Design method for variable helix angle milling groove

Abstract

The invention relates to a variable helix angle milling groove design method. The method comprises the following steps: selecting N sections in a molded surface length L range of a to-be-designed milling groove; according to the material of the inner wall, the groove bottom wall thickness delta of each section is preliminarily selected; preliminarily selecting a rib width b, a groove depth h, a helix angle beta and a groove number n according to a cross section; according to the groove bottom wall thickness delta, the rib width b, the groove depth h, the helix angle beta, the groove number n and the diameter Di of each section, the groove width c of each section is calculated; according to the regeneration coolant flow # imgabs0 # groove number n, the groove width c, the groove depth h and the coolant density rho, the flow velocity v of each section is calculated; and calculating and checking the flow resistance, heat transfer and strength of the helical milling groove according to the flow velocity v, the groove width c and the groove depth h until the flow resistance, the heat transfer and the strength meet the use requirements. Under the condition of meeting the heat transfer and strength use requirements, the flow resistance of the coolant along the milling groove is effectively reduced, and the flow resistance requirement of the system is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of liquid rocket engine cooling and relates to a variable helical angle milling slot design method. Background Art

[0002] Liquid rocket engine thrust chambers operate in high-temperature, high-pressure environments, making thermal protection of the inner wall a critical issue that must be addressed during thrust chamber development. Common thermal protection methods for liquid rocket engine thrust chambers include external cooling and internal cooling. Regenerative cooling is the most basic external cooling method used in higher-thrust liquid rocket engines.

[0003] Regenerative cooling generally uses a straight groove structure. In high-pressure regenerative liquid rocket engines, to increase the flow rate of the regenerative coolant, spiral milling grooves are used on the inner wall in areas with high heat flux density. Currently, spiral milling grooves generally use a fixed spiral pitch angle. When applied to the convergent section before the throat, the flow rate in the milling groove increases sharply as the profile diameter decreases. Although this is beneficial for cooling the inner wall, it will significantly increase the flow resistance in the milling groove and increase the system burden. If the spiral pitch angle is selected based on the minimum flow rate to ensure reliable cooling of the throat, the flow rate in the milling groove at the beginning of the convergent section will be too low, and reliable cooling of the wall cannot be guaranteed. Summary of the Invention

[0004] The technical problem solved by the present invention is: to overcome the shortcomings of the existing technology and propose a variable spiral angle milling groove design method to solve the problem that the flow velocity in the milling groove at the beginning of the convergence section of the fixed spiral angle method is low and cannot ensure reliable cooling of the wall surface.

[0005] The technical solution of the present invention is: a variable helix angle milling slot design method, comprising the following steps:

[0006] Step 1: Select N cross sections within the length L of the milling groove to be designed;

[0007] Step 2: Preliminarily select the groove bottom wall thickness δ of each section based on the inner wall material;

[0008] Step 3: Preliminarily select the rib width b, groove depth h, helix angle β and number of grooves n according to the cross section;

[0009] Step 4. Calculate the groove width c at each section based on the groove bottom wall thickness δ, rib width b, groove depth h, helix angle β, number of grooves n, and diameter Di at each section:

[0010]

[0011] Step 5: According to the regeneration coolant flow The number of grooves n, groove width c, groove depth h and coolant density ρ are used to calculate the flow velocity v at each cross section:

[0012]

[0013] Step 6: Calculate and check the flow resistance, heat transfer, and strength of the spiral milling groove based on the flow velocity v, groove width c, and groove depth h. If the flow resistance, heat transfer, and strength meet the requirements, end the design; otherwise, return to step 2.

[0014] Furthermore, the number N of cross sections is selected to be 4 to 5.

[0015] Furthermore, based on the inner wall material, the groove bottom wall thickness δ of each section is preliminarily selected, including:

[0016] For the inner wall of copper alloy, the groove bottom wall thickness δ is initially selected to be 1 to 1.4 mm; for the inner wall of stainless steel, the groove bottom wall thickness δ is initially selected to be 0.8 to 1.1 mm.

[0017] Furthermore, the rib width b and the number of grooves n are kept consistent on N sections within the profile length L, and the rib width b is selected to be 1 mm to 1.5 mm.

