bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous Optimization of Mistuned Bladed Disks for Forced and Self-Excited Vibration Considering Amount of Unbalance
Authors: Kaneko Yasutomo , Watanabe Toshio , Furukawa Tatsuya
Published: September 2021

Actual bladed disks with small variations are called mistuned systems. Many researchers suggest that mistuning, although negatively affecting the forced response, has a beneficial (stabilizing) effect on blade flutter (self-excited vibration). Therefore, in blade design, a bladed disk must be optimized for forced vibration and blade flutter. We proposed a simultaneous optimization method of bladed disks for forced and self-excited vibration, considering the amount of unbalance that causes rotor vibration. This method uses alternate mistuning to suppress the blade flutter. We measured the natural frequency and weight of all the blades of a disk, as in the traditional development process. Then, we assembled a mistuned system retaining the alternate mistuning, and generated analysis models based on the measured natural frequencies and weights of the blades. Finally, we analyzed the resonant stress and the amount of unbalance in the mistuned system repeatedly, sorting the blades and retaining the alternate mistuning of the disk. The simultaneous optimal solution was explored by MCS or DDE (Genetic algorithm). To reduce the computational time, we used the reduced order model FMM to calculate the resonant stress and the stability of the mistuned bladed disks. Further, we verified the validity of the proposed method by applying it to a mistuned bladed disk of a steam turbine.
A Discrete Element Methods-Based Model for Particulate Deposition and Rebound in Gas Turbines
Authors: Gaskell Jack G. , McGilvray Matthew , Gillespie David R. H.
Published: September 2021

The secondary air system and cooling passages of gas turbine components are prone to blockage from sand and dust. Prediction of deposition requires accurate models of particle transport and thermo-mechanical interaction with walls. Bounce stick models predict whether a particle will bounce, stick, or shatter upon impact and calculate rebound trajectories if applicable. This paper proposes an explicit bounce stick model that uses analytical solutions of adhesion, plastic deformation and viscoelasticity to time-resolve collision physics. The Discrete-Element Methods (DEM) model shows good agreement when compared to experimental studies of micron and millimetre-scale particle collisions, requiring minimal parametric fitting. Non-physical values mechanical properties, artifices of previous models, are thus eliminated. Further comparison is made to the best resolved and industry standard semi-empirical models available in literature. In addition to coefficients of restitution, other variables crucial to accurately model rebound, for example angular velocity, are predicted. The time-stepping explicit approach allows full coupling between internal processes during contact, and shows that particle deformation and hence viscoelasticity play a significant role in adhesion. Modelling time-dependent internal variables such as wall-normal force create functionality for future modelling of arbitrarily shaped particles, the physics of which has been shown by previous work to differ significantly from that of spheres. To date these effects have not been captured well using by higher-level energy-based models.
A Reduced Order Modeling Approach to Probabilistic Creep-Damage Predictions in Finite Element Analysis
Authors: Hossain Md Abir , Cottingham Jacqueline R. , Stewart Calvin M.
Published: September 2021

This paper introduces a computationally efficient Reduced Order Modeling (ROM) approach for the probabilistic prediction of creep-damage failure. Component-level probabilistic simulations are needed to assess the reliability and safety of high-temperature components. Full-scale probabilistic creep-damage modeling in finite element (FE) approach is computationally expensive requiring many hundreds of simulations to replicate the uncertainty of component failure. To that end, ROM is proposed to minimize the elevated computational cost while controlling the loss of accuracy. It is proposed that full-scale probabilistic simulations can be completed in 1D at a reduced cost, the extremum conditions extracted, and those conditions applied for lower cost 2D/3D probabilistic simulations of components that capture the mean and uncertainty of failure. The probabilistic Sine-hyperbolic (Sinh) model is selected which in previous work was calibrated to alloy 304 stainless steel. The Sinh model includes probability density functions (pdfs) for test condition (stress and temperature), initial damage (i.e., microstructure), and material properties uncertainty. The Sinh model is programmed into ANSYS finite element software using the USERCREEP.F material subroutine. First, the Sinh model and FE code are subject to verification and validation to affirm the accuracy of the simulations. Numerous Monte Carlo simulations are executed in a 1D model to generate probabilistic creep deformation, damage, and rupture data. This data is analyzed and the probabilistic parameters corresponding to extreme creep response are extracted. The ROM concept is applied where only the extreme conditions are applied in the 2D probabilistic prediction of a component. The probabilistic predictions between the 1D and 2D model is compared to assess ROM for creep. The accuracy of the probabilistic prediction employing the ROM approach will potentially reduce the time and cost of simulating complex engineering systems. Future studies will introduce multi-stage Sinh, stochasticity, and spatial uncertainty for improved prediction.
Influence of Hole-to-Hole Interaction on the Acoustic Behavior of Multi-Orifice Perforated Plates
Authors: Javareshkian Alireza , Dancelme Alexis , Chen Hongyu , Sattelmayer Thomas
Published: September 2021

