bluuebunny/crossref_metadata_2025_split huggingface dataset:
Constraint Mechanical Model and Investigation for Rub-Impact in Aero-Engine System
Authors: Ma Yanhong , Cao Chong , Zhang Dayi , Liang Zhichao , Hong Jie 
Published: August 2015

A mechanical model for rub-impact was proposed considering the additional constraints caused by rubbing. Based on the constraint mechanical model, some characteristics of response such as resonant range expansion, contact unstability and amplitude jump during rubbing were studied. The influences of typical parameters on rotor’s vibration response with rub constraint were also evaluated. The result reveals that additional constraint stiffness causes the unstable contact range and the resonant range to be wider. While greater friction coefficient between rotor and casing results in smaller response and narrower resonant range.
A simplified dynamic model for the aero-engine was built, which takes the constraint effect into account. The numerical simulation result shows that in addition to the resonant range expansion caused by the constraint, the rotor response is also closely related to rubbing location and mode shapes. The rotor response shows a feature of quasi-periodic in slight rubbing, while the rotor motion tends unstable in heavy rubbing.
Numerical Investigation of Non-Axisymmetric Endwalls in a High Pressure Axial Flow Turbine
Authors: Na Zhenzhe , Liu Bo 
Published: August 2015

In this paper, an optimization system was applied to design the non-axisymmetric endwalls for the stator of a high pressure axial flow turbine. This optimization system combines the endwall parameterization, 3D Navier-Stokes flow field calculation and genetic algorithm based on artificial neural network, which has the advantages of flexible geometry representation and automatic design of the optimal non-axisymmetric endwalls.
And, the 3D steady flow field calculation was carried out to analyze the detailed behavior of complex flow structures pre and post optimization and to examine the influences of the optimized endwalls on the stage performance as well. The results of investigation show that the optimized non-axisymmetric endwalls can significantly decrease the flow loss in the stator, but also affect other aerodynamic parameters at the stator exit, especially the flow angle, and then the flow loss at the rotor exit caused by both the passage vortex in the rotor passage and the tip leakage vortex were increased by changing the incidence angle of the rotor due to the non-axisymmetric endwalls. Finally, the stage performance of the HP turbine is not improved as expected.
Scaling of Adiabatic Effectiveness and Net Heat Flux Reduction From Near Ambient to Engine Temperatures
Authors: Greiner Nathan J. , Polanka Marc D. , Rutledge James L. 
Published: August 2015

The present work computationally examines the scaling of a fan-shaped hole’s film-cooling performance from a near ambient temperature to an engine temperature on a flat plate. Heat flux distributions for both film-cooled and non-film-cooled cases were computed for several isothermal boundary conditions. Cases with engine representative freestream temperatures and near ambient temperatures were examined.
This study first shows that the adiabatic wall temperatures interpolated from the isothermal results were lower than those measured directly using an adiabatic wall boundary condition. This was due to the presence of a thermal boundary layer in the isothermal results, which would not develop for the adiabatic case. As a result, the adiabatic effectiveness found with adiabatic models will not represent the true thermal condition found in the engine. Finally, this study shows that both the adiabatic effectiveness interpolated from the isothermal results and Net Heat Flux Reduction can be scaled from low temperature to high temperature by proper non-dimensional matching.
Effects of Composition on the Flame Stabilization of Alternative Aviation Fuels in a Toroidal Well Stirred Reactor
Authors: Vijlee Shazib Z. , Novosselov Igor V. , Kramlich John C. 
Published: August 2015

The use of alternative/synthetic fuels in jet engines requires improved understanding and prediction of flame stabilization envelopes relative to the behavior of conventional fuels. Previous studies using the Toroidal Well Stirred Reactor (TWSR) found that synthetic alternatives to JP8 behave similarly in terms of lean flameout, but there is significant difference in the flameout behavior of a highly aliphatic fuel versus that of a highly aromatic fuel. Detailed computational fluid dynamics (CFD) and chemical reactor modeling (CRM) is necessary to understand differences in flame stabilization.
The first portion of this study employs CFD models of the TWSR with reduced methane combustion chemistry. The models provide insight into the mechanism of flame stabilization inside the reactor as equivalence ratio is decreased to flameout. The CFD domain is expanded over earlier published TWSR CFD studies to capture previously unknown asymmetrical flame behavior. The Reynolds Stress Model (RSM) is used for turbulence closure, and the Eddy Dissipation Concept (EDC) model is used to include turbulence-chemistry interaction. The CFD results show that radical species (specifically OH) are transported around the reactor to interact with the incoming premixed fuel-air jet and initiate chain branching reactions. As the equivalence ratio decreases, and flameout is approached, the species concentration in the reactor becomes less homogenous. Radical production is delayed and eventually insufficient radical concentrations are available to ignite the incoming jet. The production and transport of radical species throughout the reactor are, thus, responsible for stabilizing the flame. CFD and PSR studies with methane agree that the radical behavior dictates blowout.
The second portion of this study focuses on the importance of radical species in flame stabilization, but now employs a single perfectly stirred reactor (PSR) model, which allows the study of detailed chemistry for individual components of jet fuel. An aliphatic compound (iso-octane) and an aromatic compound (toluene) are used as investigative fuels to compare the differences in the chemical kinetic behavior of blowout for aliphatic versus aromatic fuel classes. The models show that the rates at which radical species (O, H, and OH) destroy the original fuel molecule are significantly different for iso-octane and toluene. During combustion, the radical destruction of toluene is much slower than for iso-octane at a constant temperature. In PSR systems, the toluene flame blows out at a higher temperature because a higher temperature is needed to provide sufficient radical concentrations and reaction rates to maintain a stable flame.
A Simplified Theory to Justify Forward Sweep in Low Hub-to-Tip Ratio Axial Fan
Authors: Masi Massimo , Lazzaretto Andrea 
Published: August 2015

