JPH07159278A - Impact wind tunnel - Google Patents

Abstract

PURPOSE:To protect the facility against damage by buffering the final stage of the stroke of a free piston by means of air cushion depending on the variation in the area of gap between a buffer plug and the inner circumference of an impact wave pipe. CONSTITUTION:A bullet type buffer plug 4 having a pointed end entering an impact wave pipe 3 and a base part of substantially equal diameter to the inner diameter of the impact wave pipe 3 projects along the axis thereof on the downstream side from a free piston 1. When the free piston 1 approaches the end of a compression pipe 2, i.e., the inlet of the impact wave pipe 3, and the pointed end of the buffer plug 4 begins to enter the pipe 3, the gap between the plug 4 and the pipe 3 decreases gradually because of the bullet-like profile thereof. Consequently, the flow rate of air from the compression pipe 2 to the impact wave pipe 3 decreases abruptly and the residual air in the compression pipe 2 is subjected to significant compression. This structure provides a buffering effect equivalent to an air cushion provided between the free piston 1 and the final end of the compression pipe 2, i.e., the inlet of the impact wave pipe 3, thus preventing solid state collision against the inlet end of the impact wave pipe 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impact wind tunnel, and more particularly to a collision mitigation means for its free piston.

[0002]

2. Description of the Related Art An impact wind tunnel is a device for generating a high-speed wind near the speed of sound in an instant by a free piston that moves at high speed in a cylindrical compression tube, and requires buffering when the free piston is stopped.

FIG. 2 is a side sectional view of the end portion of the compression tube of the conventional impact wind tunnel. At the end of the compression tube 52, a free piston 51, which has been moving at high speed from the left side of the figure, is attached to a shock wave tube 53. In this example, the shock absorber (urethane resin or the like) 54 collides with the shock absorber 54 and stops while rebounding (a rebound phenomenon of the free piston 51 due to rapid gas compression).

The shock absorber tube 5 comprises a plurality of shock absorbers 54.
It is attached to the 4 side. The shock load acting on the shock absorber 54 is extremely large, and energy is absorbed by the shape deformation of the shock absorber 54 (urethane resin). Therefore, the shock absorber 54 is severely damaged and is treated as a consumable item that can be replaced after several uses.

[0005]

The above conventional impact wind tunnel has the following problems to be solved.

That is, in the conventional impact wind tunnel, since the free piston collides at high speed with the shock absorber made of urethane resin at the end of the compression pipe, the shock absorber is severely damaged, and the compression pipe is broken due to scattering of crushed pieces. There was a problem that the shock wave tube, etc., became dirty and, in rare cases, were damaged.

Further, there is a problem that the test specimen set in the downstream measuring section is contaminated and damaged.

Further, since the free piston always rebounds due to the collision, the so-called piston-cylinder fitting, that is, the free piston and the compression pipe which are subjected to high precision finish for simultaneously achieving airtightness and slidability, are provided. There is also a problem that the precision fitting of both is impaired.

Further, there is a problem that seizure is rarely caused by collision heat.

When the above problems occur, it is necessary to recover the heavy free piston of about 1 ton in order to recover it, and also the outer diameter of the large free piston and the inner diameter of the compression tube and shock wave tube. There is also a problem that it requires re-precision finishing, requires a great deal of labor and a schedule, and accordingly, the development schedule of the flying object to be tested is delayed.

In order to solve the above-mentioned problems, the present invention aims to prevent damage,
An object of the present invention is to provide an impact wind tunnel provided with a shock absorbing means that does not scatter.

[0012]

As a means for solving the above problems, the present invention intends to provide an impact wind tunnel described in the following (1) to (3). (1). In a shock wind tunnel that is equipped with a free piston that can move at high speed in a compression tube having a shock wave tube with a small inner diameter on the wake side, and when the free piston reaches the end of the compression tube, it is required to mitigate the collision with the shock wave tube inlet. A shock-absorbing plug, which has a tip that can be inserted into the shock tube formed on the downstream side of the free piston along the axis of the shock tube and can enter the interior of the shock tube, and whose base portion approximately corresponds to the inner diameter of the shock tube. An impact wind tunnel characterized by (2). The shock wind tunnel according to (1) above, further comprising a shock wave tube and a conduit tube provided so that a flow path to the atmosphere can be selected in the vicinity of the downstream end of the compression tube. (3). In the shock wind tunnel described in (1) above, the buffer plug forms a rod body having a uniform cross section substantially corresponding to the inner diameter of the shock wave tube, and the inner diameter near the upstream end of the shock wave tube is formed in a divergent shape toward the upstream end. An impact wind tunnel characterized by becoming.

