RU203856U1 - SHOCK TUBE FOR HIGH-SPEED SHOCK WAVE GENERATION - Google Patents

Abstract

The claimed utility model relates to the physics of strong shock waves, the physics of combustion and explosion and can be used in the process of creating a device capable of initiating a shock wave propagating at a speed of more than 11 km / s. The technical result achieved with the use of the claimed utility model consists in providing the possibility of generating a shock wave propagating in the low-pressure chamber of the shock tube at a second cosmic (or more) speed and reducing energy costs for its production. The claimed technical result is achieved by the fact that in a shock tube for generating a high-speed shock wave, containing a high-pressure chamber (HPC), at one end is equipped with a prechamber with a perforated end facing in the direction of wave propagation, and at the other end through a diaphragm connected to the low-pressure chamber. pressure (LPC), while the diaphragm separating the HPC and LPC is made of a copper sheet with a thickness of 0.3 to 0.7 mm, from the side of the LPC equipped with cross-shaped notches with a depth of 0.2 to 0.3 mm evenly applied to the surface, ensuring the prevention of the scattering of the diaphragm particles during its destruction, while the perforation of the end of the prechamber is made in the form of channels evenly spaced along the end of the prechamber and expanding in the direction of wave propagation with a length of no more than 4 mm with the ratio of the areas of the inlet and outlet perforation holes in the range of 1: 4–1: 10. 4 ill.

Description

Technology area

The claimed utility model relates to the physics of strong shock waves, the physics of combustion and explosion and can be used in the process of creating a device capable of initiating a shock wave propagating at a speed of more than 11 km / s. Measurement of the spectral and kinetic characteristics of gases obtained at such velocities of the shock wave is necessary for solving scientific and technical problems, and can be used, for example, when creating thermal protection required when various bodies enter the atmosphere of the Earth and other planets, in particular, space descent devices. In addition, the claimed utility model can be used to verify physicochemical models of nonequilibrium dissociation and ionization processes of various gases under extreme conditions.

State of the art

In classical devices for initiating detonation, direct initiation of detonation is used - a short-term release of energy significantly greater than the specified value (Zeldovich Ya.B., Kogarko S.M., Simonov N.N. // ZhTF, 1956, volume 26, No. 8, p. 1744-1752), or the transition of combustion to detonation: the combustible mixture is ignited with a weak ignition source in a pipe with regular annular obstacles and provides a progressive acceleration of the flame with a transition to detonation at distances (pre-detonation distance) and for a time (pre-detonation time) significantly exceeding the indicated values (See, for example, O. Peraldi, R. Knystautasand JH Lee "Criteria for transition to detonation in tubes." Twenty-First Symposium (International) on Combustion / The Combustion Institute, 1986, pp. 1629-1637). However, all of them are characterized by significant energy consumption, while the speed of propagation of the shock wave created by such devices does not exceed 10 km / s.

A device for initiating detonation in a tube with a combustible mixture is known from the prior art (RF patent No. 2672244). The device for detonation in a pipe with a combustible mixture includes a smooth detonation pipe, in the end part of which a bottom is installed, containing a prechamber with a weak ignition source, as well as nozzles for supplying fuel and oxidizer. Cross supersonic jets of fuel and oxidizer are fed through the nozzles into the smooth detonation tube. As a result of their interaction due to turbulent mixing in a smooth pipe, a high-speed turbulent flow of a combustible mixture is formed. In this case, the prechamber is also filled with a combustible mixture, which is ignited by a weak ignition source. As a result of the combustion of the mixture in the semi-closed volume of the prechamber, the pressure and temperature in it increase, which leads to the formation of a high-temperature high-speed torch coming from the prechamber into the smooth detonation tube, which ignites the turbulent flow of the combustible mixture in it.

However, as a result of using the known device, a shock wave with a low propagation velocity is obtained. So, the speed of the reaction front at a distance of ~ 300 mm is about 2300-2400 m / s, and increases to 2500 m / s depending on the average composition of the mixture.

