The flow behavior of a sword or plate-shaped body (such as the PoetterSensor®) compared to conventional pitot tube (similar cylinder), is well known by fluid mechanics. However, for many users the dramatic instrumentation and mechanical difference is still not clear.
Pöttersonden® cause unlike conventional pitot pressure-induced release large areas, but only an extremely small recirculation, exclusively in the lee of Pöttersonde® that does not cause the least disturbance to the measured value.
For operators and planners we´ll try to present the significant difference. Do you want to take advantage of the superior Pöttersonden®, or will you accept the major drawbacks of conventional pitot tubes?
On the left you can see a conventional
high-pressure steam pitot tube:
On the right a PoetterSensor® for high pressure steam:
Conventional pitot tubes: Behave in the flow (vortex) hardly like a circular cylinder or square and cause extreme vertebrae. The swirl and flow behavior of a circular cylinder has been documented in great detail in the science and can be transferred in full to conventional pitot tubes. As long as a probe profile is approximately the same length as wide (four or more angular, T-shaped, oval, etc.) there is no significant difference from a circular cylinder.
Quote from fluid mechanics A - Z, Heinz Herwig, page 408 above.
"When bodies, where there is pressure-induced release large areas, the influence of the Reynolds number may be strong, because the transition point (laminar / turbulent) can interfere with the separation point and different, and therefore caused detachment regions of very different sizes.” […] A typical example is the flow around a circular cylinder ".
"The critical point is reached at a further increased number of revolutions. The value is in most bodies at Reynolds numbers between 2·10⁵ and 7·10⁵ .From this point the flow dissolves away from the body. In turbulent flow, however, the flow of the fluid adheres more to the body before it detaches and forms vortices whose direction is no longer predictable and calculable. This has the result that the non-measurable part is reduced behind the body, and thus also the area which acts to hinder the forward movement. This has an abrupt drop in the cw - value to its minimum result. This means the most aerodynamic condition for a body."
Below you can see the visualization according to wool thread method, on the flow behavior of a conventional high-pressure steam probe type, compared to a high-pressure steam Pöttersonde® type DF 10, under completely identical conditions.
Visualization Pöttersonde® DF 10 with steam:
In a conventional pitot tube, the differential pressure theory constitutes about 80% of the dynamic pressure (inflow) and low pressure (downstream) and about 20% from the friction. However, this approach lacks the significant influence of a very strong vortex formation, which on the one hand does not changed the vacuum quadratic and on the other is associated with an increased permanent pressure loss through the vortex brake. This is almost always pure energy dissipation.
Extreme vortex conventional pitot tubes also cause very high mechanical stress, despite the necessary thrust bearing in HD - vapor region lead to fractures often vibration. Never a PoetterSensor® was broken.
There are often forgotten the fact that in conventional pitot tubes integrated pressure recording on the under pressure side, does not allow accurate recording of the pressure required for the calculation of static pressure, because this does not change square due to eddy and brake. Unnecessary measurement errors are generated.
PoetterSensor®: The sword-like (or plate-like) Pöttersonden® (W x L = 1: 3.5 with an immersion depth <0.5 x D) are not adversely affected by eddy. The Pöttersonde® forms an ideal flow profile, a sharp together running backwards ellipse. Couldn´t get any better.
PoetterSensor® form the differential pressure from the difference between the pure dynamic pressure (build +) and the static pressure (-) of those being under a laminar overlay leeward. Emerge with no interference from eddy, eddy brake or expansion factor. Also, different Reynolds numbers do not result in PoetterSensor® to the feared turning the detachment. This is the most important requirement for high precision Rising CHP balance sheets at high Re - areas.
The resistance (Cw) of PoetterSensor® forms, in contrast to conventional pitot tubes, from the pure unadulterated dynamic pressure of the flow surface.
The very low frictional resistance, which forms on the laminar sliding layer of smooth machined surface of the PoetterSensor® is negligible and can not be calculated because the value is to low. In addition, the dynamic pressure of Pöttersonden® solves almost entirely in the frictional resistance (see Euler`sche / d`Alembertsche paradox), and so are almost no pressure losses compared to conventional pitot tubes. PoetterSensor® are not adversely affected by the expansion in the number linearity (because constant). The physics explain the extremely high accuracy of PoetterSensor®.
Mechanically PoetterSensor® are not affected by eddies. Therefore, they won´t need any thrust bearing. In addition, never one of the many installed PoetterSensors® is demolished or broken.
Quote of the University of Magdeburg:
"In the front and side area of the PoetterSensor® no vortices are noted. Only in the downstream area is a very small recirculation . Any negative accuracy effects on the measurement result or on the stability of the probe is not expected"