bluuebunny/crossref_metadata_2025 huggingface dataset:
Total Cooling Effectiveness on Laminated Multilayer for Impingement/Effusion Cooling System
Authors: Kim Seon Ho , Ahn Kyeong Hwan , Jung Eui Yeop , Park Jun Su , Hwang Ki-Young , Cho Hyung-Hee
Published: September 2014

The next generation aircraft combustor liner will be operating in more severe conditions. This means that the current cooling system needs significant amounts of cooling air to maintain cooling intensity. The present study investigates experimentally the total cooling effectiveness of an integrated impingement/effusion cooling system (thin perforated laminate plate) and effusion cooling system (single plate) at the same blowing ratio of 0.2 to 1.2. The infrared thermography method was employed to evaluate total cooling effectiveness and to determine the fully developed region of cooling performance. The holes arrays on both plates are 13 × 13 and the centers formed a square pattern (i.e., an in-line array). The perforated laminate plate is constructed of three layers and pins that were installed between the layers. In order to avoid increasing the thickness and volume, the layer thickness-to-hole diameter ratio was 0.29, and the pin height-to-hole diameter ratio, which is equivalent to the gap between the plates, was 0.21. The single plate had the same total plate thickness-to-hole diameter, but was composed of only one layer. As a result, the total cooling effectiveness of the laminate plate is 47% ∼ 141% better than single plate depending on the blowing ratio. Also, a fully developed region appears on the 2nd or 3th row of holes.
Development of Scallop Cut Type Damper Seal for Centrifugal Compressors
Authors: Takahashi Naohiko , Miura Haruo , Narita Mitsuhiro , Nishijima Noriyo , Magara Yohei
Published: September 2014

This paper deals with a new type of damper seal developed for a high-pressure centrifugal compressor. Honeycomb seals and hole-pattern seals are popularly used as damper seals and provide superior rotordynamic damping characteristics. Honeycomb seals are expensive because the manufacturing process is complex. Hole-pattern seals are easier to manufacture, but they are still expensive. Use of a scallop pattern is one way to reduce manufacturing cost and time. A new seal that has a scallop pattern and small teeth on the stator surface is proposed. This pattern is cut on the stator surface using a disc type tool. To estimate the rotordynamic coefficients of this new seal, a bulk flow model code that is based on a two-control-volume model developed by Matsuda for labyrinth seals was newly developed. This model uses the Hirs model for the viscous shear stresses. The friction factor coefficients for the rotor surface, the stator surface and the surface between the two control volumes were determined by CFD steady analysis. The rotordynamic coefficients can also be obtained by using CFD perturbation analysis. The high accuracy of the bulk flow model was demonstrated by comparing its results with CFD perturbation analysis results. In the perturbation analysis, the whirling motion was treated as a steady state problem by using a rotating frame of reference. For the damper seal, the rotor surface and its neighboring region were treated with a rotating frame of reference and the neighboring region of the stator was treated with a stationary frame of reference. The damping property of the new seal was evaluated by conducting rotor stability tests using a high-pressure compressor with an electromagnetic exciter. The new seal equipped with swirl brakes was used for the balance piston of the compressor. Stability was evaluated by exciting the rotor during operation and identifying the eigenvalues of the rotor. The experimental results showed that the new seal increases damping. Comparison of the damping effect with calculations based on the bulk flow analysis showed good agreement.
Flow Studies in a Centrifugal Compressor Stage
Authors: Rajendran R.
Published: September 2014

The overall efficiency of a compressor is dependent on the design of both the impeller and the diffuser. The vaned diffuser reduces the operating range compared to the vaneless diffuser. However, by proper setting of the diffuser with reference to the impeller, it is possible to achieve a good stage performance. This paper describes the experimental investigation of the detailed flow behavior inside a centrifugal compressor stage for three different setting angles of the vaned diffuser with reference to the fixed impeller blade outlet angle. It is seen that diffuser setting angles lower than the impeller outlet flow angle gives wide operating range.
Numerical Analysis of Fan Transonic Stall Flutter
Authors: Aotsuka Mizuho , Murooka Takeshi
Published: September 2014

