Rotor blade having passive bleed path
A rotor blade includes a bleed path opening to a suction surface, extending through the blade, exiting to at least one of the suction or a trailing surface, and through which working fluid flows under centrifugal pumping forces when the blade rotates, to passively bleed working fluid from the suction surface.
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1. Technical Field
This invention relates generally to rotors having radially extending working members and, more particularly, to impellers and propellers having blades with fluid passages open to a working fluid.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Rotors typically include a hub for coupling to some other device like a prime mover or an electrical machine, and one or more radially extending working members for acting on, or reacting with, a working fluid. For example, an aircraft propeller typically includes a hub coupled to an engine output shaft, and several blades extending radially outwardly from the hub. The engine output shaft rotates the hub to rotate the blades, which convert rotational forces into aerial thrust forces to propel an aircraft through the air. In another example, a wind turbine impeller typically includes a hub coupled to a generator input shaft, and several blades extending radially outwardly from the hub. Wind impacts the blades, which convert wind thrust to hub rotation for rotating the generator input shaft to generate electricity within the generator. Similar examples exist for marine propellers, turbine engine rotors, helicopter rotors, and the like.
BRIEF SUMMARYA rotor blade includes a root region, a tip region disposed radially outwardly of the root region, leading and trailing surfaces extending between the root and tip regions, and pressure and suction surfaces extending between the root and tip regions and the leading and trailing surfaces. The blade also includes a bleed path that opens to the suction surface, extends through the blade, and exits to at least one of the suction or trailing surfaces. Working fluid flows through the bleed path under centrifugal pumping forces when the blade rotates, to passively bleed working fluid from the suction surface.
Additionally provided is a rotor including the aforementioned rotor blade, wherein the bleed path is configured such that the working fluid passively flows through the bleed path under negative pressurization, but does not actively flow therethrough by positive pressurization from some external pressurizing device or from a path open to the pressure surface. The bleed path includes an inlet in the suction surface to receive the working fluid on the suction surface, a conduit in communication with the inlet to convey the working fluid from the inlet toward the tip region, and an outlet in communication with the conduit and disposed radially outwardly of the inlet to exhaust the working fluid out of the blade.
Also provided is a rotor blade that includes a root region, a tip region disposed radially outwardly of the root region, leading and trailing surfaces extending between the root and tip regions, and pressure and suction surfaces extending between the root and tip regions and the leading and trailing surfaces. The rotor blade also includes a bleed path opening to the suction surface and including an inlet in the suction surface to receive working fluid on the suction surface. The bleed path further includes a conduit in communication with the inlet to convey the working fluid from the inlet toward the tip region, and an outlet in communication with the conduit and disposed radially outwardly of the inlet to exhaust the working fluid out of the blade.
These and other features and advantages will become apparent to those skilled in the art in connection with the following detailed description and drawings of one or more embodiments of the invention, in which:
The example embodiment will be described and illustrated with reference to its use in an aircraft propeller environment. However, it will be appreciated as the description proceeds that the invention is useful in many different applications and may be implemented in many other embodiments. In this regard, and as used herein and in the claims, it will be understood that the term “rotor” refers not only to aircraft propeller applications, but also to windmill impellers, marine propellers, turbine engine rotors, helicopter rotors, and various other applications, and regardless of the type of working fluid used in conjunction with the rotor.
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In one embodiment, the conduit 14 and/or the outlet(s) 36 (36′) may be shaped and/or sized to reduce a differential between a velocity of working fluid transmitted from the outlet 36 and a velocity of working fluid in a free stream adjacent the outlet 36. Those of ordinary skill in the art will recognize that such shaping and sizing is application specific and may be determined via empirical testing or by modeling or both.
The presently disclosed bleed path 30 reduces, eliminates, or prevents boundary layer separation over the suction surface 28 of the rotor blade 14, with concomitant reduction, elimination, or prevention in drag and inefficiency of the blade 14. For example, the bleed path 30 may be used to reduce, eliminate, or prevent boundary layer separation whether the flow is laminar or turbulent, and may be particularly beneficial for use in applications with low Reynolds numbers. For instance, it is believed that the presently disclosed bleed path 30 will reduce power required to rotate a propeller and may increase propeller efficiency particularly for relatively small, slowly rotating propellers at high altitudes. Moreover, the bleed path 30 reduces product weight, is low in cost, and does not have any separate moving parts.
Generally, airfoils are designed such that the boundary layer transitions from laminar to turbulent prior to laminar separation. The turbulent boundary layer then naturally remains attached longer because it can tolerate a more adverse pressure gradient than that of a laminar boundary layer. However, at low Reynolds numbers, the laminar boundary layer may separate before transition occurs. If the laminar flow separates, then the process of separation usually induces rapid transition to turbulence. In many cases, this turbulent flow then reattaches because it is more tolerant of the adverse pressure gradient which caused the laminar flow to separate. This laminar separation and turbulent reattachment is called a laminar separation bubble and is a common source of high drag on airfoils used at low Reynolds numbers. In other cases, the separated flow does not reattach, and the resulting drag is even higher.
