RU2581686C2 - Radial diffuser blade for centrifugal compressors - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: devices, systems and methods in accordance with exemplary embodiments provide diffusers, for example as part of a turbomachine 300 with the diffuser vanes having S-shaped midline. Such S-shaped center lines defined functions having inflection point.

EFFECT: use of such forms of diffuser vanes leads to performance, in which a part of diffuser vanes arranged near the leading edge is not loaded during operation under design conditions, with the load gradually increases to its maximum value toward the center of the diffuser vanes.

20 cl, 18 dwg

Description

The present invention relates to compressors and, more particularly, to diffuser vanes for centrifugal compressors.

A compressor is a machine that accelerates gas particles to ultimately increase the pressure of a compressible fluid, such as gas, through the use of mechanical energy. Compressors are used in a number of different areas, including for operation as an initial stage of a gas turbine engine. Among the various types of compressors, there are so-called centrifugal compressors in which mechanical energy is transferred to the gas entering the compressor by centrifugal acceleration, for example by rotating a centrifugal impeller (sometimes also called a “rotor”) through which a compressible fluid passes. In general, it can be said that centrifugal compressors are part of a class of machines known as “turbomachines” or “rotating turbomachines”.

Centrifugal compressors can be equipped with one impeller, that is, be single-stage, or several consecutive impellers, in which case they are often called multi-stage compressors. Each stage of a centrifugal compressor usually contains an inlet channel (guiding apparatus) for compressible gas, an impeller that can give kinetic energy to the incoming gas, and a diffuser that converts the kinetic energy of the gas leaving the rotor / impeller into pressure energy.

In particular, as shown in an exemplary longitudinal section in FIG. 1 (a), taken along the axis of the compressor in the direction of the process gas stream, the centrifugal compressor stage 100 comprises an impeller 102 attached to the rotor 104, followed by a diffuser 106 and a return duct or the outlet spiral chamber 108. At a high velocity, fluid flows from the outlet of the impeller 102 to the diffuser 106 and causes a slowdown of the fluid, thereby converting the dynamic pressure into static pressure. In order to provide a view from a different point of view of this design, FIG. 1 (b) shows a cross section of the compressor stage 100 taken along a different axis, i.e. perpendicular to the flow direction of the process gas. In this drawing, in the center of the image, a rotor 104 is seen surrounded by an impeller 102 containing a certain number of blades 114. The impeller blades 114 can be attached, on the one hand, to the impeller sleeve 116, and, on the other hand, to the working disk 118. wheels 102.

The present invention generally relates to a diffuser 106. Blade diffusers 106 (ie, diffusers that have a circumferential array of profiles (diffuser blades 110) along the flow path, as best seen in FIG. 1 (b)) are used to achieve more high stage efficiency, directing a highly tangential fluid flow at the outlet of the impeller in a more radial direction to the outlet of the diffuser. In contrast, some centrifugal compressors have a bladeless diffuser 120, as shown in FIG. 1 (c). Giving the fluid a more radial direction inside the diffuser 106 by means of vanes reduces the distance the fluid covers the passage through the diffuser 106. This concept is illustrated by the arrows of the flow direction in the centrifugal pump shown in FIG. 1 (d).

Reducing the distance covered by the fluid reduces the friction losses associated with the movement of the process fluid, and thereby increases the efficiency of compressors that use blade diffusers compared to compressors that use bladeless diffusers. On the other hand, the stages of centrifugal compressors that use blade diffusers 106 are also known for their lower operating range compared to stages with bladeless diffusers.

The operating range of a centrifugal compressor 100 having a blade diffuser 106 is determined based at least in part on the shape of the diffuser blades 110 used. The shape of the diffuser blade (or any aerodynamic profile in general) can be reflected by the middle line of its profile (i.e. the line drawn in the middle between the upper surface and the lower surface of the diffuser blade), as well as the distribution of thickness along the midline of the profile. Two forms of known diffuser vanes are shown in FIGS. 2 (a) and 2 (b). Shown in FIG. 2 (a), the diffuser blade 200 has a straight center profile line 202, i.e. the middle line without changing the slope, shown by a dashed line between the upper surface 204 of the diffuser blade and the lower surface 206 of the diffuser blade.

