Axial force balance flow path for multistage hydrogen turbine pump of liquid rocket engine

Abstract

The invention provides an axial force balance flow path for a multistage hydrogen turbine pump of a liquid rocket engine. Comprising a balance piston gap, a floating ring gap, a third-stage impeller backflow hole, a shaft diameter hole, a backflow groove, an axis hole, a second-stage impeller backflow hole I, a second-stage impeller backflow hole II, a first-stage impeller backflow hole, a pump end bearing rear sealing gap, a front sealing gap, a first-stage and second-stage rear sealing gap, a third-stage rear sealing gap and an inter-stage sealing gap. According to the downstream containing cavity of the balance piston, backflow grooves are formed in the shaft and the impeller, backflow holes of the second-stage impeller and the third-stage impeller are formed in the shaft and the impeller, water is directly drained to an inlet of the second-stage impeller, the balance capacity of the balance piston is improved in a large range, and the balance piston is suitable for axial force balance of a large hydrogen turbine pump of a high-thrust afterburning circulating liquid rocket engine.

Description

Technical Field

[0001] The invention relates to an axial force balancing flow path for a liquid rocket engine turbopump, and is particularly suitable for a multi-stage turbopump structure of a large thrust regenerative cycle cryogenic liquid rocket engine, belonging to the technical field of axial force balancing of cryogenic rocket engine turbopumps. Background Art

[0002] Since the beginning of the 21st century, the world's major space powers have proposed manned Mars and deep space exploration plans. High-thrust rockets are indispensable means of transportation, and high-pressure, high-flow turbopumps are one of the core components of high-thrust, cryogenic liquid rocket engines. Ensuring that the rotor can achieve automatic axial force balance is crucial to the reliability, life and reusability of the turbopump in a high-thrust liquid rocket engine. Whether the axial force can be automatically balanced can even affect the success or failure of the entire engine. With the substantial increase in engine thrust, the turbopump speed, shaft diameter and pressure have also increased significantly, resulting in very large axial forces in the turbopump, even up to hundreds of tons.

[0003] The balance piston of a multistage centrifugal pump usually returns the fluid to the impeller of this stage. The high-pressure, high-flow multistage centrifugal pump and high-pressure, high-flow turbine used in the high-thrust engine liquid hydrogen turbine pump cannot meet the axial force balance requirements because the turbine generates a large axial force pointing to the pump end. The balance flow path from the balance piston to the inlet of the third-stage impeller cannot meet the axial force balance requirements; the conventional civilian multistage pump is drained to the pump inlet through an external lead pipe. The high-pressure liquid hydrogen turbine pump of a rocket engine is greatly affected by the temperature because the liquid hydrogen state has a great influence on the performance of the hydrogen turbine pump. The external lead flow path will greatly increase the risk of normal and stable operation of the hydrogen turbine pump. Therefore, in order to ensure the normal start-up and stable operation of the hydrogen turbine pump, to balance the unbalanced axial force generated by the various components of the rotor, and to avoid damage to the turbine rotor structure and bearings by excessive axial force, it is necessary to design a balance flow path that can meet the automatic balancing requirements of the axial force of the high-pressure, high-flow hydrogen turbine pump. Therefore, an axial force balancing flow path for a high-thrust liquid rocket engine hydrogen turbine pump is invented. Summary of the invention

[0004] The technical problem solved by the present invention is: in order to balance the large unbalanced axial force generated by a high-pressure and large-flow hydrogen turbopump, an axial force balancing flow path is proposed, which can meet the axial force balance and working safety and reliability requirements of a high-thrust liquid rocket engine hydrogen turbopump.

[0005] The technical solution of the present invention is: an axial force balance flow path of a multi-stage hydrogen turbine pump for a liquid rocket engine, comprising: a balance piston gap, a floating ring gap, a third-stage impeller reflow hole, an axial diameter hole, a reflow groove, an axial center hole, a second-stage impeller reflow hole I, a second-stage impeller reflow hole II, a first-stage impeller reflow hole, a pump end bearing rear seal gap, a front seal gap, a first and second-stage rear seal gap, a third-stage rear seal gap and an inter-stage seal gap;

