Geology Reference
In-Depth Information
Figure 9.12a.
Early long wind tunnel wound on small diameter reels.
Consider the long wind tunnel and apparatus in Figure 9.12a, whose
development was funded in part by the Gas Research Institute (Gardner, 2002).
That public domain report utilized fixtures summarized in the present write-up.
At the left is a test fixture allowing simultaneous siren rotation and rotor-stator
gap axial reciprocation for amplitude modulation. The upstream “drillpipe” in
the middle drawing, in reality a thousand feet of plastic tubing wound on reels,
is connected to an air compressor to provide the oncoming flow; the downstream
“annulus” in the far right drawing is likewise wound on reels. Because
pressures are large up to and including the solid plastic test section, dangerous
cracking with flying debris is likely. For this reason, a pressure relief valve is
installed, which is no more than a “cork” located in a suitably drilled orifice;
ring clamps are also used to reinforce the plastic test section.
We note that signal distortion due to desurger bladder elasticity can also be
evaluated. The wind tunnel “desurger” is simply a balloon or rubber “hot water
bottle” installed along the flow path. Desurger charge levels are modeled using
different types of balloon skin stiffnesses. Expansion and contraction of the
plastic tubing may also distort pressure signals. This occurs with strong pulser
movements such as those associated with poppet valves, but the effects are
much less so with siren pulsers. For Figure 9.12a, the test section is operated
hydraulically from a management and data acquisition station in the same
laboratory outside of the flow loop. The mechanical layout for the research test
siren, which is driven hydraulically, is shown in Figure 9.12b, together with its
control system. The control system, used for research purposes, rotates the siren
while, and at the same time, axially reciprocates rotor-stator gap if desired. This
allows testing of phase-shift-keying (PSK), frequency-shift-keying (FSK) and
multi-level amplitude modulation (AM) of constant frequency carrier waves.
Details of the design are offered in Gardner (2002), developed under the lead
author's guidance. We emphasize that care must be undertaken to eliminate
area changes within the tubing system, which can lead to spurious reflections.
Also, flexible tubing may not be suitable for positive pulser testing at small
closing gaps, since flow rates cannot be held steadily under these circumstances.
We emphasize that bit and annular reflections are not always accurately studied.
Very often, math models like those in Chapter 2 are preferable.
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