The closest in technical essence to the claimed utility model is the shock tube design disclosed in the publication "EXPERIMENTAL STUDY OF RADIATION OF SHOCK-HEATED AIR ON TWO-DIAPHRAGM IMPACT TUBE" P.V. Kozlov, Yu.V. Romanenko, Research Institute of Mechanics, Moscow State University. M.V. Lomonosov (http://chemphys.edu.ru/media/published/011_5whp3ut.pdf). The known shock tube includes a high-pressure chamber connected by means of flanges, with a perforated prechamber located at its end, an intermediate pressure chamber and a low-pressure chamber. Between the flanges of the sections of the high-pressure chamber (HPC) and the intermediate-pressure chamber (KP) filled with helium, as well as the sections of the KP and the low-pressure chamber (LPC), there are cassettes with type-setting diaphragms made of mylar film with a thickness of 20 μm.

When forming a detonation wave in accordance with this source, it was possible to achieve speeds of 4-7 km / s, however, the method disclosed in the publication materials, as well as its modes, do not allow achieving higher speeds, in particular, due to the fact that during the generation of a shock wave In the known device, polyethylene terephthalate (polyethylene terephthalate) diaphragms were used, which, when ruptured, significantly limit the flow, fly into the pipe, create hydrocarbon impurities and settle on the walls.

Brief disclosure of the essence of the utility model

The technical result achieved with the use of the claimed utility model consists in providing the possibility of generating a shock wave propagating in the low-pressure chamber of the shock tube at a second cosmic (and more) speed and reducing energy costs for its production due to the most complete use of combustion energy diluted with helium oxygen -hydrogen mixture in a high-pressure chamber (HPC) as a result of the combustion of its main mass in the Chapman-Jouguet detonation wave, which provides the energetically most efficient combustion mode in a limited volume (see, for example, Y.B. Zeldovich. On the energy use of detonation combustion // Journal of technical physics. - 1940. - T.10, No. 17. - S. 1453-1461).

The claimed technical result is achieved by the fact that in a shock tube for generating a high-speed shock wave, containing a high-pressure chamber (HPC), at one end is equipped with a prechamber with a perforated end facing in the direction of wave propagation, and at the other end through a diaphragm connected to the low-pressure chamber. pressure (LPC), according to the technical solution , the diaphragm separating the HPC and LPC is made of a copper sheet with a thickness of 0.3 to 0.7 mm, from the side of the LPC equipped with cross-shaped notches with a depth of 0.2 to 0.3 mm, ensuring the prevention of the scattering of diaphragm particles during its destruction, while the perforation of the end of the prechamber is made in the form of channels evenly spaced along the end of the prechamber and expanding in the direction of wave propagation with a length of no more than 4 mm with the ratio of the areas of the inlet and outlet perforations in the range 1: 4– 1:10. The HPC length does not exceed 1.5 m. The perforation channels can be made in the form of a Laval nozzle. The edges of the perforation inlets can be rounded. The length of the notches on the diaphragm can be up to 50 mm.

Ignition and combustion of an explosive mixture in the prechamber provides injection of hot jets of combustion products into the HPC cavity through the perforation holes, which leads to the formation at a distance of no more than 3 UT diameters from the HPC end wall of a plane incident shock wave in the HPC, destroying the copper diaphragm with subsequent formation the reflected Chapman - Jouguet detonation wave and the shock wave passing through the LPC at a speed of more than 11 km / s, the propelling gas for which is the combustion products of an explosive mixture with helium. The incident shock wave ignites the gas in the HPC. The resulting flame maintains the intensity of the incident shock wave, but quickly lags behind the shock front. The initial pressure in the HPC is in the range from 8 to 10 atm, and the partial pressure of helium in the HPC is from 50 to 65%.

