WO2025036664A1 - Stator for a pump comprising main blades and secondary blades - Google Patents

Abstract

The invention relates to a pump stator comprising a hub and a casing which are coaxial about a longitudinal axis, an axial inlet and an axial outlet, a first series of main blades (50) and a second series of secondary blades (60), the generatrices of the main (50) and secondary (60) blades extending substantially axially, the secondary blades (60) being inserted circumferentially between the main blades (50), the leading edges of the main blades (50) being on a single first transverse plane. Moreover, the leading edges of the secondary blades (60) are positioned on a second transverse plane parallel to the first transverse plane, at a first predetermined distance from the first transverse plane, in the direction of the axial outlet, the first predetermined distance being between 0.1 and 0.3 times the axial length (Lm) of the main blades (50). The invention also relates to a pump with such a stator.

Description

STATOR FOR PUMP COMPRISING MAIN BLADES AND BLADES

SECONDARY

Technical field

The invention relates to the field of fluid compression or pumping devices and more particularly relates to a stator of a fluid compression or pumping device.

A compression device generally comprises one or more compression stages. Each compression stage comprises at least one moving part with a rotating wheel (this moving part is also called a “rotor” or “impeller”) and at least one fixed part, a rectifier (also called a “stator” or “diffuser”). These elements can be placed within a housing of the compression device.

The stator is placed downstream of a rotating wheel and its role is to straighten the flow of fluid leaving the wheel, the flow being driven in rotation by the rotating wheel. Its purpose is to be able to supply the next compression stage (another rotating wheel downstream of the stator) or to use the fluid flow directly. The stator is used to convert the kinetic energy of the fluid into potential energy. For this, the stator generally includes blades.

The stator is static, i.e. fixed relative to the external casing of the compression device, while the rotating wheels are mobile in rotation around a longitudinal axis. The purpose of these rotating wheels is to increase the kinetic energy and potential energy of the fluid. They are generally fixed to a rotating shaft and generally include blades.

More particularly, the invention relates to a pump and a pump stator intended to pump a compressible fluid, in particular CO2.

Previous technique

Figure 1 is from patent application US2018/106270 AA. It shows an example of a multiphase pump comprising at least one or more compression stages (Figure 1 shows only one stage), each stage comprising a rotating impeller 1 and a stator 2. The rotating impellers are fixed to the hub 10. The rotating impellers 1 may comprise a plurality of blades 3 and the stators 2 may comprise a plurality of blades 4. In this figure, the direction of the fluid flow is represented by an arrow S. Due to the geometric shape of some compression devices, the flow may form, with the axis of rotation of the device, a very large angle at the dynamic outlet of the rotating wheel (for example, of the order of 60 degrees to 70 degrees). The geometry of the stators seeks to limit the residual angle at the stator output, with the axis of rotation of the device.

Patent application US2018/106270 AA relates to a pump stator. The stator may be in two successive parts, located axially one behind the other and separated by an intermediate piece forming an axial distance between these two successive parts.

However, the space formed between the upstream blades of the upstream part of the stator and the downstream blades of the downstream part of the stator generates significant performance losses.

Patent application CN 115 388 038 A relates to a stator of a centrifugal compressor with a radial inlet and an axial outlet. The stator comprises two series of blades.

The aim of the invention is to seek to improve the performance of the stator of a pump, such as a multiphase pump, where the fluid flow is directed essentially axially along the pump and the stator, in particular by limiting separation phenomena, and this more particularly for compressible fluids, such as CO2.

Summary of the invention

The invention relates to a pump stator comprising a hub and a casing coaxial about a longitudinal axis, an axial inlet for introducing a fluid into the stator and an axial outlet for discharging the fluid from the stator, a first series of main blades and a second series of secondary blades, said main and secondary blades extending radially from the hub to the casing, the generatrices of the main and secondary blades extending substantially axially, the secondary blades being intercalated circumferentially between the main blades, the leading edges of the main blades being on the same first transverse plane. Furthermore, the leading edges of the secondary blades are positioned on a second transverse plane parallel to the first transverse plane, the second transverse plane being positioned axially at a first predetermined distance from the first transverse plane, in the direction of said axial outlet, the first predetermined distance being between 0.1 and 0.3 times, preferably between 0.15 and 0.25 times, the axial length of the main blades.

Preferably, the axial length of the secondary blades is less than or equal to said axial length of the main blades.

Advantageously, the trailing edges of the secondary blades form a third transverse plane positioned at a second predetermined distance from a fourth transverse plane formed by the trailing edges of the main blades, the second predetermined distance being between -0.3 times and +0.3 times, preferably between -0.1 times and +0.1 times, said axial length of the main blades, preferably, the second predetermined distance is zero.

