bluuebunny/crossref_metadata_2025 huggingface dataset:
High-Pressure Optical Measurements of Temperature at Turbine Rotor Inlet Conditions
Authors: Egbert Scott C. , Zeltner Darrel , Rezasoltani Mohsen , Tree Dale R.
Published: January 2021

In gas turbine engines, the measurement of the rotor inlet temperature remains particularly challenging because of harsh operating conditions and limited access. The integrated spectral band ratio (ISBR) method is a nonintrusive optical emission gas temperature measurement technique suitable for this application. Optical fibers made of sapphire were used to transmit the radiative signal from the postcombustion zone to a Fourier transform infrared (FTIR) spectrometer. The ratio of spectral bands of H2O, nominally 100 cm−1 wide between 4600 and 6200 cm−1, was used to infer temperature. ISBR and thermocouple measurements were obtained during two temperature sweeps: one at high load and one at low load (pressures of 1.2 and 0.7 MPa, respectively). The average of three thermocouples 76 mm downstream of the ISBR measurements was on the order of 200 K lower than the ISBR temperatures, consistent with a radiative correction and the heat loss between the two measurements. The change in ISBR temperature (95 K) during the sweep was similar to the change in average thermocouple temperature (89 K). Repeatability of the optical measurement at a given operating condition was on the order of ±15 K and the absolute uncertainty of a single ISBR temperature measurement was estimated to be ±61 K. A linear correlation with an R2 value of 0.97 was also found between raw optical signal and thermocouple measurements, suggesting that once a calibrated measurement is obtained.
Single Task Optimization-Based Planar Box Delivery Motion Simulation and Experimental Validation
Authors: Xiang Yujiang , Tahmid Shadman , Owens Paul , Yang James
Published: January 2021

Box delivery is a complicated task and it is challenging to predict the box delivery motion associated with the box weight, delivering speed, and location. This paper presents a single task-based inverse dynamics optimization method for determining the planar symmetric optimal box delivery motion (multi-task jobs). The design variables are cubic B-spline control points of joint angle profiles. The objective function is dynamic effort, i.e., the time integral of the square of all normalized joint torques. The optimization problem includes various constraints. Joint angle profiles are validated through experimental results using root-mean-square-error (RMSE) and Pearson’s correlation coefficient. This research provides a practical guidance to prevent injury risks in joint torque space for workers who lift and deliver heavy objects in their daily jobs.
Elimination of Numerical Damping in the Stability Analysis of Noncompact Thermoacoustic Systems With Linearized Euler Equations
Authors: Hofmeister Thomas , Hummel Tobias , Berger Frederik , Klarmann Noah , Sattelmayer Thomas
Published: January 2021

The hybrid computational fluid dynamics/computational aeroacoustics (CFD/CAA) approach represents an effective method to assess the stability of noncompact thermoacoustic systems. This paper summarizes the state-of-the-art of this method, which is currently applied for the stability prediction of a lab-scale configuration of a perfectly premixed, swirl-stabilized gas turbine combustion chamber at the Thermodynamics institute of the Technical University of Munich. Specifically, 80 operational points, for which experimentally observed stability information is readily available, are numerically investigated concerning their susceptibility to develop thermoacoustically unstable oscillations at the first transversal eigenmode of the combustor. Three contributions are considered in this work: (1) flame driving due the deformation and displacement of the flame, (2) visco-thermal losses in the acoustic boundary layer and (3) damping due to acoustically induced vortex shedding. The analysis is based on eigenfrequency computations of the Linearized Euler Equations with the stabilized finite element method (sFEM). One main advancement presented in this study is the elimination of the nonphysical impact of artificial diffusion schemes, which is necessary to produce numerically stable solutions, but falsifies the computed stability results.
Modeling of Partially Wetting Liquid Film Using an Enhanced Thin Film Model for Aero-Engine Bearing Chamber Applications
Authors: Singh Kuldeep , Sharabi Medhat , Jefferson-Loveday Richard , Ambrose Stephen , Eastwick Carol , Cao Jing , Jacobs Adrian
Published: January 2021

In the case of aero-engine, thin lubricating film servers dual purpose of lubrication and cooling. Prediction of dry patches or lubricant starved region in bearing or bearing chambers are required for safe operation of these components. In this work, thin liquid film flow is numerically investigated using the framework of the Eulerian thin film model (ETFM) for conditions, which exhibit partial wetting phenomenon. This model includes a parameter that requires adjustment to account for the dynamic contact angle. Two different experimental data sets have been used for comparisons against simulations, which cover a wide range of operating conditions including varying the flowrate, inclination angle, contact angle, and liquid–gas surface tension coefficient. A new expression for the model parameter has been proposed and calibrated based on the simulated cases. This is employed to predict film thickness on a bearing chamber which is subjected to a complex multiphase flow. From this study, it is observed that the proposed approach shows good quantitative comparisons of the film thickness of flow down an inclined plate and for the representative bearing chamber. A comparison of model predictions with and without wetting and drying capabilities is also presented on the bearing chamber for shaft speed in the range of 2500 RPM to 10,000 RPM and flowrate in the range of 0.5 liter per minute (LPM) to 2.5 LPM.
Effects of Atmospheric Uncertainties on Sonic Boom Perceived Level
Authors: Reddy Sohail R. , Chitale Janhavi , Dulikravich George S.
Published: January 2021