This paper describes numerical investigation of fan transonic stall flutter, especially focused on flutter bite. A transonic stall flutter occurs in high loaded condition at part rotating speed. A region of the transonic stall flutter occasionally protrudes to an operating line at narrow rotational speed range. This protrusion of flutter boundary is called flutter bite. In that case, it is necessary to re-design the blade for securing sufficient operating range. The re-design process might require some compromise on performance and/or weight, and takes long time. So it is important to understand the mechanism of the flutter bite. Two types of fan blade, one has a flutter bite and another dose not, are numerically studied with a 3D Navier Stokes CFD code. Numerical results show agreement with rig test results for the fans in qualitative sense. Detailed flow fields reveal that a detached shock wave and separation due to the shock boundary layer interaction play significant role for the flutter stability.
Effect of Crystallographic Properties on Low Cycle Fatigue Strength at Elevated Temperature for Ni-Based Directionally Solidified Superalloy
Authors: Yokoyama Takashi , Sekihara Masaru
Published: September 2014

Low cycle fatigue tests at elevated temperature were conducted on a Ni-based directionally solidified superalloy subjected to transverse loading. To investigate the effect of the arrangement and crystal orientation of grains on the crack initiation, the electron back-scatter diffraction (EBSD) method was applied on the surface of the tested specimens. In addition, finite element analysis that considered the plastic behavior of crystal grains was performed to evaluate the relationship between the crack initiation and the local stress or strain that develops near the grain boundaries. The results are summarized below. As for the effect of crystallographic properties in the specimen surface, cracks generally initiated near the grain boundaries that neighbored the grain whose secondary axis inclined to loading direction by more than 20 degrees and Schmid factor to uniaxial loading was more than 0.48. The crack location was not confirmed to correlate with the grain boundary misorientation of the neighboring grains on the surface. However, most cracks initiated near the grain boundaries that neighbored the grain whose secondary axis met the loading direction at a larger angle than the grain located in the opposite surface. The results of FEM analysis revealed that the location where high cumulative equivalent plastic strain developed generally corresponded to the crack location and that the cumulative equivalent plastic strain correlated with the number of crack initiation cycles.
A Reactor Model for the NOx Formation in a Reacting Jet in Hot Cross Flow Under Atmospheric and High Pressure Conditions
Authors: Hoferichter Vera , Ahrens Denise , Kolb Michael , Sattelmayer Thomas
Published: September 2014

Staged combustion is a promising technology for gas turbines to achieve load flexibility and low NOx emission levels at the same time. Therefore, a large scale atmospheric test rig has been set up at the Institute of Thermodynamics, Technical University of Munich to study NOx emission characteristics of a reacting jet in hot cross flow. The premixed primary combustion stage is operated at ϕ = 0.5 and provides the hot cross flow. In the second stage a premixed jet at ϕ = 0.77 is injected perpendicular to the first stage. In both stages natural gas is used as fuel and air as oxidant. This paper presents a reactor model approach for the computation of the resulting NOx concentrations. The mixing and ignition process along the jet streamline of maximum NOx formation is simulated using a perfectly stirred reactor with Cantera 1.8. The reactor model is validated for the ambient pressure case using experimental data. Afterwards, a high pressure simulation is performed in order to investigate the NOx emission characteristics under gas turbine conditions.

The NOx formation is divided into flame NOx and post flame NOx. The reactor model reveals that the formation of post flame NOx in the second combustion stage can be efficiently suppressed due to fast mixing with cross flow material and the corresponding temperature reduction. Compared to single stage combustion with the same power output, no NOx reduction was observed in the experiment. However, the results from the reactor model suggest a NOx reduction potential at gas turbine conditions caused by the increased influence of post flame NOx production at high pressure.
Fluid Structure Interaction Problems in Turbomachinery Using RBF Interpolation and Greedy Algorithm
Authors: Rozenberg Yannick , Aubert Stéphane , Bénéfice Guillaume
Published: September 2014

