Department of Engineering - Annual Report 1997/98

Energy

Acoustics
Internal Combustion Engines
Computational Combustion
Nuclear Engineering
Fluid Mechanics in Process Metallurgy
Magnetohydrodynamics

References

Acoustics

High-speed transport is a major source of noise and reducing its environmental impact presents considerable technological challenges. Research continues on aircraft noise. In particular, models are being developed to predict fan noise in high bypass ratio aeroengines. The ingestion of atmospheric turbulence and its subsequent chopping by rotating fan blades can lead to high-amplitude noise in ground tests and in aircraft approach conditions. Reduction in radiated sound can be achieved by appropriate shaping of the aeroengine inlet(A26). New work has begun on reducing the noise of road transport. A mathematically based model is being developed to predict the exterior noise generated at the tyre-to-road interface under various conditions of traffic operation. This EPSRC-funded project is being carried out in collaboration with Dunlop Tyres Ltd, Rover Cars and the Transport Research Laboratory (TRL). It involves modelling the vibration of the tyre surface near the contact patch and predicting the sound field generated. Vibrating surfaces are also a major source of noise in a range of underwater applications(A17) where fluid structure interaction is significant(A34).

Flow instabilities and acoustics are closely coupled. An acoustic wave perturbs an unstable flow leading to flow disturbances. In general, these flow disturbances are sources of sound and self-excited oscillations can occur(A15). Highly unstable fluid flows can be controlled by suitably designed feedback controllers(A21). A control method based on maximising the rate of energy extraction from a wave field has been successfully demonstrated to reduce sound and vibration(A22). A new method for predicting the transition to turbulence on swept aircraft wings has been developed by exploiting ideas from the theory of absolute instability(A44,A45). The same technique has been used to model the interaction between vorticity and blades in a transonic flow(A19). Particular attention has been given to predicting the acoustic resonances in turbomachinery(A47). The convection of vorticity(A43) past a blade row invariably generates sound. Conversely, interaction of an incident sound wave with appropriate surfaces in a mean flow leads to vorticity: an effect that can be exploited to design effective passive sound absorbers(A18).

Gas turbine combustors are being driven to operate increasingly close to instability in order to meet ever more stringent emission requirements. By burning in a lean premixed mode NOx emissions can be reduced to less than one-tenth of the levels from conventional combustors. However, this has the disadvantage that premixed flames are particularly susceptible to thermoacoustic oscillations and many premixed systems have experienced structural damage caused by combustion instability(A16). The instability arises due to an interaction between the acoustic waves and the unsteady combustion. Five post-doctoral researchers have been appointed to investigate different aspects of this instability. With financial support from the EU, a major experimental facility has been installed in the Hopkinson Thermodynamics Laboratory consisting of a half-scale industrial burner operating at atmospheric conditions. The rig is being used to validate theoretical modelling and to test out control strategies. In collaboration with Rolls-Royce, work is in progress on a theoretical model of the complex acoustics/flame interaction in a typical industrial gas turbine(A23). CFD is proving to be a useful tool, both in analysing premixed combustion of a gaseous fuel (in a project funded by Hitachi) and the oscillations that occur at idle in liquid-fuelled aeroengines (funded by EPSRC). We are interested in both active and passive means of controlling damaging oscillations. The most practical means of active control is through the suitably phased addition of extra fuel. Work in this area includes both model-based(K20) and adaptive(A20) control strategies.

Internal Combustion Engines

The activities in the engines group have again been ominated by emissions research. Following their development in previous years, further studies of the behaviour and application of a very high frequency response emissions system for unburnt hydrocarbons (uHCs) and oxides of nitrogen (NOx) continues. A review paper has appeared discussing research conducted over the last 10 years with the uHC instrument(A9). Combined application of the two instruments has revealed new insights into the emission characteristics of gasoline and Diesel engines(A35,A40). Detailed investigations of the flow distribution in space and time over an automotive catalyst have been made using the fast uHC instrument in a novel application(A27). The high speed NOx instrumentation has also been used to look at catalysts under transient conditions(A10).

Gasoline direct injection engines have become a topic of intense research interest, and we have been involved with studies of how to achieve the rapid changes in mixture strength required for these engines(A32). Continued support from the Ford Motor Company has enabled the group to maintain some of the best engine research facilities in the country.

