bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of Cavity Flows Modeling on Centrifugal Compressor Stages Performance Prediction Across Different Flow Coefficient Impellers
Authors: Guidotti Emanuele , Toni Lorenzo , Rubino Dante Tommaso , Tapinassi Libero , Naldi Giovanni , Koyyalamudi V. V. N. K. Satish , Prasad Sridhar 
Published: September 2014

Computational Fluid Dynamics (CFD) is becoming fundamental to predict turbomachinery performance. However, only using advanced numerical models coupled with high fidelity grid generation is possible to reach a very good matching with test data. In this regard, secondary flow modeling plays a critical role in the accuracy of performance prediction for centrifugal compressor stages. This study analyses the effects of cavity models on centrifugal compressor stages performance across the full range of impeller flow coefficients used in common industrial applications. Both bi-dimensional low flow coefficients with splitter and non splitter blades and three-dimensional high flow coefficients stages have been used as test cases to compare the numerical prediction with test data. Furthermore the effects of secondary flows modeling have been assessed when comparing detailed flow features with advanced experimental data both in terms of 1D profiles and 2D maps.
The effects of cavity flows modeling is growing, as expected, moving to very low flow coefficients, reaching several points of difference in efficiency calculation with respect to simpler models. Furthermore, the agreement with experimental data is very good both in terms of overall performance and detailed flow features. Finally, the high fidelity CFD is capable to give deep in-sides into the flow evolution inside the machine allowing aero designers to design centrifugal compressor stages with higher performance. It should be remarked here that a good matching of CFD prediction with test data is possible only by using high fidelity models.
Impact of Turbulator Design on the Heat Transfer in a High Aspect Ratio Passage of a Turbine Blade
Authors: Naik S. , Retzko S. , Gritsch M. , Sedlov A. 
Published: September 2014

The trailing edge region of gas turbine blades is generally subjected to extremely high external heat loads due to the combined effects of high mach numbers and gas temperatures. In order to maintain the metal temperatures of these trailing edges to a level, which fulfils both the part mechanical integrity and turbine performance, highly efficient and reliable cooling of the trailing edges is required without increasing the coolant consumption.
In this paper, the heat transfer and pressure drop characteristic of three different turbulator designs in a very high aspect ratio passage have been investigated. The turbulator designs included angled and tapered ribs, broken discrete ribs and V-shaped small chevrons ribs.
The heat transfer and pressure drop characteristics of all the turbulator configurations was initially investigated via numerical predictions and subsequently in a scaled experimental perspex model. The experimental study was conducted for a range of operational Reynolds numbers and the TLC (thermochromic liquid crystal) method was used to measure the detailed heat transfer coefficients on all surfaces of the passage. Pressure taps were located at several locations within the perspex model and both the local and average heat transfer coefficients and pressure loss coefficients were determined.
The measured and predicted results show, that for all cases investigated, the local internal heat transfer coefficient, which is driven by the highly three dimensional passage flows, is highly non-uniformly within the passage. The highest overall average heat transfer was obtained for the angled and tapered turbulator. Although the average heat transfer coefficient of the discrete broken turbulator and the small chevron turbulator were slightly lower than the baseline case, they had much higher pressure losses. In terms of the overall non-dimensional performance index, which incorporates both the heat transfer and the pressure drop, it was found that the angled and tapered turbulator gave the best overall performance.
Impact of Low Load Operation on Plant Lifetime
Authors: Vogt Jan , Schaaf Thomas , Sun Hongtao , Helbig Klaus 
Published: September 2014

