A tailrace pipe with a helical airfoil structure for suppressing tailrace vortices

Abstract

This invention discloses a tailrace pipe with a helical airfoil structure for suppressing wake vortices, comprising a tailrace pipe and several anti-helical airfoil structures. The anti-helical airfoil structures are disposed on the upper wall of the tailrace pipe near the inlet end, spaced circumferentially along the tailrace pipe, extending axially downstream and continuously deflecting circumferentially, with their helical direction opposite to the rotation direction of the water flow inside the tailrace pipe. The cross-section of each anti-helical airfoil structure is semi-elliptical, formed by continuously sweeping along a predetermined helical path, maintaining its shape and size unchanged during the sweeping process. The anti-helical airfoil structures guide the rotating water flow in the opposite direction along the flow path, weakening the circumferential rotation of the water flow and the development of wake vortices, reducing pressure pulsation in the tailrace pipe, and minimizing the impact on the flow performance of the tailrace pipe.

Description

Technical Field

[0001] This invention relates to the field of hydraulic machinery and hydroelectric power generation equipment, specifically to a tailrace pipe with a helical airfoil structure for suppressing tailrace vortices, thereby achieving tailrace pipe rotation flow regulation and pressure pulsation suppression. Background Technology

[0002] As the scale of new energy sources such as wind and solar power continues to expand into the power system, the volatility of new energy output places higher demands on the grid's regulation capabilities. Hydropower units, with their superior load regulation capabilities, are undertaking peak shaving and frequency regulation tasks more frequently, leading to more frequent changes in their operating conditions. Under this operating context, the internal flow conditions of the turbines are more prone to change, and pressure pulsations and the resulting operational stability issues are becoming increasingly prominent. Therefore, reducing pressure pulsations during unit operation is of great significance for ensuring the safe and stable operation of hydropower units.

[0003] The draft tube is a crucial flow-through component of the turbine, located downstream of the runner outlet. Its primary function is to transport the water flowing from the runner to the downstream water body and recover some of the water's energy through diffusion. After leaving the runner and entering the draft tube, the water's motion is influenced by both the inflow from the runner outlet and the diffusion process within the draft tube. The stability of the water flow inside the draft tube not only affects energy recovery but also directly impacts pressure pulsation levels and the overall operational stability of the unit.

[0004] When the turbine's operating state changes, the water flow at the runner outlet may carry a significant circumferential motion component. After entering the draft tube, the axial motion and circumferential rotation superimpose, forming a rotating flow that propagates downstream along the draft tube, and may further develop into a spiral draft vortex. During its movement, the draft vortex causes periodic pressure changes within the draft tube, generating pressure pulsations, and may induce unit vibration and noise. Because the rotating flow has a definite direction of rotation and continues to develop downstream, simply obstructing or disturbing the flow at a localized location is insufficient to exert a sustained effect on its entire development process.

[0005] Several draft tube flow control and pressure pulsation suppression schemes have been proposed in the prior art. For example, CN202211453033.2 discloses an energy recovery turbine draft tube with guide vanes, which reduces the circumferential velocity of the water flow and guides the water flow axially by using rotatable upper vanes and fixed lower vanes; CN201920994833.2 discloses a bidirectional full-flow turbine draft tube, which weakens the circumferential motion of the water flow by setting guide plates on the inner wall of the diffuser section; CN202010660757.9 discloses a draft tube that uses a guide grid composed of rectangular guide vanes as a vortex suppression device, which limits the development of eccentric vortex bands through the internal guide grid. The above schemes can improve the draft tube flow to a certain extent, but the adjustable guide structure requires an additional adjustment mechanism, the internal guide grid occupies a certain flow space, and the straight guide structure on the wall mainly affects the local water flow, and still lacks effective control over the development process of the vortex within the draft tube.

