bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Investigation on a High Endwall Angle Turbine With Swept-Curved Vanes
Authors: Meng Fusheng , Gao Jie , Fu Weiliang , Liu Xuezheng , Zheng Qun
Published: August 2018

In a high endwall angle turbine, large meridional expansion can cause the strong secondary flow at the endwall, which results in a larger endwall flow loss than the small meridional expansion turbine. The endwall heat transfer is strongly affected by secondary flow effect. In order to optimize the endwall flow to reduce the flow loss and optimize the distribution of heat load, the swept-curved method was used in this study.

The swept-curved method was investigated on a transonic second stator (S2) with large meridional expansion in a Low-Pressure (LP) Turbine. Validation studies were performed to investigate the aerodynamic and the heat transfer prediction ability of shear stress transport (SST) turbulence model. The influence of different shapes of the stacking line, including forward-swept, backward-swept, positive-curved and negative-curved, were investigated through numerical simulation. The parameterized control of swept-curved height and angle were adopted to optimize the performance of the aerodynamic and heat transfer. 3D flow field calculation captured the relatively accurate flow structures in the parts of endwall and near endwall. Heat transfer behaviors were explored by means of isothermal wall temperature and Nusselt number (Nu) distribution. The results show that the maximal heat transfer coefficient at the leading edge, for the formation of horseshoe vortexes that cause the high velocity towards the endwall. The swept vane can improve the static pressure and heat load distribution at the endwall region, which decreases the area-averaged shroud heat flux by 2.6 percent and the loss coefficient 1.3 percent.
Modeling Partial Admission in Control Stages of Small Steam Turbines With CFD
Authors: Bellucci Juri , Rubechini Filippo , Arnone Andrea
Published: August 2018

This work aims at investigating the impact of partial admission on a steam turbine stage, focusing on the aerodynamic performance and the mechanical behavior.

The partialized stage of a small steam turbine was chosen as test case. A block of nozzles was glued in a single “thick nozzle” in order to mimic the effect of a partial admission arc. Numerical analyses in full and in partial admission cases were carried out by means of three-dimensional, viscous, unsteady simulations. Several cases were tested by varying the admission rate, that is the length of the partial arc, and the number of active sectors of the wheel. The goal was to study the effect of partial admission conditions on the stage operation, and, in particular on the shape of stage performance curves as well as on the forces acting on bucket row.

First of all, a comparison between the flow field of the full and the partial admission case is presented, in order to point out the main aspects related to the presence of a partial arc. Then, from an aerodynamic point of view, a detailed discussion of the modifications of unsteady rows interaction (potential, shock/wake), and how these ones propagate downstream, is provided. The attention is focused on the phenomena experienced in the filling/emptying region, which represent an important source of aerodynamic losses. The results try to deepen the understanding in the loss mechanisms involved in this type of stage. Finally, some mechanical aspects are addressed, and the effects on bucket loading and on aeromechanical forcing are investigated.
Experimental Investigation of Droplets Splashing With Varying Pressures and Impact Angles to Predict Behaviour During Wet Compression
Authors: Bröder Jascha , Günther Christoph , Joos Franz
Published: August 2018

Wet compression is a powerful means to increase gas turbine power output and to perform fast load changes. These characteristics make this process suitable to compensate the unsteady supply of electric energy from renewable sources or to increase overall power output in times of high demand without the necessity to invest in higher peak capacity.

In case of high fogging water sprays are injected inside the intake duct of the gas turbine compressor resulting in droplets entering the first stages of the compressor. Inside, droplets above a specific size cannot follow the airflow properly, which makes it likely for them to collide with compressor surfaces and disintegrate. Characteristics of the ejected secondary droplets influence evaporation and condensation processes and thereby the thermodynamics of the compression process.

To investigate the characteristics of ejected secondary droplets, collisions between droplets and surfaces were recorded with a high-speed camera using the shadowgraphy method. From these recordings, quantity, diameter and velocity of secondary droplets were obtained. To resemble conditions at the first stages of a compressor under high fogging conditions, the experiments were conducted at elevated pressures up to 500 kPa and with varying impact angles from 0° to 30°. The Weber number normal to the surface was held constant at 550 and 700. The paper discusses the measured influence of splashing at simulated compressor conditions.
Towards the Structural Optimization of Bladed Components Featuring Contact Interfaces
Authors: Lainé Julien , Piollet Elsa , Batailly Alain
Published: August 2018

