bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Turbine Shroud Distortions on the Aerodynamics of a One and One-Half Stage High-Pressure Turbine
Authors: Crosh Eric A. , Haldeman Charles W. , Dunn Michael G. , Holmes D. Graham , Mitchell Brian E.
Published: February 2010

As part of a proactive effort to investigate the ability of computational fluid dynamic (CFD) tools to predict time-accurate surface-pressure histories, a combined experimental/computational investigation was performed examining the effect of rotor shroud (casing) out-of-roundness on the unsteady pressure loading for the blade row of a full-stage turbine. The casing out-of-roundness was idealized by designing a casing ring with a sinusoidal variation. This casing ring was used to replace a flat casing for an existing turbine and direct comparisons were made between the time-accurate pressure measurements and predictions obtained using the flat and “wavy” casings. For both casing configurations, predictions of the unsteady pressure loading for many locations on the blade and vane were obtained using Numeca’s FINE/Turbo code and the General Electric TACOMA code. This paper will concentrate on the results obtained for the “wavy” casing, but the results for the flat casing are presented as a baseline case. The time-accurate surface-pressure measurements were acquired for the vane and blade of a modern, 3-D, stage and 1/2 high-pressure turbine operating at the design corrected speed and stage pressure ratio. The research program utilized an un-cooled turbine stage for which all three airfoil rows are heavily instrumented at multiple spans to develop a full dataset. The vane-blade-vane count for this machine is 38-72-38. The number of waves in the distorted shroud “wavy wall” is approximately 1.5-times the number of vanes. The resulting changes in aerodynamic surface-pressure measurements were measurable at all blade span wise locations. Variations in time-average surface pressure of up to 5% of the flat casing values were observed. In addition, the frequency content of the time-resolved blade data for the “wavy” casing changed substantially from that measured using the flat casing, with changes in both amplitudes and frequencies. Imposing the casing irregularity changed the fundamental physics of the problem from a single frequency and its harmonics to a multi-frequency problem with mixed harmonics. The unsteady effects of this type of problem can be addressed using the harmonic method within Numeca’s FINE/Turbo code, which is designed to handle multiple blade passing frequencies and harmonics for one blade row. A more traditional approach is included in the paper by employing the TACOMA code in a linearized mode that produces results for a single frequency. These results show that casing irregularity can have a significant influence on the blade surface-pressure characteristics. Further, it is demonstrated that the FINE/Turbo code experienced difficulty predicting the unsteady pressure signal attributed to the “wavy” casing configuration, while at the same time capturing the unsteady signal attributed to the vane passing due to limitations in the current methodology.
The Dynamic Frictional Performance of Damping-Rings in Labyrinth Air Seal for Vibration Control
Authors: Zeng Liang , Li Lin
Published: February 2010

The application of damping-rings to rotor/stator components in aero-engine was proved effective in protecting labyrinth air seals and the cylindrical walls of annular chambers against flexural vibration and fatigue failures excited by various disturbing forces. In view of the possibility of resonance, determination of the vibration characteristics of the labyrinth air seals with damping-rings by theoretic model, experiment or both is of vital importance in the design and development procedure. This paper built up the equivalent linear model of interface between the seals and damping-rings by introducing the local contact stiffness, and then researched the forced response of labyrinth air seals with two types of damping-ring under single-point exciter with sine signal. The dynamic response experiments of the shell with different damping-rings verified the validity of the proposed simplified model and the simulation results. The influence of variable parameters, such as the width and installed position of damping-rings was also discussed. In the experiments the damping-ring showed the great effect in vibration control by friction damping and contact stiffness.
Performance Improvement of a Centrifugal Compressor Stage by Increasing Degree of Reaction and Optimizing Blade Loading of a 3D-Impeller
Authors: Shibata Takanori , Yagi Manabu , Nishida Hideo , Kobayashi Hiromi , Tanaka Masanori
Published: February 2010

Performance improvement of 3D impellers in a high specific speed range was investigated using computational fluid dynamics (CFD) analyses and experimental tests. In order to reduce the loss production within the stator passages, the backsweep angle of the impellers was increased. At the same time, the inlet-to-exit relative velocity diffusion ratio was also increased by increasing impeller exit width to prevent the reduction in pressure ratio. Moreover, the blade loading distribution at the impeller shroud side was optimized to suppress the surge margin reduction caused by the increased relative velocity diffusion ratio. Five types of unshrouded impellers were designed, manufactured and tested to evaluate the effects of blade loading, backsweep angle and relative velocity diffusion ratio on compressor performance. The design suction flow coefficient was 0.125 and the machine Mach number was 0.87. Test results showed that compressor stage efficiency was increased by 5% compared to the base design without reducing the pressure coefficient and surge margin. It was concluded that an increased relative velocity diffusion ratio coupled with large backsweep angle was a very effective way to improve compressor stage efficiency. An appropriate blade loading distribution was also important in order to achieve a wide operating range as well as high efficiency.
Duct Aerodynamics for Intercooled Aero Gas Turbines: Constraints, Concepts and Design Methodology
Authors: Walker A. Duncan , Carrotte Jonathan F. , Rolt Andrew M.
Published: February 2010