This work quantifies the uncertainty in Stevens Mark VII Perceived Level of sonic booms due to uncertainties in atmospheric profiles. The influence of temperature, humidity, and wind profiles, at six cities around the globe, on the sonic boom loudness is calculated. The flow field around an aircraft was obtained by solving the three-dimensional (3D), compressible Euler equations using the UNS3D solver. The near-field pressure signature is then propagated through the atmosphere by solving the augmented Burgers equation using the sBOOM solver. The uncertainty is modeled using a nonintrusive polynomial chaos approach. A sensitivity analysis is performed to identify the altitude range and the atmospheric variable to which the Perceived Level is most sensitive. It was shown that the Perceived Level is not sensitive to any particular altitude but rather the atmospheric profiles. It was also seen that the Perceived Level is highly sensitive to humidity and temperature profiles and less sensitive to the wind profiles.
Multiscale Simulations of Polymer Flow Between Two Parallel Plates
Authors: Yan Hong-Ji , Wan Zhen-Hua , Qin Feng-Hua , Sun De-Jun
Published: January 2021

A modified multiscale method without constitutive equation is proposed to investigate the microscopic information and macroscopic flow properties of polymeric fluid with the memory effect between parallel plates. In this method, the domain is entirely described by macromodel with isolated molecular dynamics simulations applied to calculate the necessary local stresses. The present method is first verified by the creep-recovery motion and pressure-driven flow, and all results are in excellent agreement with the available numerical solutions in literature. Then, the method is extended to simulate two typical problems of relatively large spatial scale in general beyond the capability of molecular dynamics simulations. In the planar Couette flow, the relationship between macroscopic properties and the time evolution of local molecular information is investigated in detail without long time averaging. All results that are consistent with nonequilibrium molecular dynamics and literature qualitatively or quantitatively demonstrate the validity of present multiscale method in simulating transient viscoelastic flows and the capacity to obtain the polymer information. In the pressure-driven flow, a general monotonically decreasing relationship between the maximum or average velocities and the polymer concentrations has been found regardless of the polymer chain length. Particularly, the reference concentration that satisfies a power law with chain length is closely related to the overlap concentration, and the reference velocity is exactly the relevant velocity of Newtonian fluid with corresponding zero shear rate viscosity.
Verification of Probabilistic Fracture Mechanics Analysis Code for Reactor Pressure Vessel
Authors: Li Yinsheng , Katsumata Genshichiro , Masaki Koichi , Hayashi Shotaro , Itabashi Yu , Nagai Masaki , Suzuki Masahide , Kanto Yasuhiro
Published: January 2021

Nowadays, it has been recognized that probabilistic fracture mechanics (PFM) is a promising methodology in structural integrity assessments of aged pressure boundary components of nuclear power plants, because it can rationally represent the influencing parameters in their inherent probabilistic distributions without over conservativeness. A PFM analysis code PFM analysis of structural components in aging light water reactor (PASCAL) has been developed by the Japan Atomic Energy Agency to evaluate the through-wall cracking frequencies of domestic reactor pressure vessels (RPVs) considering neutron irradiation embrittlement and pressurized thermal shock (PTS) transients. In addition, efforts have been made to strengthen the applicability of PASCAL to structural integrity assessments of domestic RPVs against nonductile fracture. A series of activities has been performed to verify the applicability of PASCAL. As a part of the verification activities, a working group was established with seven organizations from industry, universities, and institutes voluntarily participating as members. Through one-year activities, the applicability of PASCAL for structural integrity assessments of domestic RPVs was confirmed with great confidence. This paper presents the details of the verification activities of the working group, including the verification plan, approaches, and results.
An Improved Creep-Fatigue Life Model Involving the Cyclic Softening/Hardening and Stress Relaxation Effect
Authors: Zhang Xiao-Cheng , Gong Jian-Guo , Gao Fu-Hai , Xuan Fu-Zhen
Published: January 2021

In this work, improved creep-fatigue life prediction models based on time fraction (TF) and ductility exhaustion (DE) rule are established for creep-fatigue life prediction of components at elevated temperatures. Cyclic softening/hardening and stress relaxation models for cyclic softening/hardening material are incorporated in the model. Materials data conducted by authors and collected from references are employed for validations. Results indicated that the improved models proposed could present more realistic evolution behavior of materials than the half-life models. The differences of the predicted lives based on the improved models and half-life models are dependent on cyclic behaviors of materials. The predicted life by the improved model is lower than that gained by the half-life model for cyclic softening steels, while it is higher than that by the half-life model for cyclic hardening steels. In addition, the DE rule could overcome the influence of cyclic softening/hardening on creep-fatigue life prediction more significantly than the TF rule.
Model-Based Thermodynamic Analysis of a Hydrogen-Fired Gas Turbine With External Exhaust Gas Recirculation
Authors: Bexten Thomas , Jörg Sophia , Petersen Nils , Wirsum Manfred , Liu Pei , Li Zheng
Published: January 2021