Advantageously, the secondary blades are offset, in the circumferential direction, from the main blades directly preceding them in the circumferential direction, by an angle of between 0.2 and 0.5 times, preferably between 0.25 and 0.35 times, the circumferential angular offset of the main blades.

Preferably, the ratio between the section of the axial outlet and the section of the axial fluid inlet is between 0.5 and 2.5, preferably between 0.5 and 1.5.

According to an advantageous configuration of the invention, the ratio between said axial length of the main blades and the external radius at the leading edge of the main blades is between 0.36 and 1.80, preferably between 0.65 and 1.64.

According to a preferred variant of the invention, the external diameter of the main and/or secondary blades decreases from the axial inlet towards the axial outlet.

Advantageously, the internal diameter of the main and/or secondary blades decreases from the axial inlet to the axial outlet.

Preferably, the main blades are offset two by two successively in the circumferential direction by a circumferential angular difference Ad _mis substantially verifying:

Ae _mis = {l - OL') - Ad _mb OL = a * ALR + b

With A6 _mb the circumferential angular deviation of the main blades, corresponding substantially to the circumferential angular deviation generated between the leading edge and the trailing edge of each main blade;

ALR: the ratio between said axial length of the main blades and the external radius at the leading edge of the main blades and a and b being predetermined values.

The invention also relates to a pump, preferably a multiphase pump, the pump comprising an outer casing, an axial succession of fixed parts and rotating parts inside the outer casing, a first axial inlet opening for the inlet of a fluid into the pump and a second axial outlet opening for the outlet of the fluid from the pump. At least one fixed part comprises a stator as described above, preferably the outer casing corresponding to the stator housing.

Preferably, the outer casing comprises at least one portion with an internal surface of strictly decreasing inner diameter, in the direction of flow of the fluid axially through the pump and preferably, the outer casing comprises several portions, each with an internal surface of strictly decreasing inner diameter, in the direction of flow of the fluid axially through the pump. List of figures

Other characteristics and advantages of the stator and/or the pump according to the invention will appear on reading the following description of non-limiting examples of embodiments, with reference to the figures appended and described below.

Figure 1 (already described) shows an example of a polyphase pump according to the prior art.

Figure 2 illustrates a first example of a pump according to the invention.

Figure 3 illustrates a second example of a pump according to the invention.

Figure 4 illustrates a view in a longitudinal plane of a pump stator according to the invention.

Figure 5 illustrates a developed view along the circumferential direction of a pump stator with certain parameters according to the invention.

Figure 6 illustrates a developed view along the circumferential direction of a pump stator with additional parameters to those of Figure 5 according to the invention.

Figure 7 illustrates a performance curve as a function of the axial offset of the leading edge of the secondary blades relative to the leading edge of the main blades, of a pump stator according to the invention.

Figure 8 illustrates a performance curve as a function of the circumferential angular offset of the leading edge of the secondary blades relative to the leading edge of the main blades, of a pump stator according to the invention.

Figure 9 illustrates in diagram a) the profiles of the hubs and housing of the pump stator, along the longitudinal axis, and in diagram b) the profile of the blades, on the parts connected to the hub and to the housing.

Figure 10 illustrates a comparison of the axial velocity fields of a stator of the prior art (a)) and of the invention (b)) in a longitudinal plane. Description of the embodiments

The terms "axial" and "axially" generally mean along or parallel to a longitudinal axis, while the terms "radial" and "radially" generally mean perpendicular to the longitudinal axis. For example, an axial length refers to a distance measured along or parallel to the longitudinal axis, and a radial length refers to a distance measured radially, i.e., perpendicular to the longitudinal axis. The use of "top", "bottom", "above", "below" and variations of these terms is for convenience, with reference to the figures, without prejudice to their spatial positioning in use, and does not require any particular orientation of the components.

In this document, the term "fluid compression device" refers to compressors and pumps intended respectively to compress or pump a fluid. These devices may be surface, subsea or downhole (i.e. in subterranean formations) devices.

The terms “upstream” and “downstream” refer to the direction of flow of the fluid passing through the stator or the pump.

The leading edge is the edge of the blade that faces the fluid. Thus, it separates the fluid that arrives upstream of the blade into two flows, one that passes on one side of the blade (at the extrados for example) and the other that passes on the opposite side (at the intrados for example).