In order to maximize their efficiency, modern aircraft engines feature reduced nominal clearances between rotating (such as bladed disks) and static (casing) components. As a consequence, structural contacts between these components are now more likely to occur and must be accounted for as early as in the design stage of the engine. To this day, there exists no relevant criterion to discriminate contacting components, such as blades, according to their sensitivity to contact events. In a recent study, it was found that a redesigned blade, featuring significant improvements with respect to its vibratory response following structural contacts, essentially differed from the original design with respect to its clearance consumption — a quantity that characterizes the evolution of blade/casing clearance as the blade vibrates over its first free-vibration modes. From this observation, it was decided to carry out a thorough investigation on the possible relation between clearance consumption and the nonlinear vibratory response following structural contacts. This paper presents an automated structural optimization procedure of a blade design using an objective-function related to the blade’s clearance consumption. Thus, optimized blades feature a lower clearance consumption. By means of an in-house numerical tool dedicated to the simulation of structural contact events with a surrounding casing, it is found that optimized blades feature lower amplitudes of vibration following contacts in comparison with the original blades. Overall, it is evidenced that the blade sensitivity to contact has been lowered as certain critical speeds vanish for the optimized profile. The current paper aims at establishing a proof-of-concept and thus only considers structural aspects. Aerodynamic considerations that are key for designing efficient blades are purposely left aside in order to focus on the feasibility of blade dynamics optimization.
Multi-Physics Simulations With OpenFOAM in the Re-Design of a Commercial Combustor
Authors: Konle Marco , de Guillebon Ludovic , Beebe Christopher
Published: August 2018

The numerical description of combustion provides a good understanding of the thermal boundary conditions of a combustor already in the early design phase. With an accurate simulation, the thermal load on the combustor wall as well as the turbine inlet profile can be estimated and potentially tailored to the structural requirements.

At MTU Aero Engines AG, the authors set up a multi-physics solver in OpenFOAM to support the development process for combustors. This article shows the activities for a redesign of a commercial engine combustor and the successful numerical description of all related physical aspects. The comparison of combustor liner temperatures predicted via Conjugate Heat Transfer (CHT) with thermal paint results show excellent agreement. The numerical results allow the evaluation of different redesign options with respect to maximum liner temperatures and impact on turbine inlet temperature profiles.

The application of a multi-physics solver to real engine combustor designs is limited to the availability of computational power and acceptable running time. The applicability of the presented approach to complex engine designs is not only shown by the successful simulation results. The choice of an open source code allows the usage of massive parallelization. A parallelization up to 1024 CPUs was tested to evaluate the potential of speeding up the simulations. The results are encouraging and show that complex meshes with ∼15 million cells can be simulated within acceptable calculation time.
A Critical Analysis on Low-Order Simulation Models for Darrieus VAWTs: How Much Do They Pertain to the Real Flow?
Authors: Bianchini Alessandro , Balduzzi Francesco , Ferrara Giovanni , Persico Giacomo , Dossena Vincenzo , Ferrari Lorenzo
Published: August 2018

To improve the efficiency of Darrieus wind turbines, which still lacks from that of horizontal-axis rotors, Computational Fluid Dynamics (CFD) techniques are now extensively applied, since they only provide a detailed and comprehensive flow representation. Their computational cost makes them, however, still prohibitive for routine application in the industrial context, which still makes large use of low-order simulation models like the Blade Element Momentum (BEM) theory. These models have been shown to provide relatively accurate estimations of the overall turbine performance; conversely, the description of the flow field suffers from the strong approximations introduced in the modelling of the flow physics.

In the present study, the effectiveness of the simplified BEM approach was critically benchmarked against a comprehensive description of the flow field past the rotating blades coming from the combination of a two-dimensional unsteady CFD model and experimental wind tunnel tests; for both data sets, the overall performance and the wake characteristics on the mid plane of a small-scale H-shaped Darrieus turbine were available. Upon examination of the flow field, the validity of the ubiquitous use of induction factors is discussed, together with the resulting velocity profiles upstream and downstream the rotor. Particular attention is paid on the actual flow conditions (i.e. incidence angle and relative speed) experienced by the airfoils in motion at different azimuthal angles, for which a new procedure for the post-processing of CFD data is here proposed. Based on this model, the actual lift and drag coefficients produced by the airfoils in motion are analyzed and discussed, with particular focus on dynamic stall. The analysis highlights the main critical issues and flaws of the low-order BEM approach, but also sheds new light on the physical reasons why the overall performance prediction of these models is often acceptable for a first-design analysis.
Full High Pressure Compressor Investigations to Determine Aerodynamic Changes due to Deterioration
Authors: Reitz Gerald , Kellersmann Andreas , Friedrichs Jens
Published: August 2018

The Institute of Jet Propulsion and Turbomachinery of the TU Braunschweig owns a jet engine of the type V2500-A1 from the International Aero Engines AG. To conduct research on the jet engine and its components, computer models are necessary. In this paper, the reverse engineering process of the high pressure compressor (HPC) regarding its aerodynamics is presented. Thereby, the reverse engineering process starts from digitizing newly manufactured airfoils, followed by FEM-calculations to enforce the operating forces on the geometries. A computational fluid dynamics (CFD) model using these geometries is set up, considering all relevant geometric and aerodynamic features such as bleed ports and the variable stator vane (VSV) system. Using this CFD-model, the compressor map is calculated and afterwards validated by available manufacturing data [18] and by the institute’s jet engine’s test cell data. Because this jet engine is a highly operated and deteriorated one, a map scaling is necessary before comparing the CFD-model with the test cell data. Nevertheless, an adequate agreement of the operating behavior between scaled compressor map and test cell data is shown. To estimate the deterioration level of the jet engine’s compressor and to evaluate the used scaling factors, the tip gaps inside the CFD-model were doubled and the compressor behavior was simulated. The observed effect of reduced compressor capacity and efficiency is in accordance with literature but is not able to explain the amount of the scaling factors completely.
S-Duct Diffuser Offset-to-Length Ratio Effect on Aerodynamic Performance of Propulsion-System Inlet of High Speed Aircraft
Authors: Asghar Asad , Allan William D. E. , LaViolette Marc , Stowe Robert , Alexander Derrick , Ingram Grant
Published: August 2018

