Active cooling method applied to engine

Abstract

The invention relates to an active cooling method applied to an engine. The active cooling method comprises the steps that firstly, an active thermal protection theoretical analysis model suitable for an oblique detonation engine is established; 2, preliminarily determining parameters of an active thermal protection theoretical analysis model; 3, loading heat flow conditions, and carrying out active cooling simulation analysis on the active thermal protection theoretical analysis model to obtain coolant temperature distribution; 4, whether coolant temperature distribution meets the coolant temperature upper limit requirement and the solid wall material temperature use requirement or not is determined, if yes, the sixth step is executed, and if not, the fifth step is executed; 5, changing parameters of the active thermal protection theory analysis model, and repeating the steps 3-4; sixthly, the rectangular cooling channel in the local high heat flow area is modified into a cooling channel structure with different bending structures till the requirement is met; and 7, processing the active thermal protection structure according to the final active thermal protection theoretical analysis model and parameters. The problem of heat protection of the inclined detonation engine structure is solved.

Description

Technical Field

[0001] The invention belongs to the field of detonation force and relates to an active cooling method applied to an engine. Background Art

[0002] The oblique detonation engine is a highly promising power type that is expected to expand air-breathing power to a higher Mach number. It has the characteristics of high operating speed, high specific impulse performance, and small volume share. It is a potential power type for future horizontal take-off and landing aerospace vehicles and an important development direction of cutting-edge power technology.

[0003] Currently, the research on oblique detonation engine technology is in its infancy. Related research mainly focuses on stable combustion and detonation stationary under ultra-high-speed incoming flows. There has been no systematic research on the thermal protection of large-molecule hydrocarbon fuel engines working for a long time.

[0004] Compared with the external heat protection problem of flight, which mainly adopts passive heat protection, the internal heat protection of the engine faces the problem of ensuring that the structure is not ablated or damaged in an aerobic environment with high total temperature and high heat flux. The regenerative cooling method using engine fuel as a coolant is currently a widely used cooling method for high Mach number air-breathing engines. However, the current active cooling of air-breathing power is mainly used under Mach number 6 conditions and has not yet been expanded to Mach numbers above 8.

[0005] Compared with traditional ramjets, oblique detonation engines have higher operating Mach numbers and higher combustion efficiency. The dual effects of aerodynamic heating and combustion heat release significantly increase the difficulty of thermal protection, especially the oblique detonation engine's detonation oblique split structure, which has high heat flux and small structural space, extremely high local heat flux peak, and uneven heat flux distribution, which increases the difficulty of thermal protection. The operating speed range of oblique detonation engines is above Mach number 8. Under this condition, the heat sink requirement is about 4.0MJ / kg. As the most commonly used fuel for current engines, large molecular hydrocarbon fuels have a heat sink of about 2.9 to 3.6MJ / kg. They face thermal protection problems such as insufficient available heat sinks for kerosene and structural temperatures exceeding the allowable temperature. Summary of the invention

[0006] The technical problem solved by the present invention is to overcome the deficiencies of the prior art and to provide an active cooling method for an engine.

[0007] The solution of the present invention is:

[0008] An active cooling method for an engine, the method comprising the steps of:

[0009] Step 1, establishing an active thermal protection theoretical analysis model suitable for an oblique detonation engine, wherein the active thermal protection theoretical analysis model comprises a cooling thin plate and a wall plate processed with cooling grooves, wherein the cooling thin plate covers the thick wall plate, the upper surface of the cooling thin plate is a hot wall, and the lower surface is a cold wall; the cooling grooves are a plurality of rectangular cooling channels evenly distributed along the flow direction;

[0010] Step 2: Preliminarily determine the parameters of the active thermal protection theoretical analysis model, including the cooling plate and wall panel materials, and design the rectangular cooling channel size and cooling plate thickness;

[0011] Step 3, loading the heat flow condition as the thermal boundary input of the active thermal protection theoretical analysis model, performing active cooling simulation analysis on the active thermal protection theoretical analysis model, and obtaining the coolant temperature distribution;

[0012] Step 4: confirm whether the coolant temperature distribution and the fuel temperature distribution meet the coolant temperature upper limit requirement and the solid wall material temperature use requirement. If so, proceed to step 6; if not, proceed to step 5.