Brief Description of Drawings

The claimed utility model is illustrated by the following drawings, where

figure 1 shows a diagram of a high-pressure chamber;

figure 2 shows a drawing of the prechamber;

Fig. 3 shows a sample oscillogram of signals from pressure sensors (the distance between sensors P9 and P10, which register the speed of the shock wave in the low-pressure chamber of the shock tube, is 100 mm);

figure 4 presents a diagram of the installation containing the inventive shock tube.

Positions in the drawings indicate:

1 - prechamber,

2 - diaphragm,

3 - high pressure chamber,

4 - pressure sensors

5 - a candle that initiates the ignition of an explosive mixture in the prechamber,

6 - perforated end of the prechamber.

When describing the proposed device, the following conventions are used:

CHP - shock tube high pressure chamber;

CIP — intermediate chamber (intermediate pressure chamber) of the shock tube;

CLP - shock tube low pressure chamber;

CV1 - vacuum chamber for gas mixture preparation;

CV2 - vacuum chamber of the damper volume;

CV3 - vacuum chamber for helium preparation in the intermediate chamber of the shock tube;

NI - rotary vane pump 2НВР-5ДМ;

NR - oil-free pumping station DRYTEL-1025;

PD1 ÷ PD6 - deformation vacuum gauges and manometers;

PM - vacuum gauge VMB-14 with a magnetic electric discharge sensor PMM-32-1;

V1 ÷ V10 - straight-through shut-off valves;

VT - damper;

VF1 ÷ VF7 regulating valves;

VM - shut-off valve with electromagnetic drive.

Implementation of the utility model.

The inventive device is a shock tube (UT), generally consisting of two sections: a high-pressure chamber (HPC) with a length of no more than 1.55 m and a low-pressure chamber (LPC) with a length of no more than 3 m. The listed chambers are made of solid sections seamless hot-deformed steel pipe GOST 9940-81 (made of steel 12X18H10T), outer diameter of about 60 mm, wall thickness of at least 5 mm. At the ends, collar flanges are welded to the chambers, made, for example, of steel 12X18H9T by hot pressing. Each section (chamber) is placed on two adjusting tables mounted on steel posts fixed to the floor. Cassettes with diaphragms are located between the flanges of adjacent sections. The flanges are tightened with four 20mm bolts. The device can also contain an intermediate chamber (CPC) with a length of not more than 3.5 m, located between the HPC and LPC. The efficiency performs an auxiliary function, and is intended mainly to exclude the influence of the pushing gas (hydrogen) during kinetic studies. Nevertheless, it was found that the presence of efficiency in the composition of the shock tube leads to an increase in the speed of the recorded shock wave by 10-20%.

Each chamber is equipped with a gas admission and evacuation system.

The LPC inlet system consists of three cylinders 1-3 with a volume of 40 liters, a standard PD1 vacuum gauge, three VF1-VF3 leaks connected to the measuring volume CV1, and a bypass valve V1 (DN10 mm). The filling system is evacuated through the bypass valve V1 and valve V2 by an oil-free pumping station NR.

The helium filling system in efficiency, when used, consists of a 40-liter cylinder, a VF4 leak, a CV3 measuring volume, a PD2 vacuum gauge and a V8 bypass valve. The helium filling system is evacuated through bypass valve V8, intermediate chamber CIP and valve V7 with an NI backing pump.

The HPC filling system includes three 40-liter cylinders containing hydrogen, oxygen and helium. The cylinders are connected to the high-pressure chamber by leak valves VF5-VF7 and bypass valve V5. The push gas pressure in the high pressure chamber is monitored with PD4 and PD5 pressure gauges. The PD6 pressure gauge monitors the pressure in the hydrogen cylinder. Valve V10 provides an emergency release of hydrogen from the high-pressure chamber.

The distribution of the inlet systems is carried out with a stainless steel pipe ∅3 × 0.5 mm. The tube is soldered with PSR-40 silver solder to the corresponding valve and pressure gauge nipples. All seals of the venting systems are made of fluoroplastic.

