RU2788480C1 - Method for increasing the working time of a shock tube and a device for its implementation - Google Patents

Abstract

FIELD: aerodynamics.

SUBSTANCE: invention relates to the field of experimental aerodynamics and can be used to obtain a high-speed gas flow with large Mach numbers in laboratory conditions in non-diaphragm shock tubes of short-term action. The method consists in the fact that the gas under pressure flows from the high-pressure chamber into the low-pressure chamber due to the evacuating of air, which presses the movable cap of the pneumatic valve. The air is evacuated into the additional cavity through an opening connected to the valve and remains there under the spring-loaded lid until the pressure of the pressurizing air in the additional cavity becomes greater than the pressure of the expansion fan in the high-pressure chamber. In this case, the lid is squeezed out of the hole facing the high-pressure chamber, and the evacuated air enters the high-pressure chamber, and the additional cavity has an initial pressure of no more than 1 atm. The device contains a high-pressure chamber connected in series, a means of closing the channel in the form of a pneumatic valve with a movable cap due to the pressurizing air, and a low-pressure chamber. The pneumatic valve has an additional cavity adjacent to the valve, facing towards the high-pressure chamber, with two openings, one of them connected to the valve and the other to the high-pressure chamber, closed by a spring-loaded lid, which is closed at the initial moment.

EFFECT: increase in the working time of the shock tube due to the deceleration of the rarefaction wave.

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Description

The present invention relates to the field of experimental aerodynamics and can be used to obtain a high-velocity gas flow with high Mach numbers under laboratory conditions in non-diaphragm short-duration shock tubes.

The shock tubes contain a series-connected high-pressure chamber, a means of closing the channel and a low-pressure chamber in the form of a cylindrical channel. The means of closing the channel, instead of a destructible membrane, is a high-speed pneumatic solenoid valve [1].

The working time of shock tubes includes the time the sum of times, starting from the shock wave falling into the end of the low-pressure chamber, the reflected shock wave following the shock wave of the contact surface, and ending with the arrival of the rarefaction wave.

A known method of increasing working time by lengthening the low pressure channel [2]. In the contact gap between the high and low pressure chambers, a shock wave is formed, which "runs" along the cylindrical channel of the low pressure chamber with acceleration. The low pressure chamber is made optimally long. However, the implementation of this method is economically expensive, requires an increase in the metal-intensive part of the shock tube and large laboratory areas.

A known method of using a pneumatic valve [3] high speed (4...7 ms), instead of a destructible membrane, installed between the high and low pressure chambers. Before starting the tests, the pneumatic valve is filled with air under low pressure, which makes it possible to lock the passage section of the low-pressure chamber with a movable cap. When the valve solenoid is actuated, the filled air is released into the environment, the movable cap moves and opens the annular gap between the cap walls and the wall of the low pressure chamber. The gas flows out of the high-pressure chamber with acceleration and it is filled with a rarefaction wave.

However, this method of initiating the shock wave does not increase the operating time of the shock tube.

The closest in terms of essential features is a hypersonic shock wind tunnel, known from the description [4]. The well-known hypersonic shock wind tunnel comprises a high-pressure chamber, a cylindrical channel, a hypersonic nozzle, a vacuum chamber, and a means of closing the channel installed between the high-pressure chamber and the cylindrical channel, which form a common channel and are connected in series. The tube is equipped with high-frequency dynamic pressure sensors placed in a high-pressure chamber, a cylindrical channel, a vacuum chamber and connected to the recording equipment.

The disadvantage of the device is the rapid arrival of the rarefaction wave to the end of the cylindrical channel, which reduces the pressure before entering the nozzle and does not increase the operating time of the installation.

The objective of the invention is to increase the working time of the shock tube due to the deceleration of the rarefaction wave.

