Rolls-Royce Limited

About: Rolls-Royce Limited is a based out in . It is known for research contribution in the topics: Gas compressor & Rotor (electric). The organization has 624 authors who have published 623 publications receiving 10751 citations. The organization is also known as: Rolls Royce Limited.

The role of shear-layer instability waves in jet exhaust noise

Abstract: Large-scale structures in the form of instability waves are an inherent part of a shearlayer mixing process. Such structures are shown to be present in an acoustically and aerodynamically well behaved jet even at high Mach numbers. They do not directly radiate significant acoustic power in a subsonic jet, but do govern the production of the turbulent fluctuations which radiate broad-band jet noise. Over the whole subsonic Mach number range, a significant increase in jet noise can be produced by exciting the shear layer with a fluctuating pressure at the nozzle of only 0·08 % of the jet dynamic head but with the correct Strouhal number. Such excitation by internal acoustic, aerodynamic or thermal fluctuations could explain the variability of jet noise measurements between different rigs and could also be responsible for some components of ‘excess’ noise.

The strength of fused silica

Abstract: Silica fibres and flame polished rods having strengths around 600 Kg/mm2 were prepared and the preparation conditions studied. The effects on fibre strengths of atmospheric and temperature changes, and of variations in rate of stressing and previous heat treatment, were extensively investigated. From the results obtained a comprehensive qualitative picture of the strength of silica has been deduced; it is found to be strongly dependent on the testing conditions and to extend over the range 280 to 1500 Kg/mm2. INTRODUCTION With the increasing interest in composite materials, in which the load is borne by fibres of a brittle material, it becomes more and more important to understand the factors which govern the strength of brittle materials. This work on fused silica formed part of a more general study of composites and the context was briefly described by Morley (i964). The strength of silicate glasses has been studied for many years but until quite recently all work was carried out with 'weak' specimens which had suffered abrasive surface damage in their preparation or testing. Since the importance of surface damage was scarcely recognized and handling techniques varied widely, this led to very variable strengths, irreproducibility of results from one laboratory to another and a large apparent size dependence of strength. Further, true variations in the strength of the material (due to temperature, moisture, etc.) were often obscured or confused by the effects these variables had on the nature of the existing surface flaws. In this work high strength silica samples were prepared by adapting and extending the techniques of fibre production and handling described by Morley, Andrews & Whitney (i964). Stringent precautions were taken to avoid any contact whatso- ever with the surface of the silica under test and strengths up to 150OKg/mm2 were obtained under certain test conditions. It seems possible that the true strength of the material was being measured. These same high strength samples were studied under a wide range of conditions and the strength was seen to be a complex function of the atmosphere in which the silica was stressed, the temperature, and the rate of stressing. Specific damaging or weakening effects due to heat treatment or specimen preparation could be superimposed on the other factors. In attempting to present a clear account of the strength behaviour we describe each effect in a separate section of the paper. Some discussion of proposed mechan- isms has been introduced at each stage since this appeared necessary to explain the results described in following sections.

Multi-layer acoustic linings

Abstract: A multi-layer acoustic lining, e.g. for a flow duct in a gas turbine aeroengine, includes Helmholtz-type and tube-type resonators sandwiched between backing and facing sheets. In the invention, the ends of the tube-type resonators abut the Helmholtz resonators but are acoustically divided from them by partition means in such a way that the tube-type resonators differ from each other in resonant frequency. Variation of resonant frequency in the tube-type resonators is achieved by variation of their lengths according to which portion of the partition means acoustically divides them from the Helmholtz-type resonators, the partition means being arranged either step-wise or inclinedly between the backing and facing sheets.

Fuel control system for a gas turbine engine

Abstract: A fuel control system for a gas turbine engine comprises a main fuel controller and an overspeed limiter arranged to prevent overspeed of the engine in the case of a fault in the main controller To ensure that the limiter is tested regularly, the logic capacity of the main controller (which is preferably a digital electronic unit) is used to vary the parameters of the limiter each time the engine is started up This variation is such as to cause the limiter to operate and produce an observable reduction in the engine speed which is detected by the main controller and uses as an indication of correct limiter operation

The Response of Axial Flow Compressors to Intake Flow Distortion

Abstract: The response of a lift engine model compressor to inlet pressure distortion is studied in detail to determine the nature and extent of the critical area of spoiling. This is found to be a sector of width between 60 and 90 deg. On this basis a simple distortion index is proposed which implies that only the circumferential pressure gradients of a complex distortion pattern are significant. The “Parallel Compressor” model satisfactorily explains surge and this experience is related to different types of compressors and to complex spoiling patterns. Comments are made on the differences in behavior between compressors operating on rig test and in engines.Copyright © 1969 by ASME