This paper reports the internal performance evaluation of S-duct diffusers with different offset-to-length ratios. The geometric parameters of S-duct diffusers are currently of great interest because of increasing demand for stealth and consequently, their effects on drag and aero-engine stability margin. The generic S-duct diffuser selected as a baseline had a rectangular-entrance and circular exit. Test articles were tested with the high subsonic, Ma = 0.8 and 0.85, flow and were manufactured using 3D printing. stream-wise static pressure and exit-plane total pressure were measured in a test rig using surface pressure taps and a 5-probe rotating rake, respectively. The baseline and variant S-ducts were also simulated through computational fluid dynamics. The investigation indicated the presence of stream-wise and circumferential pressure gradients leading to a separated flow in the S-duct diffusers and distortion at the exit plane. The static pressure recovery decreased and total pressure loss increased with an increase in the offset-to-length ratio. The circumferential distortion at the engine face clearly indicated a trend with respect to the offset-to-length ratio, however radial distortion did not.
A Biogas Fuelled Micro Gas Turbine Using Dual-Fuel Approach
Authors: Calabria Raffaela , Chiariello Fabio , Massoli Patrizio , Reale Fabrizio
Published: August 2018

In this study, research activity concerning the utilization of biogas into a commercial micro gas turbine (MGT) Ansaldo Turbec T100P is presented. The use of biogas in MGT has been already quite explored in literature. However, conflicting and not yet fully comprehensive results highlight the need for further scientific investigations. Although several authors have demonstrated, through numerical studies, the possibility of using biogas with amounts of CO2 up to 40–50% in volume in commercial MGT, experimental evidences of this condition are not yet present in literature. In fact, the CO2 concentration limit experimentally validated in literature, after which phenomena of detachment and instability of the flame happen, is considerably lower (∼12%). The utilization of biogas in micro gas turbines generally requires structural adaptations, often invasive and expensive, to the fuel compression unit and control valves. Not infrequently a partial redesign of the combustor is often necessary. Costs associated with the modifications significantly reduce the benefits of a rational and sustainable exploitation of energy resources of lower value as the biogas.

Aim of this activity is to overcome these issues, by identifying a non-invasive and cost-effective technical solution to increase the CO2 concentration in the fuel and to extend the operation domain when low calorific value fuels are used. It has been studied, implemented and tested an innovative management strategy of fuel feeding and combustion. Experimental layout and preliminary results of this novel approach are shown and discussed.
The Use of Fluid-Solid Cell Transformation to Model Volcanic Ash Deposition Within a Gas Turbine Hot Component
Authors: Connolly Jonathon , Forsyth Peter , McGilvray Matthew , Gillespie David
Published: August 2018

Creating robust empirical and computational models of the process of deposition of salts, dust, sand and volcanic ash has gained increased importance over the last two decades as civil aircraft flights in regions with particulate laden atmospheres have increased. This is associated with increased costs of maintenance to engine suppliers in a market where there is pressure from carriers to continue to fly. Thus, knowledge of the build-up of particulates within the engine over long or multiple deposition events is required in addition to predicting its onset. In this paper deposition in idealised geometries typical of internal cooling passages is examined. The fluid phase is modelled using the commercial flow solver FLUENT and a simple RANS approach. The discrete phase was then solved using Lagrangian particle tracking and a continuous random walk model using one-way coupling. Following identification of deposition fluxes, the local surface of the solid domain was modified using a bespoke cell transformation process. Particular care was taken to distribute deposited mass appropriately to surface cells to avoid large discontinuities at the boundaries. The model was implemented using user-defined functions. The functionality of the technique, is demonstrated through application two impingement cooling geometries for which experimental validation data are available. Here the solution was highly sensitive to the changing target surface geometry as deposition advanced temporally. Fair agreement was found with the experimental data of Burwash et al.[1] though the level of accretion found was an order of magnitude too high, highlighting the need to combine this approach with accurate stick-bounce and shedding models. Significant changes in deposition locations were observed as the deposition site grew in size. Comparison to a second validation case, by Clum et al [2], was used to test further the effect of deposition on the local flow field. Again, good qualitative agreement was obtained. The procedure is shown to create believable deposits of volcanic ash for all cases tested, without many of the typical problems encountered with mesh morphing — overlapping volumes and indeterminate boundary layer resolution. For the commercial computational fluid dynamic (CFD) code used, the process of identifying cells which are to be modified and their neighbours is, disappointingly, an order of magnitude slower than using a mesh morphing strategy. The procedure does, however maintain high, known, resolution throughout the thermal boundary layer, will allow the redistribution of particles to take into account features such as the fusing of neighbouring accretions and the breakaway of deposits from the surface as they grow.
APU-Noise Reduction by Novel Muffler Concepts
Authors: Knobloch Karsten , Enghardt Lars , Bake Friedrich
Published: August 2018

