bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation on the Effect of a Realistic Flow Field on the Adiabatic Effectiveness of an Effusion-Cooled Combustor
Authors: Andrei L. , Andreini A. , Bianchini C. , Facchini B. , Mazzei L. , Turrini F. 
Published: September 2014

Effusion cooling represents the state of the art of liner cooling technology for modern combustors. This technique consists of an array of closely spaced discrete film cooling holes and contributes to lower the metal temperature by the combined protective effect of coolant film and heat removal through forced convection inside each hole. Despite many efforts reported in literature to characterize the cooling performance of these devices, detailed analyses of the mixing process between coolant and hot gas are difficult to perform, especially when superposition and density ratio effects as well as the interaction with complex gas side flow field become significant. Furthermore, recent investigations on the acoustic properties of these perforations pointed out the challenge to maintain optimal cooling performance also with orthogonal holes, which showed higher sound absorption.
The objective of this paper is to investigate the impact of a realistic flow field on the adiabatic effectiveness performance of effusion cooling liners to verify the findings available in literature, which are mostly based on effusion flat plates with aligned crossflow, in case of swirled hot gas flow. The geometry consists of a tubular combustion chamber, equipped with a double swirler injection system and characterized by twenty-two rows of cooling holes on the liner. The liner cooling system employs slot cooling as well: its interactions with the cold gas injected through the effusion plate are investigated too.
Taking advantage of the rotational periodicity of the effusion geometry and assuming axisymmetric conditions at the combustor inlet, steady state RANS calculations have been performed with the commercial code ANSYS® CFX simulating a single circumferential pitch. Obtained results show how the effusion perforation angle deeply affects the flow-field around the corner of the combustor, in particular with a strong reduction of slot effectiveness in case of 90° angle value.
Rotor Blade Heat Transfer Characteristics for High Pressure Turbine Stage Under Inlet Temperature and Velocity Traverses
Authors: Rahim A. , He L. , Romero E. 
Published: September 2014

One of the key considerations in high pressure (HP) turbine design is the heat load experienced by rotor blades. The impact of turbine inlet non-uniformities on the blades in the form of combined temperature and velocity traverses, typical for a lean burn combustor exit, has rarely been studied. For general HP turbine aerothermal designs, it is also of interest to understand how the behavior of a lean burn combustor traverses (hot streak and swirl) might contrast with those for rich burn combustion (largely hot streak only).
In the present work, a computational study has been carried out on the aerothermal performance of a HP turbine stage under non-uniform temperature and velocity inlet profiles. The analyses are primarily conducted for two combined hot streak and swirl inlets, with opposite swirl directions. In addition, comparisons are made against a hot streak only case and a uniform inlet. The effects of three NGV shape configurations are investigated; namely, straight, compound lean (CL) and reverse compound lean (RCL).
The present results show that there is a qualitative change in the roles played by heat transfer coefficient (HTC) and fluid driving (‘adiabatic wall’) temperature, Taw. It has been shown that the blade heat load distribution for a uniform inlet is dominated by HTC, whilst for a hot streak only case it is wholly influenced by Taw. However, in contrast to the hot streak only case, the case with a combined hot streak and swirl shows a role reversal with the HTC being dominant in determining the heat load. Additionally, it is seen that the swirling flow radially redistributes the hot fluid within the NGV passage considerably, leading to a much ‘flatter’ rotor inlet temperature profile compared to its hot streak only counterpart. Further, the rotor heat transfer characteristics for the cases with the combined traverses are shown to be strongly dependent on the NGV shaping and the inlet swirl direction, indicating the potential for future design space exploration. The present findings underline the need to clearly define relevant combustor exit temperature and velocity profiles when designing and optimizing NGVs for HP turbine aerothermal performance.
Efficient Time Resolved Multistage CFD Analysis Applied to Axial Compressors
Authors: Cornelius Christian , Biesinger Thomas , Zori Laith , Campregher Rubens , Galpin Paul , Braune André 
Published: September 2014

