JPS5836207B2 - Boundary layer control device for circulating water tank - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a boundary layer control device for a circulating water tank, and in particular, even if the flow velocity of the general flow is varied, the flow velocity distribution within the boundary layer formed at the boundary surfaces such as the wall and bottom of the tank is controlled. The present invention relates to a boundary layer control device for a recirculation aquarium that can easily improve the flow velocity distribution to a desired flow velocity distribution, reduce flow velocity fluctuations in the boundary layer, and thereby maintain a constant flow velocity distribution of the general flow in the aquarium.

In general, circulating water tanks are used for simulation experiments in fields such as shipping and fisheries engineering, but they are especially used in the fisheries industry where experiments are carried out on fishing gear, fishing nets, etc. When conducting experiments, there was a problem in that experimental errors became large due to the influence of the boundary layer that formed near the bottom of the tank.

For this reason, conventional boundary layer control methods that accelerate the boundary layer flow, which is slower than the general flow outside the boundary layer, have been proposed, such as a method of blowing a jet into the boundary layer and a method of sucking fluid within the boundary layer. ing.

However, in both of the conventional methods, the blowout amount and the suction amount are set constant, which is not satisfactory as a method for controlling a boundary layer where the flow velocity tends to fluctuate.

In addition, when experimenting with various flow velocities of the general flow,
Each time, the flow velocity distribution in the boundary layer was set to the optimal flow velocity distribution through trial and error, such as manually changing the blowout amount or suction amount while measuring the flow velocity in the boundary layer.

The present invention was devised to effectively solve the above problems.

An object of the present invention is to detect the dynamic pressures in the boundary layer flow and the general flow using a dynamic pressure detection means, and to detect the dynamic pressure in the boundary layer flow and in the general flow, and to control the control means so as to approximate the dynamic pressure value of the boundary layer flow to the dynamic pressure value of the general flow. By controlling the operation of the acceleration means that accelerates the boundary layer flow, even if the flow velocity of the general flow is varied, the flow velocity distribution of the boundary layer can be easily improved to a desired flow velocity distribution, and the boundary layer flow velocity distribution can be easily improved to a desired flow velocity distribution. It is an object of the present invention to provide a boundary layer control device for a circulating water tank that can prevent fluctuations in flow velocity and maintain a constant flow velocity distribution in the boundary layer.

According to the present invention, the above object is achieved by the following configuration.

That is, the configuration of the present invention is a boundary layer control device for a circulating water tank that controls and improves the flow velocity distribution in the boundary layer formed in the circulating water tank, which is provided in the circulating water tank and controls the fluid in the boundary layer. Accelerating means for accelerating the boundary layer by sucking in or blowing a jet into the boundary layer, and an acceleration means provided in the boundary layer flow and in the general flow outside the boundary layer, respectively, and the respective dynamic pressures (first-flow velocity) The dynamic pressure detection means for detecting the flow compares the dynamic pressure value of the general flow obtained from the dynamic pressure detection means with the dynamic pressure value of the flow in the boundary layer, and the dynamic pressure value of the flow in the boundary layer is calculated as control means for controlling the operation of the acceleration means so as to approach the pressure value, and a differential pressure between the dynamic pressure value of the general flow obtained from the dynamic pressure detection means and the dynamic pressure value of the flow in the boundary layer is preset. When the differential pressure exceeds the preset upper limit, the control means increases the forced acceleration force of the acceleration means that accelerates the boundary layer, while when the differential pressure is less than the preset lower limit, the control means increases the forced acceleration force of the acceleration means. It is characterized in that it is controlled so as to reduce the.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

In FIG. 1, 1 is a circulating water tank, and 2 is its waterway.

In waterway 2, fluid such as water flows to the right in the figure, and 3
is the bottom wall of waterway 2.

The bottom wall 3 is provided with a suction port 4 that sucks in the boundary layer near the bottom wall 3 and a discharge port 5 that discharges the fluid sucked from the suction port 4 into the water channel 2 again. are communicated with each other by a pipe 6 disposed outside the water channel 2.

The piping 6 is provided with a pump 7 for sucking fluid in the boundary layer into the piping 6 from the suction port 4 and a valve 8 for adjusting the amount of fluid sucked from the suction port 4.

Pitot tubes 910, which serve as dynamic pressure detection means D, are provided above and below in the general flow and the boundary layer flow of the waterway 2, respectively.

Using the dynamic pressure p1 in the general flow detected by the pitot tube 9 and the dynamic pressure p2 in the boundary layer detected by the pitot tube 10 as input, the differential pressure between the dynamic pressure of the general flow and the dynamic pressure of the boundary layer p1P2 A differential pressure converter 11 is provided that outputs an electrical signal proportional to .

