RU2164618C1 - Method of altitude control of overextended reaction nozzle for rocket engine - Google Patents

Abstract

FIELD: rocketry. SUBSTANCE: method consists in separation of supersonic gas flow from wall of nozzle by interaction of flow with mechanical obstacle found on wall and with secondary working medium introduced into main gas flow at area before obstacle; interaction is effected in definite succession; secondary working medium is fed upon complexion of engine start; mechanical obstacle is consumed. EFFECT: increased specific impulse of rocket engine; engine reliability of engine start; repeatability of working characteristics. 3 cl

Description

 The invention relates to rocket technology, and in particular to jet nozzles used in rocket engines (RD).

где T_к - температура газа в камере сгорания, град. K;
μ - молекулярная масса;
λ = (n - 1)/n,
где n - средний показатель изоэнтропы расширения газа в сопле (находится в пределах 1,1 - 1,3).The jet nozzle is a functional part of the traction chamber of the taxiway, which also includes a combustion chamber. The gaseous products of fuel combustion formed in it expand in the jet nozzle from the initial pressure p _k (pressure in the combustion chamber) to the outlet pressure p _a , while accelerating to a supersonic speed W _a :

where T _to - gas temperature in the combustion chamber, deg. K;
μ is the molecular weight;
λ = (n - 1) / n,
where n is the average exponent of the isoentropic expansion of the gas in the nozzle (is in the range 1.1 - 1.3).

The values of T _to , μ, n are determined mainly by the composition of rocket fuel.

The thrust of the RD chamber, that is, the resultant of all internal and external pressure forces on the walls of this unit, is connected with the parameter W _{and the} formula:
P = mW _a + F _a (p _a - p _n ),
where m is the mass of fuel consumed through the chamber in 1 s;
F _a - the area of the outlet section of the nozzle;
p _n - external pressure.

Along with the thrust characterizing the scale of the taxiway, the primary parameter for the taxiway is the specific impulse of thrust I _y , which is defined as the ratio P / m. Parameter I _y characterizes the efficiency of the taxiway and ultimately determines the required fuel supply on board the rocket aircraft. When the nozzle operates in the design mode, that is, under the conditions p _a = p _n , the specific thrust momentum is numerically equal to the speed of the jet and is maximum for a given, specific value of p _n (that is, for a specific flight altitude); accordingly, the thrust of the taxiway reaches its maximum value.

Among the main areas of application of the RD are rocket launchers for the delivery of payloads into space. During the flight (rise) of the launch vehicle, the external working pressure for the launch stage RD varies over a wide range, decreasing from normal atmospheric to close to zero. In this case, the values of the parameters P and I _y increase with the flight altitude, however, they remain less than ideal values corresponding to the condition p _a = p _n in the entire flight range. The practical fulfillment of the latter condition, that is, the creation of a nozzle design with ideal height control, seems unrealistic. In practice, jet nozzles for RD rocket carriers in each case are projected onto well-defined optimal values of p _a , which are significantly lower than normal atmospheric pressure. Thus, the nozzles in the launching stages are overexpanded: at the initial stage of the flight, the gas flow in them expands below ambient pressure. The output section of the nozzle with a pressure lower than atmospheric creates a negative component of the thrust. This energy loss has to be compensated by an increase in fuel consumption through the taxiway and, therefore, to store additional fuel on board the aircraft - to the detriment of the mass of the payload.

Significant energy losses can be avoided if, for the designed nozzle, the value of p _{а is} reduced to a certain value at which external pressure penetrates into the nozzle in the initial section of the launch vehicle flight due to the entrance of the shock wave. It will tear off the gas stream from the wall at the exit section of the nozzle, and within this section, the pressure of the stream at the wall is restored to close to p _n . Thus, the nozzle portion that creates the negative component of the thrust is partially excluded from operation, and the operating mode of the nozzle approaches the calculated one. As a result, the parameters P and I _have increased relative to the corresponding flow unseparated.

However, the implementation of this opportunity is hindered by a number of circumstances. First, in many practical cases, the quantity p _a corresponding to the separated flow is substantially distant from the optimal one (taking into account, along with the variable current value I _y , the dimensions and mass of the nozzle). Secondly, the flow pattern is unstable: the location of the shock wave oscillates along the axis of the nozzle. Thirdly, the separation zone is asymmetric with respect to the axis of the nozzle. Due to the last two circumstances, random lateral loads on the nozzle walls arise, which can destroy it; this danger is especially great during the launch of the taxiway. To eliminate the above adverse factors, various methods of high-altitude regulation of an overexpanded jet nozzle are proposed. Of these, the most promising is the method consisting in the forced separation of the supersonic gas flow from the nozzle wall.

