JPH0610609A - Steam turbine vane and vane reliability optimization method - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a steam turbine vane of an optimum airfoil shape having inner and outer rings integrally formed with an airfoil. A plurality of vanes 42 are connected by welding their inner ring 48 and outer ring 46 to form an annular nozzle assembly. In particular, the vane 42 employs a diaphragm structure to provide a smoother transition between the airfoil 44 and the inner and outer rings 48, 46 to provide improved performance. In addition, thinner blade trailing edges and reduced manufacturing tolerances are achievable compared to prior art segmented assemblies. Then, the steam flow separation is also controlled by controlling the rate of change of the narrowing and the turning angle, and the steam velocity is substantially continuous over a considerable range of the suction surface of the blade to avoid the steam flow separation. And is increasing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to steam turbines for utility power generation applications, and more particularly to vanes used in low pressure steam turbines.

The blades (or rotor blades) and vanes of a steam turbine are arranged in rows or stages. The plurality of blades in a given row are the same as each other and are mounted in mounting grooves provided in the turbine rotor. On the other hand, the stationary blade is attached to a cylindrical body or a blade ring surrounding the rotor.

The blades in a turbine typically share the same basic components. Each blade has a root that is received in a corresponding mounting groove in the rotor, a platform that overlaps the rotor outer surface at an upper end of the root, and an airfoil that extends upward from the platform.

The vane also has an airfoil, the airfoil of the vane extending downwardly toward the rotor. Such an airfoil includes a blade leading edge, a blade trailing edge, a concave suction surface, and a convex pressure surface. In most turbines, the airfoil shape common to one particular row is generally different than the airfoil shape in other rows in one particular turbine. Generally, no two turbines of different designs share the same shaped airfoil. Structural differences in airfoil shape result in significant changes in vane aerodynamics, stress patterns, operating temperatures, and natural frequencies. These changes then determine the expected life of the turbine blade under operating conditions (turbine inlet temperature, pressure ratio, and rotational speed), which are generally determined prior to airfoil shape development.

Development of a new commercial steam turbine turbine requires several years to complete. When designing a blade for a new steam turbine, the developer of the contour geometry is given a certain flow field to operate. This flow field determines, among other parameters, the inlet angle (for steam passing between adjacent blades in a row), gauging, and the force acting on each blade. What is "gauging"?
The ratio of pitch to pitch, "throat" is the linear distance between the trailing edge of one blade and the suction surface of the adjacent blade, and "pitch" is the blade of the adjacent blade. The tangential distance between the trailing edges, each of these measurements being measured at a particular radial distance from the turbine axis.

The parameters of these flow fields depend on a number of factors, including the length of the blades in a particular row. The blade length is set early in the design phase of the steam turbine and is essentially a function of the total power of the steam turbine and the power for that particular stage.

FIG. 1 illustrates a cross section of two adjacent blades in a row, showing some of the features of a typical blade. These two wings are numbered 10 and 12. These blades have convex suction surfaces 14 and 16, concave pressure surfaces 18 and 20, leading blade edges 22 and 24, and trailing blade edges 26 and 28, respectively.

In FIG. 1, the throat is indicated by the letter "O" and is the shortest linear distance between the trailing edge of blade 10 and the suction surface of blade 12. Pitch is indicated by the letter "S" and represents the linear distance between the trailing edges of two adjacent blades.

The width of the blade is indicated by the distance W _m , the inlet angle of the blade is α ₁ and the outlet angle is α ₂ .

"Β" is the blade edge metal angle of the blade leading edge, and the symbol "s" is the stagger angle.

When operating a particular turbine in the above flow field, it is important to consider the interaction of adjacent blade rows. The preceding row affects that succeeding row by potentially creating a mass flow rate near the base that cannot pass through the succeeding row. Therefore, it is important to design a blade having an appropriate flow distribution in the vertical direction of the blade length.

The pressure distribution along the concave and convex surfaces of the airfoil can cause secondary flow, which causes inefficiency of the airfoil arrangement. The loss due to this secondary flow is due to the difference in steam pressure between the suction surface and the pressure surface near the end wall of the blade.

Regardless of the airfoil shape, as defined by the flow field parameters above, the airfoil designer must also consider the cost of producing the optimum airfoil shape. The flow field parameters may define an economically unmanufacturable contour, or conversely the optimum airfoil shape may not be economically practical. Therefore, the optimum blade shape should also be considered for manufacturability.

