Geology Reference
In-Depth Information
9.3.4
Intermediate wind tunnel test procedure.
1.
Record time, date, and air temperature and humidity, and note any unusual
conditions, e.g., exposure of the room to sunlight. Using standard
engineering formulas, determine the mass density U of the air and the
corresponding speed of sound c.
2.
Place the siren in the wind tunnel with the rotor-stator gap located at x = 0.
Insert flow straighteners at the blower outlet and also just downstream of
the rotor. Install the differential pressure transducer and single pressure
transducer at the upstream location x = - ½ L ahead of the stator.
3.
The siren will be turned by an electric motor installed in the upstream or
downstream location (upstream may be preferable since this mimics the role
of the central hub in the MWD tool). The torque acting on different sirens
will be different, so that different electrical settings will be required to
maintain the same rotation. Again, siren torques will depend on the design
geometry and also the oncoming flow rate.
4.
Install all electronic instrumentation, e.g., DC controllers for the electric
motor, differential pressure and single transducer outputs to signal
analyzers, simultaneous measurements for dynamic torque, and so on (refer
to the “long wind tunnel” section for details).
5.
We now perform tests. With the siren rotating at the desired frequency,
determine the average volume flow rate Q as described in Chapter 8. First,
measure p
s
using the differential transducer; this p
s
is the one in 'p = p
s
e
i
Zt
= p
s
cos Zt in Chapter 3. Second, perform single transducer measurements.
Set x = - ½ L in Equation 3-A-14 and introduce L, Z and c. The result is
p
1
(-
L
/
2
,t) = - {p
s
/(
2
tan
ZL
/c)} [- sin
ZL
/
2
c + (tan
ZL
/c) cos
ZL
/
2
c] cos
Z
t.
The transducer signal is p
1
(-
L
/2,t). Its measured peak-to-peak value equals
-{p
s
/(2 tan Z
L
/c)} [- sin Z
L
/2c + (tan Z
L
/c) cos Z
L
/2c] which can be
solved for p
s
. Do the differential and single transducer p
s
values agree?
6.
For the same frequency, repeat the above with different values of Q. Is the
dependence on Q linear, quadratic or something else?
7.
Repeat the test for different frequencies, and then, different Q's for each
frequency. What is the dependence of p
s
on frequency, or better, as a
function p
s
(Q,Z) of both frequency Z and volume flow rate Q?
8.
Actual signals will be additionally dependent on the mud density U
mud
.
With all other quantities fixed, p
s, mud
= p
s, air
(U
mud
/U
air
). When further
extrapolated to the downhole flow rate, is the signal strong enough to
overcome attenuation?
9.
Our analytical model assumes that p
s
is a constant and that the transient
delta-p takes the form 'p = p
s
e
i
Zt
. With the rotor turning at a constant
frequency Z, we wish to determine experimentally if p
s
is, in fact, constant.
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