bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of the Turbulence Length Scale and Intensity on Spark Ignition of Kerosene Jet-A1–Air Mixtures at High Altitude Relight Conditions
Authors: Majcherczyk Michał , Zarzalis Nikolaos , Turrini Fabio 
Published: September 2014

In recent years Avio Aero and the Karlsruhe Institute of Technology (KIT) have significantly enhanced their available experimental technology level in order to consolidate and deepen the investigation of some critical phenomena in aero-engine gas turbine combustion. A key parameter in the development of a lean-burn combustor is the design of the ignition system. The increase in the amount of air that flows through the primary zone to approximately 60% of the overall air proves to be beneficial for emissions reduction. In return it causes shorter residence times in the primary zone and makes the flame kernel generation and propagation a real challenge.
With the scope to enhance the fundamental understanding of the ignition process at altitude conditions, the ISCRA rig (Ignition in Subatmospheric Conditions – Rig for Altitude Relight Investigation) has been designed and manufactured at the KIT. The design of the rig allows the generation of altitude conditions at variable flow velocities and turbulence characteristics. An optical access for ignition recording by a CCD camera is also provided.
The paper presents the results of a fundamental investigation at the KIT using a generic setup. It consists of a pressure atomizer with known atomization properties mounted in a test rig which allows the variation of several parameters that influence ignition, namely: air pressure; air temperature; velocity; Fuel-Air-Ratio (FAR); Sauter Mean Diameter (SMD); spark energy; turbulence intensity and length scale. Two grey spots that exist in the knowledge map of the ignition process are addressed in this paper. These are data on kerosene spray ignition at temperatures below 293 K, where data is scarce and the relationship between flame kernel generation and propagation, which has not been broadly investigated nor is well understood. The ignition probabilities of kerosene sprays as a function of ignition energy in the temperature range from 253 K to 293 K, pressure of 0.7 bar, flow velocities up to 6 m/s at different turbulence intensities and length scales are measured. Furthermore, the influence of the above mentioned parameters on the kernel generation and propagation is presented and discussed.
Results show that the energy required for flame kernel propagation is higher than for flame kernel generation. This difference increases at lower temperature and higher turbulence intensity. The paper gives an insight in magnitude of this difference in energy and compares the tendencies with an earlier model. The absolute values need to and will be corrected by future in situ measurements.
Effect of a Recirculation Device on the Performance of Transonic Mixed Flow Compressors
Authors: Numakura Ryusuke , Tamaki Hideaki , Hazby Hamid , Casey Michael 
Published: September 2014

Two transonic mixed flow compressors with an extremely high flow coefficient of ϕ = 0.25 and pressure ratios of 2.5 and 2.65 have been designed and tested. CFD simulations indicated that both impellers operate with a suction surface relative Mach number of above 1.5 at their design conditions. Both compressors achieved a narrow stable operating range when tested without recirculation devices.
The effects of two different recirculation devices on the compressor performance maps were investigated both experimentally and numerically. The first type is a widely used recirculation device which consists of an upstream slot, bleed slot and an annular cavity which connects both slots. The other has vanes installed in the cavity which were designed to provide a recirculation flow with negative swirl at the impeller inlet. Measurement data demonstrated the effect of the recirculation devices on increasing the range of these two transonic mixed flow compressors and showed the superiority of the recirculation device with vanes.
The effects of the recirculation devices on the impeller flow field at near surge conditions are studied using steady state 3D CFD calculations. Both measurements and simulations showed that the stability enhancement is partly caused by a steeper pressure rise characteristic.
Improvement of Flow Conditions for the Stages Subsequent to Extraction Modules in Industrial Steam Turbines
Authors: Schramm Andreas , Müller Tim , Polklas Thomas , Brunn Oliver , Mailach Ronald 
Published: September 2014