Climate science shows that the limitation of global warming requires a rapid transition toward net-zero emissions of green house gases on a global scale. Expanding renewable power generation in a significant way is seen as an imperative measure within this transition. To compensate for the inherent volatility of wind- and solar-based power generation, flexible and dispatchable power generation technologies such as gas turbines are required. If operated with CO2-neutral fuels such as hydrogen or in combination with carbon capture plants, a green house gases-neutral gas turbine operation can be achieved. An effective leverage to enhance carbon capture efficiency and a possible measure to safely burn hydrogen in gas turbines is the partial external recirculation of exhaust gas. By means of a model-based analysis of a state-of-the-art industrial gas turbine, this study initially assesses the thermodynamic impact caused by a fuel switch from natural gas to hydrogen. Although positive trends such as increasing net electrical power output and thermal efficiency can be observed, the overall effect on the gas turbine process is only minor. In a following step, the partial external recirculation of exhaust gas is evaluated and compared both for the combustion of natural gas and hydrogen, regardless of potential combustor design challenges. The influence of altering working fluid properties throughout the whole gas turbine process is thermodynamically evaluated for ambient temperature recirculation and recirculation at an elevated temperature (303.15 K). A reduction in thermal efficiency as well as non-negligible changes in relevant process variables can be observed. These changes are more distinctive at a higher recirculation temperature.
Partial Premixing Effects on the Reacting Jet of a High-Pressure Axially Staged Combustor
Authors: Genova Tommy , Otero Michelle , Reyes Jonathan , Martin Scott , Ahmed Kareem
Published: January 2021

The effects of partial premixing on a reacting jet-in-crossflow is investigated in a five atmosphere axially staged combustor at stationary gas turbine relevant conditions. The facility consists of a dump style headend burner that provides a crossflow with a quasi-uniform velocity and temperature profile to the axial stage to isolate the effects of the jet-in-crossflow. The headend burner is run with methane and air at a lean equivalence ratio to match industry emission standards. For this work, the total air to the headend and axial stage is kept constant, and fuel is split between the headend and axial stage to represent different gas turbine loading conditions. For the cases analyzed, the fuel split to the axial stage went up to 25%. The axial stage consists of an optically accessible test section with a coaxial injector that provides variability to how long the methane and air can mix before entering the facility. Three different premixed levels are studied: fully premixed, nonpremixed, and partially premixed. The flow-field characteristics of the reacting jet-in-crossflow are analyzed using particle image velocimetry (PIV), and flame behavior is quantified by employing CH* chemiluminescence. NO measurements are made at the exit of the facility using a Horiba emissions analyzer. Two different flames are observed: flames that burn in the leeward recirculation region and flames that burn at the core of the jet.
Employing Computational Fluid Dynamics to Derive Beddoes–Leishman Model Airfoil Parameters for Vertical Axis Wind Turbines
Authors: Hand Brian , Kelly Ger , Cashman Andrew
Published: January 2021

The blades of a vertical axis wind turbine (VAWT) experience large variations in the angle of attack at low tip-speed ratios and induce blade force oscillation. These unsteady aerodynamic effects must be considered in the VAWT aerodynamic modelling methodology by utilizing a dynamic stall model. The Beddoes–Leishman (B–L) dynamic stall model is a popular method to simulate the unsteady VAWT blade dynamic stall aerodynamics. However, a limitation of the B–L dynamic stall model is the number of the airfoil dependent parameters derived from both steady and unsteady experimental measurements. In this paper, a methodology is described to compute these B–L dynamic stall model airfoil coefficients utilizing a computational fluid dynamics (CFD) model. This method permits the calculation of the blade dynamic stall characteristics over a range of reduced pitch rates by employing a user-defined sliding mesh motion technique. Furthermore, the variation in the blade Reynolds number is accounted for by conducting simulations at the maximum and minimum VAWT envelope operating limits. Aerodynamic blade force experimental measurements are used to compare the predictions from a low-order model with airfoil data extracted CFD and experiments. This approach expands the applicability of the B–L dynamic stall model for large-scale VAWTs.
Wave Interaction With a Pair of Submerged Floating Tunnels in the Presence of An Array of Submerged Porous Breakwaters
Authors: Kaligatla R. B. , Sharma Manisha , Sahoo T.
Published: January 2021

