bluuebunny/crossref_metadata_2025 huggingface dataset:
Demonstrated Operability and Reliability Improvements for a Prototype High-Speed Rotary-Disc Atomizer Supported on Active Magnetic Bearings
Authors: Khatri Rasish K. , Hawkins Lawrence A. , Bazergui Claude
Published: August 2015

A state-of-the-art, rotary-disc atomizer driven by a permanent-magnet electric motor and supported by active magnetic bearings (AMB) was designed, fabricated, and tested as part of a spray-dryer system within a pharmaceutical-processing plant. The atomizing process imposed several challenges on the AMBs, including large, highly-dynamic rotor imbalances and large, quasi-periodic external radial impulses. Several design changes were systematically implemented to mitigate the effects of large rotor imbalances. A novel impulse detection and recovery system was introduced to alleviate the effects of external impulses. These changes, which have steadily improved the operability and reliability of the machine, are described here along with field test data.
An Experimental Investigation on the Wake Characteristics and Aeromechanics of Dual-Rotor Wind Turbines
Authors: Ozbay Ahmet , Tian Wei , Hu Hui
Published: August 2015

An experimental study was carried out to investigate the aeromechanics and wake characteristics of dual-rotor wind turbines (DRWTs ) in either co-rotating or counter-rotating configuration, in comparison to those of a conventional single-rotor wind turbine (SRWT). The experiments were performed in a large-scale Aerodynamic/Atmospheric Boundary Layer (AABL) wind tunnel available at Iowa State University with the oncoming Atmospheric Boundary Layer (ABL) airflows under neutral stability conditions. In addition to measuring the power output performance of DRWT and SRWT models, static and dynamic wind loads acting on those turbine models were also investigated. Furthermore, a high resolution digital particle image velocimetry (PIV) system was used to quantify the flow characteristics in the near wakes of the DRWT and SRWT models. The detailed wake flow measurements were correlated with the power outputs and wind load measurement results of the wind turbine models to elucidate the underlying physics to explore/optimize design of wind turbines for higher power yield and better durability.
Local Heat and Mass Transfer Characteristics for Multi-Layered Impingement/Effusion Cooling
Authors: Kim Seon Ho , Ahn Kyeong Hwan , Park Jun Su , Jung Eui Yeop , Hwang Ki-Young , Cho Hyung Hee
Published: August 2015

Multi-layered impingement/effusion cooling is an advanced cooling configuration that combines impingement jet cooling, pin cooling, and effusion cooling. The arrangement of the pins is a critical design factor because of the complex heat transfer in the internal structure. Therefore, it is important to measure the local heat transfer at all internal surfaces as a function of the pin spacing. In this study, a naphthalene sublimation method was employed to measure the details of the heat/mass transfer at the internal surfaces, including the injection plate, effusion plates, and the pins. An staggered array of holes was formed at the injection plate and effusion plates where the ratio of the height to the diameter of the pins, h/d, was fixed at 0.25. The ratio of the pin spacing to the diameter, sp/d, was varied in the range 1.5≤sp/d≤6, and the Reynolds number based on the hole diameter was 3000. As a result, a vortex ring formed near the pin, leading to re-impingement flows in the narrow channel. The jet flow impinged strongly on the pin, resulting in a large heat transfer region at each surface. The total average Sherwood number with sp/d=1.5 was larger than that with sp/d=6 by a factor of 1.5.
Effect of Unsteady Wakes on Local Heat Transer of 1st Stage Blade Endwall
Authors: Choi Seok Min , Park Jun Su , Chung Heeyoon , Chang Byung Moon , Cho Hyung Hee
Published: August 2015

We investigated the local heat and mass transfer on the endwall surface at different Strouhal numbers. The Strouhal number represents the interaction between the turbine stator and rotor. Thus, characteristics of flow and heat transfer on the endwall surface change for different Strouhal numbers. The experiment was performed in five-bladed linear cascade blades with moving cylindrical rods simulating unsteady wakes effects. The Reynolds number which was based on the blade cord length and inlet velocity was 100,000. The range of the Strouhal number varies from 0 to 0.22 to investigate the effect of unsteady wakes on the endwall surface. The local heat and mass transfer were measured on the endwall surface using the naphthalene sublimation method. The results showed that the local heat transfer characteristics changed depending on the Strouhal number. In the steady case, the occurrence of a horseshoe vortex, passage vortex and corner vortex caused non-uniform heat transfer on the endwall surface. However, in the unsteady case, the unsteady wake effect caused more uniform heat transfer on the endwall surface. As the Strouhal number increased, heat transfer increased and became more uniform compared with the steady case. Thus, an appropriate cooling system is necessary for stator and rotor endwalls in situations of real gas turbine operation.
Experimental Study of Stream-Wise Vortex Formation on Swept Circular Cylinders in Cross-Flow
Authors: Allan W. D. E. , Gostelow J. P. , Hogg Simon I.
Published: August 2015