In the past steam turbines were designed to operate on a certain load level. However, plant operators are often forced to operate their steam turbines on various load levels depending on the fluctuating demand of the grid. Due to the influence of renewable energies on the electricity market, these fluctuations significantly increased in the last decade.
One possibility to increase a plant’s flexibility and adapt to these altered conditions is to operate it in low load during periods of reduced electricity demand, instead of shutting the plant down. Doing so, the plant can provide power very quickly, if demanded from the grid and it saves the costs for start-up.
However, like all transient events, the transition to Low Load Operation (LLO) can cause temperature differences in the rotor and thick-walled components resulting in deformations and thermal stresses which increase the lifetime consumption of the turbine or might even damage the turbine. Since LLO was mostly only a secondary criterion in the design of the turbine and installed turbine protection systems (e.g. stress controllers) do not offer sufficient protection in many cases, the possible risks of LLO should be investigated before the implementation of LLO for a plant.
This paper analyses the lifetime consumption and damaging mechanisms at different components of the steam turbine that can be caused by LLO. Therefore, test runs in LLO (down to 15% of nominal load) performed by a hard-coal fired plant are investigated. In a first step the thermal stresses occurring in the rotor during transition to LLO are evaluated. Therefore, the rotor is modeled with Finite-Element-Method and the thermal boundary conditions during transient operation are derived from measurement data recorded during the test runs. The influence of these additional stress cycles on the overall lifetime consumption is analyzed.
In a second step operation data is examined with regard to critical operation regimes (e.g. elevated temperatures at HP and IP outlet caused by windage effects).
The results show that certain components can be exposed to increased lifetime consumption during a start-stop cycle containing LLO phases. Moreover, the analysis of operation data indicates that a close monitoring of steam temperatures and pressures is necessary to avoid operation in critical regimes which might cause damage to turbine components.
Implementation of a CFD-Based Aeroelastic Analysis Toolbox for Turbomachinery Applications
Authors: Romanelli G. , Mangani L. , Casartelli E. 
Published: September 2014

The understanding of aeroelastic phenomena is fundamental for the structural integrity of many applications in aerospace and mechanical engineering and even in some other disciplines (e.g. civil engineering) where flexible structures possibly undergo unsteady fluid-dynamic loads. Therefore the availability of accurate analysis tools for the study of the aeroelastic interaction between aerodynamic and elastic forces is an important asset for the design of modern, high performance turbomachinery.
Together with the more and more powerful computing resources, current trends pursue the adoption of high-fidelity tools and state-of-the-art technology within the research fields of Computational Structural Dynamics (CSD) and Computational Fluid Dynamics (CFD). This choice is somehow obliged when dealing with highly non-linear aeroservoelastic phenomena.
The approach typically used for turbomachinery aeroelastic analysis features the so-called “one-way coupling”, i.e. the loads predicted by the aerodynamic model are transferred to the structural model to evaluate relevant stresses and displacements.
The objective of the present work is to illustrate the design and implementation of a platform for solving multidisciplinary non-linear Fluid-Structure Interaction (FSI) problems with a “two-way coupling” or fully coupled approach, that is linking together high-fidelity state-of-the-art CSD and CFD tools by means of a robust, flexible aeroelastic interface scheme.
The credibility of the proposed aeroservoelastic analysis toolbox is assessed by tackling a set of aeronautical and turbomachinery-oriented benchmark test problems such as: the evaluation of the fully coupled non-linear aeroelastic trim of HIRENASD (HIgh REynolds Number AeroStructural Dynamics) wing and the identification of the aerodynamic damping coefficient of Standard Configuration 10, high subsonic/transonic, 2D/3D compressor cascade. The results are compared with reference experimental and numerical data available in literature.
Development of a New Design Method for High Efficiency Swept Low Pressure Axial Fans With Small Hub/Tip Ratio
Authors: Lindemann Thore Bastian , Friedrichs Jens , Stark Udo 
Published: September 2014