For a GTCP36-28 auxiliary power unit (APU), a set of mufflers has been designed and tested for some representative operating conditions. The first muffler design uses cavities of different sizes in conjunction with a bias flow for efficient broadband sound absorption. The second design — also expected to perform well over a large frequency range — makes use of a variable perforation and some porous absorber material. The acoustic damping performance of the mufflers was assessed using a downstream section of dedicated microphone probes. Individual spectra and circumferential averages have been computed and are used for a comparison to a hard-walled duct section of the same length. Results show a reasonable broadband absorption for most configurations. For one operating point, significant differences were found while comparing the performance of the cavity muffler with and without bias flow. The results suggest, that a small amount of air — less than initially expected — is sufficient to obtain the desired noise reduction.
Maximum Loading Capacity of Tandem Blades in Axial Compressors
Authors: Liu Baojie , Fu Du , Yu Xianjun
Published: August 2018

Tandem blades are widely reported to be superior to a single-blade configuration under the aerodynamic circumstance with a large flow turning in a stator or a high work input in a rotor. Aiming at the design of a highly loaded rear stage of a high pressure compressor with the advanced concept, the maximum loading capacity of a tandem-blade configuration, which is rarely described in open literature, is fundamentally necessary to be explicit in order to determine a stable operation range. A diffuser analogy is carefully carried out between the tandem-blade geometry and the diffuser passage using a reliable and robust numerical method. The analysis approach to effectively predicting the maximum static pressure rise is verified by the limited results of computational fluid dynamics (CFD) and experiments. In addition, the maximum loading capacity of the tandem-blade configuration is compared with that of the single-blade configuration to define a more favorable design range of meanline parameters. The results indicate that the tandem blade outperforms the conventional blade in a specific design space and the approach can be a potential design tool to guide the selection of one-dimensional parameters of tandem blades in a highly loaded axial compressor.
Near-Wing Multi-Sensor Diagnostics of Jet Engine Components
Authors: Frackowiak W. , Barton S. , Reimche W. , Bruchwald O. , Zaremba D. , Schlobohm J. , Li Y. , Kaestner M. , Reithmeier E.
Published: August 2018

Engine maintenance and repair is a large part of the total airplane operating cost. Routine maintenance is essential for providing a positive impact on lifetime, engine performance and reliability. The sector of on-wing and near-wing maintenance is growing because of its potential to reduce the expenses and inspection time, with diagnostics taking place close to the airplane or inside a hangar on the airport. Due to the high complexity of modern jet engines, this task creates special needs towards the measurement systems regarding flexibility and robustness.

This paper describes four design approaches of such measurement systems to determine the engine parts’ health status with complex geometries in narrow or occluded spaces between blades and individual discs. The utilized nondestructive technologies are endoscopic fringe projection for geometry measurement, adapted low coherence interferometry to determine surface microstructures, high frequency inductive thermography with an optical mirror and miniaturized high frequency eddy current testing for inspection of the protection coating system and for the detection of subsurface cracks and defects. The inspection information obtained by all these techniques can be further used for regeneration process simulations and functional simulations to predict the optimal overhaul strategy.
On the Periodically Unsteady Interaction of Wakes, Secondary Flow Development and Boundary Layer Flow in an Annular LPT Cascade: Part 1 — Experimental Investigation
Authors: Sinkwitz Martin , Winhart Benjamin , Engelmann David , di Mare Francesca , Mailach Ronald
Published: August 2018

The results reported in this two-part — combined experimental and numerical — paper address the time-dependent impact of periodically unsteady wakes on the development of profile and end wall boundary layers and consequently on the secondary flow system. Experimental investigations are conducted on an annular 1.5 stage axial turbine rig at Ruhr-Universität Bochum’s Chair of Thermal Turbomachines and Aeroengines. The object under investigation is a modified T106 profile LPT stator row at a representative exit flow Reynolds number of 200,000. By making use of an annular geometry instead of a linear cascade, the influence of curvilinear end walls, non-uniform, increasing pitch across span and radial flow migration can be represented. Incoming wakes are generated by a variable-speed driven rotor equipped with cylindrical bars. Special emphasis is put on the wake-induced recurrent formation, suppression, weakening and displacement of individual vortices and separated flow regimes. For this, based on a comprehensive set of time-resolved measurement data, the interaction of impinging bar wakes and boundary layer flow and thus separation and its periodic manipulation along the passage end walls and on the blade suction surface are studied within the frequency domain.
Impact of Impeller Casing Treatment on the Acoustics of a Small High Speed Centrifugal Compressor
Authors: Sharma Sidharath , García-Tíscar Jorge , Allport John M. , Jupp Martyn L. , Nickson Ambrose K.
Published: August 2018