The trailing edge is the edge of the blade that is opposite the leading edge. At the trailing edge, the two flows separated by the leading edge can mix again to form a single flow. In other words, the leading edge is at the upstream end of the blade and the trailing edge is at the downstream end of the blade.

The generator of a blade is the center line of the blade, that is, the line located at an equal distance from the extrados and the intrados. It is generally curved and extends approximately axially.

The extrados is the convex outer surface of a blade while the intrados is the concave inner surface of a blade.

For the purposes of this description, a transverse plane is a plane orthogonal to the longitudinal axis of the stator or pump.

The invention relates to a stator (also called a “rectifier” or “diffuser”) of a pump, preferably multiphase, comprising:

- a hub (or “internal hub”) and a casing (also called “external hub”) coaxial around a longitudinal axis,

- an axial inlet for the introduction of a fluid into the stator,

- an axial outlet for the evacuation of the stator fluid, - a first series of main blades,

- and a second series of secondary blades.

Thus, in the stator of the invention, the fluid flow extends essentially axially from the axial inlet to the axial outlet. This type of stator is therefore suitable for pumps, such as so-called “multiphase” pumps, i.e. capable of pumping a multiphase fluid.

According to the invention, the main and secondary blades extend radially from the hub to the housing and the generatrices of the main and secondary blades extend substantially axially. By "substantially axially" is meant that the blades and their generatrices are curved, and therefore they do not of course extend only in the axial direction.

The main and secondary blades may preferably not have openings, such as holes and/or grooves, so as to limit stator and pump performance losses. This is especially true when the purpose of the stator is to convert kinetic energy into potential energy because the openings can generate turbulence.

In addition, the secondary blades are intercalated circumferentially between the main blades. Thus, the stator of the invention comprises as many main blades as secondary blades and circumferentially comprises an alternation of main blades and secondary blades. The secondary blades, thus intercalated, make it possible to limit the separation of the fluid between the main blades.

In addition, the leading edges of the main blades are on the same first transverse plane: in other words, their projections on the longitudinal axis form a single point on the longitudinal axis. In the same way, the leading edges of the secondary blades are positioned on a second transverse plane parallel to the first transverse plane. In other words, the projections of the leading edges of the secondary blades on the longitudinal axis also form a single point on the longitudinal axis.

According to the invention, the second transverse plane is positioned axially at a first predetermined distance from the first transverse plane, in the direction of said axial outlet, i.e. downstream of the first transverse plane. The first predetermined distance is between 0.1 and 0.3 times, preferably between 0.15 and 0.25 times, the axial length of the main blades. This makes it possible to improve the performance of the stator and therefore of the associated pump, by improving the pressure recovery coefficient C _p , defined as follows:

With

^Pstatic: static pressure difference of the fluid between the axial outlet and the axial inlet Dynamic in dynamic pressure of the fluid at the axial inlet

P s, out: static pressure of the fluid at the axial outlet

P _s , tn : static pressure of the fluid at the axial inlet

Pt, in: total fluid pressure at the axial inlet.

Thus, the pressure recovery coefficient C _p reflects the stator's ability to transform the dynamic pressure due to the kinetic energy of the fluid into static pressure. The larger this coefficient, the higher the stator's performance.

The position of the leading edges of the secondary blades relative to the leading edge of the main blades makes it possible to define a stator capture zone, located between the first transverse plane and the second transverse plane. Increasing this capture zone makes it possible to increase the potential operating range of the stator by reducing its sensitivity to high incidences. Indeed, high incidences can generate fluid separations on the extrados of the blade, obstructing the diffuser inlet. With a large capture zone, the separated fluid can more easily be transported within the stator. Depending on the viscosity of the fluid, significant separations can be generated. This is particularly the case when the viscosity is relatively low, such as the viscosity of CO2.

The invention also makes it possible to maintain the straightening capacities of the stator, by reducing the tangential speed of the fluid leaving the rotor: the tangential speed of the fluid is reduced at the outlet of the stator compared to its entry into the stator.

Thus, compared to a stator design without secondary blades, the stator of the invention has fewer main blades. In other words, the stator has substantially the same total number of blades but comprises half of this number in main blades and the other half in secondary blades. This makes it possible to increase the capture area, upstream of the secondary blades, and then to improve the flow support in the stator thanks to the secondary blades.

According to a variant of the invention, the axial length of the secondary blades may be less than or equal to said axial length of the main blades. This makes it possible to limit the size of the stator and to obtain a good compromise between the expected performance of the stator, its compactness and therefore its cost.

