Recirculation flow control for mixed-flow fan

Abstract

Described herein is a mixed-flow fan assembly (100). The assembly comprises an impeller (100A) comprising a plurality of blades (102) extending from a rotatable hub (104) , and a shroud (106) extending circumferentially around the impeller (100A), wherein the shroud (106) is secured to the plurality of blades (102), a casing (110) with a bellmouth (112) disposed circumferentially around the shroud (106), defining a cavity (C) between the casing (110) and the shroud (106), with flow control clearance gaps at a downstream end and an upstream end of the casing. The assembly (100) further comprises one or more first circular ribs (118) extending axially from the shroud (106) within the cavity (C) and substantially parallel to a rotational axis of the impeller (100A), and a plurality of de-swirl vanes (116) configured at predefined positions on an inner surface of the bellmouth (112).

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This patent application claims the benefit of U.S. Provisional Patent Application No. 63 / 697,564, filed on September 22, 2024, which is incorporated by reference herein in its entirety.TECHNICAL FIELD

[0002] The present invention relates to a mixed-flow fan assembly and more specifically to a shrouded mixed-flow fan assembly with improved airflow characteristics using rotor clearance flow control features.BACKGROUND

[0003] Rotor clearance recirculation flow is a general problem that occurs in fans. These recirculation flows are driven by a pressure difference across fan rotor blades and various techniques are used to minimize performance loss associated with such clearance flows. Rotating shrouds are used on fan rotors to manage the clearance flow in a cavity region between the shroud and the stationary casing. Many configurations of "casing treatments" have been developed to address clearance flow recirculation, most of which are applicable to unshrouded axial fans and compressors, while a limited number are suitable for use with shrouded fans. One effective treatment is the use of vanes extending from the interior of the casing toward the shroud to reduce swirl in the recirculating flow. Mixed flow fans utilize an inclined blade tip and shroud that differs from axial fans. Mixed-flow fans are also referred to as diagonal flow fans. Rotating shrouded fans are also referred to as banded fans or ringed fans.SUMMARY

[0004] According to a first aspect of the invention there is provided a mixed-flow fan assembly. The assembly comprises an impeller comprising a plurality of blades extending from a rotatable hub, and a conically shaped shroud extending circumferentially around the impeller, wherein the shroud is secured to the plurality of blades, a casing with a bellmouth disposed circumferentially around the shroud, defining a cavity between the casing and the shroud, with flow control clearance gaps at a downstream end and an upstream end of the casing. The assembly further comprises one or more first circular ribs extending axially from the shroud within the cavity and substantially parallel to a rotational axis of the impeller, and a plurality of de-swirl vanes configured at predefined positions on an inner surface of the bellmouth.

[0005] In one or more embodiments, the plurality of de-swirl vanes extends axially from a forward inner surface of the bellmouth towards the shroud, such that corresponding de-swirl vanes remain upstream of a forward flow clearance gap of the casing.

[0006] In one or more embodiments, a forward junction of the plurality of de-swirl vanes has a first profile concurrent to a forward inner surface of the bellmouth, and a rear edge of the plurality of de-swirl vanes has a second profile based on a profile of the one or more first circular ribs that are adjacent to corresponding de-swirl vanes.

[0007] In one or more embodiments, a first rib of the one or more first circular ribs is positioned on the shroud, wherein a junction of the first rib aligns with a transition in the casing from a nominally conical aft section to a nominally axial forward section, thereby forming a forward axial flow passage within the cavity.

[0008] In one or more embodiments, the casing comprises a cylindrical section with a flange adapted to be attached to a fan deck, and a conical section having a downstream end connected to an end of the cylindrical section such that the conical section remains substantially parallel to the shroud, with the cavity defined therebetween, wherein a length of the conical section is less than a length of an inclined surface of the shroud such that a forward end of the conical section terminates and transitions to the nominally axial section, and wherein the bellmouth is connected to the nominally axial section.

[0009] In one or more embodiments, the one or more first circular ribs extend axially from the forward end of the shroud to define a shroud lip that extends substantially parallel to a lip of the bellmouth within the cavity to form a forward flow clearance gap therebetween.

[0010] In one or more embodiments, one of the one or more first circular ribs extends axially from the rear end of the shroud to define an aft rib that remains substantially parallel to the cylindrical section of the casing to form a rear flow clearance gap therebetween.

[0011] In one or more embodiments, the one or more first circular ribs extends axially from the inclined surface of the shroud, such that a corresponding first rib extends within the cavity of the bellmouth.

[0012] In one or more embodiments, a first gap remains between the inclined surface of the shroud and the conical section of the casing.

[0013] In one or more embodiments, a second and a third gap remains between an apex of the one or more first circular ribs and a rear edge of the plurality of de-swirl vanes.

[0014] In one or more embodiments, the one or more first circular ribs extend axially from the inclined surface of the shroud, such that corresponding first rib extends within the cavity at the conical section of the casing.

[0015] In one or more embodiments, the mixed-flow fan assembly comprises one or more second circular ribs that extend axially from the conical section of the casing within the cavity, such that the one or more first circular ribs and the one or more second circular ribs remain parallel to each other, forming a labyrinth structure within the cavity.

[0016] In one or more embodiments, the bellmouth comprises an outer section having a diameter decreasing from a rear end to a forward end, wherein the rear end of the outer section is connected to the forward end of the conical section of the casing, and an inner section defining a lip of the bellmouth, connected to the forward end of the outer section by a curved section, wherein the diameter of the inner section is less than the diameter of the forward end of the outer section, and the height of the inner section is less than the height of the outer section, thereby forming the bellmouth.

[0017] In one or more embodiments, the plurality of de-swirl vanes extends radially between the outer section and the inner section and axially at least partially from the curved section of the bellmouth, such that corresponding de-swirl vanes remain upstream of a forward flow clearance gap of the casing.

[0018] In one or more embodiments, a rear edge of the plurality of de-swirl vanes comprises a first portion extending from the outer section towards the inner section, and a second portion extending from the first portion to the inner section of the bellmouth, such that an apex of a first rib downstream of the shroud lip remains aft of the first portion, and an apex of the shroud lip remains aft of the second portion, wherein height of the first portion from a forward inner surface of the bellmouth is more than the height of the second portion from the forward inner surface.

[0019] In one or more embodiments, the first portion has a substantially planar profile and the second portion has a curved profile.

