Showing papers by "Rolls-Royce Holdings published in 2012"

Eddy-current induced thermography—probability of detection study of small fatigue cracks in steel, titanium and nickel-based superalloy

Abstract: Eddy-current induced thermography (induction thermography, hereon referred to as eddytherm) is an active thermographic method which is capable of rapid and non-contacting detection of out-of-plane cracks in electrically conductive parts. In an eddytherm inspection, the part is induction heated; cracks cause localised changes in the induced eddy-current flow and the associated Joule heating is imaged at the surface of the part with an infrared camera. In this study the detectability of fatigue cracks in steel, titanium and Waspaloy is quantified by novel but simple image processing routines which are specifically applicable to eddytherm inspection. The quantitative detection data is then input into a cumulative log-normal probability of detection model to estimate the probability of detecting the fatigue cracks as a function of crack length. a90,95 (i.e., the crack length which can be detected 90% of the time with 95% confidence) is found to be 0.60 mm for steel, 0.78 mm for titanium and 1.50 mm for Waspaloy (a nickel-based superalloy), showing eddytherm to be an extremely sensitive method.

Application of Value-Driven Design to Commercial Aero-Engine Systems

Abstract: Value-Driven Design provides a framework to enhance the systems engineering processes for the design of large systems. By employing economics in decision making, Value-Driven Design enables rational decision making in terms of the optimum business and technical solution at every level of engineering design. This paper explains the application of ValueDriven Design to the aero-engine system through two case studies, which were conducted through workshops under the Rolls-Royce plc Advanced Cost Modeling Methodologies project. The Surplus Value Theory was utilized to provide a metric that can trade-off component designs with changes in continuous and discrete design variables. Illustrative results are presented to demonstrate how the methodology and modeling approach can be used to evaluate designs and select the value-enhancing solution.

Measurement of the fracture toughness associated with the longitudinal fibre compressive failure mode of laminated composites

Abstract: The fracture toughness associated with the fibre compressive failure was obtained from testing notched unidirectional carbon/epoxy four-point-bend specimens. Microscopy of failed specimens revealed that onset of damage was characterised by the formation of a single line of fibre breaks at approximately 45° to the plane of the initial notch. A micromechanical finite element model was used to investigate this failure scenario and it was concluded that the most probable cause of the damage morphology was compression-induced shear failure of the composite. An intrinsic material property in this case was deemed to be the mode II critical strain energy release rate associated with the initiation of the 45° crack. For IM7/8552, this was measured to be G IIc = 4.5 ± 0.8 kJ/m 2 .

The oxidation characteristics of the nickel-based superalloy, RR1000, at temperatures of 700–900°C

Abstract: The oxidation kinetics are presented for a coarse-grained RR1000 alloy in the temperature range 700 – 900°C for times up to approximately 100 hours. The tests were undertaken in laboratory air in thermo-balances. The kinetics tended to sub-parabolic but were treated as parabolic to allow comparison with literature data. These parabolic rate constants were appreciably higher than expected for the growth of a protective oxide layer but were similar to those found previously on other Cr-rich Ni-based superalloys. SEM and confocal microscopy were used to show that the regions of emergent grain boundaries on the alloy surface oxidised faster than the grain centres. The surface oxide formed was Cr-rich with an enhancement of titanium in its outer regions. This is the situation at the grain boundaries and over the grain centres. Sub-surface oxidation of aluminium was observed, principally as intergranular fingers but also as intragranular particles. Ahead of this internal oxidation zone, at least for the...

Effects of Winglet Geometry on the Aerodynamic Performance of Tip Leakage Flow in a Turbine Cascade

Abstract: Experimental and numerical methods were used to investigate the aerodynamic performance of a winglet tip in a linear cascade. A flat tip and a cavity tip are studied as baseline cases. The flow patterns over the three tips are studied. The flow separates over the pressure side edge. For the cavity tip and the winglet tip, vortices appear in the cavity. These vortices reduce the discharge coefficient of the tip.The purpose of using a winglet tip is to reduce the driving pressure difference. The pressure side winglet of the winglet geometry studied in this paper has little effect in reducing the driving pressure difference. It is found that the suction side winglet reduces the driving pressure difference of the tip leakage flow near the leading edge, but increases the driving pressure difference from midchord to the trailing edge. This is also used to explain the findings and discrepancies in other studies. Compared with the flat tip, the cavity tip and the winglet tip achieve a reduction of the loss to the size of the tip gap.The effects of the rounding of the pressure side edge of the tips were studied to simulate the effects of deterioration. As the size of the pressure side edge radius increase, the tip leakage mass flow rate and the loss increase. The improvement of the aerodynamic performance by using a winglet remains similar when comparing with a flat tip or a cavity tip with the same pressure side radius.Copyright © 2012 by ASME

Turbomachine casing assembly

Abstract: A turbomachine casing assembly comprises a first casing portion for at least partially encasing one or more rotating aerofoil structures of a turbomachine and a second casing portion; the first casing portion being movable with respect to the second casing portion. One or more resilient elements are arranged so as to resist movement of the first casing portion with respect to the second casing portion.

