bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of Supercritical CO2 Brayton Cycle for Simple Cycle Gas Turbines Exhaust Heat Recovery Using Genetic Algorithm
Authors: Khadse Akshay , Blanchette Lauren , Kapat Jayanta , Vasu Subith , Ahmed Kareem
Published: August 2017

For the application of waste heat recovery (WHR), supercritical CO2 (S-CO2) Brayton power cycles offer significant suitable advantages such as compactness, low capital cost and applicable to a broad range of heat source temperatures. The current study is focused on thermodynamic modelling and optimization of Recuperated (RC) and Recuperated Recompression (RRC) S-CO2 Brayton cycles for exhaust heat recovery from a next generation heavy duty simple cycle gas turbine using a genetic algorithm. The Genetic Algorithm (GA) is mainly based on bio-inspired operators such as crossover, mutation and selection. This non-gradient based algorithm yields a simultaneous optimization of key S-CO2 Brayton cycle decision variables such as turbine inlet temperature, pinch point temperature difference, compressor pressure ratio. It also outputs optimized mass flow rate of CO2 for the fixed mass flow rate and temperature of the exhaust gas. The main goal of the optimization is to maximize power out of the exhaust stream which makes it single objective optimization. The optimization is based on thermodynamic analysis with suitable practical assumptions which can be varied according to the need of user. Further the optimal cycle design points are presented for both RC and RRC configurations and comparison of net power output is established for waste heat recovery.
Simultaneous Spectral Imaging of C2*/CH* at Low-to-High Pressure Combustion
Authors: Reyes Jonathan , Ahmed Kareem
Published: August 2017

This paper presents the correlation of the intensity ratio of the C2* and CH* radicals to fuel-air measurements over a range of pressures using 93% octane gasoline as the fuel. The measurements are conducted for the first time at high pressures. The study utilizes beam splitting technology to simultaneously view C2* and CH* as a line of sight, global measurement at the cost of resolution. A heavily instrumented constant volume combustor, with optical access, was employed to acquire the data. The ratio of C2* and CH* has been proven to be a good index of the equivalence ratio of premixed laminar flames. This index is attained, quite simply, by filtering each at their respected emissive peaks and taking the ratio of C2* over CH*. This technique shows great promise for use in turbomachinery as it will allow for identification of rich and lean locations in a combustor. By knowing the fuel-air field, combustor inefficiencies can be addressed to allow for greater energy release in combustion. The issue lies with the application of the indexing technique. Presented data to date has been performed on laboratory based diffusion flames exhausting to atmosphere, or premixed, steady, combustor type flames at low pressure (1atm) conditions. These types of flames are not relevant for engine combustor conditions. Understanding the fuel distribution at relevant regimes will reveal where inefficiencies may lie in injector or combustor design. Propagating flame kernels pose a problem in that they do not produce as much light as a steady flame, this makes spectral data difficult to obtain. Steady flames also do not address the effects that pressure may have on the index of C2* and CH*. The authors of this work seek to address three main issues associated with the indexing technique: The feasibility of its application to combustors (hardware design), The ability to operate at low-light ignition events, and the effects pressure may have on the correlation of intensity ratio to the fuel-air measurement.
The Effect of Upstream Ramps With Different Shapes on Film Cooling Efficiency
Authors: Zheng Daren , Wang Xinjun , Zhang Feng , Zhou Junfei , Yuan Qi
Published: August 2017

This paper presents a numerical investigation on a concept for enhancing the film cooling performance by modifying the shape of upstream ramps. The novel shape ramp, which is placed in front of the film cooling holes, is presented to alter the approaching boundary-layer flow and its interaction with coolant to increase the lateral spreading of the coolant. Five different shape ramps are investigated, including rectangular, wedge-shaped, convex, concave and wave-shaped ramps. The film cooling performance of different shape ramps are evaluated at the density ratio about 1, with blowing ratios ranging from 0.3 to 1.2. The numerical results for the upstream ramp show an agreement with experiment data when solving three dimensional average Navier-Stokes analysis with the k-ε model. Detailed adiabatic cooling effectiveness and total pressure loss coefficient are simulated. Results obtained indicate that film cooling characteristics in the region downstream of the film cooling holes are sensitive to the ramp shapes. The wave-shaped ramp shows the lowest total pressure loss coefficient among these five ramps. For M = 0.3 and 0.6, the highest centerline adiabatic cooling effectiveness occurs in the convex ramp. And this shape ramp also shows the highest spanwise averaged adiabatic cooling effectiveness at the blowing ratio of 0.3. Compared with the other shape ramps, the concave ramp can greatly increase both the centerline and the spanwise averaged adiabatic cooling effectiveness for M = 1.0 and 1.2.
Heat Transfer and Pressure Loss Characteristics of Pin-Fins With Different Shapes in a Wide Channel
Authors: Xu Jin , Yao Jiaxu , Su Pengfei , Lei Jiang , Wu Junmei , Gao Tieyu
Published: August 2017

