Effect of Radiation on Heat Transfer inside Aeroengine Compressor Rotors

The blade clearance in aero-engine compressors is mainly controlled by the radial growth of the compressor discs, to which the blades are attached. This growth depends on the radial distribution of the disc temperature, which in turn is determined by the heat transfer inside the internal rotating cavity between adjacent discs. The buoyancy-induced convection inside the cavity is significantly weaker than that associated with the forced convection in the external mainstream flow, and consequently radiation between the cavity surfaces cannot be ignored in the calculation of the disc temperatures. In this paper, both the Monte Carlo Ray-Trace (MCRT) method and the view factor (VF) method are used to calculate the radiative flux when the temperatures of the discs, shroud, and inner shaft of the compressor vary radially and axially. The Monte Carlo Ray-Trace method is computationally expensive, but it is able to incorporate the effect of complex geometries on radiation. The view factor method is quick to compute and, although the derivation becomes complicated when geometrical details are considered, it can be used as a first check of the effect of radiation in compressor cavities. Given distributions of surface temperatures, the blackbody and gray body heat fluxes were calculated for the discs, shroud, and inner shaft in two experimental compressor rigs and in a simulated compressor stage. For the experimental rigs, although the effect of radiation was relatively small for the case of large Grashof numbers, the relative effect of radiation increases as Gr (and consequently the convective heat transfer) decreases. For the simulated compressor, with a pressure ratio of 50:1 for state-of-the-art aircraft engines, radiation could have a significant effect on the disc temperature and consequently on the blade clearance; the effect is predicted to be more prominent for the next generation of aircraft engines with pressure ratios up to 70:1.<br/

Armed violence, governance, security sector reform, and safety security and access to justice

This briefing aims to highlight and clarify the importance of the availability and misuse of small arms and light weapons (SALW), and associated armed violence, for development programming in the areas of governance, security sector reform (SSR), and safety, security and access to justice (SSAJ). By doing so the effectiveness of governance, SSR and SSAJ programmes can be enhanced. Moreover, governance, SSR and SSAJ programmes can be developed to contribute more to the reduction of armed violence perpetrated with SALW and facilitated by their availabilit

Would Two Dimensions be World Enough for Spacetime?

We consider various curious features of general relativity, and relativistic field theory, in two spacetime dimensions. In particular, we discuss: the vanishing of the Einstein tensor; the failure of an initial-value formulation for vacuum spacetimes; the status of singularity theorems; the non-existence of a Newtonian limit; the status of the cosmological constant; and the character of matter fields, including perfect fluids and electromagnetic fields. We conclude with a discussion of what constrains our understanding of physics in different dimensions.Comment: 31 pages, 1 figur

Armed violence and conflict assessments

This briefing aims to clarify and highlight ways in which the spread, possession and (mis)use of SALW and related armed violence issues can be relevant in conflict assessments, and how they can be integrated better within such assessments. It employs the conflict assessment framework set out in DFID¿s conflict assessment guidelines, and thus aims particularly to assist people who may be: commissioning and developing terms of reference for a specific assessment; undertaking a desk-based and/or field assessment; and those taking forward the analysis to the development of programming responses. There already exists the potential for SALW issues to be addressed within DFID¿s existing conflict assessment guidelines, and thus this paper does not suggest that DFID¿s methodology has to change but rather `opened-up¿ to include SALW more fully within their analyses and the strategies they generate

Radial evolution of sunward strahl electrons in the inner heliosphere

The heliospheric magnetic field (HMF) exhibits local inversions, in which the field apparently “bends back” upon itself. Candidate mechanisms to produce these inversions include various configurations of upstream interchange reconnection; either in the heliosphere, or in the corona where the solar wind is formed. Explaining the source of these inversions, and how they evolve in time and space, is thus an important step towards explaining the origins of the solar wind. Inverted heliospheric magnetic field lines can be identified by the anomalous sunward (i.e. inward) streaming of the typically anti-sunward propagating, field aligned (or anti-aligned), beam of electrons known as the “strahl”. We test if the pitch angle distribution (PAD) properties of sunward-propagating strahl are different from those of outward strahl.We perform a statistical study of strahl observed by the Helios spacecraft, over heliocentric distances spanning ≈ 0.3 – 1 AU. We find that sunward strahl PADs are broader and less intense than their outward directed counterparts; particularly at distances 0.3 – 0.75 AU. This is consistent with sunward strahl being subject to additional, path-length dependent, scattering in comparison to outward strahl.We conclude that the longer and more variable path from the Sun to the spacecraft, along inverted magnetic field, leads to this additional scattering. The results also suggest that the relative importance of scattering along this additional path length drops off with heliocentric distance. These results can be explained by a relatively simple, constant-rate, scattering process

Considering armed violence in the post-conflict transition: DDR and small arms and light weapons reduction initiatives

This briefing paper seeks to increase awareness of and review the linkages between disarmament, demobilisation and reintegration (DDR) and small arms and light weapons (SALW) reduction in the context of post-conflict reconstruction (PCR). It is targeted at those working on poverty reduction at both the policy and programme level, particularly those with comparatively modest engagement in these areas. Its objective is to outline the types of activities that have been undertaken under these rubrics, the difficulties and constraints encountered at the level of implementation, and, in particular, to identify opportunities in linking SALW programmes and DDR. It also seeks to highlight the problems created by widespread arms availability and usage in PCR. This briefing paper is not intended as a comprehensive review of the state of DDR/SALW/PCR programming and policy, but rather an introduction to some of the core issues

A simple model to quantify the potential trade-off between water level management for ecological benefit and flood risk

Throughout the world, historic drainage of wetlands has resulted in a reduction in the area of wet habitat and corresponding loss of wetland plant and animal species. In an attempt to reverse this trend, water level management in some drained areas is trying to replicate a more natural ‘undrained’ state. The resulting hydrological regime is likely to be more suitable to native wetland species; however the raised water levels also represent a potential reduction in flood water storage capacity. Quantifying this reduction is critical if the arguments for and against wetland restoration are to be discussed in a meaningful way. We present a simple model to quantify the hydrological storage capacity of a drainage ditch network under different water level management scenarios. The model was applied to the Somerset Levels and Moors, UK, comparing areas with and without raised water level management. The raised water level areas occupy 11% of the maximum theoretical storage but when put in the context of the recent severe flooding of winter 2013/2014 occupy only 0.6% of the total flood volume and represent an average increase in flood level of 7 mm. These results indicate that although the raised water level scheme does occupy an appreciable volume of the maximum possible ditch storage, in relation to a large flood event the volume is very small. It therefore seems unlikely that the severity of such large flood events would be significantly reduced if the current water level management for ecological benefit ceased