Ported shroud casing treatment is widely used to delay the onset of surge and thereby enhancing the aerodynamic stability of a centrifugal compressor by recirculating the low momentum fluid in the blade passage. Performance losses associated with the use of recirculation casing treatment are well established in the literature and this is an area of active research. The other, less researched aspect of the casing treatment is its impact on the acoustics of the compressor. This work investigates the impact of ported shroud casing treatment on the acoustic characteristics of the compressor. The flow in two compressor configurations viz. with and without casing treatment operating at the design operating conditions of an iso-speed line are numerically modelled and validated with experimental data from gas stand measurements. The pressure fluctuations calculated as the flow solution are used to compute the spectral signatures at multiple locations to investigate the acoustic phenomenon associated with each configuration. Propagation of the frequency content through the ducts has been estimated with the aid of method of characteristics to enhance the content coming from the compressor. Expected tonal aerodynamic noise sources such as monopole (buzz-saw tones) and dipole (Blade Pass Frequency) are clearly identified in the acoustic spectra of the two configurations. The comparison of two configurations shows higher overall levels and tonal content in the case of a compressor with ported shroud operating at design conditions due to the presence of ‘mid-tones’.
Non-Uniform Tip Clearance Effects on Turbocharger Compressor Performance
Authors: Adjei Richard A. , Wang Weizhe , Peng Di , Liu Yingzheng , Bamba Takahiro
Published: August 2018

In most turbocharger compressors, diffusers a re designed with contractions along the passage mainly for delaying surge. The width ratio parameter, B, which defines the diffuser inlet width to diameter ratio significantly affects the losses in the diffuser. Changes to tip clearance, for example, due to the impeller rubbing the shroud casing changes the fluid flow angle at the impeller exit. The sensitivity of the absolute flow angle to the width ratio parameter has a significant influence on diffuser effectiveness and stage performance. This paper reports an investigation of tip clearance sensitivity to vaneless diffuser and stage performance of a turbocharger compressor. To assess the correlation between performance parameters and the tip clearance, Design of Experiments (DoE) was used to sample 40 design cases by changing the clearance at the leading (LE) and trailing edges (TE) of the impeller. Parameters correlation was subsequently used to determine their relationship. The key findings were that stage efficiency and pressure ratio increased linearly with decreasing LE and TE clearances having a maximum sensitivity value R = 0.7. Diffuser Cp showed a strong positive correlation for TE and a weak negative correlation for LE. Similarly, work input and diffuser loss coefficient showed an inverse relation to diffuser Cp with a maximum R value of 0.9. It was concluded that increasing the tip clearance at TE improves the diffuser effectiveness. The main source of low diffuser Cp for small tip clearances was due to higher diffusion losses as a result of flow non-uniformity when the width ratio and absolute flow angle were large. As the width ratio decreases along the passage appreciable frictional losses occur in larger tip clearance further increasing the losses. The absolute flow angle and width ratio were observed to be key to diffuser and stage performance.
Use of Operating Parameters, Digital Replicas and Models for Condition Monitoring and Improved Equipment Health
Authors: Carlevaro Fausto , Cioncolini Stefano , Sepe Marzia , Parrella Ilaria , Allegorico Carmine , De Stefanis Laura , Mastroianni Mariagrazia , Escobedo Ernesto
Published: August 2018

Several operating parameters for the control and protection of the units are acquired by the control and protection systems used in industrial applications. The use of these parameters in conjunction of physical models, empirical models and transfer functions (that represent digital replicas of the engine) allows for a broader scope of condition monitoring, taking into account the wing to wing process which spans from data acquisition to end user actionable insight. This paper describes 3 specific cases: 1) an algorithm based on the performance model of the overall GT used to monitor the axial compressor degradation and optimize the planned axial compressor water wash of an aero-derivative GT; 2) an analytic based on the flow function physic model used to monitor the clogging of the fuel nozzles in a heavy duty GT and to plan their maintenance; 3) an analytic based on a hybrid model used to monitor the axial thrust acting on a roller bearing of an aero-derivative GT and used to verify the status of the bearing and to plan its maintenance. Moreover, the paper provides details about the evaluation of the measurements, describes the model accuracy and explains how the results obtained are affected by these uncertainties and the methods used to mitigate these uncertainties. In addition, this paper shows a method to aggregate and weigh the monitoring of each single component and its own status into an overall health view.
Digital Geometry and Morphing to Support Analysis and Design
Authors: Meah N. , Hunt M. , Evans R. , Racz T. , Verdicchio J. , Kudryavtsev A. , Dawes Bill
Published: August 2018

This paper describes the application of geometry morphing, integrated with meshing and flow simulation, to the topological optimisation of gas turbine film cooling holes.

