bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effect of Airfoil Clocking on Efficiency and Noise of Low Pressure Turbines
Authors: Vázquez Raúl , Torre Diego , Serrano Adolfo 
Published: November 2013

The effect of airfoil clocking (stator-stator interaction) on efficiency and noise of low pressure turbines (LPT) was investigated experimentally in a multistage turbine high-speed rig. The rig consisted of three stages of a state-of-the-art LPT. The stages were characterized by a very high wall-slope angle, reverse cut-off design, very high lift and very high aspect ratio airfoils.
The rig had identical blade count for the second and third stators. The circumferential position of the second stator was individually adjusted with respect to the third stator. Eight different circumferential clocking locations over one pitch were back-to-back tested.
The rig was heavily instrumented with miniature five hole probes, hot wires, hot films, total pressure and temperature rakes, pressure tappings on the airfoil surface, two array of Kulites in a rotatory module, etc. Every clocking location was tested with the same instrumentation and at the same operating conditions with the intention of determining the impact of the clocking on the overall efficiency and noise.
Due to the large amount of data, the results of this test will be reported in several papers. The present paper contains the impact on the overall efficiency, radial traverses, static pressure fields on the airfoils and averaged sound pressure levels in the duct.
The comparison of the results suggests that the efficiency is weakly affected by clocking; however the effect on noise is noticeable for some acoustic tones at certain operating conditions.
Aerodynamics of Linearly Arranged Rad-Rad Swirlers, Effect of Number of Swirlers and Alignment
Authors: Kao Yi-Huan , Tambe Samir B. , Jeng San-Mou 
Published: November 2013

A series of experiments have been conducted to study the aerodynamic characteristics of a confined swirling flow generated by multiple rad-rad swirlers arranged linearly. The rad-rad swirlers used in this study are identical, and consist of an inner, primary swirler generating counter-clockwise rotation and an outer, secondary swirler generating clockwise rotation. A two-component Laser Doppler Velocimetry (LDV) system was employed to measure the velocity in the flow field. Initial measurements were conducted on unconfined and confined flow generated by a single swirler to serve as the baseline reference for the multi-swirler arrangements. Tests were conducted for 3 and 5 swirlers arranged in a line, with a spacing of 2D between the swirler centers, where D is the swirler exit diameter. An additional 5 swirler configuration was tested, where the exit plane of the center swirler was shifted 3.2 mm (1/8 inch) in the streamwise direction.
The flow field generated by the multi-swirler arrangement is very complex, due to the interaction between the swirling jets of adjacent swirlers. The number of swirlers is seen to have a clear impact on the entire flow structure, as well as each recirculation zone. For the 3 swirler arrangement, a weak CTRZ is observed for the center swirler, whereas strong CTRZs are observed for the two outer swirlers. For the 5 swirler arrangement, the CTRZ pattern for the 3 inner swirlers is the same strong-weak-strong as seen for the 3 swirler arrangements, with weak CTRZs observed for the two outer swirlers. Higher interaction between swirlers is observed for the 5 swirler arrangement, as compared to the case with 3 swirlers. Since the swirlers are identical, the region between swirlers features merging of two opposing swirling jets, producing high turbulence intensity in the near field region.
For the case with the offset center swirler, the swirling jet from this swirler did not merge with its neighbors in the near field region. This resulted in strong CTRZ for the center swirler, accompanied by weaker CTRZs at its immediate neighbors, which is reverse of the CTRZ strength pattern observed for the initial 5 swirler arrangement.
Assessment of a Gas Turbine NOx Reduction Potential Based on a Spatiotemporal Unmixedness Parameter
Authors: Dederichs Stefan , Habisreuther Peter , Zarzalis Nikolaos , Beck Christian , Krebs Werner , Prade Bernd 
Published: November 2013