For a competitive low pressure axial fan design low noise emission is as important as high efficiency. In this paper a new design method for low pressure fans with a small hub to tip ratio including blade sweep is introduced and discussed based on experimental investigations. Basis is an empirical axial and tangential velocity distribution at the rotor outlet combined with a distinctive sweep angle distribution along the stacking line. Several fans were designed, built and tested in order to analyze the aerodynamic as well as the aeroacoustic behavior.
For the aerodynamic performance particular attention was paid to compensate the influence of reduced pressure rise and efficiency due to increasing blade sweep. This was achieved by a method of increasing the blade chord depending on the local sweep angle which is based on single airfoil data. The tested fans without this compensation revealed a significant noise reduction effect of up to approx. 6 dB(A) for a tip sweep angle of 64° which was accompanied by an unsatisfactory effect of reduced overall aerodynamic performance.
The second group of fans did not only confirm the method of the aerodynamic compensation by a nearly unchanged pressure rise and efficiency characteristic but also revealed an increased aeroacoustic benefit of in average 9.5 dB(A) compared to the unswept version. Beside the overall characteristics the individual differences between the designs are also discussed using results of wall pressure measurements which show some significant changes of the blade tip flow structure.
Upgrading the Undergraduate Gas Turbine Lab
Authors: Lee Zachary , Lowe Shane , Van Poppel Bret P. , Benson Michael J. , St. Leger Aaron 
Published: September 2014

A study of gas turbine engines is an important component of an integrated thermodynamics and fluid mechanics two-course sequence at the United States Military Academy (USMA). Owing to the ubiquity of gas turbines in military use, graduating cadets will encounter a variety of these engines throughout their military careers. Especially for this unique population, it is important for engineering students to be familiar with the operation and applications of gas turbines. Experimental analysis of a functional auxiliary power unit (APU) from an Army utility helicopter has been a key component of this block of instruction for several decades. As with all laboratory equipment, the APU has experienced intermittent maintenance issues, which occasionally render it unusable for the gas turbine laboratory in the course. Because of this, a very basic virtual laboratory was implemented which integrated video of the physical laboratory with key parameters and behind-the-screen data collection for use in engine analysis.
A revitalized version of both the physical and virtual gas turbine laboratory experiences offered in the thermal-fluids course will include substantial improvements over the existing setup. The physical laboratory, which is centered on a refurbished APU from a medium-sized commercial aircraft, will continue to incorporate measurements of temperature and pressure throughout the combustion process, as well as fuel flow rate. In an improvement over the original laboratory setup, an orifice plate will be used to measure the flow rate of bleed air exiting the turbine, which had not previously been open during engine testing. Additionally, the air flow through the anti-surge valve was not metered in the original version of the physical laboratory. However, the anti-surge air flow can account for nearly 25% of the total air flow, and performance calculations in the physical laboratory will now account for this loss. The turbine output shaft will run a water-brake dynamometer. All instrumentation will be converted to digital signals and projected on a large screen outside the test area through a LabVIEW front panel. The virtual laboratory will include the same metering options as the operational APU. In addition, the virtual laboratory will include the option to alter engine operating parameters, such as inlet temperature and pressure or exhaust temperatures, and students may conduct broad parameter sweeps across ranges of possible inputs or desired outputs. These improvements will enable students to gain a deeper understanding of gas turbine operation and capabilities in practical applications. The improved laboratory will be implemented in Spring, 2014.
Thermodynamics Cycle Analysis, Pressure Loss and Heat Transfer Assessment of a Recuperative System for Aero Engines
Authors: Goulas A. , Donnerhack S. , Flouros M. , Misirlis D. , Vlahostergios Z. , Yakinthos K. 
Published: September 2014