Economic and environmental concerns are a major driving force behind the development of aero gas turbine technology, with ever more stringent legislation dictating significant reductions in specific fuel consumption and pollutant emissions. Intercooling has long been of interest as it has the potential for lower compressor delivery and turbine cooling air temperatures, together with reduced NOx and higher overall pressure ratios, which enable reduced fuel consumption. However, thus far the technical complexities, both aerodynamic and mechanical, have been prohibitive. For example, improvements in core cycle thermal efficiency could easily be offset by reduced component efficiencies and pressure losses in the intercooler and its associated ducting. This paper describes an intercooled concept typical of those that may be used for a large, high by-pass ratio, high OPR aero-engine. The paper goes on to describe the aerodynamic challenges of designing a duct system to transfer the core air, issuing from the low pressure compressors, into the intercooler modules. A design methodology is developed which includes consideration of: system loss, the inclusion of local constraints such as a radial drive shaft, the need to provide core access for ancillary services, and minimization of aerodynamic interaction with surrounding components. Finally a preliminary duct design is presented for a specific intercooled aero-engine design.
Experimental and Numerical Analysis of Axial Skewed Slot Casing Treatments for a Transonic Compressor Stage
Authors: Danner Florian C. T. , Kau Hans-Peter , Mu¨ller Martin M. , Schiffer Heinz-Peter , Brignole Giovanni A.
Published: February 2010

An investigation of a single-stage transonic compressor with axial skewed slot casing treatments is presented. The studied compressor stage is characterised by a design mass flow rate of 16 kg/s at a total pressure ratio of 1.5 and a rotor tip speed of 400m/s. The research comprises experimental measurements as well as time-resolved simulations at full and part speed. Total pressure ratio measurements and efficiency speedlines are complemented by traversing downstream of the stator and static pressure measurements at the rotor end wall. The experimental work is supported by unsteady computational fluid dynamics analysis to provide further insight into the ruling flow phenomena. The simulations were carried out fully three-dimensionally in a computational domain with approximately 4.8 million grid points including the cavity mesh. The application of the axial skewed slots led to both, an enhanced operating range and an increased design point efficiency. Rises in total pressure ratio along the entire speed lines were observed.
Influence of Rim Seal Purge Flow on Performance of an Endwall-Profiled Axial Turbine
Authors: Schuepbach P. , Abhari R. S. , Rose M. G. , Gier J.
Published: February 2010

Non-axisymmetric endwall profiling is a promising method to reduce secondary losses in axial turbines. However, in high-pressure turbines, a small amount of air is ejected at the hub rim seal to prevent the ingestion of hot gases into the cavity between the stator and the rotor disk. This rim seal purge flow has a strong influence on the development of the hub secondary flow structures. This paper presents time-resolved experimental and computational data for a one-and-1/2-stage high work axial turbine showing the influence of purge flow on the performance of two different non-axisymmetric endwalls and the axisymmetric baseline case. The experimental total-to-total efficiency assessment reveals that the non-axisymmetric endwalls lose some of their benefit relative to the baseline case when purge is increased. The first endwall design loses 50% of the efficiency improvement seen with low suction, while the second endwall design exhibits a 34% deterioration. The time-resolved computations show that the rotor dominates the static pressure field at rim seal exit when purge flow is present. Therefore, the purge flow establishes itself as jets emerging at the blade suction side corner. The jet strength is modulated by the first vane pressure field. The jets introduce circumferential vorticity as they enter the annulus. As the injected fluid is turned around the rotor leading edge a streamwise vortex component is created. The dominating leakage vortex has the same sense of rotation as the rotor hub passage vortex. The first endwall design causes the strongest circumferential variation in the rim seal exit static pressure field. Therefore, the jets are stronger with this geometry and introduce more vorticity than the other two cases. As a consequence the experimental data at rotor exit shows the greatest unsteadiness within the rotor hub passage with the first endwall design.
Design Optimization of a Centrifugal Compressor Impeller Using Radial Basis Neural Network Method
Authors: Kim Jin-Hyuk , Choi Jae-Ho , Kim Kwang-Yong
Published: February 2010

This paper presents a procedure for design optimization of a centrifugal compressor. The centrifugal compressor consists of a centrifugal impeller, vaneless diffuser and volute. And, optimization techniques based on radial basis neural network method are used to optimize the impeller of the centrifugal compressor. Latin hypercube sampling of design of experiments is used to generate thirty design points within design spaces. Three-dimensional Reynolds-averaged Navier-Stokes equations with shear stress transport turbulence model are discretized by using finite volume approximations and solved on hexahedral grids to evaluate the objective function of an isentropic efficiency. Four variables defining impeller hub and shroud contours are selected as design variables in this optimization. The results of optimization show that the isentropic efficiency of the optimized shape at the design flow coefficient is enhanced by 1.0% and the efficiencies at the off-design points are also improved significantly by the design optimization.
Effects of Surface Groove on Separated Flow Transition on a High-Lift Low-Pressure Turbine Profile Under Steady Inflow Conditions
Authors: Luo Hualing , Qiao Weiyang , Xu Kaifu
Published: February 2010