[0013] Step 5: Change the active thermal protection theoretical analysis model parameters according to the active cooling simulation analysis results, and repeat steps 3-4;

[0014] Step 6: Modify the rectangular cooling channel in the local high heat flux area into a cooling channel configuration with different bending structures, and perform a refined simulation analysis on the active thermal protection theoretical analysis model to verify whether it meets the thermal protection requirements of the local high heat flux area. If so, proceed to step 7; if not, continue to modify the cooling channel configuration of the local high heat flux area until the requirements are met;

[0015] Step seven: Process the active thermal protection structure according to the final active thermal protection theoretical analysis model and parameters.

[0016] Preferably, the cooling plate and the wall plate are connected by brazing or diffusion welding.

[0017] Preferably, the heat flow conditions in step three include three types of thermal boundary conditions in the local high heat flow peak area and three types of thermal boundary conditions in the engine inner flow channel;

[0018] The three types of thermal boundary conditions refer to given wall heat flow conditions, given wall temperature conditions, and given total temperature and heat transfer coefficient conditions of the fluid near the wall.

[0019] Preferably, active cooling simulation analysis refers to performing gas-solid-liquid coupling calculation based on thermal boundary input under given incoming flow and engine operating mode.

[0020] Preferably, in step 3, the method of performing active cooling simulation analysis on the active thermal protection theoretical analysis model to obtain the coolant temperature distribution is as follows:

[0021] Establish the momentum equation and energy equation for coolant flow;

[0022] Solve the heat flux loaded on the hot wall corresponding to each cooling channel;

[0023] Calculate the convective heat transfer generated by the flow in each cooling channel;

[0024] Calculate the total heat absorption of the coolant;

[0025] The along-the-process distribution of hot wall temperature, cold wall temperature and coolant temperature of the active thermal protection theoretical analysis model is obtained.

[0026] Preferably, the heat flux Q loaded on the hot wall surface corresponding to each cooling channel within time t w1 satisfy:

[0027]

[0028] q w is the heat flux density distribution on the hot wall, W is the total width of the cooling structure, L is the total length of the cooling structure, T w1 is the hot wall temperature, T w2 is the cold wall temperature, k w is the thermal conductivity of the cooling sheet, dx is the length of each microelement, and each cooling channel is divided into a number of microelements; the cooling structure is the active thermal protection theoretical analysis model.

[0029] Preferably, each cooling channel is loaded with heat flux on all four sides of the circumference, and the convective heat transfer Qw of the coolant flowing in each dx is cool satisfy

[0030] QUR cool =N*dx*(h2+s / 2)*η f h f (Tw2-T f )+N*dx*h1*(Tw2-T f )

[0031] N is the total number of cooling channels, h1 is the cross-sectional width of the cooling channel, h2 is the cross-sectional height of the cooling channel, s is the distance between the adjacent walls of two adjacent cooling channels, h f is the convective heat transfer coefficient, T f is the coolant temperature, η f is the correction factor.

[0032] Preferably,

[0033]

[0034] th() is the hyperbolic tangent function, and H is the equivalent length of the solid wall part between adjacent cooling channels.

[0035] Preferably, the total heat absorption of the coolant Q w2 satisfy

[0036]

[0037] It is the chemical endothermic heat of kerosene cracking.

[0038] Preferably, the coolant is kerosene.

[0039] The beneficial effects of the present invention compared with the prior art are:

[0040] (1) The present invention matches the different structural characteristics of the flow channel and local structure of the engine, optimizes the channel size parameters through comprehensive gas-solid-liquid coupling simulation analysis, and establishes a new cooling structure optimization design method to effectively enhance the convective heat transfer effect in the high heat flow area and reduce the structural temperature.

[0041] (2) The present invention designs a feasible regenerative cooling scheme and a universal design process for kerosene-fueled oblique detonation engines above Mach 8, preliminarily solving the problem of structural heat protection of oblique detonation engines, and at the same time provides a technical basis for expanding its application to other high Mach number air-breathing engines. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of the theoretical analysis model of active thermal protection;

[0043] Figure 2 It is a schematic diagram of the equivalent "fin" of the cooling structure;

[0044] Figure 3 Schematic diagram of the cooling structure and the coolant temperature, coolant convective heat transfer coefficient, pressure and flow velocity distribution along the process, where (a) is the temperature distribution, (b) is the convective heat transfer coefficient distribution, (c) is the pressure distribution, and (d) is the flow velocity distribution;

[0045] Figure 4 1 and 2 are the cooling channel design and heat transfer analysis results in the embodiments, wherein (a) is the cooling channel design for a local high heat flow area such as a cleaved structure, and (b) is the heat transfer analysis result for a local high heat flow area such as a cleaved structure. DETAILED DESCRIPTION

[0046] The present invention will be further described below in conjunction with the accompanying drawings.