Unsteady computations are necessary if blade row interactions effects are relevant, for example for detailed optimization of a compressor at off-design conditions towards the aerodynamic stability limit, or for structural mechanical tuning of the blades. Modeling time accurate transient multistage flow is expensive both in terms of computer time and memory. Recently the implicit time-resolved Time Transformation method (based on Giles’ time inclining) has been shown to be computationally efficient and a good alternative for modeling transient flow in a single stage (one pitch ratio) turbomachinery configuration. A further advantage of this time resolved method is its ability to capture not only blade passing frequencies but also self-excited frequencies such as in wakes and tip vortex shedding.
In this work, an extension of the Time Transformation method (TT) to multistage modeling has been employed to assess the method’s ability in predicting modern multistage compressor performance speedline curve, as well as its ability in capturing dominant machine frequencies. The multistage TT method is verified on a two and a half stage modified Hannover compressor, followed by an industrial validation on a Siemens Energy half scale six stage axial compressor based on the last stages of the Siemens Platform Compressor (PCO). Reference transient solutions on reduced portions of the compressor and/or modified blade count solutions are obtained and compared directly to single passage multistage Time Transformation predictions for the Hannover compressor. The method is then applied directly to the full six stage Siemens compressor employing the true blade counts for all six stages.
The first goal of this work is to investigate the ability and accuracy of the multistage TT method to capture all relevant blades passing frequencies, including the impact of different degrees of pitch change between components. The second goal of this work is to explore how best to apply the method for the prediction of a compressor map, up to the surge line. Solutions are compared to experimental test rig data. Physical explanations of the key flow features observed in the experiment, as well as of the differences between the predictions and experimental data, are given.
Siemens SGT5-4000F: Performance Measurements and Validation of Design Tools
Authors: Restemeier Mirko , Buchal Tobias , Biesinger Thomas , Popiolek Grzegroz 
Published: September 2014

The leading technology of the Siemens SGT5-4000F heavy duty gas turbine is demonstrated through recent engine measurements at customer sites. The 4000F fleet comprises more than 240 engines that exceed performance targets because of well established, non-heuristic design processes that are continuously enhanced.
On-site measurements of pressure, temperature and flow were performed at various locations in the flow path of the 4-stage turbine to support validation of Siemens’s proprietary 3D Computational Fluid Dynamics (CFD) analysis suite. Despite inherent but well understood modeling deficiencies, these advanced CFD prediction capabilities surpassed other tools and increased the accuracy of the overall turbine design process.
The performance of each turbine stage and flow features related to the exhaust diffuser were captured by the calculations. Overall performance characteristic shapes coincided with heat balances based on measurements. Radial traverses at the turbine exit, static pressure along the engine axis, and temperature sensors were matched well. The level of accuracy in delta predictions exceeded industry standards.
The design suite was able to predict performance parameters prior to measurement within respective confidence levels. Therefore, this advanced 3D CFD design suite, validated with the test data, will form the basis for future turbine development programs.
The Experimental Investigations of Centripetal Air Bleed With Tubed Vortex Reducer for Secondary Air System in Gas Turbine
Authors: Chen Xiao , Feng Ye , Wu Lijun 
Published: September 2014

In a modern gas turbine, the air bled through High Pressure Compressor (HPC) rotor drums from the main flow is transported radially inwards and then transferred to cool the High Pressure Turbine (HPT). The centripetal air flow creates a strong vortex, which results in huge pressure losses. This not only restricts the mass flow rate, but also reduces the cooling air pressure for down-stream hot components. Adding vortex reducer tubes to the centripetal air bleed can reduce the pressure loss and ensure the pressure and mass flow rate of the supply air. Design optimization of the tubed vortex reducer is essential in minimizing the pressure losses.
This paper describes experimental investigations of different configurations of tubed vortex reducers at different rotational speeds and mass flow rates. Particular attention is paid to the shape of the drum hole, the length of the tubed vortex reducers at the same installation location, and the angles of the nozzle guide vane outlets. The core section of test rig is comprised of two steel disks, one drum rotor and stationary cases with nozzle guide vanes. It operates at representative engine parameters, such as the turbulent flow parameter, λT(0.2–1.8) and the Rossby number Ro(0.05–0.08). Three conclusions can be drawn based on the experimental results. 1) The shape of the drum hole is a key factor of the bleed system pressure loss. An oval hole configuration has less flow resistance and results in lower pressure losses compared with a circular hole design. 2) The tests prove that tubed vortex reducers are instrumental in minimizing centripetal air flow. These components effectively restrain the free vortex development and decrease the pressure losses in the cavity. 3) Basically, the flow field consists of a free vortex and a forced vortex. The length of the tube influences the flow field and the pressure losses at the inlet and outlet of the tubed vortex reducer. However, the tube length is less important when compared with the shape of drum hole.
Hot-Film Measurements on a LPT Linear Cascade With By-Pass Transition
Authors: Gomes Reinaldo A. , Stotz Stephan , Blaim Franz , Niehuis Reinhard 
Published: September 2014

