Clearance flow control for mixed-flow fan

Abstract

Described herein is a mixed-flow fan assembly. The assembly comprises an impeller comprising a plurality of blades extending from a rotatable hub, and a 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.

1 . A mixed-flow fan assembly comprising:
 an impeller comprising a plurality of blades extending from a rotatable hub;   a shroud having a conical shape 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;   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 disposed on an inner surface of the bellmouth.   
     
     
         2 . The mixed-flow fan assembly of  claim 1 , wherein the plurality of de-swirl vanes extend 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. 
     
     
         3 . The mixed-flow fan assembly of  claim 1 , wherein a forward junction of the plurality of de-swirl vanes has a first profile concurrent to a forward inner surface of the bellmouth, and wherein 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. 
     
     
         4 . The mixed-flow fan assembly of  claim 1 , wherein 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 point in the casing from a nominally conical section to a nominally axial section, thereby forming an axial flow passage within the cavity. 
     
     
         5 . The mixed-flow fan assembly of  claim 4 , wherein the casing comprises:
 a cylindrical section with a flange adapted to be attached to a fan deck; and   a conical section having the 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.   
     
     
         6 . The mixed-flow fan assembly of  claim 5 , wherein the one or more first circular ribs extend axially from a 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. 
     
     
         7 . The mixed-flow fan assembly of  claim 6 , wherein the one or more first circular ribs extend axially from a rear end of the shroud to define an aft rib of the shroud that remains substantially parallel to the cylindrical section of the casing to form a rear flow clearance gap therebetween. 
     
     
         8 . The mixed-flow fan assembly of  claim 5 , wherein 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. 
     
     
         9 . The mixed-flow fan assembly of  claim 5 , wherein a first gap remains between the inclined surface of the shroud and the conical section of the casing. 
     
     
         10 . The mixed-flow fan assembly of  claim 9 , wherein second and third gaps remain between an apex of the one or more first circular ribs and a rear edge of the plurality of de-swirl vanes. 
     
     
         11 . The mixed-flow fan assembly of  claim 5 , wherein the one or more first circular ribs extend axially from the inclined surface of the shroud, such that a corresponding first rib extends within the cavity at the conical section of the casing. 
     
     
         12 . The mixed-flow fan assembly of  claim 11 , further comprising 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. 
     
     
         13 . The mixed-flow fan assembly of  claim 12 , wherein 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 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.   
     
     
         14 . The mixed-flow fan assembly of  claim 13 , wherein 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 at the upstream end of the casing. 
     
     
         15 . The mixed-flow fan assembly of  claim 14 , wherein 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 height of the second portion from the forward inner surface.   
     
     
         16 . The mixed-flow fan assembly of  claim 15 , wherein the first portion has a substantially planar profile and the second portion has a curved profile. 
     
     
         17 . The mixed-flow fan assembly of  claim 15 , wherein the first portion and the second portion have one of: a curved profile, an inverted-arc profile, or a U-shaped profile, or a J-shaped profile. 
     
     
         18 . The mixed-flow fan assembly of  claim 15 , wherein a transitioning or connection point between the first portion and the second portion of the rear edge extends axially and at least partially aft of a line connecting the apex of the first rib and the apex of the shroud lip. 
     
     
         19 . The mixed-flow fan assembly of  claim 1 , wherein number of the plurality of de-swirl vanes in the assembly is in a range of 6 to 80. 
     
     
         20 . The mixed-flow fan assembly of  claim 5 , wherein a ratio between a length of the conical section of the casing and a length between junctions of the shroud lip and an aft rib of the shroud is in a range of 0.3 to 0.7.