bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Novel Bulk-Flow Model for Pocket Damper Seals
Authors: Cangioli Filippo , Vannini Giuseppe , Chirathadam Thomas 
Published: November 2019

Abstract
In this paper a novel bulk-flow model for pocket damper seals (PDS) is introduced. The model is based on two control volumes for each circumferential pocket of the seal. The continuity, circumferential momentum and energy equations are considered for each control volume. The circumferential recirculating flow within the pocket is modelled for the first time. The boundary layer theory is used to estimate the recirculating flow area, and the Swamee-Jain friction factor correlation allows for defining the dissipation of the circumferential velocity. The perturbation method is used to solve the partial derivative governing equations in the zeroth and first-order system of equations. The rotordynamic coefficients are evaluated by integrating the dynamic pressure and rotor shear stresses along the circumferential direction.
The predictions are compared to the experimental data, which refer to test conditions representative of high-pressure centrifugal compressors. Numerical predictions are accurate for both high positive-negative inlet pre-swirl ratios. Leakage predictions are also aligned with measurements.
Finally, sealing selection approach is introduced in the paper for comparing the dynamic behaviour of two different sealing technologies and identifying stable regions as a function of the rotor natural frequency and pre-swirl ratio.
An Innovative Development of a Five-Hole Pressure Probe for Highly Unsteady Flow Phenomena
Authors: Heckmeier Florian M. , Iglesias Daniel , Kienitz Sascha , Breitsamter Christian 
Published: November 2019

Abstract
An advanced unsteady multi-hole pressure probe is developed in cooperation between the Chair of Aerodynamics and Fluid Mechanics of the Technical University of Munich, the probe manufacturer Vectoflow GmbH and the sensor producer fos4X GmbH. The application of additive manufacturing enables a wide variation in probe geometries. The spatial characteristics of the unsteady probe are determined in the aerodynamic calibration in a known steady uniform jet. Furthermore, the acoustic system inside the channels of the probe is investigated experimentally in the dynamic calibration. Both aerodynamic and dynamic calibration ensure an accurate reconstruction of the velocity components. Measurements of the near wake of a circular cylinder have been recorded with the unsteady probe and compared to data from the literature and corresponding hotwire anemometry measurements. Further improvements to enhance the range of applications of the probe have been initiated: This includes the miniaturization of the probe. Moreover, an unsteady differential fiber-optic sensor and its optic and passive measurement principle are introduced which shall improve the main dynamic specifications of the probe. By combining the additive manufactured pressure probe design and the novel fiber-optic sensor, more accurate measurements of high frequency flow phenomena are expected.
Modelling Axisymmetric Centrifugal Compressor Characteristics From First Principles
Authors: Powers Katherine H. , Brace Chris J. , Budd Chris J. , Copeland Colin D. , Milewski Paul A. 
Published: November 2019

Abstract
Turbochargers are a vital component for aiding engine manufacturers in meeting the latest emissions standards. However, their range of operation is limited for low mass flows by compressor surge. Operation in surge results in pressure and mass flow oscillations that are often damaging to the compressor and its installation. Since surge is a highly complex flow regime, full unsteady 3D models are generally too computationally expensive to run. The majority of current low-dimensional surge models use a cubic compressor characteristic that needs to be fitted to experimental data. Therefore, each time a compressor is studied using these models, costly experimental testing is required.
In this paper, a new technique for obtaining an axisymmetric centrifugal compressor characteristic is presented. This characteristic is built using the equations of mass, momentum and energy from first principles in order to provide a more complete model than those currently obtained via experimental data. This approach enables us to explain the resulting cubic-like shape of the characteristic and hence to identify impeller inlet stall as a route into surge. The characteristic is used within a quasi-steady, map-based surge model in order to demonstrate its ability to predict the onset of surge while only providing geometric data as input. Validation is provided for this model by discussion of the qualitative flow dynamics and a good fit to experimental data, especially for low impeller speeds and pressure ratios.
Spray Characteristics of Alternative Jet Fuel at Elevated Ambient Conditions
Authors: Kannaiyan Kumaran , Sadr Reza 
Published: November 2019

