bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Investigation of NOx Emissions Characteristics of a Natural Gas Premixed Burner Based on Chemical Reactor Network Model
Authors: Mu Bin , Lei Fulin , Shao Weiwei , Liu Xunwei , Zhang Zhedian , Xiao Yunhan
Published: November 2019

Numerical optimization of nitrogen oxides (NOx) formation is an essential factor during developing low pollution combustor of gas turbine. The Computational Fluid Dynamics-Chemical Reactor Network (CFD-CRN) hybrid method has a great advantage in fast and accurate prediction of combustor NOx emissions. In this work, a hybrid CFD-CRN approach is established to predict pollutant emissions of a lean premixed model burner for gas turbine applications. Several criteria are compared for separating the combustor into chemically and physically homogeneous zones, and the crucial parameters such as residence time and flue gas recirculation ratio are calculated. The CRN model is preliminarily verified with experimental data. The effects of pressure and fuel-air unmixedness on NOx formation are subsequently investigated. In addition, the effects of changes in fuel/air flow distribution and crucial parameters of CRN model on NOx emissions are also estimated under different pressures and fuel-air unmixedness. The combustor is divided into several zones including reaction preheating region, flame front region, flame transition region, post flame region, main recirculation region and corner recirculation region based on CFD results of fuel-air mixing characteristics, velocity field, temperature field, distribution of OH mass fraction and Damkohler number. The complex CRN model has the advantage of predicting NOx emission characteristics under higher Tad conditions compared with the simple model, and its prediction of NOx emission shows good agreement with experimental data under various equivalence ratio conditions. The structure and distribution of several regions of CRN model are analogous but not significant when Reynolds number exceeds 105 under high pressure. The pathway analysis shows that the NOx emission gradually decreases through N2O and NNH mechanisms, resulted from the decreasing concentration of O radical under low Tad and high pressure. However, the pressure could significantly promote thermal NOx formation resulting form increase of temperature. The fuel-air unmixedness results in the increase of maximum flame temperature, which has significant effect on change of the CRN regions-separating. The fuel-air unmixedness causes the significant increasing of thermal NOx formation.
Numerical Study of Radiation Heat Transfer for a Supercritical CO2 Turbine Linear Cascade
Authors: Khadse Akshay , Curbelo Andres , Kapat Jayanta S.
Published: November 2019

The fundamental research and technology development for supercritical CO2 (sCO2) power cycles is gaining worldwide popularity. This is due to their promise of high efficiency, compactness, wide-range-applicability and eco-friendliness. One of the active research areas in the sCO2 power cycle field is to increase cycle efficiency by utilizing a higher turbine inlet temperature. At high temperatures within turbines, radiation may contribute a significant portion of overall heat transfer. The purpose of this paper is to investigate and quantify the effects of radiation heat transfer within a first stage sCO2 turbine linear cascade. This particular topic has not been explored by researchers yet. The correct estimation of radiation heat transfer can prove to be critical for the design of turbine blade cooling system. The aerodynamic and heat transfer analysis of a turbine cascade is carried out using a commercial computational code, STAR-CCM+. Spectral absorption coefficient for CO2 is derived using HITRAN database at required temperature and pressure. Broadening and shifting of intensity lines due to high pressure and temperature are taken into consideration. A second approach utilizes Planck mean absorption coefficient as a function of temperature. Although the data can be extrapolated for the required higher pressure, accuracy of that extrapolated data cannot be verified. Hence the secondary purpose of this study is to encourage researchers to fill the fundamental gaps in the knowledge of CO2 radiation. Findings presented here suggest that radiation can be neglected for cooling system design of the sCO2 turbine stage 1 vane for both inlet temperatures of 1350K and 1775K.
Manufacture, Characterization and Stability Limits of an AM Prefilming Air-Blast Atomizer
Authors: Crayford Andrew P. , Lacan Franck , Runyon Jon , Bowen Philip J. , Balwadkar Shrinivas , Harper Joseph , Pugh Daniel G.
Published: November 2019