Many modern axial flow compressor and fan rotors feature forward swept blades. However, there was no general consensus on advantages due to blade forward sweep until some years ago, also because of the difficulties in isolating the effect of blade sweep alone from the global aerodynamic blading behaviour. Thus, while some researchers try to collect in a “sweep package” all modifications connected to the introduction of blade sweep, there is no attempt in the recent literature to formalise a theory on the aerodynamic effect of sweep angle on axial flow fan blades.
This paper first recalls the swept wing concept suggested by Adolf Busemann, then the original swept wing meaning is reinterpreted to present a simplified theory of blade forward sweep. This theory allows to explain the not yet completely understood changes in total pressure and efficiency due to the inclusion of sweep in the design of high circulation gradient controlled vortex design rotors.
A methodology to select the degree of forward sweep to be chosen in the preliminary design of constant-swirl bladings for rotor-only axial flow fan featuring low hub-to-tip ratio is suggested as well.
A specifically designed unswept fan and its modified configurations according to the suggested theory has been verified by using CFD.
The forward swept design increases the unswept fan total pressure in the whole operation range from about 1% to 4% and expands the stall margin at throttling by more than 10% of the design flow rate leaving efficiency and duty unchanged.
Experimental Results and CFD Simulations of Labyrinth and Pocket Damper Seals for Wet Gas Compression
Authors: Vannini Giuseppe , Bertoneri Matteo , Nielsen Kenny Krogh , Iudiciani Piero , Stronach Robert 
Published: August 2015

The most recent development in centrifugal compressor technology is towards wet gas operating conditions. This means the centrifugal compressor has to manage a liquid phase which is varying between 0 to 3% Liquid Volume Fraction (LVF) according to the most widely agreed definition. The centrifugal compressor operation is challenged by the liquid presence with respect to all the main aspects (e.g. thermodynamics, material selection, thrust load) and especially from a rotordynamic viewpoint. The main test results of a centrifugal compressor tested in a special wet gas loop [1] show that wet gas compression (without an upstream separation) is a viable technology. In wet gas conditions the rotordynamic behavior could be impacted by the liquid presence both from a critical speed viewpoint and stability wise. Moreover the major rotordynamic results from the previous mentioned test campaign [2] show that both vibrations when crossing the rotor first critical speed and stability (tested through a magnetic exciter) are not critically affected by the liquid phase. Additionally it was found that the liquid may affect the vibration behavior by partially flooding the internal annular seals and causing a sort of forced excitation phenomenon.
In order to better understand the wet gas test outcomes, the authors performed an extensive CFD analysis simulating all the different types of balance piston annular seals used (namely a Tooth on Stator Labyrinth Seal and a Pocket Damper Seal). They were simulated in both steady state and transient conditions and finally compared in terms of liquid management capability.
CFD simulation after a proper tuning (especially in terms of LVF level) showed interesting results which are mostly consistent with the experimental outcome. The results also provide a physical explanation of the behavior of both seals, which was observed during testing.
Investigation of Water Film Formation on Blade Surfaces of a Wet Compression Transonic Compressor Rotor
Authors: Zhang Hai , Jiang Bin , Luo Mingcong , Liu Xiangkun , Fan Shuangming , Yang Lu , Zheng Qun 
Published: August 2015