[0006] Reflow grooves are arranged at the splines of the rotating shaft, the secondary impeller and the tertiary impeller, and the reflow grooves and the spline teeth are alternately distributed; the downstream of the balance piston gap is connected to the secondary impeller inlet through the tertiary impeller reflow hole, the reflow groove and the secondary reflow hole II; a floating ring is arranged between the downstream volume of the balance piston gap and the bearing cavity, and the flow entering the tertiary reflow hole and the reflow groove channel is reduced through the floating ring gap, and the tertiary impeller reflow hole is arranged at the tertiary impeller hub; the interstage sealing gap is composed of a straight-through labyrinth seal and a straight-through impeller hub; the front sealing gap adopts a multi- The first and second stage rear sealing gaps are composed of single-stage multi-tooth labyrinth seals and single-stage step shoulders, and the third stage rear sealing gaps are composed of straight-through labyrinth seals and straight-through shoulders; the second-stage impeller is simultaneously provided with a second-stage reflux hole I and a second-stage reflux hole II, which are staggered and do not intersect or intersect with each other; an axial diameter hole, an axial center hole and a rear sealing gap of the pump end bearing are arranged on the rotating shaft to connect the downstream of the balancing piston cavity with the inlet of the first-stage impeller, and the axial diameter hole is located at the installation position of the third-stage impeller to connect the reflux groove and the axial center hole.

[0007] Preferably, the three-stage impeller reflow hole is respectively connected with the shaft diameter hole, the reflow groove and the two-stage impeller reflow hole II, the cross-sectional area of ​​the three-stage impeller reflow hole is recorded as A1, the cross-sectional area of ​​the reflow groove is recorded as A2, and the cross-sectional area of ​​the two-stage impeller reflow hole I is recorded as A4; it is ensured that the reflow path areas A1, A2, and A4 are all larger than the flow area A0 of the sealing gap behind the three-stage impeller.

[0008] Preferably, the groove width L2, groove depth H1, groove length L4 of the reflux groove on the shaft and the groove depth H2 of the reflux groove on the impeller satisfy: groove width L2≯L3, groove depth H1≯0.1R S , the radius of the fillet of the reflux groove bottom R≮1mm, the depth of the reflux groove H2≯the height of the spline tooth of the impeller, the groove length L4 is as short as possible under the premise of ensuring smooth connection between the secondary impeller reflux hole II and the tertiary impeller reflux hole, the maximum width between the spline groove bottoms on both sides of the spline tooth is recorded as L3, R S is the radius of the rotating shaft.

[0009] Preferably, the axial diameter hole area A3 satisfies A3<0.5×A7, and A7 is the minimum cross-sectional area of ​​the axial center hole.

[0010] Preferably, the unilateral radial dimension X1 of the front sealing gap, the unilateral radial dimension X2 of the first and second stage rear sealing gaps, the unilateral radial dimension X3 of the third stage rear sealing gap, the radial dimension X4 of the inter-stage sealing gap, and the pump end bearing rear sealing gap X6 are less than 1 mm, and should be as small as possible while ensuring safety.

[0011] Preferably, the number of steps and the number of sealing chambers of the front sealing gap, the number of sealing chambers of the first and second stage rear sealing gaps, and the number of sealing chambers of the third stage rear sealing gap should all be ≮4; the step height of the front sealing gap is 3 to 5 mm; the outlet diameter dimension D3 of the first and second stage rear sealing gaps and the outlet diameter dimension D4 of the third stage rear sealing gap are less than 0.5 mm different from the diameters of the first and second stage impellers and the third stage impeller, respectively.

[0012] Preferably, the axial length L1 of the balance piston gap is not greater than 4 mm, and the flow area Am when L1 is at the maximum working gap should be smaller than the flow area A0 of the three-stage rear sealing gap and Am should always be the minimum flow area of ​​the flow path.

[0013] Preferably, the third-stage impeller reflow hole area A1, the reflow groove area A2, and the secondary impeller reflow hole II area A5 should all be larger than the flow area A0 of the third-stage rear sealing gap, i.e., to ensure that the secondary impeller reflow hole II, the third-stage impeller reflow hole and the reflow groove should not be the throttling part of the flow path.

[0014] Preferably, the area A4 of the secondary impeller recirculation hole I, the area A6 of the primary impeller recirculation hole, the single-sided radial dimension X2 of the primary and secondary rear sealing gaps, and the balance piston gap outlet diameter D1 should satisfy A4≮X2×D1×π, A6≮X2×D1×π, to ensure the smooth flow path of the recirculation and the structural strength requirements.

