Regenerative cooling structure of combustion chamber

Abstract

The invention discloses a combustion chamber regenerative cooling structure which comprises flow dividing cavities and cooling unit sets which are periodically and alternately arranged, turbulent flow columns are arranged in the flow dividing cavities, each cooling unit comprises a flow dividing channel, a vortex backflow cavity and a gradually-expanded outlet section, the vortex backflow cavity is of a U-shaped cavity structure, and the vortex backflow cavity is of a U-shaped cavity structure. The flow dividing cavity is connected with the two sides of the small-head area of the vortex backflow cavity through two flow dividing channels, each flow dividing channel comprises an inlet section and an outlet section, the outlet sections are obliquely connected with the vortex backflow cavity, the divergent outlet sections are arranged at the tail of the large-head area of the vortex backflow cavity, and the tail of each divergent outlet section is connected with the next flow dividing cavity; when fuel oil enters the vortex backflow cavity from the flow dividing channel, two strands of inclined jet flow collide, vortex is formed at the jet flow outlet of the inclined part, and due to the interaction of jet flow collision and vortex, the fuel oil generates periodic oscillation in the vortex backflow cavity and is strengthened at the gradually-expanded outlet section, so that the heat exchange performance of the fuel oil and a hot wall is improved; the purposes of effectively utilizing the fuel to cool the heat sink and improving the cooling performance of the combustion chamber are achieved.

Description

Technical Field

[0001] The present invention relates to the field of efficient cooling of scramjet engines, and particularly to a regenerative cooling structure for a combustion chamber. Background Art

[0002] A large number of studies have been carried out on engine thermal protection technology at home and abroad, which are mainly divided into passive thermal protection, active thermal protection, and combined passive and active thermal protection, etc. Passive cooling refers to a method of enabling components to work stably for a long time under certain conditions by utilizing the physical and chemical properties of the structural self - composing materials or the structural surface coating materials, such as high heat capacity, high oxidation resistance, high melting point, low coefficient of thermal expansion, high emissivity, and low thermal conductivity. However, the increase in flight Mach number has far exceeded the improvement of material properties. Passive thermal protection technology is difficult to adapt to the severe thermal field environment of scramjet engines at higher Mach numbers due to aerodynamic heating and combustion heat release. Developing a safe and reliable active cooling method is the best way to solve the insufficient passive cooling capacity. Active cooling can be divided into main forms such as regenerative cooling, film cooling, transpiration cooling, and impingement cooling according to the cooling channel structure and the flow form of the cooling working medium. The current combined passive and active cooling is still in the initial stage of development. Most combined cooling schemes still suppress the propagation of heat flux in the form of superposition of multiple cooling methods to achieve the thermal protection effect.

[0003] Scramjet engines are considered to be the most promising leading power devices for hypersonic vehicles due to their advantages of simple structure, small mass, low cost, and high specific impulse. However, with the increase in flight Mach number, the levels of aerodynamic heat and combustion heat release increase sharply, and the combustion chamber temperature exceeds the limit temperature of conventional materials. Due to the too - high total temperature of the oncoming air, it no longer has cooling capacity, and the limited propellant becomes the available cold source on the engine. Therefore, regenerative cooling based on hydrocarbon fuel is considered an important cooling method for scramjet engines. Taking the cooling of the combustion chamber surface of a scramjet engine as an example, the fuel is first injected into the regenerative cooling channels on the inner surface of the engine, absorbs the heat released during the engine combustion process through convective heat transfer and increases its own temperature, and finally returns to the combustion chamber for reaction. In order to reduce the risk of material ablation in the high - temperature environment of scramjet engines, optimizing the geometric structure of the regenerative cooling channels is an effective means to achieve enhanced heat transfer and rational utilization of the fuel cooling heat sink. Summary of the Invention

[0004] Object of the Invention: The present invention aims to provide a regenerative cooling structure that enables fuel to collide and form vortices in the combustion chamber wall to generate periodic oscillations.