A key factor for developing low-emission combustion systems in modern gas turbines and aero-engines is the acoustic liner’s optimized design. Several models are available in the literature for the acoustic impedance of perforated acoustic liners. Most of these impedance models neglect the interaction effect between the orifices. In practice, the orifices are generally closely distributed such that the interactions between acoustic radiation from neighboring orifices can affect their acoustical behavior. The hole-to-hole interaction effect may change the resonance frequency of the resonator due to the nonplanar wave propagation in the cavity, the orifices in the perforated plate, and the near-wall region in the combustor. Considering this effect may help to predict the resonance frequency of the resonator accurately. In this work, a three-dimensional (3D) analytical approach is developed to account for the nonplanar wave propagation in the cavity and orifices on the perforated plate. The present study employs the proposed 3D analytical method to determine the hole-to-hole interaction end-correction of multi-orifice perforated plates.

Additionally, the hole-to-hole interaction end-correction from a series of perforated plates with different orifice radii and spacings is obtained via the Finite Element Method (FEM). Perforated plate specimens with different center-to-center hole spacing are tested using an impedance tube. Experimental results show that the resonance frequency is shifted towards a lower frequency with decreasing holes’ spacing. The resulting model is compared with the experiments and the end-correction models available in the literature. The comparison shows that the available end-correction models cannot capture the hole-to-hole interaction effect, which is observed in experiments.

In contrast, the proposed model can reproduce measurements with high quality. The resulting model demonstrates that the acoustic end-correction length for orifices is closely related to the perforated plate’s porosity ratio and orifice radius. The proposed model is readily applicable in the design of multi-orifice perforated plates.
Static Performance of Smooth Liquid Annular Seals in the Transition and Turbulent Regimes
Authors: Childs Dara W. , Bullock Joshua
Published: September 2021

Static test results are presented for smooth annular seals with a length-to-diameter ratio of 0.50, radius R = 51.00 mm, at the nominal radial clearance Cr = 0.2032 mm. Tests were conducted for angular shaft speeds; ω = 2, 4, 6, 8 krpm, axial pressure drops; ΔP = 2.1, 4.13, 6.21, 8.27 bars, and eccentricity ratios ϵ0 = e0/Cr = 0.00, 0.27, 0.53, 0.8 where e0 is the static eccentricity. Three pre-swirl inserts were used to target zero, medium, and high (0., 0.4, and 0.8) pre-swirl ratios for a set of pre-determined operating conditions with ISO VG 2 oil at 46.1°C.

Pitot tubes measured the circumferential velocity at separate upstream and downstream seal locations and were used to calculate pre-swirl ratio, PSR = vinlet/Rω, and outlet-swirl ratio, OSR = voutlet/Rω. For all tested pre-swirl inserts, PSR tended to converge to 0.4∼0.5 as ω increased. PSR and OSR were poorly correlated.

Volumetric leakage rate Q ˙ versus pressure differential ΔP was measured. The measured vector Reynolds number Re, combining the axial and circumferential Reynolds numbers ranged from ∼1000 to ∼3500. Based on Zirkelback and San Andrés 1996 publication, almost all of the flow regime is predicted to lie in the transition regime, with fewer points in the turbulent regime.

Generally, the seals’ static centering properties were obtained by applying a static load Fs and measuring the resulting displacement vector e0. At many low-speed, low-ΔP test conditions, the seal would not remain in the desired centered or near-centered position and had to be forced into place with a centering force Fs. The authors believe that the observed de-centering effects resulted from test operations in the transition flow regime where the friction factor λ does not drop with increasing ΔP and increasing Re. A positive centering Lomakin effect requires that λ drop with increasing axial Reynolds number.

The seals had positive centering effects over a large portion of the predicted transition flow regime, supporting the view that the shift from transition-to-turbulent flow regularly occurred at lower Re values than the Re = 3000 boundary used by Zirkleback and San Andrés.
Loss Characterization of Advanced VIGV Configurations With Adjustable Blade Geometry
Authors: Frank Roman G. , Wacker Christian , Niehuis Reinhard
Published: September 2021

Variable inlet guide vanes (VIGV) are the main control element to adjust the flow rate of industrial centrifugal compressors by customized pre-swirl in the inlet plane of the impeller. The efficient working range of VIGVs is however restricted due to open flow separation occurring at critical stagger angles. In order to overcome the narrow limitations of current blade geometries and to enhance the operating range of the compressor, split blades consisting of a separate front and tail blade segment proved to be particularly promising in previous linear-cascade measurements. Each blade segment is thereby individually staggered. This enables a gradual flow deflection along the chord length. Secondary flow losses, however, were not considered in the previous investigations with linear-cascades.