[0013]

Since the present invention is constructed as described above, it has the following actions. (1). In the configuration of (1) above, the free piston has a tip projecting along the tube axis of the shock wave tube on the wake side and is capable of entering the interior of the shock wave tube, and the base portion is substantially within the inner diameter of the shock wave tube. With a corresponding shell-shaped cushioning plug,
When the free piston approaches the end of the compression tube, i.e., the entrance of the shock tube, and the tip of the shock-absorbing plug begins to enter the shock-tube's entrance, the gap between the shock-absorbing plug and the shock wave tube narrows due to the penetration depth due to the shell shape. Then, the inflow amount of air from the compression tube to the shock wave tube is rapidly reduced, and the air remaining in the compression tube is strongly compressed. As a result, the free piston has the same cushioning effect as when an air cushion is interposed between the final end of the compression tube, that is, the shock wave tube inlet end, and does not solidly collide with the shock wave tube inlet end.

When the shock-absorbing plug has completely entered the shock-wave tube for the entire length, the shock-wave tube inner diameter and the diameter of the shock-absorbing plug substantially correspond to each other, and the highly compressed air is still high due to its high pressure. The free piston does not rebound because a significant amount of air does not remain in the compression pipe by ejecting from the microscopic gap between the remaining buffer plug and the shock tube. (2). In the configuration of (2) above, in addition to the configuration of (1) above, a shock wave tube and a conducting tube that is provided so that a flow path to the atmosphere can be selected near the wake end of the compression tube are used as a buffer. Relationship between the plug shape, that is, the rate of change of the amount of air inflow (from the compression tube to the shock wave tube) per unit time when entering the shock wave tube or per unit time, and the cross-section change rate If there is an excess or deficiency and the test speed does not match at that time, either open or close either the flow path of the connecting tube to the shock wave tube or the flow path to the atmosphere appropriately, or open all. The minute residual air quantity of the compression tube, the air inflow quantity into the shock wave tube, etc. can be finely adjusted.

That is, various tests can be always performed in an optimum state by using one buffer plug. (3). In the configuration of (3) above, the buffer plug of the above configuration (1) forms a rod body having a uniform cross section substantially corresponding to the inner diameter of the shock wave tube, and the inner diameter near the upstream end of the shock wave tube faces the upstream end. The cross-sectional area change of the gap between the buffer plug and the shock tube inner diameter in the length direction can be made equal to that of the above (1), and therefore the same operation as the above (1) can be achieved. Can be played.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention according to claims 1 and 2 will be described with reference to FIG.

FIG. 1 is a side sectional view of the main part of the present embodiment. In the drawing, 1 is a free piston fitted in the compression tube 2 so as to be capable of moving from left to right in the drawing at high speed, and 2 is near its end. Only the compression tube 3 shown is connected to the end of the compression tube 2, a shock wave tube having an inner diameter smaller than that of the compression tube 2, and 4 is a free piston 1.
On the wake side of the shock wave tube 3, there is a shell-shaped buffer plug having a sharp tip protruding along the axis of the shock wave tube 3 and capable of entering the inside of the shock wave tube 3, and having a base portion approximately corresponding to the inner diameter of the shock wave tube 3,
Reference numeral 5 denotes a shock tube 3 near the rear end of the compression tube 2 and a conducting tube provided so that a flow path to the atmosphere can be selected.
A conducting tube whose upstream end communicates with the conducting tube 5 through the membrane 8 and whose downstream end communicates with the shock wave tube 3, 7 is an orifice / membrane for blocking the atmosphere side of the conducting tube 5, and 8 is a shock wave of the conducting tube 5. An orifice / membrane that closes off the tube 3 side.

It should be noted that the orifices / membranes 7 and 8 are ruptured by the pressures adapted to each of them so that ventilation is possible.
Alternatively, the ventilation is configured to be throttled by the orifice (the pressure is reduced by expansion after passing through the orifice), and the film thickness (easy to break) adapted to the test and the orifice diameter can be selected and replaced at any time. Therefore, depending on the test contents, either the orifice / membrane 7 or 8 may be vented, or neither may be vented. Further, the orifices / membranes 7 and 8 may be provided with a quick opening / closing valve or the like capable of opening and closing the flow path.

That is, any means may be used as long as it is a purposeful flow path opening / closing means.

Next, the operation of the above configuration will be described.

Buffer plug 4 mounted on free piston 1
When the free piston 1 reaches the end of the compression tube 2,
The tip of the buffer plug 4 is inserted into the upstream portion (inlet) of the shock wave tube 3, and the internal pressure at the end portion of the compression tube 2 starts to be controlled according to the predetermined shape of the buffer plug 4. That is,
Sudden drop and sudden change of the internal pressure of the end portion of the compression pipe 2 are suppressed, and the soft piston 1 is stopped softly.

When it is necessary to discharge a large flow rate within a shorter time, the gas is discharged to the wake of the wind tunnel, that is, the shock wave tube 3 or the atmosphere via the conduits 5 and 6. The outflow to the conduits 5 and 6 is
It is started by operating the orifice / membrane 7 (exhaust to the atmosphere) or the orifice / membrane 8 (exhaust to the wake of the wind tunnel) depending on the pressure value in the conduit 5. The orifices / membranes 7 and 8 require instantaneous operation, and the membrane is broken or the circuit is opened / closed by a powerful quick opening / closing valve (not shown), and the flow passage area is adjusted by the orifice. That is, the orifice can be replaced with one having an appropriate flow passage area depending on the wind test conditions.