A series of experiments has been undertaken on a swept cylinder in cross-flow in the 2m2 open-jet wind-tunnel at Durham University, at a nominal Reynolds Number of 500,000. Boundary layer instability, leading to transition has been attributed to curious sheets of stream-wise vortices on turbomachinery blades and other airfoils. Cylinders in cross-flow can be scaled to model such flows. Empirical analysis of stream-wise vortex pair spacing on cylinders was proposed in 1970 and various researchers have produced experimental data sets at various Reynolds Numbers and sweep ranges. Oil flow visualization was conducted in this work, the goal of which was to fill an important gap in experimental results, a gap of significance to turbine blade designers amongst others. In this test campaign, clear evidence of stream-wise vortices was exposed, the wavelengths of which compared well with the experimental results of others and with theory, although interesting departures were observed at high sweep angles. A physical explanation for the formation of the vortex and pair spacing, particularly at higher sweeps, is proposed.
Large Eddy Simulation of the Ignition Performance in a Lean Burn Combustor
Authors: Qiao Yingjie , Mao Ronghai , Lin Yuzhen
Published: August 2015

The ignition performance is a crucial issue for combustor design, especially when lean burn technologies are employed to reduce the NOx emission. Ignition is the initiation of a flame kernel followed by flame propagation and global establishment. The initiation of flame kernel is beyond the scope of this paper because it involves plasma formation process. The present investigation is mainly focused on flame front propagation which is modeled by solving a transport equation of reaction progress variable. Large eddy simulation (LES) with flamelet model has been employed to study the effect of various spark location under engine start condition. The numerical approach is validated by ignition experiments with turbulent bluff-body burner conducted by Ahmed and Mastorakos in Cambridge University. Mean and transient characteristics of velocity, mixture fraction and flame structures are compared with experimental data, to assess the accuracy of simulation in terms of flow structure, turbulent mixing and combustion performances. The validated LES model is then applied to study a series of physical locations of the spark plug in a single dome combustor. Successful and unsuccessful ignition sequences, time evolution of velocity and fuel/air ratio (FAR) of selected spots are recorded. Comparing the unsuccessful ignition with the successful ones, whether flame kernel enters into the CRZ and ignites the flammable mixture is a critical process which determines successful ignition. The evolution of flame kernel is correlated to flow field and fuel/air distribution to further analyze their effects on the ignition process. Since the process is highly transient, successful ignition is not only determined by parameters of spark location, but also influenced by the parameters throughout the flow path during flame propagation.
Numerical Study of the Film Cooling With Discrete-Hole Arrangement on a Cut Back Squealer Blade Tip
Authors: Zhang Xiang , Yang Zhong , Tian Shuqing , Ma Haiteng
Published: August 2015

Detailed numerical investigations of film cooling effectiveness are conducted for the holes on the tip cavity floor and near the tip pressure side. The tested blade tip is a squealer with the trailing rim wall cut to allow the accumulated coolant in the cavity to escape and cool the trailing edge. The heat transfer coefficients on the un-cooled flat and cutback squealer blade tip are studied with numerical and experimental methods. Three dust purging holes with different diameters are arranged along the camber line, which forms the basic cooled case (PG case). Additional six tip cavity holes are arranged on cavity floor near the suction side rim (PG-TF case). Another row of angled twenty-one holes is arranged along the pressure side just below the tip based on the PG case (PG-PSF case). The coolant supply pressure ratios are controlled to be 1, 1.11, and 1.22 respectively, offering local blowing ratio from 0 to 2.5. Results show that the dust purging flow cooling performance increases with the cavity depth. Discrete holes on the cavity floor offer a well-distributed coolant, which refines the cooling effect on the cavity floor. The PG-PSF case with cooling holes on the pressure side has the best overall cooling performance with more coolant consumed, when PR ≥ 1.22. However, maintaining the same coolant mass flow the PG-TF case has the best cooling performance, and the margin between PG-TF and PG-PSF case decreases with mass flow. The moving shroud cases reveal that blade movement will cause significant negative impacts on film cooling effectiveness.
Passive Control of Thermo-Acoustic Instability in Different Length Combustors Using a High-Strength Metallic Porous Insert
Authors: Kornegay John , Depperschmidt Daniel , Agrawal Ajay K.
Published: August 2015

Although lean premixed combustion (LPM) is very clean and basically soot-free, it has one serious drawback, i.e., tendency to develop thermo-acoustic instabilities. These instabilities can be very violent, at the least causing unwanted noise and vibration, and in more serious cases, complete engine failure. Current research has shown methods to address such instabilities using passive and active mitigation techniques. In this study, thermo-acoustic instabilities in a swirl-stabilized LPM combustion system are mitigated using a high-strength metallic porous insert fabricated by a 3D additive manufacturing technique. Although the technique has been demonstrated in our previous studies, the present focus is to utilize a given porous insert geometry to mitigate thermo-acoustic instabilities in different length combustion chambers producing different resonant frequencies, to overcome the typical limitation of passive techniques. For each combustor length, experiments are conducted over a range of equivalence ratios and reactant flow rates. In all cases, porous insert was effective in significantly reducing the sound pressure level (SPL) at the frequency of the instability, with reductions of 20 dB and higher. Time-resolved particle image velocimetry (PIV) measurements are acquired to describe flow and turbulence fields in the combustor without and with porous insert. Proper orthogonal decomposition (POD) analysis is used to quantify the energy content of turbulent modes, and harmonic reconstruction is performed to illustrate the dramatic changes in the oscillatory flow field when the porous insert is used. The ability of the porous insert to adjust to different geometric and operating conditions of the combustor is a unique capability, inherent to its fundamental operating principle.
Prediction of Burst Pressure in Multi Stage Tube Hydroforming of Aerospace Alloys
Authors: Saboori M. , Gholipour J. , Champliaud H. , Gakwaya A. , Savoie J. , Wanjara P.
Published: August 2015