To highlight the potential of the split blade concept under more application-oriented conditions including all relevant flow effects, highly resolved field measurements were conducted in the wake of annular VIGVs. Four different blade configurations, a customary reference case and three variations of the split blade with full, partial and missing sealing in the gap between the segments, were assessed using five-hole probe measurements. By investigating a wide range of stagger angles, the coverage of the full low-loss working range of the VIGV could be ensured. Especially, the fully sealed split blade configuration proved its capacity to extend the efficient operational range significantly.
Sweep Effects on Fan-Intake Aerodynamics at High Angle of Attack
Authors: Mohankumar Ben , Hall Cesare A. , Wilson Mark J.
Published: September 2021

Sweep in a transonic fan is conventionally used to reduce design point losses by inclining the passage shock relative to the incoming flow. However, future low pressure ratio fans operate to lower Mach numbers meaning the role of sweep at cruise is diminished. Instead, sweep might be repurposed to improve the performance of critical high Mach number off-design conditions such as high angle of attack (AOA). In this paper, we use unsteady computational fluid dynamics to compare two transonic low pressure ratio fans, one radially stacked and one highly swept, coupled to a short intake design, at the high AOA flight condition. The AOA considered is 35°, which is sufficient to separate the intake bottom lip.

The midspan of the swept fan was shifted upstream to add positive sweep to the outer span. Based on previous design experience, it was hypothesised the swept fan would reduce transonic losses when operating at high AOA. However, it was found the swept fan increased the rotor loss by 24% relative to the radial fan. Loss was increased through two key mechanisms. i) Rotor choking: flow is redistributed around the intake separation and enters the rotor midspan with high Mach numbers. Sweeping the fan upstream reduced the effective intake length, which increased the inlet relative Mach number and amplified choking losses. ii): Rotor-separation interaction (RSI): the rotor tip experiences low mass flow inside the separation, which increases the pressure rise across the casing to a point where the boundary layer separates. The swept fan diffused the casing streamtube, causing the casing separation to increase in size and persist in the passage for longer. High RSI loss indicated the swept fan was operating closer to the rotating stall point.
Cryogenic Fuel Storage Modelling and Optimisation for Aircraft Applications
Authors: Rompokos Pavlos , Rolt Andrew , Nalianda Devaiah , Sibilli Thierry , Benson Claire
Published: September 2021

Designing commercial aircraft to use liquid hydrogen (LH2) is one way to substantially reduce their life-cycle CO2 emissions. The merits of hydrogen as an aviation fuel have long been recognized, however, the handling of a cryogenic fuel adds complexity to aircraft and engine systems, operations, maintenance and storage. The fuel tanks could account for 8–10% of an aircraft’s operating empty weight, so designing them for the least added weight is of high significance.

This paper describes the heat transfer model developed in the EU Horizon 2020 project that is used to predict heat ingress to a cylindrical tank with hemispherical end caps with external foam insulation. It accounts for heat transfer according to the state of the tank contents, the insulation material properties, the environment, and the dimensions of the tank. The model also estimates the rate of pressure change according to the state of the fuel and the rate at which fuel is withdrawn from the tank. In addition, a methodology is presented, that allows for tank sizing taking into consideration the requirements of a design flight mission, the maximum pressure developed, and the fuel evaporated.

Finally, the study demonstrates how to select optimal insulation material and thickness to provide the lightest design for the cases where no gaseous hydrogen is extracted, and where some hydrogen gas is extracted during cruise, the latter giving gravimetric efficiencies as high as 74%.
CFD Analysis of the Influence of Gas Content on the Rotordynamic Force Coefficients for a Circumferentially Grooved Annular Seal for Multiple Phase Pumps
Authors: Wu Tingcheng , San Andrés Luis , Lu Xueliang
Published: September 2021

Pumping efficiency and rotordynamic stability are paramount to subsea multiphase pump operation since, during the life of a well, the process fluid transitions from a pure liquid to a mixture of gas in liquid to just gas. Circumferentially grooved seals commonly serve as balance pistons in pumps while also restricting secondary flow. Prior experimental results obtained with a grooved seal operating with a mixture of air and mineral oil show the seal rotordynamic force coefficients vary significantly with the gas volume fraction (GVF). This paper, complementing an exhaustive experimental program, presents a computational fluid dynamics (CFD) analysis to predict the leakage, drag power, and dynamic force coefficients of a circumferentially grooved seal supplied with air in oil mixture with a GVF varying from 0 to 0.7. The test seal has fourteen grooves, an overall axial length of 43.6 mm and a radial clearance of 0.211 mm. The 127 mm diameter rotor spins at constant angular speed (Ω = 3,500 rpm). The mixture enters the seal at a supply pressure (Pin) of 2.9 bar(a), and the seal exit pressure (Pout) is 1 bar(a). The CFD two-phase flow simulations utilize the Euler-Euler multiphase model to predict the mass flow rate and the pressure field as a function of the operating conditions. Using a multi-frequency shaft orbit motion method, the CFD simulations deliver the variations of reaction force on the rotor with respect to the excitation frequency. For a pure liquid condition (GVF = 0), both the CFD and experimental results produce constant stiffness, damping and added mass coefficients. The experimental and CFD results demonstrate the seal rotordynamic force coefficients are quite sensitive to the gas volume fraction (GVF). When introducing a small amount of air into the oil (GVF = 0.1), the direct damping coefficient increases by approximately 10%. For operation with a mixture with inlet GVF > 0.1, the cross-coupled stiffness coefficients develop strong frequency dependent characteristics. In contrast, the direct damping coefficient has a negligible variation with excitation frequency. The CFD predictions, as well as the experimental results, evidence that air injection in a liquid stream can significantly change the seal rotordynamic characteristics, and thus can affect the rotordynamic stability of a pump. An accurate CFD analysis thus enables engineers to design reliable grooved seals operating under two-phase flow conditions.
Assessment of Engine Operability and Overall Performance for Parallel Hybrid Electric Propulsion Systems for a Single-Aisle Aircraft
Authors: Kang Sangkeun , Roumeliotis Ioannis , Zhang Jinning , Pachidis Vassilios , Broca Olivier
Published: September 2021