In this article, a coupled model is proposed for wave interaction with a pair of submerged floating tunnels in the presence of an array of bottom-standing trapezoidal porous breakwaters. The theory of Sollitt and Cross is adopted to govern the fluid flow inside the porous medium. For constant water-depth, the eigenfunction expansion method is employed, whereas for varying water-depth, the eigenfunction expansion method along with the mild-slope approximation is employed. The solutions, thus derived, are matched at the shared boundaries under defined physical conditions. First, the performance of a single breakwater of impermeable and permeable type in reducing wave forces on tunnels is analyzed. Next, the performance of two and three submerged breakwaters is studied. The reflection and transmission coefficients of waves are high in the absence of the submerged breakwater and in the presence of an impermeable breakwater. These coefficients significantly reduce in the presence of the submerged porous breakwater. As a result, the horizontal and vertical forces acting on bridges and tunnels are substantially subsided. Wave forces on tunnels reduce with an increase in the angle of incidence. Multiple porous breakwaters show better performance in mitigating wave forces on tunnels. Higher wave force on tunnels is noticed in intermediate water-depth. The findings can enhance the knowledge of submerged porous breakwaters’ performance in reducing wave loads on bridges and tunnels.
Enhancements on Dissimilar Friction Stir Welding Between AZ31 and SPHC Mild Steel With Al–Mg as Powder Additives
Authors: bin Muhamad Mohd Ridha , Raja Sufian , Jamaludin Mohd Fadzil , Yusof Farazila , Morisada Yoshiaki , Suga Tetsuo , Fujii Hidetoshi
Published: January 2021

Dissimilar materials joining between AZ31 magnesium alloy and SPHC mild steel with Al–Mg powder additives were successfully produced by the friction stir welding process. Al–Mg powder additives were set in a gap between AZ31 and SPHC specimen’s butt prior to welding. The experiments were performed for different weight percentages of Al–Mg powder additives at welding speeds of 25 mm/min, 50 mm/min, and 100 mm/min with a constant tool rotational speed of 500 rpm. The effect of powder additives and welding speed on tensile strength, microhardness, characterization across welding interface, and fracture morphology was investigated. Tensile test results showed a significant enhancement of tensile strength of 150 MPa for 10% Al and Mg (balance) powder additives welded joint as compared to the tensile strength of 125 MPa obtained for the welded joint without powder additives. The loss of aluminum in the alloy is compensated by the addition of the Al–Mg powder during welding under a suitable heat input condition identified by varying welding speeds. Microstructural analysis revealed that the Al–Mg powder was well mixed and dispersed at the interface of the joint at a welding speed of 50 mm/min. The intermetallic compound detected in the welding interface contributed to the welding strength.
A Numerical Study on the Effects of Acoustic Forcing on Fuel Spray Dynamics in Gas Turbines
Authors: Treleaven Nicholas C. W. , Garmory Andrew , Page Gary J.
Published: January 2021

In the case of aircraft engines, the fuel is injected as a liquid spray which may play a role in thermoacoustic instabilities through creating changes to the mixture fraction inside the combustion chamber. This study uses two-phase incompressible non-reacting large eddy simulation with Lagrangian particle tracking to show how spray droplets of different sizes can be affected by large scale hydrodynamic structures and acoustic forcing. The forcing is applied at the inlets of a truncated computational domain that only includes the geometry downstream of the fuel injector using the newly developed PODFS (proper orthogonal decomposition Fourier series) method. The PODFS is a model that can reproduce the effects of acoustic forcing by extracting planes of data from an auxiliary acoustically forced compressible unsteady Reynolds averaged Navier-Stokes simulation. A proper orthogonal decomposition analysis shows that fuel droplets of a typical size seen in jet engines are more sensitive to acoustic and hydrodynamic structures than droplets with an order of magnitude larger or smaller diameter, consistent with their Stokes number. Phase and azimuthally averaged results show that fluctuations of the spray mixture fraction represented by large droplets affect the total spray mixture fraction much more than fluctuations of the small droplets. An additional intermittent spray dispersion mechanism was identified that is due to intermittent vorticity being generated between the two outer injector flow passages. An injector design modification has been suggested that will reduce the prevalence of this mechanism.
Prediction of the Unsteady Transition Behavior in Low Pressure Turbine Flows Using Time and Frequency Domain Methods
Authors: Heners Jan Ph. , Müller-Schindewolffs Christoph , Blum Frederik , Vogt Damian M.
Published: January 2021

The transient transition behavior of a two-stage low pressure turbine rig facility is investigated in terms of numerical studies. The surface of a second stage stator vane is equipped with a thin film sensor array along its suction side providing time-resolved measurement data of the underlying boundary layer. The measurement data indicate a laminar behavior over the accelerated region of the stator vane. At the decelerated region close to the vane’s trailing edge, alternating transition mechanisms of both bypass and separation induced transition combined with subsequent reattachment can be observed. The measurement data in combination with numerical results from a time-marching full-wheel simulation are used to assess the results from an unsteady flow simulation based on the harmonic balance approach in the frequency domain. For both time and frequency domain simulations, the turbulence behavior is considered by application of Wilcox’ k–ω two equation model in combination with Menter and Langtrys γ-Reθ transition model. The numerical results regarding transient distributions of intermittency and associated shape factor of the boundary layer are compared with proper measurement quantities in order to evaluate the capability of the applied harmonic balance solver to predict the unsteady transition behavior over the investigated vane’s suction side.
Analysis of Radiation-Convection Coupled Effects on the Turbine Vane With Different Gas Compositions
Authors: Sun Peng , Li Xueying , Ren Jing , Jiang Hongde
Published: January 2021

To reduce the emission of greenhouse gases, especially carbon dioxide, the combustion of hydrogen and oxy-fuel is a development direction for the gas turbine systems. Because the fuels are different from the traditional gas turbine which uses natural gas as fuel, the compositions of the working fluid are different, which can lead to differences in heat transfer characteristics. Furth more, in order to get higher overall efficacy, the turbine inlet temperature is becoming higher and higher. The radiation becomes an important factor then must be considered seriously.

