bluuebunny/crossref_metadata_2025_split huggingface dataset:
Uncertainty Analysis of Inflow Conditions on an HPT Gas Turbine Nozzle: Effect on Particle Deposition
Authors: Friso R. , Casari N. , Pinelli M. , Suman A. , Montomoli F. 
Published: January 2021

Abstract
Gas turbines (GT) are often forced to operate in harsh environmental conditions. Therefore, the presence of particles in their flow-path is expected. With this regard, deposition is a problem that severely affects gas turbine operation. Components’ lifetime and performance can dramatically vary as a consequence of this phenomenon. Unfortunately, the operating conditions of the machine can vary in a wide range, and they cannot be treated as deterministic. Their stochastic variations greatly affect the forecasting of life and performance of the components. In this work, the main parameters considered affected by the uncertainty are the circumferential hot core location and the turbulence level at the inlet of the domain. A stochastic analysis is used to predict the degradation of a high-pressure-turbine (HPT) nozzle due to particulate ingestion. The GT’s component analyzed as a reference is the HPT nozzle of the Energy-Efficient Engine (E3). The uncertainty quantification technique used is the probabilistic collocation method (PCM). This work shows the impact of the operating conditions uncertainties on the performance and lifetime reduction due to deposition. Sobol indices are used to identify the most important parameter and its contribution to life. The present analysis enables to build confidence intervals on the deposit profile and on the residual creep-life of the vane.
Fatigue Characterization of SiC/SiC Ceramic Matrix Composites in Combustion Environment
Authors: Panakarajupally Ragav P. , Elrassi Joseph , Manigandan K. , Morscher Gregory N. 
Published: January 2021

Abstract
Fatigue behavior of woven melt infiltrated (MI) SiC/SiC ceramic matrix composites (CMCs) was investigated under a tension-tension fatigue condition in a combustion environment. A special experimental facility is designed to subject the CMCs under simultaneous mechanical and combustion conditions which is more representative of some conditions experienced by the hot section components of a jet engine. The MI SiC/SiC ceramic matrix composites considered in this study consists of a SiC matrix densified with liquid Si infiltration, BN interphase and reinforced with two different fibers namely Hi-Nicalon type S and Tyranno SA fibers. A high velocity oxygen fuel (HVOF) gun is used to create the representative combustion condition and a horizontal hydraulic MTS machine to apply the mechanical loading. Several fatigue tests were conducted at different stress levels with a stress ratio of 0.1, frequency of 1 Hz and the specimen surface temperature at 1200 °C. Similar tests were conducted in an isothermal furnace condition at 1200°C for comparison. Electrical resistance (ER) was used to monitor the tests. A reduction in the fatigue life was observed for the two MI systems under combustion conditions in comparison to the isothermal furnace condition at the same applied stress level. This is attributed to the presence of harsh combustion environment present in the burner rig. Electrical resistance showed some promising results in monitoring the temperature and detecting damage in the specimen. Runout condition was set as 24 H (86400 cycles) in burner rig and 100 H (360000 cycles) in furnace environment. Specimens that achieved the runout condition were subsequently tested under monotonic tension testing at room temperature after cooldown to evaluate the residual properties. Residual strength results showed a significant strength reduction in both the furnace and burner rig environments. Post-test microscopy was conducted on the fracture surfaces and longitudinal polished sections of the failed specimens to understand the oxidation behavior and damage mechanisms.
Experimental Investigation of the Impact of Biogas on a 3 kW Micro Gas Turbine FLOX®-Based Combustor
Authors: Seliger-Ost Hannah , Kutne Peter , Zanger Jan , Aigner Manfred 
Published: January 2021