The use of diffuser vanes 200 having a straight center profile line in a centrifugal compressor is problematic since, for example, the leading edge of a diffuser blade of this shape is relatively high loaded and the compressor has a relatively low surge margin.

Figure 2 (b) shows an alternative diffuser blade 208 having a different shape, which has a so-called conformally displayed midline profile. The conformally displayed midline of the profile shown by the dashed line 210 between the upper surface 212 and the lower surface 214 can be determined, for example, using the coordinates of the midline of the aerodynamic profile in the rectangular plane (x, y), and the polar coordinates (r, θ) in the circular plane , as:

$$r=r_0\times e^{\left[\left(mx-y\right)/\left(m^2+\mathrm{one}\right)\right]}$$

$$\theta =\frac{my+x}{m^2+\mathrm{one}}$$

m = Cotα ₃

where r ₀ is the radius of the radial position of the leading edge of the diffuser blades,

α ₃ - the angle of absolute speed at the leading edge of the diffuser blades.

This shape of the diffuser blade also leads to some disadvantages when used as part of a diffuser in a centrifugal compressor. For example, using diffuser blades 208 having a conformally mapped midline in a centrifugal compressor? is problematic because the trailing edge of a diffuser blade with this shape is relatively high loaded and the compressor has a relatively low throttling limit.

Accordingly, it would be desirable to develop and provide diffuser vanes, the shape of which improves the performance of centrifugal compressors and which eliminate the above-mentioned disadvantages of the known forms of diffuser vanes.

Various devices, systems and methods in accordance with exemplary embodiments of the present invention provide diffusers, for example, as part of a turbomachine, with diffuser vanes having S-shaped center profile lines. Such S-shaped center lines are defined by functions having an inflection point along their length, or part of such curves. The use of diffuser blades having such a shape leads, among other things, to a performance characteristic in which a part of the diffuser blades located near the leading edge is substantially unloaded during operation under design conditions, and the load gradually increases to its maximum value towards the middle part of the diffuser shoulder blades.

According to an exemplary embodiment, the turbomachine comprises a rotor assembly having at least one impeller, a bearing connected to the rotor assembly and rotatably supported thereto, and a stator comprising at least one diffuser connected to the output part of the impeller, wherein said at least one diffuser comprises diffuser vanes, at least one of which has an average profile line defined by a function having an inflection point.

According to another exemplary embodiment, a method of manufacturing a turbomachine comprises using a rotor assembly comprising at least one impeller, attaching the rotor assembly to a bearing assembly to rotatably support the rotor assembly, and using a stator assembly comprising at least one diffuser coupled to the output part of the impeller, while the specified at least one diffuser contains diffuser blades, at least one of which has a midline A defined by a function having an inflection point.

According to another exemplary embodiment, the diffuser comprises an inner annular wall, an outer annular wall, a plate located between the inner annular wall and the outer annular wall, and diffuser blades located on the plate, at least one of the diffuser blades has a middle profile line defined by a function having an inflection point.

The accompanying drawings illustrate exemplary embodiments, wherein:

1 (a) to 1 (d) illustrate the prior art associated with diffusers used in centrifugal compressors;

Figures 2 (a) and 2 (b) respectively show a diffuser blade with a conventional straight rectilinear middle line and a diffuser blade with a conformally displayed middle line;

Figure 3 depicts an exemplary centrifugal compressor in which diffusers made in accordance with exemplary embodiments can be used;

Figure 4 illustrates the basic principles of aerodynamic profile;

5 depicts beta angles associated with diffusers made in accordance with exemplary embodiments;

6 depicts a profile of a diffuser blade having an S-shaped midline profile in accordance with an exemplary embodiment;

Fig. 7 is a graph showing an S-shaped midline of a profile in accordance with an exemplary embodiment compared with other midlines of the profile;

Fig. 8 is a graph showing an S-shaped midline of a profile and its inflection point in accordance with an exemplary embodiment;

9-11 are graphs showing simulation results in accordance with exemplary embodiments;

12 is a flowchart illustrating a method of manufacturing a turbomachine in accordance with an exemplary embodiment;

13 depicts a diffuser in accordance with an exemplary embodiment, and

Fig. 14 illustrates the use of Bezier curves to determine the S-shaped midline of a profile in accordance with an exemplary embodiment.