To study the influence of different gas compositions on heat transfer characteristics, three gas compositions, representing the combustion products of IGCC system, hydrogen turbine system, and the oxy-fuel turbine system, respectively, is chosen in this paper. Based on a real turbine first stage vane, the influence of radiation and gas compositions are both researched using CFD simulations. The results show that different gas compositions can lead to different heat transfer characteristics on the vane. The radiation effect can be dealt with as an independent factor in the turbine heat transfer analysis.
A New Multi-Stage Turbine Stator Design for Improved Performance Retention
Authors: Jameson Heather K. , Longley John P.
Published: January 2021

An experimental and computational investigation has been undertaken into the effects of deterioration of the first stage rotor shroud knife-edge seal clearance in a two-stage turbine which has engine representative cavity geometries. Four values of deterioration were investigated which cover the new-condition to old-condition knife-edge seal clearance.

Measurements within the first stage rotor shroud cavity show that whilst the leakage mass flow rate increases with deterioration, the angle at which the leakage flow approaches the downstream stator is essentially fixed and independent of the flow coefficient. This is in agreement with a simple over-tip leakage model. Because of the engine representative cavity geometry, the over-shroud leakage flow undergoes little mixing when it re-enters the mainstream and approaches the downstream stator at more than 60° negative incidence.

Detailed measurements at the exit of the second stage stator identified two large positive vortices which were not consistent with the horseshoe vortex model for secondary flow. A computational investigation revealed that one vortex originates from the rolling-up within the stator passage of the streamwise vorticity sheet associated with the first stage rotor over-shroud leakage. This roll-up vortex cannot be eliminated. The second vortex is generated within the stator passage by the separation of the over-shroud leakage flow at the leading-edge due to the large negative incidence. It was hypothesised that this separation vortex might be eliminated by locally redesigning the stator.

A new stator was designed, manufactured and tested. As predicted, the roll-up vortex was still present but the separation vortex was eliminated. For all the values of deterioration tested the entropy loss coefficient of the new stator and the unchanged second stage rotor were reduced. It is estimated that the new stator would improve the lifetime average efficiency by 0.5% compared to the original.
Design and Testing of a Rig to Investigate Buoyancy-Induced Heat Transfer in Aero-Engine Compressor Rotors
Authors: Luberti Dario , Patinios Marios , Jackson Richard W. , Tang Hui , Pountney Oliver J. , Scobie James A. , Sangan Carl M. , Owen J. Michael , Lock Gary D.
Published: January 2021

The change in compressor blade-tip clearance across the flight cycle depends on the expansion of the rotor, which in turn depends on the temperature and stress in the discs. The radial distribution of temperature is directly coupled to the buoyancy-driven flow and heat transfer in the rotating disc cavities. This paper describes a new test rig specifically designed to investigate this conjugate phenomenon. The rig test section includes four rotating discs enclosing three cavities. Two discs in the central cavity are instrumented with thermocouples to provide the radial distribution of temperature; the two outer cavities are thermally insulated to create appropriate boundary conditions for the heat transfer analysis. An axial throughflow of air is supplied between a stationary shaft and the bore of the discs. The temperature of the throughflow air is measured by thermocouples in rakes upstream and downstream of the central cavity. For a cold throughflow, the outer shroud of the central cavity is heated. Two independently-controlled radiant heaters allow differential shroud temperatures for the upstream and downstream discs, as found in aero-engine compressors. Alternatively, the throughflow can be heated above the shroud temperature to simulate the transient conditions during engine operation where stratified flow can occur inside the cavity. The rig is designed to operate in conditions where both convective and radiative heat transfer dominate; all internal surfaces of the cavity are painted matt black to allow the accurate calculation of the radiant heat transfer. Separate attachments can be fitted to the cobs of both central discs; the attachments reduce the axial gap between the cobs — reducing the gap to zero creates a closed cavity, which can occur in some compressor designs. Other instrumentation includes heat-flux gauges on the shroud and high-frequency pressure transducers embedded into the disc diaphragm to capture unsteady flow structures. Attention has been given to experimental uncertainty, including the computation of the thermal-disturbance errors, caused by thermocouples embedded in the rotating discs; a Bayesian statistical model is used to reduce the effect of uncertainties in temperature measurements on the calculation of the Nusselt number. The effect of relevant non-dimensional parameters on the radial distribution of the disc and throughflow temperatures has been shown for some typical cases.
Effects of Reynolds Number on Performance of Highly Loaded Multi-Stage Axial Compressors
Authors: Zhang Xiaoshi
Published: January 2021

The influence of Reynolds number on performance of a highly loaded 10-stage axial compressor has been experimentally investigated. The experiment was performed by applying different inlet Reynolds numbers at several operating speeds. Reynolds number variation was achieved by throttling the inlet pressure. Both compressor total aerodynamic characteristics and detailed single stage performance were measured and analyzed. Test results show that all the compressor performance parameters including efficiency, mass flow and pressure ratio are reduced by decreasing Reynolds number. And the influence is higher at lower operating speed. Regarding to single stage characteristics, stage matching is less affected by Reynolds number at design speed, while all single stage chics are changed at low speed. The correlation between Reynolds number and compressor performance was obtained.