With the recent advancement of metallic additive manufacturing (AM), it is perceived that future gas turbines will be manufactured with significantly fewer parts, leading to both financial and safety improvements achieved from reductions in weight, assembly processes and failure modes associated with welded parts. In addition the design and manufacture of highly intricate parts such as fuel atomizers become free from the constraints of tooling, facilitating more complex internal flow geometries to be conceived which afford improved atomization, flame stability and hence combustion efficiency. However, it is noted that increased dimensional tolerances and surface roughness resulting from this manufacturing technique can detrimentally impact internal air and fuel flow paths and hence warrant further investigation. In this study a small-scale (200kW) pre-filming airblast atomizer, based on the Parker Hannifin commercial concept, and typical of injectors utilized in RQL aviation combustors, was manufactured by Cardiff School of Engineering’s High Value Manufacturing Laboratories. Direct metal laser sintering, was utilized to produce a fully operational single component part, manufactured in 316-grade stainless steel using a Renishaw AM250 system, providing a part with measured surface roughness (Ra) values of 12–26 μm in agreement with expected values reported in the literature. Operation of the injector as a single fluid atomizer demonstrated that the fuel channel and integrated swirlers were sufficiently accurate and concentric to result in a uniform spray pattern, displaying global liquid sheet structures which were in agreement with those previously reported. However, the effective area of the atomizer’s air-flow path, when evaluated using differential pressure measurements, was shown to be smaller than predicted, resulting in an increased pressure drop. Laser diffraction droplet sizing was utilized to evaluate the global SMD of the prefilming airblast water spray at atmospheric conditions, across a range of air to liquid ratios. SMD’s between 4.2–115μm were measured at corresponding air-flow rates of 3–25 g/s, with droplet sizes observed to decrease exponentially at higher air-flow rates. This data is again in excellent agreement with SMD correlations previously proposed. Flame stability experiments conducted at ambient pressure and elevated air temperature, demonstrated the stability of a conventional (JET A-1) fuel flame across a range of air and fuel flow rates, representative of pressure drops and AFRs in commercial operation. Further post-processing of the internal flow path walls and swirl vanes to reduce surface roughness is anticipated to result in a lower pressure drop across the air-path geometry, highlighting the potential for further improvements in AM injector performance.
Life Assessment of Large Gas Turbine Blades
Authors: Narasimhachary Santosh B. , Smith Kyle , Shinde Sachin R. , Amann Christian , Kadau Kai , Iyer Saiganesh
Published: November 2019

Large gas turbine nickel based superalloys blades are typically manufactured using an investment casting process. In spite of superior processing and quality control, large turbine blades may contain manufacturing induced discontinuities such as porosities, segregation, chemical inhomogeneities, particles, etc in few of the manufactured parts. These manufacturing discontinuities can significantly influence the reliable component life if they are under a load condition where they will form a crack. A typical engineering approach is to treat these discontinuities as a crack from the beginning of the part life. This leads to a conservative life prediction, as crack nucleation and influencing geometrical details of the discontinuities are neglected. This paper presents a framework and path forward for a comprehensive life assessment. It includes computer tomography (CT) analysis, metallographic analysis, local stress analysis, crack formation, as well as state of the art fracture mechanics analysis. For instance, CT and destructive tests reveal details of the geometry of a porous region and thereby enabling the calculation of crack formation life. A subsequent fracture mechanics analysis by engineering tool, FRANC3D can then yield a comprehensive life assessment for comparisons to experimental findings and fleet experience. This approach enables Siemens to diligently ensure that comprehensive life predication assessment has been performed for the components for robust and reliable operation.
Flame Edge Dynamics and Interaction in a Multi-Nozzle Can Combustor With Fuel Staging
Authors: Doleiden Daniel , Culler Wyatt , Tyagi Ankit , Peluso Stephen , O’Connor Jacqueline
Published: November 2019

The characterization and mitigation of thermoacoustic combustion instabilities in gas turbine engines is necessary to reduce pollutant emissions, premature wear, and component failure associated with unstable flames. Fuel staging, a technique in which the fuel flow to a multi-nozzle combustor is unevenly distributed between the nozzles, has been shown to mitigate the intensity of self-excited combustion instabilities in multiple nozzle combustors. In our previous work, we hypothesized that staging suppresses instability through a phase-cancellation effect in which the heat release rate from the staged nozzle oscillates out of phase with that of the other nozzles, leading to destructive interference that suppresses the instability. This previous theory, however, was based on chemiluminescence imaging, which is a line-of-sight integrated technique. In this work, we use high-speed laser-induced fluorescence to further investigate instability suppression in two staging configurations: center-nozzle and outer-nozzle staging. An edge-tracking algorithm is used to compute local flame edge displacement as a function of time, allowing instability-driven edge oscillation phase coherence and other instantaneous flame dynamics to be spectrally and spatially resolved. Analysis of flame edge oscillations shows the presence of convecting coherent fluctuations of the flame edge caused by periodic vortex shedding. When the system is unstable, these two flame edges oscillate together as a result of high-intensity longitudinal-mode acoustic oscillations in the combustor that drive periodic vortex shedding at each of the nozzle exits. In the stable cases, however, the phase between the oscillations of the center and outer flame edges is greater than 90 degrees (∼114 degrees), suggesting that the phase-cancellation hypothesis may be valid. This analysis allows a better understanding of the instantaneous flame dynamics behind flame edge oscillation phase offset and fuel staging-based instability suppression.
CFD and Experimental Analysis of Centrifugal Fans With Forward Curved Blades Used in Electric Motors
Authors: Borges S. S.
Published: November 2019

This work presents an analysis of the aerodynamic performance of a centrifugal fan with forward curved blades (Sirocco) applied to electric motors. In this analysis were carried out computational fluid dynamics (CFD) simulations and experimental tests for comparison of results.

