bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.