Static pressure effects on calibration of velocity transducers at nozzle exits

Calibrations of velocity transducers are generally performed at nozzle exits where the turbulence level is minimal. Such nozzles require a high contraction ratio and are usually short with a consequent effect on stream static pressure due to formation of a vena contracta. Calibrations performed with a Pitot tube and no static pressure correction can lead to a significant velocity error. Measurements of static pressure, mean velocity and turbulence intensity are presented for a typical high contraction ratio nozzle. These show two distinct flow regimes which can be described very simply by the Reynolds form of the Navier-Stokes equations.