The following detailed description of exemplary embodiments is given with reference to the accompanying drawings. The same item numbers in different drawings indicate the same or similar elements. In addition, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.

In order to provide some context for the subsequent discussion regarding diffuser vanes and their shapes in accordance with exemplary embodiments, FIG. 3 schematically shows an exemplary multistage centrifugal compressor 300 in which such diffuser vanes can be used. The compressor 300 includes a casing or housing (stator) 302, in which a rotating shaft of the compressor 304 is installed, equipped with several centrifugal rotors or impellers 306. The rotor assembly 308 includes a shaft 304 and rotors 306 supported in radial and axial directions by bearings 310, which are located along both sides of the rotor 308.

A multi-stage centrifugal compressor 300 receives the process gas from the inlet 312, accelerates the process gas particles by operation of the rotor assembly 308, and then delivers the process gas through various inter-degree channels 314 (which include diffusers and diffuser vanes described below) at an outlet pressure that higher than inlet pressure. A process gas may, for example, be one of the following gases: atmospheric air, carbon dioxide, hydrogen sulfide, butane, methane, ethane, propane, natural gas, or a combination thereof. Between impellers 306 and bearings 310, sealing systems (not shown) are arranged to prevent process gas from flowing to bearings 310. Housing 302 is configured to cover both bearings 310 and sealing systems to prevent gas leakage from a centrifugal compressor 300. Those skilled in the art will appreciate that the centrifugal compressor 300 shown in FIG. 3 is purely illustrative and that the diffusers and diffuser vanes described below can be used in other compressors, for example p in sequential, counterflow, axial compressors, centrifugal pumps, turbines, turboexpander, etc.

We turn now to a discussion of diffusers and the shape of their blades. A brief discussion of aerodynamic profiles and related terminology will help the reader better understand exemplary embodiments. As shown in FIG. 4, the common aerodynamic profile 400 has a leading edge (LE) 402 and a trailing edge (TE) 404, the leading edge 402 being the end of the profile, which first contacts the fluid and which thereby separates the fluid into the upper and lower flows, and trailing edge 404 is the other end of the profile where these fluid flows converge. The chord 406 is a straight line between the LE 402 and TE 404, while the center line 408 of the profile (also sometimes referred to simply as the “middle line”) is located in the middle between the upper surface 410 of the profile 400 and its lower surface 412. The profile 400 may have a maximum thickness 414, which can be located at a certain distance from the leading edge 402. Changing these (and other) parameters associated with the profile 400 will lead to changes in aerodynamic characteristics.

Figure 5 illustrates some additional terminology that relates to the use of aerodynamic profiles as diffuser vanes 500 in the diffuser section 502 of the centrifugal compressor 300. The middle lines can, for example, be plotted as functions of beta angles (or changes in beta angles) over the entire length diffuser blades 500. For example, the orientation of the diffuser blades 500, as well as their shape determines the input and output beta angles with respect to the front and rear edges of the diffuser blades 500, respectively. On the contrary, as shown in FIG. 5, the input and output beta angles are determined with respect to (1) the radii 504, 506 associated with circles or arcs and representing the position of the leading edge and trailing edge drawn through them (from the axis of rotation of the shaft 104) , and (2) protrusions (tangent to the midline of the blade profile) 508, 510 associated with the current curvature at the point in question. Although in FIG. 5, the beta angles are shown only for the input and output points on the diffuser blade 500, the beta angles of the metal diffuser blades 500 can also be calculated for any point between the leading and trailing edges and can be used to draw midlines as a function of the beta distribution angles as described below.