Aiming in the direction of designing more efficient aero engines, various concepts have been developed in recent years, among which is the concept of an intercooled and recuperative aero engine. Particularly in the area of recuperation, MTU Aero Engines has been driving research activities in the last decade. This concept is based on the use of a system of heat exchangers mounted inside the hot-gas exhaust nozzle (recuperator). Through the operation of the system of heat exchangers, the heat from the exhaust gas, downstream the LP turbine of the jet engine is driven back to the combustion chamber. Thus, the preheated air enters the engine combustion chamber with increased enthalpy, providing improved combustion and by consequence, increased fuel economy and low-level emissions. If additionally an intercooler is placed between the compressor stages of the aero engine, the compressed air is then cooled by the intercooler thus, less compression work is required to reach the compressor target pressure.
In this paper an overall assessment of the system is presented with particular focus on the recuperative system and the heat exchangers mounted into the aero engine’s exhaust nozzle. The herein presented results were based on the combined use of CFD computations, experimental measurements and thermodynamic cycle analysis. They focus on the effects of total pressure losses and heat exchanger efficiency on the aero engine performance especially the engine’s overall efficiency and the specific fuel consumption. More specifically, two different hot-gas exhaust nozzle configurations incorporating modifications in the system of heat exchangers are examined. The results show that significant improvements can be achieved in overall efficiency and specific fuel consumption hence contributing into the reduction of CO2 and NOx emissions.
The design of a more sophisticated recuperation system can lead to further improvements in the aero engine efficiency in the reduction of fuel consumption.
This work is part of the European funded research program LEMCOTEC (Low Emissions Core engine Technologies).
Engine Testing Using Highly Reactive Fuels on Siemens Industrial Gas Turbines
Authors: Bonaldo Alessio , Andersson Mats , Larsson Anders 
Published: September 2014

Siemens Industrial Turbomachinery AB (SIT) Finspong is increasingly asked by customers to consider if a wider range of gas compositions may be operated in its gas turbines. A large part of these fuel compositions contain high concentrations of highly reactive components like hydrogen and ethane. Such fuel compositions are characterized by higher flame speeds than the standard natural gas which introduce increased risk for flashback and premature combustor and/or fuel nozzle distress.
The SIT approach for fuel flexibility testing, Experimental Burner In Test engine (EBIT) uses a separate feed for testing a selected fuel composition in one burner in a standard gas turbine installation where the other burners use fuel from the standard fuel system. The separate feed is operated as a slave to engine governor heat demand, but can also be controlled independently.
This paper describes how EBIT was used to test the capability of the SIT 3rd generation DLE burner to satisfactorily operate using highly reactive fuel components such as ethane and hydrogen. Combustion monitoring techniques and measurements to check flame behavior and assess flashback potentials of the tested fuel compositions are described. Results from testing show that the SIT 3rd generation DLE burner allows extending the levels of reactive fuel components accepted for operation on the SGT-700 33MW engine and SGT-800 50MW engine.
Film Cooling Jet Injection Effect in Heat Transfer Coefficient Augmentation for the Pressure Side Cooling of Turbine Vane
Authors: Najafabadi Hossein Nadali , Karlsson Matts , Kinell Mats , Utriainen Esa 
Published: September 2014

Improving film cooling performance of turbine vanes and blades is often achieved through application of multiple arrays of cooling holes on the suction side, the showerhead region and the pressure side. This study investigates the pressure side cooling under the influence of single and multiple rows of cooling in the presence of a showerhead from a heat transfer coefficient augmentation perspective. Experiments are conducted on a prototype turbine vane working at engine representative conditions. Transient IR thermography is used to measure time-resolved surface temperature and the semi-infinite method is utilized to calculate the heat transfer coefficient on a low conductive material. Investigations are performed for cylindrical and fan-shaped holes covering blowing ratio 0.6 and 1.8 at density ratio of about unity. The freestream turbulence is approximately 5% close to the leading edge.
The resulting heat transfer coefficient enhancement, the ratio of HTC with to that without film cooling, from different case scenarios have been compared to showerhead cooling only. Findings of the study highlight the importance of showerhead cooling to be used with additional row of cooling on the pressure side in order to reduce heat transfer coefficient enhancement. In addition, it is shown that extra rows of cooling will not significantly influence heat transfer augmentation, regardless of the cooling hole shape.
Materials Corrosion Concerns for Supercritical Carbon Dioxide Heat Exchangers
Authors: Kruizenga Alan , Fleming Darryn 
Published: September 2014

