bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Bladed Packets on Transient Vibration Localization Behaviors of Mistuned Whole Bladed Disk System
Authors: Kan Xuanen
Published: September 2021

The multi-packets whole bladed disks are usually used in the turbo-machineries. The most different characteristic of the multi-packets whole bladed disk is that some blades are connected by lacing forming a bladed packet, and several bladed packets are assembled to form a multi-packets whole bladed disk system. Mistuning of blades is an attractive vibration subject due to vibration localization problems that vibration energy focuses on some blades. The vibration localization characteristics of steady state of bladed disk are mainly discussed in previous studies, and few works focus on the transient vibration localization behaviors of the multi-packets whole mistuned bladed disk. Transient vibration characteristics of bladed disk are crucial during startup. Therefore, in this paper, transient vibration characteristics of the multi-packets whole bladed disk are studied. A developed mathematical model is used to calculate the transient vibration response of the multi-packets whole bladed disk. The number of bladed packets on the transient vibration localization of the multi-packets mistuned whole bladed disk is discussed. The results indicate that the bladed packets are able to reduce the transient vibration localization. The results suggest that the bladed packet is an alternative approach to reduce the vibration localization of bladed disk caused by mistuning. Moreover, the different number of bladed packets will produce various behaviors of transient vibration localization of multi-packets whole mistuned bladed disk system.
Study of CFD-Based Raised-Floor Data Center Cooling With Parametric CRAC Turbofan Blower Airflow Patterns
Authors: Song Zhihang , Chen Wan
Published: September 2021

Commonly encountered thermal management challenges of today’s rapidly changing power density, raised-floor hot/cold aisle data centers include typically uncontrollable tile flow non-uniformity along the above-floor cold aisle. For example, the operational cooling provision intensity near the Computer Room Airflow Conditioner (CRAC) unit can be far less than that on the other side (far away from the CRAC unit). This undesired trend leads to an unbalanced aisle-level air cooling and subsequent inefficient power consumption. In this study, the CRAC turbofan blower flow boundary conditions were thoroughly investigated. Computational Fluid Dynamics (CFD) based simulations were employed to describe and evaluate the differently configured CRAC turbofan blower flow conditions (i.e., normal, angled, and sheared CRAC flow patterns) as well as their impacts upon the air cooling performance. This work indicates that the considered turbofan blower boundary condition, together with their underlying transportation mechanism within the plenum, might contribute an essential influence to the flow structure adjacent to the tile perforations. In particular, it was found that the sheared CRAC turbofan blower airflow pattern is capable of giving rise to favorable tile flow straightening manners. This finding further promotes an improvement of the consequently obtained aisle-level air cooling effectiveness and efficiencies, contributing to more advanced data center thermal management in the future.
Structural Integrity of Serrated Leading Edge Guide Vane Blades for Noise Reduction
Authors: Cuciumita Cleopatra , Qin Ning , Stanley Felix , Shahpar Shahrokh
Published: September 2021

One of the major noise sources of high bypass ratios modern turbofan engines arises from the interaction between the turbulent rotor wake, the tip-leakage and the leading edge of the downstream outlet guide vanes. Recent research has confirmed that leading edge serrations are an effective passive control for reducing noise. However, for transferring serrated leading edges to modern, environmentally friendly aero engines, the bypass outlet guide vanes must fulfil both aerodynamic and structural requirements. The current study aims at characterizing the structural behaviour when adding serrations to the leading edge of bypass outlet guide vanes designed for a configuration without classical struts.

It was found that the structural performances deteriorate with increasing number of serrations, directly related to the serrations wavelength, and with their amplitude. The buckling loading factor decreases and the total deformation increases constantly with the increase of both parameters. The presence of the troughs of the serrations introduce stress concentrators. For large enough values of either the wave length or amplitude of the serrations, the maximum von Mises stress increases significantly, and can as much as double in value. At the same time, the location of the maximum stress on the vane moves from its original position, on the leading edge of the casing fillet, to the troughs of the serrations.
Progress in Using Liquid Bio-Fuels in DLE Industrial Gas Turbines
Authors: Saxena Priyank , Steele William C. , Cowell Luke H.
Published: September 2021

Decarbonization of electricity is paramount for the success of curbing growth of greenhouse gas emissions in the atmosphere. For many power generation applications there is a growing interest in using bio-fuels to replace fossils-based fuels, such as diesel and natural gas. Bio-fuels, being plant-based fuels, are classified as carbon neutral fuels. Several distributed power generation sites, such as universities, are interested in the feasibility of burning bio-fuels, such as biodiesel and alcohols, in stationary gas turbines to reduce their carbon-footprint as well as earn tax credits. In order to maintain its leadership in fuel-flexibility and to support its distributed power generation customers, Solar has qualified several of its gas turbine models using both the conventional and dry low emissions (DLE) combustion systems on various biodiesel blends. This paper presents results of the combustion rig tests with DLE combustion injectors using biodiesel blends and their comparison with those of No. 2 diesel and natural gas fuels. The emissions (NOx, CO, UHC) from B20 biodiesel blend were similar to that of ULSD, but higher than natural gas. The results are summarized in terms of gas turbines emissions and performance. Impacts of fuel properties on storage, handling and gas turbines operations are discussed. Finally, future development opportunities are also presented.
Comparison of Compressor Performance Map Predictions to Test Data for a Supercritical Carbon Dioxide Brayton Power System
Authors: Clementoni Eric
Published: September 2021