Transition of the state of the boundary layer from laminar to turbulent plays an important role in the aerodynamic loss generation on turbine airfoils. An accurate simulation of the transition process and of the state of the boundary layer is therefore crucial for prediction of the aerodynamic efficiency of components in rotating machines. A lot of the research in the past years dealt with the transition over laminar separation bubbles, especially concerning flows in low pressure turbines (LPT) of air jet engines. Nevertheless, by-pass transition is also frequent in turbomachines at higher Reynolds numbers as well as for properly designed profiles. Compared with transition over a laminar separation bubble, a by-pass transition is experimentally much more difficult to detect with standard measurement techniques. In such cases it becomes necessary to use more sophisticated techniques, such as hot film anemometry, hot wires or Preston probes in order to obtain accurate information on the state of the boundary layer.
The study presented is carried out using a linear cascade with a LPT blade profile with strong front loading and gentle flow deceleration at the rear suction side of the blade. Measurements were performed at the High-Speed Cascade Wind Tunnel of the Institute of Jet Propulsion at engine relevant Mach and Reynolds numbers. Emphasis is put on the evaluation of the different transition processes at mid-span and its influence on profile losses. The data post processing was adapted for compressible flows, which allows a more accurate determination of the transition area as well as qualitatively better distributions of the wall shear stress. Finally, comparisons with simulations, using computational fluid dynamics (CFD) tools, are performed and fields for improvement of the turbulence and transition models are identified.
Endoscopic Chemiluminescence Measurements as a Robust Experimental Tool in High-Pressure Gas Turbine Combustion Tests
Authors: Goers Simon , Witzel Benjamin , Heinze Johannes , Stockhausen Guido , van Kampen Jaap , Schulz Christof , Willert Chris , Fleing Christian 
Published: September 2014

The development process for gas turbine combustion systems includes single-burner high-pressure combustion tests as an important validation step. In these tests the performance of a combustor is investigated at realistic gas turbine conditions. Measurement techniques that are typically used in these tests include mass flow meters, thermocouples, pressure transducers, and probes for exhaust-gas composition measurements. These measurement techniques, however, do not provide direct information of the flame behavior.
Chemiluminescence measurements have proven to being a valuable and robust technique to close this gap [1,2]. This paper summarizes the results of chemiluminescence measurements performed at Siemens full-scale high-pressure single-burner combustion test rigs at the German Aerospace Center (DLR) in Cologne, Germany. To minimize the impact of the measurement system on the experiment, the optical access to the test rigs was provided by a water-cooled endoscopic probe. The probe was located in a side-wall downstream of the burner, viewing upstream towards the burner outlet. The probe was successfully operated up to full engine pressure and flame temperatures of approximately 1900 K.
For the detection of the chemiluminescence signal different approaches were applied:
• Spectral analyses of the chemiluminescence signal were done by using an USB spectrometer.
• For flame imaging up to two intensified CCD cameras were applied. In front of the cameras various combinations of optical filters were installed to selectively record the respective chemiluminescent species (OH*, CH*, CO2*).
• For studies with special focus on combustion dynamics an intensified high-speed CMOS camera was used. High-repetition-rate measurements were used for identifying the shapes of flame modes.
• Acoustic pressure oscillations inside the combustion chamber were recorded by pressure transducers simultaneously to the camera images. This allows the pressure oscillations to be correlated with flame fluctuations during post-processing [3,4].
Generally, the robustness of endoscopic chemiluminescence measurements was successfully demonstrated in numerous tests at realistic gas turbine conditions. The applied imaging setups provided new information about the connection between the flame position and NOx emissions as well as the correlation of flame fluctuations and pressure oscillations. Hence, they have become a valuable experimental tool to improve the evaluation and understanding of the combustor performance. Future work will focus on further improvement of quantitative evaluations by compensation of line-of-sight image integration, reabsorption of OH* by OH, and beam steering.
Numerical Analysis of the Unsteady Loads on a Steam Turbine Double Seat Control Valve
Authors: Bianchini Cosimo , Da Soghe Riccardo , Cosi Lorenzo , Imparato Enzo 
Published: September 2014

The continuously growing request for high operational flexibility also for large scale steam turbine creates new challenges for control valve design. Such components, subjected to large static loads, may also experience strong vibrations due to unsteady turbulent fluctuations downstream the throttling section, which need to be confined sufficiently far from structural natural frequencies in the entire range of operating conditions.
This work is focused on a computational analysis of the unsteady steam flow developing within a realistic double-seat control valve employed in industrial steam turbine. Actual operating conditions are considered both in terms of steam inflow pressure and temperature, flow rates and plug height. Three plug heights were considered: two corresponding to almost closed plug thus subjected to choked flow, and the third verified at 4 different steam rates.
In order to capture the unsteady nature of the flow and verify the fluid-dynamic forcing frequency, the Scale Adaptive Simulation principle, as implemented in Ansys® CFX 14.5 code, has been employed. Computations were run with a computational time step of 10−4 s and an effective simulation window of 0.2 s for time averaged values and pressure time signals. The unsteady response is monitored analyzing the frequency spectra of both integral variables (i.e. forces and moment on plug) and punctual pressure oscillations.
Analysis of results showed that it is possible to correlate the principal frequency and amplitude with the operating conditions. Strouhal number based on plug diameter and bulk flow velocity remains in fact constant independently on operating conditions.
Design of Experiments to Investigate Geometric Effects on Fluid Leakage Rate in a Balance Drum Seal
Authors: Morgan Neal R. , Untaroiu Alexandrina , Migliorini Patrick J. , Wood Houston G. 
Published: September 2014

