Variable-pitch inducer with high lift coefficient and design method thereof

Abstract

The application provides a variable-pitch inducer with a high lift coefficient and a design method thereof, and aims at solving the technical problem that a traditional variable-pitch inducer will generate serious tip backflow at the leading edge of a blade under a high lift coefficient, and the anti-cavitation performance of the leading edge of the blade is affected. The variable-pitch inducer with the high lift coefficient comprises a spiral blade, which is sequentially arranged into an equal-pitch section, a slow variable-pitch section and a rapid variable-pitch section along a wrap angle direction. The rapid variable-pitch section realizes a large-pitch section, and then realizes a high-lift section postpositioning. The influence of the tip backflow on the leading edge of the blade under the high lift coefficient is greatly reduced, and the anti-cavitation performance of the leading edge of the blade is effectively improved.

Description

Technical Field

[0001] This invention relates to variable pitch inducer and its design method, specifically to a variable pitch inducer with a high head coefficient and its design method. Background Technology

[0002] The preload pump is one of the core components of a liquid rocket engine. The cavitation resistance of the preload pump inducer determines the weight of the liquid rocket's tank, which in turn determines the overall payload capacity of the liquid rocket and has a decisive impact on the rocket's weight reduction.

[0003] With the development of reusable liquid rockets, the requirements for weight reduction are increasing year by year, while the tank pressure is gradually decreasing. Furthermore, to reduce engine weight, some engines have eliminated the pre-pressure pump. This necessitates that the main pump inducer possess both a high head coefficient and high cavitation resistance. Currently, traditional variable-pitch inducers sequentially configure the helical blades along the wrap angle direction as a constant-pitch section – a variable-pitch section – a constant-pitch section. This pitch variation pattern generates severe tip backflow at high head coefficients, affecting the cavitation resistance of the blade leading edge. Therefore, there is an urgent need to develop a variable-pitch inducer adapted to high head coefficients. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problem that traditional variable pitch inducers will generate severe tip backflow at the leading edge of the blade under high head coefficient, which will affect the anti-cavitation performance of the leading edge of the blade. The invention provides a variable pitch inducer with high head coefficient and its design method.

[0005] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0006] A high lift coefficient variable pitch inducer includes a hub and multiple helical blades circumferentially uniformly arranged on the hub. The special feature is that the outer diameter of the blade tip of the helical blade is set to be the same diameter; the helical blade is arranged in sequence along the wrap angle direction as a constant pitch section, a slowly variable pitch section and a rapidly variable pitch section; the pitch of the helical blade gradually increases from the end of the constant pitch section to the end of the rapidly variable pitch section.

[0007] The final pitch of the slowly variable pitch section Determined by the following formula:

[0008] ;

[0009] in, Where n is the induced wheel flow rate, n is the induced wheel speed, and D is the outer diameter of the tip of the helical blade;

[0010] The ending wrap angle of the slowly variable pitch segment Determined by the following formula:

[0011] ;

[0012] Where z is the number of helical blades. The pitch of the equal pitch segment;

[0013] The final pitch of the rapid pitch change section Determined by the following formula:

[0014] ;

[0015] in, The work coefficient, , The diameter at the hub outlet. It is the acceleration due to gravity;

[0016] The different wrap angles of the rapid pitch section pitch at Satisfy the following formula:

[0017] , ;

[0018] in, To the end wrap angle of the rapid pitch segment, , = 40°~80°.

[0019] Furthermore, the diameter at the hub outlet Determined by the following formula:

[0020] ;

[0021] in, This is the head of the inducer.

[0022] Furthermore, the diameter at the hub inlet... Determined by the following formula:

[0023] ;

[0024] in, This is the correction factor at the hub inlet. .

[0025] Furthermore, the different wrap angles of the slowly variable pitch segment pitch at Satisfy the following formula:

[0026] , ;

[0027] in, This is the ending wrap angle of the equal pitch segment.