[0015] Preferably, when the balancing piston gap size L1 decreases, the axial force pointing to the pump end increases; when L1 increases, the axial force pointing to the pump end decreases; the balance position of the axial force under rated operating conditions is determined to be close to the middle position of the balance range.

[0016] The beneficial effects of the present invention compared with the prior art are:

[0017] (1) The downstream chamber of the balancing piston is directly drained to the inlet of the second-stage impeller by arranging reflux grooves on the shaft and impeller and reflux holes of the second and third-stage impellers, thereby greatly improving the balancing ability of the balancing piston and being suitable for axial force balancing of large hydrogen turbine pumps in large-thrust regenerative cycle liquid rocket engines.

[0018] (2) A floating ring seal is provided between the downstream of the balancing piston cavity and the vortex end bearing cavity, which can effectively reduce the reflux flow downstream of the balancing piston.

[0019] (3) The front sealing gap adopts a multi-stage stepped sealing form, the first and second stage rear sealing gaps adopt a single-step sealing throttling form, and the third stage rear seal adopts a straight-through sealing structure. The combination of these three forms can appropriately reduce the leakage amount. At the same time, it can effectively reduce the risk of sudden changes in the sealing gap due to abnormal axial movement of the rotor, which in turn leads to the failure of the axial force balancing device, thereby improving the working safety and reliability of the turbine pump.

[0020] (4) The two types of reflow holes of the secondary impeller are staggered, and the reflow path behind the secondary impeller and the reflow path downstream of the balance piston do not affect each other, ensuring that the flow path downstream of the balance piston cavity is unobstructed.

[0021] (5) By setting an axial diameter hole and an axial center hole on the shaft and connecting the balance piston rear chamber with the first-stage impeller inlet through a sealing gap behind the pump end bearing, the reflux area requirement of the shaft and the second-stage impeller reflux groove can be appropriately reduced and can be used to cool the bearing.

[0022] (6) The designed balancing flow path has been verified through experiments to be able to meet the rotor axial force balance requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of axial force balance flow path;

[0024] Figure 2 Schematic diagram of balanced piston clearance;

[0025] Figure 3 Schematic diagram of the reflow tank;

[0026] Figure 4 Schematic diagram of floating ring gap;

[0027] Figure 5 Schematic diagram of the front seal gap;

[0028] Figure 6 Schematic diagram of the sealing gap after the first and second levels;

[0029] Figure 7 Schematic diagram of the sealing gap after the third stage;

[0030] Figure 8 Schematic diagram of interstage sealing gap;

[0031] Fig. 9 Schematic diagram of the seal clearance behind the pump end bearing.

[0032] Among them, 1. Balance piston clearance; 2. Floating ring clearance; 3. Third-stage impeller reflow hole; 4. Shaft diameter hole; 5. Reflow groove; 6. Axial hole; 7. Second-stage impeller reflow hole I; 8. Second-stage impeller reflow hole II; 9. Interstage sealing clearance; 10. First-stage impeller reflow hole; 11. Pump end bearing rear sealing clearance; 12. Front sealing clearance; 13. First and second stage rear sealing clearance; 14. Third stage rear sealing clearance; 15. Balance piston cavity. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the embodiments.

[0034] The main components of a high-thrust liquid rocket engine hydrogen turbopump include bearings, shafts, multi-stage impellers, dynamic seals, and related housings. The multi-stage impeller is connected to the shaft through a spline. When the turbopump is working, the shaft drives the impeller to rotate at high speed to do work on the fluid, which can pressurize the fluid to tens of megapascals. The fluid reacts on the impeller to form a huge axial force, which can instantly damage the bearing and cause the turbopump to fail to work properly. Therefore, it is necessary to specifically design an axial force balance flow path suitable for a high-thrust liquid rocket engine hydrogen turbopump.

[0035] like Figure 1 As shown, an axial force balancing flow path for a large-thrust liquid rocket engine hydrogen turbo pump, the flow path mainly consists of a balancing piston gap 1, a floating ring gap 2, a third-stage impeller reflux hole 3, an axial diameter hole 4, a reflux groove 5, an axial center hole 6, a second-stage impeller reflux hole I7, a second-stage impeller reflux hole II8, a first-stage impeller reflux hole 10, a pump end bearing rear seal gap 11, a front seal gap 12, a first and second-stage rear seal gap 13, a third-stage rear seal gap 14 and an interstage seal gap 9. For details, see the attached Figure 1 .

