Passive Morphing in Aerospace Composite Structures

Attempts to add the advanced technologies to aerospace composite structures like fan blade have been on in recent times to further improve its performance. As part of these efforts, it has been proposed that the blade morph feasibility could be studied by building and optimizing asymmetric lay up of composite plies inside the blade which will help generate enough passive morphing between max cruise and climb conditions of the flight. This will have a direct efficiency (Specific Fuel Consumption) benefit. This research describes the various ideas that were tried using in house-developed lay-up optimization code and Ansys commercial software to study the possibility of generating enough passive morphing in the blade. In the end, this report concludes that the required degree of passive morphing could not be generated using various ideas with passive morphing technology and only up to some extent of morphing is shown to be feasible using the technologies used here.

An Investigation of Flow, Mechanical, and Thermal Performance of Conventional and Pressure-Balanced Brush Seals

Compliant contacting filament seals such as brush seals are well known to give improved leakage performance and hence specific fuel consumption benefit compared to labyrinth seals. The design of the brush seal must be robust across a range of operating pressures, rotor speeds, and radial build-offset tolerances. Importantly the wear characteristics of the seal must be well understood to allow a secondary air system suitable for operation over the entire engine life to be designed. A test rig at the University of Oxford is described which was developed for the testing of brush seals at engine-representative speeds, pressures, and seal housing eccentricities. The test rig allows the leakage, torque, and temperature rise in the rotor to be characterized as functions of the differential pressure(s) across the seal and the speed of rotation. Tests were run on two different geometries of bristle pack with conventional, passive, and active pressure-balanced backing ring configurations. Comparison of the experimental results indicates that the hysteresis inherent in conventional brush seal design could compromise performance (due to increased leakage) or life (due to exacerbated wear) as a result of reduced compliance. The inclusion of active pressure-balanced backing rings in the seal designs are shown to alleviate the problem of bristle–backing ring friction, but this is associated with increased blow-down forces which could result in a significant seal-life penalty. The best performing seal was concluded to be the passive pressure-balanced configuration, which achieves the best compromise between leakage and seal torque. Seals incorporating passive pressure-balanced backing rings are also shown to have improved heat transfer performance in comparison to other designs.

IC Engine Air System Uni-, Bi-, and Tri-Directional Energy Flow Optimisation: Turbocharging, Turbocompounding and Turbodischarging

Air systems are becoming increasingly complex and important for achieving IC engine performance and emission targets. Turbocharging is becoming increasingly prevalent enabling high power density engines, improved pumping work and improved fuel economy. Turbo-compounding allows turbine energy to contribute directly to crankshaft work with the aim of improving fuel economy. Turbodischarging allows turbine energy to be used to extract exhaust gases from the engine reducing pumping work and residual gas fraction while simultaneously increasing the amount of energy that can be recovered by the turbine(s). The optimum energy flow split between turbocharging, turbodischarging and turbocompounding has not previously been explored. This paper presents results of a study investigating the potential of tri-directional energy flow optimisation in comparison to uni-directional optimisation and bi-directional optimisation (i.e. using all three approaches, any two approaches or turbocharging alone). Thermodynamic analysis demonstrates the potential of bi-directional optimisation to achieve realistically 4% fuel consumption benefit for both turbocharging and discharging, and turbocharging and compounding on gasoline engines from pumping work alone. The peak benefit of the former occurs at a slightly lower engine torque than the latter as the energy cost of a unit fuel consumption benefit with turbodischarging increases with increasing levels of exhaust depressurisation. The Tri-directional optimisation shows a complex optimum position utilising all three systems and achieving a realistic peak benefit of 4.4% fuel consumption improvement. Optimisation on diesel engine architectures suggests significantly lower potential in the order of 1% benefit while lean burn gas engines showed up to 2.6% benefit. Sensitivity to compression and expansion efficiencies, exhaust manifold volume and system temperatures are presented. The future hybridisation of IC engine air systems may enable energy storage. This paper offers fundamental insight into the marginal fuel cost of capturing energy from the three systems and the marginal fuel value of using stored energy in the air system.

An Investigation of Flow, Mechanical and Thermal Performance of Conventional and Pressure-Balanced Brush Seals

Compliant contacting filament seals such as brush seals are well known to give improved leakage performance and hence specific fuel consumption benefit compared to labyrinth seals. The design of the brush seal must be robust across a range of operating pressures, rotor speeds and radial build-offset tolerances. Importantly the wear characteristics of the seal must be well understood to allow a secondary air system suitable for operation over the entire engine life to be designed. A test rig at the University of Oxford is described which was developed for the testing of brush seals at engine-representative speeds, pressures and seal housing eccentricities. The test rig allows the leakage, torque and temperature rise in the rotor to be characterized as functions of the differential pressure(s) across the seal and the speed of rotation. Tests were run on two different geometries of bristle-pack with conventional, passive and active pressure-balanced backing ring configurations. Comparison of the experimental results indicates that the hysteresis inherent in conventional brush seal design could compromise performance (due to increased leakage) or life (due to exacerbated wear) as a result of reduced compliance. The inclusion of active pressure-balanced backing rings in the seal designs are shown to alleviate the problem of bristle-backing ring friction, but this is associated with increased blow-down forces which could result in a significant seal-life penalty. The best performing seal was concluded to be the passive pressure-balanced configuration, which achieves the best compromise between leakage and seal torque. Seals incorporating passive pressure-balanced backing rings are also shown to have improved heat transfer performance in comparison to other designs.

A Preliminary Parametric Study for Geared, Intercooled and/or Recuperated Turbofan for Short Range Civil Aircrafts

Aviation plays a key role in economic prosperity and quality of lifestyle. However there is an increasing concern that current trends of consumption of natural resources cannot continue. It is imperative that major targeted investments are made into economical and reliable environment friendly propulsion and power solutions. A significant amount of this investment will be in the aerospace sector. A well utilised civil aircraft may burn more than 2000 times its weight in fuel during its life, so the examination of the propulsion system is essential from an environmental point of view. A preliminary parametric study for geared, intercooled and/or recuperated turbofan for short range commercial transport applications has been performed with regard to fuel consumption and emissions. A high by-pass ratio turbofan engine with performance characteristics and technology from the year 2000 was set up as a baseline. The results offer interesting qualitative comparisons showing that, for instance, a recuperated engine will yield a lower fuel burn for lower OPR values. An engine with a mid-compressor intercooler may give significant reduction of NOx emissions whilst increasing the amount of CO2. The intercooled and recuperated cycle offers higher thermal efficiencies (i.e. higher fuel consumption benefit) in comparison to other cycles at medium OPR values; therefore NOx formation may be reduced as well as the engine core weight. Additionally, the inherent advantage of high BPR against low BPR turbofans in terms of SFC is evident (GTF). Clearly, therefore, an increase of BPR is an inevitable solution for the reduction of both fuel consumption and the level of noise produced, however this may involve NOx and integration penalties, hence innovative cycles (e.g.: ICR) and state of the art combustor technology (e.g.: PERM and LDI combustors) must be considered. This is first on the series of work that would be carried out on the cycles being proposed in this paper. Further work on the issues of weight, noise, aircraft performance, other emissions, economics, etc, so-called a multidisciplinary objective assessment, would be published when completed. Also, at this time the design has been limited to take-off being the point of maximum aerodynamic performance. An extension to full mission is currently under investigation.