According to exemplary embodiments, the center lines of the diffuser vanes are S-shaped, resulting in, among other things, a more balanced load between the leading and trailing edges of the vanes compared to the above-described forms of diffuser vanes and the associated center lines of the profile. An example of a diffuser blade 600 having an S-shaped center line 602 in accordance with an exemplary embodiment is shown in FIG. 6. Although not easily seen in FIG. 6, the S-shape of line 602 is more apparent in FIG. 7, which shows the S-shape of line 602 as a function of beta angle along the entire length of the blade 600 from the leading edge (0 along the X axis) to the trailing edge (100 along the X axis). In comparison, the straight midline 700 and the conformally displayed midline 702 are also shown in the same graph.

Although described generally as S-shaped center lines, diffuser vanes in accordance with these exemplary embodiments have center lines that are more specifically defined, for example, by at least algebraic equations or third-order functions. For comparison, the conventional diffuser vanes described above in connection with FIGS. 2 (a) and 2 (b) have midlines that are defined by linear or quadratic equations, i.e., first and second order equations. Thus, lines 602 associated with diffuser blades 600 in some exemplary embodiments can be determined by functions of the form:

y = ax ³ + bx ² + cx + d.

where a, b, c and d are constants.

As will be shown below, however, center lines associated with diffuser vanes in accordance with other exemplary embodiments can be described by functions of a different type.

Another S-shaped midline 800 connected to the diffuser blade in accordance with an exemplary embodiment is shown in FIG. Here, a change in the beta angle is built along the length of the diffuser blade, again revealing the S-shaped characteristic of the midline. A characteristic of third-order equations is that they have inflection points 802, i.e. a point on the function or on the graph at which the curvature (second derivative) changes sign. In contrast, midline functions associated with traditional designs do not have inflection points, as shown by a straight middle line and a conformal middle line, which are also shown in FIG. It should be noted that all S-shaped curves described here do not need to be used in creating diffuser blades in accordance with exemplary embodiments, i.e. curves can be cut and still provide the benefits described here. For example, a portion of the curve depicted in FIG. 8 from 0.6 to 1 along the X axis can be used to form a diffuser blade in accordance with an exemplary embodiment. Among other things, this provides a diffuser shape having center lines in accordance with some exemplary options with Δβ values that are larger than those associated with a straight linear center line (and hence a conformal-mapped middle line, as can be seen in FIG. 8 ) Thus, it will be understood by those skilled in the art that the phrase “diffuser vanes having midlines defined by a function having an inflection point” includes diffuser vanes having a shape defined by a truncated version of such functions, for example, including those where the inflection point, defined by function, has been rectified.

When using S-shaped diffuser blades, as described above, as a result, part of the blade is unloaded near the leading edge under design conditions and the load gradually increases to the maximum towards the middle part of the blade. An unloaded leading edge in accordance with exemplary embodiments will suffer less from flow separation at lower flow rates, thereby increasing the left compressor performance limit. These advantages associated with exemplary embodiments are shown using the various simulation results described below and shown in FIGS. 9-11.

Fig. 9 illustrates the results associated with two simulations performed for (1) a blade diffuser with a straight center line constructed as lines 910, 912, and for (2) a blade diffuser with an S-shaped profile (based on a sigmoid function, as described below) in accordance with these exemplary options shown by lines 900 and 902. The turbulence model used in the simulation was the Wilcox k-w model, with a design region consisting of one interscapular impeller channel (inductor, one full-length blade and one divided into I have a blade in the case of an impeller with separated blades) and one diffuser interscapular channel. The diffuser vanes in this model were designed as low strength vanes. The interface between the rotating region and the non-rotating region in this model was defined as 50% of the distance between the trailing edge of the impeller and the leading edge of the diffuser blade. The calculations associated with this simulation were carried out with the total pressure and the total temperature indicated at the inlet and the mass flow rate indicated at the outlet. It was assumed that all external walls are adiabatic, and the flow leakage through the impeller seals is insignificant and not modeled. The upstream impeller was modeled as having a calculated flow coefficient of 0.0206 and a peripheral Mach number of 0.3.

The results shown in Fig. 9 show an increase in efficiency of about 0.5 points at the design point of the centrifugal compressor and about 2 points near the left side of the operating curve, i.e. at 75% flow. This result tends to confirm the above conclusion that exemplary options increase the surge margin for centrifugal compressors. Also, a drop in efficiency is noted on the right side of the graph with respect to a centrifugal compressor modeled with diffuser blades having a straight center line.