As is known, when water injected at the inlet of the compressor, the water droplets will move onto the blade where water film could form on the blade surface. In this paper, the movement and formation of the water film on a transonic rotor, NASA Rotor 37, are simulated and analyzed by using unsteady numerical methods under different water injecting conditions.
The motions of water droplets and flows in the blade passage are presented in detail. Tearing process of water film on the blade surface is also a key point of this research. The preliminary results indicate that the movement of water droplets is tending to deviate from the suction surface and pile on the pressure surface due to the effect of inertia force, and water film could be formed on the pressure surface. Continuity and scope of the water film on the blade surface will develop with the increasing of droplet sizes and water injection rate. Based on the simulation, it is found that more discrete water films are formed on the pressure side of blade when the droplets move onto the pressure surface, tearing phenomenon may occur where the area is of lower water film thickness. Smaller enough sprayed droplet size can not only ensure the compressor performance of wet compression, but also avoid the erosion caused by water film accumulation.
First and Second Law Analysis of Intercooled Turbofan Engine
Authors: Zhao Xin , Thulin Oskar , Grönstedt Tomas 
Published: August 2015

Although the benefits of intercooling for aero engine applications have been realized and discussed in many publications, quantitative details are still relatively limited. In order to strengthen the understanding of aero engine intercooling, detailed performance data on optimized intercooled turbofan engines are provided. Analysis is conducted using an exergy breakdown, i.e. quantifying the losses into a common currency by applying a combined use of the first and second law of thermodynamics.
Optimal intercooled geared turbofan engines for a long range mission are established with CFD based two-pass cross flow tubular intercooler correlations. By means of a separate variable nozzle, the amount of intercooler coolant air can be optimized to different flight conditions. Exergy analysis is used to assess how irreversibility is varying over the flight mission, allowing for a more clear explanation and interpretation of the benefits.
The optimal intercooled geared turbofan engine provides a 4.5% fuel burn benefit over a non-intercooled geared reference engine. The optimum is constrained by the last stage compressor blade height. To further explore the potential of intercooling the constraint limiting the axial compressor last stage blade height is relaxed by introducing an axial radial high pressure compressor. The axial-radial high pressure ratio configuration allows for an ultra-high overall pressure ratio. With an optimal top-of-climb overall pressure ratio of 140, the configuration provides a 5.3% fuel burn benefit over the geared reference engine.
The irreversibilities of the intercooler are broken down into its components to analyze the difference between the ultra-high overall pressure ratio axial-radial configuration and the purely axial configuration. An intercooler conceptual design method is used to predict pressure loss heat transfer and weight for the different overall pressure ratios. Exergy analysis combined with results from the intercooler and engine conceptual design are used to support the conclusion that the optimal pressure ratio split exponent stays relatively independent of the overall engine pressure ratio.
Uncertainty Quantification and Stochastic Variations of Renewable Fuels
Authors: Montomoli F. , Insinna M. , Cappelletti A. , Salvadori S. 
Published: August 2015

Renewable fuels have been successfully used in gas turbine combustion chambers and the layout of the chamber does not require major interventions if the composition is known. However, the variation in the composition in renewable fuels is higher than in fossil ones and it is stochastic. In principle, this variation affects the stability of the combustion, the emissions and the temperature distribution.
The combustion chamber tested in this work has been designed to reproduce the temperature distribution of MT1 test case and modelled using reactive CFD simulations. The fuel is an ideal natural gas with a random mix of methane and hydrogen.
In order to account the stochastic variation of the fuel composition, a probabilistic analysis is carried out with two sampling methods: a Monte Carlo simulation with meta-models and a Probabilistic Collocation Method. The two methodologies show similar results in terms of mean value and standard deviation.
The paper proves that is possible to predict the mean value of temperature and emissions in a modern chamber and their associated standard deviation by applying an uncertainty quantification methodology. One of the major drawbacks of the composition change is the maximum temperature variation at the exit that can reduce the life of the downstream turbine. The variation in the emissions seems less important and all the major differences in the composition are mixed out before the combustion chamber exit.
Numerical Investigation of Centrifugal Compressor Tip Clearance
Authors: Jaatinen-Värri Ahti , Turunen-Saaresti Teemu , Grönman Aki , Backman Jari , Tiainen Jonna 
Published: August 2015

In this paper, the effect of the axial tip clearance on the performance and flow fields of a centrifugal compressor is studied numerically. The compressor is equipped with a pinched vane-less diffuser. Six different axial clearances were modelled and the relative axial tip clearance was varied from 0.027 to 0.154. The tip clearance was changed by transferring the shroud in the axial direction. The modelled results are compared to measured results obtained in previous projects.
The results indicate that the effect of tip clearance to the impeller performance is linear, even though the clearance is increased to such amounts which are seldom used in traditional compressors. The clearance has significant effect on the flow fields. Even though the mass flow averaged tangential velocity remained constant with the increasing clearance, the velocity fields show increase in tangential velocity in the passage wake between the suction side of the splitter blade and pressure side of the full blade and decreased in the other blade passage with increasing clearance. Radial velocity contours showed that the backflow region near the shroud increased in size when the clearance is increased. The growth was stronger on the suction side of the splitter blade.
Even though there is quite a difference in the stage efficiency between the highest and lowest clearance, the difference in velocity triangles at the impeller exit is small. This should be taken into a consideration when compressors with high relative axial tip clearances are designed.
Analysis of the Flow Field in Optimized Axial Fans
Authors: Bamberger Konrad , Carolus Thomas 
Published: August 2015