[0028] In addition, the present invention also provides a design method for the above-mentioned high lift coefficient variable pitch inducer, which is characterized by including the following steps:

[0029] Step 1: Calculate the diameter at the hub inlet according to the design specifications of the variable pitch inducer. diameter at the hub outlet Pitch of equal pitch segments The ending wrap angle of the equal pitch segment The final pitch of the gradually changing pitch section The ending wrap angle of the slowly varying pitch segment and the final pitch of the rapid pitch change section ;

[0030] The final pitch of the slowly variable pitch section Determined by the following formula:

[0031] ;

[0032] in, Where n is the induced wheel flow rate, n is the induced wheel speed, and D is the outer diameter of the tip of the helical blade;

[0033] The ending wrap angle of the slowly variable pitch segment Determined by the following formula:

[0034] ;

[0035] Where z is the number of helical blades. The pitch of the equal pitch segment;

[0036] The final pitch of the rapid pitch change section Determined by the following formula:

[0037] ;

[0038] in, The work coefficient, , The diameter at the hub outlet. It is the acceleration due to gravity;

[0039] Step 2: Based on the outer diameter D of the variable pitch inducer and the pitch of the constant pitch segment obtained in Step 1... The final pitch of the gradually changing pitch section diameter at the hub inlet The ending wrap angle of the slowly varying pitch segment and the ending wrap angle of the equal pitch segment Calculate the different wrap angles of the slowly varying pitch segment. The pitch at the point; based on the ending wrap angle of the rapid pitch change segment. And the ending pitch of the rapid variable pitch segment obtained in step 1. The final pitch of the gradually changing pitch section and the ending wrap angle of the slowly varying pitch segment Calculate the different wrap angles of the fast variable pitch segment. The pitch at the point; the different wrap angles of the rapid pitch variable segment. pitch at Satisfy the following formula:

[0040] , ;

[0041] in, The ending wrap angle of the rapid pitch change segment;

[0042] Step 3, based on the diameter at the wheel hub inlet and the diameter at the hub outlet Draw the profile of the wheel hub; based on the pitch of the equal pitch segments... The ending wrap angle of the equal pitch segment The final pitch of the gradually changing pitch section The ending wrap angle of the slowly varying pitch segment Different wrap angles in the gradually changing pitch section The pitch at the point, the final pitch of the rapid pitch change section The ending wrap angle of the rapid pitch segment and different wrap angles in the rapid pitch section Draw the profile of the helical blade at the pitch of the screw;

[0043] Step 4: Prepare the inducer by machining according to the profile of the hub and the helical blade to obtain a variable pitch inducer with a high head coefficient.

[0044] Furthermore, in step 1, the diameter at the hub outlet... Determined by the following formula:

[0045] ;

[0046] in, This is the head of the inducer.

[0047] Furthermore, in step 1, the diameter at the hub inlet... Determined by the following formula:

[0048] ;

[0049] in, This is the correction factor at the hub inlet. .

[0050] Furthermore, in step 2, the different wrap angles of the slowly varying pitch segment... pitch at Satisfy the following formula:

[0051] , ;

[0052] in, This is the ending wrap angle of the equal pitch segment.

[0053] Compared with the prior art, the present invention has the following beneficial technical effects:

[0054] 1. Compared to traditional variable pitch inducers that sequentially set the helical blades into equal pitch, variable pitch, and equal pitch sections along the wrap angle direction, the variable pitch inducer provided by this invention sets the helical blades into equal pitch, slowly variable pitch, and rapidly variable pitch sections along the wrap angle direction. The rapidly variable pitch section realizes the large pitch section, thereby achieving the rearward placement of the high-lift section. This greatly reduces the impact of tip backflow on the blade leading edge under high lift coefficient and effectively improves the cavitation resistance of the blade leading edge.

[0055] 2. This invention provides a design method for a high-lift coefficient variable pitch inducer. For the design of constant pitch, slow pitch change, and rapid pitch change sections, it innovatively proposes a series of parameter calculation formulas, which can quickly and accurately determine the final pitch of the slow pitch change section. End of wrap corner The final pitch of the rapid pitch change segment and different wrap angles in the rapid pitch section pitch at . Attached Figure Description

[0056] Figure 1 This is a schematic diagram of the structure of an embodiment of a variable pitch inducer with a high lift coefficient according to the present invention;

[0057] Figure 2 This is a schematic diagram showing the wrap angle range of the constant pitch segment and the slowly variable pitch segment in an embodiment of the present invention;

[0058] Figure 3 This is a schematic diagram of the wrap angle range of the rapid pitch segment in an embodiment of the present invention;

[0059] Figure 4 This is a schematic diagram showing the change in head reduction ratio of the variable pitch inducer of the present invention and the conventional variable pitch inducer as a function of inlet pressure.