This paper aims to assess the gas turbine operability and overall hybrid electric propulsion system performance for a parallel configuration applied to a 150 passenger single-aisle aircraft. Two arrangements are considered: one where the low pressure shaft is boosted and one where the high pressure shaft is boosted. For identifying limits in the hybridization strategy steady state and transient operation are considered and the hybridization effect on compressor operability is determined.

Having established the electric power on-take limits with respect to gas turbine operation the systems performance at aircraft level is quantified for the relevant cases. Different power management strategies are applied for the two arrangements and for different power degrees of hybridization.

The results indicate that despite the fact that pollutant emission and fuel consumption may improved for hybrid propulsion, this comes at the cost of reduced payload and operability margins. Boosting the low pressure shaft may give the highest engine performance benefits but with a significant weight penalty, while the low pressure compressor system operability is negatively affected. On the other hand boosting the high pressure shaft provides lower engine performance benefits but with smaller weight penalty and with less operability concerns.
Influence of Atomization Characteristics on Lean Blow-Out Limits in a Gas Turbine Combustor
Authors: Wang Xiwei , Huang Yong , Sun Lei , Liu Yunfeng , Wang Donghui
Published: September 2021

In order to investigate the effects of atomization characteristics on the lean blow-out (LBO) performance, an experimental study was carried out on the spray and the combustion. The LBO limits and the outlet temperature near the LBO condition of different atomizers were measured in a single dome rectangular model combustor with a dual-radial and a dual-axial swirl cup, respectively. In the combustor, the spray analysis was performed on different atomizers (without combustion) at the LBO condition. The Malvern particle size analyzer was used to measure the Sauter Mean Diameter (SMD), and the laser sheet was used to take spray images. First of all, the spray pattern determines the minimum heat release required to maintain the combustion, which corresponds to the ideal LBO fuel/air ratio (FAR), which is the maximum potential for the lean combustion. Secondly, the matching of the spray SMD, the droplet size spatial distribution and the droplet initial velocity with the flow field determines the ratio of the completely burned fuel to the total fuel ejected from the atomizer, which determines the extent to which the combustor exerts its lean combustion potential. In addition, the numerical simulation of the flow field of the combustor with two structures was carried out, which provided an important basis for the theoretical analysis of this paper.
Design and Evaluation of a Flow Capturing Device for a High-Speed Wind Tunnel
Authors: Graiff Mattia , Staggl Marian , Göttlich Emil , Wakelam Christian
Published: September 2021

Wind tunnel testing belongs to the most significant aspects of the technical development process. In order to improve the test environment conditions and open the possibility of closed loop operation, a flow capturing device is developed for a highspeed wind tunnel previously exhausting to ambient. The highspeed wind tunnel is used in conjunction with annular sector cascade test rigs to evaluate the performance of intermediate turbine ducts. In the presented paper, a modular design approach for the flow capturing device is presented; particular attention is reserved to optimal integration within the pre-existing test environment and to an efficient sealing strategy. Computational results provide the basis for the correct sizing of the device; the aerodynamic effects induced by the flow capturing device downstream of an annular sector cascade rig are shown to bear no influence on the quality of the test data. The presented results of several tests conducted under a wide range of conditions confirm the viability of the developed flow capturing device. The improvements to the pre-existing experimental setup achieved with the addition of the flow capturing device are furthermore presented in this paper, focusing on the obtained reduction in sound pressure and temperature level within the test facilities.
Effects of Surface Waviness on Fan Blade Boundary Layer Transition and Profile Loss — Part II: Experimental Assessments and Applications
Authors: Lee Jinwook , Ramaswamy Vaishnavi , Spakovszky Zoltán S. , Greitzer Edward M. , Drela Mark , Talbotec Jérôme
Published: September 2021

