Siren Design and Evaluation in Mud Flow Loops and Wind Tunnels - Measurement While Drilling Signal Analysis, Optimization and Design - page 224

9
Siren Design and Evaluation in
Mud Flow Loops and Wind Tunnels
We developed “short wind tunnel” analysis methods from a turbine design
perspective in Chapter 8. In fact, we showed how from two simple
measurements, namely, those for stall-torque and no-load rotation rate, each of
which can be taken in minutes in inexpensive wind tunnels powered by simple
blowers, the complete turbine torque and power versus rpm curves can be
obtained for drilling mud of any density flowing at any speed. Here, we
describe short wind tunnel design and test techniques further, in support of
earlier turbine development ideas.
We also introduce mud siren design in short wind tunnels, in particular,
analysis methods for stable-closed versus stable open, static versus dynamic
torque, and erosion evaluation. “Short wind tunnels” are short, say, five to ten
feet, and are used for hydraulic testing of properties that are independent of
compressibility, e.g., torque, power, erosion, flow visualization, approximate
viscous pressure drops and losses. On the other hand, acoustic properties like
signal strength, harmonic content, and constructive and destructive wave
interference, require not only longer wind tunnels that allow accurate simulation
of wave interactions and reflections, but more sophisticated math models for
data reduction, interpretation and extrapolation.
We will develop ideas for “intermediate length wind tunnels,” which are
typically 100-200 feet, and also, for “long wind tunnels” which range up to
2,000 feet in length. Some of the wind tunnels and devices described here were
designed very early on, but in recent years, very sophisticated, highly
instrumented systems have been developed. This chapter focuses on basic
principles and applications of mathematical models given earlier in this topic,
and consistent with this philosophy, applies newly developed ideas to simple test
systems that can be constructed quickly and inexpensively.
Sirens require testing using multiple wind tunnels to support detailed
evaluation of design trade-offs and compromises. For instance, strong acoustic
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