[0005] Technical solution: The regenerative cooling structure of the combustion chamber described in the present invention includes shunt cavities and a cooling unit group arranged alternately in a cycle. A number of turbulators are provided in the shunt cavity. Each cooling unit includes a shunt channel, a vortex reflux cavity, and a gradually expanding outlet section. The vortex reflux cavity is a U-shaped cavity structure. The shunt cavity is connected to both sides of the small-head region of the vortex reflux cavity through two shunt channels. The shunt channel includes an inlet section and an outlet section. The outlet section is obliquely connected to the vortex reflux cavity. The gradually expanding outlet section is arranged at the tail of the large-head region of the vortex reflux cavity, and the tail of the gradually expanding outlet section is connected to the next shunt cavity; when fuel enters the vortex reflux cavity from the shunt channel, two inclined jets collide, and a vortex is formed at the jet outlet of the inclined part, generating periodic oscillations to achieve heat exchange.

[0006] Preferably, the cooling units are arranged in a staggered pattern, that is, the outlets of the cooling units are located between two adjacent downstream cooling units.

[0007] Preferably, the shunt channel is a circular cross-section channel with a diameter of 0.15δ to 0.25δ. The inlet section of the shunt channel is perpendicular to the rectangular shunt cavity. The included angle α between the outlet section and the inlet section of the shunt channel is 50° to 70°, and the included angle β between the outlet section and the wall surface of the vortex reflux cavity is 60° to 80°. The length of a single shunt channel is 2δ to 3δ.

[0008] Preferably, the length l c of the vortex reflux cavity is 2δ to 3δ, the width w c is 1.5δ to 2.5δ, and the height h c is the same as the height of the gradually expanding outlet section, both being 0.2δ to 0.4δ.

[0009] Preferably, the outlet throat of the vortex reflux cavity is square, and the width w t of the outlet throat is 0.2δ to 0.4δ; the flow length l t of the gradually expanding outlet section is 0.5δ to 1.0δ, and the expansion angle γ is 50° to 80°.

[0010] Preferably, the shunt cavity is a circumferential channel with a square cross-section, and the channel height h f is 0.5δ to 0.7δ. The height of the shunt cavity is higher than the height of the gradually expanding outlet section and the diameter of the shunt channel.

[0011] Preferably, the turbulators are cylindrical bodies with a circular or elliptical cross-section. The turbulators are of the same height as the shunt cavity and are arranged in the shunt cavity at equal intervals, and the interval P is 1.0δ to 1.5δ.

[0012] Optionally, the number of cooling units in the cooling unit group in each cycle is the same or increasing or decreasing or distributed regularly or randomly.

[0013] Optionally, the sum of the areas of all the vortex return cavities in each cycle is the same, or increasing, or decreasing, or distributed regularly, or distributed randomly.

[0014] The regenerative cooling structure of the combustion chamber according to the present invention is applied to the combustion chamber wall with a thickness δ of 3 to 10 mm.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: 1. By combining the inclined jet channel and the U-shaped return cavity, the fuel forms periodic oscillations due to the interaction of collision and vortex in the vortex return cavity, transforming the steady flow into an unsteady flow, enhancing the complexity of the flow field, and significantly strengthening the internal heat transfer; 2. The present invention gets rid of the limitations of the commonly used simple rectangular cross-section channels in regenerative cooling, optimizes the geometric structure of the regenerative cooling channel, and thus improves the cooling efficiency of the combustion chamber; 3. The present invention uses the spoiler columns arranged at equal intervals in the shunt cavity to disturb the fuel flow field, achieving the purpose of effectively using the fuel to cool the heat sink and improving the cooling performance of the combustion chamber. Description of the Drawings

[0016] Figure 1 It is a schematic diagram of the present invention installed on the combustion chamber wall;

[0017] Figure 2 It is a schematic diagram of the local structure of the present invention;

[0018] Figure 3 It is a schematic diagram of the structure of the cooling unit. Detailed Embodiments

[0019] The present invention will be further described below with reference to the accompanying drawings.

