bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Simulation of the Influence of Steam Ingestion on Compressor Stability Using a Corrected Correlation Method
Authors: Xu Haoyang , Hu Jun , Tu Baofeng 
Published: January 2021

Abstract
In order to simulate the stall boundary of a compressor more accurately under steam ingestion condition, a two-dimensional stability analysis model is developed. The model simulates compressor flow by solving compressible, two-dimensional, unsteady Euler equations with appropriate source terms. Normally, viscosity is considered for compressor flow when compressor characteristics, expressed by the Navier-Stokes equations or experiments, are used to calculate the source terms, and engineering applications pay more attention to compressor characteristics rather than detailed flow field. Therefore, the control equations are assumed to be non-viscous in this work. A corrected correlation method that does not need numerous computations under different proportions of steam is proposed at present. The method reflects the effects of gas properties on the compressor characteristic lines — a quality absent in traditional correlation method. It is most significant for the paper to adopt the proposed corrected correlation to reduce the number of independent parameters that describe compressor characteristics under different proportions of steam compared with the traditional correlation. Then the source terms associate with compressor inlet parameters by adopting the corrected correlation method to establish a modified model. The model is used to calculate the stall boundary under steam ingestion, and the results are compared with clean condition to investigate the effects of steam properties on stall boundary. As more steam is ingested, the corrected similar flow increases at the stall point while the total pressure ratio decreases when total temperature distortion remains constant. If you want to describe compressor characteristics under ingesting other gases, just modify these parameters related to gas properties in the corrected correlation.
Protection and Identification of Thermoacoustic Azimuthal Modes
Authors: Ghirardo G. , Gant F. , Boudy F. , Bothien M. R. 
Published: January 2021

Abstract
This paper first characterizes the acoustic field of two annular combustors by means of data from acoustic pressure sensors. In particular the amplitude, orientation, and nature of the acoustic field of azimuthal order n is characterized. The dependence of the pulsation amplitude on the azimuthal location in the chamber is discussed, and a protection scheme making use of just one sensor is proposed. The governing equations are then introduced, and a low-order model of the instabilities is discussed. The model accounts for the nonlinear response of M distinct flames, for system acoustic losses by means of an acoustic damping coefficient α and for the turbulent combustion noise, modelled by means of the background noise coefficient σ. Keeping the response of the flames arbitrary and in principle different from flame to flame, we show that, together with α and σ, only the sum of their responses and their 2n Fourier component in the azimuthal direction affect the dynamics of the azimuthal instability. The existing result that only this 2n Fourier component affects the stability of standing limit-cycle solutions is recovered. It is found that this result applies also to the case of a non-homogeneous flame response in the annulus, and to flame responses that respond to the azimuthal acoustic velocity. Finally, a parametric flame model is proposed, depending on a linear driving gain β and a nonlinear saturation constant κ. The model is first mapped from continuous time to discrete time, and then recast as a probabilistic Markovian model. The identification of the parameters {α, β, κ, σ} is then carried out on engine timeseries data. The optimal four parameters {α, σ, β, κ} are estimated as the values that maximize the data likelihood. Once the parameters have been estimated, the phase space of the identified low-order problem is discussed on selected invariant manifolds of the dynamical system.
Aerodynamic Investigation of Guide Vane Configurations Downstream a Rotating Detonation Combustor
Authors: Asli Majid , Stathopoulos Panagiotis , Paschereit Christian Oliver 
Published: January 2021

Abstract
Pressure Gain Combustion (PGC) is considered a possible solution to increase gas turbine cycle efficiency, due to the lower entropy generation in the combustion process. However, the highly unsteady flow produced by PGC makes it more difficult to extract work from its exhaust gas. Any outlet restriction downstream of PGC, such as turbine blades, affects its flow field and may cause additional thermodynamic losses. The unsteadiness in the form of pressure, temperature and velocity vector fluctuations has a negative impact on the operation of conventional turbines. Therefore, evaluating early turbine design parameters for such applications is of great interest. Additionally, experimental measurements and data acquisition present researchers with challenges that have to do mostly with the high temperature exhaust of PGC and the high frequency of its operation. Numerical simulations can provide important insights into PGC exhaust flow and its interaction with turbine blades. In this paper, a Rotating Detonation Combustor (RDC) and a row of nozzle guide vanes have been modeled based on the data from literature and an available experimental setup at TU Berlin. Five guide vane configurations with different geometrical parameters have been modeled. URANS simulations were done for all guide vane arrangements to investigate the effect of solidity and blade type representing different outlet restrictions on the RDC exhaust flow. Total pressure loss and velocity fluctuation were computed upstream and downstream of the vanes. The results analzed the connection between total pressure loss and the vanes solidity and thickness to chord ratio. It is observed that more than 57% of the upstream velocity angle fluctuation amplitude was damped by the vanes. Furthermore, the area reduction was found to be the significant driving factor for damping the velocity angle fluctuations, whether in the form of solidity or thickness on chord ratio increment. A further study of the flow field details revealed that the vane passages act as convergent divergent nozzles in the unsteady flow field and no compression wave exists upstream. This RDC exhaust flow investigation is an important primary step from a turbomachinery standpoint, which provided details of blade behavior in such an unsteady flow field.
Bio-Inspired High Pressure Turbine Optimization Strategy for Hybrid-Electric Engines Operating at Off-Design
Authors: Juangphanich Paht , Paniagua Guillermo , Shyam Vikram 
Published: January 2021

