bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.