COMPRESSION OR PUMPING DEVICE COMPRISING A MEANS OF REDUCING THE TANGENTIAL VELOCITY OF THE CLEARANCE FLOW

Description

FIELD OF THE DISCLOSURE

The disclosure concerns the field of fluid compression or pumping devices, more specifically compression or pumping of multiphase fluids. The disclosure concerns more particularly a multiphase pump that can notably be used in petroleum applications or for fluid injection into and/or storage in a geological reservoir.

A fluid compression or pumping device generally comprises one or more compression stages. Each compression stage comprises at least one mobile part with a rotating wheel (this mobile part is also referred to as rotor or impeller) and at least one stationary part. The stationary part can comprise a flow straightener (also referred to as stator or diffuser). These elements can be arranged in a housing of the compression device, the stationary part also comprising the housing. The stator can be integrated in the housing.

The stator can be positioned upstream and/or downstream from a rotating wheel. When it is positioned downstream, its role can be to straighten the flow of the fluid from the wheel, the flow being rotated by the rotating wheel. Its purpose is to be able to supply the next compression stage (another rotating wheel downstream from the stator) or to use the fluid flow directly. Such a stator is used to convert the kinetic energy of the fluid into potential energy. The stator therefore generally comprises blades. The stator is static, whereas the rotating wheels are mobile in rotation about a longitudinal axis. The purpose of these rotating wheels is to increase the kinetic energy and the potential energy of the fluid. They are generally attached to a rotary shaft and they comprise blades.

More specifically, the disclosure concerns a pump intended for pumping a fluid, a multiphase fluid for example.

BACKGROUND OF THE DISCLOSURE

In the field of multiphase pumps, the “shrouded rotor” technology has been under development for some years. Patent applications US-2011/0,280,706 A1 and EP-3,536,975 A1 concern for example multiphase pumps with shrouded rotors. This technology consists in adding an external shroud surrounding the rotor blades. This rotor shroud allows to improve the mechanical stability of the assembly. Indeed, the frictional forces induced by the flow between this shroud and the external housing allow the vibrations to be damped.

However, the fluid flowing through the clearance between the shroud and the housing moves in the opposite direction to the fluid passing through the rotor blades, forming a secondary flow. Furthermore, this secondary flow, also referred to as clearance flow between the shroud and the housing, has a high tangential velocity known as swirl, which disturbs the principal flow of the fluid entering the rotor. In other words, what is referred to as “clearance flow” is a flow in the clearance between two assembled mechanical parts, the shroud and the housing here.

Indeed, the fluid leaving the clearance flow is mixed with the fluid flowing in addition towards the rotor inlet (passing through the blades). This mixture thus directly impacts the incidence angle of the fluid entering the rotor and it generates a reduction in performance.

FIG. 1 illustrates the impact of the tangential velocity resulting from the clearance flow on the fluid arriving at the leading edge of blades 20. FIG. 1 is a developed view in a longitudinal plane of the rotor.

U₁ represents the blade velocity at the leading edge, and U₂ the blade velocity at the trailing edge. V₁ represents the absolute velocity of the fluid at the leading edge, and V₂ the absolute velocity of the fluid at the trailing edge.

Ω corresponds to the rotational speed of the rotor.

Vector W₁ is the relative velocity vector resulting from velocities V₁ and U₁ at the leading edge, and vector W₂ is the relative velocity vector resulting from velocities V₂ and U₂ at the trailing edge. Angle β₂ is the angle formed between vector W₂ and the transverse plane in dotted line at the trailing edge.

The work w per unit mass generated by such a machine is written, using the Euler equation, in the form:

w = U 2 → · V 2 → - U 1 → · V 1 → = U 2 ⁢ V θ 2 - U 1 ⁢ V θ 1 = r 2 ⁢ Ω ⁢ V θ 2 - r 1 ⁢ Ω ⁢ V θ 1

with:

• • V_θ1 the absolute tangential velocity at the leading edge
  • V_θ2 the absolute tangential velocity at the trailing edge
  • r₁, r₂ the radii considered at the leading edge and at the trailing edge respectively.