In an effort to provide accurate simulations of fluid-structure interactions in turbomachinery, this paper describes a powerful method to deform mesh, using interpolation based on radial basis functions (RBF). It has been assessed on a 3D annular turbine, including a tip gap. The main difficulty of this method is to define number and position of control points. A greedy algorithm is proposed to address this issue and is tested on the annular turbine and a deforming panel placed in a shock tube. Finally, the method is slightly adapted to take into account periodic boundary conditions, which allow mesh morphing for a unique interblade channel by preserving constant pitch on lateral boundaries.
Influence of Creep on Low-Cycle Fatigue Life Assessment of Ultra-Supercritical Steam Turbine Rotor
Authors: Wang W. Z. , Zhang J. H. , Liu H. F. , Liu Y. Z.
Published: September 2014

Linear damage method is widely used to calculate low-cycle fatigue damage of turbine rotor in the long-term operation without fully considering the interaction between creep and low cycle fatigue. However, with the increase of steam turbine pressure and temperature, the influence of high-temperature creep on the strain distribution of turbine rotor becomes significant. Accordingly, the strain for each start-up or shut-down process is different. In the present study, the stress and strain during 21 iterations of continuous start-up, running and shut-down processes was numerically investigated by using the finite element analysis. The influence of high-temperature creep on low cycle fatigue was analyzed in terms of equivalent strain, Mises stress and low cycle fatigue damage. The results demonstrated that the life consumption of turbine rotor due to low cycle fatigue in the long-term operation of startup, running and shutdown should be determined from the full-time coverage of the load of turbine rotor.
Automatic Three-Dimensional Optimisation of a Modern Tandem Compressor Vane
Authors: Schlaps R. C. , Shahpar S. , Gümmer V.
Published: September 2014

In order to increase the performance of a modern gas turbine, compressors are required to provide higher pressure ratio and avoid incurring higher losses. The tandem aerofoil has the potential to achieve a higher blade loading in combination with lower losses compared to single vanes. The main reason for this is due to the fact that a new boundary layer is generated on the second blade surface and the turning can be achieved with smaller separation occurring. The lift split between the two vanes with respect to the overall turning is an important design choice.

In this paper an automated three-dimensional optimisation of a highly loaded compressor stator is presented. For optimisation a novel methodology based on the Multipoint Approximation Method (MAM) is used. MAM makes use of an automatic design of experiments, response surface modelling and a trust region to represent the design space. The CFD solutions are obtained with the high-fidelity 3D Navier-Stokes solver HYDRA. In order to increase the stage performance the 3D shape of the tandem vane is modified changing both the front and rear aerofoils. Moreover the relative location of the two aerofoils is controlled modifying the axial and tangential relative positions. It is shown that the novel optimisation methodology is able to cope with a large number of design parameters and produce designs which performs better than its single vane counterpart in terms of efficiency and numerical stall margin.

One of the key challenges in producing an automatic optimisation process has been the automatic generation of high-fidelity computational meshes. The multi block-structured, high-fidelity meshing tool PADRAM is enhanced to cope with the tandem blade topologies. The wakes of each aerofoil is properly resolved and the interaction and the mixing of the front aerofoil wake and the second tandem vane are adequately resolved.
Assessment of Aero-Thermal Design Methodology for Effusion Cooled Lean Burn Annular Combustors
Authors: Andreini A. , Facchini B. , Mazzei L. , Bellocci L. , Turrini F.
Published: September 2014

Increasingly stringent limitations imposed on aircraft engine emissions have led many manufacturers toward lean combustion technology, which involves a relevant increase in mass flow rate dedicated to primary combustion, leading as a consequence to a reduction of air dedicated to cooling of liners. One of the most promising cooling techniques in such conditions is represented by effusion cooling, which consists of an array of closely spaced discrete film cooling holes. This cooling method is based on a protective layer of cooling flow on the hot side of the liner, enhancing at the same time the heat removal within the holes. In the latest years many aero engine manufacturers have increased the research and technology investment on this combustion technology. Working in partnership with the University of Florence, specific component design tools and experimental techniques have been improved by Avio Aero for combustor gas turbine investigation.