The paper presents a one-dimensional approach to assess the reduction potential of NOx emissions for lean premixed gas turbine combustion systems. NOx emissions from these systems are known to be mainly caused by high temperatures; not only from an averaged perspective but especially related to poor mixing quality of fuel and air.
The method separates the NOx chemistry in the flame front zone and the post flame zone (slow reaction). A one-dimensional treatment enables the use of detailed chemistry. A look up table parameterized by reaction progress and equivalence ratio is used to improve the computational efficiency.
The influence of mixing quality is taken into account by a probability density function of the fuel element based equivalence ratio, which itself translates into a temperature distribution. Hence, the NOx source terms are a function of reaction progress and equivalence ratio. The reaction progress is considered by means of the two-zone approach. Based on unsteady CFD data, the evolution of the probability density function with residence time has been analyzed.
Two types of definitions of an unmixedness quantity are considered. One definition accounts for spatial as well as temporal fluctuations and the other is based on the mean spatial distribution. They are determined at the location of the flame front.
The paper presents a comparison of the modeled results with experimental data. A validation and application have shown very good quantitative and qualitative agreement with the measurements. The comparison of the unmixedness definitions has proven the necessity of unsteady simulations. A general emissions - unmixedness correlation can be derived for a given combustion system.
Study of a Rich/Lean Staged Combustion Concept for Hydrogen at Gas Turbine Relevant Conditions
Authors: Bolaños Felipe , Winkler Dieter , Piringer Felipe , Griffin Timothy , Bombach Rolf , Mantzaras John 
Published: November 2013

The combustion of hydrogen-rich fuels (> 80 % vol. H2), relevant for gas turbine cycles with “pre-combustion” carbon capture, creates great challenges in the application of standard lean premix combustion technology. The significant higher flame speed and drastically reduced auto-ignition delay time of hydrogen compared to those of natural gas, which is normally burned in gas turbines, increase the risk of higher NOX emissions and material damage due to flashback. Combustion concepts for gas turbines operating on hydrogen fuel need to be adapted to assure safe and low-emission combustion.
A rich/lean (R/L) combustion concept with integrated heat transfer that addresses the challenges of hydrogen combustion has been investigated. A sub-scale, staged burner with full optical access has been designed and tested at gas turbine relevant conditions (flame temperature of 1750 K, preheat temperature of 400 °C and a pressure of 8 bar).
Results of the burner tests have confirmed the capability of the rich/lean staged concept to reduce the NOx emissions for undiluted hydrogen fuel. The NOx emissions were reduced from 165 ppm measured without staging (fuel pre-conversion) to 23 ppm for an R/L design having a fuel-rich hydrogen pre-conversion of 50 % at a constant power of 8.7 kW.
In the realized R/L concept the products of the first rich stage, which is ignited by a Pt/Pd catalyst (under a laminar flow, Re ≈ 1900) are combusted in a diffusion-flame-like lean stage (turbulent flow Re ≈ 18500) without any flashback risk. The optical accessibility of the reactor has allowed insight into the combustion processes of both stages. Applying OH-LIF and OH*-chemiluminescence optical techniques, it was shown that mainly homogeneous reactions at rich conditions take place in the first stage, questioning the importance of a catalyst in the system, and opening a wide range of optimization possibilities.
The promising results obtained in this study suggest that such a rich/lean staged burner with integrated heat transfer could help to develop a new generation of gas turbine burners for safe and clean combustion of H2-rich fuels.
Safety Issues With Reciprocating Compressor Design, Operating Practices and Maintenance
Authors: Upreti K. C. , Dev Amar , Prasad T. V. , Pundarikaksha B. 
Published: November 2013