Preferably, the trailing edges of the secondary blades may form a third transverse plane positioned at a second predetermined distance from a fourth transverse plane formed by the trailing edges of the main blades and the second predetermined distance may then be between -0.3 times and +0.3 times, preferably between -0.1 times and +0.1 times, said axial length of the main blades. With trailing edges of the main and secondary blades close together, the size can be limited and good performance can be obtained.

More preferably, the second predetermined distance may be zero. In other words, the trailing edges of the main and secondary blades are on the same transverse plane so as to limit the size of the stator while maximizing its performance.

According to a configuration of the invention, the secondary blades can be angularly offset, in the circumferential direction, from the main blades directly preceding them in the circumferential direction (the circumferential direction being defined from the intrados to the extrados, the orientation of the intrados and extrados being the same for all the main and secondary blades), by an angle of between 0.2 and 0.5 times, preferably between 0.25 and 0.35 times, the circumferential angular offset of the main blades. In other words, the secondary blades are angularly closer to the extrados of the main blade preceding it than to the intrados of the other main blade following it. This configuration also makes it possible to increase the pressure recovery coefficient C _p defined above, in particular by limiting the potential separation located on the extrados of the main blade.

Advantageously, the ratio between the section of the axial outlet and the section of the axial fluid inlet can be between 0.5 and 2.5, preferably between 0.5 and 1.5. Indeed, too great an increase in the outlet section would lead to separations and therefore losses in performance, while too great a reduction in the outlet section then reduces the diffusion potential.

Advantageously, the ratio between said axial length of the main blades and the external radius at the leading edge of the main blades may be between 0.36 and 1.80, preferably between 0.65 and 1.64, so as to ensure a good compromise between performance and compactness. Indeed, too large a ratio reduces compactness and also causes significant friction losses on the blades. Conversely, too small a ratio improves compactness but requires too large a deviation over a short distance (with significant curvature), which generates separations.

According to one implementation of the invention, the external diameter of the main and/or secondary blades can decrease from the axial inlet to the axial outlet. By decreasing the diameter, the outlet section is reduced, which allows better compression of the fluid. This is particularly advantageous with compressible fluids such as CO2. Advantageously, the internal diameter of the main and/or secondary blades can decrease from the axial inlet towards the axial outlet, so that the internal diameter on the axial outlet side is compatible, i.e. substantially equal to the internal diameter of the impeller downstream of the stator so as to limit the pressure losses which could be generated by sudden changes in section.

Preferably, the main blades can be offset two by two successively in the circumferential direction by a circumferential angular difference A6 _{substantially} verifying: m _is = (1 - OL) ■ A0 _mb

OL = a * ALR + b

With A6 _mb the circumferential angular deviation of each main blade, corresponding substantially to the circumferential angular deviation generated between the leading edge and the trailing edge of the blade considered (the main blade here). ;

ALR: the ratio between said axial length of the main blades and the external radius at the leading edge of the main blades and a and b being predetermined values, a and b can be determined from numerical simulations or experimental tests. For example, we can have a=1.16 and b=0.57.

The terminology "substantially verifying" means "as close as possible". Indeed, the number of blades is necessarily an integer and consequently, the preceding equations can only be determined as close as possible, taking into account this integer.

Indeed, surprisingly, this formulation based on the linearization of the OL parameter as a function of the ALR ratio makes it possible to obtain an optimal position, despite numerous possible parameters for optimization and complex numerical simulations and phenomena involved.

Advantageously, the main blades can have similar generators, that is to say that the generators of the different main blades can superimpose.

Preferably, the secondary blades may also have similar generatrices to each other, i.e. the generatrices of the different secondary blades may overlap.

Even more preferably, the main and secondary blades may have at least partially similar generators: for example, when the trailing edge of the secondary blades is upstream of the trailing edge of the main blades, the generator of the secondary blades then overlaps part of the generator of the main blades. Conversely, when the trailing edge of the secondary blades is downstream of the trailing edge of the main blades, the part of the generator of the secondary blades located between the second transverse plane and the fourth transverse plane then overlaps part of the generator of the main blades.

With generators that have similar curvatures (between main and/or secondary blades), flow disturbances and therefore energy losses are limited.

The invention also relates to a pump, preferably multiphase, comprising an external casing, an axial succession of compression stages inside this external casing. Each compression stage comprises a fixed part and a rotating part. The pump also comprises a first axial inlet opening for the inlet of a fluid into the pump and a second axial outlet opening for the outlet of the fluid from the pump. In addition, at least one fixed part (preferably, each fixed part) comprises a stator as described above.

The pump of the invention allows the pumping of both multiphase fluid and single-phase fluid, in particular compressible fluid, including in particular CO2.