Abstract
In recent years, Gas-to-Liquid (GTL) jet fuel is considered as an alternative jet fuel because of its cleaner combustion characteristics. The chemical and physical properties of GTL fuels are different from those of the conventional jet fuels. The objective of the present work is to investigate the effect of ambient conditions and fuel volatilization characteristics on the macroscopic spray features. To this end, the macroscopic spray performance is visualized using the shadowgraph imaging technique at elevated ambient conditions. The near nozzle spray parameters like spray cone angle, sheet breakup length, and the sheet velocity, are determined from the shadowgraph images using an in-house program. The effect of ambient conditions on the near nozzle spray characteristics for conventional fuels has been reported in the literature. However, these effects have not been reported in detail for the alternative, GTL jet fuels. The results show that the ambient gas pressure has a significant effect on the spray performance when compared to that of the ambient gas temperature. At atmospheric conditions, the spray performance of GTL fuel is comparable to those of Jet A-1 fuel. However, with the increase in ambient conditions, the difference in spray performance of GTL and Jet A-1 is significant.
Effect of Tip Clearance on Rotating Stall in a Mixed-Flow Pump
Authors: Li Wei , Agarwal Ramesh K. , Zhou Ling , Li Enda , Ji Leilei 
Published: November 2019

Abstract
The non-uniform disturbance in the circumferential direction is the main cause for the occurrence of rotating stall in turbomachinery. In order to study the effect of tip clearance leakage flow on rotating stall, the mixed-flow pump models with different tip clearances are numerically simulated, and then the energy performance curves and internal flow structures are obtained and compared. The results show that the computed pump efficiency and the internal flow field of the pump from numerical simulation are in good agreement with the experimental results. A saddle region appears in the energy performance curves of the three tip clearances, and with decrease in tip clearance, the head and efficiency of the mixed-flow pump increase and the critical stall point shifts, and the stable operating range of the mixed-flow pump decreases, which indicates that the mixed-flow pump stalls easily for smaller tip clearance. Under the deep stall condition, the influence of the leakage flow in the end wall area increases gradually with decrease in clearance. For small clearance, the leakage flow moves away from the suction surface to some distance to form a number of leakage vortex strips with the mainstream flow and flows over the leading edge of the next blade and then flows downstream into different flow passages, generating backflow and secondary flow separation at the blade inlet, which seriously damages the spatial structure of the inlet flow. This results in the earlier occurrence of stall. With increase in clearance, the leakage vortex develops along the radial direction towards the middle of the flow channel and large flow separation occurs in the downstream channel, which induces deep stall. For 0.8mm clearance, the whole impeller outlet passage is almost blocked by the backflow of the guide vane inlet, and a deep stall is induced.
Development of an Alternative Approach for Cutting Force Determination in Broaching
Authors: Bergs Thomas , Döbbeler Benjamin , Seelbach Tobias , Seimann Martin , Klocke Fritz 
Published: November 2019

Abstract
Fir tree slots in turbine discs are used as an attachment between the disc and the blades. To a great extend, these slots are manufactured by broaching. Currently, the used cutting tool material is High Speed Steel (HSS). Due to its low high temperature stability, the manufacturing process is limited to low cutting speeds (vc = 2–5 m/min) and presents, therefore, a bottleneck in the turbine manufacturing process. To increase the productivity, cemented carbide can be used as cutting tool material with cutting speeds up to five times higher than those used for HSS. Due to the high safety demands, the broaching process requires extensive process design to ensure a high process reliability. For the tool design, profound knowledge of the mechanical loads is mandatory due to its major effect on the manufactured part. Empirical research to investigate the actual mechanical load is time-consuming and expensive due to high tool costs, especially of cemented carbide broaches, and the high amount of possible tool geometry combinations. In this paper, an alternative approach to determine the cutting forces is presented. Grooving experiments were conducted in order to reproduce the engagement conditions from the broaching process. If the transferability of this approach can be shown, the amount of broaching tools as well as the availability of a broaching machine tool for the design of new broaching tools can be decrease dramatically. This would result in a reduction of tool design time and an increase in productivity for tool manufacturers.
Loss in Axial Compressor Bleed Systems
Authors: Grimshaw S. D. , Brind J. , Pullan G. , Seki R. 
Published: November 2019

Abstract
Loss in axial compressor bleed systems is quantified, and the loss mechanisms identified, in order to determine how efficiency can be improved. For a given bleed air pressure requirement, reducing bleed system loss allows air to be bled from further upstream in the compressor, with benefits for the thermodynamic cycle. A definition of isentropic efficiency which includes bleed flow is used to account for this. Two cases with similar bleed systems are studied: a low-speed, single-stage research compressor and a large industrial gas turbine high-pressure compressor.
A new method for characterising bleed system loss is introduced, using research compressor test results as a demonstration case. A loss coefficient is defined for a control volume including only flow passing through the bleed system. The coefficient takes a measured value of 95% bleed system inlet dynamic head, and is shown to be a weak function of compressor operating point and bleed rate, varying by ±2.2% over all tested conditions. This loss coefficient is the correct non-dimensional metric for quantifying and comparing bleed system performance.
Computations of the research compressor and industrial gas turbine compressor identify the loss mechanisms in the bleed system flow. In both cases, approximately two-thirds of total loss is due to shearing of a high-velocity jet at the rear face of the bleed slot, one quarter is due to mixing in the plenum chamber and the remainder occurs in the off-take duct. Therefore, the main objective of a designer should be to diffuse the flow within the bleed slot. A redesigned bleed slot geometry is presented that achieves this objective and reduces the loss coefficient by 31%.
Effects of Labyrinth Fin Wear on Aerodynamic Performance of Turbine Stages: Part II — Mushrooming Damages
Authors: Dai Xinbo , Yan Xin 
Published: November 2019