[0047] The present invention provides an active cooling method for enhancing heat exchange in local high heat flow areas, thereby meeting the heat protection requirements of the oblique detonation engine structure and providing a technical basis for supporting the long-term operation of the oblique detonation engine.

[0048] The steps of the present invention are as follows:

[0049] Step 1: Establish an active thermal protection theoretical analysis model suitable for oblique detonation engines. The active thermal protection theoretical analysis model includes a cooling plate and a wall plate with cooling channels. The cooling plate covers the thick wall plate. The upper surface of the cooling plate, the side that contacts the high-temperature combustion gas, is a hot wall, and the lower surface is a cold wall. The cooling channels are multiple rectangular cooling channels evenly distributed along the flow direction. Figure 1 The active thermal protection theoretical analysis model is referred to as the cooling structure below.

[0050] Step 2: Preliminarily determine the parameters of the active thermal protection theoretical analysis model, including the cooling plate and wall panel materials, and design the rectangular cooling channel size and cooling plate thickness.

[0051] Step three: load the heat flow conditions as the thermal boundary input of the active thermal protection theoretical analysis model, perform active cooling simulation analysis on the active thermal protection theoretical analysis model, and obtain the coolant temperature distribution.

[0052] For the flow of coolant in each cooling channel, steady-state one-dimensional mass, momentum and energy conservation equations are established. According to the heat transfer process, the coolant velocity, temperature and density distributed along the flow direction are obtained by differentially solving the physical parameters at discrete points along the flow direction.

[0053] (1) The momentum equation is as follows:

[0054]

[0055] in, is the coolant flow rate, A f is the channel cross-sectional area, dx is the length of each microelement, set to 0.0001m; each cooling channel is divided into several microelements. f 、u f are coolant density and velocity respectively; p f is the kerosene pressure; τ w is the shear stress of the cold wall, which can be determined by the friction formula; G is the circumference of the cross section of the cooling channel, that is, G=2(h1+h2).

[0056] (2) The energy equation is as follows:

[0057]

[0058] Wherein, h is the coolant enthalpy, u is the coolant flow rate, and the subscript f represents the coolant. It refers to the convective heat transfer generated by the coolant flowing in the channel and the wall.

[0059] In addition, the friction coefficient C f With τw The relationship is: The friction coefficient can be calculated using the classic Prandtl formula or determined based on a relationship fitted with kerosene experimental data.

[0060] Prandtl's formula is: C f =0.046Re -0.2 (3)

[0061] The fitting relationship is: C f =0.046Re -0.2 (μ f / μ w ) -0.25 (4)

[0062] (3) The heat flux is first conducted through the cooling plate and then absorbed by the coolant in the cooling channel. The heat flux loaded on the hot wall of each microelement can be solved by the one-dimensional heat conduction equation:

[0063]

[0064] Among them, Q w1 is the heat flux loaded on the hot wall surface of each microelement, W is the total width of the cooling structure, L is the total length of the cooling structure, T w1 is the hot wall temperature, T w2 is the cold wall temperature, k w is the thermal conductivity of the cooling plate, dx is the length of each microelement, and each cooling channel is divided into several microelements.

[0065] (4) The mechanism by which the fuel in the cooling channel absorbs structural heat consists of two parts:

[0066] (i) Convective heat transfer caused by flow in the cooling channel, especially turbulence.

[0067] at this time:

[0068]

[0069] where h f is the convective heat transfer coefficient, T f is the kerosene temperature.

[0070] The calculation formula for the convection heat transfer coefficient can be based on the classic Sider-Tate formula, as shown below:

[0071] Nu=0.027Re 0.8 Pr 1 / 3 (μ f / μ w ) 0.14 (7)

[0072] Among them, Nu is the dimensionless heat transfer coefficient - Nusselt number, d is the hydraulic diameter of the cooling channel, λ is the thermal conductivity of the coolant; Re is the Reynolds number, Pr is the Prandtl number, μ f , μ w are the viscosity coefficients of the coolant determined based on the coolant temperature and the cold wall temperature, respectively.

[0073] When the coolant is kerosene, the empirical formula fitted by kerosene heat transfer experimental data is used, as shown in formula (8):

[0074] Nu=0.0126Re 0.87 Pr 0.4 (μ f / μ w ) 0.1 (8)

[0075] Considering the heat transfer of the four circumferential surfaces of the rectangular channel in the actual cooling structure and the unilateral loading effect of the heat flux in the actual problem, this paper uses the rib efficiency η f The concept of (correction factor) Make corrections.