Distributed propulsion system and method of control

Abstract: This invention relates to a method and apparatus for controlling power distribution in an electrical aircraft propulsive system having at least one electrical propulsion unit which includes a plurality of rotatable blades, each blade having an adjustable pitch; a pitch adjusting mechanism for adjusting the pitch of the blades; at least one electrical machine electrically connected to the electrical propulsion unit so as to provide electrical power when in use; and, a control system, the method comprising the steps of: determining the required propulsion; determining whether the propulsive units are delivering the required propulsion; and, adjusting the pitch angle of the blades of at least one propulsive unit so as to increase or decrease the propulsion provided by that propulsive unit.

Solution Heat Treatment Optimization of Fourth-Generation Single-Crystal Nickel-Base Superalloys

Abstract: The optimization of the solution heat treatment (SHT) of fourth-generation single-crystal nickel-base superalloys LDSX-6B and LDSX-6C is presented. The methodological approach to optimizing the SHT process is particularly highlighted. Differential scanning calorimetry (DSC) measurements and electron-probe microanalysis (EPMA) mapping were carried out to investigate material properties in the as-cast condition and after SHT. The DSC equipment was also adopted as a vacuum furnace to evaluate the suitability of the SHT ramp profile and to check the safety margins with regard to incipient melting during SHT. SHT trials were carried out in a laboratory-scale vacuum furnace, after which the heat-treated samples were subjected to DSC experiments, microstructural analysis, and EPMA mapping to assess the effects of SHT peak temperatures and soak periods. From the DSC and EPMA results, as-cast LDSX-6B shows a lower degree of elemental microsegregation; hence, this alloy is relatively easier to homogenize in the SHT trials. In contrast, as-cast LDSX-6C was found to have a higher degree of elemental microsegregation; therefore, it is much more difficult to homogenize and is highly prone to incipient melting. The results of this study indicate that an increase in the SHT peak temperature and/or soak period will lead to an improved compositional homogeneity in the material as expected. After SHT, both alloys retained some residual elemental microsegregation and the LDSX-6C alloy showed precipitation of topologically close-packed (TCP) phase at the dendrite cores. The most appropriate and economic SHT process may be determined based on the methodological approach presented in this study and the requirements of the materials during service.

PADRAM: Parametric Design and Rapid Meshing System for Complex Turbomachinery Configurations

Abstract: This paper reports the progress made in a parametric design and rapid meshing system (PADRAM) developed under two recent UK national sponsored research programs. PADRAM is designed to parametrically change the blade geometry and rapidly generate body-conformal high-quality viscous meshes. This allows speeding up the CFD loop by making the meshing process fully automatic on the basis of pre-designed templates. The geometry parameterisation is done within the mesh generator, making its integration within the optimisation loop straightforward. The paper presents examples that demonstrate how incorporating real geometry features into PADRAM is fundamental to achieve numerical models closer to reality. This is key factor in trusting the CFD solution and making use of it to further improve current designs. It also shows that featurebased structured mesh is good for cases that need to be repeatable across sites and teams, where consistency of the mesh is crucial and quick answers required to cope with tight project deadlines. The incorporation of additional complex geometrical features limits the applicability of the template structured approach and can be sometimes at the expense of mesh quality. In this regard, novel unstructured meshing technologies have been developed and implemented into PADRAM in order to deal with non standard and complex configurations. Two of these methods are presented in this paper (i.e., Zipper Layer and Delaunay Cavity). The paper shows how these can be used to paste together various multi-block structured meshes, hence providing the most suitable meshing topology to be used for each components separately. This makes the PADRAM code a unique meshing tool, able to combine the advantages of the template-topology approach to the flexibility of fully unstructured meshes. A number of supportive examples are reported in the paper. NOMENCLATURE