Bursting, an irreversible failure in tube hydroforming (THF), results mainly from the local plastic instabilities that occur when the biaxial stresses imparted during the process exceed the forming limit strains of the material. To predict the burst pressure, Oyane’s and Brozzo’s decoupled ductile fracture criteria were implemented as user material models in a dynamic nonlinear commercial 3D finite element (FE) software, Ls-Dyna. THF of a round to V-shape was selected as a generic representative of an aerospace component for the FE simulations and experimental trials. To validate the simulation results, THF experiments up to bursting were carried out using Inconel 718 (IN 718) tubes with a thickness of 0.9 mm to measure the internal pressures during the process. When comparing the experimental and simulation results, the burst pressure predicated based on Oyane’s decoupled damage criterion was found to agree better with the measured data for IN 718 than Brozzo’s fracture criterion.
A Study of Performance and Flow Mechanism of a Slot-Groove Hybrid Casing Treatment in a Low-Speed Compressor
Authors: Du Juan , Li Fan , Li Jichao , Ma Ning , Lin Feng , Chen Jingyi
Published: August 2015

A “slot-groove” hybrid casing treatment (CT) is proposed elicited from the recent research on the role of axial location for stall margin improvement (SMI). This combination is expected to display the advantages of both slots and grooves while minimizing their disadvantages. A comparative study is conducted among the “slot-groove”, traditional circumferential groove CT (called the “full-groove” CT) and axial skewed slot CT (known as the “full-slot” CT) to evaluate performance and to explore the stability enhancement and efficiency loss mechanisms of the “slot-groove” CT in a low-speed axial compressor. Results of the combination of laboratory tests and computational fluid dynamics (CFD) data demonstrate that the performance level of the hybrid CT lies in between those two traditional CTs. Simulation results indicate that the difference in the SMIs generated by CTs is closely related to their influences on the vortex trajectory of tip leakage. The stronger and tighter the vortex is, the more the vortex trajectory is inclined toward the blade suction side. Consequently, the interface between tip leakage flow and incoming main flow is pushed downstream and stability is enhanced. The flow loss induced by CTs is explored based on the entropy contours, and the high entropy in the “slot-groove” treated casing produces more efficiency decrease than the “full-groove” CT. Incorporating the “full-slot” CT not only increases entropy generation in the axial skewed slots but also induces considerable flow loss in the blade passage near the casing, thus reducing efficiency most significantly.
NOx Emissions Modeling and Uncertainty for Exhaust-Gas-Diluted Flames
Authors: Lipardi Antonio C. A. , Bergthorson Jeffrey M. , Bourque Gilles
Published: August 2015

Oxides of nitrogen (NOx) are pollutants emitted by combustion processes during power generation and transportation that are subject to increasingly-stringent regulations due to their impact on human health and the environment. One NOx reduction technology being investigated for gas-turbine engines is exhaust gas recirculation (EGR), either through external exhaust-gas recycling or staged combustion. In this study, the effects of different percentages of EGR on NOx production will be investigated for methane-air and propane-air flames at a selected adiabatic flame temperature of 1800K. The variability and uncertainty of the results obtained by the Gri-Mech 3.0, San-Diego 2005, and the CSE thermochemical mechanisms are assessed. It was found that that key parameters associated with postflame NO emissions can vary up to 192% for peak CH values, 35% for thermal NO production rate, and 81% for flame speed, depending on the mechanism used for the simulation. A linear uncertainty analysis, including both kinetic and thermodynamic parameters, demonstrates that simulated post-flame nitric oxide levels have uncertainties on the order of ±50–60%. The high variability of model predictions, and their relatively-high associated uncertainties, motivates future experiments of NOx formation in exhaust-gas-diluted flames under engine-relevant conditions to improve and validate combustion and NOx design tools.
Bump-Type Foil Bearings and Flexure Pivot Tilting Pad Bearings for Oil-Free Automotive Turbochargers: Highlights in Rotordynamic Performance
Authors: Ryu Keun , Ashton Zachary
Published: August 2015