Using a stator as described above can improve pump performance.

The outer casing of the pump can serve as a stator housing. In other words, the outer casing of the pump can advantageously correspond to the stator housing described above to limit the number of parts and simplify assembly.

Preferably, the outer casing may comprise at least one portion with an internal surface of strictly decreasing inner diameter, in the direction of flow of the fluid axially through the pump (i.e. the portion has a strictly decreasing inner diameter between the first axial inlet opening and the second axial outlet opening). This portion of the outer casing may in particular be located opposite the stator of the invention so as to improve the compression performance. This is particularly advantageous when the fluid is compressible such as CO2.

Preferably, the outer casing may comprise several portions each with an internal surface of strictly decreasing inner diameter, in the direction of the flow of the fluid axially through the pump (i.e. the portion has a strictly decreasing inner diameter between the first axial inlet opening and the second axial outlet opening). These portions of the outer casing may in particular be located opposite each of the stators of the pump so as to improve the compression performance. This is particularly advantageous when the fluid is compressible such as CO2. For example, the outer casing may comprise a succession of cylinders, facing each rotating part, and portions each with an internal surface of strictly decreasing inner diameter (i.e. the portion has a strictly decreasing inner diameter between the first axial inlet opening and the second axial outlet opening), facing each stator. This configuration is preferred for efficiently compressing compressible gases such as CO2.

Figure 2 illustrates, in a schematic and non-limiting manner, a first example of a multiphase pump according to the invention.

The multiphase pump 100 thus represented in a longitudinal plane with Z(m), the position along the longitudinal axis of the pump and R(m) the radial position, comprises several mobile rotors Ro1, Ro2 and Ro3 and several fixed stators St1, St2 and St3. Thus, the multiphase pump 100 here has three compression stages (but could comprise a different number of compression stages), each compression stage comprising a rotor followed by a stator.

The multiphase pump 100 also comprises an external casing 101 (in which the different rotors Ro1, Ro2 and Ro3 and the different stators St1, St2 and St3 are inserted), which can also serve as a stator casing. In this example, the external casing is formed by a cylinder of constant internal diameter.

Figure 3 illustrates, in a schematic and non-limiting manner, a second example of a multiphase pump according to the invention.

The multiphase pump 100 thus represented in a longitudinal plane with Z(m), the position along the longitudinal axis of the pump and R(m) the radial position, comprises several mobile rotors Ro1, Ro2 and Ro3 and several fixed stators St1, St2 and St3. Thus, the multiphase pump 100 here has three compression stages (but could comprise a different number of compression stages), each compression stage comprising a rotor followed by a stator.

The flow through the pump starts with the rotor Ro1 , then the stator St1 , followed by the rotor Ro2 and then the stator St2. The fluid then passes through the rotor Ro3 and then the stator St3. In the figure, the flow is therefore from left to right

The multiphase pump 100 also comprises an external casing 101 (in which the different rotors Ro1, Ro2 and Ro3 and the different stators St1, St2 and St3 are inserted), which can also serve as a stator casing. In this example, the external casing is formed by a cylinder with an internal diameter decreasing between the inlet of the pump and its outlet. The external casing comprises in particular portions 102, facing each stator St1, St2 and St3 in which the internal diameter decreases along the longitudinal axis, in the direction of movement of the fluid flow through the pump. This configuration is particularly advantageous for highly compressible fluids, such as CO2. Indeed, this high compressibility generates a reduction in volume which requires a reduction in section. The rotors Ro1, Ro2 and Ro3 are then adapted to the decrease in the volume flow rate of the fluid.

Figure 4 illustrates, in a schematic and non-limiting manner, a view in a longitudinal plane of a stator according to the invention. Z(m) represents the position along the longitudinal axis.

The leading edges 10 of the main blades are positioned upstream of the leading edges 20 of the secondary blades (the fluid flowing from left to right) and the trailing edges 30 of the secondary blades are positioned upstream of the trailing edges 40 of the main blades (alternatively, the trailing edges 30 of the secondary blades could be downstream of the trailing edges 40 of the main blades or be positioned on the same transverse plane as the trailing edges 40 of the main blades).

The stator comprises an input section A1 and an output section A2. r _lh , r _lt , r _2h and ^r 2t respectively represent the radius at the hub at the stator input, the radius at the housing at the stator input, the radius at the hub at the stator output, and the radius at the housing at the stator output.

L _d represents the axial length of the stator.