If the fluid flowing toward the leading edge was orthogonal to the transverse plane (shown by the dotted line), velocity V₁ would be horizontal in the figure (as represented by the dotted arrow). However, here, velocity V₁ forms a non-zero angle to the horizontal, as shown by the solid arrow. This is due to angle δβ due to the tangential velocity of the fluid coming from the clearance flow as explained above. This fluid from the clearance flow disturbs the fluid flowing toward the blades. This phenomenon is known as pre-swirl or as pre-rotation. Thus, the incidence angle of the fluid with respect to the transverse plane (orthogonal to the longitudinal axis) that would be β₁ without the impact of the clearance flow is modified to β₁+δβ. The modification of the incidence angle of the fluid directly impacts the turbomachine performance.

Patent application US-2014/0,205,444 A1 proposes anti-swirl devices positioned in the clearance in order to limit dynamic rotor instabilities. However, this does not prevent a tangential velocity of the fluid leaving the clearance flow.

Patent application US-2015/211,543 A1 proposes anti-swirl devices positioned at the flow between the shroud and the housing, in order to reduce the tangential velocity and rotor instabilities. However, this does not prevent a tangential velocity of the fluid leaving the clearance flow.

Patent application WO-2014/153,345 A1 concerns a pump with a balance piston and no blades. This balance piston is used to counteract the thrust force for multiphase pumps with a high differential pressure. An anti-swirl device is positioned between the balance piston and the housing to stabilize the pressure field, notably when the pump has a significant differential pressure.

Patent application EP-3,913,227 A1 concerns a multiphase pump with a shrouded rotor. Anti-swirl devices are provided on the stator, at the clearance flow or at the fluid inlet into the clearance flow, to slow down the swirls. However, this does not prevent a tangential velocity as the fluid leaves the clearance flow.

The goal of the disclosure is to reduce or to eliminate the tangential velocity of the fluid leaving the clearance flow of a shrouded rotor, in order to increase the device performance while ensuring mechanical stability and vibration reduction of the device.

SUMMARY OF THE DISCLOSURE

The disclosure concerns a device for compressing or pumping a fluid, preferably a multiphase fluid, comprising a stationary part, at least one rotor and a rotor shaft, each rotor being integral with the rotor shaft, the rotor shaft being configured to be rotated about a longitudinal axis, each rotor comprising blades extending substantially radially to the longitudinal axis and at least one of the at least one rotor being a shrouded rotor comprising a circumferential shroud connecting the peripheral radial tips of the blades, the stationary part comprising at least one stator and at least one external portion surrounding each rotor, the device comprising a clearance between the outer surface of each circumferential shroud of the shrouded rotor and the inner surface of the external portion surrounding this shrouded rotor, allowing a clearance flow in the opposite direction to the fluid flow through this shrouded rotor. Furthermore, the stator upstream from the shrouded rotor comprises a means for reducing the tangential velocity of the fluid from the clearance flow, each reduction means being positioned axially opposite the shroud of the shrouded rotor and/or said clearance, upstream from the shrouded rotor in the direction of flow through the shrouded rotor.

Preferably, the device comprises several stators and/or several rotors, preferably the stators and the rotors follow one another alternately along the longitudinal axis.

Advantageously, each rotor comprises at least one series of blades, each series of blades comprising blades evenly distributed around the rotor shaft, preferably each rotor comprises at least two series of blades following one another longitudinally.

Preferably, the device comprises several shrouded rotors.

Advantageously, the circumferential shroud of the shrouded rotor extends longitudinally over a length allowing to cover at least one of the series of blades, preferably all the series of blades and more preferably the length of the shroud equals the length of the rotor concerned.

Preferably, the circumferential shroud is circumferentially complete or circumferentially incomplete with at least one opening.