From a design perspective, CFD analysis has become a key tool up to the early stages of novel combustor design process, producing affordable direct 3D optimization of combustor aerodynamics. Nevertheless, a RANS simulation of even only a single sector of an annular combustor still presents a challenge when the cooling system is taken into account. This issue becomes more critical in case of modern effusion cooled combustors, which may contain up to two thousand holes for the single sector. For this reason, many efforts have been devoted to develop methodologies based on film cooling modeling. Among the approaches published in the literature, models based on local sources represent a good compromise between simplicity and accuracy, with the capability to automatically perform a Conjugate Heat Transfer analysis. This type of methodology has been already defined and validated by the authors, with comparison on effusion cooled plates in terms of experimental overall effectiveness measurements as well as the application on a tubular combustor test case. In the context of this work, the proposed approach has been applied to the analysis of a lean annular combustor with the purpose of investigating pressure losses, flow split and metal temperature field. The results obtained have been compared to experimental data and different numerical tools exploited during the preliminary design of these devices.
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.
Experimental Study on the Organic Rankine Cycle Power System Adopting Dual Expanders in Parallel
Authors: Yoon Eunkoo , Park Hyun Jun , Kim Hyun Dong , Kim Kyung Chun , Yoon Sang Youl
Published: September 2014

This study aims to evaluate the performance of an organic Rankine cycle (ORC) power system adopting dual expanders in parallel by experiment. A dual-expander ORC system was designed to provide competitive advantages over a general single expander ORC system in typical applications with large thermal fluctuation of heat sources such as solar heat, marine waste heat, and etc. The ORC system consists of two scroll expanders installed in parallel, a hydraulic diaphragm type pump to feed and pressurize the working fluid, R-245fa, two plate heat exchangers for the evaporator and the condenser, and two generators with shaft power torque meters. The two scroll expanders were modified from two oil-free air scroll compressors, and were tested in the ORC loop with R245fa. The maximum isentropic efficiency of each expander was measured about 53%, and the shaft power was reached to about 2kW. The hot water was used as heat source, and the water temperature was controlled up to 150 °C by the 100 kW-class electric heater. A circulating air-cooled chiller was utilized for the control of the cooling water temperature. In order to determine the static performance of the system, efficiencies and shaft powers were measured with 130 °C heat source temperature. In addition, performance tests were conducted with various working fluid mass flow rates to control pressure ratios. The characteristics and total thermal efficiency of the dual parallel expander ORC system and optimal operating modes are addressed.
Experimental Determination of a Four Stage Axial Compressor Map Operating in Wet Compression
Authors: Schnitzler J. P. , von Deschwanden I. , Clauss S. , Benra F. K. , Dohmen H. J. , Werner K.
Published: September 2014

Injecting water in the air upstream of an axial compressor intake is an effective method to increase the efficiency and the power output of a gas turbine application especially at hot days. Reasoned by their complex two phase flow axial compressors which operate in wet compression mode are in the focus of present thermodynamic analysis, numerical investigations and experimental research. Recently the evaporation process of water droplets, especially at high temperature and pressure levels has been investigated with the laser based measurement technique Phase Doppler Particle Analyzer (PDPA) in detail in a stationary test rig at the University of Duisburg-Essen. The focus of these investigations has been laid on the analysis of the evaporation process in a free stream or cross flow behavior without droplet wall interaction. In this paper the first results of the novel four stage axial compressor test rig are published. This test rig is arranged for high amount of water injection with special optical access for laser based measurements. The first part of the paper outlines the general design, geometric facts and aerodynamic reference parameters of the test rig and gives an introduction to the installed conventional measurement technique. Discrete measurement results from dry runs are compared with CFD results to validate the gathered experimental data. In the second part of the paper the previously discussed dry runs are compared with measurement results of runs with water injection. The amount of water to air ratio is varied and the effects on the operating behavior of the four stage axial compressor are pointed out in detail. Furthermore results from the laser based PDPA measurements at the inlet and at the outlet of the compressor outline the impact on the water droplets moving through the compressor in wet compression mode.
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.
Nonflammable Low GWP Working Fluid for Organic Rankine Cycles
Authors: Minor Barbara , Kontomaris Konstantinos (Kostas) , Hydutsky Bianca
Published: September 2014