Figure 5 illustrates, in a schematic and non-limiting manner, a developed view of a stator according to the invention. Z(m) represents the position along the longitudinal axis and 6 represents the azimuthal evolution of the stator.

The capture zone ZC is the zone located between the first transverse plane defined by the leading edges of the main blades 50 and the second transverse plane defined by the leading edges of the secondary blades 60. It therefore corresponds to the gray zone.

The first transverse plane is defined by the position zLEm which corresponds to the position along the longitudinal axis of the leading edges of the main blades 50.

The second transverse plane is defined by the position zLEs which corresponds to the position along the longitudinal axis of the leading edges of the secondary blades 60.

The trailing edges of the secondary blades 60 define a third transverse plane corresponding to the position zTEs along the longitudinal axis.

The trailing edges of the main blades 50 define a fourth transverse plane corresponding to the position zTEm along the longitudinal axis.

The stator shown therefore comprises a circumferential succession of main blades 50 and secondary blades 60 (only one part of the blades is shown; of course, the stator comprises as many main blades 50 as secondary blades 60 and the number of main blades 50 and secondary blades 60 depends on the chosen application.

The main blades 50 have an axial length L _m and the secondary blades 60 have an axial length L _s , which is here strictly less than the axial length L _m of the main blades 50.

The generators (represented by the dotted curved lines) of the main blades 50 are similar: they can overlap. The generators of the secondary blades 60 can overlap the generators of the main blades 50 over their axial length Ls between the second transverse plane and the third transverse plane defined by the trailing edges of the secondary blades 60.

Furthermore, the main blades are defined by the angular gap A9 _mb between the leading edge and the trailing edge of each main blade 50 and the stator is defined by the angular overlap, A0 _Oi , which is the gap between the trailing edge of one main blade 50 and the leading edge of the next main blade 50 (directly in the circumferential direction, from the intrados of the blades to the extrados).

This angular overlap A9 _0L is defined, surprisingly, by a linear equation as a function of the parameter ALR which is the ratio between the axial length of the main blades and the external radius at the inlet (at the leading edge) of the main blades, as expressed below:

With for example a= 1.16 and b=-0.57

A9 _0L can be positive when it is directed towards (+): in this case, there is indeed a partial overlap of the main blades 50. It can also be negative when it is directed towards (-): in this case, there is no overlap of the main blades but on the contrary an offset.

Indeed, numerical simulations have shown that this linearization makes it possible to obtain an optimum, despite the presence of numerous influential parameters for these complex multi-parameter simulations.

The angular distance A9 _placed between two successive main blades directly (distance between the generators of these two blades) can be defined as follows:

A9 _mis = A9 _0L + A9 _mb = (1 - OL-)A9 _mb

Figure 6 illustrates, in a schematic and non-limiting manner, a developed view of a stator according to the invention with other parameters. Z(m) represents the position along the axis longitudinal and X=r0 represents the azimuthal evolution of the stator, r being the radial position and 0 the circumferential angle.

The first transverse plane is defined by the position zLEm which corresponds to the position along the longitudinal axis of the leading edges of the main blades 50.

The second transverse plane is defined by the position zLEs which corresponds to the position along the longitudinal axis of the leading edges of the secondary blades 60.

The trailing edges of the secondary blades 60 define a third transverse plane corresponding to the position zTEs along the longitudinal axis.

The trailing edges of the main blades 50 define a fourth transverse plane corresponding to the position zTEm along the longitudinal axis.

The stator shown therefore comprises a circumferential succession of main blades 50 and secondary blades 60 (only part of the blades is shown; of course, the stator comprises as many main blades 50 as secondary blades 60 and the number of main blades 50 and secondary blades 60 depends on the chosen application).

The main blades 50 have an axial length L _m and the secondary blades 60 have an axial length L _s , which is here strictly less than the axial length L _m of the main blades 50 (but this axial length L _s of the secondary blades could be greater than or equal to the axial length L _m of the main blades).

The generators (represented by the dotted curved lines) of the main blades 50 are similar: they can overlap. The generators of the secondary blades 60 can overlap the generators of the main blades 50 over their axial length Ls between the second transverse plane and the third transverse plane defined by the trailing edges of the secondary blades 60.

Furthermore, the secondary blades 60 are defined by the axial offsets of the leading edges ôz _LE and the trailing edges <Sz _rE respectively relative to the leading edges and the trailing edges of the main blades 50. Thus, these axial offsets 8z _LE and 8z _EE can be defined by ôz _EE — zLE _s — zLE _m

8Z _TE = zTE _s - zTE _m

In addition, the secondary blades 60 are also defined by the offset of the circumferential distance between the extrados of the main blade and the intrados of the intermediate blade <5 _s and the main blades are also defined by the inter-main blade circumferential distance AX _m .