Convective heat transfer enhancement and pressure loss characteristics in a wide rectangular channel (AR = 4) with staggered pin fin arrays are investigated experimentally. Six sets of pin fins with the same nominal diameter (Dn = 8mm) are tested, including: Circular, Elliptic, Oblong, Dropform, NACA and Lancet. The relative spanwise pitch (S/Dn = 2) and streamwise pitch (X/Dn = 4.5) are kept the same for all six sets. Same nominal diameter and arrangement guarantee the same blockage area in the channel for each set. Reynolds number based on channel hydraulic diameter is from 10000 to 70000 with an increment of 10000. Using thermochromic liquid crystal (R40C20W), heat transfer coefficients on bottom surface of the channel are achieved. The obtained friction factor, Nusselt number and overall thermal performance are compared with the previously published data from other groups. The averaged Nusselt number of Circular pin fins is the largest in these six pin fins under different Re. Though Elliptic has a moderate level of Nusselt number, its pressure loss is next to the lowest. Elliptic pin fins have pretty good overall thermal performance in the tested Reynolds number range. When Re>40000, Lancet has a same level of performance as Circular, but its pressure loss is much lower than Circular. These two types are both promising alternative configuration to Circular pin fin used in gas turbine blade.
Tip-Clearance Measurements on an Engine High Pressure Turbine Using an Eddy Current Sensor
Authors: Sridhar V. , Chana K. S.
Published: August 2017

Gas turbine health monitoring is an important area of research. As the performance of aircraft and power plants increase, they will require better sensors for health monitoring systems to prevent failures. Health monitoring systems help in preventive maintenance reducing unnecessary downtime and maintenance costs.

Gas turbine blades are subjected to dynamic loads caused by rotor imbalances, distortions in the intake flows etc. These loads cause low or high cycle fatigues and the blades can fail over time. Tip-timing and tip-clearance systems makes it possible to assess turbomachinery blade vibration by using non-contact measurement systems such as optical, eddy current, hall effect, capacitve etc. The most widely used systems in industry are optical, however, these systems are still largely prone to contamination problems from dust, dirt, oil, water etc. Further development of these systems for in-service use is problematic because of the difficulty in eliminating contamination of the optics. Other systems, although immune to contamination, may not be able to measure both tip-clearance and tip-timing at the same time due to their operating principle. Another limitation is that they cannot be used in high temperature applications such as in a high pressure turbine where the temperatures can reach 1400°C. Eddy current sensors are found to be quite robust and can measure both tip-timing and tip-clearance. They are currently being used for gas turbine health monitoring applications at low temperatures such as in the compressor stage and last stage of a steam turbine.

A new high temperature eddy current sensor has been developed in-house at the University of Oxford for application in gas turbine tip-timing and tip clearance measurements to assess blade vibrations. The current sensor is a modified version of the existing eddy current sensor that is able to operate at high temperatures of about 1400°C. The paper presents the development of the sensor and experimental results of tip clearance measurements in the high pressure turbine stage of a jet engine. In the engine tests, two blades were reduced in height to increase the tip-clearance and the measurements were taken at both idle and max operating speeds. The sensor was found to work in these harsh environments and was sufficiently sensitive to accurately determine the tip clearance at these elevated temperatures. Tests were carried out mainly to demonstrate the technique of obtaining good tip clearance measurements and the survivability of the sensors in the high temperature and pressure environment.
Multi-Scale Computational Simulation of Combustion Instability and Transition in a Model Afterburner
Authors: Kalathoor Sriram , Chakravarthy S. R.
Published: August 2017

A multiple length and time scale approach is adopted to perform large eddy simulation (LES) of combustion instability in a model afterburner. In this framework, the full compressible Navier-Stokes equations are decomposed into incompressible flow to leading order and acoustic equations to first order. The basis for this decomposition is the disparity in the time and length scales of the flow and acoustic propagation respectively. The present framework yields a coupling between the flow field and acoustic field, in terms of the flow dilatation and acoustic Reynolds stress (ARS). Test cases for various Reynolds numbers (based on mass flow rates) are simulated within this framework, and used to study the dynamics of transition and instability in a model afterburner. As the Reynolds number is increased, the dominant frequency switches from being that of the acoustic mode to the hydrodynamic mode. When the excitation to the acoustic field from the combustion is switched off, a high frequency relating to the transverse acoustic mode of the combustor is observed to be excited in the flow field as an acoustic feedback to the flow. When the acoustic excitation is turned back on, the transverse acoustic mode excitation of the hydrodynamics continues to prevail, illustrating a hysteretic effect. The dominant excitation of hydrodynamic mode at high Reynolds number clearly shows a rapid mixing and shortened length of heat release rate zone, when compared to the case at low Reynolds number as well as when the flow and acoustic simulations are uncoupled.
Turbine Blade Leading Edge Cooling With One Row of Normal or Tangential Impinging Jets
Authors: Wang Nian , Chen Andrew F. , Zhang Mingjie , Han Je-Chin
Published: August 2017