The focus of this analysis is the performance comparison among three different models of general connection interface that are required for the connection between the grids of the rotating and stationary domains of CFD simulation, considering the method adopted by the Ansys CFX, software used as computational tool. Thereby, Frozen Rotor, Stage, and Transient Rotor-Stator were the interface models evaluated.

For comparison reference, the experimental data were used to evaluate the performance of each interface models for overall operating range of the fan.
Constitutive Modeling of TMF and Creep-Fatigue of a Ni-Base Alloy
Authors: O’Nora Nathan , Bouchenot Thomas , Geiger Grant , Gordon Ali P.
Published: November 2019

Engineering materials are often subjected to high temperatures and varying mechanical load, making them display both creep and fatigue. Viscoplastic models have been an attractive way to simulate the behavior of materials under these conditions due to their ability to capture the hysteresis, load rate, and stress relaxation effect exhibited by materials. Nickel-base alloys experience widespread use throughout pressure vessels and turbomachinery due to their ability to retain high strength at high temperature. In this study, the low-cycle fatigue (LCF), thermo-mechanical fatigue (TMF), and creep-fatigue (CF) of candidate material IN617 is modeled using the Chaboche viscoplasticity model. The Chaboche model is implemented using three non-linear kinematic hardening terms with static recovery included as well as nonlinear isotropic hardening. Methods for finding the kinematic and isotropic hardening from Ramberg-Osgood constants are presented to allow for model development to encompass all available data instead of fitting to specific data sets. A novel method for fitting the static recovery portion of the model from creep data is presented, allowing for the capture of complex loadings such as CF from standard creep tests. New temperature-dependent formulations of the Chaboche constants are presented for IN617. The model is compared to available test data and simulations are presented to show future experiments that could be run to further validate or improve the model.
Lagrangian Saddle Point Analysis in the Flow-Field of a Bluff-Body Stabilized Combustor
Authors: Premchand C. P. , George Nitin B. , Raghunathan Manikandan , Unni Vishnu R. , Sujith R. I. , Nair Vineeth
Published: November 2019

Experiments are performed in a partially-premixed bluff-body stabilized turbulent combustor by varying the mean flow velocity. Simultaneous measurements obtained for unsteady pressure, velocity and heat release rate are used to investigate the dynamic regimes of intermittency (10.1 m/s) and thermoacoustic instability (12.3 m/s). Using wavelet analysis, we show that during intermittency, modulation of heat release rate occurring at the acoustic frequency fa by the heat release rate occurring at the hydrodynamic frequency fh results in epochs of heat release rate fluctuations where the heat release is phase locked with the acoustic pressure. We also show that the flame position during intermittency and thermoacoustic instability are essentially dictated by saddle point dynamics in the dump plane and the leading edge of the bluff-body.
Effect of Blade Profile on Four-Passage Serpentine Configuration Designed to Negate Coriolis Effect on Heat and Fluid Flow
Authors: Sarja Ajay , Madhavan Srivatsan , Singh Prashant , Ekkad Srinath V.
Published: November 2019

Gas turbine blades are equipped with serpentine internal cooling channels with 180-degree bends, through which relatively colder air is routed to cool the internal walls. It has been established that under the influence of rotation, pressure and suction side internal wall heat transfer characteristics are very different, which leads to non-uniform metal temperatures, and hence higher levels of thermal stresses. Present study addresses this non-uniformity in heat transfer using parallel rotation to negate Coriolis effect. Further, the blade curvature does not allow rectangular or trapezoidal passages, which are typically studied. In this paper, we have numerically investigated a realistic design for the four-passage channel, where the cooling design can actually be incorporated in a blade. Four-passage configuration also features 90-degree square shaped rib turbulators, and the corresponding baseline case is smooth channel. Numerical simulations have been carried out at Reynolds numbers of 5000, 10000 and 25000 and Rotation numbers were varied between 0 and 0.25. For smooth case, heat transfer enhancement was found to be higher on suction (leading) side compared to pressure (trailing) side under both stationary and rotating conditions. The enhancement levels between stationary and rotation conditions varied marginally in these designs, indicating that buoyancy effects were insignificant. For ribbed case, the effect of 90-degree rib turbulators on local heat transfer was more pronounced on the suction side when compared to smooth case. Under rotating conditions, it was found that the cooling levels were similar to the stationary condition for both pressure and suction side internal walls.
A Non-Dimensional Approach for Generalizing the Particle Impact Behavior of Gas Turbine Fouling
Authors: Suman Alessio , Casari Nicola , Fabbri Elettra , Pinelli Michele , di Mare Luca , Montomoli Francesco
Published: November 2019

The consequences of particle deposition on gas turbine blade surface are studied since the first gas turbine application. The effects generated by particle adhesion range from performance deterioration to life reduction to complete loss of power. Even if, the effects generated by fouled blade surface are well known, the mechanisms responsible for the particle adhesion are still less clear. The variability related to the nature of materials, the impact conditions and the presence of promoting substances (such as water, oil, glue agents, etc.) imply several difficulties for comparing the results and for extracting general trends and rules useful for generating up-to-date predictive models.