[0014]

SUMMARY OF THE INVENTION In the present invention, a steam turbine blade includes inner and outer rings integrally formed with an airfoil.
The plurality of vanes are joined by welding the inner and outer rings to form an annular nozzle assembly. The blade diaphragm structure according to the present invention
The agm structure is a conventional segmented assembly where the forged airfoil is welded to the inner and outer rings.
compared to assemblies), provides smoother transitions between the airfoil and the inner and outer rings to provide improved performance over all wings of the same length. Further, the present invention, compared to prior art segmented assemblies having thick airfoil trailing edges and forged airfoils requiring relatively large tolerances,
It enables thinner blade trailing edges and reduced manufacturing tolerances. In a particular design of the blade according to the invention, steam separation is also controlled by controlling the rate of change of the tapering and the turning angle. The vapor velocity increases substantially continuously over the major extension of the suction surface of the blade to avoid flow separation.

[0015]

EXAMPLE FIG. 2 shows a low pressure fossil fuel steam turbine 3
0 is equipped with a rotor 32 that carries moving blades 34 in several rows or stages. The inner cylinder 36 includes a plurality of rows of stationary blades including a final row of stationary blades 38, a row of stationary blades 40 adjacent to the stationary blade final row, and a second stationary blade 42 from the stationary blade final row. I support you. Each vane row has a row name. The vanes 38 are in row 7C and the last row of blades is designated 7R. Immediately upstream vane 40 is in blade row 6C and the next vane 42 is in blade row 5C.
The present invention is specifically intended for use within cascade 5C.

As shown in FIG. 3, the vane 42 includes an airfoil 44 and an outer ring 4 which connects the vane to the inner cylinder 36.
6 and an inner ring 48 connected to the "inner diameter" end of the airfoil 44. The "outer diameter" end of the airfoil 44 is integrally formed with the outer ring 46 during the diaphragm structure manufacturing process. In the diaphragm construction, the airfoil and outer and inner rings are machined from a single piece casting. Typically, about 8.65 inches (219.71 mm) of vanes, typically used in the 5C row, are segmented assemblies where the inner and outer rings are welded to a separately formed airfoil. Was formed as. The diaphragm structure provides improved performance due to a smoother airfoil to ring transition, thinner airfoil trailing edges at the airfoil, and reduced manufacturing tolerances. The diaphragm assembly or nozzle assembly is formed by welding the inner and outer rings to adjacent rings to create an annular array of vanes. Inner ring 48 is separated from rotor 32 by a play gap. The seal 50 is located in this play gap and limits steam leakage under the vanes.

Inner ring 48 and airfoil 44 are configured to tune the fundamental mode of the entire assembly between multiples of turbine operating speed, ie, with respect to harmonic excited frequencies, and high cycle fatigue and Minimizes the risk of damage. In particular, the vane mass / stiffness is distributed radially to provide the characteristics shown in FIGS. The fundamental harmonic frequencies are then finely tuned by optimizing the inner ring shape, i.e. by adjusting the mass and stiffness.

In order to reduce the possibility of high cycle fatigue and damage, the diaphragm blade structure is preferably analyzed by assuming the total steam load of the vane acting as an in-phase excitation. This analysis is performed using the Goodman diagram technique that is usually applied for blade analysis. The vibrational stresses obtained from this analysis are then compared with the experimentally obtained allowable stresses. If necessary, this vane structure is then retuned and the above analysis and comparison repeated until satisfactory results are obtained. This technique has only been used for this type of wing. Historically, diaphragm structures have only been tested for frequency response.

In assembling the vanes of the present invention into a vane row 5C, the efficiency of the vane row or vane stage is optimized by minimizing the angle of incidence of steam flow and secondary flow losses. It Optimal inlet angle and gauging distributions are obtained using pseudo-three-dimensional flow field analysis. The unique shape of the airfoil 44 affects the flow conditions leaving the row of blades 5R and the performance of the last two stages in this low pressure turbine 30. Stationary blade 5C
The inlet angle of is influenced by the conditions of the steam leaving the blade row 4R.