Jet impingement cooling has been extensively used in the leading edge region of a gas turbine blade. This study focuses on the effect of jet impinging position on leading edge heat transfer. The test model is composed of a semi-cylindrical target plate, side exit slots, and an impingement jet plate. A row of cylindrical injection holes is located along the axis (normal jet) or the edge (tangential jet) of the semi-cylinder, on the jet plate. The jet-to-target-plate distance to jet diameter ratio (z/d) is 5 and the ratio of jet-to-jet spacing to jet diameter (s/d) is 4. The jet Reynolds number is varied from 10,000 to 30,000. Detailed impingement heat transfer coefficient distributions were experimentally measured by using the transient liquid crystal technique. To understand the thermal flow physics, numerical simulations were performed using RANS with two turbulence models: realizable k-ε (RKE) and shears stress transport k-ω model (SST). Comparisons between the experimental and the numerical results are presented. The results indicate that the local Nusselt numbers on the test surface increase with the increasing jet Reynolds number. The tangential jets provide more uniform heat transfer distributions as compared with the normal jets in the stream-wise direction. For the normal jet impingement and the tangential jet impingement, the RKE model provides better prediction than the SST model. The results can be useful for selecting a jet impinging position in order to provide the proper cooling distribution inside a turbine blade leading edge region.
Experimental Investigation of Oil Shedding From an Aero-Engine Ball Bearing at Moderate Speeds
Authors: Santhosh R. , Hee Jee Loong , Simmons Kathy , Johnson Graham , Hann David , Walsh Michael
Published: August 2017

In civil aero-engine transmission system bearings are used for shaft location and load support. An experimental test facility in the University of Nottingham’s Gas Turbine Transmissions Research Centre (G2TRC) was designed and commissioned to investigate oil behaviour as it exits an engine-representative ball bearing. In the rig, oil is delivered to the bearing inner race and cage via under-race feed at three delivery locations i.e. front, mid and rear of the bearing assembly. An electromagnetic load system is designed and implemented to allow engine representative axial loads up to 35 kN to be applied to the bearing. This paper details the rig design including the load and under-race lubrication systems and gives information about bearing oil shedding mechanisms observed.

In this phase of testing high speed images are acquired at shaft speeds between 1000 and 7000 rpm at an oil flowrate of 5.2 litres per minute and bearing axial load of 10 kN. The work presented here focusses on oil shedding from the bearing cage. Oil shedding behaviour from aeroengine ball bearing is identified to share many similarities to that observed in the past for shedding from rotating disks and cups. However, it is shown that it not possible to predict the conditions at which transition in flow regimes will occur for the aeroengine bearing on the basis of correlations for simpler geometries (spinning disks and cups). The work presented here is the first observation of flow regimes in an aeroengine ball bearing involving high-resolution highspeed imaging.
Heat Transfer Deterioration Onset of Hydrocarbon Fuel at Supercritical Pressure
Authors: Cheng Zeyuan , Tao Zhi , Zhu Jianqin , Li Haiwang , Wang Longyun
Published: August 2017

The present study pays attention to the pressure effect and geometric effect on heat transfer deterioration onset to supercritical hydrocarbon fuel. Numerical simulation about heat transfer deterioration of hydrocarbon fuel flowing upward in vertical round tubes with various diameter at supercritical pressure was performed. In the simulation, a four-species surrogate model of RP-3 based on the generalized corresponding states law was used and LS low-Reynolds number eddy viscosity turbulence model was selected. For the boundary conditions, inlet temperature was 623K, pressure ranged from 3 to 4MPa, tube diameter varied from 3 to 9mm, and wall heat flux to mass flux ratio changed from 0.07 to 3.18kJ/kg. Comparative analyses between the predicted results and the experimental data revealed the accuracy of thermophysical property model and numerical method. The results indicated that the operating pressure and tube diameter have significant effect to the heat transfer deterioration onset of supercritical hydrocarbon fuel: heat transfer deterioration aggravates and heat transfer deterioration onset moves upstream when the diameter increases. With the increase of operating pressure, heat transfer deterioration becomes weak and the heat transfer deterioration onset moves downstream. Based on current results, several existing correlations of the heat transfer deterioration onset were reviewed and assessed, showing different prediction performance. A new correlation of the threshold value for the ratio between heat flux and mass flux for determining the boundary for heat transfer deterioration under various tube diameter and operating pressure was obtained. The effect of length to diameter ratio on safety margin was discussed. The present study provides the optimization design of regenerative cooling on reducing heat transfer deterioration.
Analysis of Runback Water Flow on Anti-Icing Surface Using Volume-of-Fluid Method
Authors: Zheng Mei , Dong Wei , Guo Zhiqiang , Lei Guilin
Published: August 2017

