bluuebunny/crossref_metadata_2025 huggingface dataset:
Aerodynamics of a Covered Trailing Edge Vane: Effects of Blowing Rate, Reynolds Number, and External Turbulence
Authors: Jaswal I. , Erickson E. , Ames F. E.
Published: February 2010

A covered trailing edge vane was developed by opening a fully loaded incompressible vane to accept an internal flow passage. The internal passage was filled with a high solidity internal cooling scheme. Exit survey measurements were acquired downstream from a large scale low speed linear cascade test section using a 5-hole cone probe at 1/4 axial chord downstream from the vane trailing edge. Exit survey measurements detailed total pressure loss, turning angle and secondary velocities. Exit survey measurements were conducted across a range of blowing rates (25% to 150% design), Reynolds numbers (500,000, 1,000,000 and 2,000,000) and turbulence levels [low (0.7%), grid (8.5%) and aero-combustor (13.5%)]. Losses for a thickened baseline vane (no blowing, same profile) were also acquired across the Reynolds number range and turbulence conditions. Vane midspan pressure and heat transfer distributions were acquired to help document the state of the boundary layers developing on the vane surface. Measurements are presented in terms of total pressure loss contours with secondary velocities and spanwise distributions of circumferentially averaged losses and turning angles. Overall loss values have been compared with measurements taken using the original base vane and a conventional gill slot vane. Comparisons between the base vane and the covered base vane show an incremental increase in total pressure losses of about 0.95% due the thicker trailing edge. Comparisons between the gill slot (pressure side cutback) and the covered trailing edge vane at comparable flow conditions show a much smaller loss penalty. Loss data for the gill slot vane suggest that both separation off the gill slot lip and the discharge of low momentum fluid are responsible for significant incremental losses above the base vane. The covered trailing edge vane has no additional surface with separation losses which penalizes the aerodynamics. Heat transfer rates for the internal cooling scheme are documented in a separate paper [1].
Analysis of Finger Seal Lift Pads
Authors: Galimutti Peter P. , Sawicki Jerzy T. , Fleming David P.
Published: February 2010

Analyses were performed on finger seal pads having a pressure drop across the pad at right angles to the direction of runner velocity. The film was tapered; the clearance could decrease in both the pressure flow and velocity directions. A substantial load could be carried solely due to the pressure flow; however, the bearing exhibited negative stiffness without film convergence in the velocity flow direction. This is in marked contrast to a full circular bearing or ring seal, where pressure flow alone produces a significant stiffness as long as the clearance converges in the flow direction. The performance of three different pad configurations has been evaluated: aspect ratios L/B of 0.5, 1 (square pad), and 2. Design examples pertaining to each aspect ratio were studied for a gas turbine seal. Results show that lowest leakage, highest load carrying capacity, and highest stiffness are attained for the wide-pad configuration, L/B = 0.5. This paper presents a detailed study of the pad; additional analysis needs to be done for the inclusion of the finger and many other considerations for designing a complete seal.
Stability Enhancement of a Multi Stage Compressor by Air Injection
Authors: Hiller Sven-Ju¨rgen , Matzgeller Roland , Horn Wolfgang
Published: February 2010

Cold and hot air injection upstream of the first rotor tip of a multi stage compressor was tested experimentally. The compressor operating range was extended towards lower mass flow by more than 60% indicating a better throttling capability when air injection was activated. A strong dependency of the stability enhancement on the injected mass flow and injection velocity was found. Both, increasing injection mass flow rate and increasing injection velocity led to a considerable extension of the throttling line. Comparable enhancements were achieved when reducing the number of nozzles and hence the injection mass flow. It was also found that injection of hot air, at temperatures comparable to air bled off at a following stage, had no penalty on the stability enhancement. Investigation of the influence of air injection on radial work distribution showed that only small amounts of injected air were sufficient to lead to a significant radial work re-distribution. This in turn changed the operating point of the first stage, leading to axial re-matching and thus changed the whole operational behavior of the compressor.
High Pressure Turbine Stage Endwall Profile Optimisation for Performance and Rim Seal Effectiveness
Authors: Lott Philippe T. , Hills Nick J. , Chew John W. , Scanlon Timothy , Shahpar Shahrokh
Published: February 2010

This paper describes the numerical optimisation of a high pressure turbine stage using non-axisymmetric endwall profiling. The aim of the work has been to use the endwall profiling to optimise not only the stage performance, but also the effectiveness of the rim seal in preventing mainstream gas ingestion. Any improvement in rim seal effectiveness may allow a lower coolant flow rate, and hence increased performance due to the lower bleed requirement from the compressor and the lower aerodynamic losses re-introducing the coolant flow into the turbine. To this end, the objective functions used in the optimisation have included the pressure asymmetry above the rim seal, which acts a driver for mainstream gas ingestion, as well as traditional measures of stage performance. Separate steady state optimisations have been carried out for the nozzle guide vane passage and the rotor passage with these objectives and good improvements in the figures of merit have been obtained. Since mainstream gas ingestion is a strongly unsteady phenomenon, unsteady CFD calculations have then been carried out for the datum and optimised stage geometries. These calculations show that the reduction in pressure asymmetry in the steady state calculations is maintained in the unsteady calculation and does indeed reduce predicted mainstream gas ingestion. However, the improvements in stage performance predicted by the steady state CFD are only partially obtained in the unsteady CFD calculations.
Validation of the Non-Linear Harmonic Approach for Quasi-Unsteady Simulations in Turbomachinery
Authors: Hembera Michael , Loos Andreas , Ku¨hrmann Andreas , Danner Florian C. T. , Kau Hans-Peter , Johann Erik
Published: February 2010

