet temperature as well as exhaust gas emissions. Furthermore, the results are discussed with respect of the difference compared to a Hamilton Sundstrand APS3200. Though the efficiencies of the GTCP36-28 are lower compared to the APS3200, the general behavior is in good agreement. In particular, the effects of separate compressors for load and power section are discussed in contrast to the GTCP36-28 system design comprising a single compressor. In general, it was shown that the GTCP36-28 is still appropriate for the utilization as a demonstration platform for cycle modification studies.
TOPICS: Optimization, Aircraft, Cycles, Compressors, Stress, Flow (Dynamics), Temperature, Turbines, Simulation, Exhaust systems, Emissions, Boundary-value problems, Electricity (Physics), Fuels, Design, Engineering simulation, Instrumentation, Pressure
Yoshihide Imamura, Ken Ikawa, Kojiro Motoyama, Hayato Iwasaki, Takeo Hirakawa and Hiroshi Utsunomiya
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041161
A mandrel-free hot-spinning was developed as a near-net-shape titanium alloy plate forming technique. In this work, a Ti-6Al-4V alloy conical product with a wall angle of 34 degrees and 170mm height was formed from a large size Ti-6Al-4V plate (890~920mm dia. x 30mm thick). The product was characterized metallurgically and mechanical properties were measured, and the shape of formed products was investigated. It was found that the mandrel-free hot-spinning is able to form a large size titanium alloy plate. Material properties including tensile strength and microstructure of the formed products satisfied the material specifications. Fatigue stress of the formed product was higher than that of the typical Ti-6Al-4V material. For a further improvement, a forming method using pre-formed material was proposed and which was successfully conducted with two types of preforms and found to be effective in the forming process.
TOPICS: Spinning (Textile), Titanium alloys, Spin (Aerodynamics), Shapes, Tensile strength, Materials properties, Mechanical properties, Preforms, Stress, Fatigue, Alloys, Forming techniques
Jie J Yuan, Fadi El-haddad, Loic Salles and Chian Wong
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041147
This work presents an assessment of classical and state of the art reduced order modelling (ROM) techniques to enhance the computational efficiency for dynamic analysis of jointed structures with local contact nonlinearities. These ROM methods include classical free interface method (Rubin method, MacNeal method), fixed interface method (Craig-Bampton), Dual Craig-Bampton (DCB) method and also recently developed joint interface mode (JIM) and trial vector derivative (TVD) approaches. A finite element jointed beam model is considered as the test case taking into account two different setups: one with a linearized spring joint and the other with a nonlinear macroslip contact friction joint. Using these ROM techniques, the accuracy of dynamic behaviors and their computational expense are compared separately. We also studied the effect of excitation levels, joint region size and number of modes on the performance of these ROM methods
TOPICS: Dynamic analysis, Modeling, Springs, Excitation, Finite element analysis, Friction
Charles B. Burson-Thomas, Richard Wellman, Terry Harvey and Robert Wood
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041149
When modelling a droplet impingement, it is reasonable to assume a surface is flat when the radius of curvature of the surface is significantly larger than the droplet radius. In other contexts where Water Droplet Erosion (WDE) has been investigated, the typical droplet size has either been sufficiently small, or the radius of curvature of the surface sufficiently large, that it has been sensible to make this assumption. The equations describing the kinematics of an impinging water droplet on a flat surface were reformulated for a curved surface. The results suggest the relatively similar radii of curvature, of the leading-edge of a fan blade and the impinging water droplet, will significantly affect the application of the initial high-pressures, along with the onset of lateral outflow jetting. Jetting is predicted to commence substantially sooner and not in unison along the contact periphery, leading to an asymmetric flow stage. This is likely to have significant implications for the WDE that occurs, and thus, the engineering approaches to minimise the WDE of fan blades.
TOPICS: Drops, Modeling, Blades, Water, Outflow, Erosion, Kinematics, Flow (Dynamics)
Pavan Naik, Bernhard Lehmayr, Stefan Homeier, Michael Klaus and Damian M. Vogt
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041152
In this paper, a method to influence the vibratory blade stresses of mixed flow turbocharger turbine blade by varying the local blade thickness in spanwise direction is presented. Such variations have an influence on both the static and the vibratory stresses and therefore can be used for optimizing components with respect to High-Cycle Fatigue (HCF) tolerance. Two typical cyclic loadings that are of concern to turbocharger manufacturers have been taken into account. These loadings arise from the centrifugal forces and from blade vibrations. The objective of optimization in this study is to minimize combined effects of centrifugal and vibratory stresses on turbine blade HCF and moment of inertia. Here, the conventional turbine blade design with trapezoidal thickness profile is taken as baseline design. The thicknesses are varied at four span-wise equally spaced planes and three stream-wise planes to observe their effects on static and vibratory stresses. The summation of both the stresses is referred to as combined stress. In order to ensure comparability among the studied design variants, a generic and constant excitation order dependent pressure field is used at a specific location on blade. The results show that the locations of static and vibratory stresses, and hence the magnitude of the combined stresses, can be influenced by varying the blade thicknesses while maintaining the same eigenfrequencies. By shifting the maximum vibratory stresses farther away from the maximum static stresses, the combined stresses can be reduced considerably, which leads to improved HCF tolerance.