Whether or not to use the extraction pipe such as the conducting pipe 5 is arbitrary.

Next, the embodiment according to claim 3 is shown in FIG.
The shock-absorbing plug 4 is a rod having the same thickness as the base and extending over the entire length, and the shock-wave when the shock-absorbing tube 4 of the first embodiment enters the shock-wave tube 3 with the upstream inner diameter of the shock-wave tube 3. The structure of claim 3 can be obtained by forming the inner diameter of the shock wave tube 3 in a divergent shape toward the upstream end, that is, toward the inlet in the figure, so as to correspond to the gap area which changes with the inner circumference of the tube 3. (Not shown). Therefore, also in the case of the present embodiment, the same operational effects as those of the above embodiment can be obtained.

As described above, according to the above-described embodiment, when the free piston 1 approaches its end, that is, the upstream end of the shock wave tube 3, the buffer plug 4 starts to enter the shock wave tube 3 and the inside of the compression tube 2 is compressed. Since it proceeds while controlling the outflow of air to the optimum state, the buffer plug 4 is kept in the compression tube 2 until the end of the entry, that is, when the base of the free piston 1 approaches the upstream end (inlet) of the shock wave tube 3. The remaining air pressure is properly controlled,
There is an advantage that the free piston 1 does not collide with the shock tube 3 because it acts as an air cushion.

When the free piston 1 comes into contact with the shock wave tube 3, the speed of the free piston 1 is sufficiently reduced, and the residual air (and thus the air pressure) is left in the compression tube 2.
Therefore, there is an advantage that the free piston 1 does not rebound.

Further, because of the above advantages, there is an advantage that the buffer plug 4 is not damaged and can be repeatedly used for a long period of time.

Further, since the buffer plug 4 is not damaged, there is an advantage that the free piston 1, the compression tube 2, the shock wave tube 3 and the not-shown downstream side specimen, measuring equipment, etc. are not contaminated or damaged as in the conventional case. There is.

Further, since there is no substantial solid collision or severe solid friction, the kinetic energy of the free piston does not change into collision heat and friction heat in an instant, and therefore seizure may occur. There is an advantage that it does not.

Further, from the above advantages, there is almost no trouble caused by the test equipment, and there is an advantage that the development schedule of the test object such as a flying object is not delayed.

[0031]

Since the present invention is constructed as described above,
It has the following effects.

That is, the free piston is controlled while the amount of air flowing out from the compression tube is controlled by changing the gap area between the shell-shaped (or rod-shaped) buffer plug projecting on the downstream side of the free piston and the inner circumference of the shock wave tube. Since the end of the stroke is cushioned by an air cushion, there is no collision between solids, and therefore no damage to the impact wind tunnel equipment or contamination due to shattering and scattering occurs. Therefore, no harmful vibration is generated.

Further, since the kinetic energy is gradually reduced while avoiding solid collision, there is no rebound of the free piston.

Further, since the entire equipment is not damaged, the life of the equipment is extended.

Further, by using the extraction pipe in the vicinity of the downstream end of the compression pipe, a single buffer plug can be used for testing at any speed.

Further, since most of the objects can be achieved only by mounting a shock absorbing plug on the downstream side of the free piston, handling and maintenance are easy and a shock absorbing device can be obtained at an extremely low cost.

[Brief description of drawings]

FIG. 1 is a side sectional view of a main part of an impact wind tunnel according to an embodiment of the present invention,

FIG. 2 is a side sectional view of a conventional example.

[Explanation of symbols]

 1 Free piston 2 Compression tube 3 Shock wave tube 4 Buffer plug 5,6 Conducting tube 7,8 Orifice / membrane

Claims (3)

[Claims] 1. A free piston capable of moving at a high speed is provided in a compression tube having a shock wave tube having a small inner diameter on the wake side, and when the free piston reaches the end of the compression tube, the collision mitigation with the shock wave tube inlet is mitigated. In a required shock wind tunnel, the free piston has a tip projecting along the tube axis of the shock tube on the wake side and is capable of entering the interior of the shock tube, and the base has a shell-like shape that approximately corresponds to the inner diameter of the shock tube. An impact wind tunnel comprising a cushioning plug. 2. The impact wind tunnel according to claim 1, further comprising a shock wave tube and a conducting tube provided so that a flow path to the atmosphere can be selected in the vicinity of a wake end of the compression tube. Wind tunnel. 3. The shock wind tunnel according to claim 1, wherein the buffer plug forms a rod body having a uniform cross section substantially corresponding to the inner diameter of the shock wave tube, and the inner diameter near the upstream end of the shock wave tube widens toward the upstream end. An impact wind tunnel characterized by being configured into.