Part II describes the experimental assessment and the application of the ideas in Part I concerning the mechanisms that determine the role of blade surface waviness on laminar-turbulent transition and their consequent effect on civil aircraft fan performance. A natural transition wind tunnel was designed and constructed to characterize the impact of surface waviness on transition, using both hotwire anemometry and infrared thermography. The experimental results support the new hypothesis presented in Part I, concerning the way in which blade surface waviness affects fan performance through motion of the transition onset location due to interaction between surface waviness and Tollmien-Schlichting (TS) boundary layer instability. In particular, the theoretical amplification of the TS waves, and the corresponding transition onset location movement due to surface waviness, was borne out over a range of variations in Reynolds number, non-dimensional surface wavelength, non-dimensional surface wave height, and location of surface wave initiation, relevant to composite fan blade parameters. Further, the increase of receptivity coefficient, and thus the initial amplitude of disturbances due to geometric resonance between surface wavelength and TS wavelength, was also confirmed by the experiments. Surface waviness was estimated, in some cases, to result in a nearly 1% decrease in fan efficiency compared to a non-wavy blade. Suggestions are given for mitigation of the effects of waviness, including the idea of blade curvature rescheduling as a method to delay transition and thus decrease loss.
Mechanical and Thermal Deformation Analysis of a Large Polymer Lined Tilting Pad Journal Bearing
Authors: Stottrop Michael , Bender Beate
Published: September 2021

An increase of specific load in large tilting pad journal bearings (TPJB) leads to major mechanically and thermally induced deformation of the pads and limits the load carrying capacity. In this paper, we present a theoretical approach to determine deformation of a TPJB with PEEK (Polyetheretherketone) polymer lined pads by means of a thermo-elasto-hydrodynamic model. The objective of this investigation is a quantitative analysis of the deformation characteristics of a five-pad TPJB with a nominal diameter of 500 mm. Mechanical and thermal deformations are simulated for both the steel backing and the polymer lining. The deformation characteristics calculated with the numerical model are compared to simulation results of an experimentally validated model with a white-metal lining.

The results indicate an improvement in bearing characteristics with the PEEK lining, as maximum pressure decreases and minimum film thickness increases. Due to the insulating properties of the PEEK layer, thermally induced pad deformation is reduced significantly.
Flow Physics in a Large Rotor Tip Gap in a Multi-Stage Axial Compressor
Authors: Hah Chunill
Published: September 2021

The flow physics in a large rotor tip gap in a 1.5-stage axial compressor is investigated in the current study. The flow structure in the rotor tip region is complex with several dominant vortical structures of opposite rotation, resulting in inhomogeneous and highly anisotropic turbulence. Earlier measurements show that eddy viscosity is negative over large parts of the tip region and eddy viscosity varies among stress/strain components. The present study aims to understand how the complex nature of rotor tip leakage flow affects compressor performance when the tip gap size is greater than 4–5% of the rotor span, which is typical of advanced small core engines. Unsteady Reynolds-averaged Navier-Stokes (URANS) and Large Eddy Simulation (LES) techniques are applied to study flow physics in a large rotor tip gap (5.5% of rotor span) in a 1.5-stage axial compressor. Calculated flow fields from the two different approaches are compared with available measurements and examined in detail. LES calculates the pressure rise in the present compressor fairly well, while URANS with a standard two-equation turbulence closure underpredicts the pressure rise by 15–20% of the measured values. The current study shows that URANS with the current turbulence closure produces much higher all-positive eddy viscosity in the tip-gap region compared to measurements and LES. The distribution of eddy viscosity in the URANS simulation is also wrong. Consequently, the flow in the tip region is highly damped with significantly larger blockage generation, which results in the tip leakage vortex (TLV) staying closer to the blade suction side compared to the measurement. When the TLV stays closer to the blade, both flow turning and the pressure rise across the compressor are reduced compared to the measurements. It appears that this effect is amplified by a large rotor tip gap.
Numerical Investigation on the Influence of Tip Shroud Design Characteristics on the Aerodynamic Damping of a Last Stage Blade
Authors: Rozendaal Alexander V. , Torkaman Alex , Fiebiger Stephen W.
Published: September 2021

The accurate predication of aerodynamic flutter margin continues to be an area of growing importance in the design of rotating turbomachinery, especially when considering the ongoing industry objectives for increased operating efficiency, higher power output, and reduced fuel consumption. Improvements in these areas are commonly achieved through incremental design changes to existing hardware, and often trend with higher pressure ratios and mass flow rates through the machine. In many cases, the extent of these flow improvements become constrained by the stability margins of flutter-limiting components such as front-stage compressor blades and last stage turbine blades. In such cases, designers are left with the difficult task of mitigating the flutter risk, but without limiting the overall performance of the machine.

The tip shroud of a typical last stage turbine blade can significantly influence the flutter response of the blade. It is this reason that underlines the importance for understanding the sensitivity of shroud design parameters when attempting to achieve a flutter-free design, especially if the aerodynamic qualities of the airfoil need to be preserved. This paper evaluates the flutter performance of a last stage industrial gas turbine blade with multiple tip shroud configurations and demonstrates the influence of the selected design parameters with respect to the aerodynamic damping characteristics of the blade.
Energy Dissipation Metrics for Fatigue Damage Detection in the Short Crack Regime for Aluminum Alloys
Authors: Dharmadhikari Susheel , Basak Amrita
Published: September 2021

