JPS6033107Y2 - Stern flow field control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stern flow control device that alleviates stern flow asymmetry and reduces hull resistance.

If there is one propeller on the center plane of the hull, and the shape of the lower part of the water surface is larger than that of a streamlined boat, one propeller
The rotational flow induced by the directional rotation may cause the flow near the stern to become significantly asymmetrical.

- This aspect is schematically shown in Figure 1.

In the figure, 1 is the main hull, 2 is the propeller, 3 is the rudder, 4 is the streamline (especially near the water surface), 5 is the stagnation point, and 6 is the hull centerline.

The stagnation point 5 is a place where the water flow divided to the left and right meets again at a very slow speed, but since hydrodynamic pressure increases at such a place, the stern of the main hull 1- is where the stagnation point 5 occurs. You will be pushed from the side you are holding to the other side.

Therefore, if the rudder 3 is kept at the center, the main hull 1 will start turning due to the above force.

Therefore, in order to maintain a given azimuth without turning, °“
It is necessary to maintain a state in which the forces acting on the entire system (main hull 1 + propeller 2 + rudder 3) are balanced.

FIG. 2 shows this balanced state.

In the figure, the same reference numerals as in Figure 1 indicate the same parts. F is the force acting on the main hull (vector quantity), Fun is the force (vector quantity) generated by the asymmetric flow near the stern, and FP is the force generated by the propeller. (vector quantity), FR is the rudder force (vector quantity), δ is the rudder angle, 7 is the forward direction, and β is the oblique angle.

When the force Fun acts, in order to cancel the turning caused by this force, the steering angle δ is determined to generate the steering force FR.

Although it is possible to balance the moments (around the center of gravity) with this, generally the forces in the left-right direction and the front-back direction are not balanced.

Therefore, the force in the left and right direction, the force in the front and back direction, and the moment (around the center of gravity) are balanced for the first time in a form that is oblique by the oblique angle β with respect to the forward direction 7.

In such a diagonal sailing state, the normal straight sailing state (β = 0
), the resistance increases by at least the amount of ■ and ■ below, which is unfavorable in terms of propulsion performance.

■ Increase in resistance due to oblique sailing (F) Increase due to β of the resistance component of I) ■ Resistance component of rudder force (PIO resistance) The above describes the problems as a steady phenomenon that does not change over time. However, it is also possible to point out the following problems as unsteady phenomena.

In other words, the asymmetric flow near the stern as shown in Figures 1 and 2 is closely related to the separation phenomenon of viscous fluid.
It can also change significantly over time.

It is also known that the stagnation point 5 moves from the starboard side to the port side depending on the state of motion of the ship, the propeller rotation speed, the rudder angle, etc., and exhibits a very complicated behavior.

Such unsteady changes in fluid force result in fluctuations in the azimuth angle when sailing with a constant rudder angle, and when trying to maintain a constant azimuth angle, it is difficult to change the rudder angle depending on the situation. Both of these are not desirable in terms of ship operational performance.

In addition, when we understand the various phenomena caused by the separation of the flow near the stern from the perspective of the ship's propulsion performance, we can find unstable phenomena,
From the perspective of maneuverability, it was commonly referred to as an abnormal phenomenon.

One known method for suppressing the above-mentioned instability and abnormal phenomena is to attach a centerline fin to the main hull above the propeller.

FIG. 3 shows an overview of this method.

In Figure 3, 1 is the main hull, 2 is the propeller, 3 is the rudder, and 4
A indicates the flow that is about to cross above the propeller, and 8 indicates the center line fin.

Of these, the flow 4a that tends to cross above the propeller occurs because the flow near the stern described in the previous section is extremely asymmetrical, but the centerline fin 8 effectively blocks this flow 4a.

Therefore, the asymmetry of the flow near the stern and the problems associated with this are also improved.

・“However, the method of installing the centerline fin 8 has the following drawbacks.

It is necessary to ensure sufficient clearance between the upper part of the propeller 2 and the main hull, taking into account measures against stern vibration.

When the centerline fins 8 are installed, this clearance becomes small, and as a result, the pressure fluctuations that the centerline fins 8 receive each time the blades of the propeller 2 approach are directly transmitted to the main hull.