According to one embodiment of the disclosure, the reduction means consists of cavities in the stator intended to reduce the tangential velocity of the fluid from the clearance flow, the cavities facing the outlet of the fluid from the clearance flow, the cavities being circumferentially distributed over the stator and separated from one another by interfaces, preferably some of the interfaces comprising stator blade extensions.

Preferably, the cavities comprise grooves of crenellated shape or of triangular section developed in the circumferential direction.

Advantageously, the number of cavities between two successive blades of the rotor opposite the reduction means ranges between 3 and 10.

Advantageously, the ratio of the cavity height to the blade height ranges between 10% and 40%, preferably between 15% and 25%.

Preferably, the ratio of the cavity depth to the longitudinal rotor length ranges between 2% and 20%, preferably between 5% and 10%.

The disclosure also concerns a multiphase pump comprising a device according to one of the variants or variant combinations described above.

The disclosure further concerns using the device as described according to one of the variants or variant combinations described above or the multiphase pump described above for extracting oil or gas from a geological reservoir and/or for injecting a fluid into a geological reservoir.

BRIEF DESCRIPTION OF THE FIGURES

Other features and advantages of the device and/or of the pump according to the disclosure will be clear from reading the description hereafter of embodiments given by way of non-limitative example, with reference to the accompanying figures wherein:

FIG. 1 (already described) shows the composition of the velocity components of the incoming fluid on the rotor blades of the device according to the prior art,

FIG. 2 shows an embodiment of a compression or pumping device according to the disclosure,

FIG. 3 shows various shrouded rotor compositions of the compression or pumping device according to the disclosure,

FIG. 4 shows the effect of the fluid from the clearance flow in the tangential velocity reduction means of a compression or pumping device according to the disclosure,

FIG. 5 shows different tangential velocity reduction means variants of a compression or pumping device according to the disclosure,

FIG. 6 shows a first example of a stator with a tangential velocity reduction means of a compression or pumping device according to the disclosure,

FIG. 7 shows a second example of a stator with a tangential velocity reduction means of a compression or pumping device according to the disclosure,

FIG. 8 shows a comparison of the fluid velocities via CFD simulations around an unshrouded rotor according to the prior art (a), around a shrouded rotor according to the prior art (b) and around a shrouded rotor and a stator comprising a tangential velocity reduction means of a compression or pumping device according to the disclosure (c),

FIG. 9 shows photographs of a stator of the prior art (a) and of a stator comprising a tangential velocity reduction means (b),

FIG. 10 shows the composition of the velocity components of the incoming fluid on the rotor blades, and

FIG. 11 shows an example of an incomplete circumferential shroud of a compression or pumping device according to the disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The disclosure concerns a device for compressing or for pumping a fluid, preferably a multiphase fluid. A multiphase fluid is understood to be a fluid comprising at least two phases: for example two separable liquid phases, a gas phase and a liquid phase, or a liquid phase and a solid phase. Of course, the multiphase fluid can comprise more than two phases.

The device according to the disclosure comprises at least one stator, at least one rotor and a rotor shaft. Each rotor is integral with the rotor shaft, itself configured to be rotated about a longitudinal axis. The rotor shaft can therefore drive each rotor in rotation so as to allow pumping or compression of the fluid.

Each rotor comprises blades extending substantially radially to the longitudinal axis. The incoming fluid thus flows along the longitudinal axis, and it is pumped or compressed while passing through the rotor, by flowing between the rotor blades.

Furthermore, at least one rotor is a shrouded rotor comprising a circumferential shroud connecting the peripheral radial tips of the blades. In other words, the circumferential shroud forms an outer shell of a shrouded rotor, integral therewith. This outer shell surrounds the outer blade tips. This circumferential shroud can notably consist of a cylindrical shroud of annular section or of a tubular shroud.