Using a Genetic Algorithm to manage the digitally represented geometry a wide range of novel cooling hole shapes can be generated and useful improvements in film cooling effectiveness are observed. The simulations suggest that modified vortical flow structures are responsible for improved coolant distribution and coverage at hole exit.
Impact Analysis of Pocket Damper Seal Geometry Variations on Leakage Performance and Rotordynamic Force Coefficients Using CFD
Authors: Griebel Clemens
Published: August 2018

In this paper, different notch and partition wall arrangements of a fully partitioned pocket damper seal (FPDS) are investigated using Computational Fluid Dynamics (CFD).

The CFD model is derived for a baseline FPDS design reflecting the full sealing configuration with a structured mesh. Steady-state simulations are performed for eccentric rotor position and different operational parameters. The results are validated using experimental cavity pressure measurements.

In transient computations, rotor whirl is modeled as a circular motion around an initial eccentricity using a moving mesh technique. Different whirl frequencies are computed to account for the frequency-dependent behavior of damper seals. The stiffness and damping coefficients are evaluated from the impedances in the frequency domain using a Fast Fourier Transform.

The validated model is then transferred to varying designs. In addition to the baseline design, six different notch arrangements with constant clearance ratio were modeled. Moreover two partition wall design variations were studied based on manufacturability considerations. Predicted leakage as well as frequency-dependent stiffness and damping coefficients are presented and the impact of geometry variations on these parameters is discussed. The results suggest that a single centered notch is favorable and indicate considerably higher effective damping for a design with staggered partition walls. A rounded partition wall design with significantly eased manufacturing reveals good performance.
Three Dimensional Velocity and Temperature Field Measurements of Internal and External Turbine Blade Features Using Magnetic Resonance Thermometry
Authors: Benson Michael J. , Van Poppel Bret P. , Elkins Christopher J. , Owkes Mark
Published: August 2018

Magnetic Resonance Thermometry (MRT) is a maturing diagnostic used to measure three-dimensional temperature fields. It has great potential for investigating fluid flows within complex geometries leveraging medical grade MRI equipment and software along with novel measurement techniques. The efficacy of the method in engineering applications increases when coupled with other well established MRI-based techniques such as Magnetic Resonance Velocimetry (MRV). In this study, a challenging geometry is presented with direct application to a complex gas turbine blade cooling scheme. Turbulent external flow with a Reynolds number of 136,000 passes a hollowed NACA-0012 airfoil with internal cooling features. Inserts within the airfoil, fed by a second flow line with an average temperature difference of 30 K from the main flow and a temperature-dependent Reynolds number in excess of 1,800, produce a conjugate heat transfer scenario including impingement cooling on the inside surface of the airfoil. The airfoil cooling scheme also includes zonal recirculation, surface film cooling, and trailing edge ejection features. The entire airfoil surface is constructed of a stereolithography resin — Accura 60 — with low thermal conductivity. The three-dimensional internal and external velocity field is measured using MRV. The fluid temperature field is measured within and outside of the airfoil with MRT and the results are compared with a computational fluid dynamics (CFD) solution to assess the current state of the art for combined MRV/MRT techniques for investigating these complex internal and external flows. The accompanying CFD analysis provides a prediction of the velocity and temperature fields, allowing for errors in the MRT technique to be estimated.
Process Optimization of Wire Based Laser Metal Deposition of Titanium
Authors: Schulz Martin , Klocke Fritz , Riepe Jan , Klingbeil Nils , Arntz Kristian
Published: August 2018

Titanium alloys are used instead of steel and nickel-based alloys to lower the weight of turbines whenever it is applicable. Due to the high manufacturing costs of titanium, near-net-shape processes like laser metal deposition (LMD) processes are an approach to improve the production of new turbomachinery components. Additionally, these processes are also suitable for repair. LMD uses wire or powder as additional material. When highly reactive materials like titanium grade 5 (Ti6Al4V) are processed, wire-based laser metal deposition (LMD-W) processes are superior to powder-based processes due to the smaller reactive surface. Nowadays, three main challenges exist when titanium grade 5 (Ti6Al4V) is processed by additive manufacturing (AM): First of all the high affinity to oxygen combined with the increased brittleness of the material in case of a contamination with already low amounts of oxygen has to be faced. Secondly, the material is prone to distortion induced by thermal stress during the manufacturing process. Finally, the material has a complex bimodal microstructure, which has to be adjusted properly to generate optimal strength. The following publication will present how these technical challenges are faced. A local shielding gas concept demonstrates how flooding of the process chamber was avoided. The distortion was lowered by minimizing the heat input. Therefore, the laser spot was adapted. Its size was reduced to physical minimum nearly matching the size of the wire. To avoid process aborts, the proper feeding of the wire was improved. With this optimized process, it was possible to generate several specimens for metallurgical analysis. Finally, treatments to modify the alpha-martensitic-structure into a bimodal structure were performed. Summarizing the results show that the LMD-W process was improved to overcome the main challenges. Thereby the process has become suitable for manufacturing turbomachinery components made from titanium grade 5.
Gas Turbine Fouling: A Comparison Among One Hundred Heavy-Duty Frames
Authors: Aldi Nicola , Casari Nicola , Morini Mirko , Pinelli Michele , Spina Pier Ruggero , Suman Alessio
Published: August 2018