Supercritical Carbon Dioxide (S-CO2) is an efficient and flexible working fluid for power production. Research to interface S-CO2 systems with nuclear, thermal solar, and fossil energy sources are currently underway. To proceed, we must address concerns regarding high temperature compatibility of materials and compatibility between significantly different heat transfer fluids.
Dry, pure S-CO2 is thought to be relatively inert [1], while ppm levels of water and oxygen result in formation of a protective chromia layer and iron oxide [2]. Thin oxides are favorable as diffusion barriers, and for their minimal impact on heat transfer. Chromia, however, is soluble in molten salt systems (nitrate, chloride, and fluoride based salts) [3–8]. Fluoride anion based systems required the development of the alloy INOR-8 (Hastelloy N, base nickel, 17%Mo) [9] to ensure that chromium diffusion is minimized, thereby maximizing the life of containment vessels.
This paper reviews the thermodynamic and kinetic considerations for promising, industrially available materials for both salt and S-CO2 systems.
Enhanced CFD Modelling and LDA Measurements for the Air-Flow in an Aero-Engine Front Bearing Chamber: Part II
Authors: Aidarinis J. , Goulas A. 
Published: September 2014

A detailed computational study of the air-flow through the outer gap of the front bearing of an aero-engine is presented. The reason to carry out this study was to understand the flow through the bearing as a function of the operational parameters of the engine, which was necessary for the modeling of the flow in the whole bearing chamber. The complex geometry and the size of the bearing gap relative to the overall dimensions of the bearing chamber and the need for very precise and detailed information of the effect on the flow within the chamber of the bearing operational parameters, prohibited the solution of the flow through the gap together with the rest of the bearing chamber. A 3-D modeling of the flow through the outer bearing gap, which included a section of the ball bearing, was performed. Functions relating the pressure drop of the air coming through the bearing gap and the tangential component of velocity of the air exiting the bearing region, to the mass of air through the gap of the ball bearing and the rotational speed of the shaft were developed. The effect of the lubrication oil within the bearing was modeled as an anisotropic porous medium with a predefined law. In order to acquire in a mathematical form the above relationships a series of computational runs were performed. These relationships, in the form of second order curves, were subsequently introduced to the model of the bearing chamber as described in [1]. The constants of the relationships were derived through comparisons of the calculations with the experimental data. From the analysis it was concluded that the pressure drop across the bearing increases with the square of the rotational speed of the shaft with the mass flow of air through the ball bearing as a parameter and vice versa. For this particular ball bearing there is a region where, for any combination of rotational speed of the shaft and pressure drop through the bearing, there is no flow of air through the bearing.
In this paper the detailed modeling methodology, the computational flow field, the boundary conditions and finally the results are presented and discussed.
Numerical Investigations of History Temperature Field and Stress Field of Main Steam Valve
Authors: Xu Sihua , Hu Zhiqiang , He Jin , Xiao Lei , Jiang Puning 
Published: September 2014

The flexible start up stop, quick start have been considered as essential functional requirements in the development of new steam turbines. To develop a steam turbine with 566 °C live steam temperature, not only the flexible start up and stop, quick start function, but also the reasonable working life of units influenced by the transient thermal stress are going to be considered. The design of above factors faces challenge. On the other hand, benefited from improved computing technique and ability, it is possible to calculate history temperature field and thermal stress more accurate for each project-specific component.
In this paper, certain supercritical unit inlet valve will be investigated. The valve has been operated for more than 6 years in certain power plant. Thermocouples are equipped in both stop valve chamber and control valve chamber at 100% wall depth to obtain actual operation data. According to the characteristics of different heat transfer stages, numerical analysis is performed to obtain accurate history temperature field and stress field using varied boundary conditions from the cold start at room temperature until the unit at full load.