Abstract
Incident tolerant turbine design is a major challenge for any turbomachinery designer. High Pressure Turbines experience large aerodynamic losses when operating at reduced massflow and lower RPM. Turbine performance is adversely impacted at positive incidence angles due to shifting of the stagnation point towards the pressure side. This can cause a separation bubble in the aft suction side region. In marine life, a diverse range of animals have developed wavy surfaces along their fins and bodies to prevent stall or flow separation at engine-relevant Reynolds numbers, but for incompressible fluids.
This paper describes a novel parameterization strategy for optimizing wavy-shaped airfoils to offer superior performance at off-design operation, in the present case, at positive incidence. The methodology can be applied to all types of aircraft engines: one, two, or three spool engine configurations. The parameterized geometries are compatible with existing gas turbine manufacturing processes including casting and additive manufacturing [1,2]. The objective of the optimization was to discover the appropriate waveform combinations at the airfoil leading edge, trailing edge, and suction side characterized by their amplitude, phase, and frequency, such that the airfoils offer the lowest possible pressure losses at 15 degrees positive incidence. The optimization was performed on a high pressure turbine passage, optimized for best efficiency at nominal conditions, while maintaining the same exit flow angle and massflow. The Reynolds number is 850,000. Based on 286 designs produced, the results of the optimization show a clear benefit at positive incidence, at the expense of a slightly lower performance at nominal conditions. A final comparison of the optimized rotor with stage is included in the analysis.
Numerical Modeling and Design Challenges of Boundary Layer Ingesting Fans
Authors: Sieradzki Adam , Kwiatkowski Tomasz , Turner Mark , Łukasik Borys 
Published: January 2021

Abstract
Studies show that Boundary Layer Ingesting (BLI) propulsion systems can provide significant fuel burn reduction relative to pylon-mounted turbofan engines. However, together with great potential, this type of propulsion can lead to serious difficulties and engineering challenges. A low-speed fan has been designed for a uniform flow at the inlet using an open source design code with optimization. Numerical analyses of the fan with a uniform flow at the inlet, and one exposed to the distorted non-axisymmetric flow were performed. These required the use of full-annulus unsteady time-marching CFD model. The model was validated with experimental data obtained in a test rig which was designed and built specially for that research.
The first crucial negative effect of the distorted inlet velocity profile is a variable incidence angle of the rotor. Both the CFD calculations and the experiment show the axial velocity non-uniformity and induced non-uniform swirl in front of the rotor, due to boundary layer ingestion and flow redistribution. As a result, significant changes in the angle of attack of the blades and corresponding unsteady rotor loads are observed. The simulations and measurements were performed for different operating conditions to obtain performance curves and assess the BLI influence at the design point and beyond. This demonstrated the second problem arising from the operation of the fan with the distorted flow at the inlet, which is a reduction of the stall margin (48% reduction from experimental results). The whole stage was previously optimized for axisymmetric flow in order to simultaneously ensure a required value of stall margin and the highest possible efficiency at the design point. The experimental efficiency of the rig at the design point with distorted inlet was 2.05% lower than the undistorted inlet. The CFD model show a 1.25% reduction. Similar reductions are shown for other operating points.
Aero Engine Concepts Beyond 2030: Part 3 — Experimental Demonstration of Technological Feasibility
Authors: Schmitz Oliver , Kaiser Sascha , Klingels Hermann , Kufner Petra , Obermüller Martin , Henke Martin , Zanger Jan , Grimm Felix , Schuldt Simon , Marcellan Anna , Cirigliano Daniele , Kutne Peter , Heron-Himmel Alex , Schneider Stephan , Richter Judith , Weigand Bernhard , Göhler-Stroh Anne , Seitz Arne , Hornung Mirko 
Published: January 2021

