Impact turbine spray needle and manufacturing method

Abstract

The invention discloses an impulse turbine spray needle and a manufacturing method, the impulse turbine spray needle comprises a spray needle body (4), the head of the spray needle body (4) is a conical contraction section; the micro groove array (2) is arranged on the whole outer wall surface of the conical contraction section; wherein the extension direction of the micro-groove array (2) is consistent with the generatrix direction of the surface of the contraction section of the spray needle body (4), and the cross section of the micro-groove array (2) is triangular. The micro-groove array (2) is located in a spray needle contraction section area of the nozzle, the groove spacing is 203 microns, the depth is 0.75 times of the spacing, and the cross section is triangular. The structure uses a sharkskin resistance reduction mechanism for reference, and by inhibiting near-wall turbulence, delaying boundary layer separation and reducing air entrainment, the jet energy density is improved by 10%-20%, and the turbulence energy is reduced by 15%-25%. The design method comprises the steps that the size of the micro-groove is determined based on working condition parameters, and a groove entity is generated through a three-dimensional modeling method. The invention is suitable for the impulse turbine, is especially suitable for variable working condition operation, and has the advantages of reliable structure, high manufacturing compatibility and the like.

Description

Technical Field

[0001] This application relates to the field of hydropower equipment technology, and in particular to an impact turbine nozzle and its manufacturing method. Background Technology

[0002] An impulse turbine is a hydraulic prime mover that converts water energy into mechanical energy by using a special guide vane mechanism to draw a free jet with kinetic energy towards the runner's buckets, causing the runner to rotate and perform work. Its performance is highly dependent on the quality of the jet produced by the nozzle. Traditional nozzles typically have smooth surfaces or macroscopic streamlined designs. When high-pressure water accelerates rapidly within the nozzle, the boundary layer on the surface develops and is prone to separation, leading to large-scale turbulence and vortices. This causes the jet to rapidly diverge after leaving the nozzle, mixing violently with air, resulting in a decrease in energy density (approximately 15%–30%), a reduction in the momentum effectively impacting the runner, and the induction of cavitation and vibration. To address the jet divergence problem, existing technologies mainly attempt to address the following aspects:

[0003] Optimizing the macroscopic profile: This method improves the velocity distribution and reduces flow separation by modifying the curve equation of the nozzle contraction section. However, this method is extremely sensitive to machining accuracy, its effectiveness is unstable under varying operating conditions, and its ability to suppress separated turbulence is limited.

[0004] Adding guide vanes or flow stabilizers: Guide vanes are installed in the flow channel to guide the water flow. However, this introduces new solid wall boundaries and flow bypass problems, increases additional hydraulic losses, and makes the structure complex and prone to cavitation and clogging.

[0005] Improving surface finish: Precision polishing reduces surface roughness to decrease frictional resistance. However, its effect on suppressing boundary layer separation and turbulence is negligible, and it cannot solve the fundamental problem of jet mixing with air.

[0006] Therefore, there is an urgent need for a new method that can effectively suppress turbulence and stabilize the boundary layer at the micro-flow level without introducing additional structural resistance, so as to fundamentally improve the jet quality and operating efficiency of impulse turbines. Summary of the Invention

[0007] In order to solve the technical problems existing in the background art, the present invention proposes an impact turbine nozzle and a manufacturing method thereof.

[0008] To solve the technical problem, the technical solution of the present invention is as follows:

[0009] An impact turbine nozzle, comprising:

[0010] The nozzle body has a conical constricted head.

[0011] A microgroove array, wherein the microgroove array is disposed on the entire outer wall surface of the conical contraction section;

[0012] The microgroove array extends in the same direction as the generatrix of the surface of the constricted section of the nozzle body, and has a triangular cross-sectional shape.

[0013] For example, in the technical principle, the microgroove array is modeled after shark skin. The surface of shark skin is not smooth, but rather covered with a layer of tiny, groove-like structures arranged along the body's direction (from head to tail), called "riblets." These tiny grooves effectively guide water flow, suppress the generation and development of turbulent eddies, and make chaotic water flow more orderly, thereby significantly reducing the frictional resistance between the water flow and the skin surface. Furthermore, the mucus secreted by the shark's epidermis also plays a drag-reducing role. The combination of mucus and the groove micromorphology forms a nanoscale self-lubricating interface, and the two work synergistically to produce a coupled drag-reducing effect.

[0014] Impulse turbines rely on high-pressure water flowing through nozzles to form a high-speed jet that impacts the runner's buckets to generate work. The nozzle interior, especially the nozzle needle region, is where water velocity is extremely high, pressure changes drastically, and turbulence and energy loss are easily generated. Applying a sharkskin-inspired microgroove structure to the nozzle needle surface aims to improve the boundary layer flow conditions.