Regulatory pressure has been increasing globally to address the issue of climate change. In particular, there are plans to reduce the use of hydrofluorocarbon (HFC) based working fluids across many applications, as HFCs are forecast to be significant contributors to global warming in the future. Therefore, there is a need to find low global warming potential (GWP) fluids suitable for organic rankine cycles (ORCs) in those systems where HFCs have historically been preferred. These are usually systems that require a non-flammable working fluid. A new ORC working fluid, cis-1,1,1,4,4,4-hexafluoro-2-butene, also called DR-2 (cis-CF3CH=CHCF3) has been developed which is nonflammable with very low GWP of 8.9 and an ozone depletion potential (ODP) of zero because it contains no chlorine or other halogen atoms other than fluorine. DR-2 also has a favorable toxicity profile based on testing to date. DR-2 is thermally stable in the presence of lubricant and metals, air and oxygen up to the maximum temperature tested of 250°C. DR-2 has a boiling point of 33.4°C and a relatively high critical temperature of 171.3°C, which result in relatively low vapor pressures and high cycle energy efficiencies. It can enable more environmentally sustainable ORC platforms to generate electrical power from widely available heat at higher temperatures and with higher energy efficiencies than incumbent working fluids.
Virtual Turbine Engine Test Bench Using MGET Test Device
Authors: Kho Seong Hee , Ki Ja Young , Kong Chang Duk
Published: September 2014

Test device using virtual engine simulator can help reduce the number of engine tests through tests similar to the actual engine tests and repeat the test under the same condition, and thus reduce the engine maintenance and operating costs [1]. Also, as it is possible to easily implement extreme conditions in which it is hard to conduct actual tests, it can prevent engine damages that may happen during the actual engine test under such conditions. In this study, an upgraded MGET test device was developed that can conduct both real and virtual engine test by applying real-time engine model to the existing MGET test device that was developed and has been sold by the Company. This newly developed multi-purpose MGET test device is expected to be used for various educational and research purposes.
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.
Advanced Flutter Analysis of a Long Shrouded Steam Turbine Blade
Authors: Petrie-Repar Paul , Makhnov Vasily , Shabrov Nikolay , Smirnov Evgueni , Galaev Sergey , Eliseev Kirill
Published: September 2014

An advanced flutter analysis of a final stage turbine row with a new 1.2 meter long shrouded blade is presented. The three-dimensional (3D) unsteady Reynolds Averaged Navier-Stokes (URANS) equations with the Spalart and Allmaras turbulence model were employed to model the flow. The flow entering the last stage is a mixture of saturated vapor and liquid. An equilibrium wet-steam equation of state was used to model the properties of the mixture. Multi-row steady state simulations of the upstream stator row, the turbine row and the extended exhaust section were performed. It was considered important to include the exhaust section in the steady-state simulations in order to accurately predict the pressure profile at the exit of the turbine. The flow simulations were relatively high resolution and the single passage turbine mesh had 798 208 cells. Linearized flow simulations for the turbine row were performed to determine the unsteady aerodynamic work on the blades for the possible aeroelastic modes. An exact 3D non-reflecting boundary condition (3D-NRBC) was applied at the inlet and outlet for the linearized flow simulations to eliminate non-physical reflections at these boundaries. The calculated logarithmic decrement values for the new turbine blade are compared with a reference case for a similar steam turbine blade at a condition known to have a long and safe working history. The new last stage was found to be more stable than the reference case at the flow condition examined.
Critical Speed of Flawed Rotors: Global vs Local Approach
Authors: Scolavino L. , Beretta S. , Madia M. , Zerbst U.
Published: September 2014