Unsteady simulations, which are necessary to resolve the time-dependent flow between stationary and rotating parts in axial compressors, require an appropriate rotor-stator interface. For this interface, usually the so called domain-scaling or sliding mesh approach is used. This method requires the pitch of the simulated blades to be equal, to allow the usage of periodic boundary conditions and to cut down the number of represented blade passages in order to save computational time. This is based on the assumption that the flow is identical inside all blade passages. When it comes to the simulation of modern multi-stage compressors, it becomes almost impossible to conduct unsteady simulations with this approach, as blade numbers of different rows usually don’t have common multiples. In order to overcome that problem, a new method called the nonlinear harmonic approach has been introduced. The main idea of the method is, that the different calculated flow variables are divided into a time-averaged part and another part based on a Fourier decomposition, which represents the oscillating influence of the perturbations caused by the adjacent rows. Superimposing these two parts leads to a quasi-unsteady solution. For this simulation method, the pitches of the different blade rows don’t have to be changed, so that it also becomes possible to simulate multistage machines with discretizing only one passage per blade row. For this paper, a full-annulus unsteady simulation with about 40 million gridpoints was performed and the results are compared to a NLH simulation with only 1 simulated blade passage per row with 1.38 million gridpoints. Additionally, a NLH simulation with a much finer mesh with 7 million gridpoints is also included.
Multiobjective Optimization Approach to Multidisciplinary Design of a Three-Dimensional Transonic Compressor Blade
Authors: Luo Chang , Song Liming , Li Jun , Feng Zhenping
Published: February 2010

An automatic multiobjective optimization approach to multidisciplinary design of turbomachinery blades is proposed in this paper. Based on this approach, an algorithm named Multiobjective Differential Evolution (MDE) is introduced as an optimizer to find the Pareto solution sets of the multidisciplinary design problem. A typical multiobjective function has been applied to demonstrate the performance of the presented multiobjective optimization algorithm. The Non-uniform B-Spline method is adopted to parameterize the turbomachinery blade profiles. The aerodynamic performance of design blade candidates is predicted by using a three–dimensional Reynolds-Averaged Navier-Stokes (RANS) solution. The blade stresses and vibration frequencies are evaluated by means of a finite element analysis coupled with the surface pressure of blades obtained from CFD calculation. To validate the optimization capability of the multiobjective optimization algorithm, the multidisciplinary design of a typical transonic compressor blade, NASA Rotor 37, is conducted. The blade is optimized for the maximization of the isentropic efficiency and the minimization of the maximum stresses with constraints on mass flow rate, total pressure ratio, and dynamic frequencies. The Pareto solutions are obtained from the multiobjective optimization. Based on the analysis of the design objectives between the Pareto designs and reference design, it is indicated that the overall performance of the optimized designs is improved. The results demonstrate that the presented multiobjective optimization algorithm has a potential in blade performance optimization and it is a promising method for the multidisciplinary design of turbomachinery blades.
Design and Off-Design Flow Fields of a Transonic Centrifugal Compressor Impeller
Authors: Ibaraki Seiichi , Sumida Kunio , Suita Toru
Published: February 2010

For reasons of their small dimensions, relatively higher efficiency and wider operating range transonic centrifugal compressors are usually applied to turbochargers and turboshaft engines. The flow field of a transonic centrifugal impeller is completely three dimensional and accompanied by shock waves, tip leakage vortices, secondary flows and interactions of them. Especially the operating range of a transonic centrifugal compressor decreases rapidly with increased pressure ratio. The expansion of the compressor operating range is one of the important issues. Also the higher off-design performance is strongly required for the applications like as turbochargers which have to operate from near surge limit to choke limit. The authors carried out the detailed flow measurement of a transonic centrifugal impeller with an inlet Mach number of 1.3 at design and off-design conditions by using Laser Doppler Velocimeter (LDV) and high frequency pressure transducers. The flow fields of design and off-design conditions were compared and discussed in this paper. As a result authors found out the difference and the similarity of the flow structure between design and off-design conditions. The location of the shock wave differs with the flow rate and influences the flow field of the inducer. The interaction of the shock wave and tip leakage vortex shows the same manner. Also detailed Navier-Stokes computations were conducted to elucidate the complicated vortical flow structure with the experimental results.
Understanding Blade Walking: Phenomenon and Mechanism
Authors: Duong Loc Q. , Gupta Shiv C. , Hu Charlene X.
Published: February 2010