The differential pressure transducer 11 is schematically shown here, and a commercially available one can be used, but its mechanism includes, for example, a diaphragm 13 that divides the casing 12 into two chambers, one of which is A transmission pipe 16 is interposed between the chamber 14 and the pitot tube 9 to transmit the dynamic pressure of the general flow obtained in the pitot tube 9 to the chamber 14, and in the same way, the other chamber 15 and the pitot tube 10 are A transmission pipe 17 is provided between the two.

In principle, the differential pressure converter 11 has chambers 14 1
Based on the amount of displacement of the diaphragm 13, for example, which is displaced by the dynamic pressure difference of 5, this is calculated as the dynamic pressure difference pI between the general flow and the boundary layer flow.
I) An electric circuit (not shown) is provided for converting into an electric signal jp proportional to 2.

The transmission pipes 16 and 17 are provided with air reservoirs 18 and 19, respectively, which have the function of converting relatively fast dynamic pressure fluctuations obtained by the pitot tubes into smoothed dynamic pressure fluctuations.

The differential pressure converter 11 and the control circuit 20 are electrically connected,
The control circuit 20 amplifies the electrical signal Ap proportional to the dynamic pressure difference 1)1 1)2 between the general flow and the boundary layer flow output from the differential pressure converter 11.

Furthermore, in order to control this amplification value within a preset range, in other words, to control the dynamic pressure difference (speed difference) between the general flow and the boundary layer flow within a certain pressure difference, the control circuit 20 uses the pump described above. It is configured to output a control signal for controlling the rotational speed of a motor 21 that operates the valve 7 or the opening degree of the valve 8, thereby adjusting the amount of suction from the suction port 4.

In this embodiment, the control means C mainly includes the air reservoir 18 1
9, a differential pressure converter 11, and a control circuit 20, and the boundary layer flow acceleration means A mainly includes a pump 7 and a motor 2.
1, a suction port 4 and piping 6.

In summary, the device of this embodiment includes an accelerating means A that sucks and accelerates the fluid in the boundary layer of the circulating water layer 1, a pitot tube 9 that is installed in the general flow and detects the dynamic pressure P1, and a representative fluid in the boundary layer. Pitot tube 1 installed at a position and detecting the dynamic pressure P2
Dynamic pressure detection means D consisting of 0, dynamic pressure value P1 of the general flow obtained from the dynamic pressure detection means D, and dynamic pressure value P2 of the flow in the boundary layer.
and a control means C that controls the operation of the acceleration means A based on the differential pressure P1P2 between the accelerating means A and the pressure difference P1P2 within a predetermined range.

Next, the operation of this embodiment will be described.

The flow velocity of the fluid flowing near the bottom wall 3 is slower than the flow velocity U of the general flow due to friction etc. due to the presence of the bottom wall 3. A boundary layer is formed with a large velocity gradient as shown in FIG. 2, which shows the distribution.

However, when the pump 7 is operated and the boundary layer is sucked into the pipe 6 from the suction port 4, as shown in FIG. The flow velocity U1 becomes a flow velocity shown by U3 in the figure, which is a combination of the flow velocity U1 and the flow velocity U2, and the boundary layer flow is accelerated.

As a result, the flow velocity distribution on the downstream side of the suction port 4 is improved from the flow velocity distribution shown in FIG. 2 to the flow velocity distribution shown in FIG. 3.

(It can be considered that the fluid corresponding to the volume of the shaded portion V in FIG. 3 is sucked out from the suction port 4.

) Furthermore, by increasing or decreasing the amount of suction sucked in from the suction port 4, the degree of acceleration of the boundary layer flow can be adjusted.

The dynamic pressure p1 caused by the flow velocity of the general flow is detected by the pitot tube 9, and the dynamic pressure p2 caused by the flow velocity at a representative position in the boundary layer is detected by the pitot tube 10.

As the flow velocity changes, the dynamic pressure detected in the pitot tubes 9 and 10 also changes, but these dynamic pressure fluctuations are converted into dynamic pressure fluctuations smoothed by air reservoirs 1819 provided in the transmission pipes 16 and 17, respectively. be done.

In particular, the fluctuations in the flow velocity within the boundary layer are usually irregular and relatively fast fluctuations, as shown in FIG.

(FIG. 4 shows the fluctuating pressure value P accompanying the flow rate fluctuation with respect to time t.

). However, by providing the air reservoir, rapid pressure fluctuations are smoothed or averaged, resulting in gentle fluctuations as shown in FIG.

Since pressure fluctuations are averaged in this way, stable control can be performed even for fluctuating flows that are normally difficult to control.

The averaged dynamic pressure is transmitted via transmission pipes 16, 17 to differential pressure transducers 110 and chambers 14 and 15, respectively, and an electric signal j proportional to the dynamic pressure difference pI P2 between the general flow and the boundary layer flow is transmitted.
p and is input to the control circuit 20.

