Improved shock physics modelling as an alternative to nuclear testing
Submitting InstitutionCranfield University
Unit of AssessmentAeronautical, Mechanical, Chemical and Manufacturing Engineering
Summary Impact TypeTechnological
Research Subject Area(s)
Earth Sciences: Other Earth Sciences
Engineering: Interdisciplinary Engineering
Summary of the impact
Cranfield University's research in computational fluid dynamics (CFD),
turbulence models, studies of instabilities and the development of
multi-scale methods has reduced the computational uncertainty in the
modelling and simulation used by the Atomic Weapons Establishment (AWE) to
support the safety and performance of nuclear weapons.
Cranfield's research in compressible turbulent flow for Low Mach numbers
is now employed to increase accuracy in CFD codes employed by the German
Aerospace Agency DLR, Pennsylvania State University, and the French
Commissariat a l'Energie Atomique, which use this work to model flows
ranging from turbulent mixing through inertial confinement fusion (ICF) to
Now that it is no longer possible to conduct live tests of nuclear
weapons, accurate computer modelling is essential to underwrite their
safety and performance. Modelling to understand instabilities and
turbulent mixing at material interfaces is an area that demands better
Cranfield's work on CFD (2004 to date) concerns:
- the development of computational fluid dynamics methods, turbulence
models and engineering physics studies of instabilities
(Richtmyer-Meshkov and Rayleigh-Taylor) and compressible turbulent
- development of multi-scale methods and study of dynamic friction
across material interfaces.
The research is motivated by a range of diverse applications in science
and engineering, including: inertial confinement fusion (ICF); micro and
nanocrystalline materials and interfacial friction in materials; nuclear
energy; detonation; supersonic combustion; and astrophysics.
In ICF, the main area of application of the research, the dense shell,
filled with deuterium-tritium (DT) gas, implodes when irradiated by laser
beams or by other means. When a shock wave refracts through the shell-fuel
interface, the boundary experiences Richtmyer-Meshkov instability (RMI).
RMI leads to the growth of perturbations on the shell-fuel interface and
causes turbulent mixing of the materials. Rayleigh-Taylor instability
(RTI) and mixing also occurs at the shell-fuel interface towards the end
of the implosion phase, when the less dense gas decelerates the shell. RMI
and RTI turbulent mixing reduce the heating of the gas during the
implosion phase and inhibit the thermonuclear reaction after ignition,
degrading the performance of the ICF target. Accurate modelling of RMI and
RTI is a major uncertainty in calculating how an ICF target will behave.
In the framework of the present research, Cranfield developed new
high-resolution and high-order computational methods that improve the
accuracy in compressible turbulent mixing simulations [P1, P2, P3]. The
results from the simulation and modelling studies were validated against
specially designed experiments performed at AWE, as well as simulation and
modelling data using AWE's industrial codes. Cranfield investigated the
influence of the initial conditions on RMI, RTI and turbulent mixing in a
range of ICF mixing problems.
In the course of the research [P4, P5], Cranfield also developed
multi-scale models that couple continuum and molecular dynamics methods in
order to study dynamic friction between material interfaces. Friction at
the interface between dissimilar metallic components as a result of high
velocity impact or explosive loading can have a profound effect on the
subsequent motion. A comprehensive understanding of the processes involved
across a wide range of initial conditions is still not available. This
research revealed the growth of epitaxial layers of the softer material,
shifting of the sliding interface due to formation of shear-bands,
development of amorphous structures, and ultimately the resultant motion
of the components. Analysis of the results also linked these processes to
the changes in the state of the material through growth of dislocations
and thermal effects [P5].
The research enhanced our understanding in compressible turbulent mixing
and dynamic friction, which are core activities of AWE's technical
|Dr Ben Thornber
||2004 - 2013
||Compressible turbulent mixing, CFD
|Dr Marco Hahn
||2004 - 2010
||Compressible turbulent mixing, CFD
|Prof Dimitris Drikakis
||2003 - present
||Turbulent mixing, CFD, multi-scale modelling, dynamic friction,
engineering turbulence modelling
References to the research
Evidence of quality — Peer Reviewed Journal Papers
P1 M Hahn, D Drikakis, D L Youngs and R J R Williams, "Richtmyer-Meshkov
turbulent mixing arising from an inclined material interface with
realistic surface perturbations and reshocked flow", Physics of Fluids, 23,
p. 046101 (11 pages), 2011.
*P2 B Thornber, D Drikakis, D L Youngsa and R J R Williamsb
"The influence of initial conditions on turbulent mixing due to
Richtmyer-Meshkov instability", Journal of Fluid Mechanics, 654,
pp. 99-139, 2010.
*P3 B Thornber, A Mosedale, D Drikakis, D Youngsa and R J R
Williamsb, "An Improved Reconstruction Method for Compressible
Flows with Low Mach Number Features'', Journal of Computational Physics, 227,
pp. 4873-4894, 2008.
*P4 P Barton, B Obadia, and D Drikakis, "A conservative level-set based
method for compressible solid/fluid problems on fixed grids", Journal of
Computational Physics, 230, pp. 7867-7890, 2011.