Oil-free turbochargers require gas bearings in compact units of enhanced rotordynamic stability, mechanical efficiency, and improved reliability with reduced maintenance costs compared with oil-lubricated bearings. Implementation of gas bearings into automotive turbochargers requires careful thermal management with accurate measurements verifying model predictions. Foil bearings are customarily used in oil-free microturbomachinery because of their distinct advantages including tolerance to shaft misalignment and centrifugal/thermal growth, and large damping and load capacity compared with rigid surface gas bearings. Flexure pivot tilting pad bearings are widely used in high performance turbomachinery since they offer little or no cross-coupled stiffnesses with enhanced rotordynamic stability. The paper details the rotordynamic performance and temperature characteristics of two prototype oil-free turbochargers; one supported on foil journal and thrust bearings and the other one is supported on flexure pivot tilting pad journal bearings and foil thrust bearings of identical sizes (OD and ID) with the same aerodynamic components. The tests of the oil-free turbochargers, each consisting of a hollow rotor (∼0.4 kg and ∼23 mm in outer diameter at the bearing locations), are performed for various imbalances in NVH (i.e, cold air driven rotordynamics rig) and gas stand test facilities up to 130 krpm. No forced cooling air flow streams are supplied to the test bearings and rotor. The measurements demonstrate the stable performance of the rotor-gas bearing systems in an ambient NVH test cell with cold forced air into the turbine inlet. Posttest inspection of the test flexure pivot tilting pad bearings after the hot gas stand tests evidences seizure of the hottest bearing, thereby revealing a notable reduction in bearing clearance as the rotor temperature increases. The compliant flexure pivot tilting pad bearings offer a sound solution for stable rotor support only at an ambient temperature condition while demonstrating less tolerance for shaft growth, centrifugal and thermal, beyond its clearance. The current measurements give confidence in the present gas foil bearing technology for ready application into automotive turbochargers for passenger car and commercial vehicle applications with increased reliability.
Roughness Effects on Flow and Heat Transfer for Additively Manufactured Channels
Authors: Stimpson Curtis K. , Snyder Jacob C. , Thole Karen A. , Mongillo Dominic
Published: August 2015

Recent technological advances in the field of additive manufacturing (AM), particularly with direct metal laser sintering (DMLS), have increased the potential for building gas turbine components with AM. Using DMLS for turbine components broadens the design space and allows for increasingly small and complex geometries to be fabricated with little increase in time or cost. Challenges arise when attempting to evaluate the advantages of DMLS for specific applications, particularly because of how little is known regarding the effects of surface roughness. This paper presents pressure drop and heat transfer results of flow through small, as produced channels that have been manufactured using DMLS in an effort to better understand roughness. Ten different coupons made with DMLS all having multiple rectangular channels were evaluated in this study. Measurements were collected at various flow conditions and reduced to a friction factor and a Nusselt number. Results showed significant augmentation of these parameters compared to smooth channels, particularly with the friction factor for mini-channels with small hydraulic diameters. However, augmentation of Nusselt number did not increase proportionally with the augmentation of the friction factor.
The Effect of Rib Turbulators on Film Cooling Effectiveness of Round Compound Angle Holes Fed by an Internal Cross-Flow
Authors: Klavetter Sean R. , McClintic John W. , Bogard David G. , Dees Jason E. , Laskowski Gregory M. , Briggs Robert
Published: August 2015

Early stage gas turbine blades feature complicated internal geometries in order to enhance internal heat transfer and to supply coolant for film cooling. Most film cooling experiments decouple the effect of internal coolant feed from external film cooling effectiveness, even though engine parts are commonly fed by cross-flow and feature internal rib turbulators which can affect film cooling. Experiments measuring adiabatic effectiveness were conducted to investigate the effects of turbulated perpendicular cross-flow on a row of 45° compound angle cylindrical film cooling holes for a total of eight internal rib configurations. The ribs were angled to the direction of prevailing internal cross-flow at two different angles: 45° or 135°. The ribs were also positioned at two different span-wise locations relative to the cooling holes: in the middle of the cooling hole pitch, and slightly intersecting the holes. Experiments were conducted at a density ratio of DR = 1.5 for a range of blowing ratios including M = 0.5, 0.75, 1.0, 1.5, and 2.0. This study demonstrates that peak effectiveness can be attained through the optimization of cross-flow direction relative to the compound angle direction and rib configuration, verifying the importance of hole inlet conditions in film cooling experiments. It was found that ribs tend to reduce adiabatic effectiveness relative to a baseline, smooth-walled configuration. Rib configurations that directed the internal coolant forward in the direction of the mainstream resulted in higher peak adiabatic effectiveness. However, no other parameters could consistently be identified correlating to increased film cooling performance. It is likely that a combination of factors is responsible for influencing performance, including internal local pressure caused by the ribs, the internal channel flow field, in-hole vortices, and jet exit velocity profiles. This study also attempted to replicate the possibility that film cooling holes may intersect ribs and found that a hole which partially intersects a rib still maintains moderate levels of effectiveness.
Investigation on Acoustic Resonance for Different Diffuser and Effect on Centrifugal Compressor Pipeline Failure
Authors: Li Hongkun , Zhang Xiaowen , Liu Yan , Xu Fujian , Zhou Shuai
Published: August 2015