Then the Wassell semi-empirical correlation method was applied to predict the Reynolds number influences for the same compressor. Comparison was made between experimental results and calculating results based on Wassell correlation. Results indicate that Wassell correlation is reliable for predicting trends. Wassell correlation works well for efficiency at design speed, but providing calculating inaccuracy at low speed. For mass flow correlation, Wassell correlation overestimated the influence of Reynolds number. Test results from this compressor are added to Wassell correlation curve, that provide reference for modern design application.
Experimental Investigation on the Rubbing Process of Labyrinth Seals Considering the Material Combination
Authors: Hühn Lisa , Munz Oliver , Schwitzke Corina , Bauer Hans-Jörg
Published: January 2021

Labyrinth seals are used to prevent and control the mass flow rate between rotating components. Due to thermally and mechanically induced expansions during operation and transient flight maneuvers, a contact, the so-called rubbing process, between rotor and stator cannot be excluded. A large amount of rubbing process data concerning numerical and experimental investigations is available in public literature as well as at the Institute of Thermal Turbomachinery (ITS). The investigations were carried out for different operating conditions, material combinations, and component geometries. In combination with the experiments presented in this paper, the effects of the different variables on load due to rubbing are compared, and discussed with the focus lying on the material combination. The influence of the material on the loads can be identified as detailed as never before. For example, the contact forces in the current experiments are higher due to a higher temperature resistance of Young’s modulus. The analysis will also be based on the rubbing of turbine blades. Design guidelines are derived for labyrinth seals with improved properties regarding tolerance of rub events. Based on the knowledge obtained, guidelines for designing reliable labyrinth seals for future engines are discussed.
Thermal Profiling of Cooled Radial Turbine Wheel
Authors: Pilgrim Christopher C. , Castillo Daniel , Araguás-Rodríguez Silvia , Karagiannopoulos Solon , Feist Jörg P. , Redwood Alex , Zhang Yang , Copeland Colin , Scobie James , Sangan Carl
Published: January 2021

Compliance with incoming new emission standards such as Euro6d and China6b will require new approaches to the design of thermally loaded automotive components e.g. turbochargers, exhaust valves and manifolds. However, the validation of those new designs and the need for a rapid market entry will require new temperature measurement technologies to provide accurate data across the entire component. A limited number of techniques are currently available, and all have limitations in the harsh operating conditions of turbomachinery. A new technique, called Thermal History Paint (THP), has been developed to overcome these limitations to enable accurate temperature profiles to be recorded in harsh environments. There are limited publications that cover the use of this technique and this paper demonstrates the capability of the THP through the implementation on turbocharger turbine wheels.

A cooled, hollow radial turbine wheel was designed, manufactured via 3D printing and tested. A solid wheel of the same external dimensions was manufactured and tested under the same conditions to act as a baseline. The THP was used to measure the temperature profile of the blade surfaces and to quantify the effectiveness of the cooling. The paint exhibited good durability through the tests of both wheels in a hot gas rig at the University of Bath.

Specific calibration data were generated for the test and the repeatability of the measurements was determined to be within 8K. Both the cooled and baseline wheels were measured at many locations and the THP recorded a significantly higher temperature on the baseline solid wheel. The measured temperature profiles were in good agreement with expectation and CFD simulations. The results enable the validation of thermal models and demonstrate the capability of the new measurement technique.
A Model-Based Prediction of Balancing Behavior of Rotors Above the Speed Range in Available Balancing Systems
Authors: Pennacchi Paolo , Ferraro Riccardo , Chatterton Steven , Checcacci Damaso
Published: January 2021

Rotor balancing is probably the most discussed topic in the entire literature about rotor dynamics. It would therefore seem that, from the point of view of theory, this is a problem of little interest, however, balancing is very relevant in the industrial practice and sometimes there are very particular cases that cannot be addressed and solved by traditional methods. Moreover, many papers deal with only simulated results or with small-scale tests-rigs, which can hardly reproduce the behavior of real rotors. The case described in this paper is just one of these and presents what could be defined as “predicting the effect of balancing” at rotational speeds that are higher than those possible on balancing machines. Rotordynamics modeling, identification techniques developed by the authors and the available vibration measurements allow the simulation of the behavior, i.e. the vibrations, of the considered turbine rotor on the balancing machine, even at rotational speeds higher than those are possible to be reached, but that correspond to the trip speed in the plant.
Investigation of Working Line Variation Onto Forced Response Vibrations of a Compressor Blisk
Authors: ElMasry Seif , Kühhorn Arnold , Figaschewsky Felix
Published: January 2021