Computational Combustion

Work on computational combustion has continued to expand within the framework of the Computational Fluid Dynamics (CFD) Laboratory, which is run as a joint activity between Professor W.N. Dawes, Dr A.M. Savill and Dr R.S. Cant. The intention is that computational combustion should proceed at all levels, from Direct Numerical Simulation (DNS) through Large Eddy Simulation (LES) to Reynolds-Averaged Navier-Stokes (RANS) simulation of a range of combustion problems.

At the fundamental level, DNS offers the capability to conduct numerical experiments in turbulent combustion by solving the governing equations directly without any form of modelling, and to obtain insight and statistical data that is unobtainable by other means. Two projects are currently under way in this area, both supported by EPSRC. One is making use of high-order finite-difference methods and massively parallel computers to compute statistical data on turbulent flame kernel growth(A24,A25). The other is investigating the use of wavelet-based discretisation methods which has been shown to offer major advantages in numerical efficiency for problems involving complex chemistry(A37,A38).

It is becoming increasingly clear that LES is the way forward for many industrial problems in combustion CFD, particularly where unsteady effects are important. The focus is applications to lean premixed gas turbine combustion, where emissions legislation is driving a major advance in combustion technology. Two projects in this area, sponsored by Alstom Gas Turbines, are investigating new sub-grid scale models for turbulent transport and reaction rate effects, with a view towards their implementation in future industrial codes. Information obtained from DNS calculations is being used extensively to guide model development and to validate model predictions, while questions arising from LES are being fed back to the DNS projects.

For many industrial problems there remains no alternative to RANS in terms of computational efficiency and proven capability within a specific class of problems. RANS-based model development is continuing in the context of stratified-charge spark-ignition engines(A39), in gas-turbine combustors, in large-scale accidental explosions in the offshore oil and gas industry(A4,A5), and in deflagration-to-detonation transition modelling. Sponsors for this work include Ricardo Consulting Engineers, Hitachi Europe, HSE, Shell, BG Research and Technology and EPSRC. Several different CFD codes are in use, including structured 2D pressure-based solvers
used mainly for model validation, and an unstructured adaptive 3D code incorporating a tetrahedral mesh system that is able to deal with geometries of arbitrary complexity(B14). Once again, model development is carried out in the light of information cascaded from the DNS and LES levels of activity.

Nuclear Engineering

Longstanding research in collaboration with Nuclear Electric (British Energy) and North Carolina State University continued into the optimisation of in-core fuel cycles (reload design) for Pressurised Water Reactors. Further advances were made in the development of a method for solving multiobjective reload design problems using a Genetic Algorithm(A33). A collaboration with Imperial College investigating the potential of Tabu Search for in-core fuel cycle optimisation was initiated.

Research into the use of variational techniques in the solution by Monte Carlo simulation of neutron transport equations continued(A3), and the first results demonstrating the effectiveness of the novel "virtual sampling" method were obtained.

Extensive investigations into the Monte Carlo simulation of system reliability were made. Results demonstrating the use of the concept of "life cycle revenue loss" to assess system performance were published(A7). Variance reduction techniques for use in logistics simulation were examined(A6) and a novel variational principle for reliability studies was developed(A31) and demonstrated(A6).

Two notes concerning the teaching of thermodynamics were published(A29,A30) and an entry was contributed to a major new encyclopedia(A28).

Fluid Mechanics in Process Metallurgy

Fluid mechanics plays a critical rôle in the production and casting of metals. For example, aluminium is produced by electrolysis in large reduction cells. This process is highly energy intensive, requiring around 30 MWatt hrs to produce one tonne of semi-finished product (about seven times the energy required to produce steel). Yet the bulk of the energy expended in reduction cells is not required for electrolysis, but rather is lost in resistive heating of the electrolyte. Attempts to increase the efficiency of these cells, by reducing the volume of electrolyte, have been fundamentally limited by the appearance of an instability which manifests itself as a sloshing of the electrolyte and is directly triggered by the reduction in electrolyte volume. The fundamental nature of these instabilities is just beginning to be understood(A12,A13).

In the casting industry, on the other hand, fluid flow plays a critical rôle in determining the metallurgical structure, quality and surface finish of an ingot. There are vigorous turbulent flows within the liquid zone of a partially solidified ingot, driven by thermal buoyancy, by compositional variations throughout the melt, and by the flow of liquid into the mould. This flow is the dominant mechanism for transporting heat, chemical species and crystal fragments within the liquid metal pool. Modest changes in the structure of this flow can produce a large difference in the distribution of impurities and dendrite size and morphology within the final ingot.

Research Council awards in this area are supporting our work on: the influence of fluid flow on macrosegregation in aluminium ingots; the control of high-temperature titanium jets in spray-forming processes; and the fluid mechanics of vacuum-arc remelting(A41,A42,A46).