Another simulation, the results of which are shown in FIGS. 10 and 11, was carried out with respect to centrifugal compressors with diffuser vanes with conformally displayed middle lines (functions 1000 and 1100), straight middle lines (functions 1004, 1104) and with bezelless diffusers ( functions 1006, 1106), with the obtained approximate S-shaped middle line shown in the graph as a function of 1002 and 1102. FIG. 10 shows a higher overall efficiency of the exemplary embodiments. In particular, this comparison shows that, for example, in this embodiment, there was an increase in efficiency of about 1.5 percent on the left side of the operating range compared to a centrifugal compressor with diffusers with a straight middle line, although slightly lower than the efficiency of a compressor with conformal mapped midline. In addition, on the right side of the graph in FIG. 10, it can be seen that the S-shaped midline in accordance with exemplary embodiments is much better in terms of efficiency than the conformal displayed midlines, and only slightly below the straight midline.

To summarize, some improvement in efficiency and benefits associated with the use of diffuser vanes having an S-shaped midline in centrifugal compressors include: increasing efficiency in the direction of the left (lower) operating range, thereby increasing the compressor's surge limit, better or comparable efficiency at the design point with respect to other structures and low efficiency in the direction of the throttle limit relative to some structures (i.e., with the exception of the design with conformal displayed midlines).

This simulation also showed a higher rise in polytropic head for a diffuser with an S-shaped middle line in accordance with an exemplary embodiment with respect to a diffuser with a straight middle line and a bladeless diffuser, as shown in Fig. 11. It can be seen that a pressure increase of 6.5% was measured for function 1102 of the diffuser with an S-shaped middle line in accordance with an exemplary embodiment, compared with 5.2% increase in pressure for function 1104 of a diffuser with a straight middle line and with 6 , 2% increase in pressure for a bladeless diffuser. Conformal display diffuser function 1100 shows a slightly better head lift than lift in exemplary embodiment 1102.

Exemplary options also include a method of manufacturing a turbomachine, which may be expressed in the flowchart shown in FIG. In this flowchart, at 1200, a rotor assembly is used comprising at least one impeller. The rotor assembly in step 1202 is attached to a bearing assembly that rotatably supports the rotor assembly. At step 1204, a stator assembly is used comprising at least one diffuser attached to the outlet of the impeller and containing vanes, at least one of which has a midline profile defined by a function having an inflection point.

In addition to producing centrifugal compressors with diffuser vanes having S-shaped center lines, in accordance with these various exemplary embodiments, there may also be a desire to modify existing centrifugal compressors with vanes without diffusers or with diffusers with vanes of a different shape, equipping them with diffusers, having S-shaped center lines in accordance with exemplary embodiments, in order, for example, to increase efficiency with respect to the bladeless diffusers or the mind nshit range restriction associated with existing vane diffuser. Thus, exemplary embodiments further plan the production of the diffusers themselves for the modernization and / or repair of existing compressors.

13 illustrates an exemplary diffuser 1300 comprising an inner annular wall 1302, an outer annular wall 1304, a plate 1306 located between the inner annular wall 1302 and the outer annular wall 1304, and diffuser vanes 1308 located on the plate 1306. One or more diffuser vanes 1308 have an S-shaped midline, i.e. a line defined by a function having an inflection point. The diffuser 1300 may be a diffuser with high strength or weak aerodynamic profiles. In some exemplary embodiments, the S-shaped diffuser blades discussed herein can be used with diffusers 1300 that have more than 10 blades 1308.

As mentioned above, third-order algebraic equations can be used to determine midlines in accordance with some exemplary embodiments. However, other types of equations, for example, exponential equations, can also be used to determine midlines in accordance with exemplary embodiments. For example, sigmoid functions or Gompertz functions can also be used to define midlines in accordance with exemplary embodiments. Sigmoid functions, also known as logistic functions, can be expressed as:

$$Y=\frac{\mathrm{one}}{\mathrm{one}+e^{-x}}$$

while the Gompertz functions are of the form:

$$y=a{e}^{\left[-b{e}^{\left(-cx\right)}\right]}$$

Like the third-order algebraic equations described above, these exponential equations also create functions that have inflection points.