Unsteady Interaction Between Annulus and Turbine Rim Seal Flows

Abstract: In core gas turbines relatively cold air is purged through the hub gap between stator and rotor in order to seal the disc space against flow ingestion from the main annulus. Although the sealing mass flow rate is commonly very small compared to the main annulus mass flow rate, it can have significant effects on the development of the passage endwall flows and on the overall loss generation.In this paper, the interaction between annulus and rim sealing flows is investigated using numerical simulations of a generic high-pressure turbine. At first, the numerical approach is validated by comparing the results of calculations to measurement data at the design flow conditions. Following that, results from steady and unsteady calculations are used to describe in detail the aerodynamics in overlap-type rim seals and their effects on the blade passage flow. It is found that the flow interaction at the rim seal interface is strongly influenced by the velocity deficit of the rim sealing flow relative to the annulus flow as well as by the circumferentially non-uniform pressure field imposed by the rotor blades. At typical sealing flow conditions, the flow interaction is found to be naturally unsteady, with periodical vortex shedding into the rotor passage.Finally, the influence of the specific rim seal shape on the flow unsteadiness at the rim seal interface is investigated and the impact on turbine performance is assessed.Copyright © 2012 by ASME

Advances in the Wilshire extrapolation technique—Full creep curve representation for the aerospace alloy Titanium 834

Abstract: Structural alloys applied to aerospace and power generation applications are expected to operate at temperatures exceeding those originally envisaged during their design to meet the tightening regulations on emissions and also to improve the efficiency of operation. Extended periods of high stress over time will induce creep deformation and, eventually, static failures in such alloys. For this reason, prior to using these alloys in such applications, their deformation behaviour has to be studied through mechanical testing. However, testing might vary from few hours up to several months which, in return, will have a considerable influence on the cost of these components. As an alternative, a new extrapolation technique, ‘The Wilshire Equations’, has been developed at Swansea University in order to predict the creep rupture behaviour. In addition, this technique has been extended to re-construct full creep curves based on short-term measurements. This new capability will, thus, reduce the cost and the time required to carry out such long-term tests. As a model material, Titanium 834, which is currently used in aeroengine applications, has been employed for the analysis using the Wilshire approach.

The Magnitude and Origin of Residual Stress in Ti-6Al-4V Linear Friction Welds: An Investigation by Validated Numerical Modeling

Abstract: The linear friction welding (LFW) process—of the type required for production of bladed discs for the next-generation aeroengines—was modeled using numerical methods developed previously. An elastic–viscoplastic material formulation was considered to allow for residual stress calculations to be included in the numerical solution. A study of the evolution of residual stress during the welding and cooling processes was made. It was evident that residual stresses arose primarily as a consequence of the cooling of the part after joining is completed. The sensitivity of predicted residual stress to the applied forge load was investigated and compared with measurements from X-ray diffraction methods. Only small changes in residual stress were predicted for large changes in forge load, supporting the hypothesis that the welding process is only of secondary importance to residual stress formation, after the cooling process. Finally, a sensitivity study was carried out investigating the accuracy of modeling the welding process with a simpler, viscoplastic material law, and only switching to the more computationally demanding elastic–viscoplastic law for the cooling modeling. Predictions suggested that this was a sufficient modeling method, given that stress during the welding stage is almost uncorrelated to that present once ambient temperature is reached.

A sacrificial anode

Abstract: This invention relates to a body including a sacrificial anode, comprising: a first layer of a first material; and, a second layer of a second material which is electrically connected to the first layer, wherein the first material is more anodic with respect to a galvanic series than the second material.

Bonding of metal components

Abstract: A method of bonding a first component (10) comprising a titanium-containing alloy to a second metal component (12), wherein a coating layer (14,16) is applied to each of the first and second components in the region to be bonded. The coating layers (14,16) comprise a precious metal. An intermediate metallic layer (18) is interposed between the coating layer (14) of the first component and the coating layer (16) of the second component. The respective coating layers are held in contact with the intermediate layer (18) and the coating layers and the intermediate layer are heated to initiate melting of at least one of said layers so as to form a bond between the first and second components by brazing.

Microstructural Characterization of a Prototype Titanium Alloy Structure Processed via Direct Laser Deposition (DLD)

Abstract: Processing trials have produced a three-dimensional, thin-walled structure of representative aerospace component geometry, fabricated directly by laser melting of Ti 6Al4V powder. This additive-built form has been subjected to metallographic characterization. The fabrication technique is evaluated as an economic, commercial process that can add features such as bosses or flanges as a hybrid-manufacturing route for existing forms of gas turbine components. The samples were extracted from six locations with different wall thickness, varying forms, and intersecting ligament geometries. A fine-scale Widmanstatten colony microstructure was consistent throughout the structure within grains elongated parallel to the axis of epitaxy. Evidence of limited grain boundary α was detected; however, this was never continuous around individual grains. A moderate Burgers texture was measured employing electron backscatter diffraction (EBSD), which is consistent with the melt/cast titanium alloy forms cooling through the β transus.