The measurement of train aerodynamic phenomena in operational conditions

There are a variety of aerodynamic effects associated with train design and operation - the determination of aerodynamic drag, the effect of cross winds on train stability, pressure transient loading on trackside structures, the physiological effect of tunnel pressure transients, the effect of train slipstreams and wakes on waiting passengers and trackside workers etc. The magnitude of these effects broadly increases as the square of the vehicle speed and thus with the continued development of high speed train lines aerodynamic effects will become more significant in terms of design and operation. Now it can be hypothesised that the techniques that have been used to predict aerodynamic effects in the past (wind tunnel and CFD methods) are likely to determine magnitudes of pressures, velocities, forces etc. that are higher than those observed in practice, where other effects - such as track roughness, variability in meteorological conditions etc. are likely to usually obscure aerodynamic effects to some extent and, because of this, some of the current design methodologies are unnecessarily restrictive and/or conservative. Thus the aim of the current project is to investigate and measure a range of aerodynamic phenomena observed in real train operation, both relative to the train and relative to a fixed point at the trackside, and to compare how such effects match model scale measurements and various types of CFD calculation, and thus to test the validity, or otherwise, of the above hypothesis. This will be achieved through the instrumentation of the Network Rail High Speed Measuring Train to measure aerodynamic effects, as the train carries out its normal duty cycle around the UK rail network. Also trackside instrumentation will be installed at a suitable site that will allow off-train phenomena to be measured. Calibration wind tunnel, CFD and moving model tests will be carried out in the conventional way for comparison with data measured at full scale. The full scale, model scale and computational trials will be carried out by experienced RFs and will provide data for two doctoral studies, one of which will investigate how the train based measurements of cross wind forces, pressure transients etc compare with those predicted by conventional methodologies, and one of which will investigate how the track side measurements compare with conventional test results. The investigators will synthesise the results and make recommendations for future aerodynamic test methods.

In the last few decades there has been a renewed interest in high speed railways. A number of new lines have been built in mainland Europe and in the Far East and there is also a real possibility that new high speed trains will be running in the UK, north of London, in the not too distant future. These new schemes pose a number of technical challenges not only in terms of the development of new infrastructure but also in terms of the effect that they may have on existing infrastructure and trains. Among these challenges that have to be considered are a number of aerodynamic phenomena such as the pressure pulses at trackside and in tunnels, the slipstreams and wakes of trains, train stability in cross winds etc, all of which have significant safety implications. Since, very broadly, the magnitude of these phenomena increase with the square of train speed, they can be expected to become of increasing significance in the future. Now there is a concern that current design procedures for aerodynamic effects are currently overly conservative and restrictive. The research aims to address this concern through a co-ordinated study which involves measurements on real trains, at the trackside, wind tunnel experiments and flow field calculations. The measurements on the real trains are particularly important since they provide an insight into how different factors (e.g., track roughness and meteorological conditions) combine to affect the overall forces acting on trains.

Conservatism in design leads to increased design costs and increased costs as a result of slower train speeds, a component of which are ultimately borne by the travelling public. Thus, train manufactures, network rail and station operators will be benefit from an alleviation of restrictive design procedures. Engineering consultancies will benefit from an increased understanding of the fundamental issues associated with high speed trains which will ultimately lead to a reduction in their costs and the travelling public is also likely to benefit from reduced fares which should follow as industry's costs are reduced. However, an important benefit to this particular group will be an increase in the safety standards applied to the rail network. For example, it is known that increasing train speeds also increases the wind flow around passengers standing on platforms as a non stopping train passes through (i.e., the train's slipstream). Any increase in the wind flow (or wind speed) will potentially make the forces experienced by passengers standing on platforms increase significantly. This work aims to not only examine this issue through experiments but also to bring together existing data from across Europe in order to provide a comprehensive database of measurements. The examination and interpretation of this data will enable informed decisions to be taken regarding passenger safety.

Finally, this research will also benefit a section of the public not traditionally targeted by University research, i.e., school children. In addition to running an art competition which will engage and enthuse a relatively large number of pupils, the proposers have chosen to work closely with two schools at different ends of the educational spectrum: a specialist language and science secondary school has been chosen, in addition to a primary school where the majority of pupils have family incomes below the national average and where there are a number of pupils who have a wide range of learning difficulties and/or disabilities. It is envisaged that working closely with these schools will encourage pupils to take an interest in their environment, current political issues and also consider pursing scientific careers.