77513
For this were used models having the form of right
angle parallelepipeds, which were drawn along In
the whole speed range shown above for five different
depths of submersion. Influence of lateral walls
of tray In both series of experiments was determined
by means of drawing models similar in plan and
photographing deformation of suspension surface
with chalky lines perpendicular to walls of tray
(Fig. 5) preliminarily drawn on it.
Form and dimensions of models are shown In
the table. Investigations were conducted on
suspensions of gray clay. Density of suspension p changed from 1.59 to 1.64 g/cm^.
For every veiue of density was constructed a rheological curve according to
measurement on rotary viscosimeter PB-8, and standard method were determined
corresponding values of coefficient of viscosity and limiting stress of shift.
Method of treatment of experimental data was chosen on the basis of the following
considerations.
In the general case of motion of a model In a tray its drag coefficient will
depend on parameters
Pig. 5. Characteristic form
of chalky lines on surface of
suspension during notion of
model in tray.
.
'r.
(2.1)
where a — the biggest thickness of model, D — width of tray, L — Its length and
H — thickness of layer of suspension In tray.
Comparison of (2.1) with (1.7) shows that for possibility of comparison of
theoretical and experimental results experiments could be conducted so that Influence
of the last four parameters In (2.1) was removed.
Independence of experimental data from D/a and L/a was controlled by results
of drawing models geometrically similar in plem (table) in the tray.
In accordance with general Ideas of flow around bodies of a vlscoplastlc
medium, region of flow has bounding dimensions. Location of walls, limiting volume
of vlscoplastlc medium. Inside which Is Included the region of flow, does not
Influence meignitude of resistance of body. Inasmuch as medium outside region of flow
is In the hard state [2], Therefore, to control Independence of from D/a and
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deflections frcan one-dimensional laws of preservation on front of shock wave during
Its reflection frc® closed end of tube. Below is compared an optical picture of
the process with measurements of pressure by piezotransducer and with other methods
of "sounding" the state of the medium after the shock wave - for more detailed
Information about degree of deflections frcan one-dimenslonallty. Corresponding
oscillograms and developments are shown In Pigs. 1-5.
1. Combination of picture of glow with recording of pressure In wall of tube.
For simultaneous registration of front of pressure and front of glow of shock waves
I f j a tube from plastic with a right angle cross
section 15 x 50 mm, and length 160 cm, with
discharge section of the type; axial elongated
'J electrode-wall, C - 600-750 microfarad,
i V » 5-5.8 kv. Discharge was produced In air
Fi,,. 1. cTTSieous re^ ^ at Initial pressure P
q
- 0.2 mm Hg. Speed of
cording of lumlnescense
■(PM) and pressure (p);
D ~ 1.5 cm/usec.
shock wave could be determined accurate to
1-2?K both by scannings made by photoregister
and also with the help of a [FEU] (®py) (photOTiultlpller, PM) and two transverse
slots. Pressure was measured bv pulse piezoelectric transducer [6] with diameter of
sensing device 1 mm. Calibration by sensitivity
■
* »W5
•~^nd check of accuracy of reproduction of form
cf signal by transducer were conducted on a
diaphragm shock tube. Error In determination
of absolute value of pressure was not more than
The transducer was embedded In the lateral
••wall of the tube strictly opposite slot of
recording channel of PM, dimensions of which
were 1 x 0.3 mm.
Comparison of oscillograms of pressure and
glow (Fig. 1) Indicates ccanbinatlon In time of
maxima of measured magnitudes accurate to '-0.1
usee. However beginning of growth of glow, as
a rule, noticeably leads beginning of rise of
pressure. Difference in time constant of buildup
Fig. 2. Combined In time
frame of glow, taken through a
Q
transverse slot 46 x 0.5 mm ,
and oscillogram of pressure,
recorded by a piezotransducer
embedded in lateral wall of
tube strictly opposite slot.
Narrow luminescent band on
frame Is obtained during
passage of perturbation through
auxiliary slot 4 x 0.5 mm^,
located 25 mm ahead of basic
slot. A light signal, passing
the auxiliary slot simulta
neously Is recorded by the FM.
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I
■>
Fig. ;'.
(a) Phototracing of process of
collision cf two waves of identical intensity;
D ~ 5 cm/kisec. (b) Frame of luminoscense
of propagating perturbation.
of signals for waves with a speed
~1.5i cm/msec was near 0.3 usee or
(in space solution) near 0.5> cm.
The most graphic explanation of
this fact can be found in comparison
of recording of pressure with
simultaneous registration of form
of contour of luminescent front
of shock wave. For this purpose
the gas luminescense was photographed
through a transverse slot by the
method of partial (to 0.9)
ccanpensatlon of motion of wave
(image on film In photoregister
moves with a speed close to speed
of wave In that same direction,
see [6]). Cki Fig. 2 are given
typical photographs of contour of
luminescent front with recordings
of pressure in corresponding section
superimposed on them. On photographs
there is a characteristic absence of a clear and smooth line of the front — in
undisturbed gas it is as though clusters of plasma are "introduced," forming their
own kind of "semipermeable piston." Considering difference in internal energy
of plasma of discharge and gas compressed by shock wave due to mixing, as a whole
it is possible to expect deflections of mean values of temperature, density, and
pressure of medium after the front fran those calculated freas one-dimensional laws
of preservation for plane wave.