Supercritical carbon dioxide (sCO2) Brayton power cycles are typically designed to operate with compressor inlet conditions near the critical point to take advantage of the high density of the fluid at these conditions. While designing the cycle to operate here improves cycle efficiency, it also creates challenges for designing the compressor and predicting off-design compressor performance due to real gas fluid properties near the critical point. Multiple compressor performance map evaluation methodologies which incorporate real gas corrections have been proposed in literature with only limited evaluation of the accuracy of these methods compared to operational data from compressors designed for sCO2 power cycles. This paper evaluates compressor performance from the 100 kWe Integrated System Test (IST), which was operated at the Naval Nuclear Laboratory, over a range of compressor inlet conditions and rotational speeds relative to one real gas performance map correction methodology and assesses the impact of additional terms proposed in literature for improving the accuracy of off-design performance predictions.
A Computationally Efficient Method That Predicts Light-Around for Both Gas- and Liquid-Fueled Combustion
Authors: Meeks Ellen , Naik Chitralkumar V. , Litrico Giuliana , Rida Samir
Published: September 2021

Controlling light-around and re-light presents design challenges for gas-turbine manufacturers. Researchers have studied the detailed phenomena in laboratory experiments to elucidate controlling factors and modes of behavior. Several groups have reported high-fidelity simulations of the fluid dynamics, turbulent mixing and light-around phenomena using large eddy simulations (LES) on highly refined computational meshes. While such simulations can reproduce experimental observations, they are computationally expensive and tend to be impractical for routine design analyses. In this work, we present a less computationally intensive CFD approach, which has been tested against laboratory experiments using both gaseous-fuel injections and liquid-fuel injections. Results show that a consistent practice of mesh and model settings can be used for all the test cases considered. The simulations generate light-around sequences and total-ignition times that agree well with experimental measurements. Observed trends are predicted when varying burner spacing as well as the fuel and injection method.
Measurements to Quantify the Effect of a Reduced Flow Rate on the Performance of a Tilting Pad Journal Bearing (LBP) With Flooded Ends
Authors: San Andrés Luis , Toner Jonathan , Alcantar Andy
Published: September 2021

Operation of tilting pad journal bearings (TPJBs) with a reduced flow decreases pumping costs and oil sump storage. A low supplied oil flow improves system energy efficiency by reducing drag power losses, albeit the temperature rise in both the bearing pads and the lubricating oil become a concern. This paper presents measurements of the static and dynamic load performance of a flooded ends TPJB lubricated with an ISO VG 46 oil supplied at 60 °C, and with flowrate ranging from 150% to just ∼5% of a nominal supply condition. The flow range covers both over-flooded and starved flow conditions. The test bearing is a four-pad, 102 mm diameter, center pivot, with single orifice feeds, and configured with end seals to flood the bearing housing. The experiments include operation at two shaft speeds = 6 krpm and 12 krpm (= 64 m/s surface speed) and under three specific loads = 0.345 MPa, 1.03 MPa and 2.07 MPa applied in between pads (LBP). The measurements show the bearing drag power loss decreases by nearly 20% when the flow rate drops to 50% of nominal. However, halving the flow produces a raise in pad subsurface temperatures, ∼7 °C for operation at 12 krpm. Flow reduction below 50% does result in even more substantial power savings; however, it also produces too hot pad temperatures that approach 130 °C, a known limit for Babbitt material safe operation. The bearing static eccentricity (e) and direct stiffnesses Kxx < Kyy (load direction) do not show a significant dependency on the supplied flow, either above or below the nominal condition. A minor stiffness hardening does occur for very low flow conditions, 5% or so of nominal. Damping coefficients (Cxx ∼ Cyy) decrease by ∼30% as the flow rate decreases from 150% to just a few % of nominal flow. The experimental results are first to quantify operation of a TPJB supplied with minute amounts of lubricant flow. A test with a very low flow rate at ∼2% of nominal and under a light load produced the emergence of a broadband subsynchronous vibration frequency, albeit with very small amplitude.
Influence of Disc Modes and Sideband Excitations on the Mistuned Forced Response Behaviour of an Embedded Compressor Rotor
Authors: Hegde Shreyas , Madden Andrew , Kielb Robert
Published: September 2021