The burst of a disc in rotating machinery can cause catastrophic damage of the equipment and, more importantly, it can represent a mortal threat to anyone in the sphere of influence of the event. In order to minimize the danger associated to a rotating component failure, burst testing is required by the authorities in order to set safety margins to the normal operating speeds. Moreover more accurate predicting tools are required for designing the components. This paper presents the results of a numerical and analytical study on the assessment of the crack driving force for discs containing surface flaws. The aim is to provide a simple, though reliable, tool in order to be able to calculate the possible dangerous in-service speed for a rotating component and, therefore, to set burst margins above the normal operating conditions of the equipment. An R6-like flaw assessment procedure is adopted considering different assumptions in the definition of the critical speed and the analytical predictions are compared with the results of elastic-plastic finite element analysis of disc. In particular, the validity and potentiality of the method is proved for surface flaws in different positions in the disc.
Modeling of Flexible Coupling to Connect Misaligned Flexible Rotors Supported on Ball Bearings
Authors: Gupta T. C. , Gupta K.
Published: September 2014

Parallel or/and angular misalignment between rotors connected by flexible coupling causes deformation of coupling elements and rotor shafts both. The forces and moments from flexible coupling act on driver and driven rotors simultaneously and depend upon dynamic response of coupled rotor system. The authors’ aim in the present work is to propose a methodology to incorporate the coupling stiffness matrix and coupling loads into the finite element model of flexibly coupled flexible rotors supported on deep groove ball bearings. The coefficients of coupling stiffness matrix and coupling loads are nonlinear and depend upon the amount of parallel and angular misalignments. To segregate the effect of nonlinear stiffness of coupling on the dynamic response of the system, the stiffness of ball bearing is initially considered to be linear. Thereafter, ball bearing nonlinearities arising from radial clearance, Hertzian deformation of balls and races, and varying compliance effect are included into the FE model of the system. Considering different types of misalignments in succession and combination, the dynamic response is characterized by the presence of 1N, 2N and other super or sub harmonics. The misalignment in one plane is found to affect the dynamic response in both the orthogonal planes. Comparing to the stiffness of flexible coupling, the stiffness of ball bearing is of higher order and therefore, nonlinear coupling forces and moments have dominant influence on the dynamic response of the system.
Aerodynamic Investigations of a Variable Inlet Guide Vane With Symmetric Profile
Authors: Händel David , Niehuis Reinhard , Rockstroh Uwe
Published: September 2014

In order to determine the aerodynamic behavior of a Variable Inlet Guide Vane as used in multishaft compressors, extensive experimental investigations with a 2D linear cascade have been conducted. All the experiments were performed at the High-Speed Cascade Wind Tunnel at the Institute of Jet Propulsion. They covered a wide range of Reynolds numbers and stagger angles as they occur in realistic turbomachines. Within this work at first the observed basic flow phenomena (loss development, overturning) will be explained. For the present special case of a symmetric profile and a constant decreasing chord length along the vane height, statements about different spanwise position can be made by investigating different Reynolds numbers. The focus of this paper is on the outflow of the VIGV along the vane height. Results for an open flow separation on the suction side are presented, too. Stall condition can be delayed by boundary layer control. This is done using a wire to trigger an early boundary layer transition. The outcomes of the trip wire measurement are finally discussed. The objective of this work is to evaluate the influence of the stagger angle and Reynolds number on the total pressure losses and the deviation angle. The results of the work presented here, gives a better insight of the efficient use of a VIGV.
Numerical Investigations of NOx Emissions of a Partially Premixed Burner for Natural Gas Operations in Industrial Gas Turbine
Authors: Innocenti Alessandro , Andreini Antonio , Giusti Andrea , Facchini Bruno , Cerutti Matteo , Ceccherini Gianni , Riccio Giovanni
Published: September 2014