LES (Large-Eddy Simulation) computations for a high-lift low-pressure turbine profile equipped with the span-wise groove on the suction surface are done to investigate the mechanism of the surface groove for separated flow transition control under steady inflow conditions, employing the dynamic Smagorinsky model. In addition to the baseline case (no groove), three groove positions which depend on the relative position of the groove trailing edge and the separation point on the suction surface are considered at two Reynolds numbers (Re, based on the inlet velocity and axial chord length). The results show that all grooves can reduce the calculated loss for Re = 50000, due to the further upstream transition inception in the separated shear layer. The analyses indicate two kinds of control mechanism such as the thinning of boundary layer behind the groove and the introduction of disturbances within the groove, depending on the groove position and Reynolds number. At Re = 50000, for the groove located upstream of the separation point, the reason for the further upstream transition inception location is the thinning of boundary layer behind the groove, and for the groove located downstream of the separation point, the reason is the introduction of disturbances within the groove. At Re = 100000, disturbances can also be generated within the groove located upstream of the separation point, promoting earlier transition inception.
Fully Three-Dimensional Viscous Semi-Inverse Method for Subsonic Mixed-Flow and Radial Impeller Design
Authors: Ji Min , Dang T. Q. , Cave Michael J.
Published: February 2010

A new semi-inverse design method for turbomachinery blading is proposed in this paper. Built on a time-marching Reynolds-Averaged Navier-Stokes solver, the proposed design method takes pressure loading, blade tangential thickness, blade stacking line, and flow path contour as prescribed quantities and computes the corresponding three-dimensional blade camber surface. In order to have the option of imposing geometrical constraints on the designed blade shapes, a new algorithm is developed to solve the camber surface at specified spanwise grid-lines, after which the blade geometry is constructed through ruling (e.g. straight-line element) at the remaining spanwise stations. The new semi-inverse algorithm involves re-formulating the boundary condition on the blade surfaces as a hybrid inverse/analysis boundary condition while preserving the fully three-dimensional nature of the flow field. The new design method can be interpreted as a fully three-dimensional viscous semi-inverse method. The ruled camber surface design procedure ensures blade surface smoothness and some control of mechanical integrity, and results in cost reduction for the manufacturing process. The proposed fully three-dimensional semi-inverse method is demonstrated through design modifications of generic industrial mixed-flow and radial impellers which are typically used for gas process applications.
Measurement and Computation of Flowfield in Transonic Turbine Nozzle Blading With Blunt Trailing Edges
Authors: Gostelow J. P. , Mahallati A. , Andrews S. A. , Carscallen W. E.
Published: February 2010

Experimental and computational results are presented from cascade testing on the nozzle blading of a high pressure ratio single stage turbine. Testing on this blading in 1986 showed surprising evidence of a redistribution of the downstream total temperature field. The nozzle midspan section has subsequently been tested in a large scale low aspect ratio planar cascade, having a continuous room-temperature inlet flow, to obtain more detailed information over the subsonic and transonic speed ranges. The blades had a blunt trailing edge which caused strong von Ka´rma´n vortex shedding throughout the subsonic range. This was shown to result in Eckert-Weise effect temperature redistribution. The first time-resolved measurements of this effect were measured in this cascade. Unusual vortex configurations were also observed at transonic speeds. The purpose of the current observations was to obtain reliable time-averaged measurements of flow through the cascade, which is proving to be an excellent vehicle for validating CFD predictions. A three-hole finger probe was traversed at the inlet and outlet of the cascade to evaluate the aerodynamic performance. Mach number and base pressure distributions, together with schlieren and surface oil-flow visualization, aided understanding of flow and loss behavior. Two-dimensional numerical simulations were performed over the speed range. The results assisted understanding of the influence of Mach number on losses and flow structures, specifically the shock configurations and base pressures. Comparisons of numerical results and experimental measurements of the flow-field showed good agreement.
Computational Studies of the Unbalance Response of a Whole Aero-Engine Model With Squeeze-Film Bearings
Authors: Bonello Philip , Hai Pham Minh
Published: February 2010

The computation of the unbalance vibration response of aero-engine assemblies fitted with nonlinear bearings requires the retention of a very large number of modes for reliable results. This renders most previously proposed nonlinear solvers unsuitable for this application. This paper presents three methods for the efficient solution of the problem. The first method is the recently developed impulsive receptance method (IRM). The second method is a reformulation of the Newmark-Beta method. In addition to these two time-domain methods, a whole-engine receptance harmonic balance method (RHBM) is introduced that allows, for the first time, the frequency domain calculation of the periodic vibration response of a real engine. All three methods use modal data calculated from a one-off analysis of the linear part of the engine at zero speed. Simulations on a realistically-sized representative twin-spool engine model with squeeze-film damper bearings provide evidence that the popular Newmark-Beta method can be unreliable for large order nonlinear systems. The excellent correlation between the IRM and RHBM results demonstrates the efficacy of these two complementary tools in the computational analysis of realistic whole-engine models.
Duct Design in Subsonic and Supersonic Flow Regimes With and Without Normal Shock Wave Using Flexible String Algorithm
Authors: Nili-Ahmadabadi Mahdi , Hajilouy-Benisi Ali , Durali Mohammad , Ghadak Farhad
Published: February 2010