Over recent decades, the variability and high costs of the traditional gas turbine fuels (e.g. natural gas), have pushed operators to consider low-grade fuels for running heavy-duty frames. Synfuels, obtained from coal, petroleum or biomass gasification, could represent valid alternatives in this sense. Although these alternatives match the reduction of costs and, in the case of biomass sources, would potentially provide a CO2 emission benefit (reduction of the CO2 capture and sequestration costs), these low-grade fuels have a higher content of contaminants. Synfuels are filtered before the combustor stage, but the contaminants are not removed completely. This fact leads to a considerable amount of deposition on the nozzle vanes due to the high temperature value. In addition to this, the continuous demand for increasing gas turbine efficiency, determines a higher combustor outlet temperature. Current advanced gas turbine engines operate at a turbine inlet temperature of (1400–1500) °C which is high enough to melt a high proportion of the contaminants introduced by low-grade fuels. Particle deposition can increase surface roughness, modify the airfoil shape and clog the coolant passages. At the same time, land based power units experience compressor fouling, due to the air contaminants able to pass through the filtration barriers. Hot sections and compressor fouling work together to determine performance degradation.

This paper proposes an analysis of the contaminant deposition on hot gas turbine sections based on machine nameplate data. Hot section and compressor fouling are estimated using a fouling susceptibility criterion. The combination of gas turbine net power, efficiency and turbine inlet temperature (TIT) with different types of synfuel contaminants highlights how each gas turbine is subjected to particle deposition. The simulation of particle deposition on one hundred (100) gas turbines ranging from 1.2 MW to 420 MW was conducted following the fouling susceptibility criterion. Using a simplified particle deposition calculation based on TIT and contaminant viscosity estimation, the analysis shows how the correlation between type of contaminant and gas turbine performance plays a key role.

The results allow the choice of the best heavy-duty frame as a function of the fuel. Low-efficiency frames (characterized by lower values of TIT) show the best compromise in order to reduce the effects of particle deposition in the presence of high-temperature melting contaminants. A high-efficiency frame is suitable when the contaminants are characterized by a low-melting point thanks to their lower fuel consumption.
Enhancement of Impingement Heat Transfer With the Crossflow Normal to Ribs and Pins Between Each Row of Holes
Authors: El-Jummah Abubakar M. , Andrews Gordon E. , Staggs John E. J.
Published: August 2018

Impingement heat transfer investigations with obstacle (fins) on the target surface were carried out with the obstacles aligned normal to the cross-flow. Conjugate heat transfer (CHT) computational fluid dynamics (CFD) analysis were used for the geometries previously been investigated experimentally. A 10 × 10 row of impingement jet holes or hole density, n, of 4306 m−2 with ten rows of holes in the cross-flow direction was used. The impingement hole pitch X to diameter D, X/D, and gap Z to diameter, Z/D, ratios were kept constant at 4.66 and 3.06 for X, D and Z of 15.24, 3.27 and 10.00 mm, respectively. Nimonic 75 test walls were used with a thickness of 6.35 mm. Two different shaped obstacles of the same flow blockage were investigated: a continuous rectangular ribbed wall of 4.5 mm height, H, and 3.0 mm thick and 8 mm high rectangular pin-fins that were 8.6 mm wide and 3.0 mm thick. The obstacles were equally spaced on the centre-line between each row of impingement jets and aligned normal to the cross-flow. The two obstacles had height to diameter ratios, H/D, of 1.38 and 2.45, respectively. Comparison of the predictions and experimental results were made for the flow pressure loss, ΔP/P, and the surface average heat transfer coefficient (HTC), h. The computations were carried out for air coolant mass flux, G, of 1.08, 1.48 and 1.94 kg/sm2bar. The pressure loss and surface average HTC for all the predicted G showed reasonable agreement with the experimental results, but the predictions for surface averaged h were below the measured values by 5–10%. The predictions showed that the main effect of the ribs and pins was to increase the pressure loss, which led to an increased flow maldistribution between the ten rows of holes. This led to lower heat transfer over the first 5 holes and higher heat transfer over the last 3 holes and the net result was little benefit of either obstacle relative to a smooth wall. The results were significantly worse than the same obstacles aligned for co-flow, where the flow maldistribution changes were lower and there was a net benefit of the obstacles on the surface averaged heat transfer coefficient.
Measurement of Hysteresis Energy Using Digital Image Correlation With Application to Energy Based Fatigue Life Prediction
Authors: Celli Dino , Shen M.-H. Herman , Holycross Casey , Scott-Emuakpor Onome , George Tommy
Published: August 2018