[0060] The annotations in the attached figures are explained as follows:

[0061] 1-Hub, 2-Helical blade, 21-Equal pitch section, 22-Slowly variable pitch section, 23-Rapidly variable pitch section. Detailed Implementation

[0062] To make the objectives, advantages, and features of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0063] like Figure 1 As shown, a high-lift coefficient variable-pitch inducer includes a hub 1 and z helical blades 2 circumferentially evenly arranged on the hub 1. The outer diameter of the blade tips of the helical blades 2 is of equal diameter. The number of helical blades 2 z is usually 2 to 5, and in this embodiment z=3.

[0064] This high-lift-coefficient variable-pitch inducer is mainly suitable for variable-pitch inducers with a lift coefficient ψ ≥ 0.2. Typically, the lift is determined by the outer diameter D of the helical blade 2 at the tip and the head of the inducer. Given the induced wheel speed n, the head coefficient ψ can be calculated, as shown in the following expression:

[0065] ;

[0066] Among them, the outer diameter D of the tip of the helical blade 2 can be determined comprehensively based on design specifications and size limitations, and the head of the inducer is... The known quantity is the inducer speed n, which is determined by the required net positive suction head (NPSH) of the inducer. r NPSH speed C and flow rate Q v The calculated cavitation specific speed C is a set value, such as 4500. This is the acceleration due to gravity.

[0067] If the head coefficient ψ < 0.2, the variable pitch inducer can be designed using traditional methods; if the head coefficient ψ ≥ 0.2, the variable pitch inducer can be designed using the method of this invention.

[0068] In this invention, the helical blade 2 is sequentially configured along the wrap angle direction as a constant pitch section 21, a slowly variable pitch section 22, and a rapidly variable pitch section 23; the pitch on the helical blade 2 gradually increases from the tail end of the constant pitch section 21 to the tail end of the rapidly variable pitch section 23. The rapidly variable pitch section 23 corresponds to the large pitch section, thus achieving a rearward placement of the high-lift section, significantly reducing the impact of tip backflow on the blade leading edge under high lift coefficients, and effectively improving the cavitation resistance of the blade leading edge.

[0069] The design method for the above-mentioned high-lift coefficient variable-pitch inducer specifically includes the following steps:

[0070] Step 1, as follows Figure 2 , Figure 3 As shown, the wrap angle range of the equal pitch segment 21 is defined as [0, ... The wrap angle range of the slowly variable pitch segment 22 is [ , The wrap angle range of the rapid pitch segment 23 is [ , Meanwhile, the outer diameter of the tip of the helical blade 2 is defined as D. The outer diameter of the tip of the helical blade 2, D, is determined comprehensively based on design specifications and dimensional constraints, and is a known quantity.

[0071] Based on the design specifications of the variable pitch inducer, the diameter at the inlet of hub 1 is calculated. Diameter at the outlet of hub 1 The pitch of the equal pitch segment 21 The ending wrap angle of the equal pitch segment 21 The final pitch of the slowly varying pitch section 22 The ending wrap angle of the slowly variable pitch segment 22 and the final pitch of the rapid pitch-changing section 23 .

[0072] Among them, the diameter at the inlet of hub 1 The outer diameter D of the tip of the helical blade 2 is determined by the following expression:

[0073] ;

[0074] in, This is the correction factor at the inlet of hub 1. , Based on the mechanical strength of the supporting spindle of the mounting hub 1 and the reserved installation space at the front end of the inducer, the smaller value within the range is preferred in the engineering design.

[0075] The pitch of the equal pitch segment 21 and the ending wrap angle of the equal pitch segment 21 All of these can be determined using existing methods for equal pitch segments, which will not be elaborated upon here. Meanwhile, the different wrap angles of the equal pitch segment 21... The pitch is the same at all points, and the different wrap angles of the equal pitch segments 21. pitch at , .

[0076] In this invention, the helical blade 2 is sequentially configured along the wrap angle direction as a constant pitch section 21, a slowly variable pitch section 22, and a rapidly variable pitch section 23. The core issue lies in determining the following parameters: (1) the ending pitch and ending wrap angle of the slowly variable pitch section 22; (2) the diameter at the outlet of the hub 1; (3) the ending pitch and ending wrap angle of the rapidly variable pitch section 23; and (4) the different wrap angles of the slowly variable pitch section 22 and the rapidly variable pitch section 23. The pitch at that point.