Blade walking or axial dislocation of a turbine blade along its fixings in the disk is a common and undesirable problem in turbomachinery since it eventually leads to the premature failure of the engine either due to rubbing of the rotor with the adjacent stator stages or due to the overload fracture of the disk fixings. The objective of this paper is to develop a clear understanding of the contributing factors and the mechanism behind the phenomenon of blade walking. Finite element method is used to illustrate the blade walking phenomena and its underlying mechanism.
Misalignment Modeling in Rotating Systems
Authors: Bahaloo Hassan , Ebrahimi Alireza , Samadi Mostafa
Published: February 2010

Misalignment is a common source of high vibration and malfunction in rotating machinery. Despite its importance and prevalence, no sufficient documentation exists treating this problem. In this paper, a method is introduced for modeling a continuous rotor system which incorporates a misaligned coupling element. It is assumed that both the angular and parallel misalignments are present in the coupling location. The energy expressions are derived and then, applying the Ritz series method, the equations of motion are constructed in matrix form. Because of the special characteristics of the system due to misalignment, a Harmonic Balance Method (HBM) is utilized to obtain the multi harmonic response to an unbalance excitation in disk location. A study on shaft center orbits is also provided and the effect of misalignment type and severity on the orbits is analyzed.
Application of Flow Control in a Novel Sector Test Rig
Authors: Simpson Alexander , Aalburg Christian , Schmitz Michael , Pannekeet Robbert , Larisch Florian , Michelassi Vittorio
Published: February 2010

An experimental and numerical study has been performed to evaluate the effectiveness of steady injection flow control for the reduction of losses in the return channel of a radial compressor. This investigation formed part of an overall attempt to develop a strategy for reducing the diffusion ratio of radial compressors. It is envisaged that this flow control would be activated at off-design conditions where separation levels on the return channel vanes are considerable. A novel radial compressor sector test rig, supported by a blow-down facility and equipped with a range of instrumentation, was used for the experimental portion of the study. This allowed multiple flow control configurations to be studied in a simplified environment. A set of exchangeable, inlet guide vanes provide the test vanes with the correct inlet three-dimensional flow-field whilst airfoil static pressure taps allowed the blade loading to be assessed. The numerical portion of the study was conducted using 3D-CFD and involved simulations of both the sector test rig and a “substitute system”. In this paper the rationale for the inclusion of flow control in a radial compressor return channel is discussed. The sector test rig is then described including the implementation of flow control. The results of the matrix of flow control experiments are then discussed with comparison to the numerical results.
Quasi-Three Dimensional Verification of the Modular Axial Compressor Design Approach
Authors: Attia Magdy S. , Hemerly Christopher
Published: February 2010

In an article published some time ago [1], the authors investigated the idea of breaking down the [multi-stage] compressor component of the typical turbofan engine into modules. The motivation for this work stems from a “Lean Engineering” approach to gas turbine engine design. Five (5) modules were created; they are the inlet, front, core, rear, and exit modules. The intent is to maximize the size of the core module, as represented by the number of stages. Thus, many different compressors can share the core module, which will greatly reduce the Lifecycle costs for the fleet. The next stage of this work focuses on the Meanline and Throughflow design and analysis of two different compressors that share an 8-stage core. The first compressor, HPC-1, is a 10-stage compressor operating at 9,000 rpm, having 100 Kg/sec inlet mass flow rate, and a 13.5:1 overall pressure ratio. HPC-2 is a 13-stage modular upgrade of HPC-1, operating at 9,700 rpm, having an inlet mass flow rate of 140 Kg/sec, and a 27:1 overall pressure ratio. Applying the modular concept, the first and last stages (of HPC-1) have been removed and replaced by 2 and 3 stages, respectively. Additionally the inlet and exit modules have been redesigned as well. Preliminary Meanline analysis showed that this concept could present challenging boundary conditions for the design of the interface stage; the name assigned to the first stage of the core module. The conditions entering that stage represent a critical hurdle to the viability of this method. Slight variations in corrected speed and pressure ratios for stages 1 and 2 of the modular upgrade, HPC-2, provided the necessary realignment of the core module. The pressure ratio of the core module differs by less than 1% for both compressors. And in both instances, the corrected speed is virtually identical. Throughflow analysis, conducted using T-AXI [2], confirms the redesign and the viability of the method.
Dynamic Analysis of a Bladed Disk With Friction and Fretting-Wear in Blade Attachments
Authors: Salles Loi¨c , Blanc Laurent , Thouverez Fabrice , Gouskov Aleksander M. , Jean Pierrick
Published: February 2010

