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A fluid dynamicist studies how fluids move and how their motion exchanges mass, momentum and energy. The work can combine mathematical models, controlled measurements and computation. Choosing what to resolve, what to approximate and which observations test the result is as central as solving an equation. A fluid dynamicist may work on applications ranging from aerodynamic drag force to transport in a blood.

For an original example, consider steady water flow through a duct with negligible density changes. Mass conservation gives $\rho A_1{U}_1=\rho A_2{U}_2$, with $U$ the cross-sectionally averaged speed.^[ref] If a circular duct doubles its radius while maintaining the same volume flow rate, its area becomes four times larger and its mean speed falls to one quarter. A researcher can compare that prediction with measured flow and velocity. Predicting the required pressure difference is another question, requiring information about losses and the velocity field.

In turbulence research, direct numerical simulation and large eddy simulation resolve different ranges of motion. A useful validation compares the same observable and averaging convention rather than simply comparing two pictures of complicated flow. Parviz Moin's institutional research profile describes this combination of computational methods with questions about turbulent-flow physics.^[ref]

Parviz Moin is a researcher in computational fluid dynamics and turbulence. Stanford's institutional profile identifies him as the founding director of the Center for Turbulence Research and describes his use of direct numerical simulation and large eddy simulation to investigate turbulent shear flows.^[ref]

With Massimo Germano, Ugo Piomelli and William H. Cabot, he coauthored work on the dynamic subgrid-scale model. The approach uses information at different resolved scales to determine a model coefficient during the calculation.^[ref] The participant account places the collaboration at the 1990 summer program and distinguishes that report from the subsequent 1991 journal paper.^[ref]

A useful scientific distinction is between a numerical method's resolution and its physical accuracy. A finely detailed flow visualization can still give an inaccurate mean drag force. Conversely, a carefully tested coarse model can predict a specified average while omitting individual small eddies. Moin's computational research makes the choice of observable, reference calculation and physical question part of evaluating a simulation.