[0077] For the final pitch of the slowly varying pitch segment 22 induced wheel flow The speed n of the inducer and the outer diameter D of the tip of the helical blade 2 are combined to determine the following expression:

[0078] .

[0079] For the ending wrap angle of the slowly variable pitch segment 22 The pitch of the equal pitch section 21 is adopted. The final pitch of the slowly varying pitch section 22 The outer diameter D of the tip of the helical blade 2 and the number z of the helical blades 2 are combined and the expression is as follows:

[0080] .

[0081] For the diameter at the outlet of hub 1 The parameters used are: inducer head H, inducer speed n, outer diameter of the tip of the helical blade 2 D, and work coefficient. The expression is determined as follows:

[0082] ;

[0083] in, It is the acceleration due to gravity. , Based on the reserved installation space at the rear end of the inducer and the head requirement, the smaller value within the range is preferred in the engineering design.

[0084] For the final pitch of the rapid pitch change segment 23 induced wheel flow The induced wheel speed n, the outer diameter of the tip of the helical blade 2 D, and the diameter at the outlet of the hub 1 are all factors that need to be considered. and work coefficient The expression is determined as follows:

[0085] .

[0086] For the ending wrap angle of the rapid pitch segment 23 It is usually in Based on this, add 40°~80° to the range of values. The overall axial length of the inducer is determined comprehensively, and the larger value within the range is preferred during engineering design.

[0087] Step 2: Determine the different wrap angles for the slow pitch section 22 and the fast pitch section 23. The pitch at that point.

[0088] Slowly variable pitch section 22 with different wrap angles pitch at It satisfies the following formula:

[0089] , ;

[0090] Rapidly variable pitch section 23 with different wrap angles pitch at It satisfies the following formula:

[0091] , .

[0092] Step 3: Draw the profiles of hub 1 and helical blade 2.

[0093] Based on the diameter at the inlet of hub 1 and the diameter at the outlet of hub 1 Draw the profile of hub 1. Simultaneously, based on the pitch of the equal pitch segment 21... The ending wrap angle of the equal pitch segment 21 The final pitch of the slowly varying pitch section 22 The ending wrap angle of the slowly variable pitch segment 22 22 different wrap angles in the slowly varying pitch section The pitch at the point, the ending pitch of the rapid pitch change section 23 The ending wrap angle of the rapid pitch segment 23 And the 23 different wrap angles of the rapid pitch section Draw the profile of helical blade 2 based on the pitch at the specified location.

[0094] Step 4: Based on the obtained profiles of hub 1 and helical blade 2, determine the thickness of helical blade 2 according to the traditional method, and round and grind the leading edge of the inducer to obtain a variable pitch inducer with a high lift coefficient. The specific rounding and grinding methods will not be described in detail.

[0095] The parameters of the high lift coefficient variable pitch inducer designed in this embodiment are shown in Table 1:

[0096] Table 1

[0097]

[0098] Figure 4 The diagram shows the head reduction ratio of the variable pitch inducer of this invention and the conventional variable pitch inducer as a function of inlet pressure. It can be seen that, compared with the conventional variable pitch inducer, the head reduction ratio of the variable pitch inducer of this invention is significantly reduced when the inlet pressure continues to decrease. That is, the improved variable pitch inducer of this invention can operate at a lower inlet pressure, effectively reducing the impact of tip backflow on the blade leading edge under high head coefficient, and improving the cavitation resistance of the blade leading edge.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. A high lift coefficient variable pitch inducer, comprising a hub (1) and a plurality of helical blades (2) circumferentially uniformly arranged on the hub (1), characterized in that: The outer diameter of the tip of the spiral blade (2) is set to be constant; the spiral blade (2) is set to a constant pitch section (21), a slowly variable pitch section (22) and a rapidly variable pitch section (23) in sequence along the wrap angle direction; the pitch of the spiral blade (2) gradually increases from the tail end of the constant pitch section (21) to the tail end of the rapidly variable pitch section (23). The final pitch of the slowly variable pitch section (22) Determined by the following formula: ； in, The flow rate of the induction wheel is n, the rotational speed of the induction wheel is n, and the outer diameter of the tip of the helical blade (2) is D. The ending wrap angle of the slowly variable pitch segment (22) Determined by the following formula: ； Where z is the number of helical blades (2), The pitch of the equal pitch segment (21); The final pitch of the rapid pitch-changing section (23) Determined by the following formula: ； in, The work coefficient, , The diameter at the outlet of the hub (1) It is the acceleration due to gravity; The fast variable pitch section (23) has different wrap angles. pitch at Satisfy the following formula: ， ； in, For the ending wrap angle of the rapid pitch segment (23), , =40°~80°.