FIG. 4 shows a schematic diagram of the filling and pumping of the shock tube. With the help of an NI pump connected by a VM solenoid valve (DN30 mm) to a vacuum line laid along the entire pipe, and valves V3, V5, and V7, all sections (chambers) of the shock pipe are evacuated. With the help of valve V6, atmospheric air or neutral gas is injected into the pipe when changing diaphragms. The vacuum line is made of 18 mm diameter stainless pipe sections joined by quick-release flanges welded to the pipe through bellows. The foreline pressure in the pipe is controlled by a PD3 vacuum gauge. On the side of the low-pressure chamber, a 47-liter CV2 damper tank made of stainless steel is connected to the pipe through the VT damper valve, bellows and L-shaped branch pipe. The VT damper valve has a flow area of 60 mm. An oil-free pumping station NR is connected to the damper tank through valve V2 (DN60 mm). To control the degree of pumping out of the shock tube, a PM vacuum gauge with a magnetic electric discharge sensor is also connected to the damper tank. The VT valve makes it possible to change the diaphragms in the shock tube without letting atmospheric pressure into the damper tank, thereby significantly reducing the time for final pumping of the shock tube. All connections of the vacuum system are made by quick disconnect flange connections. As seals for the vacuum system of pipe sections, tanks, valves, etc. standard seals made of high vacuum rubber are used.

The high-pressure chamber (inner diameter up to 50 mm, length 30-60 pipe diameters) and the low-pressure chamber are separated by a diaphragm. If used as part of an efficiency unit, the diaphragm is located at the interface between HPC and efficiency. In general, the diaphragm is a copper sheet (foil) with a thickness of 0.3 to 0.7 mm. Preferably, 0.3-0.4 mm copper foil is used as the diaphragm between the chambers. The use of this type of diaphragm has made it possible to attain shock wave velocities of 11.4 km / s at an initial air pressure in the low-pressure chamber of 0.25 Torr. Along the diaphragm area from the LPC side, special cruciform notches are made to facilitate rupture, full disclosure and prevent copper "petals" from being carried away into the flow, that is, there is practically no entrainment of diaphragm material scraps into the flow. The notches are made evenly over the surface of the diaphragm. For each mode (gas pressure, percentage of gases in the mixture, geometric dimensions of the pipe), a certain thickness of the diaphragm and the depth of the notches are selected. So, the most optimal is to make notches with a depth of 0.2-0.3 mm, while the length of the notches is no more than 50 mm. The diaphragm is functionally designed to reflect a plane shock wave formed as a result of the ignition of an explosive mixture, simultaneously with its opening without destruction and detachment of the petals, which leads to the combustion of the bulk of the gas stored in the high-pressure chamber in a mode close to Chapman-Jouguet detonation.

At the end of the HPC, located on the side opposite to the diaphragm, there is a prechamber intended for igniting the explosive mixture. The prechamber can be formed by the end and walls of the HPC and bounded by a perforated stainless steel sheet. In another embodiment, the prechamber can be formed by inserting a steel "cup" with a perforated bottom into the HPC end. Thus, the prechamber has a diameter that practically coincides with the inner diameter of the pressure build-up pump and a length of about 20 mm. The stainless steel sheet (end of the prechamber), in which the perforation is made, has a thickness of up to 4 mm, so the length of the perforation channels is also 4 mm. Perforation is a set of extended holes (channels) evenly distributed over the area of the end of the prechamber, with each channel being made in the form of an analogue of a Laval nozzle. The diameter of the inlet and outlet holes of the perforation channels is different, and in general, the ratio of the area of the inlet holes to the area of the outlet holes of the perforation is in the range of 1: 2-1: 10. Most preferred is the ratio of said areas of 1: 4. The edges of the inlet holes of the perforation are rounded in order to ensure the uninterrupted outflow of hot jets of the combustion products of the explosive mixture. Perforation in the wall of the prechamber provides the outflow of uniform hot jets and the formation of a plane shock wave at a distance of several UT diameters (no more than 3 UT diameters) from the HPC end, near which the prechamber is formed. In the general case, the ratio of the area of the inlet holes of the perforation channels to the sectional area of the UT (or the area of the end of the prechamber) is 20-50%.

