[GTP] GTP/MMM seminar Harmen Jonker--July 20

[Silvia Gentile]

NCAR
JOINT SEMINAR
MMM/GTP
Petascale Direct Simulations to Determine the Growth-Rate Law of 
Convective Boundary Layers
Harmen Jonker
Department of Multi-Scale Physics
Delft University
The Netherlands

The pioneering water tank experiments on convective entrainment by 
Deardorff et al. in the seventies, laid an important foundation for the 
now widely used 1/Ri growth-rate law for convective atmospheric boundary 
layers. Yet a nagging issue is that other water tank experiments, that 
employ different methods to create stratification and buoyancy, tend to 
produce significantly different entrainment laws. The essential problem 
that seems to remain is how to properly extrapolate the findings 
obtained from moderately low Reynolds/Peclet-number experiments to their 
huge Re/Pe-number atmospheric counterpart.
In this study we examine this issue by conducting "ground truth" Direct 
Numerical Simulations of convective boundary layers. Of course one 
cannot simulate the high Reynolds number of atmospheric turbulence, but 
present computer resources do allow one to faithfully mimic the 
classical laboratory experiments, and to even push the Reynolds number 
by more than an order of magnitude. The simulations were conducted 
within a European "Extreme Computing Initiative" framework, entailing 
simulations on five different supercomputing platforms. The largest 
simulations, which ran on the Juelich Bluegene supercomputer, used 
3072-cubed gridpoints employing 32,768 cores.
The simulations shed light on why different laboratory experiments with 
different set-ups, produced different growth-rate laws. By mimicking 
these experimental conditions in our simulations, that is by accounting 
for the actual fluid properties that were used in the experiments, we 
gain insight into how the Reynolds/Peclet number combination influences 
the resulting growth-rate behaviour. In addition, the results indicate 
which entrainment law is most appropriate for the large Reynolds number 
case associated with atmospheric convection.
Wednesday, 20 July 2011, 3:30 PM
Refreshments 3:15 PM
NCAR-Foothills Laboratory
3450 Mitchell Lane
Bldg 2 Small Seminar Room 1001

-- 
Silvia Gentile
NCAR IMAGe
1850 Table Mesa Drive
Boulder, CO 803035
www2.image.ucar.edu/IMAGe