Influences of Recess Geometry and Restrictor Dimension on Flow Patterns and Pressure Distribution of Hydrostatic Bearings

This paper studies the influences of recess geometry and restrictor dimensions on the flow patterns and pressure distribution of lubricant film, which are coupled effects of hybrid characteristics of a hydrostatic bearing. The lubricant flow is described by using the Navier-Stokes equations. The Galerkin weighted residual finite element method is applied to determine the lubricant velocities and pressure in the bearing clearance. The numerical simulations will evaluate the effects of the land-width ratio and restriction parameter as well as the influence of modified Reynolds number and the jet-strength coefficient on the flow patterns in the recess and pressure distribution in lubricant film. On the basis of the simulation drawn from this study, the simulated results are expected to help engineers make better use of the design of hydrostatic bearing and its restrictors.

Characteristics in Response Integration and Bifurcation of a Forced Duffing Oscillator

The Duffing oscillator is well-known models of nonlinear system, with applications in many fields of applied sciences and engineering. In this paper, a response integration algorithm is proposed to analyze high-order harmonic and chaotic motions in this oscillator for modeling rotor excitations. This method numerically integrates the distance between state trajectory and the origin in the phase plane during a specific period and predicted intervals with excitation periods. It provides a quantitative characterization of system responses and can replace the role of the traditional stroboscopic technique (Poincare´ section method) to observe bifurcations and chaos of the nonlinear oscillators. Due to the signal response contamination of system, thus it is difficult to identify the high-order responses of the subharmonic motion because of the sampling points on Poincare´ map too near each other. Even the system responses will be made misjudgments. Combining the capability of precisely identifying period and constructing bifurcation diagrams, the advantages of the proposed response integration method are shown by case studies. Applying this method, the effects of the change in the stiffness and the damping coefficients on the vibration features of a Duffing oscillator are investigated in this paper. From simulation results, it is concluded that the stiffness and damping of the system can effectively suppress chaotic vibration and reduce vibration amplitude.

Reduced-Order Model of a Bladed Rotor With Geometric Mistuning

This paper deals with the development of an accurate reduced-order model of a bladed disk with geometric mistuning. The method is based on vibratory modes of various tuned systems and proper orthogonal decomposition of coordinate measurement machine (CMM) data on blade geometries. Results for an academic rotor are presented to establish the validity of the technique.

Additional Investigations Into the Natural Frequencies and Critical Speeds of a Rotating, Flexible Shaft-Disk System

Traditional rotor dynamics analysis programs make the assumption that disk components are rigid and can be treated as lumped masses. Several researchers have studied this assumption with specific analytical treatments designed to simulate disk flexibility. The general conclusions reached by these studies indicated disk flexibility has little effect on critical speeds but significantly influences natural frequencies. This apparent contradiction has been reexamined by using axisymmetric harmonic finite elements to directly represent both disk and shaft flexibility along with gyroscopic effects. Results from this improved analysis show that depending on the thickness-to-diameter (slenderness) ratio of the disk and the axial position of the disk on the shaft, there are significant differences in all natural frequencies, for both forward and backward modes, including synchronous crossings at critical speeds.

Life Remaining Prognostics for Structural Components

Retirement criteria for many structural components and particularly landing gear structural parts, are generally based on analytical fatigue methods because the current means of detecting actual component damage cannot detect sufficiently small levels of damage such that safe operation for a useful interval can be confidently determined; limiting the capability to apply damage tolerance methods. The testing completed in these projects demonstrated that Induced Positron Analysis (IPA) technologies are sensitive to the tensile plastic strain damage induced in aerospace material specimens and components. The IPA process has shown that IPA methods can reliably detect and quantify plastic strain and plastic deformation under simulated and operational conditions. A preliminary functional relationship between total strain and the normalized IPA S parameter has been developed for several aerospace materials. The fatigue testing has demonstrated the IPA technologies have potential to detect fatigue damage induced in specimens and operational components when the loads are large enough to cause plastic deformation.

Mitigation of Fretting Fatigue Damage in Blade and Disk Pressure Faces With Low Plasticity Burnishing