Abstract
The use of biogas has currently two disadvantages. Firstly, processing biogas to natural gas quality for feeding into the natural gas grid is a rather energy consuming process. Secondly, the conversion into electricity directly in biogas plants produces waste heat, which largely cannot be used. Therefore, a feed-in of the desulfurized and dry biogas to local biogas grids would be preferable. Thus, the biogas could be used directly at the end consumer for heat and power production. As biogas varies in its methane (CH4) and carbon dioxide (CO2) content, respectively, this paper studies the influence of different biogas mixtures compared to natural gas on the combustion in a FLOX®-based six nozzle combustor. The single staged combustor is suitable for the use in a micro gas turbine (MGT) based combined heat and power (CHP) system with an electrical power output of 3 kW. The combustor is studied in an optically accessible atmospheric test rig, as well as integrated into the MGT system. This paper focuses on the influence of the admixture of CO2 to natural gas on the NOX and CO emissions. Furthermore, at atmospheric conditions the shape and location of the heat release zone is investigated using OH* chemiluminescence (OH* CL). The combustor could be stably operated in the MGT within the complete stationary operating range with all fuel mixtures.
An Experimental and Computational Investigation of Absolute Pressure Effects on Deposition in an Effusion Cooling Geometry
Authors: Bowen Christopher P. , Bons Jeffrey P. 
Published: January 2021

Abstract
The effect of absolute pressure on deposition is studied in the High-Pressure Deposition Facility at The Ohio State University. Mass flow blockage trends are presented for the case of deposition in a single-wall flat plate effusion cooling geometry. Arizona Road Dust in the ranges of 0–10 μm and 0–3.5 μm is delivered to a 950 K coolant flow at a pressure ratio of 1.03 at absolute pressures ranging from 1 to 15.77 atm. The primary results indicate a non-linear decrease in blockage with increasing absolute pressure. Additional targeted experimental and companion computational fluid dynamics simulations are used to elucidate the relative importance of 3 physical mechanisms responsible for the trend with pressure: (1) the increase in effusion hole discharge coefficient (2) altered particle trajectories due to reduced effective Stokes and (3) altered erosion due to reduced effective Stokes. Results reveal that blockage and sticking rates are minimally affected by the changing velocity field due to the increase in discharge coefficient, thus the increased particle drag effect on particle trajectories and erosion due to changing flow density is the primary candidate. To support these conclusions, mesh morphing simulations of a 0–10 μm test are performed at 1 and 15.77 atm using the OSU Deposition Model, which captures both impact velocity and angle dependencies of deposition. The resulting structures and their unique characteristics are compared to experimental deposits, and the computational and experimental blockage histories support the conclusion that increased drag is the primary mechanism.
Experimental Investigation of an Ultra-High Bypass Ratio Embedded Boundary Layer Ingesting Propulsor for Subsonic Cruise Aircraft
Authors: Arend David J. , Wolter John D. , Hirt Stefanie M. , Gazzaniga John A. , Cousins William T. , Hardin Larry W. , Voytovych Dmytro M. , Sharma Om P. 
Published: January 2021

Abstract
An experimental investigation has been completed of the performance and operability of a first of its kind 0.289 scale boundary layer ingesting propulsor within the new 6.5ft × 6ft transonic embedded propulsor testbed of NASA’s 8ft × 6ft Supersonic Wind Tunnel. This propulsor consisted of a coupled inlet and distortion-tolerant fan stage design embedded in a simulated upper aft hybrid wing body aircraft installation. The boundary layer ingesting inlet had a length-to-diameter ratio of 0.67. The distortion tolerant fan was 22 inches in diameter and had a stage pressure ratio of 1.34 and a bypass ratio of 16. The embedded propulsor was evaluated at its Mach 0.78 local freestream conditions. At peak efficiency 100% design speed test conditions, it provided a mass flow weighted inlet total pressure recovery of 96.5% and an adiabatic fan stage efficiency of 87.9%. These values differed meaningfully from the pre-test computational fluid dynamic analysis based design intent. At this operating condition, the effects of inlet-fan coupling extended approximately 0.45 fan diameters upstream into the inlet. The inlet was measured to have a stability margin of approximately 28% and was pre-entry boundary layer separation limited. The fan had approximately 12% of stability margin at 100% corrected speed at which conditions it was flutter limited. It exhibited otherwise flutter free operation over its entire aircraft cruise operating map. Consistently increasing levels of fan stability margin were demonstrated at successively lower fan speeds to in excess of approximately 24% at 80% corrected speed. At each of these reduced speeds, fan stability margin was full annulus stall limited. Inlet airflow distortion remained one-per-rev throughout all tested conditions. At peak efficiency 100% speed test conditions, the boundary layer ingesting inlet airflow had steady state radial and circumferential ARP1420 distortion intensities of 1.2 and 7.2%, respectively. Peak time-variant distortion intensities of 2.3% radial and 8.9% circumferential were also recorded. Comparisons to pre-test computational fluid dynamic predictions are also provided.
Influence of Boundary Layer Skew on the Tip Leakage Vortex of an Axial Compressor Stator
Authors: Koppe Björn , Lange Martin , Mailach Ronald 
Published: January 2021