Assembled bladed disks have many contact interfaces (blade-disk joint, blade shrouds, friction dampers...). Because of relative displacements at these interfaces, fretting-wear occurs, which affects negatively the lifetime of the structure. Methods exist to predict fretting-wear in quasi-static analysis. However they don’t predict all the phenomena observed in blade attachments on real industrial plants. This paper studies the assumption of a responsibility of dynamics for fretting-wear damage. A numerical treatment of fretting-wear under vibratory loading is proposed. The method is based on the Dynamical Lagrangian Frequency Time method. It models unilateral contact through Coulomb’s friction law. The basic idea is to separate time in two scales, slow scale for tribological phenomena and fast scale for dynamics. For a chosen number of periods of vibration, a steady state is assumed and the variables are decomposed in Fourier series. An Alternating Frequency Time procedure is performed to calculate the non-linear forces. Then, a Hybrid Powell’s algorithm is used as solver. A quasi-analytical expression of the Jacobian matrix decreases the duration of calculations. This expression is also used to predict new relative displacement at the interfaces due to the increase of wear depth. This method is similar to a prediction-correction method, with wear depth as the term of continuation. Numerical investigations on a bladed-disk with friction contact interfaces illustrate the performances of this method and show the coupling between dynamical and tribological phenomena.
Visualization and Post-Processing of Centrifugal Compressor Computational Fluid Dynamics Flow Fields
Authors: Garrison Loren , Cooper Nate
Published: February 2010

Centrifugal compressor flow fields from computational fluid dynamics analyses are inherently difficult to visualize and quantify due to their highly three-dimensional nature. In the following paper, techniques for advanced visualization and post-processing of centrifugal compressor computational fluid dynamics flow fields are described. Numerical flow field visualization was performed using turbomachinery-based cutting plane surfaces that are based on meridional, spanwise, and pitchwise coordinates to aid in the identification and understanding of the development of flow field structures in the main gas path of centrifugal impellers. The turbomachinery-based cutting plane tools are also used to quantify bulk area averaged and mass averaged quantities as well as circumferentially averaged spanwise and meridional profiles within the main gas path of the centrifugal impeller. Examples of how these tools were used to help identify flow structures and quantify flow properties in a centrifugal impeller are presented. In addition, results of a new procedure to calculate two-dimensional blockage for centrifugal impeller applications are discussed. The new blockage calculation methodology combined with the meridional cutting plane tools are used to quantify the blockage development throughout an entire centrifugal impeller from inlet plane to exit plane.
Experimental Evaluation of Foil Bearing Performance: Steady-State and Dynamic Results
Authors: Conlon M. J. , Dadouche A. , Dmochowski W. M. , Payette R. , Be´dard J.-P. , Liko B.
Published: February 2010

An experimental facility dedicated to measuring both the steady-state and dynamic properties of foil bearings, under a variety of operating conditions, has been designed and commissioned. The bearing under test is placed at the midspan of a horizontal, simply-supported, stepped shaft which rotates at up to 60 krpm. Static and dynamic loads of up to 3500 N and 450 N (respectively) can be applied by means of a pneumatic cylinder and two electrodynamic shakers. This paper outlines the test procedures and data analysis methods pertaining to the operation of the high-speed, oil-free bearing test rig, and presents steady-state and dynamic results for a first-generation foil bearing. The test bearing, which was fabricated in-house, is 0.07 m diameter and has an aspect ratio of 1; bearing manufacturing details are provided.
Test Rig and Simulation Environment for Model-Based Monitoring
Authors: Heckmann Benjamin , Ginzinger Lucas , Ulbrich Heinz
Published: February 2010

With the aim to provide the basis for model-based monitoring of rotor systems a test rig and an appropriate simulation environment has been developed. Therewith several damages shall be replicated and investigated. In a first approach an unbalanced rotor system and an increasing clearance in a journal bearing are analysed. Therefore extensive experiments with the rotor test rig have been conducted. The implemented test system is modelled with a simulation environment called MBSim (http://mbsim.berlios.de). This simulation environment, developed at the Institute of Applied Mechanics, is based on a framework for the efficient simulation of multi-body-systems with unilateral contacts and elastic elements. Therewith typical defects in rotating machinery can be replicated and critical effects can be investigated. The simulation includes a spatial bending-torsional beam and unilateral contacts with friction and impacts. So it’s possible for instance to model unilateral contacts in journal bearings with clearance between shaft and bearing. Experiment and simulation are consistent with each other in a very wide range, so the basis for the higher aim of a model-based fault detection and identification is provided.
Comparison of Tilting-Pad Journal Bearing Dynamic Full Coefficient and Reduced Order Models Using Modal Analysis
Authors: Dimond Timothy W. , Younan Amir A. , Allaire Paul E.
Published: February 2010

