Static pressure effects on calibration of velocity transducers at nozzle exits

Abstract

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.