The runback water flow and heat transfer on the surface of aircraft components has an important influence on the design of anti-icing system. The aim of this paper is to investigate the water flow characteristics on anti-icing surface using numerical method. The runback water flow on the anti-icing surface, which is caused by the impinging supercooled droplets from the clouds, is driven by the aerodynamic shear forces and the pressure gradient around the components. This is a complex model of flow and heat transfer that considers flow field, super-cooled droplets impingement and runback water flow simultaneously. In this case of gas-liquid two phase flow, the Volume-of-Fluid (VOF) method is very suitable for the solution of thin liquid film flow so that it is applied to simulate the runback water flow on anti-icing surfaces in this paper. Meanwhile, the heat and mass transfer of the runback water flow are considered in the calculation using the User-Defined Functions (UDFs) in ANASYS FLUENT. The verification is conducted by the comparison with the results of the experimental measurement and the mathematical model calculation. The effect of the airflow velocity and contact angle on the water flow are also considered in the numerical simulation.
Effect of Blade Aspiration Slot Configuration on the Aerodynamic Performance of a Highly Loaded Aspirated Compressor Cascade
Authors: Zhang Longxin , Cai Le , Liu Bao , Ding Jun , Wang Songtao
Published: August 2017

As a promising active flow control method, boundary layer suction (BLS) can be used to enhance the aerodynamic performance of the highly-loaded compressor effectively, and due to this reason, extensive studies have been carried out on it. However, contrast to those abundant studies focusing on the flow control effects of BLS, little attention has been paid on the design method of the aspiration flow path.

This work presents a 3-D steady numerical simulation on a highly-loaded aspirated compressor cascade. The aspiration slot is implemented at its best location based on the previous experimental studies and the aspiration flow rate is fix to 1.5% of the inlet massflow. The plenum configuration follows the blade shape and remains unchanged. One-side-aspiration manner is adopted to simplify the aspiration devices. Two critical geometry parameters, slot angle and slot width, are varied to study the effects of blade aspiration slot configuration on the cascade loss, radial distribution of the aspiration flow rate and inner flow structures within the aspiration flow path. Results show that the slot configuration does affect the cascade performance. In comparison with the throughflow performance, it is especially true once the flow loss caused by the aspiration flow path is also taken into account, and higher flow loss will be generated within the aspiration flow path if an inappropriate scheme is adopted. In the present investigation, apart from the cases with larger negative slot angle, a wider slot is more preferable to a narrower one, since it could enhance the aspiration capacity near the endwall regions and lower the dissipation loss within the aspiration flow path. In terms of the slot angle, a larger negative value, i.e., the slot direction more aligned with the incoming flow, is not beneficial to improve the throughflow performance, while concerning the flow loss yield by the aspiration flow path, a proper negative slot angle is always optimal.
The Aerodynamic Design of the Low Pressure Air Delivery Ducts for a Cooled Cooling Air System
Authors: Spanelis A. , Walker A. D. , Beecroft P. A.
Published: August 2017

As aero gas turbines strive for higher efficiencies and reduced fuel burn, the trend is for engine overall pressure ratio to increase. This means that engine cycle temperatures will increase and that cooling of various engine components, for example the high pressure turbine, is becoming more difficult. One solution is to employ a cooled cooling air system where some of the compressor efflux is diverted for additional cooling in a heat exchanger fed by air sourced from the by-pass duct. Design of the ducting to feed the heat exchangers with coolant air is challenging as it must route the air through the scenery present in the existing engine architecture which leads to a convoluted and highly curved system. Numerical predictions using ANSYS Fluent demonstrated that a baseline design was unsuitable due to large amounts of flow separation in the proximity of the heat exchangers. This paper is mainly concerned with the aerodynamic design of this component of the duct. In order to produce a viable aerodynamic solution a numerical design methodology was developed which significantly enhances and accelerates the design cycle. This used a Design of Experiments approach linked to an interactive design tool which parametrically controlled the duct geometry. Following an iterative process, individually optimized 2D designs were numerically assessed using ANSYS Fluent. These designs were then fed into an interactive 3D model in order to generate a final aerodynamic definition of the ducting. Further CFD predictions were then carried out to confirm the suitability of the design. RANS CFD solutions, generated, using a Reynolds stress turbulence model, suggested that the new design presented significant improvement in terms of diffusion and flow uniformity.
Partially Vaned Diffuser With Variable Cross-Section for Centrifugal Fans
Authors: Fischer Tore , Burgmann Sebastian , Rudersdorf Manuel , Seume Joerg R.
Published: August 2017

The present research focuses on the efficiency improvement at part-load of a centrifugal fan for a 30 kW fuel cell combined heat and power (CHP) unit. For this purpose, the fan stage is equipped with a partially vaned diffuser with a variable cross-sectional area using a moving backplate.

The design and the performance of the partially vaned diffuser with a variable cross-sectional area are described in the first part of this paper. The performance results are compared to measurements of the same centrifugal fan with a vaneless diffuser carried out for the previous investigation. For the second part, the influence of the variable cross-sectional area on the diffuser flow field is investigated using optical PIV (Particle Image Velocimetry) measurements and CFD (Computational Fluid Dynamics) simulations.

