Theoretical Basis for Extrapolation of Calibration Data of PTC 6 Throat Tap Nozzles

Equations for the extrapolation of calibration data for ASME/PTC 6 throat tap nozzles are derived from boundary layer theory. The results match published coefficients with a maximum difference of +0.03 percent. It is also shown that the effects of transition in the boundary layer extend to throat Reynolds numbers in excess of 10,000,000, far beyond the capacity of any known calibration laboratory. The present PTC 6 requirement that calibration data must be in the fully turbulent range cannot be met with current facilities.