In the present work, an attempt to realize a general comparison among several different particle deposition tests is carried out. Starting from the previous review work, which has collected experimental tests carried out over thirty years, in the present study, an original elaboration data is proposed. Over seventy adhesion tests realized with particle composition, size, velocity, and temperature similar to those characterize gas turbine fouling are collected and post-processed. After a dimensional analysis, the data are then classified using non-dimensional groups such as Reynolds, Weber, and Ohnesorge numbers. In this way, general threshold values for the transitions between erosion, deposition, and splashing are identified according to the literature data. This general tool allows the a priori identification of the driving phenomena (such as inertia, viscous/capillary forces), based on the knowledge of basic inputs (such as impact and particle characteristics). The general approach adopted in this work gives the opportunity to increase the gas turbine fouling knowledge based on an interdisciplinary approach.
Evaluation of Compressor Blading With Blade End Slots and Full-Span Slots in a Highly Loaded Compressor Cascade
Authors: Tang Yumeng , Liu Yangwei , Lu Lipeng
Published: November 2019

High loading design is a permanent pursuit in the field of the modern compressors to reduce the size and weight of the aero-engine. Blading with slots is a potential way to improve compressor performance. An innovative double-slot scheme was proposed and validated to control corner separation in a highly loaded compressor cascade in our previous studies. To evaluate the three-dimensional (3D) performance of blading with slots, the current research compares the performance of blading with full-span slots to that with blade end slots. First, the two-dimensional (2D) configuration performance is evaluated both for the datum and slotted profiles. The slotted configuration could effectively supress separation, especially under positive incidence conditions where the separation of the datum profile is large. Thus, two 3D blading forms, the full-span slots and the blade end slots (covering 20% of the span from the endwall), are compared within. Results show that blading with full-span slots could effectively reduce the loss under positive incidence angles, while blading with blade end slots could effectively reduce the loss above an incidence angle of −4°. The loss for the end slotted blade is lower than that of the full-span slotted blade under most incidence angles (within the range of 4°). The additional mixing loss of the jet and the main flow are caused by the full-span slots at the mid-span regions where the flow remains attached for the unslotted geometry. Blading with slots alters the flow structures and reorganises the flow in the blade end regions. The self-adaptive jets from the slot outlet push the accumulated low-momentum flow downstream and restrain its migration toward the mid-span, such that the uniform main flow in the blade mid-span region is enhanced.
Gas Turbine Fouling: The Influence of Climate and Part-Load Operating Conditions
Authors: Aldi Nicola , Casari Nicola , Morini Mirko , Pinelli Michele , Spina Pier Ruggero , Suman Alessio , Vulpio Alessandro
Published: November 2019

Energy and climate change policies associated with the continuous increase in natural gas costs pushed governments to invest in renewable energy and alternative fuels. In this perspective, the idea to convert gas turbines from natural gas to syngas from biomass gasification could be a suitable choice. Biogas is a valid alternative to natural gas because of its low costs, high availability and low environmental impact. Syngas is produced with the gasification of plant and animal wastes and then burnt in gas turbine combustor. Although synfuels are cleaned and filtered before entering the turbine combustor, impurities are not completely removed. Therefore, the high temperature reached in the turbine nozzle can lead to the deposition of contaminants onto internal surfaces. This phenomenon leads to the degradation of the hot parts of the gas turbine and consequently to the loss of performance. The amount of the deposited particles depends on mass flow rate, composition and ash content of the fuel and on turbine inlet temperature (TIT). Furthermore, compressor fouling plays a major role in the degradation of the gas turbine. In fact, particles that pass through the inlet filters, enter the compressor and could deposit on the airfoil.

In this paper, the comparison between five (5) heavy-duty gas turbines is presented. The five machines cover an electrical power range from 1 MW to 10 MW. Every model has been simulated in six different climate zones and with four different synfuels. The combination of turbine fouling, compressor fouling, and environmental conditions is presented to show how these parameters can affect the performance and degradation of the machines. The results related to environmental influence are shown quantitatively, while those connected to turbine and compressor fouling are reported in a more qualitative manner.

Particular attention is given also to part-load conditions. The power units are simulated in two different operating conditions: 100 % and 80 % of power rate. The influence of this variation on the intensity of fouling is also reported.
Thermoacoustic Spectrum of a Swirled Premixed Combustor With Partially Reflecting Boundaries
Authors: Yong Kah Joon , Meindl Max , Polifke Wolfgang , Silva Camilo F.
Published: November 2019

This study investigates the effect of partial acoustic reflection at inlet or outlet of a combustor on thermoacoustic stability. Parametric maps of the thermoacoustic spectrum are utilized for this purpose, which represent frequencies and growth rates of eigenmodes for a wide range of model parameters. It is found that a decrease of the acoustic reflection at the boundaries does not always imply an increase in the stability margin of the thermoacoustic system. As a matter of fact, a reduction in the acoustic reflection may sometimes destabilize a thermoacoustic mode. Additionally, we show that perturbed passive thermoacoustic modes may become ITA modes in the fully anechoic case. We briefly discuss the mode definitions ‘acoustic’ and ‘intrinsic’ commonly found in the literature.