The combination of a variable cross-section, partially vaned diffuser was able to achieve a 10 percent increase in pressure ratio, a 5 percentage points increase in part-load efficiency while maintaining the whole operating range of the vaneless, constant cross section reference design.
Investigation of Heat Transfer and Flow Characteristics in Fractal Tree-Like Microchannel With Steam Cooling
Authors: Shui Linqi , Huang Bo , Dong Kunkun , Zhang Chunyan
Published: August 2017

Using closed-loop steam to cool blades is beneficial to improve the gas turbine thermal efficiency. Although the steam-cooled blade can provide sufficient cooling for the main body of high temperature blade, the high thermal load is found in the leading and trailing edge. To alleviate the thermal loads as well as thermal stresses, it is necessary to optimize the cooling configuration of closed loop steam-cooled blades. The tree-like branching network systems have the unique high cooling efficiency and low flow resistance as well as even temperature distribution characteristics. Utilizing the efficient transportation branching network as the internal cooling configuration for the steam-cooled blades, is likely to provide useful hits of optimal solution for solving the uneven and insufficient cooling problems at the high thermal load regions. For this purpose, the heat transfer and flow friction features of coolant flow in the tree-like branching microchannel is studied experimentally and numerically. The results indicate that, influenced by the branch effects, the fractal tree-like microchannel provides a desirable low friction factor for the turbulent flow, and an expected better heat transfer performance under the conditions of a higher Re number and larger heat flux. In addition, compared the wall temperature distributions between the fractal tree-like microchannel and serpentine channels with different coolant, adopting the tree-like branching channel configuration combination with steam cooling could provide an excellent even cooling performance for the high temperature metal wall.
Experimental Optimization of Rolls-Royce AE3007 Sump Design
Authors: Chandra Budi W. , Collicott Steven H. , Munson John H.
Published: August 2017

The original sump design of Rolls-Royce AE3007 central sump is a tangential sump. An experimental program at Purdue University was conducted to investigate the characteristics of a tangential sump design. The research employed a bespoke experimental rig consisting of modular transparent chamber to allow unprecedented view of the two-phase flow inside the bearing chamber. It was found that a persistent liquid pooling near the drain entrance of a tangential sump obstructs the outflow to the scavenge off-take. While space requirement is minimal, the scavenge performance of a tangential sump is poor. A prototype advanced sump was proposed and built with features to address various issues found in the tangential sump.

In this paper, further experimental work on the refinements of the advanced sump is presented. This includes experimental study on the effect of a fence and splitter plate, off-take hole diameter and its location, the effect of gravity by tilting, upstream wall fairing, as well as the depth of the sump itself. The experiments showed that the faired upstream wall modification can reduce residence volume significantly across different operating conditions, indicating improvement in scavenge performance. The other modifications help to reduce residence volume only in certain operating conditions. The results of this study helped towards the birth of an optimized sump design, known as Indy sump. The Indy sump has been accepted as a superior sump design and has been used as a benchmark in many sump design studies.
The Effect of Manufacturing Variations on Unsteady Interaction in a Transonic Turbine
Authors: Clark John P. , Beck Joseph A. , Kaszynski Alex A. , Still Angela , Ni Ron-Ho
Published: August 2017

This effort focuses on the comparison of unsteadiness due to as-measured turbine blades in a transonic turbine to that obtained with blueprint geometries via computational fluid dynamics (CFD). A Reynolds-averaged Navier-Stokes flow solver with the two-equation Wilcox turbulence model is used as the numerical analysis tool for comparison between the blueprint geometries and as-manufactured geometries obtained from a structured light optical measurement system. The nominal turbine CFD grid data defined for analysis of the blueprint blade was geometrically modified to reflect as-manufactured turbine blades using an established mesh metamorphosis algorithm. The approach uses a modified neural network to iteratively update the source mesh to the target mesh. In this case the source is the interior CFD surface grid while the target is the surface blade geometry obtained from the optical scanner. Nodes interior to the CFD surface were updated using a modified iterative spring analogy to avoid grid corruption when matching as-manufactured part geometry. This approach avoids the tedious manual approach of regenerating the CFD grid and does not rely on geometry obtained from Coordinate Measurement Machine (CMM) sections, but rather a point cloud representing the entirety of the turbine blade. Surface pressure traces and the discrete Fourier transforms thereof from numerical predictions of as-measured geometries are then compared both to blueprint predictions and to experimental measurements. The importance of incorporating as-measured geometries in analyses to explain deviations between numerical predictions of blueprint geometries and experimental results is readily apparent. Further analysis of every casting produced in the creation of the test turbine yields variations that one can expect in both aero-performance and unsteady loading as a consequence of manufacturing tolerances. Finally, the use of measured airfoil geometries to reduce the unsteady load on a target blade in a region of interest is successfully demonstrated.
Large-Eddy Simulation of Light-Round in an Annular Combustor With Liquid Spray Injection and Comparison With Experiments
Authors: Lancien Théa , Prieur Kevin , Durox Daniel , Candel Sébastien , Vicquelin Ronan
Published: August 2017