2. Pressure after front of shock wave. Ckd Fig. 6 are given absolute values
of measured pressures after the front of a wave. Prom comparison of them with
given one-dimensional calculation it is possible to see that there is a divergence
of approximately twice in understating data of experiment. Let us note that a
decrease of pressure can be shown also in measurements of [4](after a reflected
wave), where the author relates this to errors of experiment. It is necessary
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to note »l«o that small values of measured pressures are directly connected with
appraisals of deviations from calculation In temperature and density, given In
[2], where It Is shown that the ratio of experimental values of temperature to
theoretical values have an order of 2, and the ratios of experimental values of
density to theoretical values equal ~l/3.
5. Speed of reflected and refracted shoclc waves. Comparison of measured
speeds of reflected euid refracted shock waves with calculated speeds can also
serve as a method of appraisal of deflections from one-dlmenslonalness (registered
deflections from equilibrium In this case are difficult to expect due to large
values of temperature of medium). Experiments on collision and reflection of shock
waves were conducted In a round tube with Internal diameter 27 mm and with coaxial
discharge device. As also In tube with right angle cross section, front of glow
of wave at 60 cm from discharge turns out to be Irregular (most frequently — convex,
see Pig. 3b). Typical scannings of collision of waves of equal Intensity are shown
on Fig. 3a. Scannings of reflection of wave from closed end of tube In virtue of
symmetry of phenomenon are fully analogous to each of the halves of a scanning of
(PI*.
IT
n 0
t
2
i
S
i usee
Fig. 4, Phototracing of reflection of wave from end
of tube.
Scannings with resolution In time and space essentially larger than on Pig. 3a
(~50 times) were processed (Pig. 't). On Pig. 7 values of speed of reflected waves,
desired at ~1 cm near reflecting wall, are compared with one-dlmenslonal
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equilibrium calculation (solid curve). Prom this comparison it is simple to verify
that speed of reflected (refracted) wav’s is
times higher than the calculated
value. If one were to consider that speed of reflected wave D* is connected with
compression in this wave 3 and flow rate u is a simple relationship. D » u/(p - 1)*
obtained data will correspond not to computed value of compression Pg ~ ^
®
wave in air (D = 2 cm/iisec), but to compression 3^' ~ 5. This result does not
contradict observations by mutual penetration ^d mixing of olectrodlscharge and
thermal plasma in an incident wave, if one considers that dlscliarge plasma has
higher temperature than thermal plasma. Tlius, if it is considered that change of
noted above is connected only with increase of temperature (speed of sound) after
an incident wave with corresponding change of Mach number of reflected wave M* ~ 0.6M,
then the necessary Increase of temperature sliould compose ~
l.e.,
somewhat lower than in [2], where ’ ~ 2T^, However if one were to take obtained
value for
t
' and, according to [2], to consider ~ l/3pj, then we obtain
Pj^'/p^ ~ 1/2, which more nearly corresponds above obtained data on measurement of
pressure than estimates of expected decrease of pressure according to (2).
4
Pig. 5. Diagram of experiment and time scanning of flow around by a wave of
a cylinder 5 nun in diameter with axis coinciding with axis of tube.
^. Shock wave during flow around an obstacle. For the diagram of the
experience shown on Pig, 8, the scanning is given on Pig. 5. With respect to
position of shock wave forming for braking surface of obstacle (end of cylinder of
area S), it is possible to watch state of flow after Incident shock wave, in
particular it is possible to estimate Mach number of flow of medium incident on the
body. In accordance with data of (7, 8], ratio of distance between fonirard shock
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2. Measurement of speed of front of shock wave. At the majority of stations
speed of propapiation of shock wave In channel of pipe is determined by the time
during, which a wave passes the distance between two piezo pressure transducers.
Every station consists of three piezotransducers.
Intensive signal of first piezotransducer starts the
i .jrcan of oscillograph 0K-17M. Pre imlnary starting of
VoK-17M permits considering fronts of pressure pulses
t
'' n one beam of the osclllo*7,raph. Steepness of pulse
' li'e of pressure is determined by dimensions of plate
barium tltanate and speed of the shock wave proceeding
'Jpast the piezoelement. The second beam of oscillograph
^""oK-17M serves for registration of "oscillogram tine
marks" fresn generator of standard signals [GSS-6] (rCC-6).
Accuracy of determination of Interval of time is of
order 15f. A typical oscillogram of signals fran
piezotransducers is shown on Fig. 2a.
The method of determination of speed of shock waves
In shock tubes with the help of light screens Is widely
known fl]. Every light screen constitutes a small
streak system co- sistir.g of a source of light, two objectives and a blade. Not
less exact, but a simpler method of measurement of speed Is the photoelectric
method, the basis of which is the simple shadow method of registration of shock
waves.
The setup contains two basic elements; point source of light and two phot«nultl-
pllers. The point source of light Is mercury quartz tube of super high pressure
(DRSh-100](lOPOI-lOO) with dimension of arc 0.? x 0.3 mm, working In steady state con
ditions. The light receivers are photcaaultlpllers [PM-19]or[PM-33](®?y-33)
Photomultiplier together with cathode follower Is enclosed in a metallic light
tight housing, face of which has adjustable slot [UP-1](yoperating conditions Is carried out by variation of supply voltage (stabilized
rectifier [VS-16] (BC-16)), by width and height of slot. Conditions are controlled
In magnitude of current on PM load. To lower natural noises of photaaultlpller
minimum supply voltage of PM Is chosen (600-700 v). Width of slot Is several
-265-
Flg.
:'S.:illogluj;i.-
for measurement of
speed of front cf
shock wave:
a — by
plezotransducers ;
b — by photomult 1-
pllers; c - font, of
signal on PM.
‘If
Fig. 5. Ir.» r 1 • ! i. . f shocK wave with cylinder in shocK
tube. Simple* spark survey.
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