Numerical studies have shown that optimal results are obtained for the following criteria:

< 0,3 et de préférence 0,15 < SLES = —

< 0,25 Lm m -0,3 < STES = — < 0,3 et de préférence -0,1 < STES = ^ < 0,1 m _m x v x v - 0.1 < SLES = —

< 0.3 and preferably 0.15 < SLES = —

< 0.25 Lm m -0.3 < STES = — < 0.3 and preferably -0.1 < STES = ^ < 0.1 m _m xvxv

0.2 < SCP = -^ < 0.5 and preferably 0.25 < SCP = -^ < o.35

Figure 7 illustrates, in a schematic and non-limiting manner, the curve of the pressure recovery coefficient Cp as a function of the SLES parameter defined previously in the description of figure 6.

Curve Ref represents the curve of the recovery coefficient Cp for a stator of the prior art (without secondary blades, with only main blades). The characteristics of the main blades are identical to those used for the invention (apart from the number of blades which is twice the number of main blades).

The Sim points represent the results from the numerical simulations of the stator of the invention and the FC curve represents the curve passing best through the Sim points. The dotted Ref+10 curve represents a 10% increase in the pressure recovery coefficient Cp of the Ref curve. It is observed that this increase of at least 10% is obtained when the SLES parameter is between 0.1 and 0.3 and that the increase is maximum when the SLES parameter is between 0.15 and 0.25.

This increase has little or no impact on the fluid outlet angle, meaning that fluid flow straightening performance is maintained.

Figure 8 illustrates, in a schematic and non-limiting manner, the curve of the pressure recovery coefficient Cp as a function of the SCP parameter defined previously in the description of figure 6.

Curve Ref represents the recovery coefficient curve for a prior art stator (without secondary blades, with only main blades). The characteristics of the main blades are identical to those used for the invention (apart from the number of blades which is twice the number of main blades).

The CFD Values points represent the results from the numerical simulations of the stator of the invention and the black curve represents the curve passing best through the CFD_Values points.

This figure shows a gain obtained when the SCP parameter is less than 0.5 and a more interesting gain when it is between 0.25 and 0.35.

Figure 9 illustrates, in a schematic and non-limiting manner, examples of hub and casing profiles and blade profiles of a stator according to the invention. Diagram a) illustrates the profiles of the hub P1 (curve in black) and the housing P2 (in lighter gray) as a function of the position Z(m) along the longitudinal axis and as a function of the radial position R(m).

Diagram b) illustrates the profile of the main blades at the hub P1 and at the casing P2, as a function of the position Z(m) along the longitudinal axis and as a function of the circumferential position X(m) which depends on the azimuth angle and the radial position.

The geometric data of the various parameters defined in this description and fixed by these profiles of the main blades are grouped in the following table.

The stator of the invention comprises, for example, 13 main blades and 13 secondary blades.

The secondary blades are defined by the following parameters, also previously defined in this description.

Example

The stator of the invention, in particular with the parameters described previously for figure 9, was compared to a stator of the prior art for which the main blades are identical in their characteristics and for which the number of main blades is double that of the number of main blades of the stator of the invention.

Numerical simulations have the following input conditions:

- The fluid is CO2;

- The inlet pressure in the stator is 23 bar (i.e. 2.3 10 ⁶ Pa);

- The density of the fluid is: 1061.89 kg/m;

- The viscosity of the fluid is: 1.5567 10“ ⁴ Pa. s;

- The flow angle at the stator inlet is: 71.14°;

- The mass flow rate at the stator inlet is: 31.7 kg/s.

The pressure coefficient represents the stator's ability to transform the dynamic pressure of the flow into static pressure. The outlet angle provides information on its ability to straighten the flow (bring it back into the axial direction) for the next stage of the pump.

The addition of secondary blades allows an increase in the pressure recovery coefficient Cp of more than 38%, from 0.52 to 0.72, thus reflecting the good capacity of the stator to transform the dynamic pressure of the flow into static pressure. The fluid outlet angle remains within a range of +/-10% compared to the prior art version without secondary blades, which ensures sufficient flow straightening. The significant gain obtained for the pressure recovery coefficient Cp is directly attributable to a modification of the flow topology in the stator of the invention thanks to the offset of the leading edges of the secondary blades, downstream of the leading edges of the main blades.