P5 P T Barton, M Kalweit, D Drikakis and G Ball "Multi-scale analysis of
high-speed dynamic friction", Journal of Applied Physics, 110, p.
093520 (8 pages), 2011.
* 3 identified references that best indicate the quality of the research
Key to co-authors
a, b: AWE, Aldermaston, UK.
Further evidence of quality — underpinning research grants
G1 AWE William Penney Fellowship, total £263K: Advanced Turbulence
Modelling for Compressible Turbulent Mixing £135k, 04/2008-03/2011
and £128k, 01/2012-12/2014, Prof Drikakis for his contributions to
computational science, fluid dynamics and materials in relation to design
physics, aerospace and defence.
G2 EPSRC (EP/C515153) and MoD-AWE Joint Grant Scheme (JGS 971) Computational
and Theoretical Modelling of Shock-Induced Instability and Mixing across
Material Interfaces, £242,609, 10/2005-01/2009. PI: Prof Drikakis
G3 EPSRC (EP/D051940/1) and MoD- AWE Joint Grant Scheme (JGS 607) Multiscale
Modelling of Meso and Nano Scale Interfacial Dynamics Phenomena,
£249,728, 02/2006-10/2009. PI: Prof Drikakis
Details of the impact
Due to the nature of AWE's work, focused on nuclear weapons, national
security makes it impossible to provide accessible published evidence of
the impact of Cranfield's research. What we can provide, detailed below,
is an explanation of the context in which the work has been applied, and
quotes from senior individuals at AWE, attesting to the impact of this
research on their work.
Accurate computer modelling is needed to underwrite the safety and
performance of nuclear weapons. Instabilities and turbulent mixing at
material interfaces is one area where better understanding is essential
[C1]. A decade ago, the type of "Large Eddy Simulation" used at AWE to
gain a fundamental understanding of the mixing processes was much
criticised by the academic community with respect to its ability to
capture accurately the correct turbulent-flow physics.
The numerical methods developed at Cranfield University have been used by
AWE to investigate the influence of initial conditions of mixing due to
Richtmyer-Meshkov instability. Turbulence modelling simulations often
ignore the influence of initial conditions on turbulent mixing, so
Cranfield's work has a substantial impact in reducing computational
uncertainty in turbulent mixing predictions and is now taken into account
in AWE's modelling.
"The collaboration between AWE and Cranfield University, which has
involved simulation methods at both institutions and experiments at AWE,
has led to a high degree of confidence in the computer modelling we now
use to understand turbulent mixing." [C2, C4]
The methods developed at Cranfield have also been used for 3D simulation
of complex flows where mixing is on average two-dimensional. These results
have led to a substantial advance with respect to validation and
verification of computational models by improving the accuracy of
engineering turbulence models (Reynolds-Averaged Navier-Stokes models)
used in ICF applications at AWE.
During the course of this research, a key improvement was made by
Cranfield to the Godunov methods used at Cranfield to simulate
compressible turbulent flow, in particular the behaviour at low Mach
number. This improvement significantly increases the accuracy of
computational fluid dynamics (CFD) codes in turbulent flow simulations.
Furthermore, it enhances the efficiency of CFD codes because high accuracy
can be attained even with low numerical grid resolution, thus leading to
shorter computing times.
Low-Mach corrections developed at Cranfield — as well as variants of
Cranfield's work produced by other research groups — are now employed in
CFD codes in the German Aerospace Agency DLR [C5], Pennsylvania State
University [C6] and the French Commissariat a l'Energie Atomique [C7].
These organisations use these CFD codes for flows ranging from turbulence
mixing through to scramjets.
Cranfield's work has inspired further developments in the international
research community, eg, the French nuclear hydraulics code FLICA-OVAP and
at Tsinghua (China) in relation to turbine blades A related area of
physics that is also of concern to AWE is dynamic friction at material
interfaces under extreme conditions of velocity and normal stress. AWE's
previous modelling using continuum hydrocodes, and work at the US Los
Alamos National Laboratory (LANL) using molecular dynamics simulations,
had produced conflicting predictions of behaviours in this regime. AWE
resolved this by adopting Cranfield's approach and has incorporated this
in model development.
"Research performed by Professor Drikakis' group led to the
development of a hybrid method in which continuum and molecular dynamics
codes were directly coupled. This approach has helped to reconcile
apparent contradictions in the earlier work, and has provided new
insights that will inform future model development at AWE." [C3]
Sources to corroborate the impact
C1 K O'Nions, R Pitman, C Marsh: "Science of nuclear warheads", Nature,
415, 853-7, 2002
C2 Contact: Distinguished Scientist, AWE Aldermaston, UK
C3 Contact: Division Manager, AWE Aldermaston, UK
C4 Contact: Team Leader, AWE Aldermaston, UK
C5 Contact: Research staff, DLR, Braunschweig, Germany
C6 Contact: Research Associate, Navy Research Laboratory, USA
C7 Contact: Research Scientist, Atomic Energy and Alternative Energy
Commission (CEA), France