[0036] like Figure 2-9As shown in the figure, in the designed axial force automatic balancing flow path, the impeller front sealing gap is composed of a multi-stage stepped labyrinth structure and a multi-stage stepped shoulder, and the minimum single-sided radial dimension of the gap is recorded as X1; the first and second stage rear sealing gaps are composed of a single-stage multi-tooth labyrinth structure and a single-stage stepped shoulder, and the minimum single-sided radial dimension of the gap is recorded as X2, and the diameter dimension of the shoulder at the gap outlet is recorded as D1; ​​the third stage impeller rear sealing gap is composed of a straight-through labyrinth seal and a straight-through shoulder, and the minimum single-sided radial dimension of the gap is recorded as X3, and the diameter dimension of the shoulder at the gap outlet is recorded as The gap is D2, and the flow area of ​​the gap is recorded as A0; the interstage sealing gap is composed of a straight-through labyrinth seal and a straight-through impeller hub, and the minimum single-sided radial dimension of the gap is recorded as X4; the axial length of the balance piston gap is recorded as L1, the radial length is recorded as S, and its outlet diameter size is recorded as D3; the three-stage impeller reflow hole is set at the three-stage impeller hub, connecting the rear cavity of the balance piston gap and the reflow groove, the number of the reflow holes is recorded as N1, and the area of ​​the reflow holes is recorded as A1; the reflow groove is set at the shaft spline and the impeller spline, the number of the reflow groove is recorded as N2, and the area of ​​the reflow groove is recorded as A1. The maximum width between the spline groove bottoms on both sides of the spline teeth is recorded as L3, the length of the reflow groove is recorded as L4, the depth of the reflow groove on the shaft is recorded as H1, and the depth of the reflow groove on the impeller is recorded as H2; the shaft diameter hole is set on the rotating shaft near the installation position of the third-stage impeller, connecting the reflow groove and the axial hole, the number of shaft diameter holes is recorded as N3, and the area of ​​the shaft diameter hole is recorded as A3; the radial dimension of the floating ring gap on one side is recorded as X5; the secondary impeller reflow hole I is set at the secondary impeller hub, connecting the reflow groove and the secondary impeller inlet, the number of the reflow hole is recorded as N4, and the reflow The hole area is recorded as A4; the secondary impeller reflow hole II is also arranged at the secondary impeller hub, and is staggered with the secondary impeller reflow hole I, connecting the rear cavity of the secondary impeller rear seal gap and the secondary impeller inlet. The number of reflow holes is recorded as N5, and the reflow hole area is recorded as A5; the primary impeller reflow hole is arranged at the primary impeller hub, connecting the rear cavity of the primary impeller rear seal radial gap and the primary impeller inlet. The number of reflow holes is recorded as N6, and the reflow hole area is recorded as A6; the rear seal gap of the pump end bearing is composed of the pump casing and the impeller hub, and the single-sided radial dimension is recorded as X6.

