Kiel probe

The Kiel probe, also called Kiel cal tube, is a further development of the pitot tube and is named after its inventor George Kiel, a NACA employee named. It is used to measure the total pressure in turbulent flows and has over the normal pitot tube has the advantage that it has a lower sensitivity to the angle of incidence.

Design and operation

The Kiel probe consists essentially of a Venturi nozzle, inside of which is a pitot probe. The venturi nozzle deflects the flow in the axial direction, thus ensuring a more constant flow to the pitot probe. Essential for the quality of the measurement arrangement is the geometry of the inlet. In addition to rounding radius of the inlet, ramp angle and diameter ratio of the venturi and the position of the pitot probe in the axial direction plays an important role in the sensitivity to the angle of incidence. Mach number dependent good measurement results up to angles of attack 60 ° can be achieved relative to the axis of symmetry.

Use

Kiel probes are used in all applications where the total pressure is to be determined at widely varying flow direction. Especially with modern combat aircraft that fly at higher and higher angles of attack, precision total pressure measurements are necessary for determining velocities, even at high angles of attack. A well-known aircraft model using a Kiel probe is the Rockwell - MBB X -31, an experimental aircraft that served at high angles of attack, among others, the study of flight behavior. Also during flight testing, as well as helicopters, where large changes in direction of flow can occur, Kiel probes are used. Also in the HASI sensor package of the Huygens probe that landed on Saturn's moon Titan, a Kiel probe for scientific measurements during descent was contained by the atmosphere.

Alternatives

In addition to the aerodynamic design of the measuring point, there are other ways to measure total pressures in flows with fluctuating directions. On the one hand, there are systems having a plurality of measurement points with different orientation. The results of the individual measuring points are evaluated and then determined an overall solution. The other hand, tracking systems are used, in which the pitot probe is aligned by means of a vane according to the flow. The latter system was implemented in the Euro Fighter.