The task is achieved by the fact that the gas under pressure flows out of the high-pressure chamber into the low-pressure chamber due to the bleeding of air pressing the movable cap of the pneumatic valve, while the air is bled into the additional cavity through the hole associated with the valve and remains there under the spring-loaded cover until until the pressure of the pressurizing air in the additional cavity becomes greater than the pressure of the rarefaction fan in the high-pressure chamber, while the cover is squeezed out of the hole facing the high-pressure chamber, and the bleed air enters the high-pressure chamber, and the additional cavity has an initial pressure of not more than 1 atm .

The task is also achieved by the fact that the device for increasing the working time of the shock tube contains a series-connected high-pressure chamber, a means for closing the channel in the form of a pneumatic valve with a movable, due to the pressurizing air, a cap and a low-pressure chamber, and that the pneumatic valve has an additional cavity, adjacent to the valve, facing the high-pressure chamber, with two holes, one of them is connected to the valve, and the other to the high-pressure chamber, closed by a spring-loaded cover, which is closed at the initial moment by high pressure pressing it from the side of the high-pressure chamber.

The present invention is illustrated by the following graphics:

In FIG. 1 - shows a device for increasing the working time of the pipe

In FIG. 2 shows graphs of high-frequency dynamic pressure sensors installed: 1- at the end of the high-pressure chamber; 2 - in the middle and 3 - at the end of the low pressure chamber.

The device for increasing the working time of the shock tube consists of a high pressure chamber 1; pneumatic valve 2; low pressure chambers (cylindrical channel) 3; valve cavity for filling the valve with pressure 4; additional cavity for gas bleed 5. The letters "a", "b" and "c" indicate the hole covers.

The method is implemented in the operation of the device as follows. Before starting the shock tube, the cavity for filling the pneumatic valve 4 first has a pressure of not more than 1 atm and is filled with air at standard pressure. When the pneumatic valve 2 is actuated, the air from the cavity 4 for filling the pneumatic valve is vented into the additional cavity 5 through the hole "b" and is held there by the spring-loaded cover of the hole "c". The pressurized gas flows out of the high pressure chamber 1 into the low pressure chamber 3. The pressure in the high pressure chamber 1 decreases and a rarefaction fan rushes into it. When the pressure of the pressurizing air in the additional cavity 5 becomes greater than the pressure of the rarefaction fan in the high-pressure chamber 1, the cover of hole "c" is squeezed out and the bleed air enters the high-pressure chamber 1, slowing down the rarefaction wave.

The method differs in that an additional cavity of the valve 5 is introduced, initially having a pressure of not more than 1 atm, into which the gas is bled and which is released from the bleed gas into the high pressure chamber 1, when the pressure of the rarefaction wave in it is less than the pressure in the additional cavity 5.

The additional cavity has a blocked hole “b” on the side of the valve 2. The pressure in it, not lower than 1 atm, allows the blocking gas to be bled not into the atmosphere, but into the additional cavity 5. The additional cavity 5 has a movable spring-loaded cover of the hole “c”, which is closed at the initial moment, pressing it with high pressure from the high pressure chamber 1. When the high pressure chamber 1 is empty and the pressure becomes lower than the pressure in the additional cavity 5, the gas from the additional cavity 5 will squeeze the cover and flow into the high pressure chamber 1, which will increase the pressure and will change the intensity and time of formation of the head wave of the rarefaction fan.

In this case, "b" is opened by a known mechanism (for example, a high-speed pneumatic solenoid valve set forth in RF patent No. 2066656). The spring-loaded port cover "c" opens automatically due to the differential pressure.

In Fig.1. shows the last moment of the outflow of high pressure gas (red arrows) into the low pressure chamber 3 (blue arrows) and the filling of the high pressure chamber 1 with a rarefaction fan (blue lines). Pneumatic valve 2 is shown in two positions: dotted lines - the valve is closed, solid lines - the valve is pressed inward and air from the high pressure chamber flows into the low pressure chamber 3.