The computational analysis is based on a state-space formulation of the Linearized Navier-Stokes Equations (LNSE) with discontinuous Galerkin discretization. This approach allows to describe the thermoacoustic system as a linear combination of internal acoustics, flame dynamics and acoustic boundaries. Such a segregation grants a clear analysis of the respective effects of the individual subsystems on the general stability of the system, expressed in terms of adjoint-based eigenvalue sensitivity. The state-space formulation of the LNSE proposed in this paper offers a powerful and flexible framework to carry out thermoacoustic studies of combustors with arbitrary geometry and acoustic boundary conditions.
The Effect of Step Misalignment on Purge Flow Cooling of Nozzle Guide Vane at Transonic Conditions
Authors: Luehr Luke , Sibold Ridge , Mao Shuo , Ng Wing F. , Li Zhigang , Xu Hongzhou , Fox Michael
Published: November 2019

This study describes a detailed investigation on the effects that step misalignment and upstream purge film cooling have on the endwall heat transfer for 1st stage nozzle guide vanes in a land-based power generating gas turbine at transonic conditions. Endwall Nusselt number and adiabatic film cooling effectiveness distributions were experimentally measured and compared with flow visualization. Tests were conducted in a transonic linear cascade blowdown facility where data were gathered at an exit Mach number of 0.85 with a freestream turbulence intensity of 16% at an exit Re = 1.5 × 106 based on axial chord. Varied upstream purge blowing ratios and a no blowing case were tested for 3 different upstream step geometries, the baseline (no misalignment), a span-wise upstream step of +4.86% span, and a step of −4.86% span.

Experimentation shows that the addition of upstream purge film cooling increases the Nusselt number at injection upwards of 50% but lowers it in the throat of the passage by approximately 20% compared to no blowing case. The addition of a backward facing step induces more turbulent mixing between the coolant and mainstream flows, thus reducing film effectiveness coverage and increasing Nusselt number by nearly 40% in the passage throat. In contrast, the presence of a forward step creates a more stable boundary layer for the coolant flow aiding to help keep the film attached to the endwall at higher blowing ratios. Increasing the blowing ratio increases film cooling effectiveness and endwall coverage up to a certain point, beyond which, the high momentum of the coolant results in poor cooling performance due to jet liftoff.
A Study for Rotordynamic and Leakage Characteristics of a Long-Honeycomb Seal With Two-Phase, Mainly Air Mixtures
Authors: Zhang Min , Childs Dara W.
Published: November 2019

This paper investigates the impact of the oil (silicone oil PSF-5cSt) presence in the air on the leakage and rotordynamic characteristics of a long-honeycomb seal with length-to-diameter ratio L/D = 0.748 and diameter D = 114.656 mm. Tests are carried out with inlet pressure Pi = 70.7 bars, pressure ratio PR = 0.35 and 0.25, inlet liquid volume fraction LVF = 0%, 3.5%, and 7%, and shaft speed ω = 10, 15, and 20 krpm. During the tests, the seal is centered. Test results show that leakage mass flow rate ṁ increases (as expected) as inlet LVF increases. Increasing inlet LVF makes direct stiffness K increase more rapidly with increasing excitation frequency Ω. Increasing inlet LVF has a negligible effect on K at low Ω values, but increases K at high Ω values. The value of effective damping Ceff at about 0.5ω is an indicator to the system stability since an unstable centrifugal compressor rotor can precess at about 0.5ω. Increasing inlet LVF increases the value of Ceff at about 0.5ω, reducing the possibility of sub-synchronous vibrations SSVs at about 0.5ω. San Andrés’s model is used to produce predictions. The model assumes that the test fluid in the seal clearance is an isothermal-homogenous mixture. The model adequately predicts ṁ, K, and the value of Ceff at about 0.5ω.
Effect of Switching Impulse on Piezoelectric-Based Vibration Reduction With Multiple Patches
Authors: Kelley Christopher R. , Kauffman Jeffrey L.
Published: November 2019

Piezoelectric-based vibration reduction has the potential to improve the lifetime and structural integrity of turbomachinery blades by reducing the risk of high-cycle fatigue. Semi-active techniques produce small, self-powered implementations that can meet the strict design requirements for rotating machinery. Most semi-active techniques switch piezoelectric transducers between an open circuit and a shunt circuit in a way that reduces vibration. However, these switches produce a small impulse on the structure due to the electromechanical coupling of the piezoelectric material. Since multiple-mode vibration reduction typically requires distributed sections of piezoelectric material, the switching impulse generated by one transducer may affect others. This study investigates the effect of the switching impulse on the non-switched piezoelectric transducers. Experimental testing shows the switching impulse induces a voltage response at the natural frequencies of the structure, with the strongest responses occurring at modes where both the switched and non-switched piezoelectric transducers have high electromechanical coupling. Furthermore, piezoelectric sections that lack coupling at the excitation frequency of the structure exhibit a more noticeable response to the switching impulse. This response enables remote sensing of switches, which may facilitate wireless coordinated switch timing.
Influence of the Gas-to-Wall Temperature Ratio on the Boundary Layer Transition: Investigation of the Wake Behind a Turbine Nozzle Guide Vane
Authors: Formisano Pietro , Cação Ferreira Tânia S. , Arts Tony
Published: November 2019