[0020] The regenerative cooling structure of the combustion chamber described in the present invention includes shunt chambers 1 and a cooling unit group arranged in a periodic and alternating manner. A number of turbulators 2 are provided in the shunt chamber 1. Each cooling unit includes a shunt channel 3, a vortex return chamber 4, and a gradually expanding outlet section 5. The vortex return chamber 4 is a U-shaped cavity structure. The shunt chamber 1 is connected to both sides of the small-head region of the vortex return chamber 4 through two shunt channels 3. The shunt channel 3 includes an inlet section and an outlet section, and the outlet section is obliquely connected to the vortex return chamber 4. The gradually expanding outlet section 5 is provided at the tail of the large-head region of the vortex return chamber 4, and the tail of the gradually expanding outlet section 5 is connected to the next shunt chamber. After the fuel enters the square shunt chamber, it flows circumferentially and then flows into the circular shunt channels in pairs. Due to the inclination of the outlet section of the shunt channel, the two fuel jets in the same group form obliquely opposite jets and collide after entering the U-shaped return chamber. Due to the special configuration of the U-shaped return chamber, the fuel forms a periodically changing vortex characteristic in the return chamber. The two obliquely jets form a periodic oscillation through the collision and vortex interaction in the vortex return chamber, converting the steady flow into an unsteady flow. And after passing through the narrow square throat, a sweeping flow is formed in the outlet expansion section, and then enters the next shunt chamber. The cooling units in different rows are arranged in a staggered manner, that is, the outlet of the cooling unit is located between two adjacent downstream cooling units. Optionally, the number of cooling units in the cooling unit group in each cycle is the same or increasing or decreasing or distributed regularly or randomly. Optionally, the sum of the areas of all the vortex return chambers in each cycle is the same or increasing or decreasing or distributed regularly or randomly.

[0021] In this embodiment, the unsteady flow process of the fuel in the vortex return chamber is as follows: the outlet section of the shunt channel is inclined, and the two fuel jets in the same group form obliquely opposite jets and collide after entering the U-shaped vortex return chamber. At the same time, due to the special configuration of the U-shaped vortex return chamber, the vortex characteristics generated by the collision of the fuel in the return chamber are unstable. The two jets alternately form vortices at the bottom of the U-shaped cavity. When one jet deflects towards the bottom region of the U-shaped cavity, the other jet serves as the main body of the outlet jet. The two obliquely jets form a periodic oscillation through the collision and vortex interaction in the vortex return chamber, converting the steady flow into an unsteady flow, enhancing the complexity of the flow field, and significantly strengthening the internal heat transfer. After passing through the narrow square throat, a sweeping flow is formed in the outlet expansion section.

[0022] In this embodiment, the working principle of the turbulators in the shunt chamber is as follows: the turbulators will interfere with the flow path of the fluid, destroy the original laminar boundary layer, and cause a turbulent wake region to form behind the column. The thermal resistance of the turbulent boundary layer is smaller, which can significantly improve the convective heat transfer efficiency; the turbulators themselves, as convex structures, directly increase the effective contact area of the heat transfer surface, thereby increasing the total heat transfer amount.

[0023] In this embodiment, the computational domain includes the combustor flow field of a scramjet engine, the solid domain of the combustor with the regenerative cooling structure applied, and the regenerative cooling structure flow field. The total inlet pressure and the airflow temperature are given at the combustor inlet, and the fuel temperature and the mass flow rate are given at the regenerative cooling structure inlet. The fuel mass flow rate corresponds to the fuel supply mass flow rate of the combustor. The wall thickness δ of the combustor is 4 mm, the diameter of the flow splitting channel is 0.8 mm, the total length is 8 mm, and the length l c of the vortex recirculation cavity is 10 mm, and the width w c is 8 mm. The height h of the vortex recirculation cavity and the gradually expanding outlet section c is 1.2 mm, and the width w of the outlet throat t is 1.2 mm. The length l of the gradually expanding outlet section t is 3 mm, and the height h of the flow splitting cavity f is 2 mm. The pitch P of the turbulator bars is 5 mm. The turning angle α between the outlet section and the inlet section of the flow splitting channel is 60°, the angle β between the outlet section and the wall surface of the vortex recirculation cavity is 75°, and the expansion angle γ of the gradually expanding outlet section is 60°. As a comparison, the height of the rectangular cross-section straight regenerative cooling channel is 1.2 mm, the width is 2.4 mm, and multiple channels are arranged at equal intervals circumferentially, keeping the total heat transfer area the same as that of the novel regenerative cooling structure.

[0024] In this embodiment, the flow field and the temperature field are calculated and solved by the commercial computational software Ansys Fluent.

