Patent Application
20190178252
The subject matter disclosed herein relates to vane axial flow fans. More specifically, the subject matter disclosed herein relates to structures to improve fan stall performance and/or improve stall recovery hysteresis performance of vane axial flow fans.
Axial flow fans are widely used in many industries ranging from automotive to aerospace to HVAC but are typically limited in their application by operating range restrictions and noise considerations. While vane-axial fans can achieve high static efficiencies, their limited operating range due to blade stall typically makes the vane-axial fan impractical for use in many systems that have extended operating range requirements. Furthermore, the stall and stall recovery performance of an axial fan can be degraded due to sensitivity to non-optimal or off-design inflow conditions. For example, when an axial fan is subjected to inflow that is substantially at a right angle to the axis of rotation of the fan, the fan may experience reduced stall performance and/or increased stall recovery hysteresis. In certain HVAC applications, such as an indoor fan system for a residential or commercial packaged product or split system, the reduction in operating range driven by this deficient stall/recovery hysteresis performance can hinder the application of vane-axial fan technology.
In one embodiment, a fan assembly includes a shrouded fan rotor having a plurality of fan blades extending from a rotor hub and rotatable about a central axis of the fan assembly, and a fan shroud extending circumferentially around the fan rotor and secured to an outer tip diameter of the plurality of fan blades. A fan casing encloses the shrouded fan rotor. The fan casing defines a fan inlet of the fan assembly and includes an inlet extension at an outer diameter of the fan casing, extending axially upstream of a conventional bell mouth inlet, relative to a direction of airflow through the shrouded fan rotor.
Additionally or alternatively, in this or other embodiments the inlet extension extends between 5% and 20% of the fan rotor tip diameter axially upstream of the conventional bell mouth inlet.
Additionally or alternatively, in this or other embodiments the conventional bell mouth inlet transitions to the inlet extension, the inlet extension including a convex portion and a concave portion.
Additionally or alternatively, in this or other embodiments the concave portion extends from an inlet extension leading edge axially to a transition point and the convex portion extends from the transition point to a rotor leading edge.
Additionally or alternatively, in this or other embodiments the convex portion axially overlaps the fan shroud.
Additionally or alternatively, in this or other embodiments the inlet extension tapers radially from the conventional bell mouth inlet to an inlet extension leading edge at a taper angle.
Additionally or alternatively, in this or other embodiments the taper angle is between 0.5 degrees and 45 degrees.
Additionally or alternatively, in this or other embodiments a primary direction of airflow approaching the fan inlet is transverse relative to the central axis.
In another embodiment, a casing assembly for an axial fan includes a fan casing extending circumferentially about a central axis, the fan casing defining a fan inlet of the axial fan, and an inlet extension at an outer diameter of the casing, extending axially upstream of a conventional bell mouth inlet, relative to a direction of airflow through the shrouded fan rotor.
Additionally or alternatively, in this or other embodiments the inlet extension includes a concave surface extending from an inlet extension leading edge axially to a transition point and a convex portion extending axially rearwardly from the transition point.
Additionally or alternatively, in this or other embodiments the inlet extension is configured to extend axially upstream of a conventional bell mouth inlet, relative to a direction of airflow through the fan assembly.
Additionally or alternatively, in this or other embodiments the inlet extension is configured to extend between 5% and 20% of the fan rotor tip diameter axially upstream of the conventional bell mouth inlet.
Additionally or alternatively, in this or other embodiments the inlet extension tapers radially from the conventional bell mouth inlet to an inlet extension leading edge at a taper angle.
Additionally or alternatively, in this or other embodiments the taper angle is between 0.5 degrees and 45 degrees.
Additionally or alternatively, in this or other embodiments the inlet extension is configured to axially overlap a fan shroud of the fan assembly.
Additionally or alternatively, in this or other embodiments a primary direction of airflow approaching the fan inlet is transverse relative to the central axis.
The subject matter is particularly pointed out and distinctly claimed at the conclusion of the specification. The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawing.
Shown in
Referring now to
Referring now to
The casing extension 54 extends axially upstream of a conventional bell mouth inlet 58 to condition the airflow 14 prior to the airflow entering the fan rotor 18. A casing extension leading edge 60 defines an axially forward-most portion of the casing extension 54. In some embodiments, the casing extension 54 is formed integral with the conventional bell mouth inlet 58, while in other embodiments the casing extension 54 is a separate component from and discontinuous with the conventional bell mouth inlet 58.
In some embodiments, the casing extension 54 is an axial ring extending upstream of the conventional bell mouth inlet 58. In other embodiments, the casing extension 58 transitions from the conventional bell mouth inlet 58 at an inlet angle 80 (shown in
In some embodiments, as shown in
While ideally an axially longer casing extension 54 improves the condition of airflow 14 entering the fan rotor 18, the performance improvement of the fan 10 must be balanced with packaging constraints on the fan 10.
The utilization of casing extension 54 in the fan 10 improves stall performance of the fan 10 and further reduces stall recovery hysteresis in comparison to prior fans. These improvements allow for expansion of the operating envelope of shrouded axial fans, thus increasing their applicability to a wide range of conditions, such as rooftop HVAC&R systems, allowing such systems to take advantage of the performance advantages of shrouded axial fans.
While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate in spirit and/or scope. Additionally, while various embodiments have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments. Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2017/030728 | 5/3/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62330975 | May 2016 | US | |
| 62330963 | May 2016 | US | |
| 62369349 | Aug 2016 | US |