Previous investigations performed at the von Karman Institute for Fluid Dynamics (VKI) have shown an influence of the gas-to-wall temperature ratio on the bypass transition development along the VKI LS89 blade suction side. In the present work, the influence of this quantity on the flow field downstream of this highly-loaded nozzle guide vane is studied through the evaluation of the aerodynamic losses. The investigation is organized in three sections with different combinations of exit Mach numbers and freestream turbulence intensity (FSTI) while Tgas/Twall is varied between 1.1 and 1.3 for all the tests. The Isentropic Compression Tube facility (CT-2) at VKI allowed the determination of the total pressure loss across the cascade by means of a Pitot tube in the upstream region and a downstream three-hole needle probe. The latter is traversed in the pitch-wise direction by a pneumatic traversing system. Finally, the cascade aerodynamic efficiency is quantified by means of the kinetic energy loss coefficient ζ and the total pressure drop profile distortions in the wake region.
Multi-Objective Optimization for Piezoelectric-Based Approaches With Applications Toward Bladed Disks
Authors: Lopp Garrett K. , Kauffman Jeffrey L.
Published: November 2019

Recent years have seen a wealth of research interest in piezoelectric-based applications for turbomachinery blades covering areas including vibration actuators and sensors in test environments, as well as vibration reduction approaches. The success of these applications relies on efficient exchange of vibration energy between the mechanical and electrical domains through inclusion of the piezoelectric elements on the vibrating structure. The effective electromechanical coupling coefficient measures the quality of this energy exchange for the various vibration modes of the structure; however, there is often trade-offs between the size of the piezoelectric elements and the electromechanical coupling for the various modes of interest. As such, this paper applies a multi-objective optimization algorithm that generates Pareto-optimal fronts to aid in the selection of the optimal location of off-the-shelf piezoelectric patches on the surface of each blade of an academic blisk. As the off-the-shelf patches have a fixed geometry, this paper simplifies the optimization to only include the electromechanical coupling of the modes of interest. Both a numerical and experimental application of this optimization procedure to an 8-sector blisk machined from a single sheet of aluminum shows the effectiveness of the approach.
Impact of Sweeping Jet on Area-Averaged Impingement Heat Transfer
Authors: Osorio Andrea , Hodges Justin , Zawati Husam , Fernandez Erik J. , Kapat Jayanta S. , Rodriguez José
Published: November 2019

A series of sweeping jet-impingement experiments are conducted over a circular heated surface, with a main objective of understanding the impact of the unique flow field on the resulting heat transfer. The sweeping motion of the fluidic oscillator is influenced by the sweeping frequency and sweeping angle where each is directly dependent on the geometric design (i.e. internal feedback loops, mixing chamber, etc.). The target surface consists of a heated copper disk, where heater power is supplied to the bottom surface of the disk and adjusted until a differential of 30°C is obtained between the jet and target surface temperatures. An energy balance over the target surface temperatures provides a means for calculating area-averaged heat transfer rate, hence Nusselt number. An increase in the sweeping jet’s thermal inertia initiates an augmentation in heat transfer due to sweeping motion of the jet across the target surface. PIV data was acquired for two jet configurations, confined and unconfined, so that the recirculation behavior can be determined. The fluidic oscillator is found to improve only at a low z/d. At large z/d (greater than 4 in this study), the fluidic oscillator adversely affects the heat transfer.
A Crystal Visco-Plastic Model for Ni-Base Superalloys Under Low Cycle Fatigue
Authors: Wijeyeratne Navindra , Irmak Firat , Geiger Grant , Jeon Jun-Young , Gordon Ali
Published: November 2019