6 to 10 show the general shape of the vane 42 according to the present invention, and the vane 42 and the contour line 4 on the pressure side.
3 shows the narrowed configuration of the steam passage between adjacent stator vanes indicated by 3. The cross section of FIG. 6 is taken adjacent to the radially inner end (tip) of the stationary blade 42, and FIG. 10 is taken adjacent to the radially outer end (base end) of the stationary blade 42. Is. Table 2 lists the important properties of each cross section of FIGS. 6-10 with the corresponding continuity. It should be noted that certain characteristics such as stagger angle, exit opening angle and principal coordinate (α) angle are substantially constant over the extension of the airfoil 44. The stagger angle is the angle formed between the horizontal line and the tangent to each circle at the blade leading edge and blade trailing edge in the cross-sectional view. The principal coordinate angle is the angle between the horizon and the minimum moment of inertia of area. One measurement not included in Table 2 is the nominal thickness of the vane trailing edge 44A. This nominal thickness in the vanes of the present invention can be reduced to about 80 mils (0.203 cm) to significantly reduce wake mixing losses and improve turbine performance. With reference to Table 2, the deflection (bending) of the suction surface is the change in the slope of the suction surface from the throat point of the suction surface (the point where the minimum passage chord intersects the suction surface) to the outlet of the airfoil. I know there is. The inlet metal angle is 2 with respect to the vertical line and the contact point at the blade leading edge of the suction and pressure surfaces.
It is the angle between the bisectors formed between two tangents. The inlet included angle is the angle between these two tangents.
The outlet opening is the shortest distance between adjacent airfoils at the steam passage outlet.

[0021]

[Table 2]

FIG. 11 shows another important characteristic of the present invention. As shown in FIG. 11, a vane airfoil 44
The velocity ratio of the steam flow on the suction surface (convex surface) of the airfoil continuously increases over substantially the entire width of the airfoil. This acceleration characteristic keeps the steam in contact with the vane surface or in close proximity to it. Therefore, this characteristic is due to the reduction rate of the area reduction between adjacent vanes from the blade leading edge to the blade trailing edge,
It is also achieved by controlling the rate of change of the turning angle. The turning angle is the angular turning amount from the inlet to the outlet of the vane.

The vanes 42 of the present invention provide improved performance and efficiency to fossil fueled steam turbines. It utilizes manufacturing and tuning techniques that are not believed to have been previously applied to vanes of this size.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of two adjacent wings showing typical wing features.

FIG. 2 is a vertical cross-sectional view of a part of a steam turbine incorporating a vane row according to the present invention.

FIG. 3 is a partially enlarged view of the steam turbine of FIG. 2, showing a vane according to the present invention.

FIG. 4 is a graph of cross-sectional area as a function of radius for a vane according to the present invention.

FIG. 5 is a graph of minimum moment of inertia (IMIN) as a function of radius for a vane according to the present invention.

FIG. 6 is a cross-sectional view of a vane according to the present invention at a predetermined radial distance.

FIG. 7 is a cross-sectional view of a vane according to the present invention at a predetermined radial distance.

FIG. 8 is a sectional view of a vane according to the present invention at a predetermined radial distance.

FIG. 9 is a cross-sectional view of a vane according to the present invention at a predetermined radial distance.

FIG. 10 is a cross-sectional view of a vane according to the present invention at a predetermined radial distance.

FIG. 11 is a graph of vapor velocities on a suction surface and a pressure surface of a vane according to the present invention.

[Explanation of symbols]

 14, 16 Convex suction surface 18, 20 Concave pressure surface 30 Steam turbine 42 Stator vane 44 Airfoil 46 Outer ring 48 Inner ring

Front Page Continuation (72) Inventor Shan Chen, Bear Creek Court 691 at Winter Springs, Florida, USA

Claims (2)

[Claims] 1. A steam turbine vane, wherein the vane is integrally formed with a radially inner end that terminates in an integrally formed inner ring portion when mounted in an operating position on the steam turbine. A vane of a steam turbine, the vane having a radially outer end terminating in an outer ring portion, the vane having the characteristics of Table 1 below. [Table 1] 2. A method for optimizing the reliability of a diaphragm turbine vane of a steam turbine having an airfoil, an integral inner ring, and an integral outer ring, wherein a minimum mass is near the inner ring. With a radial distribution of some vane mass, the vane is tuned for harmonic excitation and the mass of the inner ring section is optimized to assume resonance and at full steam load computer acting as in-phase excitation. By using simulation, the vibration characteristics of the vane are analyzed after tuning, and the tuning and retuning steps are repeated until the analyzed vane characteristics match the allowable vibration stress. Sex optimization method.