[0037] The unilateral radial dimension X1 of the front seal gap, the unilateral radial dimension X2 of the first and second stage rear seal gap, the unilateral radial dimension X3 of the third stage rear seal gap, the unilateral radial dimension X4 of the interstage seal gap and the unilateral radial dimension X6 of the pump end bearing rear seal gap should be as small as possible and less than 1mm under the premise of ensuring safety; the number of steps and sealing chambers of the front seal gap and the number of sealing chambers of the first and second stage rear seal gaps and the third stage rear seal gap can be determined according to the axial space of the turbine pump, generally should be ≮4, and the step height is generally 3-5mm; the diameter D1 of the second stage rear seal gap and the diameter D2 of the third stage rear seal gap should be as small as possible and less than 1mm; the diameter D2 of the third stage rear seal gap and the diameter D3 of the second stage rear seal gap should be as small as possible and less than 1mm; the diameter D4 of the third stage rear seal gap and the diameter D5 of the second stage rear seal gap should be as small as possible and less than 1mm; the diameter D5 of the third stage rear seal gap and the diameter D6 of the second stage rear seal gap should be as small as possible and less than 1mm; the diameter D6 of the third stage rear seal gap and the diameter D7 of the second stage rear seal gap should be as small as possible and less than 1mm; the diameter D7 of the third stage rear seal gap and the diameter D8 of the second stage rear seal gap should be as small as possible and less than 1mm; the diameter D8 of the third stage rear seal gap and the diameter D9 of the second stage rear seal gap should be as small as possible and less than 1mm; the diameter D9 of the third stage rear seal gap and the diameter D1 of the second stage rear seal gap should be as small as possible and less than 1mm; the diameter D1 of the third stage rear seal gap and the diameter D1 of the second stage rear seal gap should be as small as possible and less than 1mm; the diameter D1 of the third stage rear seal gap and the diameter D2 of The diameter D2 of the sealing gap after the stage should be equivalent to the impeller diameter under the premise of ensuring the installability of the structure; the axial length L1, radial length S, diameter D3 and flow area Am of the balancing piston gap, the number N1 and area A1 of the third-stage impeller reflow holes, the number N2, length L2, area A2 of the reflow grooves, the number N3 and area A3 of the axial diameter holes, the number N4 and area A4 of the second-stage impeller reflow holes I, the above data must be determined according to the axial force balance range required by the rotor, and the balancing capacity of the balancing piston can be adjusted by adjusting the outlet diameter D1 of the balancing piston gap. The working range of L1 is usually not more than 4mm. When L1 is at the maximum working gap, the flow area Am should be less than A0, and Am should always be the minimum flow area of ​​the flow path; A1, A2 and A5 should all be greater than A0, that is, it should be ensured that the reflow hole and the reflow groove should not be the throttling part of the flow path; the balancing capacity range of the balancing piston can be appropriately adjusted by appropriately adjusting the outlet diameter D3 of the balancing piston gap; the number of reflow grooves N2, the groove width L2, the groove depth H1 and H2, and the groove length L4 also need to consider the structural strength of the shaft and impeller, and the number of reflow grooves N2 is required to be consistent with the number of reflow holes N1 of the three-stage impeller, the groove width L2≯L3, and H1≯0.1R S (shaft radius), groove bottom fillet radius R≮1mm, groove depth H2≯(D ei -D ii )(internal spline tooth height), the groove length L4 should be shortened as much as possible under the premise of ensuring smooth connection between the secondary return hole II and the tertiary return hole, so as to reduce the loss of shaft strength safety margin.

[0038] The front sealing gap of the present invention is composed of a multi-stage stepped labyrinth seal and a multi-stage stepped shoulder, the first and second stage rear sealing gaps are composed of a single-stage stepped labyrinth seal and a single-stage stepped shoulder, and the third stage rear sealing gap is composed of a straight-through labyrinth seal and a straight-through shoulder seal. The combination of these three forms can reduce the impeller reflux loss to a certain extent, and at the same time improve the risk resistance when the rotor axial movement is excessive and the balanced flow path deteriorates.

[0039] The reflux holes of the third-stage impeller should be connected to the shaft diameter hole, reflux groove and the reflux holes II of the second-stage impeller respectively, and the reflux path areas A1, A2 and A4 should be larger than the flow area A0 of the third-stage rear seal gap; at the same time, the reflux groove dimensions L2, H1, H2, L4 and the number N2 should also ensure that the shaft and impeller structural strength have sufficient safety margins; the shaft diameter hole area A3 should satisfy A3<0.5×A7, A7 is the minimum cross-sectional area of ​​the axial hole. The area A4 and number N4 of the second-stage impeller reflux holes I, the area A5 and the number N5 of the first-stage impeller reflux holes should ensure smooth reflux of the flow path of the first and second-stage rear seal gaps. The reflux hole area A1, the reflux groove area A2 and the reflux hole II area A5 of the third-stage impeller should all be larger than the flow area A0 of the third-stage rear seal gap, that is, to ensure that the second-stage impeller reflux hole II, the third-stage impeller reflux hole and the reflux groove should not be the throttling parts of the flow path.

[0040] The number N4 and area A4 of the secondary reflow holes I, and the number N6 and area A6 of the first-stage impeller reflow holes, should satisfy A4≮X2×D1×π, A6≮X2×D1×π, to ensure the smoothness of the reflow path and the structural strength requirements; the secondary impeller reflow holes II and III should be staggered and cannot intersect or intersect, and the structural strength of the secondary impeller and the uniformity of the reflow path should be ensured.

[0041] For the above-mentioned axial force balancing flow path with determined design dimensions, when the balancing piston gap dimension L1 decreases, the axial force pointing to the pump end increases; when L1 increases, the axial force pointing to the pump end decreases; usually, under rated operating conditions, the axial force balance position is determined to be close to the middle position of the balance range, that is, L1 is 2mm. The response speed of the balancing device at this position is faster, the safety is higher, and the volume loss is relatively small.