Abstract
Recognizing the attention currently devoted to the environmental impact of aviation, this three-part publication series introduces two new aircraft propulsion concepts for the timeframe beyond 2030. The first part focuses on the novel steam injecting and recovering aero engine concept. In the second part, the free-piston composite cycle engine concept is presented.
Complementary to the two technical publications, this third part describes the cooperative project, which was initiated by an interdisciplinary consortium, aiming at the demonstration and the proof of concept of both aforementioned aero engine concepts.
At the beginning of the project, simulations on propulsion, aircraft system, and test bench level will be conducted. On this basis, preliminary tests and fundamental experiments are planned in order to establish a solid basis for the demonstration. Finally, a system demonstration will be carried out at the laboratory level. Thus, the project allows for a final judgement on both the feasibility of the new concepts and the attainability of the requirements for future aircraft propulsion systems.
Mistuning Effects on the Nonlinear Friction Saturation of Flutter Vibration Amplitude
Authors: Martel Carlos , Rodríguez Salvador 
Published: January 2021

Abstract
The blade vibration level of an aerodynamically unstable rotor is a quantity of crucial importance to correctly estimate the blade fatigue life. This amplitude is the result of the balance between the energy pumped into the blades by the gas flow, and the nonlinear dissipation at the blade-disk contact interfaces. In a tuned configuration, the blade displacements can be described as a travelling wave consisting of one fundamental nodal diameter and frequency and its higher harmonics, and the problem can be reduced to the computation of a time periodic solution in just one sector. This simplification is no longer valid for a mistuned bladed disk. The resulting nonlinear vibration of the mistuned system is a combination of several travelling waves with different number of nodal diameters, coupled through mistuning. In this case, the complete bladed disk has to be considered, which requires an extremely high computational cost, and, for this reason, reduced order models (ROM) are required to analyze this situation. In this work, we use a 3 DOF/sector mass-spring system to describe the nonlinear friction saturation of the flutter vibration amplitude of a realistic mistuned bladed disk. The convergence of the solution of the mass-spring system is still quite slow because of the presence of many unstable modes with very similar growth rates. In order to speed-up the simulations a simpler asymptotic ROM is derived from the mass-spring model, which allows for much faster integration times. The simulations of the asymptotic ROM are compared with the measurements obtained in the European project FUTURE, where an aerodynamically unstable LPT rotor was tested with different intentional mistuning patterns.
Deposition Pattern Analysis on a Fouled Multistage Test Compressor
Authors: Suman Alessio , Vulpio Alessandro , Casari Nicola , Pinelli Michele , Kurz Rainer , Brun Klaus 
Published: January 2021

Abstract
Compressor fouling is one of the main causes of gas turbine performance degradation. Microsized particles adhere to the blade surfaces increasing the surface roughness and modifying the airfoil shape. In the present work, the contamination of the Allison 250 C18 multistage compressor engine with four sorts of micrometric dust has been provided. The tests were performed changing the relative humidity at the compressor inlet and the unit rotational speed.
After each test, a photographic inspection of the internal fouled parts has been realized and the digital pictures have been analyzed employing an image processing package. The deposits build-up of stator vanes and rotor blades have been post-processed and the most affected regions of each compressor stage have been highlighted. Besides, a numerical simulation of the machine has been performed. The numerical flow field has been used to highlight the blade regions which show the most favorable conditions for particle deposition. A theoretical model has been applied to the flow field to simulate the particle deposition. The combination of the deposition model with the results of the CFD simulations gives the chance to better understand the experimentally-founded deposition patterns. Those results have been finally compared to the pictures of the patterns. The possibility to detect and measure the deposition patterns on a rotating test rig and the comparison with models and experiments gave the possibility to assess in detail the particle deposition phenomenon on a multistage axial compressor flow path.
Acquisition and Processing Considerations for Infrared Images of Rotating Turbine Blades
Authors: Knisely Brian F. , Berdanier Reid A. , Thole Karen A. , Haldeman Charles W. , Markham James R. , Cosgrove Joseph E. , Carlson Andrew E. , Scire James J. 
Published: January 2021

Abstract
As designers aim to increase efficiency in gas turbines for aircraft propulsion and power generation, spatially-resolved experimental measurements are needed to validate computational models and compare improvement gains of new cooling designs. Infrared (IR) thermography is one such method for obtaining spatially-resolved temperature measurements. As technological advances in thermal detectors enable faster integration times, surface temperature measurements of rotating turbine blades become possible to capture including the smallest features. This paper outlines opportunities enabled by the latest IR detector technologies for capturing spatially-resolved rotating blade temperatures, while also addressing some of the challenges of implementing IR for turbine rigs such as the one in the Steady Thermal Aero Research Turbine (START) Laboratory. This paper documents critical steps in achieving accurate measurements including calibration, integration times, spatial noise, and motion blur. From these results, recommendations are provided for achieving accurate IR measurements collected in a rotating turbine facility to study film cooling.
Impact of Soot Radiative Properties, Pressure and Soot Volume Fraction on Radiative Heat Transfer in Turbulent Sooty Flames
Authors: Torres Monclard Kevin , Gicquel Olivier , Vicquelin Ronan 
Published: January 2021