 There is a method of high-altitude regulation of an overexpanded jet nozzle for a taxiway, in which a supersonic gas stream is detached from the nozzle wall, acting on the stream by means of a mechanical obstruction located on the wall that is removed during engine operation - see US Pat. US N 3352495 (priority from 01.29.1965) and US Pat. USA N 3925982 (priority from 09/11/1973), FIG. 1, 2, 3 (analogues of the invention). In the first and last of the above technical solutions, the mechanical obstacle is made in the form of an ablation insert designed for gradual removal under the influence of a gas stream, which, according to the authors, should ensure smooth high-altitude regulation of the nozzle. However, the practical application of the commented solutions is hindered by difficulties in obtaining ablating materials with the necessary properties, achieving a uniform height of the insert around the nozzle circumference, and ensuring the stability (repeatability) of the characteristics of the nozzle with the time-varying form of the insert. In the other mentioned analog solutions, the insert is designed to maintain integrity for some time (up to a certain height of the rocket apparatus), after which the insert is separated from the nozzle wall and it is carried away by the gas stream. The use of such technical solutions in real RD designs is hindered by many difficulties of a material science, structural and technological nature, as well as the danger of damage to the nozzle wall by a detachable insert.

There is also known a method for altitude control of an overexpanded jet nozzle for a taxiway, in which a supersonic gas stream is detached from the nozzle wall, acting on the stream by means of a secondary working fluid introduced from the side of the wall into the main gas stream - see US Pat. USA N 3925982 (priority from 09/11/1973), FIG. 4, 5, 6 (analogue of the invention). Here, the "hydrodynamic shock ring" serves as an obstacle causing flow separation. In principle, it is possible to provide multistage, close to continuous, high-altitude regulation of the nozzle, including sequentially the secondary working fluid belts located along its axis. With all the temptation, the technical solution discussed was also not included in practice. The reason is that when starting a taxiway to create a "hydrodynamic shock ring" significant consumption is required, which violates the usual picture of the launch, complicates this crucial operation, reducing the reliability of the taxiway as a result. In addition, ensuring the necessary flow rate of the secondary working fluid requires large flow sections of the flow paths, which complicates the design of the nozzle and disrupts the smoothness of the gas-dynamic path, introducing disturbances into the main flow when the secondary working fluid is turned off and, as a result, reducing the value of I _у .

 Along with the described methods, there is also known a method for altitudinal regulation of an overexpanded jet nozzle for a taxiway, in which a supersonic gas stream is detached from the nozzle wall by means of a stream interacting in a certain sequence with a mechanical obstruction located on the wall that is removed during engine operation and with a secondary working fluid introduced from the side of the wall into the main gas stream in the place in front of the obstacle, see German patent application No. 4115720 of 05/14/91, FIG. 4b (prototype of the invention). In the specified method, the secondary working fluid belt is initially included in the operation, and its supply is stopped when the aircraft reaches a certain height, and then a mechanical obstacle comes into effect, which is subsequently removed. This prototype method is a combination of the above analogue methods and, thus, summarizes their disadvantages. That is why, until now, the prototype method, like others, has not been used.

The present invention is aimed at eliminating the inherent disadvantages of the prototype method, that is, it solves the technical problem of comprehensively increasing the efficiency of high-altitude regulation of an overexpanded jet nozzle for taxiways: achieving high energy parameters (P, I _y ) while guaranteeing reliable starting, structural integrity and repeatability of taxiway performance.

 The stated technical problem is solved in that in the method of high-altitude regulation of an overexpanded jet nozzle for a taxiway, in which a supersonic gas stream is detached from the nozzle wall by means of a stream interacting in a certain sequence with a mechanical obstruction located on the wall that is removed during engine operation and with a secondary according to the invention, the working fluid introduced from the side of the wall into the main gas stream in place in front of the obstacle flux from interaction with mechanical obstacle, and after completion of starting of the engine - the interaction with the secondary working medium, in which the expenditure of mechanical obstruction is removed.

 When carrying out the invention, a technical result is expected that coincides with the essence of the problem being solved.

The invention is illustrated using FIG. thirteen:
in FIG. 1 shows a schematic drawing chamber RD, in the device of which the invention is implemented;
in FIG. 2, 3 shows a timeline of the specific thrust impulse for the camera according to FIG. 1, operating as part of an aircraft.

= F_а/F_кр = 77,5. Это значение соответствует жидкостно-ракетному двигателю SSME, функционирующему в составе американского космического аппарата "Спейс шатл". В сечении

= 45 на стенке сопла установлена внутренняя кольцевая вставка 3 из абляционного материала, а в сечении

= 39 в сопловой стенке предусмотрен пояс отверстий 4 с коллектором 5 для ввода вторичного рабочего тела в основной газовый поток.Shown in FIG. 1, the chamber is typical of a liquid-propellant rocket engine (liquid fuel propulsion) and contains a cylindrical combustion chamber 1 equipped with nozzles and connected to a supersonic jet nozzle 2. By configuration, it is a Laval nozzle with a geometric expansion ratio, i.e., the ratio of the areas of the exit and critical sections,

= F _a / F _cr = 77.5. This value corresponds to the SSME liquid-rocket engine, which operates as part of the Space Shuttle. In section

= 45 on the nozzle wall there is an inner annular insert 3 made of ablation material, and in cross section

= 39 in the nozzle wall a belt of holes 4 with a collector 5 is provided for introducing a secondary working fluid into the main gas stream.

