Siren Design and Evaluation in Mud Flow Loops and Wind Tunnels - Measurement While Drilling Signal Analysis, Optimization and Design - page 229

Importantly, additional scientific justification supporting wind tunnel usage
was offered in these publications, premised on the “highly turbulent nature of
the flow.” The investigators' arguments, in “plain English,” point out that the
turbulent air flow found in laboratory wind measurements is similar to the
turbulent mud flow likely to be found downhole. This counter-intuitive (but
correct) approach to modeling drilling muds provides a strategically important
alternative to traditional testing that can reduce the cost of developing new
MWD systems. Again, wind tunnel use in the petroleum industry was by no
means new at the time. For instance, Norton, Heideman and Mallard (1983),
with Exxon Production Research Company, among others, had published studies
employing wind tunnel use in wave loading and offshore platform design.
9.1.4 Modern short and long wind tunnel system.
While the short wind tunnel in Figure 9.1 represents the author's very first
rudimentary design, the wind tunnel system shown in Chapter 1 represents a
state-of-the-art facility developed to handle all of the previously discussed
requirements for modern mud siren and turbine testing. This MWD wind
tunnel, developed at the China National Petroleum Corporation (CNPC) in
Beijing, together with recent high-data-rate telemetry ideas and test results, is
described by Y. Su, L. Sheng, L. Li, H. Bian, R. Shi and W.C. Chin in “High-
Data-Rate Measurement-While-Drilling System for Very Deep Wells,” Paper
No. AADE-11-NTCE-74 presented at the American Association of Drilling
Engineers' 2011 AADE National Technical Conference and Exhibition,
Houston, Texas, April 12-14, 2011. Since this paper was presented, several
more wind tunnel systems have been constructed for MWD applications.
Here we recapitulate CNPC highlights to show how the testing technology
has evolved since the 1980s to address downhole problems and issues. The
short wind tunnel system with a blower driver is shown in Figure 9.2a. After
passing through the siren test section, air blowing “out of the page” turns to the
right, flowing through the black tubing to the outside of the test shed, and then
into the long wind tunnel in Figure 9.2b. It is important to note that abrupt
turns, while affecting viscous pressure losses and pump requirements, do not
reflect MWD signals because the acoustic waves are extremely long in length.
Siren tests in mud loops for torque, erosion, signal strength, harmonic
content, constructive or destructive wave interference, and so on, are impractical
because they are time-consuming and labor-intensive, with parts expensive to
fabricate. Many geometric parameters affect the physical outcome, e.g., number
of lobes, stator-rotor gap separation, rotor taper, rotor-housing clearance, flow
angle into the siren, and so on - operational parameters include flow rate and
rotation speed. Tests, even wind tunnel tests, must be cleverly designed, and for
this reason, the computer simulation methods in Chapter 7 were developed to be
used as screening tools. However, such models are not entirely accurate.