This is not preferable as it increases the excitation force of the stern vibration, and is a drawback when the centaniline fin 8 is installed.

In addition, the behavior of the asymmetric flow near the stern changes in a complex manner depending on the loading state of the ship (stomach, trim) and motion state.

Therefore, there remains an uncertainty that a centerline fin 8 designed to be effective under certain representative loading and motion conditions may not be equally effective under other conditions.

The present invention aims to eliminate the above-mentioned drawbacks by controlling the asymmetric flow near the stern, which causes unstable navigational phenomena and abnormal phenomena, in response to changes in the loading state and motion state of the ship.
It is an object of the present invention to provide a stern flow field control device designed to effectively suppress stern vibration without increasing it.

For this reason, the stern flow control device of the present invention is provided with a flow direction meter near the centerline of the ship's hull above the propeller, and a nozzle that sprays water in the stern direction on the hull surface below the water surface in front of the propeller. A stagnation point of the asymmetric flow near the stern is detected by the current direction meter, and a water stream is ejected from the nozzle to guide the stagnation point toward the centerline of the hull.

The stern flow field control device as an embodiment of the present invention will be explained below with reference to the drawings. Fig. 4 is a perspective view showing the vicinity of the stern of the ship, and Fig. 5 is an explanation schematically showing the state of the flow around the ship's hull. It is a diagram.

In the figure, the same reference numerals as in FIGS. 1 to 3 indicate the same parts.

Reference numeral 11 is a water jet nozzle (hereinafter referred to as a nozzle) that is installed on the surface of the hull below the water surface in front of the propeller to eject a water flow toward the stern side of the centerline of the hull. Reference numeral 12 is a flow direction meter that measures the left and right components of the flow above the propeller. It is a device for detection.

゛If the stagnation point 5 of the asymmetric flow near the stern occurs mainly on the port side, the nozzle 1 on the port side as shown in Figs.
A water stream is ejected toward the stern from 1, and the water stream near the stagnation point 5 is guided in the direction of the hull centerline 6.

As a result, as shown in FIG. 5, the stagnation point 5 approaches the hull centerline 6, the asymmetry of the stern flow is reduced, and the increase in resistance due to diagonal sailing and steering is also reduced.

(If the stagnation point 5 occurs on the starboard side, the opposite is true.

) In addition, unlike centerline fins, a solid body is not installed, so by adjusting the flow rate according to loading conditions, it is possible to reduce asymmetry in the stern flow without causing an increase in stern vibration.

Alternatively, if there are a plurality of nozzles 11 on one side, it is recommended to select the nozzles 11 appropriately.

Furthermore, if the asymmetric flow near the stern is unstable and the stagnation point 5 moves alternately from the port side to the starboard side over time, the flow velocity in the left and right direction above the propeller 2 is detected by the current meter 12, and the stagnation point 5 moves from the port side to the starboard side. If the flow is in the opposite direction, operate the starboard side outlet, and if the opposite occurs, operate the port side outlet.

As a result, the stagnation point 5 does not move with time and is always near the hull centerline 6, reducing the asymmetry of the stern flow.

As described above, according to the stern flow field control device of the present invention,
This has the advantage that asymmetrical flow near the stern, which causes navigational instability and abnormal phenomena, can be effectively prevented without increasing stern vibrations in response to changes in the loading and moving conditions of the ship.

[Brief explanation of the drawings] Figures 1 and 2 are explanatory diagrams schematically showing the flow around the hull, Figure 3 is a perspective view showing the vicinity of the stern of a conventional ship, and Figure 4 is an implementation of the present invention. FIG. 5 is a perspective view showing the vicinity of the stern equipped with the stern flow field control device as an example, and FIG. 5 is an explanatory diagram schematically showing the flow around the hull. 1...Main hull, 2...Propeller, 3.
... Rudder, 4 ... Streamline, 5 ... Stagnation point, 6 ... Hull center line, 11 ... Nozzle, 12 ... ...Flow direction needle.

Claims (1)

[Scope of utility model registration request] A stern flow control device characterized in that a current meter is provided near the centerline of the ship's hull above the propeller of the ship, and a nozzle is provided on the surface of the ship's hull below the water surface in front of the propeller for ejecting a water stream toward the stern.