This paper focusses on predicting the mistuned forced response behavior of an embedded compressor rotor blade row in a 3.5 stage axial compressor. The authors in previous papers studied the multi-row influence on the forcing function for multiple operating conditions. For these investigations CFX was utilized to predict the forcing However, in the mistuned predictions a consistent underprediction of the amplification factor was noted A previous investigation by the authors [32] considered an isolated mode family. The current work considers the same configuration but looks at a non-isolated mode family which is in a frequency “veering” region. Also, since the mistuning code was formulated on the lines of the fundamental mistuning model (FMM) the model only included a single DOF per ND and hence modes in the veering region were not modeled. The current paper addresses both these shortcomings and talks about the influence of sideband travelling wave excitations at the HL operating condition (the details of the mistuned predictions at the PE operating condition can be found in [32]). The paper also talks in detail about the effect of modelling the disc modes individually using the FMM model as well as together using the component mistuning model (CMM) as present in ANSYS Mechanical. Key conclusions are: 1) The mistuned response tends to be amplified by all cases including the sideband excitations, 2) The coupled influence of including a disc mode in the FMM model and sideband excitations is dependent on the proximity of the mode to the blade alone frequency, 3) Although the CMM model predicts the peak of the response accurately, it does not offer any substantial advantage over the FMM model given the computational cost required for the CMM prediction. Also, the prediction is highly sensitive to the frequency of the individual modes that can differ between codes.
Experimental Damping Behavior of Strongly Coupled Structure and Acoustic Modes of a Rotating Disk With Side Cavities
Authors: Barabas Botond , Benra Friedrich-Karl , Petry Nico , Brillert Dieter
Published: September 2021

High cycle fatigue is a continuous research topic within the turbomachine community. One field of the investigations is the fluid-structure interaction of 2-D impellers, which can be simplified as disks with their surrounding side cavities. In modern machines the pressure ratios tend to increase along with pressure fluctuations and the excitation potential on the impellers. The vibrational interactions between side cavities, filled with high pressure fluid, and the disk structure play an important role in machine design. However, they are not fully understood, yet. Vibrations at frequencies that have been uncritical at lower pressure levels could become critical at higher pressure levels. Additionally, coupling effects between fluid and structure are becoming stronger at higher fluid densities. For a safe and reliable design, the excitation and the damping mechanism of coupled modes has to be better understood.

This paper summarizes the test rig setup and focuses on one of the main findings of an extensive experimental research project, which investigated the fluid-structure interaction of a disk with side cavities, at the University of Duisburg-Essen. The focus lays on the damping behavior of strongly coupled acoustic and structure modes.

Measurement results gathered at the aeroacoustic test rig are presented. The results show the influence of fluid pressure variations on the damping behavior of acoustic modes. Therefore, the response functions of some selected acoustic modes are evaluated with the half-width method. Compared to the weakly coupled structure mode, the damping of the strongly coupled structure mode is some orders higher at atmospheric pressure conditions. The damping ratio decreases with an increasing pressure level, however still remains some orders higher, than the damping of weakly coupled structure modes.
Supercritical Pseudo Boiling in Cubic Equations of State
Authors: Banuti Daniel T.
Published: September 2021

Today, modern combustion systems and advanced cycles often reach operating pressures exceeding the working fluid’s or fuel’s critical pressure. While the liquid-gas coexistence line is the dominant feature in the fluid state space at low pressures, a supercritical analog to boiling, pseudo boiling, exists at supercritical pressures. Pseudo boiling is the transcritical state transition between supercritical liquid states and supercritical gaseous states, associated with peaks in heat capacity and thermal expansion. This transition occurs across a finite temperature interval. So far, the relation between the pseudo boiling line of tabulated hi-fi p-v-T data and the behavior of efficient engineering cubic equations of state (EOS) is unclear. In the present paper, we calculate the slope of the pseudo boiling line analytically from cubic equations of state. The Redlich-Kwong EOS leads to a constant value for all species, Peng-Robinson and Soave-Redlich-Kwong EOS yield a cubic dependency of the slope on the acentric factor. For more than twenty compounds with acentric factors ranging from −0.38 to 0.57 calculated slopes are compared with NIST data and vapor pressure correlations. Particularly the Peng-Robinson EOS matches reference data very well. Classical empirical values of Guggenheim or Plank & Riedel are obtained analytically. Then, pseudo boiling predictions of the Peng Robinson EOS are compared to NIST data. Deviations in transition temperature interval, and nondimensional parameters of the distributed latent heat are compared. Especially the different caloric behavior of tabulated fluid data for H2, N2, CO2, and H2O cannot be reproduced by the Peng Robinson EOS. These results may open the way towards new EOS with specific emphasis on Widom line and supercritical transition behavior.
Effects of Rotation on the Flow Structure in a Compressor Cascade
Authors: Ventosa-Molina Jordi , Koppe Björn , Lange Martin , Mailach Ronald , Fröhlich Jochen
Published: September 2021

