 William H. Cabot

William H. Cabot coauthored the dynamic subgrid-scale model developed with Massimo Germano, Ugo Piomelli and Parviz Moin. Their 1990 report compared modeled unresolved stresses with data from direct numerical simulation and tested large eddy simulation of transitional and turbulent channel flow.^[ref] A participant retrospective identifies Cabot as a Stanford research associate during the collaboration.^[ref]

The numerical comparison illustrates an important issue in turbulence research: matching the objects being compared. A coarse simulation describes resolved motion, while a finely resolved reference contains additional fluctuations. The report filtered the reference data before some comparisons, so the comparison did not automatically count intentionally omitted small scales as errors in a resolved field.^[ref]

For an original arithmetic illustration, fine-grid velocities $0$ and $2$ have mean $1$ and mean square $2$. The square of their mean is only $1$. Replacing both samples by the mean preserves that mean but loses a fluctuation contribution of $1$. This elementary difference is why an averaged velocity and an averaged momentum flux contain different information, and why subgrid-scale stress requires explicit treatment.