Figure 10 illustrates views in a longitudinal plane of the axial velocity field for the stator of the prior art (diagram (a)) and for the stator of the invention (diagram (b)). In diagram (a), low-velocity zones 210 and 220 linked to flow separations are observed.

We can observe in diagram b), a massive reduction in low speed zones (and therefore a reduction in flow separations) thanks to the use of secondary blades according to the invention.

Claims

Claims 1. Pump stator (St1, St2, St3) comprising a hub and a casing coaxial about a longitudinal axis, an axial inlet (A1) for introducing a fluid into the stator and an axial outlet (A2) for discharging the fluid from the stator, a first series of main blades (50) and a second series of secondary blades (60), said main (50) and secondary (60) blades extending radially from the hub to the casing, the generatrices of the main (50) and secondary (60) blades extending substantially axially, the secondary blades (60) being intercalated circumferentially between the main blades (50), the leading edges (10) of the main blades (50) being on the same first transverse plane, characterized in that the leading edges (20) of the secondary blades (60) are positioned on a second transverse plane parallel to the first plane transverse, the second transverse plane being positioned axially at a first predetermined distance (ÔZLE) from the first transverse plane, in the direction of said axial outlet (A2), the first predetermined distance (5Z _L E) being between 0.1 and 0.3 times, preferably between 0.15 and 0.25 times, the axial length (Lm) of the main blades (50). 2. Pump stator (St1, St2, St3) according to claim 1, in which the axial length (Ls) of the secondary blades (60) is less than or equal to said axial length (Lm) of the main blades (50). 3. Pump stator (St1, St2, St3) according to one of the preceding claims, in which the trailing edges (30) of the secondary blades (60) form a third transverse plane positioned at a second predetermined distance (ÔZ _T E) from a fourth transverse plane formed by the trailing edges (40) of the main blades (50), the second predetermined distance (ÔZ _T E) being between -0.3 times and +0.3 times, preferably between -0.1 times and +0.1 times, said axial length (Lm) of the main blades (50), preferably, the second predetermined distance (5Z _T E) is zero. 4. Pump stator (St1, St2, St3) according to one of the preceding claims, in which the secondary blades (60) are offset, in the circumferential direction, from the main blades (50) directly preceding them in the circumferential direction, by an angle of between 0.2 and 0.5 times, preferably between 0.25 and 0.35 times, the circumferential angular offset (A0 _miS ) of the main blades (50). 5. Pump stator (St1, St2, St3) according to one of the preceding claims, in which the ratio between the section of the axial outlet (A2) and the section of the axial fluid inlet (A1) is between 0.5 and 2.5, preferably between 0.5 and 1.5. 6. Pump stator (St1, St2, St3) according to one of the preceding claims, in which the ratio between said axial length (Lm) of the main blades (50) and the external radius at the leading edge of the main blades is between 0.36 and 1.80, preferably between 0.65 and 1.64. 7. Pump stator (St1, St2, St3) according to one of the preceding claims, in which the external diameter of the main (50) and/or secondary (60) blades decreases from the axial inlet (A1) towards the axial outlet (A2). 8. Pump stator (St1, St2, St3) according to one of the preceding claims, in which the internal diameter of the main (50) and/or secondary (60) blades decreases from the axial inlet (A1) towards the axial outlet (A2). 9. Pump stator (St1, St2, St3) according to one of the preceding claims, in which the main blades (50) are offset two by two successively in the circumferential direction by a circumferential angular distance A6 _mis substantially verifying: dmis = (1 - O ) ■ A6 _mb and OL = a * ALR + b With A6 _mb the circumferential angular deviation of the main blades, corresponding substantially to the circumferential angular deviation generated between the leading edge and the trailing edge of each main blade (50); ALR: the ratio between said axial length (Lm) of the main blades (50) and the external radius at the leading edge of the main blades (50) and a and b being predetermined values. 10. Pump (100), preferably multiphase, comprising an outer casing (101), an axial succession of fixed parts and rotating parts (Ro1, Ro2, Ro3) inside the outer casing (101), a first axial inlet opening for the inlet of a fluid into the pump and a second axial outlet opening for the outlet of the fluid from the pump, in which at least one fixed part comprises a stator (St1, St2, St3) according to one of the preceding claims, preferably the outer casing (101) corresponding to the stator casing. 11. Pump (100) according to the preceding claim, in which the external casing (101) comprises at least one portion (102) with an internal surface of strictly decreasing internal diameter, in the direction of flow of the fluid axially through the pump (100), preferably the external casing (101) comprises several portions (102) each with an internal surface of strictly decreasing internal diameter, in the direction of flow of the fluid axially through the pump (100).