There is significant disagreement concerning the frequency response of tilting pad journal bearings (TPJBs) due to non-synchronous excitations. Two linear models for the frequency dependence of TPJBs have been proposed. The first model, the full-coefficient or KC model, considers Np tilting pads and rotor motions for Np + 2 degrees of freedom. Dynamic reduction of the KC model results in eight frequency-dependent stiffness and damping coefficients. The second model, based on results from bearing system identification experiments, yields twelve frequency-independent stiffness, damping, and mass (KCM) coefficients. Experimental data has been presented to support both models. There are major differences in the two approaches. The analysis in this paper takes a new approach of considering the pad dynamics explicitly in a state-space modal analysis. TPJB shaft and bearing pad stiffness and damping coefficients are calculated using a well known laminar, isothermal analysis and a pad assembly method. The TPJB rotor and pad full system eigenvalues and eigenvectors are then evaluated using state-space methods, with rotor and bearing pad inertias included explicitly in the model. The full bearing coefficient results are also non-synchronously reduced to the 8 stiffness and damping coefficients are and expressed as shaft complex impedances. The system identification method is then applied to these complex impedances, and the state space modal analysis is applied to the resulting KCM model. The damping ratios, natural frequencies, and mode shapes from the two bearing representations are compared. Two example TPJBs are examined in detail. The analysis indicated that four underdamped modes, two forward and two backward, dominate the rotor response over excitation frequencies from 0 to running speed. The full coefficient, non-synchronously reduced model predicts additional critically damped or overdamped modes due to the additional degrees of freedom as compared to the identified KCM model. The KCM model results in natural frequencies that are 63–65 percent higher than the full coefficient model. The difference in modal damping ratio estimates depend on the TPJB considered, with KCM being 7–17 percent higher than the full coefficient model. The full coefficient model also indicates that the bearing pads contribute significantly to the underdamped modes. The results indicate that the system identification method results in a reduced order model of TPBJ dynamic behavior. Additionally, the differences in the modal calculated system natural frequency and modal damping have potential implications for rotordynamic analyses of flexible rotors, such as critical speed and stability analyses.
An Energy Approach for Helping the Selection of Solid Lubrication Coatings Under Fretting Conditions
Authors: Luo D. B. , Fridrici V. , Kapsa Ph. , Taillandier M. , Prud’homme C.
Published: February 2010

Employing friction reduction coatings is one of the most effective methods to palliate the fretting damage. However, facing numerous available coatings, how to compare them and select the optimum one for a specific application is still a challenging task. In this paper, based on the investigation of the fretting behaviors of several bonded solid lubricant coatings, an energy approach in terms of “initial maximal dissipated energy density” was suggested to compare the tribological response of coatings. According to test results, the lifetime of each coating under different test parameters can be fitted by one master curve. The definition of this master curve for a given coating may be used for the prediction of the coating lifetime only by knowing the initial energy dissipated in the contact. The comparison of different master curves for different coatings can be employed to help the coating selection.
Nanostructured Diamond Coatings for Dry Drilling
Authors: Chou Kevin , Thompson Raymond , Qin Feng , Nolen Dustin , Miao Chao
Published: February 2010

In this study, nanostructured diamond (NSD) films were grown, by microwave plasma assisted chemical vapor deposition (MP-CVD) technology, on WC-Co drills for performance enhancement in dry drilling of A390 alloys. Surface cobalt was removed by a well-controlled precision etching process. H2/CH4 gas mixture with a small amount of N2 was applied to produce NSD films. Moreover, slight hone was applied to the cutting edges prior to the NSD deposition to relieve residual stresses generated by thermal mismatch in depositions. The results show feasibility of dry drilling of A390 alloys by NSD coated drills, substantially outperforming carbide drills.
The Static Characteristics of Bump Foil Thrust Bearing Considering Tilting Condition
Authors: Kim Tae-Young , Park Dong-Jin , Lee Yong-Bok
Published: February 2010

Air foil thrust bearings are the critical component available on high-efficiency turbomachinery which needs ability to endure the large axial force. Previous investigations about the static characteristics were obtained over the region of the thin air film using finite-difference method and the characteristics of the corrugated bump foil using finite-element method. Moreover, a recent study demonstrated that bearing performance is sensitive to tilting thrust pad condition. In this study, experimentally measured bearing static characteristics are compared with the numerical model of the foil thrust bearing considering tilting pad condition. Three geometrically different type foil bearings were tested to measure their load capacity under tilting conditions that have continuous angles from zero to 0.0002 rad. These data are presented for use i1n the development of more accurate foil thrust bearing numerical models.
Synergistic Antioxidation Properties of Tin Dialkyldithiocarbamate With Dialkyldiphenylalmine
Authors: Hu Jian-Qiang , Gao Ke-Yi , Liu Da-Wei
Published: February 2010

Differential scanning calorimetry (DSC) and thin film micro oxidation test (TMOT) were employed to evaluate the antioxidation properties of tin dialkyldithiocarbamate (SnDDC) with p,p′dioctyldiphenylamine (DODPA) antioxidant in pentaerythritol ester (PE) or polyalphaolefin synthetic lubricant (PAO), and their chemical structure were identified by fourier transform infrared spectroscopy (FTIR) analysis. DSC test shows that incipient oxidation temperature and oxidation induction time of DODPA-containing PE were improved significantly by SnDDC addition, SnDDC shows a good oxidative synergism with DODPA antioxidant. TMOT results indicates that the combination of SnDDC and DODPA in polyalphaolefin can also effectively reduce the weight lost, carbonyl peak square index and diposits of oxidized oils, which confirm that the combination of SnDDC and DODPA exhibit good synergistic antioxidation properties and deposits inhibition.
Influence of Ball Wedging Behavior in Ball Screws on Lost Motion of Its Mechanism
Authors: Ueda Masahiro , Shimoda Hirokazu
Published: February 2010

