= James W. Deardorff
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<James W. Deardorff> was an atmospheric scientist whose numerical work helped establish <large eddy simulation> as a way to study <turbulence>. His 1970 study integrated three-dimensional equations for turbulent channel flow while representing subgrid effects through coefficients tied to resolved deformation. The primary paper identifies his affiliation as the National Center for Atmospheric Research.<A numerical study of three-dimensional turbulent channel flow at large Reynolds numbers by James W. Deardorff>[Printed p. 453, byline, affiliation and abstract]{ref}
The calculation used 6720 uniform grid intervals and compared computed flow statistics with experimental measurements. The reported agreement ranged from good to marginal. This made the unresolved-motion model testable against quantities beyond the appearance of an evolving flow: the paper examined eddy structure and the <kinetic energy> balance as well as statistical averages.<A numerical study of three-dimensional turbulent channel flow at large Reynolds numbers by James W. Deardorff>[Printed p. 453, abstract: grid, comparison, eddy shapes and energy balance]{ref}
An elementary example explains why those separate statistics matter. Two equally likely <velocities> $U-a$ and $U+a$ have mean $U$ and <variance> $a^2$. A prediction that always returns $U$ has the correct mean but zero <variance>. Matching a mean velocity profile alone therefore cannot establish that a model captures turbulent fluctuations or their transport.
Deardorff's study illustrates a productive compromise: compute evolving resolved structures, model the missing influence with a <subgrid-scale model>, and compare predicted statistics with observations. Finer resolution and a different closure can change the prediction, so agreement remains a property of a specified calculation and test.
\Image[https://www.tjresearch.net/tjr/images/prof-jim-deardorff.gif]
{title=James W. Deardorff, portrait identified on the Deardorff Research profile}
{description=External portrait from <Research profile and portrait of James W. Deardorff at Deardorff Research>.}
{height=240}
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