A combined experimental and numerical study of light-round, defined as the flame propagation from burner to burner in an annular combustor, under perfectly premixed conditions has previously demonstrated the ability of large-eddy simulation (LES) to predict such ignition processes in a complex geometry using massively parallel computations. The present investigation aims at developing light-round simulations in a configuration closer to real applications by considering liquid n-heptane injection. The large-eddy simulation of the ignition sequence of a laboratory scale annular combustion chamber comprising sixteen swirled two-phase injectors is carried out with a mono-disperse Eulerian approach for the description of the liquid phase. The objective is to assess this modeling approach to describe the two-phase reactive flow during the ignition process. The simulation results are compared in terms of flame structure and light-round duration to the corresponding experimental images of the flame front recorded by a high-speed intensified CCD camera. The dynamics of the flow is also analyzed to identify and characterize mechanisms controlling flame propagation during the light-round process.
A Numerical Study of the Internal Flow in a Pressure Swirl Atomizer
Authors: Qian Weijia , Hui Xin , Zhang Chi , Xu Quanhong , Lin Yuzhen , Sung Chih-Jen
Published: August 2017

The internal flow and discharge parameters of a pressure swirl atomizer (PSA) are numerically investigated using a coupled Level-Set (LS)/Volume-of-Fluid (VOF) solver that combines the advantages of LS and algebraic VOF methods by maintaining the mass conservation and the interface sharpness simultaneously. Internal flow velocity profile and discharge parameters including discharge coefficient, film thickness, and spray cone angle are compared between simulation results and the experimental data that are available in the literature. A parametrical study is also performed to investigate the effects of the key geometric parameters of the PSA configuration on the discharge parameters. The geometric parameters studied are the length to diameter ratio of the swirl chamber, the length to diameter ratio of the exit orifice, the swirl chamber diameter to exit orifice diameter ratio, and the swirl chamber convergence angle.
CFD Driven Analysis of a Multi-Port Pressure Probe for Real Engine Testing
Authors: Lahalle Aude , Fontaneto Fabrizio , Arts Tony
Published: August 2017

During the development phase of an aircraft engine, extensive ground and flight instrumentation testing is performed. The performance of the instrumentation is quantified in terms of Recovery Factor (RF). Experimental data only provide measurement at the sensor location, but no information is available for the flow field taking place in and around the probe.

The scope of the present paper is to numerically investigate the flow field taking place inside and around a three Kiel heads rake. The study will focus on the description of the flow field and aims at highlighting the mechanisms affecting the RF. Each head has an elliptical casing and contains a pressure sensor (pneumatic pressure tap) and a temperature sensor (thermocouple).

Steady-state RANS simulations have been realized for two different Mach numbers (M = 0.30 and M = 0.65), providing a complete mesh and turbulence models sensitivity analysis. The simulated global flow field demonstrated that regardless of the Mach number, the flow topology is very similar in all cases. The Kiel heads investigation highlighted a well guided flow field confirming the sensors’ high performance.
Gas Turbine Cycle Upgrade and Validation for Heavy Duty Industrial Machines
Authors: Torkaman Alex , Vogel Gregory , Fiebiger Steve , Dietrich Doug , Washburn Ron
Published: August 2017

Two Siemens Westinghouse SW501F D2 industrial gas turbines were successfully upgraded during a Modified HGP service interval. This paper details the technical aspects of this upgrade and validation of critical turbine blade flutter related parameters during commissioning. Significant performance improvement was achieved by implementation of aerodynamic redesigns of certain compressor and turbine components. An upgraded combustion system and newly installed continuous tuning and health monitoring systems provided operational flexibility and reduction in emissions. Due to historical issues with the 4th stage blade flutter, significant analytical efforts were invested in the structural redesign of the 4th stage blade to predict and avoid flutter and resonance regions. Latest methods of aerodynamic work calculations were employed during design to ensure flutter free operation of this component. Validation steps were implemented using blade tip timing technology to determine synchronous and non-synchronous vibration characteristics of the 4th stage blades during commissioning.

Performance tests per ASME PTC-22 were conducted immediately before and after the outage to provide an accurate measurement of engine performance. Analysis of the performance data after installation and commissioning of the upgrade package confirmed the performance improvement objectives on power output and heat rate were achieved on these two units. Live monitoring and analysis of blade instrumentation data during commissioning and further analysis afterward confirmed flutter free operation of the 4th stage turbine blade.
Combustion Behavior of Jet A Droplets and its Blends With Butanol
Authors: Muelas Álvaro , Remacha Pilar , Martínez Adrián , Ballester Javier
Published: August 2017

In light of the potential of butanol as an alternative fuel for blending with petroleum fuels such as gasoline, diesel or Jet A, experimental data regarding the burning characteristics of these blends are required in order to better understand their combustion process. In this study, freely-falling droplets of butanol, Jet A, and their mixtures (10, 20 and 50% butanol by volume) were examined in a combustion chamber which provides representative conditions of real flames, both in terms of temperature and oxygen availability. The combustion characteristics reported here include evolution of droplet sizes, burning rates, soot measurements, and the occurrence of microexplosions and soot shells. Results show that the evolution of droplet diameter for butanol, Jet A and their blends are very similar, regardless of the obvious compositional differences. Sooting behaviors are found to be quite different, with a clear reduction in the sooting propensity as the butanol content in the fuel increases. These results are consistent with a previous study in a gas turbine showing similar performance among Jet A and its blends with butanol, suggesting that such mixtures are promising alternative fuels with very similar combustion characteristics to Jet A, but with much less propensity to soot. Moreover, this study provides new results on the combustion properties of Jet A/butanol blends, for which very scarce data exist in the open literature.
Modeling Surface Variation and Assessment of its Impact on Aerodynamic Performance in Turbomachinery Applications
Authors: Ray Saurya Ranjan , Avancha Ravikanth , Shankaran Sriram , Dailey Lyle
Published: August 2017