At the end of the HPC, there is also a means for igniting an explosive mixture, made, for example, in the form of a car candle. A certain pressure is maintained in each chamber of the shock tube. Thus, the pressure range in the HPC is 8-10 atm.

Measurement of the shock wave velocity in the measuring section is carried out by piezoelectric sensors. Signals from piezoelectric sensors are recorded by digital storage oscilloscopes with a bandwidth of 100 MHz.

In the low-pressure chamber, at a distance of 50 and 60 UT diameters from the diaphragm separating the HPC and LPC, pairs of optical windows with a diameter of 10 mm are located opposite each other for observing the emission of the studied gas. Through the windows in each experiment, measurements were made of both the spectral composition of the radiation and the time variation of the radiation intensity.

The inventive device is used to obtain a high-speed shock wave, for which:

1) at the first stage, gases are fed into the high-pressure chamber to form the initial gas mixture. A helium / oxygen / hydrogen mixture in the stoichiometric concentration of oxygen and hydrogen can be used as the initial gas mixture. In this case, the concentration of helium is from 50 to 65%. Gases for the formation of the initial gas mixture are fed into the high-pressure chamber (HPC), while the HPC is first filled with helium, after which oxygen and hydrogen are fed in succession. For faster mixing, gases in the HPC can be fed from two opposite ends of the chamber. The chamber is then left to mix the gases. Mixing time for 150 cm HPC is at least 60 minutes to ensure good repeatability. It is possible to pre-prepare a mixture of helium with oxygen in a separate tank and supply a ready-made mixture of helium / oxygen and hydrogen separately to the HPC. In this case, the time is somewhat reduced and, for example, for a pressure build-up with a length of 150 cm, it will be about 40 minutes.

2) an explosive mixture is fed into the prechamber for ignition. Using a car spark plug, the explosive mixture is ignited in the prechamber, the spark ignition of which leads to the formation of transverse compression waves, which equalize the pressure in the prechamber. With an increase in pressure, a jet outflow of combustion products begins through the perforation of the end of the prechamber into the main part of the high-pressure chamber, filled with an explosive mixture with helium. Jets similar in intensity and composition (entering through the perforation of the prechamber and located in the HPC) ensure uniform transverse ignition of the gas in the high-pressure chamber, which makes it possible to obtain the formation of a plane shock wave front at a small distance (no more than 3 diameters of the shock tube). which allows more efficient use of combustion energy. It should be noted that the absence of such perforation will not allow the formation of a shock wave with the declared characteristics. A shock wave (SW) when flowing through, for example, one central opening of the prechamber or slot holes will be formed much later, which will not allow reaching the declared velocities of the shock wave.

The resulting flame front generates an almost plane shock wave, which, by the time it approaches the diaphragm separating the high-pressure chamber and the low-pressure chamber, has time to move a relatively large distance from the flame front. Empirically selected values of pressure (8-10 atm in HPC) and gas composition (combination of an explosive mixture and helium in almost equal ratio), as well as material (copper foil) and diaphragm thickness (0.3-0.7 mm) lead to that the intensity of the reflected shock wave is not enough to rupture the diaphragm, but it is sufficient for the explosive ignition of the gas at the diaphragm.

The explosive release of energy increases the pressure behind the shock wave reflected from the diaphragm, which causes over-compressed detonation and rupture of the diaphragm, which quickly approaches the Chapman-Jouguet detonation mode and ensures complete combustion of the gas in the high-pressure chamber. The intensity of the shock wave that forms in the low-pressure chamber is determined by the work that the combustion products of the gas stored in the high-pressure chamber can do. It should be noted that even with complete combustion of the gas, the products of deflagration (slow) combustion perform less work than during combustion in the Chapman-Jouguet detonation mode [2].