A modified experimental method using digital image correlation (DIC), a non-contact optical method for measuring full-field displacements and strains, is used to interrogate accumulated fatigue damage for low and high cycle fatigue (LCF/HCF) at continuum scales. Previous energy based fatigue life prediction methods have shown that cyclic strain energy dissipated during fatigue acts as a key damage parameter for accurate determination of total and remaining fatigue life. DIC enables the collection of accurate strain energy measurements or damaging energy of complex geometries that would otherwise be exceedingly difficult and time consuming using traditional strain measurement techniques. Thus, the use of DIC to obtain strain energy measurements of gas turbine engine components is highly advantageous for energy-based fatigue life prediction methods. Presented in this study is the experimental characterization of the cyclic strain energy dissipation as a means of predicting fatigue performance and assessment of damage progression of Aluminum 6061 subjected to fully reversed axial fatigue loading utilizing DIC. Validation of total and cyclic strain energy dissipation DIC measurements are accomplished with the simultaneous use of axial extensometery for direct comparison and implementation to strain energy based life prediction methods.
Thermal Analysis and Pressure Loss Modeling for an Optimized Heat Exchanger Used in a Recuperated CO2 Power Cycle
Authors: Zawati Husam , Elmore Michael , Kapat Jayanta , Nagaiah Narasimha
Published: August 2018

A simple recuperated cycle is studied and optimized in this paper. Geometrical parameters for a novel recuperator design are then optimized to minimize area density. The recuperator is where the s-CO2 is analyzed and simulated for both hot and cold sides. The design of the cycle is obtained through a study of a 100 MW net power output s-CO2 cycle, where this cycle features a turbine inlet temperature of 1023 K. The main objective of this paper is to couple a recuperated cycle with a heat exchanger. This is done through Pareto optimality to study the tradeoffs between conflicting variables. The geometry of the heat exchanger features two inlet headers attached to semirectangular channels. The thermal analysis used is based on one-dimensional finite enthalpy method, where discretization is made by equal heat transferred per element. In addition, pressure drops are calculated at both sides of main heat exchanger body. Optimized cycle based on practical parametric assumptions reveals an efficiency of 45.8% and specific power of 132.1 kJ/kg. Best design reveals channel side length of 7 mm with surrounding solid sidewall thickness of 1 mm. Pressure drops for the proposed design are 4.8% and 0.6% of the initial pressure for the hot and the cold sides, respectively. Overall length of the heat exchanger is found to be 10.7 m with an effectiveness of 96.2% and an area density of 363 m2/m3.
Reaction Model Development for Synthetic Jet Fuels: Surrogate Fuels As a Flexible Tool to Predict Their Performance
Authors: Kathrotia Trupti , Richter Sandra , Naumann Clemens , Slavinskaya Nadezhda , Methling Torsten , Braun-Unkhoff Marina , Riedel Uwe
Published: August 2018

In the last years, the development of synthetic aviation jet fuels has attracted much interest, to provide alternatives to crude-oil based kerosene. Synthetic jet fuels can be produced from a variety of feedstocks and processes. To limit possible harmful effects on the environment when burning a jet fuel, discussions are attributed to the effects of the specific composition of a synthetic fuel on its performance and its emission pattern. A numerical tool, if available, would also be helpful within the specification process any aviation jet fuel must pass.

The present work contributes to the studies and efforts how to design a synthetic jet fuel to match predefined properties, e.g. the energy content or a less harmful emission characteristics compared to Jet A-1. The approach of a generic fuel will be followed in order to design a synthetic jet fuel with pre-defined chemical properties: A chemical kinetic reaction mechanism will be elaborated capable predicting the fundamental combustion properties of the generic fuel for each possible mixing ratio of the components included.

In this work, a generic mixture serving as an innovative synthetic jet fuel was studied, with n-dodecane, cyclohexane, and iso-octane chosen as single fuel components; no aromatics were added to reduce the concentration of soot precursors. Then, their fundamental combustion properties, i.e. laminar burning velocity and ignition delay time, were measured in a burner test rig and applying the shock tube technique, respectively. These experimental data were used for the validation of the reaction mechanisms developed for each single fuel component, which were then combined to the reaction mechanism for the generic fuel under consideration. To allow a comparison of the combustion behavior of the synthetic jet fuel directly, with the same reaction mechanism, to Jet A-1, toluene was added as a model component for aromatics. A reduced surrogate reaction model was produced, too.

All the reaction mechanisms elaborated are shown to reasonably predict the fundamental combustion properties within the parameter range considered. The compact reduced surrogate model can serve as a virtual jet fuel within numerical simulations. Thus, ultimately, an estimation of the suitability of an innovative synthetic jet fuel as a blending component to crude-oil kerosene is enabled. As a result, CFD simulations can be run efficiently tackling the combustion of a synthetic fuel in a jet engine under practical conditions and by taking into account the interaction between turbulence and chemistry.