bluuebunny/crossref_metadata_2025_split huggingface dataset:
Alternative Fuels Based on Biomass: An Experimental and Modeling Study of Ethanol Co-Firing to Natural Gas
Authors: Braun-Unkhoff Marina , Dembowski Jens , Herzler Jürgen , Karle Jürgen , Naumann Clemens , Riedel Uwe 
Published: September 2014

In response to the limited resources of fossil fuels as well as to their combustion contributing to global warming through CO2 emissions, it is currently discussed to which extent future energy demands can be satisfied by using biomass and biogenic by-products, e.g. by co-firing. However, new concepts and new unconventional fuels for electric power generation require a re-investigation of at least the gas turbine burner if not the gas turbine itself to ensure a safe operation and a maximum range in tolerating fuel variations and combustion conditions.
Within this context, alcohols, in particular ethanol, are of high interest as alternative fuel. Presently, the use of ethanol for power generation — in decentralized (micro gas turbines) or centralized gas turbine units, neat, or co-fired with gaseous fuels like natural gas and biogas — is discussed, besides its role within the transport sector.
Chemical kinetic modeling has become an important tool for interpreting and understanding the combustion phenomena observed; for example, focusing on heat release (burning velocities) and reactivity (ignition delay times). Furthermore, a chemical kinetic reaction model validated by relevant experiments performed within a large parameter range allows a more sophisticated computer assisted design of burners as well as of combustion chambers, when used within CFD (computational fluid dynamics) codes.
Therefore, a detailed experimental and modeling study of ethanol co-firing to natural gas will be presented focusing on two major combustion properties within a relevant parameter range: (i) ignition delay times measured in a shock tube device, at ambient (p = 1 bar) and elevated (p = 4 bar) pressures, for lean (φ = 0.5) and stoichiometric fuel-air mixtures, and (ii) laminar flame speed data at several preheat temperatures, also for ambient and elevated pressure, gathered from literature. Chemical kinetic modeling will be used for an in-depth characterization of ignition delays and flame speeds at technical relevant conditions.
An extensive database will be presented identifying the characteristic differences of the combustion properties of natural gas, ethanol, and ethanol co-fired to natural gas.
Enhancing the Centrifugal Compressor Performance Map Measurements Through a Developed One–Dimensional Calculation Tool to Analyse Local Flow Phenomena
Authors: Hamann Matthias , Chebli Elias , Müller Markus , Krampitz Alexander 
Published: September 2014

Centrifugal compressors for automotive turbochargers have large influence on the operation characteristic of combustion engines. Especially the improvement of the surge margin is one of the most important development targets. Thereby, a reliable detection of local flow phenomena within the compressor stage is necessary and a procedure to gain this information from standard measurement data is discussed in this paper.
A one–dimensional calculation methodology for a single-stage centrifugal compressor with a vaneless diffuser and casing treatment is presented. The tool calculates the flow properties at the impeller inlet and exit as well as at diffuser exit, based on the measured inlet and outlet data and the geometry information of the compressor. The calculated flow characteristics are plotted within the measured compressor performance map to show local flow parameters. The unsteady recirculation flow within the casing treatment, the inflow angle and the total pressure losses are considered.
The tool is validated on different compressor sizes. Thereby the compressor is equipped with static pressure measuring points at the impeller inlet and exit as well as at the diffuser exit. The calculated static pressure correlated well with the measured data with an accuracy of 2 % to 5 % on 95 % of the operating range.
In this paper an experimental parameter study is executed in order to improve the surge margin. Thereby the geometry of the diffuser and the casing treatment is varied and the compressor performance is measured on a turbocharger test rig. The calculation of the flow angles and other flow characteristics within the diffuser enables one to find out whether surge is triggered through the diffuser or the impeller.
The Effect of Impingement Jet Heat Transfer on Casing Contraction in a Turbine Case Cooling System
Authors: Tapanlis Orpheas , Choi Myeonggeun , Gillespie David R. H. , Lewis Leo V. , Ciccomascolo Carlo 
Published: September 2014