In the sense of the present description, inner and outer tips are relative to one another, the inner tip being relatively closer to the longitudinal axis than the outer tip (also referred to as peripheral tip).

The circumferential shroud can be circumferentially complete or incomplete (what is meant here is a partial ring). A complete circumferential shroud refers to a circumferential shroud extending circumferentially all around the rotor in one part, without an opening, while an incomplete circumferential shroud does not extend circumferentially all around the rotor: an incomplete circumferential shroud can have at least one opening (preferably a small opening) in the shroud. When the incomplete circumferential shroud has a single opening, it can consist of a single part. When the incomplete circumferential shroud has at least two openings, it can consist of at least two distinct parts separated by the openings.

The stationary part comprises at least an external portion (a part of the housing) surrounding each rotor. This external portion offers the user protection against the rotating parts on the one hand, and it also allows to contain the fluid flowing through the device on the other hand.

The device according to the disclosure also comprises a clearance between the outer surface of the circumferential shroud of the shrouded rotor (of each shrouded rotor when several rotors are shrouded) and the inner surface of the external stator portion surrounding each shrouded rotor. This clearance forms a substantially annular space between the shrouded rotor and the housing. This clearance notably allows the rotor to rotate whereas the housing is stationary. It however provides a clearance flow in an opposite direction to the principal fluid flow through each shrouded rotor (i.e. to the fluid flow through the blades of the shrouded rotor).

The stationary part can comprise a housing (with the various external portions surrounding each rotor) and at least one stator.

Besides, the stator upstream from the shrouded rotor (of each shrouded rotor when the device comprises several shrouded rotors), in the direction of the principal fluid flow in the shrouded rotor, comprises a means for reducing the tangential velocity of the fluid from the clearance flow, each reduction means being positioned axially opposite the circumferential shroud of the shrouded rotor concerned and/or said clearance, upstream from the shrouded rotor in the direction of flow through the rotor concerned (i.e. through the rotor blades).

“The stator upstream from the shrouded rotor, in the direction of the principal fluid flow in the shrouded rotor” refers to the stator that precedes the rotor in the direction of the principal flow, the one just before the rotor concerned.

By allowing to reduce the tangential velocity of the fluid from the clearance flow that mixes with the fluid flowing into the rotor, the impact of this velocity on the fluid entering the rotor can be limited. This therefore improves the performance of the compression or pumping device according to the disclosure.

Furthermore, by positioning the reduction means opposite the shroud and/or the clearance, disturbances to the fluid entering the rotor are limited, and vibrations can thus also be limited. The service life of the device can thus also be improved.

Advantageously, the device can comprise several stators and/or several rotors, preferably the stators and the rotors follow one another alternately along the longitudinal axis.

It is thus possible to provide several compression or pumping stages to improve the performance of the device.

According to a variant of the disclosure, each rotor can comprise at least one series of blades, each series of blades comprising blades evenly distributed around the rotor shaft in the same transverse plane.

According to an aspect of the disclosure, each rotor can comprise at least two series of blades, said at least two series of blades following one another longitudinally. Using at least two series of blades for each rotor allows the compression or pumping performance to be improved.

A “transverse plane” is understood to be a plane substantially perpendicular to the longitudinal axis.

One at least of the series of rotor blades can have a helical shape, and preferably the series of blades of each rotor have a helical shape.

The device can comprise several shrouded rotors. In this case, each stator preceding just upstream each shrouded rotor in the direction of the principal fluid flow in the shrouded rotor concerned can comprise a means for reducing the tangential velocity of the fluid from the clearance flow, each reduction means being positioned axially opposite the circumferential shroud of the shrouded rotor concerned and/or said clearance, upstream from the shrouded rotor concerned in the direction of the principal flow through the shrouded rotor concerned.