Acoustic resonance (AR) can lead to pipeline or blade fatigue for centrifugal compressor. It must be considered during design. But investigation in this area is very limit, especially for the lack of experiment verifications. In this research, acoustic mode simulation analysis is investigated on three different diffusers for the same centrifugal compressor by LMS Acoustics calculation software. Meanwhile, pressure pulsation (PP) experiment is carried out to verify the correctness about AR calculation. The PP level will increase typically when the blade passing frequency (BPF) is close to the acoustic modal frequency for full-height vaned diffuser. Then, the modified diffuser for half-height vaned and vaneless are applied at the same test-bench and the results show PP level is obvious decreased. In other words, by changing the structure of diffuser could effectively avoid AR. Finally, the above results applied in the field of failure compressor unit could obviously reduce the level of high frequency vibration. This research reveals the failure mechanism for pipeline, and introduce an effective method to avoid AR. It can contribute to blade condition monitoring and the prohibition failure of centrifugal compressor.
Static Structural Characterization of Multilayer Gas Foil Journal Bearings
Authors: Kim Tae Ho , Lee Jongsung , Kim Young Min
Published: August 2015

The aim of this study was to evaluate the structural performance of multilayer gas foil bearings (GFBs). Three test GFBs and a dummy rotor with a diameter of 28 mm were manufactured for application to a series of structural tests. The test bearings were designed with an identical axial length of 22.5 mm, a radial clearance of 0.170 mm, and a mechanical preload of 0.050 mm at a 50% offset within the (machined) lobe bearing housings. All the bearings had multilayer (doublelayer) thin foils supported by an elastic bump strip layer, i.e., a configuration with a top foil, shim foil, and bump strip layer. Note that the shim foil is installed between the top foil and bump strip layer to enhance the dry-friction damping effect. The first bearing (Type A) had a single top foil, single shim foil, and single bump strip layer. All had an arc length of 360°. The second version (Type B) had a single top foil with an arc length of 360°, three shim foils with an arc length of 120°, and three bump strip layers with an arc length of 120°. The third version (Type C) had three top foils, three shim foils, and three bump strip layers. All had an arc length of 120°. The top foil is spot-welded to a key that is inserted into an axial key slot in the bearing housing. The shim foil and bump strip layer are inserted into an axial foil slot in the bearing housing. A series of static load-deflection tests were conducted on the test GFBs floating on the fixed, non-rotating test rotor. The measured results for the bearing deflection and structural stiffness were found to be in very good agreement with the model predictions for a GFB with a mechanical preload. In general, the test results were found to exhibit a similar radial sway space (or assembly radial clearance) and structural stiffness for all three test GFBs. Small local hysteresis loops appeared as the magnitudes of the load increased, thus determining the local structural stiffness and structural loss factor versus the displacement. The local stiffness was found to increase while the loss factor decreased as the magnitude of the displacement increased. The estimated structural loss factor can be as large as 0.9 within the radial sway space under low-load conditions.
A Dynamic RCM Analysis Method for Natural Gas Compressor Station Based on Diagnostic and Prognostic Technology
Authors: Zhou Dengji , Zhang Huisheng , Li Yi-Guang , Weng Shilie
Published: August 2015

The availability requirement of natural gas compressors is high. Thus, current maintenance architecture, combined periodical maintenance and simple condition based maintenance, should be improved. In this paper, a new maintenance method, Dynamic Reliability-centered Maintenance (DRCM), is proposed for equipment management. It aims at expanding the application of Reliability-centered Maintenance (RCM) in maintenance schedule making to preventive maintenance decision making online and seems suitable for maintenance of natural gas compressor stations. A decision diagram and a maintenance model are developed for DRCM. Then three application cases of DRCM for actual natural gas compressor stations are shown to validate this new method.
A Mechanism-Based Approach From Low Cycle Fatigue to Thermomechanical Fatigue Life Prediction
Authors: Wu Xijia , Zhang Zhong
Published: August 2015

Deformation and damage accumulation occur by fundamental dislocation and diffusion mechanisms. An integrated creep-fatigue theory (ICFT) has been developed, based on the physical strain decomposition rule that recognizes the role of each deformation mechanism and thus relate damage accumulation to its underlying physical mechanism(s). The ICFT formulates the overall damage accumulation as a holistic damage process consisting of nucleation and propagation of surface/subsurface cracks in coalescence with internally distributed damage/ discontinuities. These guiding principles run through both isothermal low cycle fatigue (LCF) and thermomechanical fatigue (TMF) under general conditions.

This paper presents a methodology using mechanism-based constitutive equations to describe the cyclic stress strain curve and the non-linear damage accumulation equation incorporating i) rate-independent plasticity-induced fatigue, ii) intergranular embrittlement, iii) creep and iv) oxidation to predict LCF and TMF lives of ductile cast iron (DCI). The complication of the mechanisms and their interactions in this material provide a good demonstration case for the model, which is in good agreement with the experimental observations.
Modeling of Emissions in a Laboratory Swirl Combustor
Authors: Katta Viswanath R. , Roquemore William M.
Published: August 2015