It is well known that preloaded ball screws with double nut produced hysteretic motion between the rotational angle of the screw shaft and linear motion of the nut, which is called “lost motion”, causes positioning error of ball screws. Preloaded ball screws with a double nut have the characteristic that the loaded balls wedge into a right angle direction to a ball rolling direction because the directions of screw shaft and nut raceways differ from the ball rolling direction. Loaded balls of preloaded ball screws with a double nut have two contact points geometrically. When the ball screw is operated under the condition of screw shaft turning and nut stationary, the wedging forces of balls are produced by differences between the screw shaft and nut raceways, and then loaded balls wedge into nut grooves. When the ball wedging motion is significantly increased, loaded balls make contact with another flank of the nut groove, that is, three points contact occur. In the present study, the authors deal with the positioning errors of the X-table which is composed of a preloaded precision ball screw and a couple of linear air bearings, and the ball wedging behaviors. The ball wedging behavior is quantified by the variation of the distance from ball surface to gap sensors which are inserted into several holes. These hole passing through the top of Gothic arch groove are bored in the perpendicular to the outer surface of the cylindrical nut.
Frictional Behavior of Boundary Lubricated Contacts: Effect of Tribochemical Surface Films
Authors: Lorenzo-Martin C. , Ajayi O. O. , Lee JungKyu , Polycarpou Andreas A.
Published: February 2010

The friction characteristics of lubricated contacts are usually determined by the shearing of three interfacial structural elements; namely lubricant fluid film, tribochemical reaction films and the near-surface materials. The shear behavior of the fluid film components of lubrication can be adequately described by either the hydrodynamic, or elastohydrodynamic theories and calculations. The shear behavior of the near surface materials can also be approximated by contact mechanics. However, due to the complexity and lack of adequate information, description and analysis of the tribochemical film contributions to frictional behavior is more challenging. In this study we present evaluation of the friction behavior of a lubricated contact as a function of tribological test duration, as the tribochemical surface films were being formed. Tests were conducted with two different formulated lubricants, in addition to an unformulated PAO basestock lubricant. One of the formulated lubricants consists of PAO synthetic basestock with 2.5% each of ZDDP and MoDTC additives. The other formulated lubricant is a fully formulated commercial gear oil with similar viscosity. During the friction tests in a fully flooded reciprocating sliding roller-on-flat contact configuration, the friction coefficient decreased exponentially as the tribochemical films were formed; highlighting the impact of boundary films on friction. In the test with the basestock fluid, the friction remained constant for the duration of the test; although an oxide layer was formed. Nanoindentation hardness and modulus measurements were conducted on two of the tribochemical films to measure their mechanical properties and the consequent impact on measured friction during testing.
A Study of Real Area of Contact for Tire/Road Interface
Authors: Dawkins Jeremy J. , Shah Sameer G. , Jackson Robert L.
Published: February 2010

This paper investigates some of the modeling techniques available for predicting the real area of contact between two surfaces. These models are then applied to an idealized case of a rubber block in contact with a rough surface representing a tire on the road. A description of how the models work is presented. The various contact models are compared and analyzed. Qualitatively the models compare very well. Several models also compare well quantitatively.
Fretting Wear of CMSX4 at Blade Tip Interface With and Without Coating
Authors: Lavella M. , Botto D. , Gola M. M.
Published: February 2010

Fretting wear is a complex phenomenon that occurs at component interfaces that are subjected to low amplitude oscillation under high contact pressure. In turbomachinery fretting occurs also at the blade tip interfaces where shrouds, that have the aim to reduce the blade resonant vibration amplitude, are machined. To diminish the fretting damage coatings are applied to the blade tips. The aim of this study is to compare the fretting wear behaviour of single crystal CMSX-4 superalloy interfaces with and without plasma sprayed T-800 coating. Experiments have been conducted with hemispherical surface in contact with a flat surface of the same materials at temperature of 800 °C. The hysteresis cycles have been measured through the experiment. The comparison of the hysteresis cycles shown that the tangential contact stiffness of the coated surfaces is greater then that of the surfaces without coating. At the end of wear process, the mating surfaces have been characterized by three-dimensional optical interferometry and SEM analysis. After 10×106 wear cycles, the uncoated surfaces show a large change in the contact parameters and fretting cracks on the flat surface. On the other hand, the coated surfaces do not shows a measurable change in the contact parameters while the coating damage on the flat surface leads to predict an incipient catastrophic wear.
An Abrasive Wear Model of Fractal Surfaces Based on the Slip–Line Theory of Plasticity
Authors: Yin X. , Komvopoulos K.
Published: February 2010

A generalized abrasive wear model of a three-dimensional rough (fractal) surface sliding against a relatively softer material is presented. The model is based on a slip-line field of a rigid spherical asperity (or spherical wear particle) that plows through a soft surface, resulting in material removal by a microcutting process. The analysis yields a relationship of the abrasive wear coefficient in terms of the interfacial adhesion characteristics of the interacting surfaces, topography (fractal) parameters, elastic-plastic material properties, and applied normal load. Numerical results illustrate the effects of surface roughness and interfacial adhesion (lubrication effect) on the abrasive wear coefficient of fractal surfaces.
Contact Mechanics Analysis of a Rubber Piece on a Smooth Plate
Authors: Ono Kyosuke
Published: February 2010