According to an aspect of the disclosure, the circumferential shroud of the shrouded rotor can extend longitudinally over a length allowing to cover at least one series of blades, preferably all the series of blades, and more preferably the length of the shroud equals the length of the rotor concerned. In other words, the shroud can be total when its length equals that of the rotor concerned, or partial when its length is strictly less than that of the rotor concerned. A partial shroud allows to keep a tip clearance flow within the rotor generating a mixture and providing homogenization of a liquid/gas flow. This occurs at the expense of a reduction in the damping generated by the shroud, the area of high fluid friction (shroud/housing) being reduced.

Preferably, each reduction means can consist of cavities in the stators for reducing the tangential velocity of the fluid from the clearance flow. These cavities can be positioned opposite the outlet of the clearance flow fluid (therefore opposite the clearance and/or the shroud, upstream from the rotor in the direction of flow in the rotor). The cavities are thus as close as possible to the outlet of the clearance flow fluid. This position allows to minimize fluid disturbances related to the fluid coming from the clearance flow. The cavities allow to collect the fluid and to stop (or to limit) the tangential velocity of the fluid from the clearance flow.

The cavities can be distributed circumferentially over the stator so as to ensure homogeneous efficiency of the tangential velocity reduction all around the rotor, and thus to limit vibrations. The cavities can be separated from one another by interfaces. The interfaces can for example form radial walls between the cavities. A multiplicity of cavities and interfaces allows to generate fluid swirls within the cavities, which allows to considerably reduce the tangential velocity of the fluid from the clearance flow before it mixes with the fluid entering the rotor.

Preferably, some interfaces can comprise stator blade extensions (more precisely, stator wheel blade extensions).

Preferably, the cavities can comprise grooves of crenellated shape (of rectangular section in a developed plane) or of triangular section developed in the circumferential direction. Thus, opposite and upstream (in the direction of flow of the fluid in the rotor blades) from the clearance and/or the shroud, the stator can comprise an annular portion comprising crenellated or triangular grooves, separated by interfaces such as radial walls. This arrangement allows the tangential velocity of the fluid from the clearance flow to be reduced.

When the cavities comprise grooves of triangular shape, preferably in the shape of a right-angled triangle, depth d_SB and space w_SB can be defined so as to satisfy the following equation, where γ corresponds to the angle formed by the fluid leaving the clearance flow with respect to an orthogonal plane to the longitudinal direction:

tan ⁢ γ = w SB d SB

This allows the reduction in the tangential velocity to be optimized.

If it is desired to fix depth d_SB, space w_SB between the cavities can be determined according to the number of cavities N_SB around the stator and according to the number of stator blades N_s and to the outer radius R_ext of the stator (radius of the fluid flow area in the stator) from the following equation:

N SB = ⌊ 2 ⁢ π ⁢ R ext N S ⁢ w SB ⌋

Alternatively, if it is desired to fix space w_SB between the cavities, depth d_SB can be calculated.

Advantageously, the number of cavities between two successive rotor blades opposite the reduction means can range between 3 and 10. This configuration allows sufficient tangential velocity reduction.

According to an aspect of the disclosure, the ratio of the cavity height to the blade height can range between 10% and 40%, preferably between 15% and 25%.

Advantageously, the ratio of the cavity depth to the longitudinal rotor length can range between 2% and 20%, preferably between 5% and 10%.

These various configurations provide a good compromise between sufficient tangential velocity reduction and implementation complexity.

The disclosure also concerns a multiphase pump for a multiphase fluid, comprising a device as described according to one of the variants or variant combinations of the present description.

The disclosure further concerns using the device as described according to one of the variants or variant combinations described in the present description or the multiphase pump described above for extracting oil or gas from a geological reservoir and/or for injecting and/or storing a fluid in a geological reservoir.

FIG. 2 schematically illustrates, by way of non-limitative example, an example of a fluid compression or pumping device according to the disclosure.

Diagram a) is an overview and diagram b) represents a zoom on the clearance flow and the shroud.