In turbomachines, rotors and stators differ by the rotation of the former. Hence, half of each stage is directly influenced by rotation effects. The influence of rotation on the flow structure and its impact on the performance is studied through Wall-Resolving Large Eddy Simulations of a rotor with large relative tip gap size. The simulations are performed in a rotating frame with rotation accounted for through a Coriolis force term. In a first step experimental results are used to provide validation. The main part of the study is the comparison of the results from two simulations, one representing the rotating configuration, one with the Coriolis force removed, without any other change. This setup allows very clean assessment of the influence of rotation. The turbulence-resolving approach ensures that the turbulent flow features are well represented. The results show a significant impact of rotation on the secondary flow. In the tip region the Tip Leakage Vortex is enlarged and destabilised. Inside the tip gap the flow is altered as well, with uniformization in the rotating case. At the blade midspan, no significant effects are observed on the suction side, while an earlier transition to turbulence is found on the pressure side. Near the hub, rotation effects are shown to reduce the corner separation significantly.
Rotordynamic Evaluation of a Large High-Speed Rotor Equipped With Flexure Pivot Journal Bearings and Integral Squeeze Film Damper
Authors: Vannini Giuseppe , Innocenti Alice , Cangioli Filippo , Jongsoo Kim
Published: September 2021

The current oil and gas market trends lead the compressor OEMs to increase the rotational speed and maximize the efficiency given a target power output. Especially when applied to large process gas centrifugal compressors, characterized by high-flexibility ratio, the achievement of these targets pushes the rotordynamic design towards its limit in terms of API requirements.

Tiling pad journal bearings (TPJBs) are commonly adopted in high-speed applications for their inherent stability characteristics that permit to ensure the rotordynamic stability and eliminate self-induced sub-synchronous vibrations.

The experimental activities subject of this paper aim to assess, for the first time, the rotordynamic behaviour of a large dummy rotor (6 meter long and total weight of 8 tons) equipped with Flexure Pivot tilting-pad journal bearing and Integral squeeze film damper (ISFD). This system level testing program has been performed in the Authors’ high-speed balancing bunker properly equipped with special instrumentation such as: flow meters and pad temperature probes to monitor journal bearing behaviour, displacement probes to measure rotor vibrations relative to the bearings.

The main objective of the experimental activity is the full assessment of the rotordynamic response and the selection of the best configuration to target the design requirements (e.g. FPJB and “Active ISFD” vs. FPJB and “Inactive ISFD”).
On the Performance of Wave-Like Dry Friction and Piezoelectric Hybrid Flexible Dampers
Authors: Wu Y. G. , Fan Y. , Li L. , Zhao Z. M.
Published: September 2021

This paper proposes a flexible dry friction plate to mitigate the vibration of thin-walled structures for one resonance crossing. Based on a cantilever beam-friction damper finite element model, the geometry and material parameters of the friction plate are optimized numerically through steady-state response analyses by the widely-used Multi-Harmonic Balance Method (MHB-M). In order to further improve the damping effect, piezoelectric material is distributed to the flexible damper, and two types of dry friction and piezoelectric hybrid dampers are explored, namely semi-active and passive, respectively. For semi-active hybrid dampers, piezoelectric material is used as an actuator to adjust the normal load applied to the friction interface in real time, so that the friction damping is improved. For passive ones, piezoelectric material is used as a transducer, which dissipates the strain energy stored in the wave-like plate by the shunting circuit, additional shunted piezoelectric damping contributes to the total output damping accordingly. Better damping effect compared with the friction baseline is realized for the two types ideally. This damping module has a simple structure and avoids the problem of installation and maintenance of piezoelectric material which is generally bonded to the host structure. Technical challenges are: the semi-active type requires excessive voltage applied to the piezoelectric actuator, while the passive one needs to connect a programmable synthetic circuit.
Mechanism Analysis of the Influence of Blade Thickness Deviation on The Performance of Axial Flow Compressor
Authors: Ji Tianyuan , Chu Wuli , Guo Zhengtao , Yang Jibo
Published: September 2021

The deviation between the actual processed blade and the designed blade shape inevitably occurs in the process of compressor blade manufacturing. Rotor37 was used as the research object and a three-dimensional steady Reynolds averaged Navier-Stokes simulation method was adopted in order to study the influence mechanism of blade thickness deviation on blade performance. The blade was parameterized and the blade thicknesses were increased or decreased uniformly, with changes of 0.06mm and 0.1mm respectively. Results illustrate that the blade thickness deviation affects the total pressure ratio, isentropic efficiency and stability margin of the single-stage rotor. Increasing the blade thickness will inhibit the transport of low speed airflow from blade root area to blade tip area along the radial direction. In the peak efficiency condition, this inhibit will cause low speed airflow to converge in the middle of the blade and increase the flow separation loss; while in the reference near stall condition, the inhibition of low speed airflow transport will weaken the accumulation of low energy airflow in the tip area, reduce the loss in the corner area, and expand the stable working range of the blade. Further, increasing the blade thickness causes the shock wave position to move backward and the shock wave intensity will decrease.
Overview of Unsteady Phenomena Emerging in a Stalled 1.5-Stage Transonic Compressor
Authors: Mütschard Silas , Werner Jan , Karl Maximilian , Kunkel Christian , Schiffer Heinz-Peter , Biela Christoph , Robens Sebastian
Published: September 2021

A new transonic compressor test rig for gas turbine front stages was commissioned at the Technical University of Darmstadt in 2018. In the first measurement campaign numerous transient stall maneuvers were conducted by throttling the compressor beyond its stability limit. Several distinct phenomena can be observed during in-stall operation.