To study the received shock wave in the LPC, two measuring sections are provided at a distance of 50 and 60 UT diameters from the diaphragm. Each measuring section has two optical windows with a diameter of 10 mm, located opposite each other. The windows in the measuring section are located between two piezoelectric sensors Ø 4 mm, which measure the average velocity of the shock wave at the moment it passes by the corresponding optical window. Piezoelectric pressure sensors have a rise rate of 0.9 μs, the sensitivity of the sensors is ~ 0.3 V / atm. The signal from the pressure sensors is recorded with a digital oscilloscope and recorded in the computer memory. The information from the sensors is recorded by a digital oscilloscope and transferred to a computer for recording.

An example of a specific implementation

The claimed device as a prototype is implemented by the laboratory "Kinetic processes in gases" (lab. 109) Research Institute of Mechanics, Moscow State University. Pressure sensors are installed in the high-pressure chamber, the signal from which was recorded on a computer using an L-20-10 ADC. The gas filling of the high-pressure chamber is a mixture of an explosive mixture (stoichiometric oxygen-hydrogen mixture and an inert diluent gas helium in the proportions He: H2: O2 = 3: 2: 1). The working pressure in the high-pressure chamber (HPC) is 9 atm, the gas filling it consists of 50% explosive mixture and 50% helium, a spark plug with a discharge energy of 100 mJ was used to ignite the explosive mixture in the prechamber, the perforated disk is located 20 mm from the end HPC walls and has 19 micro-nozzle holes with an inlet diameter of 1 mm and an outlet diameter of 2 mm, the copper diaphragm is 0.5 mm thick, with notches 0.2 mm deep and 40 mm long. The low pressure chamber has the following characteristics: p ₁ = 0.25 Torr; 100% air. The mixture of the specified composition is fed to the HPC through the fuel mixture supply system. A pure explosive mixture is fed into the prechamber and ignited, after which the explosive mixture ignites, the hot gas enters the HPC cavity through the perforation holes, where a plane shock wave is formed, which reaches the diaphragm, is reflected from it, as a result of which the Chapman-Jouguet regime is achieved and a shock wave with a speed of 11.4 km / s. In this case, the energy costs are 84.4 kJ, which is significantly lower than the energy costs for obtaining high-speed shock waves in accordance with the prototype (more than forty times).

FIG. 3 shows a sample oscillogram of the pressure sensor signals (the distance between the sensors P9 and P10, which register the speed of the shock wave in the low-pressure chamber of the shock tube, is 100 mm).

Thus, the claimed device makes it possible to obtain a shock wave velocity equal to the 2nd cosmic one and higher, at initial pressures equal to 0.25 Torr in a shock tube with a pressure build-up pressure not exceeding 1.5 m, when burning virtually any combustible mixture, in particular, a mixture oxygen / hydrogen / helium, which corresponds to the most important launch site for spacecraft.

Claims (5)

1. A shock tube for generating a high-speed shock wave, containing a high-pressure chamber (HPC), at one end is equipped with a prechamber with a perforated end facing in the direction of wave propagation, and at the other end through a diaphragm connected to the low-pressure chamber (LPC), which is different the fact that the diaphragm separating the HPC and LPC is made of a copper sheet with a thickness of 0.3 to 0.7 mm, from the LPC side equipped with cross-shaped notches with a depth of 0.2 to 0.3 mm, evenly applied to the surface, ensuring the prevention of particle scattering the diaphragm during its destruction, while the perforation of the end of the prechamber is made in the form of channels evenly spaced along the end of the prechamber and expanding in the direction of wave propagation with a length of no more than 4 mm with the ratio of the areas of the inlet and outlet perforations in the range 1: 2 - 1:10. 2. The shock pipe according to claim 1, characterized in that the length of the pressure build-up does not exceed 1.5 m. 3. Impact tube according to claim 1, characterized in that the perforation channels are in the form of a Laval nozzle. 4. Impact tube according to claim 1, characterized in that the edges of the perforation inlet openings are rounded. 5. The shock tube according to claim 1, characterized in that the length of the notches on the diaphragm is no more than 50 mm.

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