Three design strategies for low pressure axial fans are compared. Benchmark fans are designed with the blade element momentum (BEM) method. All common validity limits are respected. Optimized fans are designed according to design guidelines obtained in earlier studies by the authors of this work. Here, “optimal” always means maximum possible total-to-static efficiency at exact fulfillment of a specific design point. One typical difference between the benchmark and optimized fans is that the optimization yields considerably smaller hub-to-tip ratios. The two design methodologies are combined for a third series of fans. These fans are also designed with the BEM method, but with the same hub size and blade number as obtained from the optimization. As a consequence of the smaller hub size, the aforementioned validity limits are violated. All three design strategies are applied at three distinct design points which are supposed to outbid the bounds of axial fans according to Cordier’s diagram. The nine resulting fans are simulated by means of steady CFD (Reynolds-averaged Navier Stokes method, RANS). Quality assurance is considered by a grid independence study and a comparison with transient simulations (SAS method).
The aerodynamic comparison reveals the weaknesses of the BEM designs which suffer from high exit losses (if designed with common validity limits) or from high hydraulic losses (if designed with small hub). Additionally, BEM designs with small hubs still have unnecessary exit losses which originate from an uneven distribution of flow velocity downstream of the fan. In contrast, the optimized designs enable a small hub without increased losses resulting in a total-to-static efficiency improvement by 2–14 percentage points depending on the design point. The flow fields of all fans are analyzed in detail to find reasons for the superiority of the optimized designs. It is found that optimized fans benefit from an evenly distributed meridional velocity profile downstream of the fan. Reasons are given why such a flow field is hardly achievable by BEM designs. Further advantages of optimized fans are found in the blade shape near the hub which strictly avoids flow separations which in standard designs often compromise the efficiency in the complete blade channel.
Concept for a Technology Assistance System to Analyze and Evaluate Materials and Tools for Milling
Authors: Auerbach T. , Gierlings S. , Veselovac D. , Seidner R. , Kamps S. , Klocke F. 
Published: August 2015

Turbine engine manufacturers permanently aim to improve the efficiency of their products. This is often accompanied by the development of new materials which have to be introduced to manufacturing. As a consequence, engineers responsible for machining process development are regularly confronted with the question, how to identify the optimal machining conditions in order to deal with the new constraints. Nowadays, the effort and success of such identification processes are to a significant degree depending on technology expert skills and experiences. From the process planning perspective, however, this circumstance is characterized by a significant degree of uncertainty.
This article presents an innovative concept for a technology assistance system (TAS) for milling. The TAS supports the operator to determine optimal machining conditions by autonomously evaluating machinability criteria such as cutting force, tool wear or surface roughness for certain work piece material/ tool combinations. This includes the planning and organization of milling experiments, its standardized and automated execution as well as the generation of surrogate models to describe the machinability criteria for a given parameter range, serving as input for a future optimization. All functionalities of the TAS are conceptually described and first results achieved using a prototype solution are introduced and discussed.
A Method to Reduce the Energy Localization in Mistuned Bladed Disks by Application-Specific Blade Pattern Arrangement
Authors: Hohl Andreas , Wallaschek Jörg 
Published: August 2015

The focus of the paper is the analysis of mistuning, that is small deviations of the blade properties e.g. due to manufacturing tolerances. The resonant amplitudes of turbine blades are very sensitive to these deviations which can lead to significantly increased vibratory response of some blades with increased risk of high cycle fatigue.
The main part of the paper discusses methods that can be used to find blade patterns which are insensitive to energy localization. The sensitivity of the forced response against harmonic mistuning, that is a harmonic alignment of the blades respective to the mistuning factors of the single blades, is examined. A previously developed reduced order model is used to efficiently conduct Monte Carlo Simulations (MCS). Especially the influence of the variance of the harmonically mistuned blade patterns is discussed. On the basis of this analysis rules are developed to suppress the energy localization. The rules are mainly focused on the alignment of the blades around the bladed disk. The approach also takes advantage of the special properties of harmonic mistuning patterns. An assignment of the blades to insensitive harmonic mistuning patterns with a specific variance and number of periods is used to reduce the maximum of the amplification factor of the forced response. A similar approach uses intentional mistuning patterns with different blade types which are aligned harmonically and are insensitive to an additional stochastic mistuning. In case of specific combinations of the dependent parameters, especially the variance of the mistuning factors and the number of periods, the energy localization can be reduced considerably.