[0020] In one or more embodiments, the first portion and the second portion have one of, a curved profile, an inverted-arc profile, a U-shaped profile, or a J-shaped profile.

[0021] In one or more embodiments, a transitioning or connection point between the first portion and the second portion of the rear edge extends axially and at least partially above a line connecting the apex of the first rib and the apex of the shroud lip.

[0022] In one or more embodiments, number of the plurality of de-swirl vanes in the assembly is in a predefined range of 6 to 80.

[0023] In one or more embodiments, a ratio between a length of the conical section of the casing and a length between junctions of the shroud lip and the aft rib of the shroud is in a range of 0.3 to 0.7.

[0024] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, features, and techniques regarding the invention will become more apparent from the following description taken in conjunction with the drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are included to provide a further understanding of the invention. The drawings illustrate exemplary embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0026] In the drawings, similar components and / or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label with a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label. FIG. 1A illustrates an exemplary view of the mixed-flow fan assembly. FIG. 1B illustrates an exemplary cross-sectional view of the fan assembly. FIG. 2A illustrates an exemplary detailed view of the casing and bellmouth region of the fan assembly depicting various components thereof. FIG. 2B depicts the airflow within the cavity of the fan assembly. FIG. 2C depicts the relationships between the casing's transition point and the ribs of the shroud in the fan assembly. FIG. 3A illustrates an exemplary view of the fan assembly having an embodiment of the de-swirl vanes. FIG. 3B illustrates an exemplary view of the fan assembly having a labyrinth-profiled path in the cavity between the shroud and the casing. FIG. 3C illustrates an exemplary view of an embodiment of the fan assembly without the shroud exit rib. FIGs. 4A and 4B illustrate exemplary views depicting multiple de-swirl vanes in the bellmouth cavity of the fan assembly. DETAILED DESCRIPTION

[0027] The following is a detailed description of embodiments of the invention depicted in the accompanying drawings. The embodiments are in such detail as clearly to communicate the invention. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as set out in the appended claims.

[0028] Various terms are used herein. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.

[0029] In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the subject disclosure, the components of this invention described herein may be positioned in any desired orientation. Thus, the use of terms such as "forward," "rear," "aft," "upstream," "downstream," "first," "second" or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components.

[0030] Mixed-flow fans can be utilized in various air-handling applications, including HVAC systems and industrial cooling units. These fans are designed to combine the characteristics of axial and centrifugal fans, offering advantages in terms of airflow efficiency and pressure generation. However, existing mixed-flow fan designs may face challenges in achieving optimal performance metrics such as pressure-rise capability, energy efficiency, and noise reduction.

[0031] There is, therefore, a need to address these challenges by providing an improved mixed-flow fan with improved shroud and inlet casing designs to enhance pressure rise, increase overall efficiency, and reduce operational noise.

[0032] The term "downstream end" herein refers to the part of a structure where the air exits after flowing through or past it. It is the point that is farthest along the direction of the airflow.

[0033] The term "upstream end" herein refers to the part of a structure where the air enters before flowing through or past it. It is the point that is closest to the source of the airflow.

[0034] The term "forward" refers to the direction toward the fan inlet.

[0035] The term "rear" refers to the direction toward the fan outlet.

[0036] Referring to FIGs. 1A to 4B, detailed schematic perspective and sectional views, respectively, of the mixed-flow fan assembly 100 are shown. Referring now to FIGs. 1A to 2C, the fan assembly 100 may include an impeller or a fan rotor 100A that may include a plurality of blades 102 extending radially from a hub 104 and terminating at a fan shroud 106. The fan may further include a fan stator (not shown) that may include a stator assembly having a plurality of stator vanes, located either upstream or downstream of the impeller. The fan assembly 100 may be driven by an electric motor 108 connected to the fan hub 104 by a shaft (not shown), or alternatively a belt or other arrangement. In operation, the motor 108 may drive rotation of the fan assembly to drive airflow across the fan assembly from an inlet at a front side of the fan assembly 100 towards an outlet at the rear side of the fan assembly 100. The impeller 100A or fan assembly 100 may have an axis of rotation (or fan axis) (A-A') that may be in line with the direction of flow (or flow path) of the air through a housing duct (not shown) in which the fan is installed.

[0037] The fan shroud 106 may be conically shaped which extends circumferentially around the impeller 100A. The fan shroud 106 is further secured to the plurality of blades 102 and rotates about the fan axis A-A' therewith. The fan assembly 100 may further include a casing 110 (also referred to as inlet casing or fan inlet casing) with a bellmouth 112. The casing 110 may be disposed circumferentially around the fan shroud 106, where the casing 110 may define a cavity CT with clearance between the casing 110 and the shroud 106 at a downstream end and an upstream end of the casing 110. The clearance may have appropriate upstream and downstream flow control clearance gaps.

[0038] In one or more embodiments, the conically-shaped shroud 106 may be inclined at a predefined inclination angle from a plane parallel to the rotational axis A-A' of the impeller 100A, such that the diameter of the shroud 106 reduces while moving from a rear end towards a forward end of the shroud 106. In one or more embodiments, an inclination angle (predefined inclination angle) of the conical portion of the shroud 106 is between 30 and 70 degrees relative to the rotational axis A-A' of the impeller 100A. Further, in one or more embodiments, the casing 110 may include a cylindrical section 110-1 with a flange 114 adapted to be attached to a fan deck or a frame associated with the duct housing in which the fan assembly 100 is installed. Further, the casing 110 may include a conical section 110-2 having a downstream end (having a larger diameter) connected to an end (opposite to the flange end) of the cylindrical section 110-1, such that the conical section 110-2 remains substantially parallel to the inclined region of the shroud 106, with the cavity C defined therebetween. The length of the conical section 110-2 of the casing 110 may be less than the length of the shroud 106, such that an upstream end (having a smaller diameter than the downstream end) of the conical section 110-2 terminates before the forward end of the shroud 106 and transitions from a point T1 to a nominally axial section. Furthermore, the bellmouth 112 may be connected to the forward end or the nominally axial section of the conical section 110-2 to define the overall shape of the casing 110. It should be obvious to a person skilled in the art that the overall casing 110 with the bellmouth 112 may be fabricated as a single structure with smooth transitioning, however, the cylindrical section 110-1, the conical section 110-2, and the bellmouth 112 can be separately fabricated, and connected to form the overall casing 110.