This paper reports full local Nusselt number distributions under an array of impinging jets typical of those used for thermal tip clearance control through casing contraction.
Characteristic features of this type of application are sparse arrays of short cooling holes flowing at low jet Reynolds numbers (700–11,000) and large stand-off distances from the surface into a semi-confined passage with multiple exits. These features are captured in a large scale model, approximately ten times engine scale. Heat transfer measurements are made using the transient thermochromic liquid crystal technique. The measurement domain was extended far downstream of the impingement array. This allowed the entire heat transfer coefficient distribution contributing to the contraction of the liner around the rotor blades to be captured. CFD studies were conducted to characterize the flow field obtained, which in turn is helpful in understanding the drivers of heat transfer.
The results are compared to existing industry standard correlations, which are generally outside the geometric and Reynolds number range of interest. It was shown that, for the tested geometries, the heat transfer was sensibly unaffected by whether the flow was exhausted through one side of the exit passage or equally in both directions, and the bulk flow field could be predicted using a modified distributed injection model.
The heat transfer coefficient distributions are linked to a thermal-mechanical finite element model to provide thermal boundary conditions on an idealized representation of the casing for casing contraction in the presence of cooling scheme.
For one of the geometries tested, data from an engine casing thermocouple survey have been compared to predictions of casing temperature determined using the measured heat transfer coefficient distributions and these show reasonable agreement.
Full-Annular Numerical Investigation of the Rim Seal Cavity Flows Using GPU’s
Authors: Basol A. M. , Raheem A. , Huber M. , Abhari R. S. 
Published: September 2014

In high pressure turbines to prevent the ingestion of the hot gas into the disk cavity cold air is purged from the cavities in-between the blade rows into the main flow. This numerical paper investigates this unsteady interaction between the main flow and the purge flow on a full-annular computational model of the LEC’s in-house axial turbine facility “LISA” at ETH Zurich. The simulations have been conducted on the GPU accelerated in-house solver “MULTI3”. One complete revolution of the 360° model could be completed in 48h using 18 GPU’s.
Two injection rates have been considered. For the 0.9% injection rate a separation bubble has been captured at the cavity neck which triggered high frequency pressure fluctuations. The 20° model also predicted the high frequency fluctuations; however their amplitude was underestimated due to the forcing of the flow field to periodicity. On the other hand, at the low injection rate of 0.4% no considerable separation bubble was formed inside the cavity. The unsteady simulations have demonstrated the inherent unsteadiness in the purge flow - main flow interaction.
Numerical Estimation of the Unsteady Force on Rotor Blades in a Partial Arc Admission Stage of an Axial Turbine
Authors: Yoshida Takeshi , Sakai Naoto , Matsumoto Atsushi , Kitajima Yosuke 
Published: September 2014

A study for numerical estimation about the unsteady blade force in a partial arc admission stage of an axial turbine is presented in this paper.
Firstly, in order to investigate the influence of modeling domains in CFD (Computational Fluid Dynamics) analysis upon unsteady blade forces and turbine performance in partial admission stages, CFD analyses of three models were carried out. The analysis models consist of “2D” model; only on a mean diameter, “Simple-3D” model; 3-Dimensional passages without a tip clearance and a disc cavity, and “Full-3D” model; 3-Dimensional passages with a tip clearance and a disc cavity.
It results in clear difference in unsteady blade forces among these models. And it was revealed that numerical estimations of unsteady blade forces in partial admission stages should be carried out with analysis models that include disc cavities and tip clearances. In a partial admission stage there is extremely large circumferential pressure distribution and it causes the typical leakage flow through the gaps around a blade row. The leakage flow affects the circumferential pressure distribution that is a dominant factor in the unsteady blade forces. Air turbine experiments were conducted to validate the accuracy of the CFD analyses. Turbine efficiency of the Full-3D model with the disc cavity and the tip clearance is the closest to that of the experiment among the three models. In addition, comparison of pressure histories on a blade surface between an experiment and a calculation of the Full-3D model shows remarkably good agreements.
Next, CFD analyses with two different cascade setups (Cascade A and Cascade B) of partial admission stages were conducted in order to reveal the relationship between unsteady blade forces and cascade geometries such as a pitch of blades and a pitch of nozzles. These results show that there are clear differences in unsteady blade forces in an admission arc and those at leaving an admission arc. And some of trade-off relationships among the unsteady blade forces due to the geometries in partial admission stages are pointed out.
Investigation of Non-Axisymmetric Endwall Contouring and 3D Airfoil Design in a 1.5 Stage Axial Turbine: Part II — Experimental Validation
Authors: Niewoehner Jens , Poehler Thorsten , Jeschke Peter , Guendogdu Yavuz 
Published: September 2014

This paper is the second part of a two-part paper reporting on the increase in efficiency of a 1.5 stage axial test rig turbine with the use of non-axisymmetric endwalls and 3D airfoil design. Contoured endwalls were developed for the inlet guide vane separately, as well as in combination with a bowed radial profile stacking. In addition, a contour endwall was applied to the hub of the unshrouded rotor. In part I the design of the profiled endwalls and 3D airfoils is presented, as well as a detailed analysis of the steady and unsteady CFD results. Part II reports on the experimental validation of the numerical results.
A distinct increase in mechanical efficiency for both new configurations in good agreement with the numerical results is observed. Additionally, performance map measurements demonstrate that the new designs are also beneficial under off-design conditions. Five- and three-hole-probes, as well as fast-response total pressure probes are used to investigate the new designs. The main effect is the homogenization of the yaw angle behind the first stator.
Aerodynamic and Aeroacoustic Optimization of a Transonic Centrifugal Compressor
Authors: Wang Peng , Zangeneh Mehrdad 
Published: September 2014