Abstract
The main function of labyrinth seal is to control leakage flow in clearance that involves with rotating and stationary parts. Therefore, the effective of clearance gap in labyrinth seal is critical to sealing, heat transfer and vibration characteristics. However, due to the mechanical expansions, vibrations, thermal stress, misalignment of seal components in transient periods of startup, shutdown and hot restart, the stationary and rotating parts of the labyrinth seal are likely to contact each other, causing wear damages in labyrinth fin. Mushrooming damages are often occurred in the rubbing events when labyrinth fin is made of soft material compared with the opposite component. To investigate how mushrooming damage affects the leakage performance of labyrinth seal, many numerical and experimental studies have been carried out in last decades. However, little attention has been paid on the influence of labyrinth fin mushrooming on aerodynamic performance of turbine stages. In this study, using the RANS equations solution methods, the effect of labyrinth fin mushrooming on isentropic efficiency, leakage rates, outlet flow angles, reaction degrees, profile static pressure distributions and flow fields in turbine stages were investigated at three different mushrooming radii and three effective clearances. It shows the leakage rate is increased with increasing the mushroom radius and effective clearance. At the same effective clearance, as the mushrooming radius increases from 0.2mm to 0.4mm, the leakage rate is increased by about 0.19–0.32%, and the overall isentropic efficiency is decreased by 0.78%. At the same mushrooming radius, as the effective clearance increases from 1mm to 1.4mm, the leakage rate is increased by 0.21–0.31%, and the overall isentropic efficiency is decreased by 0.65%. As mushroom radius and effective clearance increase, the secondary flows near hub and shroud are intensified and developed along axial direction, causing pronounced aerodynamic loss in turbine stages.
Predicting the Adiabatic Effectiveness of Effusion Cooling by the Convolution Modeling Method
Authors: Yang Li , Rao Yu 
Published: November 2019

Abstract
Effusion Cooling has a strong potential in protecting hot section components of gas turbines engines such as turbine blades, endwalls and combustor liners. By carefully distributing the cooling holes adaptively to the external thermal load, effusion cooling can dramatically reduce the temperature and thermal stress for the protected components. However, the effectiveness for effusion cooling was not easy to correlate due to the numerous parameters to study and the significant variation from the upstream to the downstream. Conventional equations used in the literature were insufficient to express the complex mechanism for effusion cooling and consequently utilized averaged parameters as variables. This study proposed a convolution method to model the local adiabatic cooling effectiveness for the entire effusion cooled surfaces. The new model treated the cooling hole distribution as an input matrix and applied convolution networks to predict the cooling effectiveness. Compared with conventional correlations, this network based model provided extensive details of the cooling effectiveness distribution while consuming computational time as short as correlations. Training of the proposed model was based on the numerical simulation results of three geometries and the validation was conducted for two additional geometries. Results indicated high accuracy and high robustness of the convolution model. With the aid of this novel model, further designing could adjust hole distribution in a random manner instead of using rows and columns, and generate adaptive effusion cooling based on thermal load.
Experimental Analysis of a Micro Gas Turbine Combustor Optimized for Flexible Operation With Various Gaseous Fuel Compositions
Authors: Bower Hannah E. , Schwärzle Andreas , Grimm Felix , Zornek Timo , Kutne Peter 
Published: November 2019

Abstract
With the push to curb dangerous atmospheric pollutant production, energy generation technologies that reduce green-house gas emissions, while still providing adequate electrical supply are of high importance. With major energy infrastructure already in place, developing enhanced pollutant-reducing combustor systems for micro gas turbines (MGTs), that can utilize low calorific fuels from renewable resources, is a major goal.
The current work focuses on the experimental testing of an optimized two-stage combustor designed to operate with various fuel types, including natural gas and syngas produced via biomass gasification. Atmospheric experimental tests were performed and the results indicate larger flame lift-off heights and slightly higher CO gas emissions levels, while displaying lower NOx gas emissions levels for all thermal loads and air-to-fuel equivalence ratios tested, compared to that of the previous combustor designs. Additionally, steady state CFD simulations were conducted and the results are in general good agreement with the experimental data. Overall, the results indicate high fuel flexibility of the combustor, as well as the ability to comply with the NOx emissions limits for a larger range of operating points, compared to that of the previously tested combustors.
A Reduced Model for Air Foil Journal Bearings for Time-Efficient Run-Up Simulations
Authors: Zeise Pascal , Mahner Marcel , Bauer Marcel , Rieken Markus , Schweizer Bernhard 
Published: November 2019