This work gives an overview of those different manifestations of stall with focus on classification and characterization. For this purpose, detailed post-processing and unsteady data analysis are conducted providing information in terms of operating points, propagation speeds of disturbances, structural behavior of the rotor as well as unsteady wall pressure fields.

The authors propose explanations for the different phenomena and possible influences of the rig on the in-stall behavior are discussed. Finally, an overview of the occurrence of the detected phenomena is given.
Effective Clearance And Differential Gapping Impact on Seal Flutter Modelling and Validation
Authors: Corral Roque , Greco Michele , Vega Almudena
Published: September 2021

This paper presents an update of the model derived by Corral and Vega (2018, “Conceptual Flutter Analysis of Labyrinth Seal Using Analytical Models. Part I - Theoretical Support”, ASME J. of Turbomach., 140 (12), pp. 121006) for labyrinth seal flutter stability, providing a method of accounting for the effect of dissimilar gaps. The original CV model was intended as a conceptual model for understanding the effect of different geometric parameters on the seal stability comprehensively, providing qualitative trends for seal flutter stability. However, the quantitative evaluation of seal flutter, and the comparison of the CV model with detailed unsteady numerical simulations or experimental data, require including additional physics. The kinetic energy generated in the inlet gap is not dissipated entirely in the inter-fin cavity of straight-through labyrinth seals, and part is recovered in the downstream knife. This mechanism needs to be retained in the seal flutter model. It is concluded that when the theoretical gaps are identical, the impact of the recovery factor on the seal stability can be high. The sensitivity of the seal stability to large changes in the outlet to inlet gap ratio is high as well. It is concluded that fin variations due to rubbing or wearing inducing inlet gaps more open than the exit gaps lead to an additional loss of stability concerning the case of identical gaps. The agreement between the updated model and 3D linearized Navier-Stokes simulations is excellent when the model is informed with data coming from steady RANS simulations of the seal.
Weldability and Properties of Newly Developed LW4280 High Gamma Prime Nickel Based Superalloy for 3D AM and Repair of Turbine Engine Components
Authors: Gontcharov Alexandre B. , Lowden Paul , Jena Ashutosh , Kwon Sunyong , Brochu Mathieu
Published: September 2021

Chemical composition, structure, mechanical and oxidation properties of welds produced utilizing laser direct energy deposition process of a newly developed LW4280 welding powder will be presented. Crack-free and high-density specimens were fabricated for manufacturing standard and subsized tensile test samples as per ASTM E-8. Optical and scanning electron microscopy revealed the formation of epitaxial grain growth during solidification of the welding pool followed by precipitation of fine gamma prime phase during the reheating from the subsequent weld layers. A sub-solvus primary aging temperature determined using Thermo-Calc software followed by secondary aging resulted in precipitation of above 49% of cuboidal γ′ phase. Excellent ultimate tensile strength of 1310 MPa (190 ksi), 0.2% yield strength of 855 MPa (124 ksi), and elongation of 18.7% were measured at ambient temperature. At 926°C (1700°F), the tensile testing yielded of 579 MPa (84 ksi), 0.2% yield strength of 462 MPa (67 ksi), and elongation of 18.8%. Cyclic oxidation resistance of the LW4280 weld material at 1120°C (2048°F) was superior to Rene 80 and Mar M247 while slightly below Rene 142.
Numerical Investigations of a High Pressure Compressor Exposed to Unsteady Pressure Gain Combustion Employing Data-Driven Methods
Authors: Bicalho Civinelli de Almeida Victor , Peitsch Dieter
Published: September 2021

Pressure gain combustion (PGC) should substantially improve the thermodynamic efficiency of gas turbines by increasing the fluid total pressure as it traverses the combustion chamber. However, PGC introduces additional unsteadiness to the intrinsically complex turbomachinery flow. A high pressure compressor, located right upstream of the PGC section, is therefore constantly exposed to flow fluctuations, experiencing drop in efficiency, increase in pressure loss as well as higher stalling and structural failure risks. This numerical work analyzes how one stage of a well-established engine, namely the NASA EEE core compressor, reacts to the disturbances induced by the potential implementation of PGC. Unsteady computational fluid dynamics are employed with boundary conditions simulating the combustion unsteadiness.