In this paper, three distinct energy dissipation metrics are proposed to enable fatigue damage detection in aluminum specimens. The metrics are (i) Energy Dissipation Rate, (ii) Cumulative Energy Dissipation, and (iii) Material Stiffness. They are created by using the force and displacement signals obtained from the fatigue testing apparatus during the testing of Al7075-T6 specimens. The apparatus is also equipped with a confocal microscope which calibrates the fatigue damage detection at a crack thickness of 10 μm, thereby, enabling precise detection in the short crack regime. Using all the three metrics, optimal thresholds are computed using receiver operating characteristics and the average accuracy of damage detection in quantified. Accordingly, the three metrics show an accuracy of 84.06%, 100%, and 84.32%, respectively in detecting the cracked specimens.
3D Printing of Ceramic Shell Molds for Precision Casting of Turbine Blades
Authors: Magerramova Liubov , Kozlov Boris , Kratt Eugene
Published: September 2021

Traditionally, the technology used in the production of gas turbine blade castings characterized by a large number of technological conversions, high labor costs with a large amount of manual labor and the need to produce various types of complex and expensive equipment at different stages of production. This work aims to reduce the time and money spent on the manufacturing of ceramic shell shapes — a form suitable for the standard methods of precision casting by traditional heat-resistant nickel alloys. The proposed approached involves obtaining a shell shape with an internal core as a single, non-assembled product, without lengthy and time-consuming design and manufacturing processes involved in forming equipment for the production of castings based on smelted models. The proposed method is based on the use of 3D printing with refractory ceramic pastes.

Using both uncooled and cooled blades as examples, models of casting molds were designed, technological processes were developed, and ceramic shell molds were manufactured.

Experimental casting into a manufactured ceramic shell mold for an uncooled blade with a bandage shelf was performed and showed satisfactory results.
Design and Development of a New Rotating Turbine Research Facility For Investigating the Interaction Between Mainstream and Various Secondary Air at Relevant Engine Conditions
Authors: Okita Yoji , Futamura Hisao , Yamane Takashi , Suzuki Masaya , Tanaka Nozomi , Tanimitsu Haruyuki , Iguchi Junichi
Published: September 2021

This paper reports a new turbine research facility that was recently completed in Japan Aerospace Exploration Agency (JAXA). The facility is a full annular rotating transonic turbine rig that allows a continuous operation of scaled and/or full-scale axial HPT or LPT.

The rig design was especially focused on the ability of simulating the aerodynamic and thermal interaction between main gas paths and various / massive secondary air flows at conditions of dominant aero-heat parameters well matched to those of modern aero-engines. Cooling air can be delivered to the airfoils of vanes/blades and the endwalls separately at a massflow range covering the typical conditions. Rotor forward and aft purge air as well as through-casing cooling air can be injected with each flowrate independently controlled.

The facility, which has significant capabilities with several large compressors of 10MW in total, 5MW mainflow heater, 6MW drive motor/generator, etc., can be applied to a very wide range of turbine designs.

A series of shakedown testing has been carried out since the completion of construction in 2019. The commissioning phase of the rig will complete in early 2021 and then the rig will enter service. The very first test with a scaled HPT is planned to start in the last quarter of 2021.
Insight on Aerodynamic Damping of the Civil Transonic Fan Blade
Authors: Lian Bo , Hu Ping , Chen Yong , Zhu Xiaocheng , Du Zhaohui
Published: September 2021

Flutter seriously affects the safety and reliability of aeroengine. In this paper, influence coefficient method (ICM) and traveling wave method (TWM) are used to calculate the aerodynamic damping of transonic fan blades of civil aviation engine at different nodal diameters (NDs) and structural modes. The results of two methods are basically consistent but the ICM only needs to simulate seven passages for all of the NDs, which has higher computation efficiency. The results show that under the design condition, the first three structural modes of the blade are aero-elastic stable for each ND, and the aerodynamic damping gets the minimum at ND1 for the first bending mode. As the back pressure deviates from design condition towards choking or stall, the aerodynamic damping obviously decrease and even negative aerodynamic damping occurs at normalized mass flow rate of 0.950. Dynamic mode decomposition (DMD) is applied to analyze the transient pressure on vibrating blade surface. Dominant flow structures like shock wave oscillating and corresponding frequency on blade surface can be acquired through DMD method. TWM simulation with DMD analysis indicates that the shock wave changes the phase of the pressure in the region next to downstream of the shock wave, which makes the aerodynamic work concentrate locally.
On the Challenge of Determining the Surge Limit of Turbocharger Compressors: Part 2 – Capabilities of a Geometrically Reduced Numerical Model
Authors: Paul Dominik , Ratz Johannes , Eißler Werner
Published: September 2021

Steady-state numerical simulations are an essential instrument in the design process of centrifugal compressors for automotive turbochargers in an industrial environment. Although this method is state-of-the-art, the natural unsteadiness of the compressor flow especially close to stall and surge is suppressed by this kind of simulation.

Unsteady numerical simulations of the complete compressor geometry are necessary to detect unstable flow structures leading to surge. As numerical costs and thus the time needed for unsteady simulations correlate with the size of numerical setup, it is not possible for industrial applications to investigate an unsteady operation condition of a centrifugal compressor. On account of that fact, it would be beneficial to reduce the model and include only the most decisive components which are responsible for the significant flow phenomena within the impeller leading to surge.