In the proposed method, the mechanism for opening hole "b" is the same as in valve 2, instead of opening hole "a". When the electromagnet is actuated, the spool moves, hole “b” opens in cavity 4 and the pressurizing cap air enters into additional cavity 5. The spring-loaded cover of hole “c” is pressed against cavity 5 due to high pressure in high pressure chamber 1. When from high pressure chamber 1 the gas will flow out, the pressure will decrease to a pressure lower than in the additional cavity 5, the spring-loaded cover of the hole "c" will be drawn in the direction of lower pressure and the gas from the additional cavity 5 will be vented into the high pressure chamber 1, in which a rarefaction wave is formed.

The technical effect of the application of the proposed method is that the arrival of the rarefaction fan to the end of the low-pressure chamber is retarded. The working time of the shock tube is increased. In addition, the pressurizing air, instead of being released into the atmosphere, remains in the shock tube and brings a positive result.

The initial signal of graph 1 in FIG. 2 corresponds to the state of rest of the gas under pressure. Then, when the electromagnet is activated, a sloping front of the valve opening is visible for 7 ms. At this time, the high pressure chamber is emptying. The horizontal line for 11 ms is the time of rarefaction wave formation.

Graph 3 in Fig. 2 shows the beginning of the countdown of the working time: the incident, reflected shock wave as "shelves" of the quasi-stationary state of the flow. The rise of the graph indicates the arrival of the contact surface and the increase in pressure until the moment the graph decreases. This was a rarefaction wave, and the working time of the shock tube was over. The duration of the working time on the graph of this mode of operation was 1.56 ms. The greater the pressure difference between the high and low pressure chambers, the higher the flow rate and the shorter the working time of the shock tube. The remaining gas from the high pressure chamber before each launch of the shock tube must be released (bled) to a pressure not higher than atmospheric.

The claimed method does not disrupt the operation of the valve. Its device provides for the opening (spool mechanism) of the hole "a" associated with the external environment. It is canceled to implement the specified method. But the opening mechanism in this method is associated with the opening of another hole "b" between the cavities 4 and 5. The spring-loaded cover of the hole "c" of the additional cavity 5 first restrains the opening with high pressure. When the pressure of the additional cavity 5 from the inside exceeds the pressure of the rarefaction wave in the high-pressure chamber, the cover is pushed out automatically, and the pressurizing gas is forced out into the high-pressure chamber.

List of used sources.

1. Patent of the Russian Federation No. 2066656 "Launcher".

2. Panasenko A.V., Ruleva L.B., Solodovnikov S.I., Increasing hypersonic aerodynamic shock tube working time duration. IOP Conference Series: Materials Science and Engineering (927), 1-7, 2020. doi:10.1088/1757-899X/927/1/012082.

3. Panasenko A.V. Calculation of the formation of a shock wave in a shock tube with a different method of initial gas outflow//Physical and chemical kinetics in gas dynamics. 2022. Vol. 23, no. 1. http://chemphys.edu.ru/issues/2022-23-1/articles/981/.

4. RF patent 152348 "Hypersonic impact wind tunnel".

Claims (2)

1. A method for increasing the working time of a shock tube, which consists in the fact that gas under pressure flows out of the high pressure chamber into the low pressure chamber due to the bleeding of air pressing the movable cap of the pneumatic valve, characterized in that the air is bled into the additional cavity through the hole connected with a valve, and remains there under the spring-loaded cover until the pressure of the pressurizing air in the additional cavity becomes greater than the pressure of the rarefaction fan in the high pressure chamber, while the cover is squeezed out of the hole facing the high pressure chamber, and the bleed air enters the chamber high pressure, and the additional cavity has an initial pressure of not more than 1 atm. 2. A device for increasing the working time of a shock tube, containing a high-pressure chamber connected in series, a means for closing the channel in the form of a pneumatic valve with a movable, due to the pressurizing air, cap and a low-pressure chamber, characterized in that the pneumatic valve has an additional cavity adjacent to valve, facing the high pressure chamber, with two holes, one of them is connected to the valve, and the other to the high pressure chamber, closed by a spring-loaded cover, which is closed at the initial moment by high pressure pressing it from the side of the high pressure chamber.

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