The fluid compression or pumping device according to the disclosure comprises a rotor 22, which is a shrouded rotor, and a stationary part. The stationary part comprises an external portion 30 (which is part of the housing) that surrounds shrouded rotor 22 and a stator with a stator wheel 31 (stator wheel 31 comprising stator blades).

Shrouded rotor 22 comprises here a series of blades of helical shape, but it could comprise several series without departing from the scope of the disclosure. Shrouded rotor 22 also comprises a circumferential shroud 21a that surrounds the blades. Here, shroud 21a is a total shroud that surrounds the series of blades, and whose axial length equals the axial length of the rotor. The shroud could however alternatively be a partial shroud.

The device comprises a clearance between the outer surface of shroud 21a and the inner surface of external portion 30, which results in a clearance flow 23a. Indeed, part of the fluid coming from shrouded rotor 22 (after passing through blades 20 of rotor 22) is drawn into the clearance and it flows in the opposite direction to principal flow 24 of the fluid passing through rotor 22.

The stator comprises here, opposite shroud 21a and the clearance, a tangential velocity reduction means 35 for reducing this velocity of the fluid from the clearance flow. This reduction means is positioned just upstream from shrouded rotor 22, in the direction of the principal fluid flow in shrouded rotor 22, i.e. in blades 20 of the shrouded rotor.

The fluid leaving clearance flow 23a enters tangential velocity reduction means 35, which limits the tangential velocity of this fluid. The fluid entering the rotor via flow 24 is thus less disturbed by the fluid leaving the clearance flow.

FIG. 3 schematically illustrates, by way of non-limitative example, three variants of the fluid compression or pumping device according to the disclosure.

In each of the three variants, the fluid compression or pumping device comprises a shrouded rotor 22 and a stationary part. The stationary part comprises an external portion 30 (which is part of the housing) that surrounds rotor 22 and a stator with a stator wheel 31 (comprising stator blades).

Shrouded rotor 22 comprises here a series of blades 20 of helical shape, but it could comprise several series of blades without departing from the scope of the disclosure.

In diagram a), the rotor also comprises a circumferential shroud 21a that surrounds the series of blades and whose axial length equals the axial length of the rotor. Shroud 21a generates a clearance flow 23a between shroud 21a and external portion 30.

In diagram b), shrouded rotor 22 also comprises a circumferential shroud 21b that surrounds the blades. Shroud 21b is a partial shroud that surrounds the series of blades, but whose axial length is strictly less than the axial length of rotor 22. Shroud 21b generates a clearance flow 23b between shroud 21b and external portion 30.

In diagram c), shrouded rotor 22 also comprises a partial circumferential shroud 21c whose axial length is strictly less than the axial length of rotor 22, and which is arranged in the principal flow section. Shroud 21c generates a clearance flow 23c between shroud 21c and external portion 30.

FIG. 4 schematically illustrates, by way of non-limitative example, a developed view in a horizontal plane of a compression and pumping device according to the disclosure.

The device comprises a shrouded rotor with a shroud 21.

Ω illustrates the rotational speed of the rotor.

The fluid passing through the clearance flow has an absolute velocity V_TL consisting of a tangential velocity V_θTL and of an axial velocity V_ZTL.

The stator just upstream the shrouded rotor comprises here a tangential velocity reduction means 35 positioned so as to capture the fluid leaving the clearance flow (i.e. upstream from the shrouded rotor, the fluid circulating in the clearance flow having a flow in the opposite direction to the fluid passing through the rotor, and “upstream” meaning in the direction of circulation of the fluid in the shrouded rotor). This reduction means 35 is located opposite shroud 21 and the clearance. Furthermore, this reduction means 35 comprises crenellated cavities 36, so that the fluid leaving clearance flow 25 enters these cavities 36 to dissipate the tangential velocity.

As can be seen in the figure, cavities 36 are therefore separated by radial walls 37 that reduce the tangential velocity of the fluid.

Cavities 36 extend in the longitudinal and radial direction.

