The concept of circulation is presented, including the physical and mathematical concepts of circulation and lift. A description of how potential flow theory is used to model flow for airfoils, including the predictions of lift. Readers are presented with the concept of the Kutta condition, including how it impacts the development of airfoil theory. Thin-airfoil theory is developed for symmetric and cambered airfoils and methods for prediction lift and pitching moment are presented. The accuracy and limitations of thin-airfoil theory is also presented. Descriptions are presented for why laminar flow airfoils have different geometries than airfoils used at higher Reynolds numbers. Finally, high-lift systems are discussed, including why they are important for aircraft design.

This chapter explores how mixing is measured, focusing on what can be measured and how accurately. It begins with probes measuring dissipation scales, i.e. thermistors and airfoils, but also includes other devices not used routinely, such as pitot tubes. Finescale sensors are also examined, with an emphasis on absolute accuracy and salinity spiking. Then the vehicles carrying the probes are described, i.e. profilers, tows, AUVs, and submersibles. Moorings and fixed platforms are also briefly examined. Finally, remote sensing, principally using backscatter from high-frequency acoustics, is reviewed, along with tracer releases for measuring net diffusivity.