Analyzing the impact of manufacturing variability on the performance of turbomachinery components supports two critical dimensions in the product life cycle. It provides a technological process to decide on the criterion of acceptability of the deviated manufactured component based on the performance assessment and secondly, provides sensitivity of the geometrical variation to the component performance to build a robust design space. Currently, non-deterministic methods based on probability distribution function of the design parameters are used to assess the impact of variability, and the output is presented as a set of correlation coefficients linking the geometrical parameters to the component performance. Though these methods provide adequate information on the robustness of the design space, the amount of computational requirement and lack of consideration of the local effect of geometry modification on the performance pose challenges. In the current work, the method presented is based on a variant of radial basis functions to construct the deviated manufactured geometry of the turbine rear frame (TRF) of a modern gas turbine engine for aerodynamic assessment. The approach is used to accurately and rapidly construct a 3D deviation map from a set of discrete measured data using a co-ordinate measuring machine (CMM). Additionally, the developed approach is used as a method of applying free-form deformation in the critical localities on the aerodynamic surface identified using the sensitivity information from an adjoint analysis to re-design the baseline geometry. Aerodynamic analysis is conducted to understand the nature of geometry change due to the manufacturing variation and explain the mechanism of performance change.
Effects of Unsteady Wakes on Heat Transfer of Blade Tip and Shroud
Authors: Bang Minho , Choi Seok Min , Sohn Ho-Seong , Park Jun Su , Cho Hyung Hee
Published: August 2017

An experimental study has been conducted to investigate the heat-transfer characteristics of blade tips and shrouds with and without unsteady wakes. Depending on the presence of unsteady wakes, the local heat/mass-transfer coefficients of the tip and shroud were measured using the naphthalene sublimation method. Wakes from unsteady blades were modeled as wakes generated from moving cylindrical rod bundles. Test conditions were set to the Reynolds number of 100,000, based on an inlet velocity of 11.4 m/s and the axial chord length. The Strouhal number was varied from 0 to 0.22. For St = 0, high heat/mass-transfer coefficients appeared in regions where various flow patterns, such as flow reattachment, swirling flow, and vortexes, occurred. For St = 0.22, the heat/mass-transfer distributions of the tip and shroud were changed due to the unsteady wakes. Unsteady wakes made high turbulence intensity of leakage flow and flow patterns such as flow reattachment, swirling flow, and tip leakage vortex in the tip and shroud were changed and dispersed. There were also variations in the pitch-wise averaged Sherwood number of the blade tip and shroud on the presence of the unsteady wakes due to vortex shedding and dispersed flow patterns. Thus, considering the effects of unsteady wakes on the heat transfer of the blade tip and shroud, proper cooling designs for blade tips and shrouds should be investigated and adopted for effective cooling of gas turbine blades.
New Modular Test Rig for Unsteady Performance Assessment of Automotive Turbocharger Turbines
Authors: Lyttek Paul , Roclawski Harald , Böhle Martin , Gugau Marc
Published: August 2017

Standard test rigs for basic research on turbochargers usually do not provide the capability of periodically changing, instantaneous process values, which are characteristic for the real application of these turbines. The challenge of testing the performance potential of turbocharger turbines under pulsating inflow conditions is mainly originated by the complex compatibility of two main issues that need to be implemented at a test facility: Firstly, a special device is required that reproducibly provides real engine-like exhaust gas pulsations with some variability representing different engine operating conditions. Secondly, appropriate real time measurement techniques for all significant transient values are required to measure both, instantaneous turbine inflow conditions and turbine power output. This paper presents a new developed test rig that enables a preferably high overlap between the above mentioned supply of approximately real engine exhaust gas conditions and the fundamental and scientifically based attempt of unsteady gas flow examinations.
Computing Fluid Structure Interaction Coupling Time Spectral Method (TSM) and Harmonic Balance Method (HBM)
Authors: Cadel Aude , Ngo Boum Ghislaine , Thouverez Fabrice , Dugeai Alain , Parent Marie-Océane
Published: August 2017

This paper deals with fluid-structure interactions (FSI), involving a blade profile, submitted to different sources of excitations, as if it were included in a real engine. Two forces of excitation will be considered on the NACA 64A010 airfoil, described in : an external force, due to a forced rotation motion of the blade, and an aerodynamic force, induced by fluid flow around the structure.

By using the Harmonic Balance Method, the airfoil’s motion equation becomes an algebraic problem. Then, this system is solved for each frequency of a chosen range. Therefore, the fluid effect on the translation motion of the profile is studied.