[0006] The rational use of a tailrace tube with a helical airfoil structure to suppress tailrace vortices can not only guide the rotating water flow in the opposite direction of the water flow rotation within the tailrace tube, thus weakening the circumferential rotation of the water flow, but also continuously act on the water flow through the anti-helical airfoil structure that extends axially and deflects continuously in the circumferential direction, thereby suppressing the formation and development of tailrace vortices and reducing tailrace tube pressure pulsation.

[0007] Therefore, how to effectively weaken the rotating water flow and tailrace vortex while reducing the impact on the tailrace flow is a technical problem that needs to be solved in this field. Summary of the Invention

[0008] The purpose of this invention is to provide a tailrace pipe with a helical airfoil structure for suppressing tailrace vortices, solving the problems of existing tailrace flow control structures being unable to continuously and directionally regulate the rotating water flow within the tailrace pipe, and the difficulty in effectively suppressing tailrace vortex structures and pressure pulsations. To achieve the above objective, this invention adopts the following technical solution: a tailrace pipe with a helical airfoil structure for suppressing tailrace vortices, characterized in that: it includes a tailrace pipe and an anti-helical airfoil structure; the anti-helical airfoil structure is disposed on the upper wall of the tailrace pipe near the inlet end region, and multiple anti-helical airfoil structures are arranged at intervals along the circumference of the tailrace pipe; the anti-helical airfoil structure extends downstream along the axial direction of the tailrace pipe, and continuously deflects circumferentially during the extension process to form a helical structure; the helical direction of the anti-helical airfoil structure is opposite to the rotation direction of the water flow within the tailrace pipe.

[0009] Preferably, the cross-section of the anti-rotor airfoil structure is semi-elliptical, and the semi-ellipse is formed by satisfying the equation x ² / a²+ y An ellipse with a length of 2 / b² = 1 is formed by symmetrically dividing its major axis, where a is the semi-major axis and b is the semi-minor axis. x and yThe coordinate variables are in the local coordinate system of the semi-elliptical cross section; the semi-elliptical cross section is continuously swept along a preset spiral path to form an anti-spiral airfoil structure, and the shape and size of the semi-elliptical cross section remain unchanged during the sweeping process.

[0010] Preferably, the major semi-axis a of the semi-elliptical cross-section satisfies 3.03%D≤a≤4.55%D, and the minor semi-axis b satisfies 1.52%D≤b≤2.27%D, where D is the diameter of the tailwater pipe inlet end face.

[0011] Preferably, the number of the anti-spiral airfoil structures is N, and satisfies 1≤N≤5, and the multiple anti-spiral airfoil structures are arranged at equal angles along the circumference of the tailrace pipe.

[0012] Preferably, the height of the anti-spiral airfoil structure extending along the axial direction of the tailrace pipe is H, and satisfies 0.1D≤H≤0.5D, where D is the diameter of the tailrace pipe inlet end face.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a tailwater pipe with a spiral airfoil structure for suppressing tailwater vortices. (1) By setting an anti-spiral airfoil structure on the upper wall of the tailwater pipe, the spiral direction of the airfoil is opposite to the rotation direction of the water flow in the tailwater pipe, thereby directionally intervening in the rotating water flow, weakening the formation and development of the tailwater vortex structure, and reducing the intensity of pressure pulsation; (2) The anti-spiral airfoil structure extends along the axial direction and deflects continuously along the circumference, thereby continuously regulating the rotating water flow and expanding the range of flow control; (3) The anti-spiral airfoil structure adopts a semi-elliptical cross section, and the structural surface is continuous and smooth, reducing local flow separation and additional hydraulic losses. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the tailrace pipe of a spiral airfoil structure for suppressing tailrace vortices according to the present invention. Figure 2 A top view of the circumferential arrangement of the anti-rotor airfoil structure and a schematic diagram of the cross-sectional geometry. Figure 3 Comparison of tailrace pipe pressure pulsation spectra under different schemes; Figure 4 A comparison chart of turbine efficiency under different numbers of anti-rotor airfoil structures.

