STUDY OF THE VELOCITY DIRECTIONS OF CIRCULATING FLOW IN THE CAVITY OF FLUID COUPLINGS

Yu. I. Kapustin

(Presented by the scientific seminar of the Department of Applied Mechanics)

In studying the external characteristics of completely filled fluid couplings, it was found that the position of the axis of rotation has a significant effect on the torque transmitted by the fluid coupling, especially in the region of small slips. Moreover, this effect is not the same for different positions of the impellers relative to one another. It is impossible to explain these phenomena on the basis of the currently accepted scheme of the working process in the cavity of fluid couplings [1] [2]. In this connection, it became necessary to investigate the velocity direction of the circulating flow in the cavity of fluid couplings in order to determine its actual form at different slips.

The direction of the flow velocity in the circulation circuit was determined by inductive sensors. Water and spindle oil were used as the filling liquids in the study. Determination of the directions of the flow velocity was carried out in the slip range from 2 to 100%.

Fig. 1

The arrangement of the inductive sensor and the calibration curve of one of them are given in Fig. 1. It was located in the turbine wheel on two strings. The movement of the sensor from the periphery of the turbine wheel to the center and back was carried out during operation of the fluid coupling manually, by means of a special device. Its position was determined by a rheochord sensor.

In the study, the measurement results were recorded by a loop oscillograph of the 8SO-114 type. The following quantities were recorded:

a) torque on the turbine shaft,
b) rotational speed of the turbine and pump wheels,
c) temperature of the fluid in the fluid coupling,
d) position of the inductive sensor,
e) angles of the velocity of the circulation flow.

Examples of oscillograms are shown in Fig. 2, a. The procedure of the study was as follows: the test stand was started; the coupling was loaded with a small torque in order to warm up the stand bearings and obtain the required temperature of the fluid in the fluid coupling (all measurements were carried out at a fluid temperature

Fig. 2, a, b

in the fluid coupling in the interval from 30 to 40°C); when the required temperature was reached, measurements were begun. For this purpose, a certain slip was set, after which the sensor of the flow-velocity direction was moved in the cavity of the fluid coupling from its initial radius to the active radius and back. Control of the torque on the turbine wheel, of the temperature of the fluid in the fluid coupling, and of the rotational speed of the turbine wheel was carried out visually by the corresponding instruments.

In the oscillograms shown in Fig. 2, the meanings of the curves are as follows:

1 — angle of the direction of the flow velocity;
2 — position of the inductive sensor;
3 — zero line of the flow-velocity angles;
4 — revolutions of the turbine wheel, measured by a tachogenerator;
5 — torque on the turbine shaft;
6 — zero line of the torque and revolutions of the turbine wheel;
7 — temperature of the fluid in the fluid coupling;
8, 9 — revolutions of the pump and turbine wheels, measured by pulse induction sensors;
10 — 50-Hz time marker.

The results of decoding oscillograms Nos. 57—01 ÷ 57—57 are shown in Fig. 3. Here curve 1 is the dependence \(R_{\mathrm{c}} = f(s)\), curve 2 is the external characteristic of the fluid coupling under test, representing the dependence \(M = f(s)\). The dashed lines in the figure indicate the limiting radii of the circulation circle.

As the results of decoding the oscillograms recorded with different filling fluids and at different pump-wheel speeds have shown, the dependence \(R_{\mathrm{c}} = f(s)\) has an identical form for the different experimental conditions.

Analyzing the direction of the flow velocity recorded by the inductive sensor near the vortex center, one may conclude that, at small slips, the vortex center of the flow is not located in the gap between the runner wheels, but is displaced into the pump wheel. As the slip increases, it moves from the pump wheel into the turbine wheel.

Fig. 3

At a slip of about 40%, it is displaced to such an extent that its center lies on the trajectory of motion of the inductive sensor. This is clearly seen from oscillogram No. 57—47 (Fig. 2, a). The sensor vane, when located in the vortex center of the circulating flow, performs rotational motions. With a further increase in slip, up to 100%, a slight displacement of the vortex center into the turbine wheel is observed.

To determine the location of the vortex center of the flow in the pump wheel, investigations were carried out of the direction of the flow velocity in the pump-wheel cavity. The method of investigation in this case was analogous to the preceding one. The difference consisted in the fact that in this case the inductive sensor was fixed immovably at various points of the interblade channel of the pump wheel. During recording of the oscillograms, only the slip of the fluid coupling was varied. An example of an oscillogram recorded in this investigation is given in Fig. 2, b. The passage of the center of the vortex zone through the point at which the inductive sensor was located is clearly visible on the oscillogram (the sensor vane in this case performs rotational motion).

Figure 4 gives the dependence of the displacement of the vortex center of the flow on the magnitude of slip, obtained by decoding oscillograms similar to oscillogram No. 131-03. In Fig. 4 the following are denoted:

\(\Delta T\) — displacement of the vortex center of the flow in the axial direction from the edges of the blades of the runner wheels,

\(T\) — depth of the meridional sections of the runner wheels.

Thus, investigation of the direction of the velocity of the circulating flow in the cavity of fully filled fluid couplings, at different rotational speeds of the pump wheel and with different filling fluids, made it possible to establish the following:

1. The radius of the vortex zone of the circulating flow, for slip regimes greater than 6%, is almost independent of them. At smaller slips it decreases somewhat, owing to the fact that in these operating regimes of the fluid coupling the flow has a strongly vortexed structure, which leads to equalization of the flow velocities over the entire flow cross section.

Fig. 4

1. At small slips, the vortex center of the circulating flow is located in the cavity of the pump wheel. As the slip increases, it shifts into the cavity of the turbine wheel.

2. The flow in the fluid coupling, at all slip regimes except slips of less than 6%, differs significantly from a uniform-velocity flow.

3. The inlet flow into the turbine wheel has a clearly pronounced pulsating character at all slip regimes. The outlet flow from the turbine wheel, however, has no appreciable pulsations.

REFERENCES

1. D. Ya. Aleksapol’skii. Hydrodynamic Transmissions. Mashgiz, 1963.
2. B. A. Gavrilenko, V. A. Minin. Hydrodynamic Couplings. Oborongiz, 1959.