[0076] The present invention equates the convective heat transfer of multiple channels to the convective heat transfer through a group of fins. First, the calculation method of the efficiency of a single fin is introduced. Figure 2 As shown, the solid wall between the channels is equivalent to a "fin" with a width of s, as shown in the area indicated by the yellow dotted line in the figure. Then, the intersection of the "fin" and the cooling thin plate between the cold and hot walls in the cooling structure is the rib root, and the temperature at the rib root is the cold wall temperature T w2 For a single fin, η f The calculation formula is

[0077]

[0078] in, is a constant, and P is the circumference of the cross section of the infinitesimal element involved in heat transfer:

[0079] P=2(1+s),A c is the cross-sectional area of ​​the infinitesimal element A c =1·s. Considering the heat dissipation at the end of the fin, the equivalent fin length H = h2+s / 2. Assuming that the cooling channels are evenly distributed, there are N "fins" when there are N cooling channels. Therefore, the convective heat transfer of the coolant flowing in each microelement length dx cooling channel is Qw cool Equivalent to the fin surface area A f and the root surface area A between the two ribs r The convective heat transfer on

[0080]

[0081] QUR cool =A f η f h f (Tw2-T f )+A r h f (Tw2-T f )=N*dx*(h2+s / 2)*η f h f (Tw2-T f )+N*dx*h1*(Tw2-T f ) (11)

[0082] (ii) The coolant undergoes an endothermic chemical reaction or a phase change.

[0083] When kerosene absorbs heat and rises to the cracking starting temperature, a cracking reaction will occur. The heat absorption of the cracking reaction will produce additional chemical heat sinks, which further absorb heat from the cooling channel wall. From this, the total heat absorption of the coolant Q w2

[0084]

[0085] It is the chemical endothermic heat of kerosene cracking, which depends on the degree of kerosene cracking and the heat endothermic heat per unit mass of kerosene cracking, and also has a certain relationship with the residence time in the cooling channel. The kerosene cracking process applies the thermal / catalytic cracking total package reaction model, and determines the chemical endothermic heat per unit mass and the degree of cracking of kerosene at different temperatures based on experimental data.

[0086] By coupling equations (1), (2), (5), and (12), we can obtain the hot wall temperature T of the cooling structure when kerosene is used as the coolant: w1 , cold wall temperature T w2 and coolant temperature T f The distribution along the route.

[0087] Step 4: confirm whether the coolant temperature distribution and the fuel temperature distribution meet the coolant temperature upper limit requirements and the solid wall material temperature use requirements. If they do, proceed to step 6; if not, proceed to step 5.

[0088] Step 5: Change the active thermal protection theoretical analysis model parameters according to the active cooling simulation analysis results, and repeat steps 3-4.

[0089] Step six, modify the rectangular cooling channel in the local high heat flux area into a cooling channel configuration with different bending structures, and perform a refined simulation analysis on the active thermal protection theoretical analysis model to verify whether it meets the thermal protection requirements of the local high heat flux area. If so, proceed to step seven; if not, continue to modify the cooling channel configuration of the local high heat flux area until the requirements are met.

[0090] Step seven: Process the active thermal protection structure according to the final active thermal protection theoretical analysis model and parameters.

[0091] Example:

[0092] First, given the wall heat flow conditions on the wedge, based on the active thermal protection theoretical analysis model established in step 1, a pipeline solution with a channel diameter of 2 mm is formed through steps 2 to 3, such as Figure 3 The figure shows the schematic diagram of the cooling structure and the coolant temperature, coolant convection heat transfer coefficient, pressure and flow rate distribution along the process, where (a) is the temperature distribution, (b) is the convection heat transfer coefficient distribution, (c) is the pressure distribution, and (d) is the flow rate distribution. Analysis of the wall temperature and the maximum temperature at the outlet of the cooling structure can meet the material temperature requirements and kerosene temperature requirements, forming a preliminary active cooling structure scheme. Further three-dimensional structural design is carried out for the oblique split structure. At the same time, considering that the vortex can enhance the heat transfer effect, the pipeline is designed to be similar to the distribution form of the spiral bend, such as Figure 4 As shown in (a). Through the fluid-solid coupling simulation analysis of the three-dimensional structure, the following Figure 4 The distribution in (b) further verifies that the active cooling structure meets the thermal protection requirements and forms the final closed-loop design solution.

[0093] Parts of the present invention that are not described in detail belong to common knowledge among those skilled in the art.