In this investigation, the Flexible String Algorithm (FSA), used before for 2D subsonic ducts inverse design, is developed and applied to inverse design of supersonic ducts with and without normal shock wave. In this method, the duct wall shape is changed under an algorithm based on deformation of a virtual flexible string in a flow. The deformation of the string due to the local flow conditions resulting from changes in wall geometry is performed until the target shape satisfying the prescribed walls pressure distribution is achieved. The flow field at each step is analyzed using Euler equations solutions by the AUSM method. Some validation test cases and design examples in subsonic and supersonic regimes are presented here which show the robustness and flexibility of the method in handling the complex geometries in various flow regimes. In the case of unsymmetrical ducts with two unknown walls, the FSA has been modified to increase the convergence rate significantly. Also, effect of boundary conditions at the duct inlet and outlet on convergence of FSA is investigated. The FSA is a physical and quick converging approach and can efficiently utilize flow analysis codes as a black box.
Film Cooling Effectiveness Measurements With Periodic Unsteady Inflow on Highly Loaded Blades With Main Flow Separation
Authors: Gomes Reinaldo A. , Niehuis Reinhard
Published: February 2010

Film cooling experiments were performed using a highly loaded HPT blade linear cascade. A large region with main flow separation is found on the pressure side and film cooling is provided into this area with three rows of either cylindrical or fan-shaped holes. The measurements comprise adiabatic film cooling effectiveness and profile static pressure measurements. The surface temperature was acquired with thermochromatic liquid crystals and using a hue to temperature correlation. The results shown are for variations of main flow Mach and Reynolds numbers at engine relevant levels and of coolant mass flows. The results for steady and periodic unsteady inflow with highly turbulent wakes created by cylindrical bars moving upstream in a plane parallel to the cascade are compared as two-dimensional surface plots, laterally averaged film cooling effectiveness and overall effectiveness over the entire surface.
Mechansims for Wide-Chord Fan Blade Flutter
Authors: Vahdati Mehdi , Simpson George , Imregun Mehmet
Published: February 2010

This paper describes a detailed wide-chord fan blade flutter analysis with emphasis on flutter bite. The same fan was used with three different intakes of increasing complexity to explain flutter mechanisms. Two types of flutter, namely stall flutter and acoustic flutter, were identified. The first intake is a uniform cylinder for which there are no acoustic reflections. Only stall flutter, driven by flow separation, can exist in this case. The second intake, based on the first one, has a ‘bump’ feature to reflect the fan’s forward pressure wave at a known location so that detailed parametric studies can be undertaken. The analysis revealed a mechanism for acoustic flutter, which is driven by the phase of the reflected wave. The third intake has the typical geometric features of a flight intake. The results indicate that flutter bite occurs when both stall and acoustic flutter happen at the same speed. It is also found that blade stiffening has no effect on aero-acoustic flutter.
A Model for Potential Deterministic Effects in Transonic Compressor Flows
Authors: Stollenwerk Stefan , Nu¨rnberger Dirk
Published: February 2010

The unsteady interaction between blade rows is very important in highly loaded compressors because of its influence on operating performance. One important effect in this context is the impact of a rotor bow shock on the wake of an upstream stator blade. A new transport model is proposed which introduces such deterministic unsteady effects in a steady solution environment. Deterministic stresses are added to the stationary RANS equations by means of an additional source term. The presented approach combines the advantages of time-accurate and stationary simulation procedures, i.e. physical accuracy and computational efficiency. A generic cascade of flat plates and a transonic stator-rotor configuration are investigated numerically using time-accurate methods in order to analyze the wake-shock interactions. The results are compared with steady mixing-plane solutions to point out their shortcomings regarding unsteady effects and to illustrate the demands of a deterministic stress approach. The model is then calibrated for the generic cascade before it is applied to the real three-dimensional compressor stage.
Three-Dimensional Aerodynamic Design Optimization of a Turbine Blade by Using an Adjoint Method
Authors: Luo Jiaqi , Xiong Juntao , Liu Feng , McBean Ivan
Published: February 2010

This paper presents the application of an adjoint method to the aerodynamic design optimization of a turbine blade. With the adjoint method, the complete gradient information needed for optimization can be obtained by solving the governing flow equations and their corresponding adjoint equations only once, regardless of the number of design parameters. The formulations including imposition of appropriate boundary conditions for the adjoint equations of the Euler equations for turbomachinery problems are presented. Two design cases are demonstrated for a turbine cascade that involves a high tip flare, characteristic of steam turbine blading in low pressure turbines. The results demonstrate that the design optimization method is effective and the redesigned blade yielded weaker shock and compression waves in the supersonic region of the flow while satisfying the specified constraint. The relative effects of changing blade profile stagger, modifying the blade profile shape, and changing both stagger and profile shape at the same time are examined and compared. Navier-Stokes calculations are performed to confirm the performance at both the design and off-design conditions of the designed blade profile by the Euler method.
Assessment of the Flow Quality of a Transonic Turbine Cascade
Authors: Woodason R. , Asghar A. , Allan W. D. E.
Published: February 2010