[0042] After the liquid hydrogen passes through each level of impeller, except for most of it entering the next level of flow channel, a part of it flows back to the impeller inlet through the impeller front sealing gap, and another part of the liquid hydrogen at the first level impeller outlet flows back to the first level impeller inlet through the first and second level rear sealing gaps of the first level impeller rear seal and the first level impeller reflux hole; another part of the liquid hydrogen at the second level impeller outlet flows back to the second level impeller inlet through the first and second level rear sealing gaps of the second level impeller rear seal and the second level impeller reflux hole I; another part of the liquid hydrogen at the third level impeller outlet flows through the third level rear sealing gap of the third level impeller rear seal, the balance piston gap, and the third level impeller reflux hole in sequence, and then is divided into two paths, one path passes through the reflux groove and the second level impeller reflux hole II, and finally flows back to the second level impeller inlet, and the other path passes through the shaft diameter hole, the axial center hole and the pump end bearing rear sealing gap and finally flows back to the first level impeller inlet; the front part of the second and third level impellers flows back to the front of the first and second level impellers through the first and second level interstage sealing gaps, the first level impeller reflux hole and the second level impeller reflux hole I respectively.

[0043] Since the axial force balance flow path of conventional multi-stage pumps is usually that the backflow after the impeller is all led to the inlet of the impeller of this stage through the impeller return hole, and the shaft and the hub are not provided with a return groove, but the high-pressure, large-flow, and large-size turbine generates a large axial force pointing to the pump end, it is necessary to reduce the axial force of the balance piston pointing to the pump end accordingly, and the liquid hydrogen after the balance piston refluxes to the inlet of the third-stage impeller cannot generate a pressure that meets the axial force balance requirement, so the balance piston outlet must be connected to a lower pressure cavity. According to the axial force calculation, the liquid hydrogen after the balance piston needs to be refluxed to the inlet of the second-stage impeller. Considering the safety of the overall structure of the turbine pump, this is achieved by setting a return groove on the shaft and the impeller; the present invention takes into account the structural strength of the shaft and the impeller and the volumetric efficiency of the centrifugal pump. The balance flow path can achieve the large-range axial force balance requirements of the high-pressure, large-flow, and large-size liquid hydrogen turbine pump, and provide important support for the normal operation of the high-pressure and large-flow liquid hydrogen turbine pump.

[0044] Parts not described in detail in the present invention belong to common knowledge of those skilled in the art.

Claims

1. An axial force balance flow path for a multi-stage hydrogen turbine pump for a liquid rocket engine, characterized in that: include: Balance piston clearance, floating ring clearance, third-stage impeller reflow hole, shaft diameter hole, reflow groove, axial center hole, second-stage impeller reflow hole I, second-stage impeller reflow hole II, first-stage impeller reflow hole, pump end bearing rear seal clearance, front seal clearance, first and second stage rear seal clearance, third stage rear seal clearance and interstage seal clearance; Reflow grooves are arranged at the splines of the rotating shaft, the secondary impeller and the tertiary impeller, and the reflow grooves and the spline teeth are alternately distributed; the downstream of the balance piston gap is connected to the secondary impeller inlet through the tertiary impeller reflow hole, the reflow groove and the secondary reflow hole II; a floating ring is arranged between the downstream volume of the balance piston gap and the bearing cavity, and the flow entering the tertiary reflow hole and the reflow groove channel is reduced through the floating ring gap, and the tertiary impeller reflow hole is arranged at the tertiary impeller hub; the interstage sealing gap is composed of a straight-through labyrinth seal and a straight-through impeller hub; the front sealing gap adopts a multi- The first and second stage rear sealing gaps are composed of single-stage multi-tooth labyrinth seals and single-stage step shoulders, and the third stage rear sealing gaps are composed of straight-through labyrinth seals and straight-through shoulders; the second-stage impeller is simultaneously provided with a second-stage reflux hole I and a second-stage reflux hole II, which are staggered and do not intersect or intersect with each other; an axial diameter hole, an axial center hole and a rear sealing gap of the pump end bearing are arranged on the rotating shaft to connect the downstream of the balancing piston cavity with the inlet of the first-stage impeller, and the axial diameter hole is located at the installation position of the third-stage impeller to connect the reflux groove and the axial center hole.