Abstract
For an axial compressor stator with tip gap the boundary layer in the hub end-wall region has a significant influence on the development and progression of the tip leakage vortex. Herein the so-called boundary layer skew, which develops through relative motion of the hub, is of particular interest. Therefore, experimental and numerical investigations of a single axial compressor stator row with varying tip gap height (tip gap height/chord length = 2.0%|5.4%|6.7%) have been conducted. Comparing cases with rotating or stationary hub end-wall segments upstream of the examined vanes allowed to determine the effect of skewed and un-skewed inflow boundary layer. The steady state flow fields up- and downstream of the stator row were measured using five-hole pressure probes. For validation and to improve the understanding of the existing flow phenomena 3D-RANS CFD simulations using a commercial flow solver were carried out. Furthermore, analog cases with no tip gap were examined and considered in the comparisons to extend the knowledge on this boundary layer characteristic. The results show that the boundary layer skew has a major influence on the trajectory and size of the tip leakage vortex for the cases with tip clearance. The effect of reduction of the produced losses decreases with increasing tip gap height.
Locked-In Phenomenon Between Tip Clearance Flow Instabilities and Enforced Blade Motion in Axial Transonic Compressor Rotors
Authors: Han Le , Wei Dasheng , Wang Yanrong , Zhang Xiaobo , Fang Mingchang 
Published: January 2021

Abstract
In this paper, tip clearance flow (TCF) instabilities and their relationship to blade motion are investigated numerically on a transonic transonic rotor with a large tip clearance. The numerical methods are verified by comparing with the experimental data of NACA0012 and show reliable results. It is found that the TCF instabilities are caused by the radial vortex formed in passage, which is induced by the interaction of tip clearance vortex (TCV) and main flow. When the blade is enforced vibrating with small amplitude, the results show that TCF instabilities are hardly affected by the blade vibration, and almost no phenomenon of locked-in is found. However, when the amplitude of blade vibration is increased, the interaction becomes stronger and the pressure fluctuation is enhanced. A wider locked-in region is observed. In addition, the simulation results show that the locked-in region is affected significantly by modal shapes. For the rotor here, it seems that the bending mode has a greater effect on the TCV instabilities than the torsional mode and causes a wider locked-in region. In locked-in region, the phase differences between TCV and the blade motion change with the flow conditions. In unlocked region, the period of TCF instabilities fluctuates over time, and the process is similar to that in the locked-in region.
Investigating the Causes of Outlet Guide Vane Buffeting
Authors: Harris Jonah R. , Lad Bharat , Stapelfeldt Sina 
Published: January 2021

Abstract
In the more aggressive architectures of future high-bypass aero engines, outlet guide vanes (OGVs) will be deployed even closer to the fan. Under certain circumstances this can lead to OGV buffeting. Buffeting is an aeroelastic instability, characterized as the structural response to aerodynamic excitations caused by self-sustaining flow instabilities. Buffeting of OGVs can cause structural fatigue within the low pressure system. This study aims to identify indications of buffet on an engine’s operating map, before assessing how the flow field interacts with the relevant vibrational mode. Steady simulations of the whole low pressure system were used to produce characteristics for three fan speeds and the operating points suspected of buffet were then subject to time-accurate simulations. The steady simulations were used to detect buffet symptoms and examine the change in shock formation, separation patterns and simulation residuals with changing conditions. The time-accurate CFD predicted the highest excitation of the first bow mode at the engine speed where high vibration levels were detected during static off-design engine tests. Time-averaged results of the time-accurate simulations were used to look for trends linking buffeting behaviour with aerodynamic parameters. The time-accurate data also gave indications of a transonic buffet phenomenon.
Quantitative Flow Imaging of Film Cooling Jets in a Cross-Flow Using Particle Image Velocimetry and Computational Fluid Dynamics
Authors: Brakmann Robin G. , Schöffler Robin , Kocian Frank , Schroll Michael , Willert Christian , Müller Martin , Kügeler Edmund 
Published: January 2021