This paper aims to study the effect of varying the working line of a compressor onto the forced response vibrations of the blades of an integrally bladed disk (blisk). The investigated rotor belongs to a transonic research compressor, where various probes are placed to measure flow data at all stations and analyze blade vibrations. A single-passage CFD model of all compressor blade-rows is used for steady computations. Using a finite element model, the natural frequencies and mode shapes of the blisk across the operational range of the compressor are predicted. Thus, resonance conditions can be identified from the Campbell diagram. The variation of the compressor working line is investigated at 90% of the maximum shaft speed, where the resonance condition of the 11th blade mode family and the engine order corresponding to the aerodynamic distortion from the upstream stator vane is predicted. Using a single-passage model, time-accurate simulations of the investigated rotor are executed at various operating points, which cover the operational range of the compressor between choke and stall conditions. Aerodynamic damping ratios are calculated using the aerodynamic influence coefficients method at each point, in order to predict the resulting vibration amplitudes of the blades. Relatively high amplitudes of the modal aerodynamic forces are observed at the low working line. A detailed post-processing analysis is performed, as the change of flow incidence contributes largely in the increase of modal aerodynamic forces on the blade. The aerodynamic damping ratios increase with higher working lines, where the rotor achieves relatively higher pressure ratios. However, the damping decreases rapidly close to stall conditions. The trend of the predicted vibration amplitudes is compared to strain gauge measurements from the rig, which are registered during multiple acceleration maneuvers performed over different working lines. A strong correlation between the predicted and measured trends of the forced response vibration is witnessed.
Investigation of Spray Formation and Turbulent Droplet Transport in High Momentum Jet Stabilized Combustor Injection Systems
Authors: Schäfer Dominik , Hampp Fabian , Lammel Oliver , Aigner Manfred
Published: January 2021

This work investigates the influence of coaxial air flow on droplet distribution, velocity, and size generated by a pressure-swirl atomizer. The experiments were performed inside a generic test section with large optical access at atmospheric conditions. The flow conditions replicate the mixing duct sections of high momentum jet stabilized combustors for gas turbines, e.g. high axial air velocities without swirl generation and high preheat temperatures.

High momentum jet stabilized combustors based on the FLOX® burner concept are used successfully in gas turbines due to its fuel and load flexibility and very low pollutant emissions. In previous and ongoing studies, different model combustors have been under investigation mainly with the focus of broadening fuel flexibility and operational limits. Operation with different liquid fuel injection systems in high pressure experiments showed a significant impact from the injector shape and injection strategy on the fuel air mixing behavior, the flame position and stability, and thus NOx emissions. This experiment will give a more detailed understanding of the turbulent mixing and interaction of primary and secondary atomization with the surrounding air in such burners. The setup will also allow for the testing of different injection systems for various burner configurations by the variation of injection type, location, fuel, and air flow properties.

In the present experiments a pressure-swirl atomizer was set to a constant pressure drop and mass flow. Liquid fuel was replaced by deionized water due to safety concerns. The coaxial air mass flow was preheated up to 473 K and set to bulk velocities of 20 m/s, 50 m/s, and 80 m/s. Particle Image Velocimetry (PIV) was used to characterize the flow field downstream of the point of injection. The droplet size and velocity distributions were quantified by double frame shadow imaging combined with a long-distance microscope with a resolution below 1 μm per pixel. Moreover, the formation of ligaments as well as primary spray break-up was visualized.

The results show a significant change of the spatial droplet distribution with increasing co-flow velocity for a given atomizer geometry. The spray cone angle widens at high co-flow velocities due to the formation of a pronounced recirculation zone behind the backward facing step of the injector near the nozzle orifice. This also leads to a change in the initial droplet momentum and the spatial distribution of large droplets. Smaller droplets are concentrated to the center of the spray due to turbulent transport.

These findings assist the ongoing developments of liquid fuel injection systems for high momentum jet based combustors and provide validation data for numerical simulations of primary and secondary atomization.
Shape Optimization of Pin Fin Arrays Using Gaussian Process Surrogate Models Under Design Constraints
Authors: Ghosh Shinjan , Mondal Sudeepta , Kapat Jayanta S. , Ray Asok
Published: January 2021