[0015] 1) Guiding water flow and suppressing turbulence: Similar to the effect on shark skin, the microgrooves on the outer wall of the nozzle can guide the water flow to pass through more orderly, reduce lateral movement and vortices perpendicular to the mainstream direction (the core feature of turbulence), thereby reducing frictional losses caused by turbulence.

[0016] 2) Reduce flow separation: Good boundary layer control helps delay or reduce the tendency of water flow to separate from the wall, ensuring that the jet is more concentrated and stable, and that energy is transferred to the impeller more effectively.

[0017] 3) Potential anti-cavitation and anti-wear benefits: Smoother water flow means fewer local pressure abrupt changes, which may reduce the probability of cavitation (cavitation can severely damage the surface of flow-through components). At the same time, reducing the scouring of the wall by eddies can also mitigate wear to some extent.

[0018] Furthermore, the apex angle α of the triangular trenches in the microgroove array ranges from 50° to 70°.

[0019] Furthermore, the spacing S of the grooves in the microgroove array ranges from 150 μm to 250 μm.

[0020] Furthermore, the ratio of the groove depth H to the spacing S in the microgroove array is H = (0.6 ~ 0.9)S.

[0021] Furthermore, the apex angle α of the triangular groove is 60°, the groove spacing S is 203μm, and the groove depth H is 152.25μm.

[0022] Furthermore, the base material of the nozzle body is one of high-strength wear-resistant stainless steel, hard alloy, and engineering ceramics.

[0023] Furthermore, the engineering ceramic is reaction-sintered silicon carbide ceramic.

[0024] A method for manufacturing an impact turbine nozzle as described in any one of the above, the method comprising:

[0025] S1: Key operating parameters acquisition; Obtain the nozzle rated flow rate Q = 0.076 m³ / s; Considering that the surface velocity of the nozzle needle changes from the inlet to the throat, a characteristic position needs to be selected for calculation. Select the diameter of the midpoint of the nozzle constriction section as D1 = 0.0388 m, the diameter of the midpoint of the nozzle constriction section as D2 = 0.0192 m, and the density of water as ρ = 1000 kg / m³, and the dynamic viscosity as μ = 1.0 × 10⁻³ Pa·s;

[0026]

[0027] The calculated characteristic velocity at the midpoint of the nozzle's contraction section is V = 85.03 m / s;

[0028] S2: Characteristic Reynolds Number Calculation; The Reynolds number Re in the nozzle contraction section is a key dimensionless number for measuring the flow state. The characteristic Reynolds number is taken as the Reynolds number at the midpoint of the nozzle contraction section. The calculation formula is:

[0029]

[0030] The calculated value is Re = 1632576;

[0031] S3: Boundary layer thickness estimation; To determine the target scale of the microgroove effect, it is necessary to estimate the turbulent boundary layer thickness δ at the midpoint of the nozzle contraction section; the boundary layer thickness at the midpoint of the nozzle contraction section is selected as the design benchmark.

[0032]

[0033] The calculated value is δ = 406 μm; considering that the spacing S of the microgrooves should be related to the average spacing of the low-velocity strips in the near-wall turbulent structure, its optimal value range is: Taking S=0.5δ, we calculate S=203μm;

[0034] S4: Trench depth design; the depth H is a function of the spacing S. Simulations have verified that the optimal ratio is: Taking H=0.75S, we calculate H=152.25μm;

[0035] S5: Trench apex angle design; the apex angle α of a triangular trench affects flow separation and reattachment; the range for selecting the apex angle is: Taking α=60°, this angle achieves the best balance between hydrodynamic performance and structural stability;

[0036] S6: After determining the geometric dimensions of the microgroove array using the above formula, the following steps are completed in sequence: nozzle geometric modeling, cross-sectional array drawing, rotational forming, and Boolean difference reduction. This will yield a three-dimensional model of the nozzle containing the biomimetic microgroove structure.

[0037] For example, in S6, 3D modeling is performed based on the calculation results of S1-S5:

[0038] (1) Generate the nozzle and nozzle inner cavity surface model in the 3D modeling software UG.

[0039] (2) Draw a plane inside the nozzle so that the nozzle axis lies on this plane.

[0040] (3) On the plane in step (2), i.e. on the edge of the cross section of the nozzle retraction section, execute the array command to draw a sketch of the micro-groove array cross section with an array spacing of S and a depth of H.

[0041] (4) Rotate the sketch in (3) 360° around the nozzle axis to form a microgroove solid.