FIG. 5 schematically illustrates, by way of non-limitative example, various types of reduction means for the compression and pumping device according to the disclosure.

The various reduction means 35 of diagrams a) to c) show developed views of these reduction means.

Diagram a) comprises a reduction means 35 with crenellated grooves 36 (of rectangular section); diagram b) comprises a reduction means 35 with triangular grooves 37; diagram c) comprises a reduction means 35 with grooves having curved portions 38.

Each reduction means 35 can comprise cavities (crenellated, triangular or with complex shapes according to diagrams a) to c)) of height h_sB, the height being understood as the length in the radial direction, of depth d_sB, the depth being understood in the longitudinal direction (according to the longitudinal axis of the compression or pumping device), and the space between the cavities w_sB.

For the rectangular cavities corresponding to the crenellated grooves of diagram a), depth d_sB corresponds to the longitudinal length of the rectangle, and space w_sB can correspond to twice (but a different value could be used) the circumferential length of the cavities.

For the triangular cavities of diagram b), depth d_sB corresponds to the maximum depth of the section of the triangle. When the triangle is a right-angled triangle where the right angle forms a substantially longitudinal surface, this surface is positioned in such a way that the fluid leaving the clearance flow arrives against this surface so as to significantly reduce the tangential velocity, depth d_sB corresponds to the length of the side of the right-angled triangle oriented in the longitudinal direction. Space w_sB can correspond to the side oriented in the circumferential direction of the cavities.

For the cavities of complex shape (curved here) of diagram c), depth d_sB corresponds to the maximum depth of the cavity. This cavity of complex shape can comprise a substantially longitudinal surface, this longitudinal surface being positioned in such a way that the fluid leaving the clearance flow arrives against this surface so as to significantly reduce the tangential velocity. Depth d_sB can notably correspond to the longitudinal length of this longitudinal surface.

FIG. 6 schematically illustrates, by way of non-limitative example, a portion of a stationary part of a compression or pumping device according to the disclosure.

This stationary part comprises a housing with an external portion 30 and a stator with a stator wheel 31. Besides, the stator comprises a tangential velocity reduction means 35 comprising crenellated grooves that are positioned just upstream from the shrouded rotor (in the direction of flow of the fluid through the shrouded rotor), so as to capture the fluid leaving the clearance flow (flow in the opposite direction to the flow through the shrouded rotor). These grooves are positioned opposite the shroud of the shrouded rotor and/or the clearance between the shroud and external portion 30 of the housing.

The crenellated grooves are here separated by radial walls forming an interface between the crenellated grooves.

FIG. 7 schematically illustrates, by way of non-limitative example, another portion of a stationary part of a compression or pumping device according to the disclosure.

This stationary part comprises a housing with an external portion 30 and a stator with a stator wheel 31. Besides, the stator comprises a tangential velocity reduction means 35 comprising grooves of triangular shape that are positioned just upstream from the shrouded rotor (in the direction of flow of the fluid through the shrouded rotor), so as to capture the fluid leaving the clearance flow (flow in the opposite direction to the flow through the shrouded rotor). These grooves are positioned opposite the rotor shroud and/or the clearance between the shroud and external portion 30 of the housing.

The triangular-shaped grooves are here separated by interfaces (radial walls) forming an interface between the triangular-shaped grooves.

It can be observed in FIGS. 6 and 7 that reduction means 35 also comprises extensions of the stator wheel blades that thus form interfaces.

FIG. 11 schematically illustrates, by way of non-limitative example, a section in a plane perpendicular to the longitudinal axis of the device according to the disclosure.

The device comprises a rotor 22 with several blades 20 (four blades in the figure, but the rotor could have a different number of blades) and a stator that comprises external part 30.

Rotor 22 comprises a circumferential shroud 21a around the blades in order to form a shrouded rotor. This circumferential shroud 21a is circumferentially incomplete because it comprises different parts separated by openings 60. In this example, the incomplete circumferential shroud comprises four distinct parts separated by four openings, but another number of parts/openings could be used. The incomplete circumferential shroud is open or partly shrouded over the circumference.