[0015] In the diagram: 1-tailflow pipe; 2-reverse propeller airfoil structure; 3-ellipse cross-section; D-tailflow pipe inlet diameter; H-axial height of the reverse propeller airfoil structure; O-ellipse center; a-major axis of the semi-ellipse cross-section; b-minor axis of the semi-ellipse cross-section. Detailed Implementation

[0016] In one embodiment of the present invention, see Figure 1 and Figure 2As shown, the draft tube of the present invention, which uses a helical airfoil structure to suppress draft vortices, includes a draft tube 1 and several anti-helical airfoil structures 2 disposed on the upper wall of the draft tube 1. The draft tube 1 is used to connect the turbine runner outlet to the downstream water body. The anti-helical airfoil structures 2 are arranged in the upper wall region of the draft tube 1 near the inlet end and extend downstream along the axial direction of the draft tube 1; multiple anti-helical airfoil structures 2 are arranged at intervals along the circumference of the draft tube 1. During the extension of the anti-helical airfoil structure 2 in the axial direction, it continuously deflects in the circumferential direction to form a helical structure, the helical direction of which is opposite to the rotation direction of the water flow inside the draft tube 1.

[0017] In one embodiment of the present invention, such as Figure 1 and Figure 2 As shown, the number N of the anti-propeller airfoil structures 2 is 4, and the four anti-propeller airfoil structures 2 are arranged at equal angles along the circumference of the tailrace pipe 1. The height H of the anti-propeller airfoil structure 2 extending along the axial direction of the tailrace pipe 1 is 30%D, where D is the diameter of the inlet end face of the tailrace pipe 1. All four anti-propeller airfoil structures 2 extend downstream from near the inlet of the tailrace pipe 1 and continuously deflect in the same direction during the extension process.

[0018] In one embodiment of the present invention, such as Figure 2 As shown, the cross-section of the anti-spiral airfoil structure 2 is semi-elliptical. This semi-ellipse is formed by symmetrically dividing an ellipse satisfying the equation x² / a² + y² / b² = 1 along its major axis, where a is the major semi-axis, b is the minor semi-axis, and x and y are coordinate variables in the local coordinate system of the semi-elliptical cross-section. In this embodiment, the major semi-axis a of the semi-elliptical cross-section is 3.78%D, and the minor semi-axis b is 1.75%D. The semi-elliptical cross-section continuously sweeps along a preset helical path to form the anti-spiral airfoil structure 2, and the shape and size of the semi-elliptical cross-section remain unchanged during the sweeping process.

[0019] In one embodiment of the present invention, such as Figure 1 and Figure 2 As shown, when the turbine deviates from its optimal operating condition, the water flow at the runner outlet has a large circumferential velocity component, forming a rotating flow after entering the draft tube 1. The helical direction of the anti-helical airfoil structure 2 is opposite to the rotational direction of the water flow inside the draft tube 1. As the rotating water flow develops downstream along the inlet area of ​​the draft tube 1, it is continuously guided and disturbed by the anti-helical airfoil structure 2, which changes the original circumferential motion state of the water flow, weakens the formation and development of the draft vortex, and reduces the intensity of pressure pulsation.

[0020] In one embodiment of the present invention, frequency domain analysis is performed on the pressure pulsation of the tailrace pipe before and after the installation of the anti-spiral airfoil structure 2. For example... Figure 3As shown, under the same operating conditions at 20% rated load, the prototype unit has the following airfoil numbers: N=0 (PT), N=3 (BT4), N=4 (BT5), and N=5 (BT6). The pressure pulsation coefficient is... C p The values ​​are 4.9338%, 3.9336%, 4.3749%, and 6.3222%, respectively. Compared with the baseline scheme (PT) without the anti-rotor airfoil structure 2, the pressure pulsation amplitude at the main characteristic frequencies of airfoil number N=3 (BT4) and airfoil number N=4 (BT5) is reduced after the anti-rotor airfoil structure 2 is installed. The airfoil number N=3 (BT4) scheme is preferred, indicating that the tailwater vortex in the tailwater pipe 1 is weakened and the flow stability is improved.