Abstract
The effect of soot radiation modeling, pressure, and level of soot volume fraction are investigated in two ethylene-air turbulent flames: a jet flame at atmospheric pressure studied at Sandia, and a confined pressurized flame studied at DLR. Both cases have previously been computed with large-eddy simulations coupled with thermal radiation. The present study aims at determining and analyzing the thermal radiation field for different models from these numerical results.
A Monte-Carlo solver based on the Emission Reciprocity Method is used to solve the radiative transfer equation with detailed gas and soot properties in both configurations. The participating gases properties are described by an accurate narrowband ck model. Emission, absorption, and scattering from soot particles are accounted for. Two formulations of the soot refractive index are considered: a constant value and a wavelength formulation dependency. This is combined with different models for soot radiative properties: gray, Rayleigh theory, Rayleigh-Debye-Gans theory for fractal aggregates.
The effects of soot radiative scattering is often neglected since their contribution is expected to be small. This contribution is determined quantitatively in different scenarios, showing great sensitivity to the soot particles morphology. For the same soot volume fraction, scattering from larger aggregates is found to modify the radiative heat transfer noticeably. Such a finding outlines the need for detailed information on soot particles. Finally, the role of soot volume fraction and pressure on radiative interactions between both solid and gaseous phases is investigated.
Numerical Stability Analysis of Oil Collector Case Self-Excited Vibrations
Authors: Shuvaev Nikolay V. , Voronova Natalia O. , Vinogradov Kirill A. 
Published: January 2021

Abstract
The investigation subject is an Oil Collector Case which is a thin axisymmetric stator part with console binding to the turbine rear frame. It had been suffering from high level vibrations and needed fixing measures to apply. Self-excited vibrations supposed as the main reason for defects to occur.
The problem was examined in the engine and test rig conditions. The energetic method which is usually applied to blade flutter problems was used for aeroelastic stability analysis.
Radial surface displacements were set according to the harmonic oscillation function that corresponds to the oil collector’s first bending eigenmode with two nodal diameters. 3D aerodynamic model represents a 180° sector, thus ensures that surface displacements and gas parameters on periodic surfaces are equal.
A set of simulations was carried out and calculated; the aerodynamic damping coefficient values showed aeroelastic instability predisposition in both the engine and test rig conditions for most test cases. Influence of such model parameters as seal radial clearance, pressure ratio, inlet air temperature, wave propagation direction and rotor speed was investigated.
A detailed analysis showed that for instability case positive aerodynamic work region lies inside the oil collector cavern downstream labyrinth seal where pressure wave and surface displacement speed wave are close to synchrony. Probable excitation mechanisms were described and discussed. It was demonstrated that aeroelastic instability of the same type as it was in the engine conditions can be reproduced in the test rig conditions.
An Experimental Study on the Leakage Flow on the Film Cooling Effectiveness of a Gas Turbine Shroud
Authors: Kim Gi Mun , Lee Soo In , Jeong Jin Young , Kwak Jae Su , Kim Seokbeom , Choi Jung Uk 
Published: January 2021

Abstract
In the vicinity of gas turbine blades, a complex flow field is formed due to the flow separation, reattachment, and secondary flows, and results in locally non-uniform and high heat transfer on the surfaces. In this study, the effects of leakage flow through the slot between gas turbine vane and blade rows on the film cooling effectiveness of the forward region of the shroud ring segment were experimentally investigated. The experiment was carried out in a linear cascade with five blades. Instead of vane, a row of rods at the location of the vane trailing edge was installed to consider the wake effect. The leakage flow was introduced through the slot between vane and blade rows and additional coolant air was injected from the cooling holes installed at the vane outer zone. The effects of the slot geometry, hole size, and blowing ratio on the film cooling effectiveness were experimentally investigated by using a pressure sensitive paint technique. CO2 gas and the mixture of SF6 and N2 (25%+75%) were used as leakage flow in order to simulate leakage flow to mainstream density ratios of 1.5 and 2.0, respectively. Results showed that the area averaged film cooling effectiveness was more affected by the slot width than the cooling hole size at the same blowing ratio, and the lower density ratio cases showed higher film cooling effectiveness than that of higher density ratio case at the same cooling configuration.