[0042] (5) Perform Boolean subtraction on the nozzle substrate to remove the microgroove entity and form a surface microgroove array.

[0043] The above steps allow you to draw the three-dimensional structure of a nozzle with microgrooves.

[0044] An impact turbine nozzle includes: a nozzle outlet, a nozzle converging section, a nozzle body, a nozzle inlet, and a nozzle needle as described above.

[0045] The nozzle body has a fluid channel inside, which includes, in sequence along the water flow direction, a nozzle inlet, a nozzle constriction section, and a nozzle outlet.

[0046] The nozzle is coaxially disposed inside the nozzle body and can move axially to adjust the flow rate; the head of the nozzle is constricted to form a nozzle constriction section, and the outer wall surface of the nozzle constriction section and the inner wall surface of the nozzle constriction section together define an annular fluid flow domain.

[0047] For example, the working principle of the impingement turbine nozzle described in this application lies in the active control of the turbulent boundary layer in the near-wall region of the nozzle using a microgroove array. Its working process is as follows:

[0048] High-pressure water flow acceleration and boundary layer development:

[0049] When high-pressure water flows from the constriction section of the nozzle to the throat and accelerates, a turbulent boundary layer with a large velocity gradient is formed on the outer surface of the nozzle due to the viscosity of the water. In a conventional smooth nozzle, this boundary layer generates strong lateral flow and turbulent vortices, setting the stage for flow separation and energy dissipation.

[0050] The suppressive effect of microgrooves on near-wall turbulence:

[0051] When water flows over the surface of the microgrooves of this invention, it constrains the lateral flow of the water. The geometry of the microgrooves effectively confines fluid particles adhering to the wall within their respective grooves, suppressing lateral flow that leads to momentum exchange and energy loss. This makes the water flow more inclined to maintain stable axial motion. Furthermore, the low-velocity fluid in the turbulent boundary layer, which would otherwise become unstable and form turbulent vortices, is confined to the bottom of the grooves by the microgrooves, making it difficult for them to mix with the high-velocity mainstream, thereby weakening the main turbulence generation mechanism of turbulence bursting.

[0052] Forming a high-quality free jet:

[0053] After being organized by the microgroove structure, the water flow exits the nozzle and forms a free jet. Because it has been organized within the nozzle, this jet has the following characteristics: high energy density in the core region, low turbulence, and reduced shear mixing.

[0054] Efficient energy transfer to the rotor:

[0055] Ultimately, this stable and high-energy jet precisely impacts the impeller bucket with minimal energy loss. Its high energy density directly translates into a more powerful impact force on the bucket; its low turbulence ensures a smooth force, reducing vibration and noise; and its reduced air entrainment effectively minimizes cavitation damage to the bucket surface.

[0056] In summary, this invention optimizes the flow state inside the nozzle from the source through a biomimetic microgroove structure, transforming the originally disordered and dissipative turbulence into a more ordered and stable flow, thus laying a foundation for high efficiency and high reliability in the initial stage of jet formation.

[0057] An impulse turbine, the impulse turbine including the aforementioned impulse turbine nozzle.

[0058] This application has the following advantages:

[0059] 1. Significantly improved jet dynamics performance:

[0060] Turbulence suppression: The microgroove array can effectively disrupt and suppress the turbulent quasi-sequence structure in the near-wall region, reducing the turbulent kinetic energy of the nozzle exit jet by 15%~25%; Jet cohesion enhancement: By delaying boundary layer separation and reducing shear mixing between the jet and air, the energy density in the jet core region is increased by 10%~20%, the jet divergence angle is reduced by about 15%~25%, and the effective impact distance is extended.

[0061] 2. Improved overall machine efficiency and operating range:

[0062] Efficiency Gain: The more stable and higher energy density jet significantly improves the momentum transfer efficiency of the turbine runner buckets. Under rated operating conditions, the turbine efficiency can be increased by 1.8 to 3.2 percentage points; under partial load or variable operating conditions, due to the more significant effect of the microgrooves on suppressing flow separation, the efficiency improvement can reach more than 5%, thus broadening the high-efficiency operating range of the unit.

[0063] 3. Significantly enhanced reliability and lifespan:

[0064] Vibration and cavitation suppression: The stable jet greatly reduces its periodic impact on the water buckets and random vibration at the tail, reducing the unit's vibration amplitude by 10% to 20%. At the same time, the reduction in air entrainment in the jet effectively reduces the cavitation intensity on the surface of the runner water buckets, reducing the cavitation damage area by 15% to 25%, thus extending the overhaul cycle and equipment life. Attached Figure Description

[0065] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0066] Figure 1 This is a structural diagram of an impact turbine nozzle proposed in this invention;

[0067] Figure 2 This is a partially enlarged view of the microgroove of an impact turbine nozzle proposed in this invention;

[0068] Figure 3 This is a schematic diagram of the microgroove structure of an impact turbine nozzle proposed in this invention.