[0039] In one or more embodiments, the bellmouth 112 may have a substantially J-shaped or U-shaped profile. As illustrated, the bellmouth 112 may include an outer section 112-1 having a diameter decreasing from a rear transition point to a forward end (upstream end), where the rear end of the outer section 112-1 may be connected to the forward end of the conical section 110-2 of the casing 110. The bellmouth 112 may further include an inner section 112-2 with a substantially curved profile or a substantially planar profile, defining a lip L of the bellmouth 112, which may be connected to the forward end of the outer section 112-1 by a curved section 112-3. Further, the diameter of the inner section 112-2 of the bellmouth 112 may be less than the diameter of the forward end of the outer section 112-1, and the height of the inner section 112-2 may be less than the height of the outer section 112-1, to define an overall shape of the bellmouth 112. In one or more embodiments, the inner section 112-2 or lip L of the bellmouth 112 may overlap the shroud 106 to direct an inlet air flow via the forward flow clearance gap G1 at the upstream end of the casing 110 while allowing a tangential re-entrant clearance recirculation flow.

[0040] In one or more embodiments, the fan assembly 100 may include a plurality of de-swirl vanes 116 of a predefined thickness configured at predefined positions on the inner surface of the bellmouth 112. The de-swirl vanes 116 may extend axially from the forward inner surface of the bellmouth 112 towards the shroud 106, such that the corresponding de-swirl vanes 116 remain upstream of the forward flow clearance gap G1 of the casing 110. The detailed construction of the de-swirl vanes 116 has been described in further paragraphs.

[0041] In one or more embodiments, the fan assembly 100 may further include one or more first circular ribs 118-1 to 118-N extending axially from the shroud 106 within the cavity C and substantially parallel to the rotational axis A-A' of the impeller 100A. As illustrated in FIG. 1B to 3C, one of the first ribs 118-1 may extend axially from the forward end of the shroud 106 to define a shroud lip 118-1, which may extend substantially parallel to the lip L of the bellmouth 112 within the cavity C to form the forward clearance gap G1 therebetween as shown in FIG. 2B. As illustrated in FIG. 3C, the first rib 118-3 can be positioned on the shroud 106 with its junction aligned with the transition T1 in the casing 110 along an axial plane, thereby forming an axial flow passage within the shroud-casing cavity. Further, as illustrated in FIG. 1B to 3B, one of the first ribs 118-2 may extend axially from the rear end of the shroud 106 to define a shroud exit rib or aft rib 118-2, which remains substantially parallel to the cylindrical section 110-1 of the casing 110 to form the rear flow clearance gap G2 therebetween as shown in FIG. 2B.

[0042] In addition, in one or more embodiments, at least one of the one or more first ribs, 118-3 adjacent to or downstream of the shroud lip 118-1, may form a first flow control rib (FCR) 118-3 of the shroud 106, which may extend axially from an inclined surface of the shroud 106 such that the first FCR 118-3 may extend within the cavity of the bellmouth 112. Accordingly, the shroud lip 118-1 and the first FCR 118-3 may extend axially from the inclined shroud 106 such that the shroud lip 118-1 and the first FCR 118-3 remain aft of the de-swirl vanes 116 within the bellmouth 112.

[0043] Further, referring to FIG. 2C, a ratio between a length (A) of the conical section of the casing 110 and a length (C) between junctions of the shroud lip 118-1 and the aft rib 118-2 of the shroud 108 can be in a range of 0.3 to 0.7, but is not limited to the like. Furthermore, the length (C) between junctions of the shroud lip 118-1 and the aft rib 118-2, and the length (B) between junctions of the FCR 118-3 and the aft rib 118-2 may be selected such that the transition point T1 of the casing 110 and the junction of the FCR 118-3 remains in the same axial plane.

[0044] Further, in one or more embodiments, at least one of the one or more first ribs may extend axially from the inclined surface of the shroud 106, forming additional first FCR(s) 118-N of the shroud 106, which may extend within the cavity in the conical section 110-2 of the casing 110 as shown in FIG. 3B.

[0045] In one or more embodiments, as illustrated in FIG. 3B, the fan assembly 100 may additionally include one or more second circular ribs 120 that may extend axially from the conical section 110-2 of the casing 110 and towards the shroud 106, forming second flow control ribs (or second FCRs) 120 on the casing 110. In such embodiments, the corresponding first FCRs 118-1, 118-2, 118-3, 118-4, and the second FCRs 120 may remain parallel and alternately arranged to form a labyrinth structure within the cavity between the shroud 106 and the casing 110.

[0046] In one or more embodiments, a first predefined gap may remain between the inclined surface of the shroud 106 and the inner surface of the conical section 110-2 of the casing 110. Further, in some embodiments, the rear end of the shroud 106 may not include any rib or shroud exit rib 118-2 as illustrated in FIG. 3C. In such embodiments, the (first predefined) gap between the inclined shroud 106 and the conical section 110-2 of the casing 110 may be kept small, compared to embodiments where the shroud 106 exit rib is provided at the rear end of the shroud 106.

[0047] In one or more embodiments, as illustrated in FIGs. 4A and 4B, the fan assembly 100 may include 6 to 80 de-swirl vanes 116. Further, in a non-limiting embodiment, the fan assembly 100 may include 24 de-swirl vanes 116. Furthermore, in one or more embodiments, the de-swirl vanes 116 may be equidistantly arranged on the forward inner surface of the bellmouth 112, however, in some embodiments, the gaps between the de-swirl vanes 116 may be variable, and all such embodiments are well within the scope of this invention.

[0048] It is to be appreciated that the number of de-swirl vanes 116 and the positions thereof mentioned above are only exemplary, and these can be changed to a higher number or a lower number without any limitation whatsoever, and all such implementations are well within the scope of the invention.

[0049] In one or more embodiments, second and third predefined gaps may remain between apex A1, of the first ribs (shroud lip 118-1) and a rear edge (RE) of the de-swirl vanes 116 and between apex A2 of the first FCR (118-3 extending within the bellmouth cavity) and a rear edge (RE) of the de-swirl vanes 116 as shown in FIG. 2A. Further, in some embodiments, the second and third predefined gaps may be equal. However, the second and third predefined gaps between the rear edge (RE) of the de-swirl vanes 116 and the adjacent first ribs 118-1, 118-3 may also be variable or different. For instance, the gap between apex A1 of the first rib 118-1 and the rear edge (RE) of the de-swirl vanes 116 may be more or less than the gap between apex A2 of the first rib 118-3 and the rear edge (RE) of the de-swirl vanes 116.