Reciprocating compressors are extensively used on high pressure and critical applications in all industries. These equipment needs through review of design of various components for a failsafe design. API-618 specifies various details about construction of various components, but due to OEM design by compressor vendor, proper review is not done or due to cost economic of equipment these are not given importance.
There are many examples when accident took place when these issues were ignored or correct assembly procedure for assembly of components is not followed and there were mistakes in design of piping system. In this paper, some of such cases are discussed and improvements are suggested for preventing any safety incidents. The issues described are designs of unloaders and venting system, unloader and vent piping, cylinder tap off connections, end clearance pocket unloaders, distance piece and crank case venting system, purge system for motors.
One of the risks with valve unloaders is the contamination of the instrument air with flammable gas specially on high pressure application. The instrument air may get contaminated with hydrocarbon if unloader leaking from stem and leak off gas tubing which is connected to flare may get interchanged with the instrument air connection. The same mistake if not noticed & compressor started, it may lead to the incident where compressor can show showed a strange vibration pattern, and instrument air header may get contaminated with hydrocarbon gases.
Another issue is crank case pressurisation due to improper venting system which can lead to pressurisation of crank case, failure of oil seals leading to flywheel end bearing failures. Further checking for finding reasons of crank case pressurisation, it is observed that excessive rod packing leaks results from incorrect leveling of compressor, distance and cylinders.
Motor purge system is one of the essential requirements for starting large reciprocating compressors; mistake in design/fabrication of vent system may create unsafe condition leading to explosion in motor.
All issues have been discussed in paper and various solutions and fail safe design have been suggested to improve safety and reliability. The studies also indicates that proper start up procedure and follow up of correct checklists during overhauling and start up can eliminate/ identify such mistakes.
Preventing Small Bore Piping/Tubing Failures in Reciprocating Compressors
Authors: Upreti K. C. , Banerjee Dwaipayan 
Published: November 2013

API-618 Standard requires pulsation and vibration analysis of reciprocating compressors systems to prevent the system from damages. This analysis is carried out on major piping but often small bore connections are missed out in analysis and mistakes in site fabrication add up to this problem. These small bore connections on reciprocating compressor causes serious problems due to vibrations around reciprocating compressor.
This paper describes the issues of small-bore connection on Refinery CCR Platformer Net Gas Compressors where series of failures observed on small bore connection and associated tubing. Vibration/pulsation was the major contributing factor to various failures. Contributory Reasons for failure were analysed and reasons was found due to inadequate design of piping & tubing supports, Transmittal of vibration to platforms. It was found that small bore connections for PT, volume bottle drains, TI/TW were vibrating with high vibration velocity and amplitude. Max Vibration readings were found 705 micron. The dominant peak of vibration frequency is located at 15/17 X RPM. All vibrations were low frequency vibrations (< 300 Hz).
The problem was overcome by reducing SBC length and provision of better supports, reduced span for tube and pipe supports, replacement of tubes with higher schedule carbon steel pipes, shifting of instruments to less vibration areas such as basement of compressor house etc. Various modifications explained for reduction of vibration levels. Study compares condition prior to modification and new modification proposals. Modification improved vibration levels and no further failure reported.
Study indicates that more attention is warranted for small-bore attachments both in design stage and during operation. It is recommended to remove SBCs wherever possible, redesigning them so they are less susceptible to vibrations and relocating them to areas of less base motion.
N+3 and N+4 Generation Aeropropulsion Engine Combustors: Part 3 — Small Engines’ Emissions and Axial Staging Combustion Technology
Authors: Mongia Hukam C. 
Published: November 2013

Comprehensive assessment of the small rich-dome engines was conducted leading to the following emissions correlations:
NOxEI LEC = 0.02991 × OPR1.9791
RMSE = 3.0%
NOxEI TALON II = 0.01666 × OPR2.1403
RMSE = 2.0%
NOxEI CFM TI = 0.06763 × OPR1.7458
RMSE = 2.1%
NOxEI CF34 = 0.0541 × OPR1.7917R2 = 0.9794
RMSE = 2.4%
NOxEI SM = 0.04782 × OPR1.8388
RMSE = 4.2%
NOxEI All = 0.03856 × OPR1.9058
RMSE = 3.9%
The best of the small engines’ gaseous emissions, albeit at lower takeoff pressure ratios, were shown to be very competitive with the best of medium and large size engines.
Axially-staged combustion with partially premixed jets in crossflow was identified as a promising concept to pursue for the (N+3) technology mixers.
Computational Engineering Design for Micro-Scale Combustion Devices: A Thermally Improved Configuration
Authors: Saddawi Salwan David , Kipouros Timoleon , Savill Mark 
Published: November 2013