[0069] Explanation of icon numbers:

[0070] 1- Nozzle outlet; 2- Microgroove array; 3- Nozzle constriction section; 4- Nozzle needle body; 5- Nozzle body; 6- Fluid flow domain; 7- Nozzle inlet. Detailed Implementation

[0071] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0072] Example 1:

[0073] This embodiment proposes a specific implementation method for an impact turbine nozzle, including the following steps:

[0074] 1. Overall structure and geometric parameters

[0075] The nozzle described in this embodiment has a conical structure, and its key area—the nozzle contraction section (from the large diameter end to the small diameter throat)—has a length L of 68.96 mm. The entire outer wall surface of this section is covered with a continuous and uniform array of microgrooves, such as... Figure 1-3 As shown. The core geometric parameters of the microgrooves are precisely designed based on the specific operating conditions of this embodiment: the spacing S is 203 μm. This dimension is related to the estimated boundary layer thickness (δ≈406 μm), and S=0.5δ is chosen to ensure effective disruption of the turbulent pseudo-sequence structure near the wall; the depth H is 152.25 μm; the depth-to-spacing ratio is H=0.75S, which has been optimized through biomimetic research and computational fluid dynamics (CFD) to achieve the best balance between significant drag reduction and ensuring structural mechanical strength; the cross-sectional shape is an isosceles triangle with a vertex angle α of 60°. This angle facilitates smooth fluid flow, promotes streamline adhesion, avoids additional flow separation points, and is easy to manufacture and replicate. The arrangement is such that all microgrooves are oriented along the surface of the nozzle constriction section to ensure optimal guidance of the water flow.

[0076] 2. Material selection and functional considerations

[0077] The nozzle operates in high-pressure, high-speed, sand-laden water flow, facing severe challenges of cavitation erosion and wear; therefore, material selection is crucial. Substrate material: In this embodiment, reaction-bonded silicon carbide (SiC) ceramic is selected. This material possesses extremely high hardness (≥2800 HV), excellent wear resistance, good thermal shock resistance, and chemical stability, making it highly suitable as a substrate for turbine flow components. Surface coating: A diamond-like carbon (DLC) coating with a thickness of not less than 15 μm is deposited on the surface of the microgroove structure using advanced deposition technology. The DLC coating has an extremely low coefficient of friction (<0.1), high hardness (≥3000 HV), and excellent hydrophobicity, which not only further reduces flow resistance but also significantly enhances the surface's resistance to cavitation erosion and wear, forming an excellent composite protective system with the SiC substrate.

[0078] 3. Detailed manufacturing process flow

[0079] Due to the extremely high hardness of silicon carbide ceramics, traditional machining methods struggle to achieve micron-level groove structures on their surface. This embodiment employs micro-replication molding technology, with the specific steps as follows:

[0080] 1) High-precision mold preparation: First, using micro-electrical discharge machining (EDM) technology, a highly precise array of raised triangular ribs, opposite to the required microgrooves, is machined on a piece of high-strength alloy steel. Strict control of dimensional tolerances and surface roughness is required during the machining process.

[0081] 2) Green body imprinting: During the green body stage of silicon carbide, i.e., the unsintered ceramic blank stage, the prepared mold is used to imprint the outer surface of the nozzle shrinkage section on a precision press. The imprinting pressure is controlled at 20-30 MPa, and the holding time is 1-2 minutes to ensure that the microgroove structure is clearly and completely transferred to the green body surface, and that the green body will not crack due to excessive pressure.

[0082] 3) High-temperature reaction sintering: The pressed green body is placed in a high-temperature sintering furnace and subjected to reaction sintering according to a set sintering curve under an inert atmosphere. The peak sintering temperature is controlled at 1800-2000℃ and held for 2-4 hours. This process melts silicon and reacts with carbon to form new SiC, while simultaneously filling the pores inside the green body, ultimately obtaining a dense, high-strength SiC ceramic nozzle matrix with a complete microgroove structure.

[0083] 4) Surface Coating Deposition: The sintered nozzle substrate is precision ground and polished to ensure its macroscopic dimensional accuracy. Subsequently, a DLC coating is deposited on the microgroove surface using physical vapor deposition (PVD) technology at a temperature below 200°C. This low-temperature process avoids thermal damage to the SiC substrate.