[0021] In one embodiment of the present invention, the efficiency of a water turbine is compared under different numbers of anti-rotor airfoil structures 2. For example... Figure 4 As shown, operating at 20% rated load, under the same operating conditions, the prototype unit's draft tube airfoil numbers N=0 (PT0), N=3 (PT1), N=4 (PT2), and N=5 (PT3) yielded efficiencies of 62.4%, 62.58%, 62.54%, and 62.36%, respectively. After installing the anti-rotor airfoil structure 2, selecting appropriate airfoil numbers N=3 and N=4 improved turbine efficiency, while N=5 resulted in a smaller overall change in turbine efficiency, greatly benefiting the control of pressure pulsation under extremely low load conditions. Therefore, the optimal embodiment employs three anti-rotor airfoil structures 2, reducing pressure pulsation in the draft tube 1 while maintaining improved turbine efficiency.

[0022] In one of the above embodiments, the invention objective of a tailpipe with a helical airfoil structure that suppresses tailwater vortices can be achieved. Those skilled in the art can make selections based on actual circumstances.

[0023] The tailrace tube with a helical airfoil structure for suppressing tailrace vortices provided by this invention can be applied to the stable operation retrofitting of existing hydropower station units and the hydraulic design of tailrace tubes for new units. In one embodiment described above, the anti-helical airfoil structure 2, through a helical structure opposite to the rotation direction of the water flow inside the tailrace tube 1, continuously and directionally regulates the rotating water flow, weakening the tailrace vortex structure and pressure pulsation, while reducing the impact on the hydraulic performance of the turbine and improving the stability of the unit's off-center operation.

[0024] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A tailrace pipe with a helical airfoil structure for suppressing tailrace vortices, characterized in that: It includes a tailrace pipe (1) and an anti-spiral airfoil structure (2); the anti-spiral airfoil structure (2) is located on the upper wall of the tailrace pipe (1) near the inlet end area, and multiple anti-spiral airfoil structures (2) are arranged at intervals along the circumference of the tailrace pipe (1); the anti-spiral airfoil structure (2) extends downstream along the axial direction of the tailrace pipe (1) and continuously deflects along the circumference during the extension process to form a spiral structure; the spiral direction of the anti-spiral airfoil structure (2) is opposite to the rotation direction of the water flow in the tailrace pipe (1).

2. The tailrace pipe with a helical airfoil structure for suppressing tailrace vortices according to claim 1, characterized in that: The cross-section of the anti-spiral airfoil structure (2) is semi-elliptical. The semi-ellipse is formed by symmetrically dividing an ellipse that satisfies the equation x² / a² + y² / b² = 1 along its major axis, where a is the major semi-axis, b is the minor semi-axis, and x and y are coordinate variables in the local coordinate system of the semi-elliptical cross-section. The semi-elliptical cross-section is continuously swept along a preset spiral path to form the anti-spiral airfoil structure (2), and the shape and size of the semi-elliptical cross-section remain unchanged during the sweeping process.

3. The tailrace pipe with a helical airfoil structure for suppressing tailrace vortices according to claim 2, characterized in that: The major semi-axis a of the semi-elliptical cross section satisfies 3.03%D≤a≤4.55%D, and the minor semi-axis b satisfies 1.52%D≤b≤2.27%D, where D is the diameter of the inlet end face of the tailwater pipe (1).

4. The tailrace pipe of the spiral airfoil structure for suppressing tailrace vortices according to claim 1, characterized in that: The number of anti-spiral airfoil structures (2) is N, and satisfies 1≤N≤5. Multiple anti-spiral airfoil structures (2) are arranged at equal angles along the circumference of the tailpipe (1).

5. The tailrace pipe with a helical airfoil structure for suppressing tailrace vortices according to claim 1, characterized in that: The height of the anti-spiral airfoil structure (2) extending along the axial direction of the tailrace pipe (1) is H, and satisfies 0.1D≤H≤0.5D, where D is the diameter of the inlet end face of the tailrace pipe (1).

Images