[0050] In one or more embodiments, the length of the shroud lip 118-1 and the first FCR 118-3 may be equal. However, in other embodiments, the length of the shroud lip 118-1 and the first FCR 118-3 may be different or unequal. For instance, the length of the shroud lip 118-1 may be more than the length of the first FCR 118-3. Further, the length of the shroud lip 118-1 may be less than the length of the first FCR 118-3.

[0051] In one or more embodiments, a forward junction (FJ) of the de-swirl vanes 116 may have a first predefined profile concurrent to the forward inner surface of the bellmouth 112 such that a de-swirling zone is created between adjacent de-swirl vanes 116. Further, the rear edge (RE) of the de-swirl vanes 116 may have a second predefined profile based on a profile of the first ribs that are adjacent to the de-swirl vanes 116 within the bellmouth 112 cavity, such that the second and third predefined gaps remain between the apex of the first ribs 118-1, 118-3 and the rear edge (RE) of the de-swirl vanes 116.

[0052] In one or more embodiments, the rear edge (RE) of the de-swirl vanes 116 may include a first portion P1 extending from the outer section 112-1 towards the inner section 112-2, and a second portion P2 extending from the first portion P1 to the inner section 112-2 of the bellmouth 112, such that an apex A2 of the first FCR 118-3 downstream of the shroud lip 118-1 remains aft of the first portion P1, and an apex A1 of the shroud lip 118-1 remains aft of the second portion P2 as shown in FIG. 2A. Further, the height of the first portion P1 from the forward inner surface of the bellmouth 112 may be more than the height of the second portion P2 from the forward inner surface.

[0053] In one or more embodiments, the first portion P1 of the rear edge (RE) may have a substantially planar profile as shown in FIGs. 2A to 2C, and the second portion P2 of the rear edge (RE) may have a curved profile or J-shaped profile as shown in FIG. 3C. Further, in one or more embodiments, the first portion P1 and the second portion P2 of the rear edge (RE) may have a curved profile, an inverted-arc profile, or U-shaped profile, or a J-shaped profile. Furthermore, in one or more embodiments, a transitioning or connection point T2 between the first portion P1 and the second portion P2 of the rear edge (RE) may extend axially and at least partially above a line L1 connecting the apex A2 of the first rib 118-2 and the apex A1 of the shroud lip 118-1 as shown in FIG. 3A.

[0054] It is to be appreciated by a person skilled in the art that the de-swirl vanes restrict the creation of air swirl between the shroud and the casing downstream at the forward flow clearance gap, thereby stabilizing the flow of air through the fan assembly and enhancing the pressure rise and efficiency.

[0055] Thus, the described embodiments address the challenges associated with existing mixed-flow fan designs, by providing an improved mixed-flow fan assembly with improved shroud and inlet casing designs to enhance pressure rise, increase overall efficiency, and reduce operational noise.

[0056] While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined by the appended claims. Modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention includes all embodiments falling within the scope of the invention as defined by the appended claims.

[0057] In interpreting the specification, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms "comprises" and "comprising" should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refer to at least one of something selected from the group consisting of A, B, C ....and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.

Examples

Embodiment Construction

[0027]The following is a detailed description of embodiments of the invention depicted in the accompanying drawings. The embodiments are in such detail as clearly to communicate the invention. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as set out in the appended claims.

[0028]Various terms are used herein. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.

[0029]In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those...

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This patent application claims the benefit of U.S. Provisional Patent Application No. 63 / 697,564, filed on September 22, 2024, which is incorporated by reference herein in its entirety.TECHNICAL FIELD

[0002] The present invention relates to a mixed-flow fan assembly and more specifically to a shrouded mixed-flow fan assembly with improved airflow characteristics using rotor clearance flow control features.BACKGROUND

[0003] Rotor clearance recirculation flow is a general problem that occurs in fans. These recirculation flows are driven by a pressure difference across fan rotor blades and various techniques are used to minimize performance loss associated with such clearance flows. Rotating shrouds are used on fan rotors to manage the clearance flow in a cavity region between the shroud and the stationary casing. Many configurations of "casing treatments" have been developed to address clearance flow recirculation, most of which are applicable to unshrouded axial fans and compressors, while a limited number are suitable for use with shrouded fans. One effective treatment is the use of vanes extending from the interior of the casing toward the shroud to reduce swirl in the recirculating flow. Mixed flow fans utilize an inclined blade tip and shroud that differs from axial fans. Mixed-flow fans are also referred to as diagonal flow fans. Rotating shrouded fans are also referred to as banded fans or ringed fans.SUMMARY

[0004] According to a first aspect of the invention there is provided a mixed-flow fan assembly. The assembly comprises an impeller comprising a plurality of blades extending from a rotatable hub, and a conically shaped shroud extending circumferentially around the impeller, wherein the shroud is secured to the plurality of blades, a casing with a bellmouth disposed circumferentially around the shroud, defining a cavity between the casing and the shroud, with flow control clearance gaps at a downstream end and an upstream end of the casing. The assembly further comprises one or more first circular ribs extending axially from the shroud within the cavity and substantially parallel to a rotational axis of the impeller, and a plurality of de-swirl vanes configured at predefined positions on an inner surface of the bellmouth.

[0005] In one or more embodiments, the plurality of de-swirl vanes extends axially from a forward inner surface of the bellmouth towards the shroud, such that corresponding de-swirl vanes remain upstream of a forward flow clearance gap of the casing.

[0006] In one or more embodiments, a forward junction of the plurality of de-swirl vanes has a first profile concurrent to a forward inner surface of the bellmouth, and a rear edge of the plurality of de-swirl vanes has a second profile based on a profile of the one or more first circular ribs that are adjacent to corresponding de-swirl vanes.

[0007] In one or more embodiments, a first rib of the one or more first circular ribs is positioned on the shroud, wherein a junction of the first rib aligns with a transition in the casing from a nominally conical aft section to a nominally axial forward section, thereby forming a forward axial flow passage within the cavity.