Claims

1. An active cooling method for an engine, characterized in that The steps of the method include: Step 1, establishing an active thermal protection theoretical analysis model suitable for an oblique detonation engine, wherein the active thermal protection theoretical analysis model comprises a cooling thin plate and a wall plate processed with cooling grooves, wherein the cooling thin plate covers the thick wall plate, the upper surface of the cooling thin plate is a hot wall, and the lower surface is a cold wall; the cooling grooves are a plurality of rectangular cooling channels evenly distributed along the flow direction; Step 2: Preliminarily determine the parameters of the active thermal protection theoretical analysis model, including the cooling plate and wall panel materials, and design the rectangular cooling channel size and cooling plate thickness; Step 3, loading the heat flow condition as the thermal boundary input of the active thermal protection theoretical analysis model, performing active cooling simulation analysis on the active thermal protection theoretical analysis model, and obtaining the coolant temperature distribution; Step 4: confirm whether the coolant temperature distribution and the fuel temperature distribution meet the coolant temperature upper limit requirement and the solid wall material temperature use requirement. If so, proceed to step 6; if not, proceed to step 5. Step 5: Change the active thermal protection theoretical analysis model parameters according to the active cooling simulation analysis results, and repeat steps 3-4; Step 6: Modify the rectangular cooling channel in the local high heat flux area into a cooling channel configuration with different bending structures, and perform a refined simulation analysis on the active thermal protection theoretical analysis model to verify whether it meets the thermal protection requirements of the local high heat flux area. If so, proceed to step 7; if not, continue to modify the cooling channel configuration of the local high heat flux area until the requirements are met; Step seven: Process the active thermal protection structure according to the final active thermal protection theoretical analysis model and parameters.

2. The active cooling method for an engine according to claim 1, characterized in that: The cooling plate and the wall plate are connected by brazing or diffusion welding.

3. The active cooling method for an engine according to claim 1, characterized in that: The heat flow conditions in step 3 include three types of thermal boundary conditions in the local high heat flow peak area and three types of thermal boundary conditions in the engine flow channel; The three types of thermal boundary conditions refer to given wall heat flow conditions, given wall temperature conditions, and given total temperature and heat transfer coefficient conditions of the fluid near the wall.

4. The active cooling method for an engine according to claim 1, characterized in that: Active cooling simulation analysis refers to the gas-solid-liquid coupling calculation based on thermal boundary input under given incoming flow and engine operating mode.

5. The active cooling method for an engine according to claim 1, characterized in that: In step 3, the active cooling simulation analysis is performed on the active thermal protection theoretical analysis model to obtain the coolant temperature distribution as follows: Establish the momentum equation and energy equation for coolant flow; Solve the heat flux loaded on the hot wall corresponding to each cooling channel; Calculate the convective heat transfer generated by the flow in each cooling channel; Calculate the total heat absorption of the coolant; The along-the-process distribution of hot wall temperature, cold wall temperature and coolant temperature of the active thermal protection theoretical analysis model is obtained.

6. The active cooling method for an engine according to claim 5, characterized in that: The heat flux Q loaded on the hot wall surface corresponding to each cooling channel within t time w1 satisfy: q w is the heat flux density distribution on the hot wall, W is the total width of the cooling structure, L is the total length of the cooling structure, T w1 is the hot wall temperature, T w2 is the cold wall temperature, k w is the thermal conductivity of the cooling sheet, dx is the length of each microelement, and each cooling channel is divided into a number of microelements; the cooling structure is the active thermal protection theoretical analysis model.

7. The active cooling method for an engine according to claim 6, characterized in that: Each cooling channel is loaded with heat flux on all four sides, and the convective heat transfer Qw of the coolant flowing in each dx cool satisfy Qw cool =N*dx*(h2+s / 2)*η f h f (Tw2-T f )+N*dx*h1*(Tw2-T f ) N is the total number of cooling channels, h1 is the cross-sectional width of the cooling channel, h2 is the cross-sectional height of the cooling channel, s is the distance between the adjacent walls of two adjacent cooling channels, h f is the convective heat transfer coefficient, T f is the coolant temperature, η f is the correction factor.

8. The active cooling method for an engine according to claim 7, characterized in that: th() is the hyperbolic tangent function, and H is the equivalent length of the solid wall part between adjacent cooling channels.

9. The active cooling method for an engine according to claim 7, characterized in that: Total heat absorption of coolant Q w2 satisfy It is the chemical endothermic heat of kerosene cracking.

10. The active cooling method for an engine according to claim 5, characterized in that: The coolant is kerosene.

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