The input electric signal Ap is amplified, and if this amplification value is larger than a preset upper limit, that is, if the speed difference between the general flow and the boundary layer flow is larger than the preset speed difference, the control circuit 20 is a motor 21 that operates the pump 7
A control signal that increases the rotational speed of the valve 8 or a control signal that increases the opening degree of the valve 8 is output, so that the amount of suction from the suction port 4 is increased and the boundary layer flow is accelerated.

Generally, pI>p2 and A p > 0, so the control circuit is controlled so that the amplification value is equal to or less than the set value.

In addition, if the amplification value is smaller than a preset lower limit value (meaning an allowable value in the range of Jp>00), the control circuit 2
0 outputs a control signal that reduces the rotational speed of the motor 21 or the opening degree of the valve 8, the suction amount of the suction port 4 is reduced, and the boundary layer flow is decelerated.

In this way, the flow velocity of the boundary layer flow is controlled so that the velocity difference between the general flow and the boundary layer flow falls within a preset velocity difference.

Therefore, the flow velocity of the boundary layer flow approaches the flow velocity of the general flow, and the influence of the boundary layer, which is a problem when conducting experiments near the bottom wall 3, is reduced.

Furthermore, even when the flow velocity U of the general flow is varied, the flow velocity within the boundary layer is controlled so that p1-p2 always falls within a certain tolerance, so the flow velocity distribution within the waterway 2 is automatically controlled. is easily maintained at the desired flow rate distribution.

Although the above embodiment shows a control device that sucks in and accelerates the boundary layer, it is also possible to blow out an accelerating fluid into the boundary layer to accelerate the boundary layer flow, and an example of this is shown in FIG.

In FIG. 6, reference numeral 22 indicates an outlet for accelerating fluid provided in the bottom wall 3.

The rest of the configuration is almost the same as the above embodiment, and the flow rate of the boundary layer flow is controlled by controlling the blowout amount.

Further, as the dynamic pressure detection means D, the dynamic pressure may be detected by a general small flow rate detection device or a semiconductor pressure detector, instead of the pitot tube.

Although the above embodiment shows an example of controlling the boundary layer formed near the bottom wall 3 of the aquarium, it is also easy to control the boundary layer near the side wall of the aquarium using the above device.

Further, the positions of the suction port 4 and the blowout port 22 may be distributed linearly or planarly at appropriate locations within the observation section of the recirculation water tank, and of course this can be applied within the scope of the principles of this precept.

As is clear from the above description, the present invention exhibits the following excellent effects.

(1) The boundary layer flow can be accelerated and its flow velocity approximated to that of a general flow, and the influence of the boundary layer, which is a problem when conducting experiments in a circulating water tank, can be eliminated or reduced.

(2) Varying the flow velocity of the general flow flowing through the aquarium will change the thickness and flow velocity distribution of the boundary layer, but it is possible to quickly control the flow velocity distribution of the boundary layer to the desired flow rate by quickly controlling it to the optimum state accordingly. The distribution can be improved.

(3) Fluctuations in flow velocity caused by the boundary layer can be prevented, and the flow velocity distribution in the boundary layer can be maintained constant, thus reducing fluctuations in the flow velocity of the general flow.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an embodiment of the device according to the present invention;
Figure 2 is a diagram showing the flow velocity distribution when no suction is performed;
Fig. 3 is a diagram explaining flow velocity changes and flow velocity distribution when suction is performed, Fig. 4 is a graph showing temporal fluctuations in pressure, and Fig. 5 is a graph showing the smoothed fluctuating pressure of Fig. 4. , FIG. 6 is a longitudinal sectional view showing another embodiment of the present invention. In the figure, 1 is a circulating water tank, A is an acceleration means, D is a dynamic pressure detection means, C is a control means, p1 is a dynamic pressure value of a general flow, and p2 is a dynamic pressure value of a boundary layer flow.

Claims (1)

[Claims] 1. A boundary layer control device for a circulating water tank that controls the intralayer flow velocity distribution of a boundary layer formed in the circulating water tank and improves the flow velocity distribution, comprising an acceleration means provided in the circulating water tank and accelerating the boundary layer flow; Dynamic pressure detection means is provided in the boundary layer flow and in the general flow outside the boundary layer to detect the respective dynamic pressures, and the dynamic pressure value of the general flow obtained from the dynamic pressure detection means and the flow inside the boundary layer are A boundary layer control device for a circulating water tank, comprising: a control means for comparing the dynamic pressure value with the dynamic pressure value of the flow in the boundary layer and operating the acceleration means so as to approximate the dynamic pressure value of the flow within the boundary layer to the dynamic pressure value of the general flow.