JPS5819037B2 - How to prevent Karman vortices in the wake of a columnar object - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing Karman vortices forming behind a columnar object placed orthogonally in a liquid flow.

When a columnar object 1 is placed perpendicular to the flow 2 in a liquid flow having an appropriate speed as shown in FIG. 1, Karman vortices 3 in opposite directions are generated alternately from the left and right sides of the object 1.

Due to this Karman vortex, an object is subjected to an alternating force perpendicular to the flow, and this alternating force becomes an excitation force, causing the fluid to vibrate and sometimes break down.

The present invention mixes air bubbles into the flow around a columnar object such as a circular pipe placed perpendicular to the liquid flow, and greatly recedes the separation point a (see Fig. 1) where the flow leaves the object surface.
The vortices from the left and right sides of the trailing side of the object are made into extremely weak fixed vortices, and the alternating force caused by the Karman vortices is suppressed to suppress the excitation force of the columnar object.

According to the inventor's experimental results, as shown in Figure 2, when air bubbles 4 are mixed into the liquid flow 2 around the columnar object 1, the Karman vortices released into the wake are suppressed or eliminated. In Fig. 1, the separation point a of the flow along the object surface when no air bubbles are mixed is within 90°, but as shown in Fig. 2, the separation point greatly retreats from point b to more than 100°, and the object 1
It was confirmed that the left and right Karman vortices formed behind the vortices become extremely weak fixed vortices 5.

From experimental results, it has been found that the minimum gas flow rate necessary to suppress the Karman vortex is 1 at a volume ratio of 3 to 6% of the liquid flow rate.

If the amount exceeds this value, flow resistance etc. will become a problem in the case of a heat exchanger with a tubular structure.

FIG. 3 shows an example of a bubble generator, in which a nozzle 6 is arranged in the flow 2 upstream of a columnar object 1 placed in the liquid flow at a slight distance from the columnar object, and air is emitted from the nozzle. The gas is ejected toward the object 1, and countless air bubbles 4 are mixed into the flow along the outer periphery of the object.

Note that the nozzle 6 is connected to a device for pumping gas such as air.

FIG. 4 shows another embodiment in which high-temperature fluid 7 such as steam is passed through the tube of a columnar object 1 consisting of a circular tube placed in a liquid stream, and the liquid around the tube is heated by heat exchange and gas is released. This generates air bubbles 4.

As described above, the present invention is capable of introducing air bubbles into a liquid flow by injecting gas into the upstream side of a columnar object such as a tube placed in the liquid perpendicular to the flow, or by evaporating from the surface of the object. This method suppresses or eliminates the Karman vortices that cause self-excited vibrations generated in the wake of the object, thereby making the vortices fixed vortices.

Therefore, it is possible to effectively suppress the occurrence of vibrations that occur when the flow in a heat/drug exchanger or the like hits the pipes at right angles, and the lifespan of the device can be extended.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the relationship between the Karman vortex and the object that forms behind a columnar object placed in a liquid flow, and Figure 2 is a Karman vortex formed by mixing air bubbles around a columnar object placed in a liquid flow. Explanatory diagram of the present invention that suppresses or eliminates the occurrence of
4 and 4 are schematic diagrams showing specific examples of carrying out the present invention, and FIG. 3 shows an example in which a gas ejection nozzle is disposed on the upstream side of a columnar object placed in a liquid stream to eject air bubbles; FIG. 4 shows a system in which a high-temperature fluid is caused to flow inside a columnar object placed in a liquid stream to generate bubbles from the surface of the object. 1: Columnar object, 2: Flow, 3: Karman vortex, 4: Bubbles,
5: Fixed vortex, 6: Nozzle, 7: High temperature fluid.

Claims (1)

[Claims] 1. A columnar object wake stream characterized by suppressing or eliminating Karman vortices that form behind a columnar object such as a pipe placed perpendicularly in a liquid flow by causing bubbles to flow along the outer periphery of the object. How to prevent Karman vortices.