Magnetohydrodynamics

Magnetic fields can be used to levitate, pump and stir liquid metals, to suppress natural convection, and to reorganise the structure of turbulent flows. We are actively involved in all of these areas. In MHD turbulence we are examining the rôle of magnetic fields in preferentially suppressing transverse components of angular momentum(A11). This leads to a strongly anisotropic turbulent structure, reminiscent of turbulence in stratified or rotating media. This may be quantified using a variant of the classic Kolmogorov/ Landau model for the decay of conventional, isotropic turbulence. We are also examining the behaviour of quasi-two-dimensional turbulence, induced by very intense magnetic fields. Here direct numerical simulation of two-dimensional turbulence is planned, funded by Fluent Europe. This has applications in MHD and geophysics.

Work on buoyancy-driven flows has been continuing both in the Department and, in collaboration, at the two French laboratories at Grenoble, Madylam and CEA-CEREM, to which reference was made in last year's Report. A comparison of numerical predictions with analytical for the flow in a Bridgman crystal-growth configuration has been published(A14). Concerning segregation, work on the improvement in dopant homogeneity has been published(A2) for the case of decoupled thermal buoyancy and developments are now oriented towards the understanding of nonlinear solute-driven convection using both analytical and numerical techniques. Studies of how a steady magnetic field may lessen the influence of convection, either of thermal or of solute origin, in the measurement of diffusivities have been undertaken analytically; the predictions have been confirmed by numerical work and also validated by the experimental results of our colleagues in France(A1).

In collaboration with R.J. Lingwood, a stability analysis has been performed for the Hartmann layer, which commonly occurs at solid boundaries to magnetohydrodynamic flows when there is a magnetic-field component perpendicular to the boundary and which may have an important influence on the whole flow field in crystal-growth and metallurgical applications. The motivation for the work lies in the discrepancy found as long ago as the 1960s between experimental results and linear stability analysis.

A1. Alboussière, T., Garandet, J.P., Lehmann, P., Moreau, R. Convective effects in the measurement of diffusivities and thermotransport coefficients. Liquid metal alloys and the use of a magnetic field. Proceedings, 3rd International Meeting on Thermodiffusion, RIT-IMT, Mons, Belgium (September 1998).

A2. Alboussière, T., Neubrand, A.C., Garandet, J.P., Moreau, R. Segregation during horizontal Bridgman growth under an axial magnetic field. Journal of Crystal Growth, 181, (1-2), 133-144 (1997).

A3. Allagi, M.O., Lewins, J.D., Parks, G.T. Variationally processed Monte Carlo transport theory. Annals of Nuclear Energy, 25, (13), 1055-1068 (1998).

A4. Birkby, P., Cant, R.S., Savill, A.M. The application of an unstructured adaptive mesh methodology to resolved computations for confined explosion hazards. Proceedings, 7th International Conference on Numerical Combustion, York (March/April 1998).

A5. Birkby, P., Cant, R.S., Savill, A.M. The application of laminar flamelet model to confined explosion hazards. Poster presentation. 27th Symposium (International) on Combustion, Boulder, CO, USA, W2C12 (August 1998).

A6. Chang, M., Lewins, J.D. Some experiences in using biasing and antithetic variance techniques in Monte Carlo logistics simulation. Proceedings, European Safety and Reliability Conference, ESREL'98, Trondheim, Norway (June 1998); Edited by S. Lydersen, G.K. Hansen, H. Sandtorv, 697-702 (Balkema, 1998).

A7. Chang, M., Lewins, J.D. Using life cycle revenue loss and Monte Carlo simulation as a prior and direct assessment of consequences of unwished events. Annals of Nuclear Energy, 25, (1-3), 117-127 (1998).

A8. Chang, M., Lewins, J.D., Parks, G.T. System reliability estimated variationally from Monte Carlo simulation. Proceedings, 4th ISSAT (International Society of Science and Applied Technologies) International Conference on Reliability and Quality in Design, Seattle, WA, USA, 92-96 (August 1998).

A9. Cheng, W., Summers, T., Collings, N. The fast response flame ionization detector. Progress in Energy and Combustion Science, 24, (2), 89-124 (1998).

A10. Collings, N., Peckham, M.S., Yufune, T. Real time NO conversion characteristics of catalysts. JSAE (Society of Automotive Engineers of Japan) Spring Convention, Yokohama, Japan (May 1998).