[0018] Furthermore, the groove depth h and the helix angle β are varied in the region with large heat flux according to the position of the cross section Ai. The groove depth h is 2 mm to 7 mm, and the helix angle β is 15° to 85°.

[0019] Furthermore, the groove width c is 1 mm to 4 mm.

[0020] Furthermore, the flow resistance of the spiral milling groove is calculated by the following formula:

[0021]

[0022]

[0023] Wherein, ΔP is the flow resistance along the spiral milling groove; λ is the flow resistance coefficient along the spiral milling groove; ρ is the coolant density; v i is the coolant flow rate at section Ai; ΔXi is the axial distance between the two sections; D h is the equivalent diameter of the spiral milling groove; α i It is the angle between the inner surface and the axis at section Ai.

[0024] The beneficial effects of the present invention compared with the prior art are:

[0025] The variable helix angle milling slot design method provided by the present invention replaces the currently used straight slot or fixed helix angle milling slot scheme. By adjusting the helix angle β in sections in the high heat flux area of ​​the thrust chamber, the heat exchange length along the path is increased, the coolant flow rate in the slot is increased, and the heat transfer coefficient between the inner wall and the coolant is increased. Under the condition of meeting the heat transfer and strength requirements, the flow resistance of the coolant along the milling slot is effectively reduced, the flow resistance requirement of the system is alleviated, and the design difficulty is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure of the variable helix angle milling groove convergence section according to an embodiment of the present invention;

[0027] Figure 2 Schematic diagram of the variable helix angle milling structure according to an embodiment of the present invention;

[0028] Figure 3 This is a flow chart of a design method for variable helix angle slot milling according to an embodiment of the present invention;

[0029] Description of reference numerals:

[0030] 1- rib of the milling groove, 2- groove of the milling groove, 3- remaining wall thickness of the groove bottom. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to the accompanying drawings and examples.

[0032] Example 1

[0033] like Figure 1 The convergent section profile shown is processed with a variable helix angle milling groove, and its cross section is as follows Figure 2 As shown, it mainly consists of ribs 1, grooves 2 and the remaining wall thickness 3 at the groove bottom.

[0034] like Figure 3 As shown, the variable helix angle milling slot design method proposed by the present invention includes the following steps:

[0035] Step 1: Select N cross sections within the length L of the milling groove to be designed;

[0036] Step 2: Preliminarily select the groove bottom wall thickness δ of each section based on the inner wall material;

[0037] Step 3: Preliminarily select the rib width b, groove depth h, helix angle β and number of grooves n according to the cross section;

[0038] Step 4. Calculate the groove width c at each section based on the groove bottom wall thickness δ, rib width b, groove depth h, helix angle β, number of grooves n, and diameter Di at each section:

[0039]

[0040] Step 5: According to the regeneration coolant flow The number of grooves n, groove width c, groove depth h and coolant density ρ are used to calculate the flow velocity v at each cross section:

[0041]

[0042] Step 6: Based on parameters such as flow velocity v, groove width c, and groove depth h, calculate and verify the flow resistance, heat transfer, and strength of the spiral milling groove according to relevant specifications. If the flow resistance, heat transfer, and strength meet the requirements, the design is completed; if not, return to step 2.

[0043] Preferably, in step 1, the number of sections N is generally selected to be 4 to 5, which can be increased or decreased according to the changes in local parameters. If the local parameters change drastically, the number of sections can be increased to improve the calculation accuracy. Conversely, the number of sections can be reduced to reduce the amount of calculation.

[0044] Preferably, in step 2, the groove bottom wall thickness δ is generally selected according to the inner wall material: for the copper alloy inner wall, the groove bottom wall thickness δ is initially selected as 1.2 mm; for the stainless steel inner wall, the groove bottom wall thickness δ is initially selected as 1 mm, and then the groove bottom wall thickness is checked according to the heat transfer calculation and strength calculation in step 6.

[0045] Preferably, in step 3, the rib width b and the number of grooves n are generally consistent in N sections within the profile length L. The rib width b is generally selected from 1 mm to 1.5 mm. The selection of the number of grooves n is related to the flow velocity v, the rib width b, the diameter Di at the section, etc.