The assessment of flow quality through a newly constructed transonic turbine cascade is presented. Although the main objective of this research was to investigate the effect of the modification of a vane profile due to repair on pressure loss, only the results for checking the flow periodicity, two-dimensionality of the flow and transonic exit flow condition are described in this paper. The cascade blades were constructed using the profiles of nozzle guide vanes of a low pressure turbine of an in-service turboshaft engine. The assessment of the flow quality in the cascade was carried out using three methods: wall static pressure measurements at the inlet and exit of each flow passage of the cascade to check the flow periodicity, surface flow visualization using blackened paraffin oil to check the two dimensionality of the flow and thirdly, Schlieren flow visualization to verify the periodicity and transonic flow conditions at the exit of the cascade. The cascade inlet and exit wall pressure showed that the flow was nominally periodic in the cascade. The surface flow visualization of the suction surface showed that the flow was two-dimensional on approximately 70% of the central span and also indicated flow separations on the suction surface. The Schlieren flow visualization confirmed the flow periodicity and revealed the existence of shock waves on the suction surface and near the trailing edge of the blades.
A Methodology to Predicting Total Damping of Axial Compressor Shrouded Stator Vanes
Authors: Peng Caetano , Zilli Andrea
Published: February 2010

The main objective of this paper is to evaluate the capability of existing numerical tools to predict the total damping Q values of axial core compressor shrouded stator vanes with a view to use them in the forced response simulations. Here, the aerodynamic damping is calculated for a wide range of vane vibration modes and nodal diameters (inter-blade-phase angles) using a CFD based aeroelasticity program. The mechanical friction damping of vane vibration modes is computed by using a multi-harmonic balance forced response code. These calculations take into account the effects of normal contact forces, friction coefficients, contact stiffness and excitation (forcing) loads. A pragmatic methodology has been developed to calculate the aerodynamic and mechanical friction damping values and hence predicting total Q values of stator vanes. Sensitivity studies are performed to assess the effects of mass flow and inter-blade-phase angles on aerodynamic damping. Moreover, the analyses allowed to identify the modeshapes associated with either high aerodynamic or mechanical damping or both. The numerical results are correlated with experimentally measured total Q values from strain gauge engine tests. This work shows that the current numerical tools have the capability to predict not only the aerodynamic forcing but also aerodynamic and mechanical friction damping values. Therefore, the analysis tools and methodologies close the stator vane forced response prediction capability loop. It means the vane force responses can be predicted as measured from strain gauge engine tests. This constitutes an important step in the development of axial compressors test-to-simulations, as more efforts are being placed towards the development of whole engines test-to-simulations.
Some Lessons Learned
Authors: Cumpsty N. A.
Published: February 2010

This paper looks at some familiar results, concepts and ideas in a different way, drawing out some common unifying threads. The topics addressed are one, two and three-dimensions; axisymmetry and its breakdown; gaps and leakage paths; and CFD and the limitation of perfection. Certain overlapping issues come up in each of the topic areas.
Influence of Turbocharger Imbalance on Subsynchronous Vibration Amplitude
Authors: Kirk R. Gordon , Sterling John , Sawyers William , Saville Mitchell , McNiff T. Bradley , Wilvert Lauren
Published: February 2010

The elimination of sub-synchronous vibration is a major task of rotating machinery engineers. The industry has used applied imbalance to improve stability of vertical pumps which would otherwise be totally unstable. The current interest is for the application of a small imbalance to determine the influence on the level of instability frequency components for a small high speed turbocharger rotor. The initial experimental results for the application of a known imbalance on the compressor end of a high speed turbocharger, indicates a reduced level for the lower instability mode.
Hydrodynamic Pressure of Thrust Step Bearings
Authors: Liu Shuangbiao , Chen W. Wayne , Hua Diann Y.
Published: February 2010

Step bearings are frequently used in industry for better load capacity. Analytical solutions to the Rayleigh step bearing and a rectangular slider with a finite width are available in literature, but none for a fan-shaped thrust step bearing. This study starts with a known solution to the Laplace equation in a cylindrical coordinate system, which is in the form of infinite summation. An analytical solution to pressure is derived in this paper for hydrodynamic lubrication problems encountered in the fan-shaped step bearing. The presented solutions can be useful for designers to maximize bearing performance as well as for researchers to benchmark numerical lubrication models.
Nanoindentation of a Deformable Substrate Covered by Patterned Nanodot Asperities
Authors: Wang Hengyu , Zou Min , Jackson Robert L. , Larson Preston R. , Johnson Matthew B.
Published: February 2010