The objective of this research paper is the investigation of the CFD simulation capabilities of a reduced radial compressor model for steady-state operation conditions using as a robust basis for further transient analysis. Thus, the results of a reduced model setup of one blade segment are compared to a full model setup.

It is concluded that the segment model approach is capable of investigating flow phenomena within the impeller without neglecting fundamental flow structures. In addition, the consequences of the geometric reduction to a diffuser segment without volute on different flow variables are studied. This provides the guidance for further transient studies.

The complete model setup, in conjunction with its validation by experimental data, serves as the starting point for this research paper. Dielenschneider et al.[1] present in the first part of the paper the procedure and a detailed comparison of complete model results with experimental analysis.
A Probabilistic Machine Learning Framework for Explicit Inverse Design of Industrial Gas Turbine Blades
Authors: Ghosh Sayan , Andreoli Valeria , Padmanabha Govinda A. , Peng Cheng , Atkinson Steven , Pandita Piyush , Vandeputte Thomas , Zabaras Nicholas , Wang Liping
Published: September 2021

One of the critical components in Industrial Gas Turbines (IGT) is the turbine blade. Design of turbine blades needs to consider multiple aspects like aerodynamic efficiency, durability, safety and manufacturing, which make the design process sequential and iterative. The sequential nature of these iterations forces a long design cycle time, ranging from a several months to years. Due to the reactionary nature of these iterations, little effort has been made to accumulate data in a manner that allows for deep exploration and understanding of the total design space. This is exemplified in the process of designing the individual components of the IGT resulting in a potential unrealized efficiency. To overcome the aforementioned challenges, we demonstrate a probabilistic inverse design machine learning framework, namely Pro-ML IDeAS, to carry out an explicit inverse design. Pro-ML IDeAS calculates the design explicitly without costly iteration and overcomes the challenges associated with ill-posed inverse problems. In this work the framework will be demonstrated on inverse aerodynamic design of 2D airfoil of turbine blades.
Performance Testing of L-PBF Produced Honeycombs Out of IN625
Authors: Heitmann Timo , Geisen Ole , Hühn Lisa , Munz Oliver , Bardenhagen Andreas
Published: September 2021

Laser Powder Bed Fusion (L-PBF) enables the production of complex metallic parts. Processes using pulsed wave (PW) laser radiation have been proven to be well suited to build thin-walled honeycomb structures. However, the behavior of these structures under load conditions remains mostly unexplored. The objective of this paper is to characterize L-PBF produced honeycombs by investigating their rub and leakage performance. A pulse modulated process based on previous studies is optimized for productivity and used to build L-PBF test samples out of Inconel 625 (IN625). The honeycomb cell geometry is adjusted for improved printability of the overhanging walls. Repeatable L-PBF production of honeycombs with a wall thickness of about 100 μm is confirmed. Conventionally manufactured honeycomb samples out of sheet metal are tested as reference. The rub experiments cover radial incursion rates of up to 0.5 mm/s and relative velocities of up to 165 ms−1 at incursion depths (ID) between 0.5 and 2.0 mm. Lower incursion forces are observed for the L-PBF components, with a higher degree of abrasion. The leakage tests examine the mass flow rate for pressure ratios between 1.05 and 2.0 at constant gap size and constant back pressure. The L-PBF honeycomb seals show a higher mass flow rate, with the slightly larger cell size and higher surface roughness appearing to be the main influencing factors. Overall, improved rubbing behavior and 10 % higher leakage than the conventional probes demonstrate the applicability of L-PBF for honeycomb sealing systems. Future performance improvements through dedicated L-PBF designs can be expected.
Influence of Acoustically Excited Airflows on a Planar Airblast Prefilmer
Authors: Christou Thomas , Stelzner Björn , Zarzalis Nikolaos
Published: September 2021

In order to meet the higher requirements for clean combustion technology in aircraft engine applications and thus reduce harmful emissions, especially nitrogen oxide emissions, the major jet engine manufacturers are developing lean premixed prevaporized (LPP) combustors that operate at very high pressure. In this context, thermoacoustic instabilities may occur within the combustion chamber. The unsteady heat released by the flame generates pressure waves, which are coupled to the inlet air velocity by a feedback loop. This loop amplifies the instabilities of the inlet air velocity, which in turn influences the atomization process.

Since the atomization process at the airblast atomizers of most jet engine combustors determines critical operating characteristics such as air-to-fuel ratio (AFR), flame stability, or NOx emissions, predicting the performance of this process under unsteady conditions has a significant value.

The present experimental study focuses on the influence of oscillating airflows on the spray characteristics at the airblast atomization process. The experimental setup was based on a two-dimensional prefilmer where a water film flow was introduced on one surface. The airflow was excited by a siren, whereby an excitation frequency near 94 Hz was investigated. The airflow oscillation under this excitation frequency was characterized using a Constant Temperature Anemometer (CTA), while the generated spray was investigated with a Phase Doppler Anemometry (PDA) system.