Components in gas turbines, specifically turbine blades are subjected to extreme loading conditions such as high temperatures and stresses over extended periods of time; therefore, predicting material behavior and life expectancy at these loading conditions are extremely important. The development of simulations that accurately predict monotonic response for these materials are highly desirable. Single crystal Ni-base superalloys used in the design of gas turbine blades exhibit anisotropic behavior resulting from texture development and dislocation substructures. A Crystal Visco-plastic (CVP) model has the capability of capturing both phenomena to accurately predict the deformation response of the material. The rate dependent crystal visco-plastic model consists of a flow rule and internal state variables. This model considers the inelastic mechanism of kinematic hardening which is captured using the Back stress. Crystal graphic slip is taken in to account by the incorporation of 12 Octahedral slip systems. An implicit integration structure that uses Newton Raphson iteration scheme is used to solve the desired solutions. The MATLAB model is developed in two parts, including a routine for the CVP constitutive model along with a separate routine which functions as an emulator. The emulator replicates a finite element analysis model and provides the initial calculations needed for the CVP. A significant advantage of the MATLAB model is its capability to optimize the modelling constants to increase accuracy. The CVP model has the capability to display material behavior for monotonic loading for a variety of material orientations and temperatures.
Experimental Study of the Static and Dynamic Characteristics of a Long (L/D=0.75) Labyrinth Annular Seal Operating Under Two-Phase (Liquid/Gas) Conditions
Authors: Shrestha Hari , Childs Dara W. , Tran Dung L. , Zhang Min
Published: November 2019

A 2-phase annular-seal stand (2PASS) at the Turbomachinery Laboratory of Texas A&M University is utilized to experimentally investigate a labyrinth seal operating under 2-phase flow conditions (a mixture of silicone oil and air).

A long labyrinth seal (length-to-diameter ratio L/D = 0.75, diameter D = 114.729 mm, and radial clearance Cr = 0.213 mm) is tested at a supply pressure of 62 bars-g with inlet gas volume fraction GVFi ranging from 90–100%. Tests were conducted at three pressure ratios PR (0.3, 0.4, 0.5), three rotating speeds (5, 10, 15 krpm), six GVFi (90%, 92%, 94%, 96%, 98%, 100%), and three inlet-preswirl inserts, namely, zero, medium, and high. Specifically, the ratio between the fluid’s circumferential velocity and the shaft surface’s velocity, are in ranges of 0.0–0.2, 0.5–1.6, and 0.5–2.7 for the zero, medium, and high preswirls, respectively.

The direct dynamic stiffness KΩ is negative. As GVFi decreases (more liquid), KΩ becomes more negative for the zero preswirl. The effect of changing GVFi on KΩ for the medium and high preswirls is not as clear as for the zero preswirl.

For the zero preswirl, as GVFi decreases, the cross-coupled dynamic stiffness kΩ and direct damping C damping increases. However, the effective damping Ceff values converge to almost the same positive value for higher frequencies. Hence, there is no significant effect of change in GVFi for the zero preswirl.

For the high preswirl, as GVFi decreases, kΩ decreases and C increases. As GVFi decreases, Ceff becomes less negative and eventually becomes positive for frequencies higher than Ωc. This result indicates that at certain frequencies, the presence of liquid can make the labyrinth seals with high preswirl more stable. For the seal tested, a compressor running at 15 krpm and PR (ratio of seal exit pressure and seal inlet pressure) = 0.5 with the first critical speed of 7500 rpm (125 Hz) would experience an increase in stability with presence of liquid in the flow stream for the medium and high preswirls. However, for the range of GVFi considered here, if swirl brakes are used in a compressor application to reduce the preswirl, there would be no impact of liquid presence on the stability of the compressor.

Concerning static measurements, leakage rate ṁ increases with decreases in GVFi but remains unchanged with increasing preswirl.
Multidimensional Numerical Simulations of Reacting Flow in a Non-Premixed Rotating Detonation Engine
Authors: Pal Pinaki , Kumar Gaurav , Drennan Scott A. , Rankin Brent A. , Som Sibendu
Published: November 2019

Over the last two decades, detonation based propulsion has received a great deal of attention as a potential means to achieve significant improvement in the performance of air-breathing and rocket engines. Detonative combustion mode is particularly interesting due to the resulting pressure gain from reactants to products, faster heat release, decreased entropy generation, more available work and higher thrust compared to conventional deflagrative combustion. Rotating detonation engine (RDE) is one such novel combustor concept. Realistic RDE configurations utilize separate fuel and air injection schemes, hence are not perfectly premixed. Moreover, RDE performance is governed by a large number of design parameters and operating conditions. In this context, computational fluid dynamics (CFD) has the potential to enhance the understanding of RDE combustion and aid future development/optimization of this technology.

In the present work, a CFD model was developed to simulate a representative non-premixed RDE combustor. Unsteady Reynolds-Averaged Navier-Stokes (RANS) simulations were performed for the full combustor geometry (including the separate fuel and air injection ports), with hydrogen as fuel and air as the oxidizer. Adaptive mesh refinement (AMR) was incorporated to achieve a trade-off between model accuracy and computational expense. A finite-rate chemistry model along with a 10-species detailed kinetic mechanism was employed to describe the H2-Air combustion chemistry. Two operating conditions were simulated, corresponding to the same global equivalence ratio of unity but different fuel and air mass flow rates. For both conditions, the capability of the model to capture the essential detonation wave dynamics was assessed. A validation study was performed against experimental data available on detonation wave frequency/height, reactant fill height, oblique shock angle, axial pressure distribution in the channel, and fuel/air plenum pressure. The CFD model predicted the sensitivity of these wave characteristics to the operating conditions with good accuracy, both qualitatively and quantitatively. The present CFD model offers a potential capability to perform rapid design space exploration and/or performance optimization studies for realistic full-scale RDE configurations.
Use of Ion Transport Membrane for Oxygen Generation to Enhance the Performance of the Integrated Gasification Fuel Cell System
Authors: Jeong Ji Hun , Ahn Ji Ho , Kim Tong Seop
Published: November 2019