This paper presents numerical and experimental studies of nanoindentation of a silicon substrate covered by patterned Ni nanodot asperities. A multi-asperity contact model was developed in this study to simulate the contact between a spherical indenter and the Ni nanodot asperities. In this model, the silicon substrate is considered to be deformable and the nanodots are allowed to interact with each other through the deformation of the substrate. The load-deformation relationship predicted by the model was found to be in good agreement with the experimental results. This model can also be used to predict indentation load-deformation relationships of a deformable substrate covered by nanodots with known size and location distributions, but not necessarily following a repetitive pattern.
Nickel-Titanium Alloys for Oil-Lubricated Bearing and Mechanical Component Applications
Authors: DellaCorte C.
Published: February 2010

Nickel-titanium (Ni-Ti) alloys are normally associated with applications that exploit their shape memory characteristics. When properly formulated and processed, however, Ni-Ti is dimensionally stable and offers a unique blend of attributes suitable for tribological applications. This paper demonstrates that Ni-Ti alloys are promising candidate structural materials for oil-lubricated rolling and sliding contact applications such as bearings and gears. Ni-Ti alloys offer a broad combination of physical properties that make it unique among bearing materials. Ni-Ti alloys are hard, electrically conductive, highly corrosion resistant, readily machined prior to final heat treatment, non-galling and non-magnetic. No other bearing alloy, metallic or ceramic encompasses all of these attributes. Spiral orbit tribometer (SOT) tests were conducted using 60NiTi balls loaded between rotating 440C disks, lubricated with synthetic oil and tested in a vacuum. Excellent tribological performance (life and friction) was observed and lubricant degradation normally associated with titanium alloys was absent. It is anticipated that the Ni-Ti family of alloys may form the basis of an entirely new class of bearing and component materials.
Thermoelastohydrodynamic Analysis of Journal Bearings With Non-Newtonian Carreau Fluids
Authors: Mongkolwongrojn M. , Aiumpornsin C.
Published: February 2010

The paper focuses on the solution of a numerical model to explore the journal bearing performance under transient thermal elastohydrodynamic lubrication with non-Newtonian lubricants based on Carreau viscosity model. The newly derived time-dependent modified Reynolds equation and the adiabatic energy equation have been formulated using a non-Newtonian Carreau viscosity model. The simultaneous systems consisting of the modified Reynolds equation, elasticity equation and energy equation with initial conditions were solved numerically using the multi-grid multi-level method with full approximation technique. The analysis showed that the fluid characteristics as defined by the Carreau model, led to large differences in minimum film thickness and maximum temperature rise for bearing liners with low elastic modulus.
Effects of High Pressure Hydrogen on Wear of PTFE and PTFE Composite
Authors: Sawae Y. , Nakashima K. , Doi S. , Murakami T. , Sugimura J.
Published: February 2010

Machine components in the fuel cell vehicle and related hydrogen infrastructures are operating within high pressure hydrogen gas. Especially, polymer seals used in gas compressors and regulator valves should be articulating against their metal counter face in pressurized hydrogen gas. However, the effect of high pressure hydrogen gas on tribological behavior of sliding surfaces has not been identified yet. In this study, effects of the pressurized hydrogen gas environment on wear behavior of polymeric sealing materials were examined by exposing polymer specimens and their sliding counterface to the high pressure hydrogen gas prior to the wear test. Unfilled polytetrafluoroethylene (PTFE) and 15% graphite filled PTFE were tested as representative polymer sealing materials and 316L austenitic stainless steel was used as a sliding counterface. Results of X-ray photoelectron spectrometer (XPS) analysis of the exposed stainless surface indicated that metal oxides in the surface passive layer of 316L stainless steel could be reduced to some extent by high pressure hydrogen. Increased metal contents of the stainless surface enhanced the development of polymer transfer film and consequently lower the specific wear rate of PTFE and PTFE composites.
Application of the Lobatto Quadrature Within Probabilistic Thermal Mixed EHL
Authors: Moraru Laurentiu , Keith Theo G.
Published: February 2010

Refined solutions of thermal lubrication problems generally require fine mesh and many iteration steps. To solve these difficulties, Elrod and Brewe [1–2] proposed an efficient algorithm based on the use of Lobatto point quadrature. Within this approach, the unknown temperature across the film is written in a series of Legendre polynomials. Over the years, the deterministic EHL approach has been widely applied, however, the probabilistic EHL methodology is still used when the main interest of the engineer is directed toward computations of bulk properties. This paper presents an application of the Lobatto point quadrature within a probabilistic EHL algorithm for the computation of the load supported by the fluid, the elastically deformed asperities and the plastically deformed asperities in a mixed EHL contact with either isotropic of non-isotropic roughness.
The Effect of Micro Dent Arrays Fabricated by Laser Shock Peening on Tribology
Authors: Caslaru R. , Guo Y. B.
Published: February 2010