Industrial steam turbines are applied for power generation as well as drive for turbo-compressors. They combine a high level of operational flexibility with highest reliability. Especially in the field of process technology they provide process heat on a certain enthalpy level for other industrial applications. Modular design concepts are used to meet these various requirements like admission or extraction of large steam quantities. Extraction modules use valves to control the amount of steam extracted from the turbine expansion path at constant steam parameters.
While extraction steam is taken from the turbine through an outlet flange, the remaining steam passes valves and downstream diffusers, flows into an annular inner casing and finally escapes through the subsequent stages. Depending on the valve lift, different flow separations can occur around the valves, resulting in unsteady transonic jets. Due to the compact and asymmetric design of the inner casing the flow into the subsequent stages is strongly disturbed. Hence, strong unsteady mechanical blade loading can occur in addition to efficiency loss.
The current work focusses on the improvement of the flow conditions in the subsequent stage. Experimental results are applied to quantify the viability of the used 3D RANS CFD-solver (ANSYS CFX 14) for these numerical investigations. Compared with the experiment, the distribution of pressure, velocity and incidence angle are well predicted by the numerical code. It is evident that the unsteady transonic jets emerging around the valves have a major influence on the distribution of the parameters considered. Thus, to quantify the impact of a modified inlet chamber design, it is sufficient to simulate the domain starting from the valves.
The influence of different design modifications on the flow parameters in comparison with the base design is discussed in detail in an extensive study. The results clarify that horizontal and vertical valve positions, as well as thorough contouring of the radial-axial deflection have a strong influence on the distribution of pressure, mass flux and incidence angle. Hence, in this contribution combinations of the most beneficial modifications are investigated numerically and compared with the base design.
Unsteady Flow in Extraction Modules of Industrial Steam Turbines
Authors: Schramm Andreas , Müller Tim , Polklas Thomas , Brunn Oliver , Mailach Ronald 
Published: September 2014

Industrial steam turbines are designed for application in power-, process- and chemical engineering. Particular modules ensure the optimum integration into power plants and other engineering processes. Extraction modules allow the controlled extraction of large steam quantities on certain and constant enthalpy levels. Valves regulate the amount of steam extracted from the turbine expansion path. Depending on the valve lift, different flow separation phenomena can occur peripherally inside the valves, causing undesired large unsteady fluid forces on the valve head and seat. Due to the compact design of the industrial steam turbines, these unsteady jets can influence the rotor dynamics as well as the blade loading of the adjacent stages. These fluctuations should be understood and avoided in order to enhance the reliability of steam turbines.
In the present study the unsteady flow phenomena due to separation occurring circumferentially inside the valve of extraction modules are investigated numerically. First, the commercial 3D RANS CFD-solver (ANSYS CFX 14) is validated in the application to experimental results. Subsequently, the various flow patterns of the examined valve design are analyzed on a standalone numerical valve model in an extensive study.
In order to assess the impact of these unsteady flow separations on other components, the complete extraction module is simulated in combination with the adjacent stages. The transient simulation results show pressure fluctuations downstream of the valves resulting in an unsteady load of the control valves, the shaft and the blading.
Phantom Cooling of Nozzle Trailing Edge Discharge on Blade Surface and Platform
Authors: Li Xueying , Ren Jing , Jiang Hongde 
Published: September 2014

Phantom cooling is defined as the cooling redistribution on airfoil surfaces and endwalls due to airfoil cooling discharges and leakages. Understanding of this effect has become especially critical in recent years, because of the restricted amount of cooling air for the achievement of higher efficiency.
The phantom cooling effect of the first stage nozzle trailing edge discharge on the first stage blade surfaces and platform are studied numerically with URANS. Both time-dependent and time-averaged cooling effectiveness distributions on the rotor under the influence of vane trailing edge discharge are presented with different discharge velocity ratios. The results show that the nozzle trailing edge ejection affects the suction and pressure side cooling of the blade as well as the platform. The effects on the triangular zones of suction surface are evident, especially the bottom and top zones which are better cooled. Under the influence of passage secondary flows and rotating, different coolant discharge velocity ratios which resulted in different inlet angles have an effect on the phantom cooling distribution.
In general, the cooling air discharged from the trailing edge of the first stage nozzle influences the temperature distribution on the blade, which can substantially improve the cooling efficiency in the bottom triangular zone. This suggests that accounting for phantom cooling can improve the cooling design and if actively controlled save cooling flow.
On the Reduction of the Pre-Processing Effort and the Application of a Contact Meshing Approach for Complex Jet Engine Component Assemblies
Authors: Hufenbach W. , Hornig A. , Böhm H. , Langkamp A. , Keskin A. 
Published: September 2014

A significant proportion of the work effort for finite element (FE) analysis is spent for pre-processing activities, especially for complex structural components and component assemblies. An exclusive use of hexahedron (hex) elements increases the meshing effort substantially compared to tetrahedral elements. An automated method to generate high quality hexahedral meshes for an arbitrary geometry does not exist. In this work, commercially available FE software tools for meshing were investigated with the focus on an advantageous pre-processing effort. The evaluation showed that the software package NX (Siemens PLM Software) offers robust advanced semiautomatic hex meshing capabilities.
Furthermore, a Contact Meshing Approach (CMA) was elaborated to reduce the effort of the challenging and time-consuming geometry decomposition significantly. Using the example of an intermediate pressure compressor it can be shown that the pre-processing effort time can be reduced up to 75%. Due to the independent meshes, element transitions in the geometry become redundant. This results in lower total element numbers and higher mesh qualities and subsequently leads to more efficient calculations. Moreover, the increased element quality has positive effects on the result quality.
Rotordynamic Investigation of Spiral Vibrations: Thermal Mode Equation Development and Implementation to Combined-Cycle Power Train
Authors: Golebiowski Mateusz , Nordmann Rainer , Knopf Eric 
Published: September 2014