The main focus of the current paper is the application of data-driven methods, including the proper orthogonal decomposition (POD) and the dynamic mode decomposition (DMD), when comparing the high pressure compressor baseline operation with the PGC-disturbed case. Representative flow features and their frequency content, not identifiable with typical methods such as phase-averaging, are easily extracted from snapshots sequences. The results not only allow the identification of the most relevant coherent structures present in the unsteady flow, but also show how they change in the presence of PGC. This contribution sheds light on how novel PGC technology can be integrated with turbomachinery components, identifying modifications in the main flow features with the use of advanced decomposition techniques.
Proof-Of-Concept of a Thermal Barrier Coated Titanium Cooling Layer for an Inside-Out Ceramic Turbine
Authors: Gauvin-Verville Antoine , Dubois Patrick K. , Picard Benoit , Landry-Blais Alexandre , Plante Jean-Sébastien , Picard Mathieu
Published: September 2021

Increasing turbine inlet temperature (TIT) of recuperated gas turbines would lead to simultaneously high efficiency and power density, making them prime candidates for low-emission aeronautics applications, such as hybrid-electric aircraft. The Inside-out Ceramic Turbine (ICT) architecture achieves high TIT by using compression-loaded monolithic ceramics. To resist inertial forces due to blade tip speed exceeding 450 m/s, the shroud of the ICT is made of carbon-polymer composite, wound around a metallic cooling ring. This paper demonstrates that it is beneficial to use a titanium alloy cooling ring with a thermal barrier coating (TBC), rather than nickel superalloys, for the interstitial cooling ring protecting the carbon-polymer from the hot combustion gases. A numerical Design of Experiments (DOE) analysis shows the design trade-offs between the minimum safety factor and the required cooling power for multiple geometries. An optimized high-pressure first turbine stage of a 500 kW microturbine concept using ceramic blades and a titanium cooling ring in an ICT configuration is presented. Its structural performance (minimum safety factor of 1.4) as well as its cooling losses (2% of turbine stage power) are evaluated. Finally, a 20 kW-scale prototype is tested at 300 m/s and a TIT of 1375 K during 4hrs to demonstrate the viability of the concept. Experiments show that the polymer composite was kept below its maximum safe operating temperature and components show no early signs of degradation.
Prediction and Validation of the Transient Pressure Field in a Centrifugal Compressor With Vaned Diffuser for the Application in High Cycle Fatigue Stress Estimations
Authors: Bacakci Gökay , Fröhlig Friedrich , Stuhldreier Lukas , Deutsch Johannes , Jeschke Peter
Published: September 2021

In this paper, the transient pressure field in a centrifugal compressor is predicted by the Nonlinear Harmonic (NLH) method, as well as the unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations and validated by transient pressure measurements. The accurate prediction of these pressure fluctuations is crucial, because they have a significant influence on the High-Cycle-Fatigue (HCF) behavior in turbomachinery applications. As the first step, excited and non-excited rotational speeds, caused by rotor-stator interactions, are identified by modal analysis performed on a single segment impeller assembly. In order to eliminate any additional pressure fluctuations caused by blade vibrations, three non-excited operating points at different rotational speed levels are selected for the transient flow simulations. The transient pressure fields predicted by these methods are validated by transient pressure measurements at three circumferentially different locations on the impeller shroud. A study of the modeling of these fast-response pressure probes in numerical calculations also falls within the scope of this work in order to identify its effect on the transient pressure amplitudes. The results of the numerical calculations and measurements are compared in the frequency domain by performing Fast-Fourier Transformations (FFT) and Short-Time Fourier Transformations (STFT) on the numerical and experimental data respectively. It is shown that the transient pressure field in a single staged centrifugal compressor is calculated accurately by both of the numerical methods in comparison to the transient flow measurements. This paper demonstrates that the numerical modeling of the fast-response pressure sensors has a significant impact on the unsteady pressure amplitudes, which needs to be taken into account for a reliable experimental validation process.
Heat Transfer Enhancement in a Double Sequential Impingement Channel
Authors: Gaffuri Michele , Ott Peter , Naik Shailendra , Henze Marc
Published: September 2021

Sequential impingement channels can reduce the adverse effect of crossflow in narrow impingement channels, as well as increase the cooling efficiency. In this work, sequential impingement channels are experimentally investigated using the transient liquid crystal technique to assess their thermal performances. A low heat transfer region is identified in the downstream part of the first channel where the flow is discharged into the second plenum. Various means of increasing the heat transfer at this location are investigated. Ribs on the target plate allow for an increase of the average heat transfer coefficient with small losses in pressure. Reducing the channel cross-section increases the mean flow velocity and, combined with the ribs, allows for a further increase of the heat transfer. Additionally, the geometrical changes of the channel caused by the addition of a ramp with a rounded corner, allow to decrease the pressure losses associated with the discharge into the second plenum, which is not optimal in the baseline configuration due to the sharp corner of the purge hole. Further reducing the cross-section to increase the heat transfer, however, increases the pressure losses due to the small open area in the transition zone.
Design and Tests of a New Damper for a Gas Turbine Thin-Shell Duct
Authors: Gabriele Serena , Di Sisto Paolo , Del Vescovo Giuseppe , Simone Conti
Published: September 2021

Gas turbine (GT) liners, transition ducts and exhaust diffusers are large thin-shell ducts bounded by two barrels, typically characterized by multiple natural frequencies inside the operating speed range of the engine rotor.

In most applications, GT ducts are supported on one side only and they are free to expand inside the gas turbine so to avoid thermal distresses.

The GT ducts are typically damped structures able to prevent high cycles fatigue failures. Damping is provided by sliding features as insulation or bolted joints.

This paper describes the redesign of a transition duct (TD) after it was discovered that in some operating conditions, duct could crack for high cycle fatigue (HCF).