TOPICS: Stress, Turbochargers, Turbine blades, Blades, Geometry, High cycle fatigue, Design, Optimization, Vibration, Inertia (Mechanics), Pressure, Flow (Dynamics), Centrifugal force, Excitation
Mirko R. Bothien, Demian Lauper, Yang Yang and Alessandro Scarpato
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041151
Lean premix technology is widely spread in gas turbine combustion systems, allowing modern power plants to fulfill very stringent emission targets. These systems are, however, also prone to thermoacoustic instabilities, which can limit the engine operating window. The thermoacoustic analysis of a combustor is thus a key element in its development process. An important ingredient of this analysis is the characterization of the flame response to acoustic fluctuations, which is straightforward for lean premixed flames that are propagation stabilized, since it can be measured atmospherically. The present study deals with the flame response of mainly auto-ignition stabilized flames to acoustic and temperature fluctuations for which a CFD system identification approach is chosen. For propagation stabilized lean premixed flames, a common approach followed in the literature assumes that the acoustic pressure is constant across the flame and that the flame dynamics are governed by the response to velocity perturbations only. However this is not necessarily the case for reheat flames that are mainly auto-ignition stabilized. In this paper, a predominantly auto-ignition stabilized flame is described as a Multi-Input Multi-Output system and its full 2x2 transfer matrix is presented. Additionally, it is elaborated how in presence of temperature fluctuations the 2x2 matrix can be extended to a 3x3 matrix relating the primitive acoustic variables as well as the temperature fluctuations across the flame. It is shown that only taking the flame transfer function is insufficient to fully describe the dynamic behavior of reheat flames.
TOPICS: Acoustics, Flames, Large eddy simulation, Fluctuations (Physics), Temperature, Ignition, Emissions, Dynamics (Mechanics), Engines, Transfer functions, Sound pressure, Combustion chambers, Combustion systems, Computational fluid dynamics, Gas turbines, Power stations
David Holst, Benjamin Church, Felix Wegner, Georgios Pechlivanoglou, Christian Navid Nayeri and Christian Oliver Paschereit
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041146
The wind industry needs reliable and accurate airfoil polars to properly predict wind turbine performance, especially during the initial design phase. Medium- and low-fidelity simulations directly depend on the accuracy of the airfoil data and even more so if e.g. dynamic effects are modeled. This becomes crucial if the blades of a turbine operate under stalled conditions for a significant part of the turbine's lifetime. In addition, the design process of vertical axis wind turbines (VAWTs) needs data across the full range of angles of attack between 0 and 180 deg. Lift, drag and surface pressure distributions of a NACA 0021 airfoil equipped with surface pressure taps were investigated based on time-resolved pressure measurements. The present study discusses full range static polars and several dynamic sinusoidal pitching configurations covering two Reynolds numbers Re = 140k and 180 k, and different incidence ranges: near stall, post stall and deep stall. Various bi-stable flow phenomena are discussed based on high frequency measurements revealing large lift-fluctuations in the post and deep stall regime that exceed the maximum lift of the static polars and are not captured by averaged measurements. Detailed surface pressure distributions are discussed to provide further insight into the flow conditions and pressure development during dynamic motion. The experimental data provided within the present paper is dedicated to the scientific community for calibration and reference purposes, which in the future may lead to higher accuracy in performance predictions during the design process of wind turbines.