Surface micro dents may act as lubricant reservoirs to reduce friction and wear in sliding and rolling contact applications. Surface patterning has become a valuable technique for fabricating micro dents. Alternative methods such as micromachining present obvious limitations in comparison with laser shock peening (LSP). In this paper, the use of LSP along with an automatic X-Y table proves to be an attractive and reliable method for producing micro dent arrays with enhanced surface integrity and free of cracks. Surface topography, residual stress, and microhardness of the fabricated micro dent arrays on polished Ti-6Al-4V have been characterized. It was found that a 10% density of micro dent array reduces coefficient of friction compared with a smooth surface. However, a higher dent density not necessarily reduces coefficient of friction.
Experimental and FEA Scratch Correlation of Magnetic Signal Degradation in Magnetic Storage Thin-Film Disks
Authors: Katta Raja R. , Polycarpou Andreas A. , Lee Sung-Chang , Suk Mike
Published: February 2010

Scratch-related magnetic signal degradation can occur during magnetic storage hard disk drive operation when the read-write heads contact the spinning multilayer disks. To investigate this phenomenon controlled nanoscratch experiments were performed on perpendicular magnetic recording media using various indenters of different radii of curvature. Various loading conditions were used to cause permanent scratches that were measured using atomic force microscopy. The nanoscratch experiments were simulated using finite element analysis (FEA) that included the detailed nanometer scale thin-film multilayer mechanical properties. The permanently deformed field in the sub-surface magnetic recording layer was extracted from the FEA results. The residual scratch widths measured on the surface of the magnetic storage disk were directly compared with the residual sub-surface widths of the region on the magnetic recording layer where extensive permanent lateral deformation was present. It was found that the sub-surface widths of the deformed regions were significantly larger than the surface scratch widths. Thus, sub-surface thin-film layers, such as the magnetic recording layer could be damaged without observable damage to the protective top surface carbon overcoat. The exact location and extent of damage to the magnetic recording layer depends on the scratch load, size of scratch tip, and the friction at the interface. Such permanent deformation in magnetic recording layer could lead to demagnetization, which has been reported in the literature.
Analysis of Topographical Changes and Adhesion Failures in Gold-to-Gold Metal RF MEMS Switches With Cycling
Authors: Yeo Seung Min , Tseregounis Spyros I. , Polycarpou Andreas A. , Fruehling Adam , Peroulis Dimitrios
Published: February 2010

Topographical changes within the contact area as a function of cycling could be a critical factor causing failure and reliability issues in RF MEMS switch operation. In this paper, gold-to-gold contact, cantilever-type RF MEMS switches were tested (cold-switching mode) for different number of cycles, namely, 10, 102, 103, 104, 105, and 106. After the cycling tests, the contact area of each switch was scanned using optical microscopy, scanning electron microscopy and atomic force microscopy to quantify the exact gold-to-gold contact surface changes, leading to adhesion failures (at about 106 cycles). Detailed roughness analysis was carried out to better quantify topographical changes on the contact surface and relate them to failures. It was found that the material transfer from the top beam to the bottom substrate was dominant, and observed after only few cycles. Adhesion failure of gold-to-gold contact switches could be attributed to large protrusions formed on the bottom surface as the switch cycles over 105 times.
Analysis of the Be´nard Cell-Like Worn Surface Type Occurred During Oil-Lubricated Sliding Contact
Authors: Lin Jen Fin , Chu Hsiao Yeh
Published: February 2010

Scuffing wear is usually used as an important indication of the initiation of lubrication failure. Components with scuffing wear should be readily replaced in order to avoid severe wear. This paper observed the change of surface structure in the scuffed area of the worn surface of oil-lubricated vanes-on-ring specimens from a microscopic and nano-scale observation and material characterization. There existed a kind of Be´nard cell-like special surface shape found from the observation of the TEM image of the scuffed surface. In order to see whether there was very hot surface temperature to produce Benard cell, structure of the surface ferrous material was used as an indirect evidence of high temperature. It showed that the temperature in the scuffed area suffered a very high temperature which was over 800°C from the TEM Result. It showed that very strong fluid convection or even evaporation may occur inside the scuffed surface. The material strength of the scuffed surface would be much lower due to this high temperature. The oil pressure of that high temperature area was also very high. These factors made it possible to form the Be´nard cell structure in microscale.
A Study of a Dual Clearance Squeeze Film Damper
Authors: Moraru L. , Keith T. G. , Dimofte F. , Cioc S. , Fleming D. P.
Published: February 2010

Squeeze film dampers (SFD) are devices utilized to control vibrations of the shafts of high-speed rotating machinery. A dual squeeze film damper (DSFD) consists of two squeeze film bearings that are separated by a sleeve, which is released when the rotor experiences abnormal operating conditions. In this part of our study of DSFD we analyze the case when both the inner and the outer oil films are active. Previous studies utilized closed form analytical expressions to describe the forces within the lubricant. In this paper the oil forces are modeled using pressure distributions obtained from numerical solutions of the Reynolds equation. Numerical results are compared with the experimental data.
A Semi-Analytical Plastic-Damage Model Using the Equivalent Inclusion Problem
Authors: Fulleringer Benjamin , Ovaert Timothy C. , Nelias Daniel
Published: February 2010