2. The axial force balance flow path of a multi-stage hydrogen turbine pump for a liquid rocket engine according to claim 1, characterized in that: The three-stage impeller reflow hole is respectively connected with the shaft diameter hole, the reflow groove and the two-stage impeller reflow hole II. The cross-sectional area of ​​the three-stage impeller reflow hole is recorded as A1, the cross-sectional area of ​​the reflow groove is recorded as A2, and the cross-sectional area of ​​the two-stage impeller reflow hole I is recorded as A4. It is ensured that the reflow path areas A1, A2, and A4 are all larger than the flow area A0 of the sealing gap behind the three-stage impeller.

3. The axial force balance flow path of a multi-stage hydrogen turbine pump for a liquid rocket engine according to claim 1, characterized in that: The groove width L2, groove depth H1, groove length L4 of the reflux groove on the shaft and the groove depth H2 of the reflux groove on the impeller satisfy: groove width L2≯L3, groove depth H1≯0.1R S , the radius of the fillet of the reflux groove bottom R≮1mm, the depth of the reflux groove H2≯the height of the spline teeth of the impeller, the groove length L4 is as short as possible under the premise of ensuring smooth connection between the secondary impeller reflux hole II and the tertiary impeller reflux hole, L3 is the maximum width between the spline groove bottoms on both sides of the spline teeth, R S is the radius of the rotation axis.

4. The axial force balance flow path of a multi-stage hydrogen turbine pump for a liquid rocket engine according to claim 1, characterized in that: The axial diameter hole area A3 satisfies A3<0.5×A7, and A7 is the minimum cross-sectional area of ​​the axial center hole.

5. The axial force balance flow path of a multi-stage hydrogen turbine pump for a liquid rocket engine according to claim 1, characterized in that: The unilateral radial dimension X1 of the front seal gap, the unilateral radial dimension X2 of the first and second stage rear seal gap, the unilateral radial dimension X3 of the third stage rear seal gap, the radial dimension X4 of the interstage seal gap, and the pump end bearing rear seal gap X6 are less than 1 mm and should be as small as possible while ensuring safety.

6. The axial force balance flow path of a multi-stage hydrogen turbine pump for a liquid rocket engine according to claim 1, characterized in that: The number of steps and the number of sealing chambers of the front sealing gap, the number of sealing chambers of the first and second stage rear sealing gaps, and the number of sealing chambers of the third stage rear sealing gap should all be ≮4; the step height of the front sealing gap should be as small as possible while ensuring no collision or wear; the outlet diameter dimension D3 of the first and second stage rear sealing gaps and the outlet diameter dimension D4 of the third stage rear sealing gap should be as small as possible with the diameter difference of the first and second stage impellers and the third stage impeller respectively while ensuring no collision or wear.

7. The axial force balance flow path of a multi-stage hydrogen turbine pump for a liquid rocket engine according to claim 1, characterized in that: The axial length L1 of the balance piston gap is not greater than 4 mm. When L1 is at the maximum working gap, the flow area Am should be smaller than the flow area A0 of the three-stage rear sealing gap and Am should always be the minimum flow area of ​​the flow path.

8. The axial force balance flow path of a multi-stage hydrogen turbine pump for a liquid rocket engine according to claim 1, characterized in that: The third-stage impeller reflow hole area A1, the reflow groove area A2, and the second-stage impeller reflow hole II area A5 should all be larger than the flow area A0 of the third-stage rear sealing gap, that is, to ensure that the second-stage impeller reflow hole II, the third-stage impeller reflow hole and the reflow groove should not be the throttling part of the flow path.

9. The axial force balance flow path of a multi-stage hydrogen turbine pump for a liquid rocket engine according to claim 1, characterized in that: The area A4 of the secondary impeller recirculation hole I, the area A6 of the primary impeller recirculation hole, the radial dimension X2 of the primary and secondary rear sealing gaps, and the balance piston gap outlet diameter D1 should satisfy A4≮X2×D1×π, A6≮X2×D1×π to ensure smooth recirculation flow and structural strength requirements.

10. The axial force balance flow path of a multi-stage hydrogen turbine pump for a liquid rocket engine according to claim 1, characterized in that: When the balance piston gap size L1 decreases, the axial force pointing to the pump end increases; when L1 increases, the axial force pointing to the pump end decreases; the balance position of the axial force under rated working conditions is determined to be close to the middle position of the balance range.

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