A multi-objective design optimisation study has been carried out with the objectives to improve the overall efficiency of the device and to reduce the fuel consumption for the proposed micro-scale combustor design configuration. In a previous study we identified the topology of the combustion chamber that produced improved behaviour of the device in terms of the above design criteria. We now extend our design approach, and we propose a new configuration by the addition of a micro-cooling channel that will improve the thermal behaviour of the design as previously suggested in literature. Our initial numerical results revealed an improvement of 2.6% in the combustion efficiency when we applied the micro-cooling channel to an optimum design configuration we identified from our earlier multi-objective optimisation study, and under the same operating conditions.
The computational modelling of the combustion process is implemented in the commercial computational fluid dynamics package ANSYS-CFX using Finite Rate Chemistry and a single step hydrogen-air reaction. With this model we try to balance good accuracy of the combustion solution and at the same time practicality within the context of an optimisation process. The whole design system comprises also the ANSYS-ICEM CFD package for the automatic geometry and mesh generation and the Multi-Objective Tabu Search algorithm for the design space exploration. We model the design problem with 5 geometrical parameters and 3 operational parameters subject to 5 design constraints that secure practicality and feasibility of the new optimum design configurations. The final results demonstrate the reliability and efficiency of the developed computational design system and most importantly we assess the practicality and manufacturability of the revealed optimum design configurations of micro-combustor devices.
Performance Cycle Analysis for a Multi-Fuel Hybrid Engine
Authors: Yin Feijia , Rao Arvind G. , van Buijtenen Jos P. 
Published: November 2013

Over the last decades, aviation has become a dominant way of travelling for human beings. However, the global warming and ozone depletion have become the major problems for humankind. Although aviation only counts for a minority of total pollutions, it shouldn’t be ignored any more. Therefore, the ACARE has set an ambitious objective for the year of 2050 to reduce CO2 emission by 75%, NOx emission by 90% and noise emission by 65% compared to these levels in 2000 [1].This reduction is to be achieved by combined improvements in aircraft, propulsion systems and air traffic management systems.
To achieve the ACARE goal, a novel multi-fuel hybrid engine concept was proposed for a multi-fuel blended wing body aircraft. A parametric analysis has been carried out in previous work, and the reference point was initially chosen at cruise. This paper continues to analyse the cycle performance of the hybrid engine. Firstly, the impacts of using a mixer was analysed at the reference point; secondly, a comparison was made between the hybrid engine and a conventional engine; furthermore, the hybrid engine performance was analysed at various operating altitudes and Mach number; additionally, the impacts of the inter-stage turbine burner were investigated. Finally, the impacts of fuel ratio on the engine performance was examined for a given thrust at take-off.
A Novel Thermally Activated R744 Heat Pump Cycle
Authors: Bannar-Martin Luke , Childs Peter 
Published: November 2013

A novel thermally activated transcritical R744 heat pump cycle, which combines the principles of both the reverse Rankine cycle and Brayton cycle has been analysed. The cycle produces simultaneous hot and cold streams at three temperature levels; 60°C for hot water, 40°C for low temperature ambient heating, 10°C for ambient cooling. The cycle has been designed to fulfil the requirements of a flexible ‘hybrid’ trigeneration scheme, where the three energy streams (electricity, heating and cooling) can be matched closely to the user demands — maximising the Energy Utilisation Factor (EUF) of the fuel. Such a system is likely to be used in environmentally resilient cities in either tertiary sector buildings, interconnected residential zones, industry or other large buildings such as hospitals and educational establishments.
The cycle is activated using recuperated thermal energy from a gas turbine exhaust stream and under certain operating conditions uses a small proportion of the electricity produced by the gas turbine generator set. Recuperation is achieved using a direct exhaust gas to R744 recuperating heat exchanger. At higher levels of thermal recuperation, the increase in expander inlet temperature results in a substantial increase in the Coefficient Of Performance (COP). With an expander inlet temperature of 250°C the cycle achieves a COP in cooling of 1.13, whilst with a expander inlet temperature of 350°C the cycle achieves a COP in cooling of 1.58. These values of COP in cooling are typical of double and triple stage absorption chillers respectively. The values for COP in heating are 1.97 for an expander inlet temperature of 250°C, and 2.41 for an expander inlet temperature of 350°C.
The cycle is also capable of acting as a power positive bottoming cycle, whilst still providing heating and cooling. Under these circumstances, and assuming an expander inlet temperature of 350°C, the cycle has a thermal to mechanical conversion efficiency of 9.7%. The corresponding values of COP in cooling and heating are 1.03 and 1.80 respectively.
Inverted Brayton Cycle With Exhaust Gas Recirculation: A Numerical Investigation
Authors: Henke Martin , Monz Thomas , Aigner Manfred 
Published: November 2013