A11. Davidson, P.A. On the application of the Kelvin-Arnold energy principle to the stability of forced, two-dimensional inviscid flows. Journal of Fluid Mechanics, 356, 221-257 (1998).

A12. Davidson, P.A., Lindsay, R.I. Stability of interfacial waves in aluminium reduction cells. Journal of Fluid Mechanics, 362, 273-295 (1998).

A13. Davidson, P.A., Lindsay, R.I. Stability of interfacial waves in aluminium reduction cells. Light Metals 1998: Proceedings, 127th TMS (the Minerals, Metals, Materials Society) Annual Meeting, San Antonio, TX, USA (February 1998); Edited by B. Welch, 437-444 (TMS, Warrendale, PA, 1998).

A14. Davoust, L., Moreau, R., Cowley, M.D., Tanguy, P.A., Bertrand, F. Numerical and analytical modelling of the MHD buoyancy-driven flow in a Bridgman crystal growth configuration. Journal of Crystal Growth, 180, (3-4), 422-432 (1997).

A15. Dowling, A.P. Acoustics of unstable flows. Theoretical and Applied Mechanics 1996: Proceedings, 19th International Congress, Kyoto, Japan (August 1996); Edited by T. Tatsumi, E. Watanabe, T. Kambe (Elsevier Science, 1997). ISBN 0 444 82446 4

A16. Dowling, A.P. Combustion noise and active control. In: Aero-Acoustic and Active Noise Control. VKI Lecture Series 1997-07 (Von Karman Institute for Fluid Dynamics, 1997).

A17. Dowling, A.P. Underwater flow noise. Theoretical and Computational Fluid Dynamics, 10, (1-4), 135-153 (1998).

A18. Dupère, I.D.J., Dowling, A.P. The absorption of sound near abrupt area expansions. 4th AIAA/CEAS Aeroacoustics Conference, Toulouse, France, AIAA Paper 98-2303 (June 1998).

A19. Evers, I., Peake, N. Interaction between waves and an airfoil in transonic flow. 4th AIAA/CEAS Aeroacoustics Conference, Toulouse, France, AIAA Paper 98-2320 (June 1998).

A20. Evesque, S.M.N., Dowling, A.P. Adaptive control of combustion oscillations. 4th AIAA/CEAS Aeroacoustics Conference, Toulouse, France, AIAA Paper 98-2351 (June 1998).

A21. Ffowcs Williams, J.E., MÖHRING, W. Active control of Kelvin-Helmholtz waves. Flowcon: Proceedings, IUTAM Symposium on Passive and Active Control, Gottingen, Germany (September 1998).

A22. Hirami, N., Ffowcs Williams, J.E. Active vibration control by maximum power absorption. Transactions of the Japan Society of Mechanical Engineers, 64-618, 444-450 (1998). (In Japanese)

A23. Hubbard, S., Dowling, A.P. Acoustic instabilities in premix burners. 4th AIAA/CEAS Aeroacoustics Conference, Toulouse, France, AIAA Paper 98-2272 (June 1998).

A24. Jenkins, K.W., Cant, R.S. Direct numerical simulation of turbulent flame kernels. Proceedings, 7th International Conference on Numerical Combustion, York (March/April 1998).

A25. Jenkins, K.W., Cant, R.S. Direct numerical simulation of turbulent flame kernels. Poster presentation. 27th Symposium (International) on Combustion, Boulder, CO, USA, W5D07 (August 1998).

A26. Keith, G.M., Peake, N. Acoustic radiation from a scarfed cylinder. 4th AIAA/CEAS Aeroacoustics Conference, Toulouse, France, AIAA Paper 98-2201 (June 1998).

A27. Lambert, H., Simon, S., Collings, N., Hands, T. The fast FID as a velocimeter for flow measurements in an automotive catalyst. Advanced Converter Concepts for Emission Control: Proceedings, 1998 SAE International Congress and Exposition, Detroit, MI, USA, SAE Paper 980879, 89-93. Society of Automotive Engineers SP1352 (February 1998).

A28. Lewins, J.D. Nuclear energy. In: The Encyclopedia of Ecology and Environmental Management; Edited by P. Calow (Butterworths, 1998). ISBN 0 86542 383 7

A29. Lewins, J.D. On a consistent use of sign convention for heat flows. International Journal of Mechanical Engineering Education, 26, (2), 163-165 (1998).

A30. Lewins, J.D. A use of Jacobians in thermodynamics to express the ratio cp to cv. International Journal of Mechanical Engineering Education, 26, (3), 250-252 (1998).