Carbon capture and storage (CCS) processes have been studied to reduce carbon dioxide in power generation, especially in coal plants because they have been highlighted as the main source of carbon dioxide emission. In this study, the impact of oxygen supply method on the performance of the integrated gasification fuel cell (IGFC) with carbon capture was compared. The target system is based on a solid oxide fuel cell and uses the syngas produced by coal gasification as a fuel. In the reference IGFC, the oxygen required for gasification and oxy-combustion is separated through an air separation unit (ASU). On the other hand, in the system proposed in this study, oxygen is separated through an ion transport membrane (ITM). The temperature and pressure conditions, as well as the purity of the oxygen separated from the ITM, were assumed to be the same as those of the oxygen separated from the ASU, and the composition of the syngas was kept constant. The proposed system indicated a 4.0% increase in output and a 1.6%p increase in efficiency compared to that of the reference IGFC. In addition, performance was analyzed according to the operating condition of the ITM, and the change in performance within its possible operating range was found to be less than 0.3%, which was insignificant.
Forced Response Analysis of a Radial Turbine With Different Modelling Methods
Authors: Gao Yang , Gutierrez Salas Mauricio , Petrie-Repar Paul , Gezork Tobias
Published: November 2019

Forced response analysis is a critical part in the radial turbine design process. It estimates the vibration mode and level due to aerodynamic excitations and then enables the analysis of high-cycle fatigue (HCF) to determine the life span of the turbine stage. Two key aspects of the forced response analysis are the determination of the aerodynamic forcing and damping which can be calculated from unsteady 3D computational fluid dynamics (CFD) simulations. These simulations are problematic due to the high level of complexity in the simulations (multi-row, full annular, tip gap, etc.) and the consequent high-computational cost. The aim of this paper is to investigate and compare different CFD methods applied to the forced response analysis of a radial turbine. Full annular simulations are performed for the prediction of the excitation force. This method is taken as the baseline and is usually the most time-consuming one. One method of reducing the computational effort is to use Phase-lag periodic boundary conditions. A further reduction can be obtained by using a frequency-based method called nonlinear harmonic. For the prediction of aero-damping, the Phase -lag periodic boundary condition method is also available. Moreover, a frequency-based method called harmonic balance can further accelerate the aero-damping calculation. In this paper, these CFD methods will be applied to the simulations of an open-geometry radial turbine with a vaned volute. A comparison of unsteady results from different methods will be presented. These unsteady results will also be implemented to a tuned forced response analysis in order to directly compare the corresponding maximum blade vibration amplitudes.
Experimental and Numerical Analysis of Additively Manufactured Inconel 718 Coupons With Lattice Structure
Authors: Parbat Sarwesh , Min Zheng , Yang Li , Chyu Minking
Published: November 2019

In the present paper, lattice geometries have been developed and tested for application in internal cooling of gas turbine blades. These geometries are suitable for embedding within a near surface or double wall cooling configuration. Two types of unit cells with variation in number of ligaments and porosity, were used to generate two lattice configurations. The first type of unit cell consisted of six ligaments of 0.5 mm diameter joined at a common vertex situated at the middle. As such, three ligaments were located on each side of the common middle vertex. In addition, the top half of the unit cell was rotated 60 degrees compared to the bottom half of the unit cell. The second type of unit cell was derived from the first type but with four mutually perpendicular ligaments added in the middle plane. Two lattices, referred to as L1 and L2, were obtained by repeating the type 1 and type 2 unit cells, respectively, in both streamwise and spanwise directions. The test coupons consisted of these lattice structures embedded inside a channel of 2.54 mm height, 38.07 mm width and 38.1 mm in length. The coupons were fabricated using Inconel 718 powder through selective laser sintering (SLS) process. The heat transfer and pressure drop performance was evaluated using steady state tests with constant wall temperature boundary condition and for channel Reynolds number ranging from 2,800 to 15,000. In addition, steady state numerical conjugate heat transfer simulations were conducted to obtain a detailed insight into the prevalent flow field and temperature distribution. Experimental results showed a heat transfer enhancement of upto 3 times at the highest Reynolds number compared to a smooth channel. Both the heat transfer and pressure drop increased with a decrease in the porosity from L1 to L2. The numerical results revealed formation of prominent vortical structures in the inter-unit cell spaces. These vortical structures were located in the upper half of the channel causing an increased heat transfer on the top end wall. As a result, these lattice structures provided an augmented heat transfer with a potential for favorable redistribution of the coolant.