[0046] Preferably, in step 3, the groove depth h and the helix angle β may vary according to the position of the cross section Ai. The groove depth h is generally 2 mm to 7 mm, and the helix angle β is generally 15° to 85°.

[0047] Preferably, in step 4, the groove width c is generally 1 mm to 4 mm.

[0048] Preferably, in step 6, the flow resistance of the spiral milling groove is calculated by the following formula:

[0049]

[0050]

[0051] Wherein, ΔP is the flow resistance along the spiral milling groove;

[0052] λ is the resistance coefficient along the path;

[0053] ρ is the coolant density;

[0054] v i is the coolant flow rate at section Ai;

[0055] ΔXi is the axial distance between the two sections;

[0056] D h is the equivalent diameter of the spiral milling groove;

[0057] α i It is the angle between the inner surface and the axis at section Ai.

[0058] The variable helix angle milling slot design method provided by the present invention replaces the currently used straight slot or fixed helix angle milling slot scheme. By adjusting the helix angle β in sections in the high heat flux area of ​​the thrust chamber, the heat exchange length along the path is increased, the coolant flow rate in the slot is increased, and the heat transfer coefficient between the inner wall and the coolant is increased. Under the condition of meeting the heat transfer and strength requirements, the flow resistance of the coolant along the milling slot is effectively reduced, the flow resistance requirement of the system is alleviated, and the design difficulty is reduced.

[0059] At present, this design method has been successfully applied to the thrust chamber of a high-pressure staged-combustion liquid oxygen-kerosene engine. While enhancing the heat exchange on the inner wall and ensuring reliable cooling, it significantly reduces the flow resistance of the thrust chamber cooling channel.

[0060] Although the present invention has been disclosed above in terms of preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solutions of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the scope of protection of the technical solutions of the present invention.

[0061] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A variable helix angle milling slot design method, characterized in that: The following steps are involved: Step 1, select N sections within the range of the profile length L of the groove to be designed; Step 2: Preliminarily select the groove bottom wall thickness δ of each section according to the inner wall material; Step 3: Preliminarily select the rib width b, groove depth h, helix angle β and groove number n according to the cross section; Step 4: Calculate the groove width c at each section based on the groove bottom wall thickness δ, rib width b, groove depth h, helix angle β, number of grooves n and diameter Di at each section: Step 5: According to the regeneration coolant flow The number of grooves n, groove width c, groove depth h and coolant density ρ are used to calculate the flow velocity v at each cross section: Step 6: Calculate and check the flow resistance, heat transfer and strength of the spiral milling groove according to the flow velocity v, groove width c and groove depth h. If the flow resistance, heat transfer and strength meet the use requirements, end the design, otherwise return to step 2.

2. A variable helix angle milling slot design method according to claim 1, characterized in that: The number of cross sections N is selected to be 4 to 5.

3. The variable helix angle milling slot design method according to claim 1, characterized in that: According to the inner wall material, the groove bottom wall thickness δ of each section is preliminarily selected, including: For the inner wall of copper alloy, the groove bottom wall thickness δ is initially selected as 1 to 1.4 mm; for the inner wall of stainless steel, the groove bottom wall thickness δ is initially selected as 0.8 to 1.1 mm.

4. The variable helix angle milling slot design method according to claim 1, characterized in that: The rib width b and the number of grooves n are kept consistent on N sections within the profile length L, and the rib width b is selected to be 1 mm to 1.5 mm.

5. The variable helix angle milling slot design method according to claim 1, characterized in that: The groove depth h and the helix angle β vary in the area with large heat flow according to the position of the cross section Ai. The groove depth h is 2 mm to 7 mm, and the helix angle β is 15° to 85°.

6. The variable helix angle milling slot design method according to claim 1, characterized in that: The groove width c is 1mm to 4mm.

7. The variable helix angle milling slot design method according to claim 1, characterized in that: The flow resistance of spiral milling is calculated by the following formula: Wherein, ΔP is the flow resistance along the spiral milling groove; λ is the flow resistance coefficient along the spiral milling groove; ρ is the coolant density; v i is the coolant flow rate at section Ai; ΔXi is the axial distance between the two sections; D h is the equivalent diameter of the spiral milling groove; α i It is the angle between the inner surface and the axis at section Ai.

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