A31. Lewins, J.D., Parks, G.T., Chang, M. A variational principle using Monte Carlo approximations for reliability studies. Proceedings, 4th ISSAT (International Society of Science and Applied Technologies) International Conference on Reliability and Quality in Design, Seattle, WA, USA, 302-309 (August 1998).

A32. Li, J., Collings, N., Ma, T. A numerical simulation of AFR switch of SI engines. New Technologies in SI and Diesel Engine Modelling: Proceedings, 1998 SAE International Spring Fuels and Lubricants Meeting and Exposition, Dearborn, MI, USA, SAE Paper 981439, pp. 9-16. Society of Automotive Engineers SP-1366 (May 1998).

A33. Parks, G.T., Miller, I. Selective breeding in a multiobjective genetic algorithm. Parallel Problem Solving from Nature - PPSN V: Proceedings, 5th International Conference, Amsterdam, the Netherlands (September 1998); Edited by A.E. Eiben, T. Back, M. Schoenauer, H-P. Schwefel, 250-259. Lecture Notes in Computer Science 1498 (Springer-Verlag, Berlin, 1998).

A34. Peake, N. Some analytical methods for fluid-structure interaction problems. CISM Course on Fluid-Structure Interactions in Acoustics, Udine, Italy (September 1998).

A35. Peckham, M.S., Hands, T., Burrell, J., Collings, N., Schurov, S. Real time in-cylinder and exhaust measurements in a production SI engine. General Emissions: Proceedings, 1998 SAE International Congress and Exposition, Detroit, MI, USA, SAE Paper 980400, 103-113. Society of Automotive Engineers SP-1335 (February 1998).

A36. PROSSER, R., CanT, R.S. On the use of wavelets in computational combustion. Journal of Computational Physics, 147, (2), 337-361 (1998).

A37. Prosser, R., Cant, R.S. On the use of wavelets in computational combustion. Proceedings, 7th International Conference on Numerical Combustion, York (March/April 1998).

A38. Prosser, R., Cant, R.S. Wavelets in the direct numerical simulation of turbulent combustion. Poster. 27th Symposium (International) on Combustion, Boulder, CO, USA, W5D12 (August 1998).

A39. Ranasinghe, D.J., Cant, R.S. A turbulent combustion model for flow fields of varying mixture strengths. Proceedings, 7th International Conference on Numerical Combustion, York (March/April 1998).

A40. Schurov, S., Collings, N., Hands, T., Peckham, T., Burrell. J. Fast response NO/HC measurements in the cylinder and exhaust port of a DI diesel engine. Combustion Processes in Diesel Engines: Proceedings, 1998 SAE International Congress and Exposition, Detroit, MI, USA, SAE Paper 980788, 159-167. Society of Automotive Engineers SP-1328 (February 1998).

A41. Short, D.J., Davidson, P.A. Electromagnetic control of high temperature liquid metal jets. Light Metals 1998: Proceedings, 127th TMS (the Minerals, Metals, Materials Society) Annual Meeting, San Antonio, TX, USA (February 1998); Edited by B. Welch, 877-884 (TMS, Warrendale, PA, 1998).

A42. Short, D.J., Davidson, P.A. Swirling, recirculating flow driven by a rotating magnetic field. Magnetohydrodynamics (translation of Magnitnaja Gidrodinamika), 33, (3), 225-264 (1998).

A43. Tang, S.K., Ffowcs Williams, J.E. Acoustic radiation from a vortex approaching a circular cylinder with surface suction. Acustica/Acta Acustica, 84, 1007-1013 (1998).

A44. Taylor, M., Peake, N. The long-time behaviour of incompressible swept wing boundary layers subject to impulsive forcing. Journal of Fluid Mechanics, 355, 359-381 (1998).

A45. Taylor, M., Peake, N. The long-time impulse response of compressible swept wing boundary layers. Journal of Fluid Mechanics, 379, 333-350 (1998).

A46. Whittington, K.R., Davidson, P.A., Hunt, J., Yun, M., Thomas, P. Electromagnetic edge dams for twin-roll casting. Light Metals 1998: Proceedings, 127th TMS (the Minerals, Metals, Materials Society) Annual Meeting, San Antonio, TX, USA (February 1998); Edited by B. Welch, 1147-1150 (TMS, Warrendale, PA, 1998).

A47. Woodley, B.M., Peake, N. Prediction of acoustic resonance in tandem cascades. 4th AIAA/CEAS Aeroacoustics Conference, Toulouse, France, AIAA Paper 98-2252 (June 1998).

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Last modified: October 1999