The performance of transonic compressors can be characterized aerodynamically and aeroacoustically. In this paper, the DLR SRV2 compressor without vaned diffusers and its redesigned version are studied. The redesign strategy (Zangeneh et al. 2011 [1]) utilized the 3D inverse design and CFD analysis. Both compressors were analyzed in ANSYS CFX 11, and the computational results show that the predicted pressure-ratio and efficiency of the original compressor have good agreement with experimental results. The simulations have also revealed that the redesigned one is superior at both design and off-design points at different rotating speeds.
This work applies a convective FW-H method to further investigate the noise radiation from these two compressors. As the blade tip speed is supersonic, the permeable integral surface scheme must be adopted. The flow quantities needed as the inputs to the FW-H solver were extracted from the CFD solutions. The numerical predictions of the noise SPLs at blade passing frequency and its harmonics match the experimental measurements reasonably well. It is found that the original compressor has significant variations of SPLs as the operating mass flow rate changes whereas the redesigned one has much slighter variations. At peak efficiency the redesigned compressor has a lower noise level.
This study provides insights for the optimal design of a transonic compressor when good aerodynamic and aeroacoustic performance are both required.
Design and Off-Design Optimization of a Low Pressure Steam Turbine Radial Diffuser Using an Evolutionary Algorithm and 3D CFD
Authors: Verstraete Tom , Prinsier Johan , Cosi Lorenzo 
Published: September 2014

The design of the radial exhaust hood of a low pressure (LP) steam turbine has a strong impact on the overall performance of the steam turbine. A higher pressure recovery of the diffuser will lead to a substantial higher power output of the turbine. One of the most critical aspects in the design of such devices is the steam guide, which guides the flow near the shroud from axial to radial direction and has a high impact on the pressure recovery.
This paper presents an extension of a design activity previously reported for the design optimization of the steam guide of a steam turbine for industrial power generation and mechanical drive of centrifugal compressors. Whereas this previous work only focused at peak efficiency, this paper will look into the off-design aspect. Peak performance, as usually used as design criteria, will now be replaced by proper off-design criteria guaranteeing a high performance level at both design and off-design conditions. On the basis of these considerations a multi-objective optimization of the steam guide has been performed keeping the exhaust outer casing unchanged.
The maximization of the objective functions is achieved by means of a numerical optimization method that uses a metamodel assisted differential evolution algorithm in combination with a CFD solver. The profile of the steam guide is parameterized by a Bezier curve. This allows for a wide variety of shapes respecting the manufacturability constraints of the design. The pressure recovery coefficient is computed over a wide operating range through several RANS computations including the last stage but introducing a mixing plane between the rotating blade and the diffuser inlet to reduce the computational burden. Steam tables are used for the accurate prediction of the steam properties.
Finally, the optimized design is analyzed by a frozen rotor computation to validate the approach. Also off-design characteristics of the optimized diffuser are shown.
Experimental Investigation of the Diffuser Vane Clearance Effect in a Centrifugal Compressor Stage With Adjustable Diffuser Geometry: Part I — Compressor Performance Analysis
Authors: Ubben Stefan , Niehuis Reinhard 
Published: September 2014

The combination of variable speed control and adjustable diffuser vanes offers an attractive design option for centrifugal compressors applied in industrial applications where a wide operating range at high efficiency level and a favorable surge line is required. However, the knowledge about the impact on compressor performance of a diffuser vane clearance between vane and diffuser wall which is mandatory since the diffuser geometry adjustment has to take place during operation, is still not satisfying.
This two-part paper summarizes results of investigations performed at the Institute of Jet Propulsion and Turbomachinery at RWTH Aachen with an industrial-like centrifugal compressor, featuring a design pressure ratio of 4 and a design speed of 35200 rpm. Particular attention was directed to the influence of the diffuser clearance on the operating behavior of the entire stage, the pressure recovery in the diffuser and on the diffuser flow by a systematic variation of the parameters diffuser clearance height, diffuser vane angle, radial gap between impeller exit and diffuser inlet, and rotor speed.
Compressor map measurements provide a summary of the operating behavior related to diffuser geometry and impeller speed, whereas detailed flow measurements with temperature and pressure probes allow a breakdown of the losses between impeller and diffuser and contribute to a better understanding of relevant flow phenomena. The results presented in Part I show that an one-sided diffuser clearance does not necessarily has a negative impact on the operation and loss behavior of the centrifugal compressor, but instead may contribute to an increased pressure ratio and improved efficiency.
The flow phenomena responsible for this detected performance behavior are exposed in Part II [28], where the results of detailed measurements with pressure probes at diffuser exit and Particle Image Velocimetry (PIV) measurements conducted inside the diffuser channel, revealing the complex and unsteady flow leaving the impeller and passing the diffuser channel, are discussed.
The experimental results are published as an open CFD testcase “Radiver 2” [26], extending the experimental data base of the testcase “Radiver” published in 2003 by Ziegler [31].
Investigations on a Test Bench for Integrated ORC-FC Micro-CHP Energy Systems
Authors: Bianchi M. , De Pascale A. , Melino F. , Peretto A. , Branchini L. 
Published: September 2014