Alternatively, circumferential shroud 21a could also consist of a single part whose circumferential ends are separated by a single opening.

According to yet another alternative, circumferential shroud 21a could be a complete circumferential shroud: this means that the circumferential shroud is then made of a single part covering the entire circumference around rotor 22, with no opening.

EXAMPLES

FIG. 8 illustrates comparisons of the tangential velocity at the rotor inlet (in the direction of flow of the fluid through the rotor) in meter per second for devices according to the prior art and according to the disclosure, based on modeling. FIG. 8 is a sectional view in a longitudinal plane.

Diagram a) illustrates an unshrouded (without a shroud) rotor of the prior art. Diagram b) illustrates a shrouded rotor of the prior art and diagram c) illustrates a shrouded rotor with a stator comprising a tangential velocity reduction means 35 positioned upstream from the shrouded rotor and opposite the shroud and the clearance between the shroud and the external portion of the housing.

A significant tangential velocity decrease is observed with the tangential velocity reduction means in diagram c) in relation to diagram b).

Furthermore, with a reduction means comprising crenellated grooves according to the disclosure, a 2.9% pressure increase and a 2.1% hydraulic efficiency increase are observed in comparison with the shrouded rotor solution of the prior art (with no reduction means opposite the shroud and/or the clearance and upstream from the rotor).

With a reduction means comprising grooves of triangular shape according to the disclosure, an 8% pressure increase and a 1.2% hydraulic efficiency increase are observed in comparison with the shrouded rotor solution of the prior art (with no reduction means opposite shroud 21 and/or the clearance and upstream from the rotor).

Besides, experimental tests were carried out to compare a shrouded rotor of a device from the prior art (with no reduction means opposite the shroud and/or the clearance and upstream from the rotor) and a shrouded rotor with a reduction means opposite the shroud and/or the clearance and upstream from the rotor of a device according to the disclosure.

FIG. 9 illustrates, in diagram a), a stator of a device from the prior art comprising a stator wheel 31, with no reduction means opposite the shroud and/or the clearance and upstream from the shrouded rotor, and in diagram b), a stator of a device according to the disclosure comprising a stator wheel 31, and a reduction means 35 arranged opposite the shroud and/or the clearance and upstream from the shrouded rotor. Reduction means 35 comprises here grooves of triangular shape (right-angled triangle).

Diagrams a) and b) are photographs of the two stators tested.

Of course, the other parameters of the two devices are substantially identical (notably the geometric data). The two devices therefore differ only regarding the reduction means 35 present in the device according to the disclosure and absent in the device according to the prior art.

FIG. 10 illustrates images taken during the tests carried out for a device according to the disclosure with a reduction means comprising grooves of triangular shape. A small amount of gas (approximately 5% gas volume fraction) was injected as a tracer for the photos and videos made during the tests. Diagram a) is an image at a flow rate representing 60% of the nominal flow rate of the device according to the disclosure, which substantially corresponds to the numerical value of 59.3% found by the numerical simulations, and diagram b) is an image at a flow rate representing 100% of the nominal flow rate of the device according to the disclosure. The rotational speed of the rotor is 2000 rpm for the two images of diagrams a) and b).

Arrows 40a and 40b, as well as swirls 41, were added in these images to facilitate understanding. Arrows 40a and 40b respectively represent the direction of flow in the clearance flow. Arrows 40a are inclined at about 41% to the longitudinal axis and arrows 40b are inclined at about 60% to the longitudinal axis. This shows that the fluid leaving the clearance flow has a non-zero tangential velocity (resulting from the rotation of the rotor and the flow rate through the rotor).

Swirls 41 in the triangular-shaped grooves of the reduction means show how the tangential velocity is reduced by the effect of the swirl generated.