In the present paper a numerical analysis of a low NOx partially premixed burner for industrial gas turbine applications is presented. The first part of the work is focused on the study of the premixing process inside the burner. Standard RANS CFD approach was used: k–ε turbulence model was modified and calibrated in order to find a configuration able to fit available experimental profiles of fuel/air concentration at the exit of the burner. The resulting profiles at different test points have been used to perform reactive simulations of an experimental test rig, where exhaust NOx emissions were measured. An assessment of the turbulent combustion model was carried out with a critical investigation of the expected turbulent combustion regimes in the system and taking into account the partially premixed nature of the flame due to the presence of diffusion type pilot flames. A reliable numerical setup was discovered by comparing predicted and measured NOx emissions at different operating conditions and at different split ratio between main and pilot fuel. In the investigated range, the influence of the premixer in the NOx formation rate was found to be marginal if compared with the pilot flame one. The calibrated numerical setup was then employed to explore possible modifications to fuel injection criteria and fuel split, with the aim of minimizing exhaust NOx emissions. This preliminary numerical screening of alternative fuel injection strategies allowed to define a set of advanced configurations to be investigated in future experimental tests.
Assessment and Prediction of Helmholtz Resonator Performance Within Gas Turbine Combustion Systems
Authors: Rupp Jochen , Peacock Graham , Regunath Gavita , Carrotte Jon
Published: September 2014

This paper is concerned with the potential use of Helmholtz resonators to provide increased acoustic damping within aero gas turbine combustion systems. Experimental measurements were undertaken using a high intensity facility into which a three burner combustor sector (non-reacting) model could be incorporated. In this way the performance of various damper geometry combinations were assessed. The effect of incident noise levels was also considered along with the associated transition from linear absorption (i.e. where absorption is directly proportional to incident pressure magnitude) to nonlinear absorption (i.e. where the proportion of acoustic loss decreases with increasing noise levels). This complicates the performance comparison between different damping geometries and means care is required when relating laboratory to engine operating conditions. In addition, all the measurements were undertaken in the presence of fuel injectors and other realistic flow field features found within a combustion system and which could affect damping performance. Finally, experimental and numerical assessment was made of the noise levels at which ingestion of hot gas will occur into the resonator cavities with and without the presence of a purging flow. For the geometries investigated ingestion occurs when the fluid displacement in the neck during an acoustic cycle is approximately equal to, or greater than, the resonator neck length. The ratio of fluid displacement and neck length provides a limit for the noise levels at which hot gas is ingested into the cavity and hence the operating condition where damping performance and system mechanical integrity is significantly compromised.
Comparison of the Experimental Results Between a 2D EGV Cascade Test and a Rig Test Under Engine Representative Conditions
Authors: Schönleitner F. , Koch H. , Selic T. , Hoeger M. , Marn A.
Published: September 2014

Today the exit guide vanes (EGV) of the turbine exit casing (TEC) of a bypass-engine have to fulfill three major functions. Firstly, they have to support the rear bearing of an aero engine and to provide space to lead through different supply lines, secondly the engine mount is supported and therefore they have to be rigid and large in thickness. Thirdly, the EGVs have to reduce swirl of the last stage LPT (carrying the aerodynamic load) in order to transform it into thrust for highest propulsive efficiency. Further, if available they have to provide the correct flow field for the following component e.g. a mixer as used in low by-pass ratio engines. Such a state-of-the-art EGV is subject to a 2D cascade test performed at the Institute for Fluid Mechanics at Technical University Braunschweig and a rig test performed at the Institute for Thermal Turbomachinery at Graz University of Technology. This work presents the differences in the results between these two tests due to three dimensional effects such as incoming wakes, turbulence and radial variations in swirl, total pressure and yaw angle over the passage height.
Augmented Heat Transfer for Angled Rib With Intersecting Rib in Rectangular Channels of Different Aspect Ratios
Authors: Chung Heeyoon , Park Jun Su , Park Sehjin , Choi Seok Min , Cho Hyung Hee , Rhee Dong-Ho
Published: September 2014

This study was an experimental investigation of the effect of an intersecting rib on heat/mass transfer performance in rectangular channels with angled ribs and different aspect ratios. In a rib-roughened channel with angled ribs, heat/mass transfer performance deteriorates as the channel aspect ratio increases, since the vortices induced by angled ribs diminish with increasing aspect ratio. A longitudinal rib that bisects the angled ribs is suggested to overcome this disadvantage. The heat transfer performance of angled rib configurations with a 60° attack angle were tested with and without an intersecting rib using naphthalene sublimation method. The channel aspect ratio is varied from 1 to 4. When the intersecting rib was present, additional vortices were generated at every point of intersection with the angled ribs. Thus the heat/mass transfer performance was significantly enhanced for all channel aspect ratios when an intersecting rib was added to an ordinary angled rib configuration.
Automated Finite Element Model Mesh Updating Scheme Applicable to Mistuning Analysis
Authors: Kaszynski Alexander A. , Beck Joseph A. , Brown Jeffrey M.
Published: September 2014