[0008] In one or more embodiments, the casing comprises a cylindrical section with a flange adapted to be attached to a fan deck, and a conical section having a downstream end connected to an end of the cylindrical section such that the conical section remains substantially parallel to the shroud, with the cavity defined therebetween, wherein a length of the conical section is less than a length of an inclined surface of the shroud such that a forward end of the conical section terminates and transitions to the nominally axial section, and wherein the bellmouth is connected to the nominally axial section.

[0009] In one or more embodiments, the one or more first circular ribs extend axially from the forward end of the shroud to define a shroud lip that extends substantially parallel to a lip of the bellmouth within the cavity to form a forward flow clearance gap therebetween.

[0010] In one or more embodiments, one of the one or more first circular ribs extends axially from the rear end of the shroud to define an aft rib that remains substantially parallel to the cylindrical section of the casing to form a rear flow clearance gap therebetween.

[0011] In one or more embodiments, the one or more first circular ribs extends axially from the inclined surface of the shroud, such that a corresponding first rib extends within the cavity of the bellmouth.

[0012] In one or more embodiments, a first gap remains between the inclined surface of the shroud and the conical section of the casing.

[0013] In one or more embodiments, a second and a third gap remains between an apex of the one or more first circular ribs and a rear edge of the plurality of de-swirl vanes.

[0014] In one or more embodiments, the one or more first circular ribs extend axially from the inclined surface of the shroud, such that corresponding first rib extends within the cavity at the conical section of the casing.

[0015] In one or more embodiments, the mixed-flow fan assembly comprises one or more second circular ribs that extend axially from the conical section of the casing within the cavity, such that the one or more first circular ribs and the one or more second circular ribs remain parallel to each other, forming a labyrinth structure within the cavity.

[0016] In one or more embodiments, the bellmouth comprises an outer section having a diameter decreasing from a rear end to a forward end, wherein the rear end of the outer section is connected to the forward end of the conical section of the casing, and an inner section defining a lip of the bellmouth, connected to the forward end of the outer section by a curved section, wherein the diameter of the inner section is less than the diameter of the forward end of the outer section, and the height of the inner section is less than the height of the outer section, thereby forming the bellmouth.

[0017] In one or more embodiments, the plurality of de-swirl vanes extends radially between the outer section and the inner section and axially at least partially from the curved section of the bellmouth, such that corresponding de-swirl vanes remain upstream of a forward flow clearance gap of the casing.

[0018] In one or more embodiments, a rear edge of the plurality of de-swirl vanes comprises a first portion extending from the outer section towards the inner section, and a second portion extending from the first portion to the inner section of the bellmouth, such that an apex of a first rib downstream of the shroud lip remains aft of the first portion, and an apex of the shroud lip remains aft of the second portion, wherein height of the first portion from a forward inner surface of the bellmouth is more than the height of the second portion from the forward inner surface.

[0019] In one or more embodiments, the first portion has a substantially planar profile and the second portion has a curved profile.

[0020] In one or more embodiments, the first portion and the second portion have one of, a curved profile, an inverted-arc profile, a U-shaped profile, or a J-shaped profile.

[0021] In one or more embodiments, a transitioning or connection point between the first portion and the second portion of the rear edge extends axially and at least partially above a line connecting the apex of the first rib and the apex of the shroud lip.

[0022] In one or more embodiments, number of the plurality of de-swirl vanes in the assembly is in a predefined range of 6 to 80.

[0023] In one or more embodiments, a ratio between a length of the conical section of the casing and a length between junctions of the shroud lip and the aft rib of the shroud is in a range of 0.3 to 0.7.

[0024] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, features, and techniques regarding the invention will become more apparent from the following description taken in conjunction with the drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are included to provide a further understanding of the invention. The drawings illustrate exemplary embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0026] In the drawings, similar components and / or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label with a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label. FIG. 1A illustrates an exemplary view of the mixed-flow fan assembly. FIG. 1B illustrates an exemplary cross-sectional view of the fan assembly. FIG. 2A illustrates an exemplary detailed view of the casing and bellmouth region of the fan assembly depicting various components thereof. FIG. 2B depicts the airflow within the cavity of the fan assembly. FIG. 2C depicts the relationships between the casing's transition point and the ribs of the shroud in the fan assembly. FIG. 3A illustrates an exemplary view of the fan assembly having an embodiment of the de-swirl vanes. FIG. 3B illustrates an exemplary view of the fan assembly having a labyrinth-profiled path in the cavity between the shroud and the casing. FIG. 3C illustrates an exemplary view of an embodiment of the fan assembly without the shroud exit rib. FIGs. 4A and 4B illustrate exemplary views depicting multiple de-swirl vanes in the bellmouth cavity of the fan assembly. DETAILED DESCRIPTION

[0027] The following is a detailed description of embodiments of the invention depicted in the accompanying drawings. The embodiments are in such detail as clearly to communicate the invention. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as set out in the appended claims.

[0028] Various terms are used herein. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.

[0029] In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the subject disclosure, the components of this invention described herein may be positioned in any desired orientation. Thus, the use of terms such as "forward," "rear," "aft," "upstream," "downstream," "first," "second" or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components.

[0030] Mixed-flow fans can be utilized in various air-handling applications, including HVAC systems and industrial cooling units. These fans are designed to combine the characteristics of axial and centrifugal fans, offering advantages in terms of airflow efficiency and pressure generation. However, existing mixed-flow fan designs may face challenges in achieving optimal performance metrics such as pressure-rise capability, energy efficiency, and noise reduction.

[0031] There is, therefore, a need to address these challenges by providing an improved mixed-flow fan with improved shroud and inlet casing designs to enhance pressure rise, increase overall efficiency, and reduce operational noise.

[0032] The term "downstream end" herein refers to the part of a structure where the air exits after flowing through or past it. It is the point that is farthest along the direction of the airflow.

[0033] The term "upstream end" herein refers to the part of a structure where the air enters before flowing through or past it. It is the point that is closest to the source of the airflow.

[0034] The term "forward" refers to the direction toward the fan inlet.

[0035] The term "rear" refers to the direction toward the fan outlet.

