 The Prandtl probe is suitable for velocity
measurements in a relatively unidirectional flow field. The total pressure is measured
with a central hole on the hemispherical head and the static pressure through four
circumferential holes at right angles to the flow direction. This permits correct readings, even when the probe is at an angle to
the flow, (-2% error for ±10' maximum orientation). Providing the local temperature and
composition (giving the density) is known, the velocity is determined directly from the
Bernoulli equation as the calibration constant is very close to unity.
From the measured pressure
distribution around the hemispherical head (central tapping surrounded by four others at
45' to the axis), the two spherical angle co-ordinates and recovery factor (for velocity
magnitude) may be determined from calibration charts giving them as a function of three
ratios of pressure differentials. The local density must be known in order to determine
the magnitude of the velocity.
The accuracy and sensitivity of the
Prandtl probe has been improved by using smaller pressure holes than those indicated by
the standards whilst maintaining an uncooled length of 35 mm at the head (stainless steel
18/8). This reduces the risk of blockage by condensed water or dust deposits. For the same
reason, periodic blowing through the probe with compressed air is needed. This can be
automatically achieved with a pressure measuring system similar to that used at the
Research Station. When accurate transducers are used, velocity magnitudes in the range
5-50 m/s may be accurately determined (within 5%). Moreover, the calibration constants for
this probe were found to be unaffected by variations of turbulence intensity from 1 to
20%.
VENDOR: IFRF Research Station b.v.
Would you be interested in :
- getting more information about
this measurement equipment?
Please contact us:
IFRF Research Station B.V.
P.O. Box 10 000
1970 CA IJmuiden
The Netherlands
email: sales@ifrf.net
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