The TD connects the flow path of the gas generator turbine with the flow path of the power turbine.

The new TD has been made more robust, but it has also been equipped of dampers capable to operate at high temperature.

Starting from the analyses of field data, a predictive FEA model has been developed and validated. After a deep investigation of the TD modes that could be excited by flow path and/or by rotor vibrations, it was decided to add two dampers, one for each barrel of the TD.

Due to internal space limitations, a new type of damper has been designed for the external barrel.

Both dampers have been sized using FEA. Harmonic analyses rather than forced response transient analyses have been performed so to verify the effectiveness of the new design. In the simulations, dampers have been replaced by harmonic forces able to reproduce the friction force of the dampers.

Validation of the method and damper calibration has been done by performing lab tests and full-size TD tests.
Design and Pre-Test Evaluation of a Low-Pressure Compressor Test Facility for Cryogenic Hydrogen Fuel Integration
Authors: Jonsson Isak , Xisto Carlos , Lejon Marcus , Dahl Anders , Grönstedt Tomas
Published: September 2021

The use of hydrogen as aviation fuel is again resurfacing with unprecedented vigor. It is well known that hydrogen is a formidable heat sink and the use of heat sinks in the compression system of an aero engine may enable not only preheating of the fuel but also improve the gas turbine cycle itself. One such opportunity arises from extracting heat to the fuel as part of the compression process. This work presents the design process and pre-test evaluation of a low-speed compressor test facility dedicated to aerothermal measurements. The design has been derived from a high-speed transonic compressor developed for a large sized geared turbofan engine. The proposed pre-test evaluation methodology provides a comprehensive and affordable way to estimate facility accuracy by virtually addressing all the experimental procedures, from data acquisition to a final performance map. The evaluation of gathering compressor performance parameters via a gas-path investigation process was achieved while relying on results from numerical simulations. The pre-test evaluation details uncertainties introduced throughout this process with transducers, flow and probe specific errors, traverse discretization, and data normalization. A suitable instrumentation configuration is presented which shows that the performance parameters pressure ratio (Π) and isentropic efficiency (ηc) can be determined with uncertainties below 1% for most operating conditions and below 0.5% at design conditions.
Combustor Wall Surface Temperature and Heat Flux Measurement Using a Fiber-Coupled Long Wave Infrared Hyperspectral Sensor
Authors: Chandh Aravind , Bibik Oleksandr , Adhikari Subodh , Wu David , Lieuwen Tim , Hsu Paul , Roy Sukesh , Sikorski Ruth , Emerson Benjamin
Published: September 2021

In this paper, we discuss the development of a non-intrusive surface temperature sensor based on long-wavelength infrared (LWIR) hyperspectral technology. The LWIR detection enables to minimize optical interferences from hot combustion gases (emission mostly within UV-MWIR region). Utilization of hyperspectral detection allows to further improve temperature measurement accuracy and precision. The developed sensor with fiber coupling provides the required flexibility to be maneuvered around/through combustor hardware. The LWIR fiber probe is fully protected by the custom-designed water-cooled probe housing. This device is designed to sustain temperature of 2400 K at pressure of 50 bar, which enables long-term optical diagnostics inside the practical high-pressure combustion facilities where extreme thermal acoustic perturbation and intense heat fluxes are present. The housing featured a diamond window to selectively measure spectra in the LWIR region to get accurate surface temperature exclusively of the combustor wall. The probe was installed into a RQL style combustor to get surface temperature of both hot and cold side of the combustor wall. Further, pointwise heat flux estimates across the combustion liner wall was derived using the temperature measurements.
Study of Oil Film Heat Transfer in Gas Turbine Engine Bearing Chamber
Authors: Petukhov Illia , Mykhailenko Taras , Lysytsia Oleksii , Kovalov Artem
Published: September 2021

A clear understanding of the heat transfer processes in a gas turbine engine bearing chamber at the design stage makes it possible to properly design the lubrication and sealing systems and ensure the future bearing safe operation. The heat transfer coefficient (HTC) calculated based on the classical Newton-Richman equation is widely used to represent the heat transfer data and useful for the thermal resistance analysis. However, this approach is only formally applicable in the case of a two-phase medium. While there is a need to model a two-phase medium, setting the flow core temperature correctly in the Newton-Richman equation is an issue that is analyzed in this study.

The heat from the flow core is transferred to the boundary of the oil film on the bearing chamber walls by an adjacent air and precipitating droplets. The analysis showed that droplet deposition plays a decisive role in this process and significantly intensifies the heat transfer. The main contribution to the thermal resistance of internal heat transfer is provided by the oil film. In this regard, the study considers the issues of the bearing chamber workflow modeling allowing to determine the hydrodynamic parameters of the oil film taking into account air and oil flow rates and shaft revolutions. The study also considers a possibility to apply the thermohydraulic analogy methods for the oil film thermal resistance determination. The study presents practical recommendations for process modeling in the bearing chamber.
Optimization of a High Pressure Industrial Fan
Authors: De Jesús Rivera Edward , Besem-Cordova Fanny , Bonaccorsi Jean-Charles
Published: September 2021

Fans are used in industrial refineries, power generation, petrochemistry, pollution control, etc. These fans can perform in sometimes extreme, mission-critical conditions.