Rotation of vibration vector caused by thermally induced unbalance changes is a frequently observed phenomenon in large rotating machinery. The heat arising from the friction losses, which are generated at the interfaces between rotating and statoric components of the machine, is partly absorbed by the shaft. This heat input is typically not uniform around the shaft circumference and the resulting temperature difference causes the rotor to bow. The excitation resulting from the sum of mechanical unbalance and thermal bow will lead to a slowly rotating (in the synchronously rotating coordinates system) whirl vector, whose magnitude can decrease or increase in time.
A generic understanding of this effect (B.L. Newkirk in 1926, [4]) had been followed by a number of physical models representing specific heat exchange mechanisms (W. Kellenberger [3], J. Schmied [6], P. Morton [11]). A hot spot on the shaft surface can be generated at various locations of a shaft-line. Typical components responsible for thermally induced modulation of vibration vector are journal bearings, seal rings, labyrinth seals (in case of a soft rubbing). Furthermore carbon brushes sliding on the slip ring, supplying the DC current to the field winding of the generator rotor, were identified as a source of nonuniform heat input that may excite spiral vibrations (L. Eckert and J. Schmied in [7], [8]). These local heat input phenomena affect consequently the vibration behavior of the overall shaft train.
This paper provides a new approach to the quantitative description of a heat exchange mechanism which leads to the hot spot generation on the surface of a slip ring. A new thermal equation has been formulated, which determines the stability and frequency of the thermal mode. Characteristics of spiral vibration are discussed based on the analytical solution of the Jeffcott rotor model coupled with the proposed thermo-elastic equation.
The implementation of the described method to a full shaft-line model of a combined cycle, single shaft power train was done using the Finite Element Method. The results of this calculation were validated against measurement data. The paper shows how the applied computational approach can be used to extend stability margin of the spiral vibration in turbo-generator shaft trains.
Dynamic Performance of Power Generation Systems for Off-Shore Oil and Gas Platforms
Authors: Pierobon Leonardo , Iyengar Krishna , Breuhaus Peter , Kandepu Rambabu , Haglind Fredrik , Hana Morten 
Published: September 2014

On off-shore oil and gas platforms two or more gas turbines typically support the electrical demand on site by operating as a stand-alone (island) power system. As reliability and availability are major concerns during operation, the dynamic performance of the power generation system becomes a crucial aspect for stable operation and prevention of unwanted shut down in case of disturbances in the local grid.
This paper aims at developing and validating a dynamic model of the gas turbine-based power generation system installed on the Draugen off-shore oil and gas platform (located in the North Sea, Norway). The dynamic model of the SGT-500 gas turbine includes dynamic equations for the combustion chamber and for the high pressure, low pressure and turbine shafts. The low and high pressure compressors are modeled by using quasi steady-state conditions by scaling the maps of axial compressors employing a similar design point. For the turbines, the Stodola equation as well as a correlation relating the isentropic efficiency and the non-dimensional flow coefficient is utilized. The model is implemented in the Modelica language.
The dynamic model of a single SGT-500 gas turbine is first verified by comparing the transient response for a given load variation with the results of a non-physical Matlab model developed by the gas turbine manufacturer and adapted to the power set-point of the original engine installed on Draugen. Subsequently, the complete power generation system consisting of three gas turbines is simulated during transient operation and the results are compared with operational data provided by the platform operator. The model is also applied to evaluate the transient response of the system during peak loads. The results suggest that the highest accuracy (average relative error ∼1%) arises on the prediction of the rotational speed of the high pressure shaft, while the largest deviation (average relative error ∼20%) occurs in the evaluation of the pressure at the outlet of the low pressure turbine.
As waste heat recovery units (e.g. organic Rankine cycles) are likely to be implemented in future off-shore platforms, the proposed model may serve in the design phase for a preliminary assessment of the dynamic response of the power generation system and to evaluate if requirements such as minimum and maximum frequency during transient operation and the recovery time are satisfied. Furthermore, as the model is based on physics it can be coupled with the measuring instruments to monitor the thermodynamic variables at the inlet and at the outlet of each engine component.
Simplified Method to Evaluate the “Under Platform” Damper Effects on Turbine Blade Eigenfrequencies Supported by Experimental Test
Authors: Bessone Andrea , Traversone Laura 
Published: September 2014