2. The variable pitch inducer with high head coefficient according to claim 1, characterized in that: The diameter at the outlet of the hub (1) Determined by the following formula: ； in, This is the head of the inducer.

3. The variable pitch inducer with high head coefficient according to claim 2, characterized in that: The diameter at the inlet of the hub (1) Determined by the following formula: ； in, The correction factor at the inlet of the hub (1) is... .

4. A variable pitch inducer with a high lift coefficient according to any one of claims 1-3, characterized in that: The slowly variable pitch segment (22) has different wrap angles. pitch at Satisfy the following formula: ， ； in, This is the ending wrap angle of the equal pitch segment (21).

5. A design method for a high-lift coefficient variable-pitch inducer as described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Calculate the diameter at the inlet of the hub (1) according to the design specifications of the variable pitch inducer. , diameter at the outlet of the hub (1) The pitch of the equal pitch segment (21) The ending wrap angle of the equal pitch segment (21) The final pitch of the slowly varying pitch segment (22) The ending wrap angle of the slowly variable pitch segment (22) and the final pitch of the rapid pitch-changing section (23) ; The final pitch of the slowly variable pitch section (22) Determined by the following formula: ； in, The flow rate of the induction wheel is n, the rotational speed of the induction wheel is n, and the outer diameter of the tip of the helical blade (2) is D. The ending wrap angle of the slowly variable pitch segment (22) Determined by the following formula: ； Where z is the number of helical blades (2), The pitch of the equal pitch segment (21); The final pitch of the rapid pitch-changing section (23) Determined by the following formula: ； in, The work coefficient, , The diameter at the outlet of the hub (1) It is the acceleration due to gravity; Step 2, based on the outer diameter D of the variable pitch inducer and the pitch of the constant pitch segment (21) obtained in Step 1. The final pitch of the slowly varying pitch segment (22) , diameter at the inlet of the hub (1) The ending wrap angle of the slowly variable pitch segment (22) and the ending wrap angle of the equal pitch segment (21) Calculate the different wrap angles of the slowly variable pitch segment (22). The pitch at the point; based on the ending wrap angle of the rapid pitch segment (23). and the ending pitch of the rapid variable pitch segment (23) obtained in step 1. The final pitch of the slowly varying pitch segment (22) and the ending wrap angle of the slowly variable pitch segment (22) Calculate the different wrap angles of the rapid variable pitch segment (23). The pitch at the point; the different wrap angles of the rapid variable pitch segment (23). pitch at Satisfy the following formula: ， ； in, The ending wrap angle of the rapid pitch segment (23); Step 3, based on the diameter at the inlet of the hub (1) and the diameter at the outlet of the hub (1) Draw the profile of the hub (1); based on the pitch of the equal pitch segment (21) The ending wrap angle of the equal pitch segment (21) The final pitch of the slowly varying pitch segment (22) The ending wrap angle of the slowly variable pitch segment (22) , Slowly variable pitch segment (22) with different wrap angles The pitch at the point, the final pitch of the rapid pitch change section (23) The ending wrap angle of the rapid variable pitch segment (23) And the different wrap angles of the rapid variable pitch section (23) Draw the profile of the helical blade (2) based on the pitch at the location; Step 4: Prepare an inducer by machining the profile of the hub (1) and the helical blade (2) to obtain a variable pitch inducer with a high lift coefficient.

6. The design method of the high head coefficient variable pitch inducer according to claim 5, characterized in that: In step 1, the diameter at the outlet of the hub (1) Determined by the following formula: ； in, This is the head of the inducer.

7. The design method of the high head coefficient variable pitch inducer according to claim 6, characterized in that: In step 1, the diameter at the inlet of the hub (1) Determined by the following formula: ； in, The correction factor at the inlet of the hub (1) is... .

8. The design method of the high head coefficient variable pitch inducer according to claim 7, characterized in that: In step 2, the slowly variable pitch segment (22) has different wrap angles. pitch at Satisfy the following formula: ， ； in, This is the ending wrap angle of the equal pitch segment (21).

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