The design of fans has historically relied on turbomachinery affinity laws, resulting in oversized machines that are expensive to manufacture and transport.

With the increasingly lower CPU cost of fluid modeling, designers can now turn to CFD optimization to produce the necessary machine performance and flow conditions while respecting manufacturing constraints.

The objective of this study is to maximize the pressure rise across an industrial fan while respecting manufacturing constraints.

First, a 3D scan of the baseline impeller is used to create the CFD model and validated against experimental data. The baseline impeller geometry is then parameterized with 21 free parameters driving the shape of the hub, shroud, blade lean and camber.

A fully automated optimization process is conducted using Numeca’s Fine™/Design3D software, allowing for a CPU-efficient Design Of Experiment (DOE) database generation and a surrogate model using the powerful Minamo optimization kernel and data-mining tool.

The optimized impeller coupled with a CFD-aided redesigned volute showed an increase in overall pressure rise over the whole performance line, up to 24% at higher mass flow rates compared to the baseline geometry.
Thermal Barrier Coating Applied to the Structural Shroud of an Inside-Out Ceramic Turbine
Authors: Dubois P. K. , Gauvin-Verville A. , Picard B. , Plante J.-S. , Picard M.
Published: September 2021

Recuperated, high-temperature microturbines (< 1 MW) could be a key enabler for hybrid powertrains of tomorrow’s small aircraft. To achieve competitive thermal efficiencies, turbine inlet temperature (TIT) must increase to 1550 K, well beyond conventional metallic microturbine limits. This calls for high-temperature refractory ceramics, which call for a new ceramic-specific, microturbine design like the Inside-Out Ceramic Turbine (ICT). This study focuses on the applicability of a refractory thermal barrier coating (TBC) to the internal surface of the ICT cooling ring. By cutting the heat transfer from the main flow to the structural rim-rotor, the use of a refractory TBC coating in an ICT enables higher TIT and lower cooling air mass flow.

A preliminary experimental assessment is done at room temperature on 1 mm-thick coatings of 8% yttria-stabilized zirconia (8YSZ), air plasma sprayed (APS) TBC, applied to Inconel 718 and Ti64 test coupons. Results show that the strongly orthotropic behaviour of the tested TBC fits perfectly with the deformation mechanics of the ICT configuration under load. First, large in-plane strain tolerance allows the large tangential deformation imposed by the structural shroud under centrifugal loading. Second, high out-of-plane stiffness and compressive resistance combine to support extreme compressive loads with no apparent damage to the TBC even at more than 3 times blade indentation average loading. An experimental demonstration on a small-scale prototype shows a reduction of 40% in cooling flow in a, 8-minute ICT test, with no damage to the TBC, proving the effectiveness and potential of the proposed TBC design.
Numerical Evaluation and High-Speed Rotating Test on Circular Arc Spring Dampers for Centrifugal Compressors
Authors: Takeuchi Ryota , Ishimaru Hidetsugu , Yamashita Hideaki , Inoue Takahiko , Yabui Shota , Inoue Tsuyoshi
Published: September 2021

A circular arc spring damper (CASD) is a recently proposed fluid-film damper that has two or more arc-shaped centering springs and dual radial clearances formed by wire electric discharge machining. CASD requires less space and weight than a conventional cage-centered squeeze film damper (SFD). It provides linear stiffness and stable damping force in rotor-bearing systems to attenuate vibration due to imbalance or to improve rotordynamic stability. The authors have been investigated the dynamic characteristics of CASD in component-level experiments. However, their performance and applicability to real machines have not been confirmed in system-level experiments. Additionally, a theoretical means of evaluation for CASD should be established to predict its dynamic coefficients, and to understand the mechanism of dynamic force generation.

In the first part of this study, a numerical evaluation method using two-way fluid-structure interaction analysis and its theoretical background is presented. Transient structural analysis and fluid-film flow analysis with a simple homogeneous cavitation model are coupled in the commercial multi-physics platform ANSYS. The accuracy of the method was validated by comparing the damping and added-mass coefficients with results from previous experiments. Furthermore, several aspects of the force generation mechanism, and the difference from conventional SFD were studied numerically.

The second part of the study addresses the application of CASD in a multi-stage centrifugal compressor. A combined 4-inch diameter, 5-Pad tilting pad journal bearing (TPJB) with 4-arc type CASD was newly designed and manufactured. To prove the applicability of the developed damper bearing, a series of rotating tests was conducted at a high-speed balancing facility with a full-scale dummy rotor with a critical speed ratio of approximately 3.1. The measured unbalance response showed a much lower amplification factor than that of the conventional TPJB without the damper, which infers a significant improvement in the stability. The measured responses agreed with the rotordynamic analysis, which uses the dynamic coefficients of CASD derived from the proposed numerical evaluation method.