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Research on Ekman at the Linné Flow Center, KTH Mechanics. Dan Henningson, Director. Funded by VR as an one of the 20 original Linné centers of excellence. http://www.flow.kth.se. Linné FLOW Centre. Vision - PowerPoint PPT Presentation
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Linné FLOW Centre
Research on Ekmanat the Linné Flow Center, KTH Mechanics
Dan Henningson, Director
Linné FLOW Centre
http://www.flow.kth.se
● Funded by VR as an one of the 20 original Linné centers of excellence
Linné FLOW Centre
Linné FLOW Centre
● Vision
“FLOW as an outstanding environment for fundamental research in fluid mechanics, where innovative research
is born and future research leaders are fostered”
Linné FLOW Centre
Activities and infrastructure
● Research projects
● Graduate school
● Summer programs
● Workshops/conferences
● Seminars and visiting scientists
● Infrastructure− World class wind-tunnels and acoustic measurement facilities− Climate and Turbulence computer Ekman
Linné FLOW Centre
Research areas
● Why do flows become turbulent?
● How does turbulence behave in the ocean and atmosphere?
● Why does turbulence generate noise?
● How can we make flows behave the way we want to?
● Why do fibers bundle?
Linné FLOW Centre
Turbulent flows are everywhere, and they can be described by …
From www.efluids.com
Linné FLOW Centre
How do we perform numerical experiments?
● Solve the Navier-Stokes equations for the velocity on grid points using super computers
Cray-1 (1976) 100 Mflops1 processor
Ekman Dell cluster (2008) 100 Tflops12000 processors
Year
MFl
ops
1970 1980 1990 2000 201010
2
104
106
108
1010
Cray X-MP
NEC SX-5
Earth Simulator
Roadrunner
Neolith
Ekman
Cray-1
Linné FLOW Centre
Efficient simulations on many processors
1
10
100
1000
10000
1 10 100 1000 100001
10
100
1000
10000
1 10 100 1000 10000
# processors # processors
speed-u
pSIMSONNek5000
How much faster does the simulation run on many processors? linear scaling measurements (IBM BG/L)
Linné FLOW Centre
How can simulations help make modern aircraft more environmentally friendly?
● Suppressing turbulence on the wings (laminar flow control) improve fuel efficiency
● Better models of turbulence on wing surfaces improve engineering design
● Example: Airbus green aircraft concept
EU NACRE project: Concept for quiet, light
fuel efficient aircraft
Linné FLOW Centre
Direct Numerical Simulations of all scales in the turbulent flow (no models)
Turbulence close to the surface Friction Drag Fuel consumption
Linné FLOW Centre
Simulations: streamwise velocity in wall-parallel plane 20 cm x 0.8 cm, simulation on BlueGene at PDC
Direct Numerical Simulations of turbulent flow● 6144 x 385 x 576 = 1.4 billion grid points
Large range of scales require huge number of gridpoints
Linné FLOW Centre
What can we learn from even larger simulations?
● 12288 x 721 x 1152 = 11 billion grid points● Overlap with large scale experiments
Large scale experiments
Re
Domain size
Ekman
Previous simulations
Ciclope project: large pipe flow facility in
130 m Italian tunnel
Linné FLOW Centre
What can we learn from even larger simulations?
● 12288 x 721 x 1152 = 11 billion grid points● Overlap with large scale experiments
− Dynamics of large scale turbulent structures and their interaction with small near-wall structures
− Provide quantities difficult to measure, input in engineering models of turbulence
− Independent prediction of quantities like drag
− How to best suppress turbulence on the wing
Linné FLOW Centre
How will the ocean circulation respond to global warming?
● Ocean large heat regulator of climate
● Great conveyor belt transport warm surface water to north pole and cold water back along bottom
● Circulation affected by global warming?
Linné FLOW Centre
The ocean is turbulent!
Simulation: ECCO code using MITgcm.
JPL. NASA Ames
Linné FLOW Centre
The global circulation is very sensitive to the turbulent diffusivity
(Nilsson et al., MISU)
There is even turbulence atcentimeter scale!
Smaller scales determine turbulent diffusivity, how fast is the cold water cooling the warmer water above ?
Linné FLOW Centre
What are we doing now?
Direct Numerical Simulation of ocean turbulence2048 x 2048 x 384 = 1.6 billion grid points
Linné FLOW Centre
What will we do?Larger DNS of ocean turbulence
4096 x 4096 x 1024 = 17 billion grid points
Ekman may give answer on turbulent diffusivity in ocean
Simulation: Kelvin-Helmholz breakdown by Colorado Res. Ass.
bridge gap between larger scales affected by density differences and smaller isotropic scales
Linné FLOW Centre
Simulations on Ekman will help fill the gap between smallest scales accounted for in climate and engineering
models and those of importance in nature
Examples …
● Simulations of ocean turbulence to predict turbulent diffusivity influencing how the ocean responds to global warming
● Simulations of turbulence in boundary layers on aircraft and ground vehicles to improve engineering predictions of drag
● Simulations of the onset of turbulence on wings to develop laminar flow control and lower fuel consumption