Micro-CHP (Combined Heat and Power) energy systems are potentially suitable for residential and tertiary utilities, typically characterized by low-grade heat demand and limited electric-to-thermal energy demand ratio values. Different innovative and under development CHP technologies are currently investigated in small scale units, but a standard has not been identified till now. Moreover, depending on the load request, the produced electricity can be used, stored in electric accumulator or in the external net, or integrated with other external sources. Contextually, the available heat can be used, accumulated inside the system or dissipated. The actual convenience of small size CHP systems depends on the demand profiles and the operation management logic.
A test facility is being developed, at the University of Bologna, for the experimental characterization of the cogenerative performance of small scale hybrid power systems, composed of micro-CHP systems of different technologies: a Micro Rankine Cycles (MRC), a Proton Exchange Membrane (PEM) Fuel Cells (FC), a battery and a heat recovery subsystem. The test set-up is also integrated with an external load simulator, in order to generate variable load profiles.
This report describes the main characteristics of the implemented test bench, the selection procedure of the adopted micro-CHP unit and expected performance.
Further the development of a calculation code able to simulate the performance of the considered systems will be described. This calculation code has been applied to design the components of the test bench. More in details, in this paper the sizing of the electrical energy storage system, and of the thermal and H2 storage tanks will be presented and discussed.
Calculation of Heat Transfer Coefficient Distribution on 3D Geometries From Transient Liquid Crystal Experiments
Authors: Ryley J. C. , McGilvray M. , Gillespie D. R. H. 
Published: September 2014

A valuable new technique to provide spatially resolved heat transfer coefficient (HTC) measurements over geometrically complex surfaces has been developed. The method is generally applicable, for use with conventional transient liquid crystal experiments, and uses the capability of commercially available finite element analysis (FEA) software. This technique has many potential applications where lateral conduction effects are significant, and can provide measurements in areas where data have not previously been possible. In the current study it has been applied to a section of a stationary internal cooling passage containing engine realistic features. The technique couples experimental data from transient liquid experiments and FEA, in an iterative procedure, to generate the solutions.
Spatially resolved maps of heat transfer have been determined over the surface of the ribs for five Reynolds number conditions (18,000–105,000) for two aspect ratio passages, 1:2 and 1:3. The results are compared to conventionally processed experimental and numerical data. Where the 1D application is applicable results agree within experimental uncertainty (∼6%) at the majority of locations. Typical 1D based methods are unable to provide reliable spatial measurements over ribbed surfaces and to the authors best knowledge this is the first time distributions of HTC have been reported for engine representative rib geometry.
Unsteady Aerodynamics and Forced Response Studies on Aeroderivative Gas Turbine Exhaust System
Authors: Di Mare Luca , Thirumurthy Deepak , Green Jeffrey S. , Myers John 
Published: September 2014

Industrial and aeroderivative gas turbines use exhaust systems for flow diffusion and pressure recovery. These processes result in a three-dimensional, unsteady, turbulent, and complex flow in the exhaust diffusers. The downstream balance-of-plant systems such as heat recovery steam generators or selective catalytic systems require, in general, a steady, uniform flow out of the exhaust system.
Aeroderivative gas turbines for power generation application have a wide operational envelope. Even though the exhaust systems are designed for 70% load to 110% load, its performance is significantly altered at low power operations. Application of gas turbines at low power can increase exhaust diffuser vibrations because of diffuser flow separations and wakes from the last stage of the power turbine. Aerodynamic excitations which result in excessive structural vibration can cause the units to trip and the power plant to stop, resulting in customer revenue loss.
The primary motivation for this research is to investigate an aerodynamic mechanism to ensure reliable operation of the exhaust system by identifying the regimes where aerodynamic instabilities can occur. In-house and university supported initiative to predict unsteady aerodynamics at low power conditions shows the presence of turbulent and time dependent flow.
The frequency spectrum results are discussed for low power and high power gas turbine operating conditions. The numerical predictions are in good agreement with test results.