Abstract
This paper introduces a time-efficient reduced model for gas foil bearings. The foil structure of the considered air foil bearing can be modeled very realistically by a quasistatic nonlinear stiffness/friction hysteresis model; the gas film is assumed to be stiff enough to be neglected for the nonlinear forced response analysis. The main objective is to carry out nonlinear simulations of rotors with foil bearings in time domain. An important feature of the model is to enable fast run-up simulations, while maintaining important physical properties of the bearing. Furthermore, the determination of the model parameters should be simple to enable a fast adaption of new foil bearing geometries into existing rotor models. Finally, it should be possible to implement the bearing model very easily into arbitrary rotordynamic or multibody software tools. The basis of the approach is a two-dimensional hysteresis model, which approximates the nonlinear relationship between the movement of the rotor journal and the corresponding bearing forces. Although the here presented reduced bearing model cannot predict instability effects generated by the air film, the model may capture the nonlinear behavior of the foil bearing accurately. Hence, the nonlinear response of the rotor-bearing system may be predicted very precisely, if the rotor speed is below the threshold speed of instability. The input data for the reduced bearing model are measured or simulated hysteresis curves. The relevant parameters that influence the accuracy and the limits of the numerical model are discussed. Different simulations with very detailed finite element bearing models are presented in order to demonstrate the accuracy of the reduced modeling approach.
Heat Transfer Enhancement for Gas Turbine Blade Leading Edge Cooling Using Curved Double-Wall/Vortex Cooling With Various Disturbing Objects
Authors: Fan Xiaojun , Li Liang , Wang Jiefeng , Wu Fan 
Published: November 2019

Abstract
A new double-wall cooling configuration combined with the vortex cooling is established to study the cooling behavior for the gas turbine blade leading edge. This configuration consists of multiple nozzles, a curved inner cooling passage, a row of bridge holes and a curved outer cooling passage with 4 kinds of disturbing objects (namely smooth wall, pin-fins, dimples and protrusions). Numerical simulations are performed based on the 3D viscous steady Reynolds Averaged Navier-Stokes (RANS) equations and the k-ω turbulence model. The cooling behavior of the Double-wall/vortex cooling configuration is compared with the Double-wall/impingement cooling configuration at the same conditions. Generally, the Double-wall/vortex cooling configuration has a better cooling performance. It is found the Nusselt number of the inner surface for the Double-wall/vortex cooling configuration is 46.7% higher. However, the Double-wall/impingement cooling configuration has a smaller friction coefficient and a total pressure loss. Different disturbing objects have significant influences on the heat transfer performance of the outer surface. The Nusselt number of disturbing objects (pin-fins, dimples and protrusions) is much higher than the smooth wall, and the value is 1.27–2.22 times larger. Configuration with protrusions has the highest globally-averaged Nusselt number. For the heat transfer performance of the inner surface and the total pressure loss coefficient, disturbing objects have no obvious influence. As bridge holes row increases, the overall cooling performance is improved. The globally-averaged Nusselt number of the outer target is enhanced while the total pressure loss is reduced.
Experimental and Numerical Investigation on an Additively Manufactured Gas Turbine Ring Segment With an In-Wall Cooling Scheme
Authors: Wimmer Thomas , Ruehmer Tobias , Mick York , Wang Lieke , Weigand Bernhard 
Published: November 2019

Abstract
An additively manufactured ring segment (AMRS) for the first row of a large gas turbine from Siemens was designed with a novel cooling scheme. The wavy rectangular channels used for in-wall cooling are only viable through Additive Manufacturing (AM). Manufacturing deviations have been tracked using an optical 3D measuring system and were accounted for in the calculation models for thermal analysis. Friction factors of the cooling channels have been investigated experimentally allowing accurate flow prediction. The AMRS was tested in an engine at “Full Speed – Full Load” operating condition. It was instrumented with thermocouples and pressure taps. All crucial engine operating conditions were monitored. The results are compared to a conventional ring segment with similar instrumentation. It was installed next to the AMRS in the wake of the same burner. From a thermal model of the conventional ring segment and the measured temperatures the external boundary conditions are scaled to fit the experimental data. These were applied to the thermal model of the AMRS which was used for performance evaluation of the cooling scheme. This work addresses and quantifies the application of AM on advanced gas turbine cooling schemes. The AMRS underwent a mechanical integrity investigation in a referenced publication.