Low Plasticity Burnishing (LPB) is now established as a surface enhancement technology capable of introducing through-thickness compressive residual stresses in the edges of gas turbine engine blades and vanes to mitigate foreign object damage (FOD). The “Fatigue Design Diagram” (FDD) method has been described and demonstrated to determine the depth and magnitude of compression required to achieve the optimum high cycle fatigue (HCF) strength, and to mitigate a given depth of damage characterized by the fatigue stress concentration factor, kf. LPB surface treatment technology and the FDD method have been combined to successfully mitigate a wide variety of surface damage ranging from FOD to corrosion pits in titanium and steel gas turbine engine compressor and fan components. LPB mitigation of fretting induced damage in Ti-6AL-4V in laboratory samples has now been extended to fan and compressor components. LPB tooling technology recently developed to allow the processing of the pressure faces of fan and compressor blade dovetails and mating disk slots is described. Fretting induced micro-cracks that form at the pressure face edge of bedding on both the blade dovetail and the dovetail disk slots in Ti-6-4 compressor components can now be arrested by the introduction of deep stable compression in conventional CNC machine tools during manufacture or overhaul. The compressive residual stress field design method employing the FDD approach developed at Lambda Technologies is described in application to mitigate fretting damage. The depth and magnitude of compression and the fatigue and damage tolerance achieved are presented. It was found that microcracks as deep as 0.030 in., (0.75 mm) large enough to be readily detected by current NDI technology, can be fully arrested by LPB. The depth of compression achieved could allow NDI screening followed by LPB processing of critical components to reliably restore fatigue performance and extend component life.

Non-Linear Aeromechanical Behaviour of Axial Core Compressor Stator Vanes

This paper highlights some engine non-linearities that can affect both performance and robustness of aero engines. It pays particular attention to non-linearities generated at the stator vane contact end joints. These non-linearities resulting from friction contact joints affect the vane modeshapes, damping and forced response. This work proposes upper and lower bound solutions based on vane end restraints non-linearities to predict conservative forced response of stator vanes. Some non-linearities such as those caused by mistuning can be beneficial to the component and system. There are also non-linearities that can be detrimental to engine performance, robustness and reliability. Moreover, it proposes and discusses the concept of temporal HCF or CCF lifing method. Recent developments in FE, CFD, mistuning, forced response and probabilistic codes can help to create more integrated design tools that incorporate time-dependent non-linearities in the lifing of aero engine components. Computations performed here demonstrated some level of component virtual testing. These analyses are important component virtual testing that will be gradually extended to whole aero engine virtual testing.

Design for Six Sigma: The First 10 Years

Six Sigma was launched at GE in 1995 by Jack Welch as a systematic way of improving the quality of delivered products and reducing cost across the entire Corporation. Soon after the first wave of Master Black Belts returned from their initial training, it was obvious that GE needed a “version” of Six Sigma adapted by a Design Engineering community that was focused on achieving specific goals of improved product performance, reliability and producibility while achieving a simultaneous reduction in the design cycle time for new products. The purpose of this paper is to share our lessons learned in adapting Six Sigma to the needs of the Design Engineering Community.

Explicit Finite Element Models of Friction Dampers in Forced Response Analysis of Bladed Discs

A generic method for analysis of nonlinear forced response for bladed discs with friction dampers of different design has been developed. The method uses explicit finite element modelling of dampers, which allows accurate description of flexibility and, for the first time, dynamic properties of dampers of different design in multiharmonic analysis of bladed discs. Large-scale finite element damper and bladed disc models containing 104–106 DOFs can be used. These models, together with detailed description of contact interactions over contact interface areas, allow for any level of refinement required for modelling of elastic damper bodies and for modelling of friction contact interactions. Numerical studies of realistic bladed discs have been performed with three different types of underplatform dampers: (i) a ‘cottage-roof’ (called also ‘wedge’) damper; (ii) seal wire damper; and (iii) a strip damper. Effects of contact interface parameters and excitation levels on damping properties of the dampers and forced response are extensively explored.

Innovative Design of a Robust Turbine Stage Using Flow Analysis and Subcomponent Rig Testing With Rapid Prototypes

Designing turbine engine components for high cycle fatigue robustness can significantly reduce operating costs and improve safety. However, obtaining an optimum design and getting the new hardware into service using traditional methods is an expensive process. A process that combines state-of-the-art computational fluid dynamics (CFD) analytical simulations with subcomponent rig testing has been developed and demonstrated on a gas turbine engine. The analytical method involves spatial Fourier decomposition of vane exit total pressure from steady flow calculations. This provides an efficient method to reduce the design space and eliminate poor designs, resulting in a small subset of near-optimum designs. To confirm that the remaining candidate designs provide less unsteady forcing and to validate the CFD analysis, a unique experimental test rig was constructed. The experiments consisted of flowing ambient air through a subsection of the engine, while measuring the exit total pressure flow field around the turbine rotor exit annulus with a unique traversing probe. The measured exit total pressure was then Fourier decomposed in space to understand the resulting unsteady forcing on the blade. The costs of the flow rig and producing numerous sets of candidate hardware were much less expensive than full-scale engine or rotating rig tests. New hardware designs tested in the rig were manufactured using a rapid prototyping procedure, which allowed for extremely quick turn around in going from design concept to experimental validation. Good correlation between analysis and test was found, except in a few cases. The majority of these discrepancies were attributed to excitation sources that were impractical to include in the CFD models. This finding indicated that there are still circumstances for which the analytical tools were insufficient and hence experimental validation is still important. Both the analysis and experiments confirmed up to a 50% reduction in the amplitude of unsteady pressure for this particular engine test case.