In addition, polynomial functions of a higher order, for example, fourth order and higher, can also be used to obtain the same S-form. In addition, according to other exemplary embodiments, more complex shapes (with multiple inflection points) may be specifically designed for a particular application. One way to define such generalized curves is to use Bezier curves. A Bezier curve forming an S-shape of midlines in accordance with exemplary embodiments can be described as shown in FIG. In this case, the shape of the midline is determined by the coordinates of the control points 1401 and 1402 with the coordinates (X1, Y1) and (X2, Y2), respectively. More control points can be used to define higher-order curves having multiple inflection points.

The exemplary embodiments described above are intended to illustrate the entire invention without limiting it. Thus, the present invention may have many variations in the detailed implementation, which can be obtained from the description given here by a specialist in this field. All such changes and modifications are deemed to be within the scope and spirit of the present invention, as defined in the claims. No element, action or instruction used in the description of this application should be construed as critical or important for the invention, unless explicitly described as such. In addition, the mention of the elements in the singular implies the presence of one or more elements.

Claims (20)

1. A turbomachine containing:
a rotor assembly having at least one impeller,
a bearing connected to the rotor assembly and intended to be rotatably supported, and
a stator containing at least one diffuser connected to the output of the impeller,
wherein said at least one diffuser comprises diffuser vanes, at least one of which has an average profile line defined by a function having an inflection point. 2. The turbomachine according to claim 1, wherein said function is y = ax ³ + bx ² + cx + d, where a, b, c and d are constants. 3. The turbomachine according to claim 1, wherein said function is a higher order polynomial function, a sigmoid function, a Gompertz function, or a Bezier curve. 4. The turbomachine according to claim 1, wherein said function is an exponential function. 5. The turbomachine according to claim 1, in which a portion of the at least one diffuser blade located near the leading edge is not substantially loaded when operating under design conditions, while the load gradually increases to its maximum value to the middle part of the at least one diffuser blade. 6. The turbomachine according to claim 1, in which each of these diffuser blades is attached to the hub or covering disk. 7. A turbomachine according to any one of claims 1 to 6, wherein said function is a Bezier curve. 8. A method of manufacturing a turbomachine, including:
use of a rotor assembly comprising at least one impeller,
attaching the rotor assembly to the bearing assembly to support rotation of the rotor assembly, and
the use of a stator assembly containing at least one diffuser connected to the output part of the impeller,
wherein said at least one diffuser comprises diffuser vanes, at least one of which has an average profile line defined by a function having an inflection point. 9. The method of claim 8, wherein said function is y = ax ³ + bx ² + cx + d, where a, b, c and d are constants. 10. The method of claim 8, wherein said function is a higher order polynomial function, a sigmoid function, a Gompertz function, or a Bezier curve. 11. The method of claim 8, wherein said function is an exponential function. 12. The method according to claim 8, in which a portion of the at least one diffuser blade located near the leading edge is not substantially loaded when operating under design conditions, the load gradually increasing to its maximum value to the middle part of the specified at least one diffuser blade. 13. The method of claim 8, in which each of these diffuser blades is further attached to a hub or covering disc. 14. The method according to any one of claims 8 to 13, wherein said function is a Bezier curve. 15. A diffuser containing:
inner annular wall
outer annular wall
a plate located between the inner annular wall and the outer annular wall, and
diffuser vanes located on the plate, and at least one of the diffuser vanes has a midline profile defined by a function having an inflection point. 16. The diffuser according to claim 15, wherein said function is y = ax ³ + bx ² + cx + d, where a, b, c and d are constants. 17. The diffuser according to claim 15, wherein said function is a higher order polynomial function, a sigmoid function, a Gompertz function, or a Bezier curve. 18. The diffuser of claim 15, wherein said function is an exponential function. 19. The diffuser according to clause 15, in which part of the specified at least one diffuser blades located near the leading edge, is essentially not loaded during operation under design conditions, while the load gradually increases to its maximum value to the middle part of the specified at least one diffuser blade. 20. A diffuser according to any one of claims 15-19, wherein said function is a Bezier curve.

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