[0036] Referring to FIGs. 1A to 4B, detailed schematic perspective and sectional views, respectively, of the mixed-flow fan assembly 100 are shown. Referring now to FIGs. 1A to 2C, the fan assembly 100 may include an impeller or a fan rotor 100A that may include a plurality of blades 102 extending radially from a hub 104 and terminating at a fan shroud 106. The fan may further include a fan stator (not shown) that may include a stator assembly having a plurality of stator vanes, located either upstream or downstream of the impeller. The fan assembly 100 may be driven by an electric motor 108 connected to the fan hub 104 by a shaft (not shown), or alternatively a belt or other arrangement. In operation, the motor 108 may drive rotation of the fan assembly to drive airflow across the fan assembly from an inlet at a front side of the fan assembly 100 towards an outlet at the rear side of the fan assembly 100. The impeller 100A or fan assembly 100 may have an axis of rotation (or fan axis) (A-A') that may be in line with the direction of flow (or flow path) of the air through a housing duct (not shown) in which the fan is installed.

[0037] The fan shroud 106 may be conically shaped which extends circumferentially around the impeller 100A. The fan shroud 106 is further secured to the plurality of blades 102 and rotates about the fan axis A-A' therewith. The fan assembly 100 may further include a casing 110 (also referred to as inlet casing or fan inlet casing) with a bellmouth 112. The casing 110 may be disposed circumferentially around the fan shroud 106, where the casing 110 may define a cavity CT with clearance between the casing 110 and the shroud 106 at a downstream end and an upstream end of the casing 110. The clearance may have appropriate upstream and downstream flow control clearance gaps.

[0038] In one or more embodiments, the conically-shaped shroud 106 may be inclined at a predefined inclination angle from a plane parallel to the rotational axis A-A' of the impeller 100A, such that the diameter of the shroud 106 reduces while moving from a rear end towards a forward end of the shroud 106. In one or more embodiments, an inclination angle (predefined inclination angle) of the conical portion of the shroud 106 is between 30 and 70 degrees relative to the rotational axis A-A' of the impeller 100A. Further, in one or more embodiments, the casing 110 may include a cylindrical section 110-1 with a flange 114 adapted to be attached to a fan deck or a frame associated with the duct housing in which the fan assembly 100 is installed. Further, the casing 110 may include a conical section 110-2 having a downstream end (having a larger diameter) connected to an end (opposite to the flange end) of the cylindrical section 110-1, such that the conical section 110-2 remains substantially parallel to the inclined region of the shroud 106, with the cavity C defined therebetween. The length of the conical section 110-2 of the casing 110 may be less than the length of the shroud 106, such that an upstream end (having a smaller diameter than the downstream end) of the conical section 110-2 terminates before the forward end of the shroud 106 and transitions from a point T1 to a nominally axial section. Furthermore, the bellmouth 112 may be connected to the forward end or the nominally axial section of the conical section 110-2 to define the overall shape of the casing 110. It should be obvious to a person skilled in the art that the overall casing 110 with the bellmouth 112 may be fabricated as a single structure with smooth transitioning, however, the cylindrical section 110-1, the conical section 110-2, and the bellmouth 112 can be separately fabricated, and connected to form the overall casing 110.

[0039] In one or more embodiments, the bellmouth 112 may have a substantially J-shaped or U-shaped profile. As illustrated, the bellmouth 112 may include an outer section 112-1 having a diameter decreasing from a rear transition point to a forward end (upstream end), where the rear end of the outer section 112-1 may be connected to the forward end of the conical section 110-2 of the casing 110. The bellmouth 112 may further include an inner section 112-2 with a substantially curved profile or a substantially planar profile, defining a lip L of the bellmouth 112, which may be connected to the forward end of the outer section 112-1 by a curved section 112-3. Further, the diameter of the inner section 112-2 of the bellmouth 112 may be less than the diameter of the forward end of the outer section 112-1, and the height of the inner section 112-2 may be less than the height of the outer section 112-1, to define an overall shape of the bellmouth 112. In one or more embodiments, the inner section 112-2 or lip L of the bellmouth 112 may overlap the shroud 106 to direct an inlet air flow via the forward flow clearance gap G1 at the upstream end of the casing 110 while allowing a tangential re-entrant clearance recirculation flow.

[0040] In one or more embodiments, the fan assembly 100 may include a plurality of de-swirl vanes 116 of a predefined thickness configured at predefined positions on the inner surface of the bellmouth 112. The de-swirl vanes 116 may extend axially from the forward inner surface of the bellmouth 112 towards the shroud 106, such that the corresponding de-swirl vanes 116 remain upstream of the forward flow clearance gap G1 of the casing 110. The detailed construction of the de-swirl vanes 116 has been described in further paragraphs.

[0041] In one or more embodiments, the fan assembly 100 may further include one or more first circular ribs 118-1 to 118-N extending axially from the shroud 106 within the cavity C and substantially parallel to the rotational axis A-A' of the impeller 100A. As illustrated in FIG. 1B to 3C, one of the first ribs 118-1 may extend axially from the forward end of the shroud 106 to define a shroud lip 118-1, which may extend substantially parallel to the lip L of the bellmouth 112 within the cavity C to form the forward clearance gap G1 therebetween as shown in FIG. 2B. As illustrated in FIG. 3C, the first rib 118-3 can be positioned on the shroud 106 with its junction aligned with the transition T1 in the casing 110 along an axial plane, thereby forming an axial flow passage within the shroud-casing cavity. Further, as illustrated in FIG. 1B to 3B, one of the first ribs 118-2 may extend axially from the rear end of the shroud 106 to define a shroud exit rib or aft rib 118-2, which remains substantially parallel to the cylindrical section 110-1 of the casing 110 to form the rear flow clearance gap G2 therebetween as shown in FIG. 2B.

[0042] In addition, in one or more embodiments, at least one of the one or more first ribs, 118-3 adjacent to or downstream of the shroud lip 118-1, may form a first flow control rib (FCR) 118-3 of the shroud 106, which may extend axially from an inclined surface of the shroud 106 such that the first FCR 118-3 may extend within the cavity of the bellmouth 112. Accordingly, the shroud lip 118-1 and the first FCR 118-3 may extend axially from the inclined shroud 106 such that the shroud lip 118-1 and the first FCR 118-3 remain aft of the de-swirl vanes 116 within the bellmouth 112.