TOPICS: Reynolds number, Experimental analysis, Airfoils, Pressure, Design, Flow (Dynamics), Wind turbines, Vertical axis wind turbines, Wind, Simulation, Fluctuations (Physics), Pressure measurement, Drag (Fluid dynamics), Engineering simulation, Turbines, Blades, Calibration
Francesco Balduzzi, Alessandro Bianchini, Lorenzo Ferrari, David Holst, Benjamin Church, Felix Wegner, Georgios Pechlivanoglou, Christian Navid Nayeri, Christian Oliver Paschereit and Giovanni Ferrara
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041150
The wind industry needs airfoil data for ranges of Angle of Attack wider than those of aviation applications, since large portions of the blades may operate in stalled conditions for a significant part of their lives. Vertical axis turbines are even more affected, since data across the full range of 180degree is necessary for a correct performance prediction. The literature lacks data in deep and post stall regions for nearly every airfoil. The present study shows experimental and numerical results for the NACA 0021 airfoil, which is often used for Darrieus VAWT design. Experimental data were obtained through dedicated wind tunnel measurements of the airfoil with surface pressure taps, which provided further insight into the pressure coefficient distribution across a wide range of AoAs. The measurements were conducted at two Reynolds numbers, 140k and180k. Each experiment was performed multiple times to ensure repeatability. Dynamic AoA changes were also investigated at multiple reduced frequencies. Moreover, dedicated unsteady numerical simulations were carried out on the same airfoil shape to reproduce the static polars and some relevant dynamic AoA variation cycles tested in the experiments. The solved flow field was exploited to get further insight into the flow mechanisms highlighted by the wind tunnel tests and to provide correction factors to discard the influence of the experimental apparatus, making experiments representative of open-field behaviour. The present study is thought to provide the scientific community with high quality, low-Reynolds data, which may enable in the near future a more effective VAWT design.
TOPICS: Reynolds number, Computational fluid dynamics, Dynamic analysis, Airfoils, Vertical axis wind turbines, Wind tunnels, Design, Pressure, Flow (Dynamics), Computer simulation, Turbines, Blades, Cycles, Shapes, Wind, Aviation
Jonathan Tobias, Daniel Depperschmidt, Cooper Welch, Robert Miller, Mruthunjaya Uddi, Dr. Ajay Agrawal and Ron Daniel Jr
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041143
Recent research has shown that rotating detonation combustion (RDC) can provide excellent specific thrust, specific impulse, and pressure gain within a small volume through rapid energy release by continuous detonation in the circumferential direction. The RDC could provide significant efficiency gains for power generating gas turbines in combined cycle power plants. However, few past studies have employed fuels that are relevant to power generation turbines, since RDC research has focused mainly on propulsion applications. In this study, we present experimental results from RDC operated on methane and oxygen-enriched air to represent reactants used in land-based power generation. The RDC is operated at high pressure using a back-pressure plate located downstream of the combustor. Past studies have focused mainly on probe measurements inside the combustor, and thus, little information is known about the nature of the products exiting the RDC. In particular, it is unknown if chemical reactions persist outside the RDC annulus, especially if methane is used as the fuel. In this study, we apply two time-resolved optical techniques to simultaneously image the RDC products at framing rate of 30 kHz: (1) direct visual imaging to identify the overall size and extent of the plume, and (2) OH* chemiluminescence imaging to detect the reaction zones if any. Results show dynamic features of combustion products that are consistent with the probe measurements inside the RDE. Moreover, presence of OH* in the products suggests that oblique shock wave and reactions persist downstream of the RDC.
TOPICS: Combustion, Explosions, Engines, Chemiluminescence, Methane, Imaging, Pressure, Probes, Combustion chambers, Energy generation, Fuels, Shock waves, Thrust, Structural frames, Propulsion, High pressure (Physics), Plumes (Fluid dynamics), Gas turbines, Turbines, Annulus, Combined cycle power stations, Framing (Construction), Impulse (Physics), Oxygen, Chemical reactions
Martin Zajadatz, Felix Güthe, Ewald Freitag, tHEODOROS Ferreira-Providakis, Torsten Wind, Fulvio Magni and Jeffrey S. Goldmeer
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041144
The gas turbine market tends to drive development towards higher operational and fuel flexibility. In order to meet these requirements the GT13E2 combustion system with the AEV burner has been further developed to extend the range of fuels according to GE fuel capabilities. The development includes operation with diluted natural gas, gases with very high C2+ contents up to liquefied petroleum gas on the gaseous fuels side and non-standard liquid fuels such as biodiesel and light crude oil. Results of full scale high pressure single burner combustion test in the test facilities at DLR-Köln are shown to demonstrate these capabilities. With these tests at typical pressure and temperature conditions safe operation ranges with respect to flame flashback and lean blow out were identified. In addition, the recent burner mapping at the DLR in Köln results in emission behavior similar to typical fuels as natural gas and fuel oil #2. It was also possible to achieve low emission levels with liquid fuels with a high fuel bound nitrogen content. Based on these results the GT13E2 gas turbine has demonstrated capability with a high variety of gaseous and liquid fuel at power ranges of 200 MW and above. The fuels can be applied without specific engine adjustments or major hardware changes over a whole range of gas turbine operation including startup and GT acceleration.