The described camera operates as follows. When starting the taxiway, which is carried out under normal atmospheric pressure, liquid rocket fuel, consisting of an oxygen oxidizer and hydrogen fuel (similar to SSME), is fed into combustion chamber 1 (by means of a turbopump system provided for in the design of the taxiway). The high-temperature gas generated during their combustion enters the jet nozzle 2, filling the flow channel bounded by the nozzle wall. When the expanding flow reaches insert 3, it breaks away from the nozzle wall, being further limited by the free current line a. With the completion of the RD launch process, a design pressure p _k is established in the chamber, which in a specific example is 20.5 MPa (corresponds to the SSME engine). At the same time, at the location of insert 3, the flow expands to a pressure of 34 kPa, and in the space between the nozzle wall and the free boundary of the flow a, a pressure close to ambient is established (p _n ). Thanks to this, the camera develops traction more than with a continuous flow.

= 77,5).Upon completion of the launch (after 1 - 5 from the taxiway operation in steady state), a secondary working fluid (for example, rocket fuel pairs) is fed through the collector 5 to the openings of the belt 4. Acting on the main stream, it causes its separation from the nozzle wall - along line b. At the location of the belt 4, the flow expands to a pressure of 41 kPa, and the subsequent nozzle portion is excluded from the operation of the chamber. In this mode, it operates for ≈60 s, after which the input of the secondary working fluid is stopped. At this point, insert 3 has time to completely ablate, so that now the gas flow can expand unhindered within the entire nozzle circuit to an outlet pressure of 17.5 kPa (corresponds to

= 77.5).

The operation of the described camera is further illustrated in FIG. 2, 3 - time chart of parameter I _у , constructed in accordance with a typical launch site of an aircraft of the Space Shuttle type. The time t = 0 corresponds to the completion of the taxiway launch and the beginning of the lift of the apparatus. With increasing flight altitude, the environmental pressure decreases - along the line p _n , and the parameter I _y increases: curves 1, 2, 3, 4. They show the change in I _y for cases:
nozzles with ideal height control (curve 1);
nozzles without insert and belt holes (2);
nozzles with insert (3);
nozzles with a belt of holes (4).

A comparison of the last three curves shows that in a specific example, the invention provides an increase in I _y during the first 63 seconds of flight of the rocket apparatus (this time corresponds to point X - intersection of curves 2, 4): the energy gain exceeds 300 m / s in the first 17 seconds of flight and reduced to 100 m / s at the 48th second. These are very high indicators for parameter I _y .

 From the above description it is seen that the implementation of the proposed method is not associated with structural and technological problems and allows for reliable and strictly controlled operation of the taxiway in the entire operating range. Indeed, it is not difficult to design, manufacture and assemble a nozzle insert capable of withstanding the direct impact of the gas stream for several seconds. The geometric shape of the insert, providing a reliable start, is determined by calculation with the necessary subsequent adjustment according to the results of mining. After the taxiway has entered the stationary mode and the secondary working fluid has been turned on, the insert is located outside the gas stream without affecting the operation of the nozzle. Now, the only requirement is imposed on the design of the insert: it must completely collapse by the estimated time of stopping the supply of the secondary working fluid. This condition, in the absence of strict requirements for uniformity of heat, is easily satisfied.

 Thus, the expected technical result from the implementation of the invention is confirmed.

 The invention is not limited to the description of a specific example of its implementation: for example, a taxiway can run on solid fuel, special means can be provided in the insert design for its forced removal, in each particular case, the locations of the insert and belt of the secondary working fluid, the start and stop time of its supply also vary, the supply may not be completely stopped, but limited to a flow rate that does not affect the main gas flow, in order to prevent burnout of the structure oyas 4, etc.

 The proposed method is most effective for spacecraft with rocket engines, operating from launch to the launch of the device in low Earth orbit. The energy gain from the implementation of the invention in such a particular Space Shuttle allows increasing its payload by ≈10%.

Claims (1)

 A method of altitude control of an overexpanded jet nozzle for a rocket engine, in which a supersonic gas stream is detached from the nozzle wall, including the interaction of the stream with a mechanical obstruction located on the wall that is removed during engine operation and with a secondary working fluid introduced from the wall into the main gas flow in place in front of the obstacle, characterized in that initially the flow interacts with the mechanical obstacle, and after the start of the engine spruce - interaction with a secondary working fluid, in the process of expenditure of which a mechanical obstacle is removed.

Images