[0025] In this embodiment, the computational model is numerically simulated with typical operating conditions of a scramjet engine combustor. When traditional rectangular cross-section channels are arranged on the combustor wall for regenerative cooling, the heat load of some areas on the combustor wall is relatively high during combustion simulation, and the wall temperature will exceed the temperature resistance limit of the material. After replacing it with the novel regenerative cooling structure of the combustor, when regenerative cooling is carried out with the same mass flow rate of fuel, the average wall temperature of the combustor is reduced by about 20%. Especially in the vortex recirculation cavity area, the average wall temperature is reduced more significantly, achieving the purpose of effectively utilizing the fuel cooling heat sink and improving the cooling performance of the combustor.

[0026] In this embodiment, after the circular or elliptical cross-section turbulator bar structure is introduced into the flow splitting cavity of the combustor regenerative cooling structure, the average wall temperature of the combustor is reduced by about 5% compared with that without the turbulator bar structure.

Claims

1. A regenerative cooling structure for a combustion chamber, characterized in that It includes shunt cavities (1) and a group of cooling units arranged alternately in a cycle. There are several turbulator columns (2) in the shunt cavity (1). Each cooling unit includes a shunt channel (3), a vortex reflux cavity (4) and a gradually expanding outlet section (5). The vortex reflux cavity (4) is a U-shaped cavity structure. The shunt cavity (1) is connected to both sides of the small-head region of the vortex reflux cavity (4) through two shunt channels (3). The shunt channel (3) includes an inlet section and an outlet section. The outlet section is obliquely connected to the vortex reflux cavity (4). The gradually expanding outlet section (5) is arranged at the tail of the large-head region of the vortex reflux cavity (4). The tail of the gradually expanding outlet section (5) is connected to the next shunt cavity. When fuel enters the vortex reflux cavity from the shunt channel, two inclined jets collide, and vortices are formed at the jet outlets of the inclined part, generating periodic oscillations to achieve heat exchange.

2. The regenerative cooling structure of the combustion chamber according to claim 1, wherein The cooling units are arranged in a staggered row, that is, the outlets of the cooling units are located between two adjacent downstream cooling units.

3. The regenerative cooling structure of the combustion chamber according to claim 1, wherein The shunt channel (3) is a circular cross-section channel with a diameter of 0.15δ - 0.25δ, where δ is the thickness of the combustion chamber wall. The inlet section of the shunt channel (3) is perpendicular to the rectangular shunt cavity. The included angle α between the outlet section and the inlet section of the shunt channel (3) is 50° - 70°. The included angle β between the outlet section and the wall of the vortex reflux cavity is 60° - 80°. The length of a single shunt channel (3) is 2δ - 3δ.

4. The regenerative cooling structure of the combustion chamber according to claim 3, wherein The length l of the vortex return cavity (4) c is 2δ to 3δ, and the width w c is 1.5δ to 2.5δ, and the height h c is the same as the height of the gradually expanding outlet section, both being 0.2δ to 0.4δ.

5. The regenerative cooling structure of the combustion chamber according to claim 1, wherein The outlet throat of the vortex return cavity (4) is square, and the width w of the outlet throat t is 0.2δ to 0.4δ; the flow length l of the gradually expanding outlet section (5) t is 0.5δ to 1.0δ, and the expansion angle γ is 50° to 80°.

6. The regenerative cooling structure of the combustion chamber according to claim 1, wherein, The flow splitting cavity (1) is a circumferential channel with a square cross-section, and the channel height h f is 0.5δ to 0.7δ. The height of the flow splitting cavity is higher than the height of the gradually expanding outlet section (5) and the diameter of the flow splitting channel (3).

7. The regenerative cooling structure of the combustion chamber according to claim 1, wherein, The turbulator column (2) is a column with a circular or elliptical cross-section. The turbulator column is of the same height as the shunt cavity and is arranged in the shunt cavity at equal intervals, and the interval P is 1.0δ - 1.5δ.

8. The regenerative cooling structure of the combustion chamber according to claim 1, wherein, The number of cooling units in the group of cooling units in each cycle is the same, or increases, or decreases, or is distributed regularly, or is randomly distributed.

9. The regenerative cooling structure of the combustion chamber according to claim 1, wherein The sum of the areas of all the vortex reflux cavities (4) in each cycle is the same, or increases, or decreases, or is distributed regularly, or is randomly distributed.

10. The regenerative cooling structure of the combustion chamber according to any one of claims 1-9, characterized in that, It is applied to the combustion chamber wall with a thickness δ of 3 - 10 mm.

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