The spray was investigated in a variety of positions along the radial axis, providing spatial information, apart from temporal. The characterization of the spray via PDA includes a two-component droplet velocity detection and diameter measurement, while the spray mass flux for each measured position was also calculated. The acquired data were phase averaged via an in-house developed processing algorithm, while through a statistical analysis the confidence intervals of the calculations were included. The excitation frequency strongly influenced all spray characteristics, namely, the Sauter Mean Diameter (SMD), the droplet velocities, the mass flux, as well as the local air-to-liquid ratio (ALR). Depending on the phase angle, the size distribution of the spray changes, explaining the observed oscillating behavior of the spray characteristics.
A Key Flow Parameter to the Profile Loss of Low-Pressure Turbine Blades
Authors: Kodama Hidekazu , Funazaki Ken-ichi
Published: September 2021

For an optimum performance design of low-pressure turbine (LPT) blades, it is crucial to understand the generation mechanism of profile loss properly. As the profile loss is usually taken to be the loss generated inside the blade boundary layer due to viscous effects, most of the efforts for the performance optimization have concentrated on the reduction in the boundary layer loss using the flow parameters that represent the loss generation in the boundary layers. Kodama and Funazaki [1] investigated the generation mechanism of profile loss from a view point of blade drag forces, friction drag force and pressure drag force, and suggested that the loss due to pressure drag is dominant in the profile loss of a typical LPT blade. The loss due to pressure drag is not a boundary layer loss that is generated in the boundary layers, but a mixing loss that is generated downstream of the trailing edge. It is necessary to clarify a key flow parameter to the loss due to pressure drag for an effective performance optimization.

This paper aims at investigating the flow parameter that is a measure of the profile loss. In the investigation, the profile loss is broken down into the loss components which are expressed by the boundary layer integral parameters at the trailing edge. Then the loss components are categorized into the loss due to friction drag or the loss due to pressure drag. The loss level of each component is evaluated by using the results of steady Reynolds Averaged Navier-Stokes (RANS) simulations to assess the contribution to the total profile loss. The evaluations are conducted for two kinds of blade profiles at three different Reynolds numbers. It is found that the largest contributor to the loss due to pressure drag, consequently to the total profile loss, is the loss associated with a mixing of accelerated free stream flow by the flow blockage at the trailing edge plane. The loss level is simply determined by the flow blockage. This suggests that the flow blockage at the trailing edge plane is the most important flow parameter for an optimum performance design of LPT blades.
Delay Identification in Thermoacoustics
Authors: Gant F. , Ghirardo G. , Cuquel A. , Bothien M. R.
Published: September 2021

The stability of thermoacoustic systems is often regulated by the time delay between acoustic perturbations and corresponding heat release fluctuations. An accurate estimate of this value is of great importance in applications, since even small modifications can introduce significant changes in the system behavior Different studies show that the nonlinear delayed dynamics typical of these systems can be well captured with low-order models. In the present work, a method is introduced to estimate the most likely value of the time delay of a single thermoacoustic mode from a measured acoustic pressure signal. The mode of interest is modeled by an oscillator equation, with a nonlinear delayed forcing term modeling the deterministic flame contribution and an additive white Gaussian noise to embed the stochastic combustion noise. Additionally, other thermoacoustic relevant parameters are estimated. The model accounts for a flame gain, for a flame saturation coefficient, for a linear acoustic damping and for the background combustion noise intensity. The pressure data time series is statistically analyzed and the set of unknown parameters is identified. Validation is performed with respect to synthetically generated time series and low order model simulations, for which the underlying delay is known a priori. A discussion follows about the accuracy of the method, in particular a comparison with existing methods is drawn.
Flow and Heat Transfer Mechanisms in a Rotating Compressor Cavity Under Centrifugal Buoyancy-Driven Convection
Authors: Gao Feng , Chew John W.
Published: September 2021

This paper presents a systematic study of flow and heat transfer mechanisms in a compressor disc cavity with an axial throughflow under centrifugal buoyancy-driven convection, comparing with previously published experimental data. Wall-modelled large-eddy simulations are conducted for six operating conditions, covering a range of rotational Reynolds number (3.2 × 105 – 2.2 × 106), buoyancy parameter (0.11 – 0.26) and Rossby number (0.4 – 0.8). Numerical accuracy and computational efficiency of the simulations are considered. Wall heat transfer predictions are compared with measured data with a good level of agreement. A constant rothalpy core occurs at high Eckert number, appearing to reduce the driving buoyancy force. The flow in the cavity is turbulent with unsteady laminar Ekman layers observed on both discs except in the bore flow affected region on the downstream disc cob. The shroud heat transfer Nusselt number-Rayleigh number scaling agrees with that of natural convection under gravity for high Rayleigh numbers. Disc heat transfer is dominated by conduction across unsteady Ekman layers, except on the downstream disc cob. The disc bore heat transfer is close to a pipe flow forced convection correlation. The unsteady flow structure is investigated showing strong unsteadiness in the cavity that extends into the axial throughflow.