Micro gas turbine (MGT) based CHP units provide a highly efficient, low-pollutant technology to supply heat and electrical power from fossil and renewable energy sources; however, pressurized MGT systems in an electrical power range from 1 to 5 kWel utilize very small turbocharger components. These components suffer from higher losses, like seal and tip leakages, resulting in a reduced electrical efficiency.
This drawback is avoided by an Inverted Brayton Cycle (IBC) based system. In an IBC hot gas is produced in a combustion chamber at atmospheric pressure. Subsequently, the exhaust gas is expanded in a turbine from atmospheric to sub-atmospheric pressure level. In order to increase electrical efficiency, heat from the turbine exhaust gas is recuperated to the combustion air. After recuperation, the gas is compressed to atmospheric pressure and is discharged from the cycle. To decrease the power demand of the compressor, and thereby increasing the electrical cycle efficiency, it is crucial to further extract residual thermal power from the gas before compression. Coolant flows provided by heating applications can use this heat supply combined with heat from the discharged exhaust gas. The low pressure levels of the IBC result in high volumetric gas flows, enabling the use of large, highly efficient turbocharger components. Because of this efficiency benefit and the described cooling demand, micro-CHP applications provide an ideal field for utilization of the IBC. To further increase the total efficiency, discharged exhaust gas can be partially recirculated to the air inlet of the cycle.
In the present paper a steady state analysis of an IBC with exhaust gas recirculation (EGR) is shown, and compared to the performance of a conventional Brayton Cycle with equivalent component properties. Using EGR, it could be found that the sensitivity of the electrical cycle efficiency to the coolant temperature further increases. The sequent discussion focuses on the trade-off between total efficiency and electrical efficiency, depending on coolant temperature and EGR rate. The results show that EGR can increase the total efficiency by 10 to 15 %-points, while electrical efficiency decreases by 0.5 to 1 %-point. If the coolant temperature is below 35 °C, condensation of water vapor in the exhaust gas leads to a further increase of heat recovery efficiency.
A validated in-house simulation tool based on turbocharger maps has been used for the calculations.
MAN’s New Gas Turbines for Mechanical Drive and Power Generation Applications
Authors: Aschenbruck Emil , Cagna Michele , Langusch Volker , Orth Ulrich , Spiegel Andreas , Wiedermann Alexander , Wiers Sven-Hendrik 
Published: November 2013

MAN Diesel & Turbo recently developed a completely new gas turbine family for the first time in its history. The first product line contains both two-shaft and single-shaft gas turbines in the 6 – 7 MW class. The two-shaft engine was thoroughly tested at MAN’s gas turbine test center, and the first engine has been delivered to a launch customer. For MAN, it constitutes a technology platform that will produce further developments and new models in the coming years.
The two-shaft design makes the new gas turbine an ideal mechanical drive for both turbo compressors and pumps. This gas turbine operates to suit the optimum duty point of the driven machine; both in a wide speed and power range. The two stage power turbine design allows for a wide speed range of 45 to 105% while maintaining high efficiency. For power generation a single-shaft version has been created by adding one additional stage to the two stage high pressure turbine. The compressor pressure ratio is 15, which is high enough for achieving the highest potential efficiency for both generator and compressor drive applications. Low pollutant emission levels are achieved with MAN’s DLN combustion technology. The gas turbine exhaust temperature is sufficiently high to reach high heat recovery rates in combined heat and power cycles. Another important feature of the new gas turbine is its unrestricted suitability for taking load quickly and rapid load changes.
Service costs have also been significantly improved upon. MAN opted for a sturdy and modular gas turbine construction, while not compromising on efficiency. The objective is to extend service life and shorten down time occurrences. The modular package assembly process helps to reduce routine maintenance and repair time, and ultimately package downtime.