[0043] Further, referring to FIG. 2C, a ratio between a length (A) of the conical section of the casing 110 and a length (C) between junctions of the shroud lip 118-1 and the aft rib 118-2 of the shroud 108 can be in a range of 0.3 to 0.7, but is not limited to the like. Furthermore, the length (C) between junctions of the shroud lip 118-1 and the aft rib 118-2, and the length (B) between junctions of the FCR 118-3 and the aft rib 118-2 may be selected such that the transition point T1 of the casing 110 and the junction of the FCR 118-3 remains in the same axial plane.

[0044] Further, in one or more embodiments, at least one of the one or more first ribs may extend axially from the inclined surface of the shroud 106, forming additional first FCR(s) 118-N of the shroud 106, which may extend within the cavity in the conical section 110-2 of the casing 110 as shown in FIG. 3B.

[0045] In one or more embodiments, as illustrated in FIG. 3B, the fan assembly 100 may additionally include one or more second circular ribs 120 that may extend axially from the conical section 110-2 of the casing 110 and towards the shroud 106, forming second flow control ribs (or second FCRs) 120 on the casing 110. In such embodiments, the corresponding first FCRs 118-1, 118-2, 118-3, 118-4, and the second FCRs 120 may remain parallel and alternately arranged to form a labyrinth structure within the cavity between the shroud 106 and the casing 110.

[0046] In one or more embodiments, a first predefined gap may remain between the inclined surface of the shroud 106 and the inner surface of the conical section 110-2 of the casing 110. Further, in some embodiments, the rear end of the shroud 106 may not include any rib or shroud exit rib 118-2 as illustrated in FIG. 3C. In such embodiments, the (first predefined) gap between the inclined shroud 106 and the conical section 110-2 of the casing 110 may be kept small, compared to embodiments where the shroud 106 exit rib is provided at the rear end of the shroud 106.

[0047] In one or more embodiments, as illustrated in FIGs. 4A and 4B, the fan assembly 100 may include 6 to 80 de-swirl vanes 116. Further, in a non-limiting embodiment, the fan assembly 100 may include 24 de-swirl vanes 116. Furthermore, in one or more embodiments, the de-swirl vanes 116 may be equidistantly arranged on the forward inner surface of the bellmouth 112, however, in some embodiments, the gaps between the de-swirl vanes 116 may be variable, and all such embodiments are well within the scope of this invention.

[0048] It is to be appreciated that the number of de-swirl vanes 116 and the positions thereof mentioned above are only exemplary, and these can be changed to a higher number or a lower number without any limitation whatsoever, and all such implementations are well within the scope of the invention.

[0049] In one or more embodiments, second and third predefined gaps may remain between apex A1, of the first ribs (shroud lip 118-1) and a rear edge (RE) of the de-swirl vanes 116 and between apex A2 of the first FCR (118-3 extending within the bellmouth cavity) and a rear edge (RE) of the de-swirl vanes 116 as shown in FIG. 2A. Further, in some embodiments, the second and third predefined gaps may be equal. However, the second and third predefined gaps between the rear edge (RE) of the de-swirl vanes 116 and the adjacent first ribs 118-1, 118-3 may also be variable or different. For instance, the gap between apex A1 of the first rib 118-1 and the rear edge (RE) of the de-swirl vanes 116 may be more or less than the gap between apex A2 of the first rib 118-3 and the rear edge (RE) of the de-swirl vanes 116.

[0050] In one or more embodiments, the length of the shroud lip 118-1 and the first FCR 118-3 may be equal. However, in other embodiments, the length of the shroud lip 118-1 and the first FCR 118-3 may be different or unequal. For instance, the length of the shroud lip 118-1 may be more than the length of the first FCR 118-3. Further, the length of the shroud lip 118-1 may be less than the length of the first FCR 118-3.

[0051] In one or more embodiments, a forward junction (FJ) of the de-swirl vanes 116 may have a first predefined profile concurrent to the forward inner surface of the bellmouth 112 such that a de-swirling zone is created between adjacent de-swirl vanes 116. Further, the rear edge (RE) of the de-swirl vanes 116 may have a second predefined profile based on a profile of the first ribs that are adjacent to the de-swirl vanes 116 within the bellmouth 112 cavity, such that the second and third predefined gaps remain between the apex of the first ribs 118-1, 118-3 and the rear edge (RE) of the de-swirl vanes 116.

[0052] In one or more embodiments, the rear edge (RE) of the de-swirl vanes 116 may include a first portion P1 extending from the outer section 112-1 towards the inner section 112-2, and a second portion P2 extending from the first portion P1 to the inner section 112-2 of the bellmouth 112, such that an apex A2 of the first FCR 118-3 downstream of the shroud lip 118-1 remains aft of the first portion P1, and an apex A1 of the shroud lip 118-1 remains aft of the second portion P2 as shown in FIG. 2A. Further, the height of the first portion P1 from the forward inner surface of the bellmouth 112 may be more than the height of the second portion P2 from the forward inner surface.

[0053] In one or more embodiments, the first portion P1 of the rear edge (RE) may have a substantially planar profile as shown in FIGs. 2A to 2C, and the second portion P2 of the rear edge (RE) may have a curved profile or J-shaped profile as shown in FIG. 3C. Further, in one or more embodiments, the first portion P1 and the second portion P2 of the rear edge (RE) may have a curved profile, an inverted-arc profile, or U-shaped profile, or a J-shaped profile. Furthermore, in one or more embodiments, a transitioning or connection point T2 between the first portion P1 and the second portion P2 of the rear edge (RE) may extend axially and at least partially above a line L1 connecting the apex A2 of the first rib 118-2 and the apex A1 of the shroud lip 118-1 as shown in FIG. 3A.

[0054] It is to be appreciated by a person skilled in the art that the de-swirl vanes restrict the creation of air swirl between the shroud and the casing downstream at the forward flow clearance gap, thereby stabilizing the flow of air through the fan assembly and enhancing the pressure rise and efficiency.

[0055] Thus, the described embodiments address the challenges associated with existing mixed-flow fan designs, by providing an improved mixed-flow fan assembly with improved shroud and inlet casing designs to enhance pressure rise, increase overall efficiency, and reduce operational noise.

[0056] While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined by the appended claims. Modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention includes all embodiments falling within the scope of the invention as defined by the appended claims.

[0057] In interpreting the specification, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms "comprises" and "comprising" should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refer to at least one of something selected from the group consisting of A, B, C ....and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.