Abstract
The investigated generic configuration consists of cylindrical film cooling holes with a diameter of D = 8.4 mm and an inclination angle of α = 35°. The jets are characterized by a momentum flux ratio of I = 0.63, a density ratio of DR = 0.94 and a cross-flow Reynolds number of Re = 5500. Stereoscopic PIV allows creating a (pseudo) three dimensional image of the flow field. High resolution PIV is used to evaluate velocity fluctuations. The numerical model uses the SST and an EARSM turbulence model. The turbulent scalar fluxes are computed by a constant turbulent Prandtl number as well as algebraic models for the turbulent heat flux. The presented results consist of field cuts and line profiles of the velocity, vorticity and turbulent kinetic energy. All considered numerical options can predict the velocity field accurately, the SST turbulence model is the numerically most stable model and has the lowest demands in computational costs.
Performance Improvement of a Mixed Flow Turbine Using 3D Blading
Authors: Elliott Matthew , Spence Stephen , Seiler Martin , Geron Marco 
Published: January 2021

Abstract
Mixed flow turbines have reached a level of maturity where iterative performance improvements are very small, with real performance benefits coming from better matching to a given application as opposed to improvements in technology. One ubiquitous design feature of mixed flow turbines used to control stress within the wheel is the radial fibre constraint, wherein blade material is stacked radially outward along the entirety of the blade. While this constraint yields a mechanical benefit, it constrains the aerodynamic design significantly, with the blade shape defined by one camberline.
One potential means of realizing a performance improvement is the use of 3D blading, where the blade is not constrained to a radially fibred structure. In such a design, the blade shape could be freely modified to better control blade loading and secondary flows. This study investigated the viability of such 3D blading through optimization of a state of the art mixed flow turbine. An equivalent design was ensured by maintaining the meridional shape and operating conditions of the baseline wheel, thus facilitating a fair comparison between the radial and 3D wheels.
The paper details the optimization including an innovative constraint-driven geometry modification tool, experimental validation of performance predictions, and an investigation into why 3D blading facilitated a performance improvement.
The optimization process identified a performance improvement across the entire turbocharger operating line. With performance improvements facilitated through a reduction in tip leakage loss, and improved pressure recovery within the conical diffuser. Importantly, the optimized design met targets for mass flow, maximum stress levels, and modal behaviour, through the use of the novel geometry modification process.
Fan Aerodynamics With a Short Intake at High Angle of Attack
Authors: Mohankumar Ben , Hall Cesare A. , Wilson Mark J. 
Published: January 2021

Abstract
Future turbofan engines seek shorter intakes to reduce the cruise fuel burn of a low pressure ratio, large diameter fan. However, shorter intakes increase the level of flow distortion entering the rotor when the aircraft angle of attack (AOA) is high, reducing thrust when critically needed. This paper considers how the fan rotor radial pressure ratio distribution and tip velocity triangle can be designed to improve thrust at high AOA. Full annulus, unsteady CFD is performed on three rotor designs coupled to a short intake. We show that rotor design for high AOA should be guided by three flow mechanisms. Mechanism i) is caused by high Mach number flow over the bottom intake lip, which chokes the rotor leading to high loss. Mechanism ii) is the loss generation in the rotor tip as it passes through an intake separation. Mechanism iii) shows radial flows through the rotor change both the amount and the way work is imparted on the flow. Two comparable rotor design philosophies for high thrust are proposed; high work or low loss. Rotors designed to a mid-high radial pressure ratio distribution impart high work on streamlines that migrate radially towards the hub and exit the rotor at highly cambered sections. Meanwhile, tip-high designs reduce choking losses in the midspan when operating with a separated intake, particularly when the tip velocity triangle is designed to high axial velocity diffusion over high camber. However, such designs suffer with higher tip losses after exiting an intake separation.
Dynamic Mode Decomposition Analysis of Separated Boundary Layers Under Variable Reynolds Number and Free-Stream Turbulence
Authors: Dellacasagrande M. , Verdoya J. , Barsi D. , Lengani D. , Simoni D. 
Published: January 2021