In order to elucidate contact and friction characteristics of rubbers, numerical analysis of asperity contact mechanics of a rubber piece with a smooth glass plate was carried out on the basis of an asperity contact model that considers van der Waal’s (vdW) pressure. First, by ignoring vdW pressure and the elastic deformation of the mean height surface, asperity contact characteristics were analyzed using the measured Young’s modulus, and surface parameter values that could yield the measured contact area were estimated. Next, asperity contact characteristics were analyzed by considering the vdW pressure and elastic deformation of a rough sphere that is a model of a large-scale asperity having small-scale asperities. It was found that the actual contact area was similar to the measured contact area; this result could not be obtained without assuming an rms asperity height of ∼0.1 μm for the small-scale asperities. It was also found that the friction coefficient decreased with an increase in the applied pressure in the cases where the friction force is proportional to the real area of contact and to the real internal contact pressure.
Numerical Analysis of a Spherical Shell Compressed by a Rigid Flat
Authors: Li Longqiu , Etsion Izhak , Ovcharenko Andrey , Talke Frank
Published: February 2010

The elastic-plastic contact between a spherical shell and a rigid flat is analyzed using finite element analysis. The effect of spherical shell geometry and material properties on the onset of plastic deformation is determined by finding the critical normal load and the critical interference which correspond to the onset of plastic yielding. The location of initial plastic deformation is identified as a function of material properties and spherical shell geometry. This work provides the dimensionless critical load as a function of the shell parameter λ = (t/R)*(E/Y), where t, R, E and Y are the spherical shell thickness, radius, Young’s modulus and yield strength, respectively. The numerical results are compared with the solid sphere model based on Hertz’s contact theory and classical shell theory in the elastic regime. The behavior of a spherical shell contacting a rigid flat plate is a strong function of the shell parameter λ.
Evaluation of the Dynamic Properties of Fluid Film Bearing Elastic Supports
Authors: Ene Nicoleta M. , Dimofte Florin , Moraru Laurentiu E. , Afjeh Abdollah A.
Published: February 2010

The purpose of this paper is to present the experimental evaluation of the stiffness and damping coefficients of a pair of elastic rings used to support a fluid film bearing into a turbojet engine body. The experimental rig, the method of analysis and the experimental data are presented.
An Experimental Study of the Effect of Global Solid Fraction and Surface Material on Couette Granular Flow
Authors: Marinack Martin C. , Jasti Venkata K. , Higgs C. Fred
Published: February 2010

The flow of solid granular material has been proposed as an alternative lubricant to conventional liquid lubricants. Since granular flows are also in numerous industrial and natural processes, they have been the subject of numerous studies. However, it has been a challenge to understand them because of their non-linear and multiphase behavior. There have been several past experiments, which have gained insight into granular flows. For example, previous work by the authors sheared grains in a two-dimensional annular shear cell by varying the velocity and roughness [1]. The present experimental work attempts to further insights from the previous work by specifically studying the interaction between rough surfaces and granular flows when the global solid fraction and grain materials are varied. A two dimensional annular (granular) shear cell, with a stationary outer ring and inner driving wheel, was used for this work. Digital particle tracking velocimetry was used to obtain local granular flow data such as velocity, local solid fraction, and granular temperature. Slip between the driving wall and first layer of granules is also extracted. This slip can be interpreted as momentum transfer or traction performance in granular systems such as wheel-terrain interaction. Parametric studies of global solid fraction and the material of the rough driving surface, attempt to show how these parameters affect the local granular flow properties.
Tribological Film Formation on Hydrogenated DLC/Steel Contacts From Fully Formulated Automotive Lubricants
Authors: Papke B. L. , Parthasarathy P. P.
Published: February 2010

Tribological film formation from fully-formulated synthetic automotive lubricants on hydrogenated DLC/steel contacts was compared with that on steel/steel contacts. Four DLC coatings containing various metal dopants (W and Si) were evaluated. Lubricants formulated with organic friction modifiers performed better on DLC/steel than on steel/steel in both sliding and rolling/sliding contacts (lower friction and wear). In contrast, lubricants formulated with MoDTC friction modifiers had higher sliding contact friction on DLC/steel than on steel/steel. No evidence was observed for tribological film formation on the DLC surfaces.
Study on Lubricant Depletion Induced by Laser Heating in Thermally Assisted Magnetic Recording Systems: Effect of Lubricant Thickness
Authors: Tagawa Norio , Andoh Hideki , Tani Hiroshi
Published: February 2010

In this study, fundamental research on lubricant depletion due to laser heating in thermally assisted magnetic recording was conducted. In particular, the effect of lubricant film thickness on lubricant depletion was investigated. The conventional lubricant Zdol2000 was used. As a result, it was found that the lubricant depletion characteristics due to laser heating depend largely on the lubricant film thickness. In addition, it was suggested that the lubricant depletion mechanism involves the evaporation of the mobile lubricant molecules, when the maximum attained temperature is not very high. Another suggested lubricant depletion mechanism involves the thermocapillary stress effect induced by the disk surface temperature gradient resulting from the non-uniformity of the laser spot intensity distribution.
A Three-Dimensional Stochastic Analysis of the Lapping Process Used for Magnetic Recording Heads
Authors: Xu H. , Komvopoulos K.
Published: February 2010