Internal cooling channels with pin-fin arrays are an important part of gas turbine blade trailing edge design. Short pin-fins act as turbulators in high aspect ratio channels to increase heat transfer and provide structural support to the trailing edge of the blade. Such pin fins however also result in a high pressure drop owing to chaotic flow phenomenon in these highly turbulent flows. High pressure-drop results in higher compressor work due to increased power consumption to push the coolant through these passages. Hence, optimizing the design of pin fin arrays is key to increasing the efficiency of real gas turbine cycles by handling higher turbine inlet temperature and increasing blade life. Moreover, the design process of such pin fin arrays can be computationally very expensive, since it typically involves high-fidelity CFD simulations. The optimization problem involves maximizing Nusselt number, while keeping the friction factor as a constraint. To address this problem, a computationally efficient approach involving Gaussian Processes (GP) surrogate modeling and constrained Bayesian Optimization (BO) has been carried out for optimizing the thermal performance of the pin fin arrays. The multidimensional search space of design parameters includes pin-fin dimensions and shape of the resulting pin-fins. The optimization problem is solved under computational budget limitations and design constraints. A ‘drop’ like optimal design is obtained which has a lower pressure drop and higher Nu compared to the baseline.
Operating Characteristics of an Electrically Assisted Turbofan Engine
Authors: van Holsteijn Merijn Rembrandt , Gangoli Rao Arvind , Yin Feijia
Published: January 2021

With the growing pressure to reduce the environmental footprint of aviation, new and efficient propulsion systems must be investigated. The current research looks at the operating characteristics of a turbofan engine in a parallel hybrid-electric propulsion system. Electric motors are used to supply power in the most demanding take-off and climb phases to achieve the required thrust, which allows the turbofan to be redesigned to maximize the cruise performance (to some extent). It was found that the turbofan’s cruise efficiency can be improved by 1.0% by relaxing the constraints of take-off and climb. It was found that the surge margins of compressors limit the amount of power that could be electrically supplied.

On a short-range mission, the hybrid-electric propulsion system showed a potential to reduce around 7% of fuel burn on an A320 class aircraft. Most of these savings are however achieved due to fully electric taxiing. The weight of the electrical propulsion system largely offsets the efficiency improvements of the gas turbine during cruise flight. A system dedicated for fully electric taxiing system could provide similar savings, at less effort and costs. Given the optimistic technology levels used in the current analysis, parallel hybrid-electric propulsion is not likely to be used in the next-generation short to medium range aircraft.
Uncertainty Analysis of Inflow Conditions on an HPT Gas Turbine Nozzle: Effect on Particle Deposition
Authors: Friso R. , Casari N. , Pinelli M. , Suman A. , Montomoli F.
Published: January 2021

Gas turbines (GT) are often forced to operate in harsh environmental conditions. Therefore, the presence of particles in their flow-path is expected. With this regard, deposition is a problem that severely affects gas turbine operation. Components’ lifetime and performance can dramatically vary as a consequence of this phenomenon. Unfortunately, the operating conditions of the machine can vary in a wide range, and they cannot be treated as deterministic. Their stochastic variations greatly affect the forecasting of life and performance of the components. In this work, the main parameters considered affected by the uncertainty are the circumferential hot core location and the turbulence level at the inlet of the domain. A stochastic analysis is used to predict the degradation of a high-pressure-turbine (HPT) nozzle due to particulate ingestion. The GT’s component analyzed as a reference is the HPT nozzle of the Energy-Efficient Engine (E3). The uncertainty quantification technique used is the probabilistic collocation method (PCM). This work shows the impact of the operating conditions uncertainties on the performance and lifetime reduction due to deposition. Sobol indices are used to identify the most important parameter and its contribution to life. The present analysis enables to build confidence intervals on the deposit profile and on the residual creep-life of the vane.
Fatigue Characterization of SiC/SiC Ceramic Matrix Composites in Combustion Environment
Authors: Panakarajupally Ragav P. , Elrassi Joseph , Manigandan K. , Morscher Gregory N.
Published: January 2021

Fatigue behavior of woven melt infiltrated (MI) SiC/SiC ceramic matrix composites (CMCs) was investigated under a tension-tension fatigue condition in a combustion environment. A special experimental facility is designed to subject the CMCs under simultaneous mechanical and combustion conditions which is more representative of some conditions experienced by the hot section components of a jet engine. The MI SiC/SiC ceramic matrix composites considered in this study consists of a SiC matrix densified with liquid Si infiltration, BN interphase and reinforced with two different fibers namely Hi-Nicalon type S and Tyranno SA fibers. A high velocity oxygen fuel (HVOF) gun is used to create the representative combustion condition and a horizontal hydraulic MTS machine to apply the mechanical loading. Several fatigue tests were conducted at different stress levels with a stress ratio of 0.1, frequency of 1 Hz and the specimen surface temperature at 1200 °C. Similar tests were conducted in an isothermal furnace condition at 1200°C for comparison. Electrical resistance (ER) was used to monitor the tests. A reduction in the fatigue life was observed for the two MI systems under combustion conditions in comparison to the isothermal furnace condition at the same applied stress level. This is attributed to the presence of harsh combustion environment present in the burner rig. Electrical resistance showed some promising results in monitoring the temperature and detecting damage in the specimen. Runout condition was set as 24 H (86400 cycles) in burner rig and 100 H (360000 cycles) in furnace environment. Specimens that achieved the runout condition were subsequently tested under monotonic tension testing at room temperature after cooldown to evaluate the residual properties. Residual strength results showed a significant strength reduction in both the furnace and burner rig environments. Post-test microscopy was conducted on the fracture surfaces and longitudinal polished sections of the failed specimens to understand the oxidation behavior and damage mechanisms.