Advancement of optical geometric measurement hardware has enabled the construction of accurate 3D tessellated models for a wide range of turbomachinery components. These tessellated models can be reverse-engineered into computer-aided design (CAD) models and input into grid generation software for finite element analyses. However, generating a CAD model from scan data is a time consuming and cumbersome process requiring significant user-involvement for even a single model. While it is possible to generate finite element models (FEMs) directly from tessellated data, current direct-grid methods produce unstructured grids that can introduce fictitious, numerical mistuning in these models, obscuring geometric mistuning. Nonetheless, as-measured scan data captured in a structured grid is essential for accurate geometric mistuning analyses, provided the tessellated scan data can be rapidly and accurately transformed into a FEM. This paper outlines and demonstrates an approach for rapidly generating structured FEMs for a population of integrally bladed rotors (IBRs) without requiring the arduous task of generating a CAD model for each as-measured IBR. This is accomplished by morphing the structured mesh of a nominal model to the tessellated data set collected from an optical scanner. It is shown that the fidelity and structure of these FEMs can be utilized for accurate mistuning analyses.
Use of Pressure Spectral Maps for Analysis of Influence of the Plenum Volume on the Surge in Centrifugal Blower
Authors: Kabalyk Kirill , Liśkiewicz Grzegorz , Horodko Longin , Kryłłowicz Władysław , Stickland Matthew
Published: September 2014

The influence of plenum volume on surge phenomenon in a centrifugal blower was studied by means of quasi-dynamic analysis. In this procedure, signals were gathered at 5 pressure tappings at 146 different positions of the throttling valve controlling the mass flow rate. Frequency spectra obtained by means of Fourier analysis are combined together in the form of colour maps with frequency as the abscissa and valve position as the ordinate. Such a map provides high-resolution information about spectral structures of pressure signals attained at different mass flow rates. Analysis was conducted at two system configurations characterized by different volumes between the blower and the valve i.e. plenum volume. Research confirmed that in both cases the first disturbances appear in the vicinity of the impeller leading edge in the same position of a throttling valve before the surge. Arising flow structure is characterized by strong and random pressure jumps and does not have any dominating frequency. At further valve closure pressure disturbances propagate towards the volute and at deep surge the strongest peaks are observed at the outlet. The moment of deep surge onset is also independent of the plenum volume, however, a difference is observed in the frequency and amplitude of the main modes. With the higher outlet volume the observed oscillations fit well to the frequency of a Helmholtz resonator while, in the case of the smaller volume, the frequency is higher than the frequency of a corresponding Helmholtz resonator.
Moment Analysis of a Scroll Expander Used in an Organic Rankine Cycle
Authors: Sengupta Amrita , Kumar Prashant , Garg Pardeep , Hui Nirmal , Orosz Matthew S. , Kumar Pramod
Published: September 2014

Recent studies on small-scale power generation with the organic Rankine cycle suggest superior performance of positive displacement type of expanders compared to turbines. Scroll expanders in particular achieve high isentropic efficiencies due to lower leakage and frictional losses. Performance of scroll machines may be enhanced by the use of non-circular involute curves in place of the circular involutes resulting non-uniform wall thickness. In this paper, a detailed moment analysis is performed for such an expander having volumetric expansion ratio of 5 using thermodynamic models proposed earlier by one of the present authors. The working fluid considered in the power cycle is R-245fa with scroll inlet temperature of 125 °C for a gross power output of ∼3.5 kW. The model developed in this paper is verified with an air scroll compressor available in the literature and then applied to an expander. Prediction of small variation of moment with scroll motion recommends use of scroll expander without a flywheel over other positive displacement type of expanders, e.g. reciprocating, where a flywheel is an essential component.