A stochastic analysis was derived for the lapping process of magnetic recording heads. Numerical results of the final surface roughness, material removal rate, and wear coefficient are presented in terms of material properties, applied pressure, topographies of original ceramic surface and lapping plate surface, kinematics, diamond particles density and sizes of lapping plate. The estimated final roughness is in good agreement with experimental results.
Response of D-Gun Sprayed Alumina-Zirconia Ceramic Composite to Particle Erosion and Sliding Wear
Authors: Rajakumar S. , Vijayaraghavan L. , Mayuram M. M.
Published: February 2010

Erosion due to solid particles has a detrimental effect on the performance of components used in many critical applications. The problem becomes more acute at high temperatures. Thermal sprayed ceramic coatings are widely used in such situations wherein the present scenario considers better coatings. The ceramic composite coatings of alumina-zirconia were developed and their response to particle erosion and high temperature sliding wear and are experimentally evaluated. Based on a brittle erosion model, parametric influence on the variation of erosion rate was mathematically modeled adopting regression analysis and its validity is verified through a set of confirmation tests. Alumina-zirconia exhibits better performance with higher wear resistance and lesser coefficient of friction, at higher temperature, compared to plain alumina or alumina-titania.
Tribological Performance of Polymer Coatings in Carbon Dioxide Refrigerant Environment
Authors: Escobar Nunez Emerson , Polycarpou Andreas A.
Published: February 2010

Natural refrigerants have gained significant interest due to environmental reasons. Among different natural refrigerants such as water, air, and ammonia, Carbon dioxide (CO2) is the main candidate to replace commonly used hydrofluorocarbon (HFC) refrigerants in air-conditioning compressors due to its environmental benefits. One of the main advantages of implementing CO2, from an environmental point of view, lies in its relative low global warming potential (GWP) which is three orders of magnitude lower than commonly used HFC refrigerants. Coupled with the new refrigerants is also the need to use some form of protective coatings on the tribopairs. In this study unlubricated (presence of CO2 refrigerant only) experiments were performed to evaluate the tribological performance of three different polymeric-based coatings deposited on Durabar G1 gray cast iron disks. Specifically, Fluorolon 325, Impreglon 1704 PEEK, and PEEK/Ceramic/ PTFE blends were tested against 52100 hardened steel pins. Results showed lower friction coefficient and wear in the Fluorolon 325 case compared to the Impreglon 1704 PEEK and PEEK/Ceramic/PTFE coatings. These results are comparable with earlier studies using PTFE-based coatings [1].
Particle Contamination on a Thermal Flying-Height Control Slider
Authors: Liu Nan , Bogy David B.
Published: February 2010

Particle contamination on a slider in a hard disk drive (HDD) affects the HDD’s reliability. With the introduction of the thermal flying-height control (TFC) slider, the temperature in the head-disk interface (HDI) becomes non-uniform, which induces a temperature-gradient dependent force on particles moving in the HDI. This paper investigates the effect of this force, the so called thermophoretic force, on a particle’s motion in the HDI as well as its effect on particle contamination on the TFC slider. By numerical simulation of the particle’s trajectory together with an analytical analysis, we show that the thermophoretic force is always negligible compared to the Saffman lift force, which points to a direction parallel to the thermophoretic force. We conclude that the current particle contamination simulator without any thermophoretic forces included would not be significantly altered by the inclusion of these forces.
Fretting Wear Between a Hollow Sphere and Flat Surface
Authors: Raeymaekers Bart , Helm Sebastian , Brunner Ralf , Fanslau Edmund B. , Talke Frank E.
Published: February 2010

Wear particles in a hard disk drive may cause the head/disk interface to fail. We have experimentally investigated wear particle generation resulting from fretting wear between the dimple on the suspension and the gimbal spring. We have found that increasing the normal load as well as using a low friction coating reduces the formation of wear particles.
Analytical Solution for the Stress Field of Eshelby’s Inclusion of Polygonal Shape
Authors: Jin Xiaoqing , Keer Leon M. , Wang Qian
Published: February 2010

Recently, we developed a closed-form solution to the stress field due to a point eigenstrain in an elastic full plane. This solution can be employed as a Green’s function to compute the stress field caused by an arbitrary-shaped Eshelby’s inclusion subjected to any distributed eigenstrain. In this study, analytical expressions are derived when uniform eigenstrain is distributed in a planar inclusion bounded by line elements. Here it is demonstrated that both the interior and exterior stress fields of a polygonal inclusion subjected to uniform eigenstrain can be represented in a unified expression, which consists of only elementary functions. Singular stress components are identified at all the vertices of the polygon. These distinctive properties contrast to the well-known Eshelby’s solution for an elliptical inclusion, where the interior stress field is uniform but the formulae for the exterior field are remarkably complicated. The elementary solution of a polygonal inclusion has valuable application in the numerical implementation of the equivalent inclusion method.