A swirl-stabilized combustor utilizes recirculation zones for stabilizing the flame. The performance of such combustors could depend on the fuel used as the cracked fuel products may enter the recirculation-zones and alter their characteristics. A numerical study is conducted for understanding the effects of fuel variation on the combustion and unburned-hydrocarbon-emission characteristics of a laboratory swirl combustor. A time-dependent, detailed-chemistry CFD model UNICORN is used. Six binary fuel mixtures formulated with n-dodecane and n-heptane, m-xylene, iso-octane or hexadecane are considered. A semi-detailed chemical-kinetics model (CRECK-0810) involving 206 species and 5652 reactions for the combustion of these fuels is incorporated into UNICORN code. Calculations are performed for a fuel-lean condition, which represents cruise operation of an aircraft. Combustor flows simulated with different fuel mixtures yielded nearly the same flowfields and flame structures. Production of the intermediate cracked fuel species that are key for the final flame structure and emissions seems to be independent of the fuel used. This finding could greatly simplify the detailed chemical kinetics used for obtaining cracked products. As the cracked fuel species are completely consumed with in the flame zone, no emissions are observed at the combustor exit for the considered fuel-lean condition.
Design Space of Foil Bearings for Closed Loop Supercritical CO2 Power Cycles Based on Three-Dimensional Thermo-Hydrodynamic Analyses
Authors: Kim Daejong
Published: August 2015

The closed loop Brayton cycle with super critical CO2 (S-CO2) as an operating fluid is an attractive alternative to conventional power cycles due to very high power density. Foil gas bearings using CO2 is the most promising for small S-CO2 turbomachinery but there are many problems to address; large power loss due to high flow turbulence, lack of design/analysis tool due to non-ideal gas behavior, and lack of load capacity when they are used for large systems.

This paper presents high level design/analysis tool involving three-dimensional thermo-hydrodynamic analyses of radial foil bearings considering real gas effect and flow turbulence inside the film. Simulations are performed for radial foil bearing with 34.9mm in diameter lubricated with CO2 and N2 under various ambient conditions up to above 40 bar gauge pressure. The simulation results using the turbulence model still under-predict the measured data in open literature. However, the error between the prediction and measurements decreases as either speed or ambient pressure increases. In addition, general behavior of substantial increase in power loss with ambient pressure agrees with the measured data. The simulation results indicate the importance of detailed THD analysis of the foil bearings for prediction of power loss under severe turbulent condition.

A conceptual layout of rotor system for 10MWe S-CO2 loop is also presented along with realistic rotor weight and bearing load. A hybrid foil bearings with diameter of 102mm is suggested for gas generator rotor, and its power losses and minimum film thicknesses at various operating conditions are presented.
CFD Analysis of Steam Turbines With the IAPWS Standard on the Spline-Based Table Look-Up Method (SBTL) for the Fast Calculation of Real Fluid Properties
Authors: Kunick Matthias , Kretzschmar Hans-Joachim , di Mare Francesca , Gampe Uwe
Published: August 2015

Accurate simulations of non-stationary processes in steam turbines by means of Computational Fluid Dynamics (CFD) require precise and extremely fast algorithms for computing real fluid properties. To fulfill these requirements, the International Association for the Properties of Water and Steam (IAPWS) issues the “Guideline on the Fast Calculation of Steam and Water Properties with the Spline-Based Table Look-Up Method (SBTL)” as an international standard. Through the use of this method, spline functions for the independent variables specific volume and specific internal energy (v,u) are generated for water and steam based on the industrial formulation IAPWS-IF97. With these spline functions, thermodynamic and transport properties can be computed. The desired backward functions of the variables pressure and specific volume (p,v), and specific internal energy and specific entropy (u,s) are numerically consistent with the spline functions from (v,u). The properties calculated from these SBTL functions are in agreement with those of IAPWS-IF97 within a maximum relative deviation of 10 to 100 ppm depending on the property and the range of thermodynamic states spanned under the given conditions (range of state). Consequently, the differences between the results of process simulations using the SBTL method and those obtained through the use of IAPWS-IF97 are negligible. Moreover, the computations from the (v,u) spline functions are more than 200 times faster than the iterative calculations with IAPWS-IF97.

In order to demonstrate the efficiency and applicability of the SBTL method, the SBTL functions have been implemented into the CFD software TRACE, developed by the German Aerospace Center (DLR). As a result, the computing times required for the simulations of steam flow in a turbine cascade considering real fluid behavior are reduced by a factor of 6–10 in comparison to the calculations based on IAPWS-IF97. Furthermore, computing times are increased by a factor of 1.4 only with respect to CFD calculations where steam is considered to be an ideal gas, through the use of the SBTL method.
Multi-Objective Optimization of a Regenerative Rotorcraft Powerplant: Quantification of Fuel Economy and Environmental Impact
Authors: Ali Fakhre , Tzanidakis Konstantinos , Goulos Ioannis , Pachidis Vassilios , d’Ippolito Roberto
Published: August 2015

