Velocity, vorticity, and mach number

Abstract

The objective of this chapter is to provide a comprehensive statement of the experimental methods that can be used to transduce the velocity and its companion quantity: vorticity (∇ × u¯). Velocity measurements can be understood to represent spatially integrated and pointwise values. Thermal transient anemometry (Sect. 5.6) and sonic anemometers (Sect. 5.7) represent the former. Pressure-based velocity measurements (Sect. 5.1), thermal anemometry (Sect. 5.2), and particle-based techniques (Sect. 5.3) represent the latter. In addition, particle image velocimetry (PIV, Sect. 5.3.2), planar Doppler velocimetry (Sect. 5.3.3), and molecular tagging velocimetry (Sect. 5.4) also provide spatial distributions of the pointwise measurements for the instant at which the image is formed. The vorticity measurements rely on some form of the above pointwise measurements. A general overview of optical methods is presented in Sect. 5.5.1.