Abstract
A flat plate boundary layer has been surveyed by means of time-resolved particle image velocimetry (PIV) under variable Reynolds number (70000 &lt; Re &lt; 150000) and turbulence intensity level (1.5% &lt; Tu &lt; 2.5%). The PIV visualizations were completed in two measuring planes, that are oriented both normal and parallel to the wall. For the wall-parallel configuration, the measuring plane is located inside the boundary layer. The PIV data were post-processed by applying Dynamic Mode Decomposition (DMD), which provides frequency based modes and their corresponding growth rate. The effects of Re and Tu variation on the amplification of the dominant wavelength within the separated shear layer, which is responsible for transition, is the main subject of the present work.
The DMD modes and related eigenvalues were computed with reference to the main streamwise coordinate. This allowed discussing the effects due to the main flow parameters on the amplification of the dominant streamwise wavelengths within the separated shear layer (Kelvin-Helmholtz modes). The growth of such streamwise modes ends with the formation of large scale vortices, whose breakup forces transition. In order to obtain the effective distribution of the maximum growth rate of fluctuations at different locations and times, the DMD domain was continuously extended in the streamwise direction, accounting for a specified number of periods characterizing the large scale K-H vortices.
In order to reduce the time-space dependent results obtained by the DMD procedure, a probability density function of the most unstable wavelength and the corresponding growth rate has been computed. For the present data set, the spatial growth rate of fluctuations is found to increase at the higher Reynolds number, while it slightly reduces with increasing the Tu level. The procedure and findings discussed in this work shall be suitable for designing active control systems, such as harmonic blowing for separation control.
Microwave Chipless Resonator Strain Sensor for Pipeline Safety Monitoring
Authors: Baghelani Masoud , Abbasi Zahra , Daneshmand Mojgan 
Published: January 2021

Abstract
Real-time hoop strain monitoring is known as an important parameter for the evaluation of pipeline safety and integrity. Internal corrosion and consequently variation of wall thickness directly reflects in hoop strain variation. In addition, leakage causes a pressure drop and strain reduction due to negative pressure wave. Due to their promising features such as extremely low cost, relatively high sensitivity, compatibility with harsh environmental conditions, distant and non-contact sensing with negligible power consumption, microwave resonator-based sensors achieved great deals of interest during the last decade. In this work, a chipless flexible microwave sensor for pipeline hoop strain real-time monitoring is presented. The sensor structure comprises a flexible chipless split ring microwave tag resonator attached to the pipeline and electromagnetically coupled to a pair of gap coupled transmission lines form the reader located at a certain distance from the tag strain sensor. Strain variations as the results of the mentioned pipeline defects change the overall length of the attached tag sensor which consequently causes a shift in its resonance frequency. For assuring the tag sensor to mechanically follow the strain variation of the pipeline, the Young modulus of its structural material should be much lower than that of the pipeline. This condition also important for the integrity of the sensor-pipe system because their connection will be accomplished by an adhesive. Since copper as the standard microwave conductive material is relatively highly stiff, it is not an appropriate candidate for such an important application. For addressing this issue, the chipless tag structure is fabricated by a conductive rubber layer in this work with extremely low Young modulus guaranteeing the length of the tag strain sensor to exactly follow the strain variation of the pipeline and forms a reliable and precise pipeline strain sensor. The spectrum of the tag sensor is reflected on the reader structure spectrum which could be measured to monitor the resonance frequency shift of the tag resulted from length variation of the tag sensor directly related to the pipeline strain fluctuation.