A computationally efficient and cost effective simulation framework has been proposed to perform a multidisciplinary design and optimization of a conceptual regenerative rotorcraft powerplant configuration at mission level. A generic rotorcraft model, representative of a modern twin-engine light civil rotorcraft has been investigated, operating under a representative passenger air taxi mission. The design space corresponding to the conceptual regenerative engine thermodynamic cycle parameters as well as engine and mission design outputs in terms of low pressure compressor pressure ratio, high pressure compressor pressure ratio, turbine entry temperature, mass flow, heat exchanger effectiveness, engine design point specific fuel consumption, engine weight, mission fuel burn and mission CO2 and NOx emissions has been thoroughly investigated through the application of a latin hypercube sampling, design of experiment approach. The interdependencies between the various engine design inputs/outputs are quantified by establishing the corresponding linear correlations between the aforementioned engine inputs/outputs as well as for the corresponding mission output parameters. A multi-objective Particle Swarm Optimizer is employed to derive Pareto front models quantifying the optimum interrelationship between the mission fuel burn and NOx emissions inventory. The acquired engine cycle design parameters corresponding to the span of the Pareto front suggest that the heat exchanger design effectiveness is the key design parameter representing the interdependency between engine fuel economy and environmental impact. The acquired optimum engine models, obtained from the Pareto front, are subsequently deployed for the design of conceptual rotorcraft engine configurations, targeting improved mission fuel economy, enhanced payload-range capability and overall environmental impact.
FMECA on Rotating Equipment Preservation for Idle LNG Plant
Authors: Hutagalung Frilo Fitrasali
Published: August 2015

An LNG Plant or any Petrochemical Plant was constructed on the basis of discovered feed gas with full scale capacity. As the feed gas has decreased, the plant capacity is required to be put in idle or mothball mode. In that period, the plant facilities have to be preserved and inspected to maintain the integrity. The static and rotating equipment, electrical equipment, and instrumentations need to be maintained. The focus in this paper is how to preserve the rotating equipment. Since they always have clearances between rotating part and stationary part, nitrogen containment only is not always adequate to preserve the internal parts.

Failure Mode Effect and Criticality Analysis (FMECA) is one of the tools to define how to preserve rotating equipment. The analysis considers the following essential factors: duration of idle period, equipment functions, equipment mode of failures, preservation method, test convenience, cost of consequence, and safety.

This paper takes the case of FMECA of one of the LNG Process Train in Badak LNG that has undergone idle period. Rotating equipment consists of Steam Turbines, Centrifugal Gas Compressors, LNG Pumps, Hydrocarbon Pumps, High Speed Pumps, Lube Oil Pumps, and Fin Fans. The evaluation is down to its auxiliary parts such as Mechanical Seal, Bearing, and Hydraulic Governors.

The FMECA study also defines criticality of equipment in the frame of future as the idle period has ended. Rotating equipment may have issues on corrosion and performance. One possibility is whether the equipment or its internal parts (such as rotors, diaphragms, etc) need to be removed from site to storage or warehouse.

The criticality also considers the mode of operation of the equipment and their fluid services. This case study presents evaluation of following fluid services: High Pressure Steam, Medium Pressure Steam, Low Pressure Steam, Lubricating Oil, Amine, Natural Gas, Liquefied Petroleum Gas (LPG), and Liquefied Natural Gas (LNG).

As the result of FMECA study, the facility has to be preserved in specific methods and measures based on the period of idle. The method provides recommendation of preservation treatment, storage specification, testing requirement, product lifecycle study. The methods and measures performed during idle period are expected to maintain the facility integrity when it needs to be in operation again.
Brush Seal Structural Analysis and Correlation With Tests for Turbine Conditions
Authors: Duran E. Tolga , Aksit Mahmut F. , Ozmusul Murat
Published: August 2015

Bristle tip contact forces and resulting stress levels under engine conditions are critical to optimizing brush seal performance as well as to achieving operational safety. Literature survey reveals the lack of test data and analysis methods for evaluating seal stiffness and stress levels under operating conditions. In an attempt to meet this need, a custom test rig design and methodology has been developed to perform stiffness tests under pressure and rotor speed of 3000 rpm. Finite element simulations have been performed for brush seals and results have been correlated with the test data of this study. Considering the critical importance of contact loads on brush seal overall performance and system health, and due to the complicated structure of brush seals, where bristles are contacting with each other as well as with the backing plate and the rotor, CAE analyses with high fidelity is required to simulate the test and turbine operating conditions. For this purpose, FE methodology has been developed for structural analyses of brush seals. 3D finite element models of brush seals have been constructed and simulations have been performed for pressurized rotor-rub conditions. CAE model of brush seals includes rotor-bristle, bristle pack-backing plate and inter-bristle contacts with friction. Simulations with non-rotating rotor and transient analyses with rotating rotor have been conducted, and the extracted bristle tip force levels are correlated with the test results. Inertial effects during dynamic tests have also been simulated through transient analyses and results show good agreement with the dynamic test data. Displacement and stress profiles obtained from correlated FE models give better understanding of brush seal behavior under turbine operating conditions.
Brush Seal Free State Stiffness Analyses, Tests and Inspection on Dynamic Effects
Authors: Duran E. Tolga , Aksit Mahmut F. , Ozmusul Murat
Published: August 2015