TOPICS: Gaseous fuels, Fuels, Gas turbines, Natural gas, Emissions, Biodiesel, Crude oil, Flames, Nitrogen, Petroleum, Test facilities, Engines, Hardware, High pressure (Physics), Combustion systems, Pressure, Temperature, Combustion, Gases, Fuel oils
Adam Shrager, Karen A. Thole and Dominic Mongillo
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041148
The complex flowfield in a gas turbine combustor makes cooling the liner walls a challenge. In particular, this paper is primarily focused on the region surrounding the dilution holes, which is especially challenging to cool due to the interaction between the effusion cooling jets and high-momentum dilution jets. This study presents overall effectiveness measurements for three different cooling hole patterns of a double-walled combustor liner. Only effusion hole patterns near the dilution holes were varied, which included: no effusion cooling; effusion holes pointed radially outward from the dilution hole; and effusion holes pointed radially inward toward the dilution hole. The double-walled liner contained both impingement and effusion plates as well as a row of dilution jets. Infrared thermography was used to measure the surface temperature of the combustor liners at multiple dilution jet momentum flux ratios and approaching freestream turbulence intensities of 0.5% and 13%. Results showed the outward and inward geometries were able to more effectively cool the region surrounding the dilution hole compared to the closed case. A significant amount of the cooling enhancement in the outward and inward cases came from in-hole convection. Downstream of the dilution hole, the interactions between the inward effusion holes and the dilution jet led to lower levels of effectiveness compared to the other two geometries. High freestream turbulence caused a small decrease in overall effectiveness over the entire liner and was most impactful in the first three rows of effusion holes.
TOPICS: Cooling, Combustion chambers, Jets, Turbulence, Momentum, Temperature, Thermography, Convection, Gas turbines, Plates (structures)
Adam Shrager, Karen A. Thole and Dominic Mongillo
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041153
The complex flowfield inside a gas turbine combustor creates a difficult challenge in cooling the combustor walls. Many modern combustors are designed with a double-wall that contain both impingement cooling on the backside and effusion cooling on the external side. Complicating matters is the fact that these double-walls also contain large dilution holes whereby the cooling film from the effusion holes is interrupted by the high-momentum dilution jets. Given the importance of cooling the entire panel, including the metal surrounding the dilution holes, the focus of this paper is understanding the flow in the region near the dilution holes. Near-wall flowfield measurements are presented for three different effusion cooling hole patterns near the dilution hole. The effusion cooling hole patterns were varied in the region near the dilution hole and include: no effusion holes; effusion holes pointed radially outward from the dilution hole; and effusion holes pointed radially inward toward the dilution hole. Particle image velocimetry (PIV) was used to capture the time-averaged flowfield. Results showed evidence of downward motion at the leading edge of the dilution hole for all three effusion hole patterns. In comparing the three geometries, the outward effusion holes showed significantly higher velocities toward the leading edge of the dilution jet relative to the other two geometries. Although the flowfield generated by the dilution jet dominated the flow downstream, each cooling hole pattern interacted with the flowfield uniquely. Approaching freestream turbulence did not have a significant effect on the flowfield.
TOPICS: Cooling, Combustion chambers, Flow (Dynamics), Momentum, Gas turbines, Impingement cooling, Metals, Particulate matter, Turbulence, Jets
Michael Presby, Nesredin Kedir, Luis Sanchez, Calvin Faucett, Sung R Choi and Gregory Morscher
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041145
The life-limiting behavior of an N720/alumina oxide/oxide ceramic matrix composite (CMC) was assessed in tension in air at 1200°C for unimpacted and impacted specimens. CMC targets were subjected to ballistic impact at ambient temperature with an impact velocity of 250 m/s under a full support configuration. Subsequent post-impact ultimate tensile strength was determined as a function of test rate in order to determine the susceptibility to delayed failure, or slow crack growth (SCG). Unimpacted and impacted specimens exhibited a significant dependency of ultimate tensile strength on test rate such that the ultimate tensile strength decreased with decreasing test rate. Damage was characterized using x-ray computed tomography (CT), and scanning electron microscopy (SEM). A phenomenological life prediction model was developed in order to predict life from one loading condition (constant stress-rate loading) to another (constant stress loading). The model was verified in part via a theoretical preloading analysis.
TOPICS: Oxide ceramics, Temperature, Composite materials, Damage, Tensile strength, Stress, Ceramic matrix composites, Fracture (Materials), Scanning electron microscopy, Computerized tomography, Failure, Tension

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