[0084] 4. Assembly

[0085] The manufactured grooved nozzle is assembled into the nozzle body. During installation, it is necessary to ensure that the direction of the microgrooves is strictly consistent with the direction of water flow.

[0086] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0087] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. An impact turbine nozzle, characterized in that, include: The nozzle body (4) has a conical constriction section at its head; Microgroove array (2), the microgroove array (2) is disposed on the entire outer wall surface of the conical contraction section; The microgroove array (2) extends in the same direction as the generatrix of the surface of the constriction section of the nozzle body (4), and has a triangular cross-sectional shape.

2. The impact turbine nozzle according to claim 1, characterized in that, The apex angle α of the triangular groove ranges from 50° to 70°.

3. The impact turbine nozzle according to claim 2, characterized in that, The spacing S of the grooves in the microgroove array (2) ranges from 150 μm to 250 μm.

4. The impact turbine nozzle according to claim 3, characterized in that, The ratio of the depth H of the grooves to the spacing S in the microgroove array (2) is H = (0.6 ~ 0.9)S.

5. The impact turbine nozzle according to claim 4, characterized in that, The microgroove array (2) has a apex angle α = 60°, a groove spacing S = 203 μm, and a groove depth H = 152.25 μm.

6. The impact turbine nozzle according to claim 1, characterized in that, The base material of the nozzle body (4) is one of high-strength wear-resistant stainless steel, hard alloy and engineering ceramics.

7. The impact turbine nozzle according to claim 1, characterized in that, The engineering ceramic is reaction-sintered silicon carbide ceramic.

8. A method for manufacturing an impact turbine nozzle as described in any one of claims 1-7, characterized in that, The method includes: S1: Key operating parameters acquisition; Obtain the nozzle rated flow rate Q = 0.076 m³ / s; Considering that the surface velocity of the nozzle needle changes from the inlet to the throat, a characteristic position needs to be selected for calculation. Select the diameter of the midpoint of the nozzle constriction section as D1 = 0.0388 m, the diameter of the midpoint of the nozzle constriction section as D2 = 0.0192 m, and the density of water as ρ = 1000 kg / m³, and the dynamic viscosity as μ = 1.0 × 10⁻³ Pa·s; ； The calculated characteristic velocity at the midpoint of the nozzle's contraction section is V = 85.03 m / s; S2: Characteristic Reynolds Number Calculation; The Reynolds number Re in the nozzle contraction section is a key dimensionless number for measuring the flow state. The characteristic Reynolds number is taken as the Reynolds number at the midpoint of the nozzle contraction section. The calculation formula is: ； The calculated value is Re = 1632576; S3: Boundary layer thickness estimation; To determine the target scale of the microgroove effect, it is necessary to estimate the turbulent boundary layer thickness δ at the midpoint of the nozzle contraction section; the boundary layer thickness at the midpoint of the nozzle contraction section is selected as the design benchmark. ； The calculated value is δ = 406 μm; considering that the spacing S of the microgrooves should be related to the average spacing of the low-velocity strips in the near-wall turbulent structure, its optimal value range is: Taking S=0.5δ, we calculate S=203μm; S4: Trench depth design; the depth H is a function of the spacing S. Simulations have verified that the optimal ratio is: Taking H=0.75S, we calculate H=152.25μm; S5: Trench apex angle design; the apex angle α of a triangular trench affects flow separation and reattachment; the range for selecting the apex angle is: Taking α=60°, this angle achieves the best balance between hydrodynamic performance and structural stability; S6: After determining the geometric dimensions of the microgroove array using the above formula, the following steps are completed in sequence: nozzle geometric modeling, cross-sectional array drawing, rotational forming, and Boolean difference subtraction. This will yield a three-dimensional model of the nozzle containing the biomimetic microgroove structure.

9. An impact turbine nozzle, characterized in that, include: Nozzle outlet (1), nozzle converging section (3), nozzle body (5), nozzle inlet (7), and the nozzle needle as described in any of claims 1-7; The nozzle body (5) has a fluid channel inside, which includes, in sequence along the water flow direction, a connected nozzle inlet (7), a nozzle constriction section (3), and a nozzle outlet (1). The nozzle is coaxially disposed inside the nozzle body (5) and can move axially to adjust the flow rate; the head of the nozzle is constricted to form a nozzle constriction section, and the outer wall of the nozzle constriction section and the inner wall of the nozzle constriction section (3) together define an annular fluid flow domain (6).

10. An impulse turbine, characterized in that, The impulse turbine includes the impulse turbine nozzle as described in claim 9.

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