Annular labyrinth seals are designed as tortuous paths that force a working fluid to expand and contract repeatedly through small clearances between high and low pressure stages of turbomachinery. The resulting expansion and recirculation reduces kinetic energy of the flow and minimizes leakage rate between regions of high and low pressure through the seal. Most current seal geometries are selected based on what has worked in the past, or by incremental improvements on existing designs. In the present research, a balance drum used in a multi-stage centrifugal pump was chosen as a starting point. A design of experiments study was performed to investigate the influence of groove scale on leakage rate across the seal for a fixed pressure differential.
The CFD model of the selected labyrinth seal has an upstream region leading to 20 evenly spaced semicircular grooves along a 267 mm seal length, with a clearance region of 0.305 mm. The seal geometry was specified by a set of five variables. The variables allow for variation in scale of the semicircular grooves within a pattern of five independently scaled grooves repeated four times along the seal length.
The seal was constructed with a parameterized CFD model in ANSYS CFX as a five degree sector of the full 3D seal. A non-central composite designed experiment was performed to investigate the effects of five parameters on leakage rate in the system. This study demonstrates a practical approach for investigating the effects of various geometric factors on leakage rate for balance drum seals. The empirical 10-parameter linear regression model fitted to the results of the experimental design yields suggested groove radii that could be applied to improve performance of future seals.
Development of a Suite of Hybrid Electric Propulsion Modeling Elements Using NPSS
Authors: Perullo Christopher A. , Trawick David , Clifton William , Tai Jimmy C. M. , Mavris Dimitri N. 
Published: September 2014

NASA is actively funding research into advanced, unconventional aircraft and engine architectures to achieve drastic reductions in vehicle fuel burn, noise, and emissions. One such concept is being explored by Boeing, General Electric, Virginia Tech, and Georgia Tech under the Subsonic Ultra Green Aircraft Research (SUGAR) project [1]. A major cornerstone of this research is evaluating the potential performance benefits that can be attributed to using hybrid electric propulsion. Hybrid electric propulsion in this context involves a non-Brayton power generation or storage source, such as a battery or a fuel cell, which can be used to provide additional propulsive energy to a conventional Brayton cycle powered turbofan engine. Employing additional power sources for thrust production increases the number of degrees of freedom both from a design and configuration standpoint and from an operational one. In order to assess and understand the myriad number of potential new configurations a modeling and simulation tool is needed; however, current state of the art propulsion modeling tools such as the Numerical Propulsion System Simulation (NPSS) are not natively capable of assessing novel hybrid electric configurations.
This research addresses the gap between hybrid electric propulsion and conventional cycle analysis tools by developing a suite of native NPSS elements suitable for hybrid electric engine cycle design and analysis. Elements have been developed for a fuel cell, battery, motor, generator, and electrical distribution system. Both room temperature and cryogenically cooled superconducting variants are developed. The elements are designed such that they can be seamlessly integrated into existing NPSS cycle models to assess any system configuration or architecture the designer can envision.
Impact of Main and Splitter Blade Leading Edge Contour on the Performance of High Pressure Ratio Centrifugal Compressors
Authors: Erdmenger Rodrigo R. , Michelassi Vittorio 
Published: September 2014

The impact of leading edge sweep in an attempt to reduce shock losses and extend the stall margin on axial compressors has been extensively studied, however only a few studies have looked at understanding the impact of leading edge contouring on the performance of centrifugal compressors. The present work studies the impact of forward and aft sweep on the main and splitter blade leading edge of a generic high flow coefficient and high pressure ratio centrifugal compressor design and the impact on its overall peak efficiency, pressure ratio and operating range. The usage of aft sweep on the main blade led to an increase of the pressure ratio and efficiency, however it also led to a reduction of the stable operating range of the impeller analyzed. The forward sweep cases analyzed where the tip leading edge was displaced axially forward showed a slight increase in pressure ratio, and a significant increase on operating range. The impact of leading edge sweep on the sensitivity of the impeller performance to tip clearance was also studied. The impeller efficiency was found to be less sensitive to an increase of tip clearance for both aft and forward sweep cases studied. The forward sweep cases studied also showed a reduced sensitivity from operating range to tip clearance.
The studies conducted on the splitter leading edge profile indicate that aft sweep may help to increase the operating range of the impeller analyzed by up to 16% while maintaining similar pressure ratio and efficiency characteristics of the impeller. The improvement of operating range obtained with the leading edge forward sweep and splitter aft sweep was caused by a reduction of the interaction of the tip vortex of the main blade with the splitter tip, and a reduction of the blockage caused by this interaction.