The formulation and modelling of tribological contacts is useful for lifetime predictions, in particular in power transmission and aeronautical systems. For this reason, contact problems are largely studied by both analytical and finite element (FE) methods. Analytical methods have been recently used for hardening problems, but are still limited to homogeneous bodies. This paper presents an elastic-plastic approach for inhomogeneities and damage using a fully-coupled contact code.
Prediction of Spur Gear Mechanical Power Losses Using an EHL Model With Time-Varying Contact Parameters
Authors: Li S. , Kahraman A.
Published: February 2010

A physics-based model is proposed to predict load dependent (mechanical) power loss of spur gear pairs by using a specialized gear elastohydrodynamic lubrication (EHL) model. The EHL model includes time variations of all key contact parameters such as surface velocities, radii of curvature and normal load in their continuous forms such that a continuous analysis of a tooth contact from its root to tip can be performed. The EHL model has the capability to simulate any gear contacts represented by condition ranging from full EHL to mixed or boundary EHL conditions. Predicted transient pressure and film thickness distributions are used to determine the instantaneous as well as the overall mechanical power loss of the gear mesh. Correction factors are introduced to account for thermal effects. At the end, capabilities and accuracy of the proposed model are demonstrated by comparing its predictions to experimental data.
Influence of Alloying Element Addition on Friction and Transfer Layer Formation in Al-Mg System: Role of Surface Texture
Authors: Menezes Pradeep L. , Kishore  , Kailas Satish V. , Lovell Michael R.
Published: February 2010

In the present investigation, sliding experiments were conducted using pins made of pure Al, Al-4Mg alloy, Al-8Mg alloy, Mg-8Al alloy and pure Mg against steel plates of various surface textures using a pin-on-plate apparatus under both dry and lubricated conditions. The primary focus of the study was to investigate the influence of alloying elements on the coefficient of friction and transfer later formation in Al-Mg systems. The morphologies of the worn surfaces of the pins and the formation of transfer layer on the counter surfaces were observed using a scanning electron microscope. It was observed for a given surface texture that the alloying element addition decreased the average coefficient of fiction to lower values under both dry and lubricated conditions. For a given material pair, the coefficient of friction and formation of transfer layer depend on the surface texture of the hard surfaces.
Influence of Inclination Angle and Surface Texture of the Plate on Friction and Transfer Layer Formation
Authors: Menezes Pradeep L. , Kishore  , Kailas Satish V. , Lovell Michael R.
Published: February 2010

In the present investigation, unidirectional grinding marks were attained on the steel plates. Experiments were then conducted using pins of Al-Mg alloy against the prepared steel plates using an inclined pin-on-plate sliding tester. The goal of the research is to understand the influence of grinding mark direction and inclination angle of hard material on the friction and transfer layer formation during sliding. The inclination angle of the plate was held at 0.2°, 0.6°, 1°, 1.4°, 1.8°, 2.2° and 2.6° in the tests. The pins were slid both perpendicular and parallel to the grinding marks direction. Experiments were conducted under both dry and lubricated conditions on each plate in ambient environment. Results showed that the coefficient of friction and formation of transfer layer depend on the grinding marks direction and inclination angle of the hard surfaces. For a given inclination angle, the coefficient of friction and transfer layer formation were found to be more for the pins slid perpendicular to the unidirectional grinding marks when compared to parallel to the unidirectional grinding marks under both dry and lubricated conditions. The stick-slip phenomenon was observed only under lubricated conditions at the highest tilt angle for the sliding perpendicular to the grinding marks direction. These variations could be attributed to the extent of plane strain conditions taking place at the asperity level during sliding.
Wear Performance of Titanium and Niobium Added MoS2 Coatings Under Isobutane Exposure
Authors: Aksit Mahmut F. , Kizil Huseyin , Efeoglu Ihsan , Sariibrahimoglu Kemal
Published: February 2010

As conventional refrigerants phased out, Hydrocarbons such as Isobutane emerged as the main alternative in refrigeration industry. However, compatibility of these new ozone friendly refrigerants with compressor oils and bearing materials need to be evaluated. This study investigates wear performance of Titanium and Niobium added MoS2 coatings running against 100Cr6 steel under isobutane exposure. Wear performance is established under starved lubrication condition by comparing the maximum achieved sliding distance before the sudden increase and fluctuation of the friction curve. Sinter steel samples were coated with MoS2, MoS2-Ti, MoS2-Nb thin films by magnetron sputtering. The concept of durability distance has been defined as the distance until a sudden fluctuation of the friction curve is observed. It was found that addition of Titanium and Niobium adversely affects wear performance of the MoS2 coatings under isobutane exposure. This can be attributed to the possible degradation of MoS2 lamellar structure that acts as solid lubricant under such exposure.
Current and Future Tribological Challenges in Wind Turbine Power Systems
Authors: Terrell Elon J. , Needelman William M. , Kyle Jonathan P.
Published: February 2010

The drive for an increase in the amount of sustainable energy sources has given rise to increasing interest in the development of wind turbine technology. Although wind turbines are being increasingly installed around the world, several of the components in a wind turbine have challenges related to tribology that can drastically reduce their expected lifetimes.