Examples

Embodiment Construction

[0027]The following is a detailed description of embodiments of the invention depicted in the accompanying drawings. The embodiments are in such detail as clearly to communicate the invention. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as set out in the appended claims.

[0028]Various terms are used herein. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.

[0029]In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those...

Claims

1. A mixed-flow fan assembly (100) comprising: an impeller (100A) comprising a plurality of blades (102) extending from a rotatable hub (104); a conically shaped shroud (106) extending circumferentially around the impeller, wherein the shroud is secured to the plurality of blades; a casing with a bellmouth (112) disposed circumferentially around the shroud, defining a cavity (CT) between the casing (110) and the shroud, with flow control clearance gaps at a downstream end and an upstream end of the casing; one or more first circular ribs (118) extending axially from the shroud within the cavity and substantially parallel to a rotational axis of the impeller; and a plurality of de-swirl vanes (116) configured at predefined positions on an inner surface of the bellmouth.

2. The mixed-flow fan assembly (100) of claim 1, wherein the plurality of de-swirl vanes (116) extend axially from a forward inner surface of the bellmouth (112) towards the shroud (106), such that corresponding de-swirl vanes remain upstream of a forward flow clearance gap of the casing (110), and / or wherein a forward junction of the plurality of de-swirl vanes (116) has a first profile concurrent to a forward inner surface of the bellmouth (112), and a rear edge of the plurality of de-swirl vanes has a second profile based on a profile of the one or more first circular ribs (118) that are adjacent to corresponding de-swirl vanes.

3. The mixed-flow fan assembly (100) of any preceding claim, wherein a first rib of the one or more first circular ribs (118) is positioned on the shroud (106), wherein a junction of the first rib aligns with a transition in the casing (110) from a nominally conical section to a nominally axial section, thereby forming an axial flow passage within the cavity.

4. The mixed-flow fan assembly (100) of claim 3, wherein the casing (110) comprises: a rear cylindrical section (110-1) with a flange (114) adapted to be attached to a fan deck; and a conical section (110-2) having a downstream end connected to an end of the cylindrical section such that the conical section remains substantially parallel to the shroud (106), with the cavity (C) defined therebetween, wherein a length of the conical section is less than a length of an inclined surface of the shroud such that a forward end of the conical section terminates and transitions to the nominally axial section, and wherein the bellmouth (112) is connected to the nominally axial section.

5. The mixed-flow fan assembly (100) of claim 4, wherein the one or more first circular ribs (118) extend axially from a forward end of the shroud (106) to define a shroud lip (118-1) that extends substantially parallel to a lip of the bellmouth (112) within the cavity (C) to form a forward flow clearance gap (G1) therebetween, and / or wherein one of the one or more first circular ribs extends axially from a rear end of the shroud to define an aft rib of the shroud that remains substantially parallel to the cylindrical section (110-1) of the casing (110) to form a rear flow clearance gap (G2) therebetween.

6. The mixed-flow fan assembly (100) of claim 4 or 5, wherein the one or more first circular ribs (118) extends axially from the inclined surface of the shroud (106), such that a corresponding first rib extends within the cavity of the bellmouth (112).

7. The mixed-flow fan assembly (100) of claim 4, 5, or 6, wherein a first gap remains between the inclined surface of the shroud (106) and the conical section (110-2) of the casing (110), and optionally wherein second and third gaps remain between an apex (A1) of the one or more first circular ribs and a rear edge, RE, of the plurality of de-swirl vanes (116).

8. The mixed-flow fan assembly (100) of any of claims 4 to 7, wherein the one or more first circular ribs (118) extend axially from the inclined surface of the shroud (106), such that corresponding first rib extends within the cavity at the conical section (110-2) of the casing (110).

9. The mixed-flow fan assembly (100) of claim 8, further comprising one or more second circular ribs (120) that extend axially from the conical section (110-2) of the casing (110) within the cavity, such that the one or more first circular ribs (118) and the one or more second circular ribs remain parallel to each other, forming a labyrinth structure within the cavity.

10. The mixed-flow fan assembly (100) of claim 9, wherein the bellmouth (112) comprises: an outer section (112-1) having a diameter decreasing from a rear end to a forward end, wherein the rear end of the outer section is connected to the forward end of the conical section (110-2) of the casing (110); and an inner section (112-2) defining a lip of the bellmouth, connected to the forward end of the outer section by a curved section (112-3), wherein diameter of the inner section is less than diameter of the forward end of the outer section, and height of the inner section is less than height of the outer section, thereby forming the bellmouth.

11. The mixed-flow fan assembly (100) of claim 10, wherein the plurality of de-swirl vanes (116) extends radially between the outer section (112-1) and the inner section (112-2) and axially at least partially from the curved section (112-3) of the bellmouth (112), such that corresponding de-swirl vanes remain upstream of a forward flow clearance gap (G1) at the upstream end of the casing (110).

12. The mixed-flow fan assembly (100) of claim 11, wherein a rear edge, RE, of the plurality of de-swirl vanes (116) comprises a first portion (P1) extending from the outer section (112-1) towards the inner section (112-2), and a second portion (P2) extending from the first portion to the inner section of the bellmouth (112), such that an apex (A1) of a first rib (118) downstream of the shroud lip (118-1) remains aft of the first portion, and an apex of the shroud lip remains aft of the second portion, wherein height of the first portion from a forward inner surface of the bellmouth is more than height of the second portion from the forward inner surface.

13. The mixed-flow fan assembly (100) of claim 12, wherein the first portion (P1) has a substantially linear profile and the second portion (P2) has a curved profile, or wherein the first portion (P1) and the second portion (P2) have one of: a curved profile, an inverted-arc profile, or a U-shaped profile, or a J-shaped profile,14. The mixed-flow fan assembly of claim 12, wherein a transitioning or connection point (T2) between the first portion (P1) and the second portion (P2) of the rear edge, RE, extends axially and at least partially aft of a line (L1) connecting the apex (A2) of the first rib (118-2) and the apex (A1) of the shroud lip (118-1), and / or wherein a ratio between a length (A) of the conical section (110-2) of the casing (110) and a length (C) between junctions of the shroud lip (118-1) and the aft rib (118-2) of the shroud (106) is in a range of 0.3 to 0.7.

15. The mixed-flow fan assembly (100) of any preceding claim, wherein number of the plurality of de-swirl vanes (116) in the assembly is in a range of 6 to 80.

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