Many turbine blades are assembled on rotors with “under platform” dampers. These devices have two main effects: increase structural damping and modify the blade eigenfrequencies. During the design development of new turbine blades it can be useful to evaluate the damper effect in terms of eigenfrequencies with a simplified method incorporating OEM experiences.
In this paper a FE modal analysis of a turbine bladed disc assembly is described, incorporating the 3D CAD simplifications and FE model boundary conditions. The ANSYS program has been used for the simulation and the different configurations for this type of analysis have been investigated. Furthermore the “under platform” damper effects have been included in the post-processing of the analysis as a percentage contribution derived from technical literature. The calculated eigenfrequencies of the blade have been compared with experimental testing in an over-speed cell to validate the methodology. These experimental tests have been performed with strain gauges applied to blades. The complete stage row has been assembled in a particular balanced configuration with and without “under platform” dampers. The data capture allows the identification of the damper effect on the blade eigenfrequencies.
Finally the Campbell diagram with the different boundary conditions during the gas turbine start-up has been prepared. Comparing calculated eigenfrequencies with gas turbine excitation sources it is possible to evaluate the blade dynamic behavior and to study different design solutions if the component has insufficient separation with the engine order excitation.
Aerodynamics and Acoustics of Turning Mid Turbine Frames in a Two-Shaft Test Turbine
Authors: Faustmann C. , Göttlich E. 
Published: September 2014

The paper deals with the investigation on the aerodynamics and the acoustics of two different turning mid turbine frames (TMTF) in the two-stage two-spool test turbine located at the Institute for Thermal Turbomachinery and Machine Dynamics (ITTM) of Graz University of Technology. The facility is a continuously operating cold-flow open-circuit plant which is driven by pressurized air. The flow path consists of a transonic turbine stage (HP) followed by a low pressure turbine stage made of a turning mid turbine frame (TMTF) and a counter-rotating low pressure rotor.
The two TMTF setups have been investigated at engine like flow conditions. The first configuration consists of 16 highly 3D-shaped turning struts. The goal of the second design was to reduce the length of the TMTF by 10% without increasing the losses and providing comparable inflow to the LP turbine rotor. This was achieved by applying 3D-contoured endwalls at the hub.
To estimate the pressure loss over the duct aerodynamic measurements are performed at the inlet and the outlet of both turning mid turbine frames by using 5-hole probes (FHP) and total pressure rakes. The FHP-measurements at the inlet of the TMTF were performed in three different ways to obtain the influence of probe positioning and traversing on the results. While the 5-hole probe was traversed only in a sector the rakes were traversed over the full circumference. The comparison between the two turning mid turbine frame setups shows from an aerodynamic point of view that it is possible to reduce the engine weight by designing a 10% shorter TMTF with endwall contouring providing the same pressure loss and comparable inflow conditions for the LP turbine rotor.
Due to the fact that noise becomes more and more an issue additional acoustic measurements were carried out downstream of the low pressure turbine. By comparing the two setups in terms of noise generation the propagating modes due to the HP turbine were found to be the same, while an increase of 10dB in amplitude of the modes related to the LP turbine was found in the 10% shorter setup. This is in good accordance with previous studies, where reducing the distance between stator and rotor increases the emitted sound.
Model Analysis of Syngas Combustion and Emission for a Micro Gas Turbine
Authors: Liu Chi-Rong , Shih Hsin-Yi 
Published: September 2014

The purpose of this study is to investigate the combustion and emission characteristics of syngas fuels applied in a micro gas turbine, which is originally designed for a natural gas fired engine. The computation results were conducted by the commercial CFD software STAR-CD, where the three-dimension compressible k-ε model for turbulent flow and PPDF (Presumed Probability Density Function) model for combustion process were constructed. As the syngas are substituted for methane, the total heat input from the blended fuels and the fuel flow rates are varied with syngas compositions and syngas substitution percentages. The computed results presented the syngas substitution effects on the combustion and emission characteristics at different syngas percentages (up to 80%) for two typical syngas compositions and the conditions where syngas applied at fixed heat input were examined.
Results showed the flame structures varied with different syngas substitution percentages. The high temperature regions were dense and concentrated on the core of the primary zone for H2-rich syngas, and then shifted to the sides of the combustor when syngas percentages were high. The NOx emissions decreased with increasing syngas percentages, but NOx emissions are higher at higher hydrogen content for the same syngas percentage. The CO2 emissions also decreased at 10% syngas substitution, but then increased as syngas percentage increased. Only using H2-rich syngas could produce less carbon dioxide. The detailed flame structures, temperature distributions, and gas emissions of the combustor were presented and compared. The exit temperature distributions and pattern factor were also discussed. Before syngas fuels are utilized as an alternative fuel for the micro gas turbine, further experimental testing are needed as the CFD modeling results provide a guidance for the improved designs of the combustor.