To compute the time periodic aerodynamic field, the Time Spectral Method, implemented in the Onera’s elsA solver, is used for a fast and efficient resolution. This method relies on a time-integration scheme that turns the resolution of the turbulent Navier-Stokes problem into the resolution of several coupled steady state problems computed at different instants of the time period of the movement. The Theodorsen approach with several hypothesis exposed in allows an analytic estimation of the unsteady lift effort. The two approaches are compared for an imposed motion.

In order to predict the dynamic behavior of the system, a fully coupled numerical methodology is developed. For each frequency and at each iteration, TSM supplies the flow field which is used by HBM as a nonlinear excitation on the structure to computate a periodic response and conversely, HBM supplies the new deformed mesh used by TSM to compute the flow field. This strategy has the advantage that all computations take place in the spectral domain, allowing thus to find the steady-state behavior of the fluid and the structure without computing any transient state. The analysis provides the Frequency Forced Response. Some frequencies in the range corresponding to a contribution change between structure and fluid damping are precisely highlighted.
Isolated and Coupled Effects of Rotating and Buoyancy Number on Heat Transfer and Pressure Drop in a Rotating Two-Pass Parallelogram Channel With Transverse Ribs
Authors: Liou Tong-Miin , Chang Shyy-Woei , Lan Yi-An , Chan Shu-Po
Published: August 2017

Detailed Nusselt number (Nu) distributions over the leading and trailing endwalls and the pressure drop coefficients (f) of a rotating transverse-ribbed two-pass parallelogram channel were measured. The impacts of Reynolds (Re), rotation (Ro) and buoyancy (Bu) numbers upon local and regionally averaged Nu over the endwall of two ribbed legs and the turn are explored for Re = 5,000–20,000, Ro = 0–0.3, and Bu = 0.0015–0.122. It is aimed to study the combined buoyancy and Coriolis effects on thermal performances as the first attempt. A set of selective experimental data illustrates the isolated and interdependent Ro and Bu influences upon Nu with the impacts of Re and Ro on f disclosed. Moreover, thermal performance factors (TPF) for the channel tested are evaluated and compared with those collected from the channels with different cross-sectional shapes and endwall configurations to enlighten the relative heat transfer efficiency under rotating condition. Empirical Nu and f correlations are acquired to govern the entire Nu and f data generated. These correlations allow one to evaluate both isolated and combined Re, Ro and/or Bu impacts upon the thermal performances of the present rotating channel for internal cooling of gas turbine blades.
Quantification of Stator Blade Shape Influence on Non-Equilibrium Condensation in Low-Pressure Steam Turbine
Authors: Patel Giteshkumar , Patel Yogini , Turunen-Saaresti Teemu , Grönman Aki
Published: August 2017

The expansion of steam flow and the condensation phenomena in an LP turbine depend on both the flow passage shape and the operating conditions. This paper presents the quantification of the influence of local geometrical details of the steam turbine blade including blade surface tapering, dimple inclusion and trailing edge shapes on flow expansion and condensation phenomena. For this purpose, the wet-steam model of ANSYS FLUENT, based on the Eulerian-Eulerian approach, was used. The mixture of vapor and liquid phases was solved by compressible Reynolds-averaged Navier-Stokes equations. The low inlet superheat case of White et al. [1] which is conducted with planar stator cascade was used as reference for this study. Various modifications including blade trailing edge shapes, blade shape modification via blade pressure and suction surfaces’ tapering, and addition of dimple feature to the blade pressure surface were applied to the blade profile. The presented results revealed that the applied blade shape modifications affected nucleation and droplet growth processes, shock wave structures and entropy generation rates. The influence of blade shape on loss generation was presented by calculating the Markov energy loss coefficients. The presented analysis exhibits that the blade shape alteration influences the overall loss generation that occur due to the irreversible heat and mass transfer during the condensation process.
Large Eddy Simulation of Tandem Blade Stator Cascades
Authors: Mitra Pratik , Kantharaju Jahnavi , Rayan Rohan , Mathew Joseph
Published: August 2017

Large eddy simulations of tandem blade compressor cascades have been performed with an explicit filtering method. A low speed case was simulated using the public domain code Incompact3d which solves incompressible flow with an immersed boundary method for embedded solid bodies, obviating the effort expended on preparing good quality meshes around blading. The LES successfully captures transition on the front blade and yields a significantly different loading compared with RANS solutions obtained before. The less substantial impact on the rear blade is traced to rapid transition forced by the turbulent wake of the front blade. LES with a refined grid was found to shorten the transition width due to the crucial role of small scales during transition. A complementary study with an in-house compressible LES solver was conducted for a transonic tandem cascade at the inlet Mach number of 0.89. Flow expands around the leading edge of the front blade and is terminated by a shock which interacts with the suction surface boundary layer. The beneficial effect of tandem blading was found to be achieved by limiting this separation. The shock-induced separation also marks a rapid transition of the suction surface boundary layer that is readily captured in the LES, showing pre-transitional streaks, but could prove difficult even for current transition-sensitive RANS.