While the efficiency of a brush seal is measured by its leakage rate, the overall performance of the seal is mostly affected by wear rate and durability. Seal stiffness and hysteresis behavior play important roles in determining the leakage performance and rotor stability due to the fact that they directly affect wear rates and pressure load capacity of the seal. The complicated nature of the bristle, rotor and backing plate interactions at typical operating conditions makes it difficult to determine the stiffness and durability of brush seals. In this study, test and computer aided engineering (CAE) methodologies have been developed to simulate brush seal stiffness and stress levels at unpressurized conditions. Unpressurized stiffness tests have been conducted by using two different test rigs, one of which uses a simple metallic pad and the other one uses a full-sized rotor for seal interference measurements. Test results for the two different rigs have been compared and the drawbacks of the simple stiffness test rig have been detailed in this study. CAE analyses at unpressurized conditions have been conducted by using 3D finite element (FE) models, and analyses have been correlated with the stiffness tests. The influence of rotor rotation has also been analyzed at unpressurized seal conditions. Transient simulation results also demonstrated good agreement with the dynamic stiffness tests of the brush seals.
Harmonic Convergence Estimation Through Strain Energy Superconvergence
Authors: Kaszynski Alexander A. , Beck Joseph A. , Brown Jeffrey M.
Published: August 2015

Grid convergence in finite element analysis, despite a wide variety of tools available to date, remains an elusive and challenging task. Due to the complex and time consuming process of remeshing and solving the finite element model (FEM), convergence studies can be part of the most arduous portion of the modeling process and can even be impossible with FEMs unassociated with CAD. Existing a posteriori methods, such as relative error in the energy norm, provide a near arbitrary indication of the model convergence for eigenfrequencies. This paper proposes a new approach to evaluate the harmonic convergence of an existing model without conducting a convergence study. Strain energy superconvergence takes advantage of superconvergence points within a FEM and accurately recovers the strain energy within the model using polyharmonic splines, thus providing a more accurate estimate of the system’s eigenfrequencies without modification of the FEM. Accurate eigenfrequencies are critical for designing for airfoil resonance avoidance and mistuned rotor response prediction. Traditional error estimation strategies fail to capture harmonic convergence as effectively as SES, potentially leading to a less accurate airfoil resonance and rotor mistuning prediction.
A-10 Wing Leading Edge Effects on Engine Stability: Part 1 — Analysis and Evaluation of Wing Leading Edge Configurations
Authors: Patterson Grant T. , Binkley Brian A. , Jenkins Jerome C.
Published: August 2015

The A-10 aircraft has fuselage mounted engines with inlets just above the rear of the wing. The A-10 employs a deployable slat system to delay wing stall directly in front of the engines. Wing stall can lead to high inlet distortion and ultimately engine stall for this aircraft. To enhance overall performance of the A-10 Close Air Support Aircraft, wing leading-edge designs that do not employ slats were considered. Fifteen potential wing leading-edge proposals including drooped wings, wings with fences, wings with vortex generators, an optimized slat and a specially designed wing were evaluated through test and analysis for replacing the A-10 slat system. The performance of the wing leading-edge candidates were characterized by their inlet engine distortion effect on the loss of stability pressure ratio (ΔPRS) on the TF-34 engine fan and compressor. The drooped wings or “droops” were designated by the amount of droop in a percent of chord. Droops tested were 3, 5, 7, 10, and 10-5% twisted (5% outboard, 10% inboard). The 7, 10, and 10-5% droops were tested with outboard fences. The 10% droop and designed wing were tested with vortex generators. The paper discusses the previous work and technical basis for selecting the wing leading edge candidates, the analysis tools and techniques, the test and analysis of the candidate configurations, the overall effectiveness of the best candidate.
Overview of A-10 Propulsion Analysis Using the HPCMP Create™-AV Kestrel Product With Firebolt Propulsion Component
Authors: Klepper Jason B. , Denny A. Greg , Nichols Robert H. , Jenkins Jerome C.
Published: August 2015

The High Performance Computing Modernization Program (HPCMP) is developing high-fidelity simulation tools through the Computational Research and Engineering Acquisition Tools and Environments (CREATE™) program. CREATE-AV is the component of the CREATE program focused on air vehicles. Kestrel is the simulation product for fixed-wing aircraft in the CREATE-AV program. To investigate engine/inlet system performance and operability issues, the Kestrel product includes the capability to model propulsion components in aircraft simulations through the Firebolt propulsion component. Firebolt Capability 1 accounts for propulsion system effects by integrating a 0-D engine model directly into the computational fluid dynamics (CFD) process. Firebolt Capability 2 extends the capability by enabling the user to couple full-annulus 3-D rotating turbomachinery into the aircraft CFD simulation. This paper gives an overview of the Kestrel product including the Firebolt propulsion capability. In addition, this paper will demonstrate Firebolt Capability 1 and 2 by applying a 0-D TF34-GE-100A engine model and a TF34 3-D full annulus rotating turbomachinery fan in an A-10 aircraft CFD simulation. Finally, the inlet performance for the nacelles with both the 0-D engine model and full-annulus turbomachinery fan will be compared to subscale wind tunnel inlet test data.