The presently disclosed passive bleed path(s) may improve efficiency over a large range of conditions, especially at low Reynolds numbers where laminar separation tends to appear. The bleed inlet(s) may be located near the region where laminar separation would occur (if bleed were absent). At low Reynolds numbers, the passive bleed prevents laminar separation such that the boundary layer transitions to turbulent while still attached. The turbulent boundary layer is then able to remain attached because it is more tolerant of an adverse pressure gradient. Therefore, a laminar separation bubble can be prevented, and a substantial source of drag can be eliminated.
Although the bleed inlet(s) may be located near the region of laminar separation, the passive bleed may also be beneficial at higher Reynolds numbers, when the flow is already turbulent over the bleed inlet(s). In this case, the natural turbulent separation point is downstream of the location of the bleed inlet(s), even if bleed were absent. With passive bleed present, the turbulent boundary layer is thinned, thereby delaying separation to a point even farther downstream. This could allow more extreme airfoil shapes to be practical.
This description, rather than describing limitations of an invention, only illustrates example embodiments of the invention recited in the claims. The language of this description is therefore exclusively descriptive and non-limiting. Obviously, it's possible to modify this invention from what the description teaches. Within the scope of the claims, one may practice the invention other than as described above.
Claims
1. A rotor blade comprising:
- a root region;
- a tip region disposed radially outwardly of the root region;
- a leading surface extending between the root and tip regions;
- a trailing surface extending between the root and tip regions;
- a pressure surface extending between the root and tip regions and the leading and trailing surfaces;
- a suction surface extending between the root and tip regions and the leading and trailing surfaces; and
- a bleed path opening to the suction surface, extending through the blade, exiting to at least one of the suction or trailing surfaces, and through which working fluid flows under centrifugal pumping forces when the blade rotates, to passively bleed working fluid from the suction surface.
2. The rotor blade of claim 1, wherein the working fluid passively flows through the bleed path under negative pressurization, but the working fluid does not actively flow through the bleed path by positive pressurization from some external pressurizing device or from a path open to the pressure surface.
3. The rotor blade of claim 1, wherein the bleed path includes:
- an inlet in the suction surface to receive working fluid on the suction surface;
- a conduit in communication with the inlet to convey the working fluid from the inlet toward the tip region; and
- an outlet in communication with the conduit and disposed radially outwardly of the inlet to exhaust the working fluid out of the blade.
4. The rotor blade of claim 3, wherein the bleed path is configured to cause centrifugal pumping forces to pull the working fluid into the inlet, through the conduit, and out of the outlet when the blade rotates.
5. The rotor blade of claim 3, wherein the bleed path is located radially outward of a circumferential axis bisecting the blade.
6. The rotor blade of claim 3, wherein the inlet is a slot extending in a generally radial direction along the blade.
7. The rotor blade of claim 3, further comprising a plurality of the inlet radially spaced from one another in correspondence to radial pressure gradients.
8. The rotor blade of claim 3, wherein the conduit is at least one of shaped or sized to reduce a differential in velocity of working fluid transmitted from the outlet and velocity of working fluid in a free stream adjacent the outlet.
9. The rotor blade of claim 3, wherein the outlet is located in at least one of the suction surface or the trailing surface.
10. The rotor blade of claim 3, wherein the outlet is located radially inward of a radially outermost tip of the blade.
11. The rotor blade of claim 1, wherein the rotor blade is a working member of at least one of an aircraft propeller, a marine propeller, a helicopter rotor, a turbine engine rotor, or a windmill impeller.
12. A rotor comprising:
- a hub defining a rotational axis of the rotor; and
- a rotor blade extending radially outwardly from the hub, and including: a root region; a tip region disposed radially outwardly of the root region; a leading surface extending between the root and tip regions; a trailing surface extending between the root and tip regions; a pressure surface extending between the root and tip regions and the leading and trailing surfaces; a suction surface extending between the root and tip regions and the leading and trailing surfaces; and a bleed path opening to the suction surface and including: an inlet in the suction surface to receive working fluid on the suction surface; a conduit in communication with the inlet to convey the working fluid from the inlet toward the tip region; and an outlet in communication with the conduit and disposed radially outwardly of the inlet to exhaust the working fluid out of the blade; wherein the bleed path is configured such that working fluid flows through the bleed path under centrifugal pumping forces when the blade rotates, to passively bleed working fluid from the suction surface, such that the working fluid passively flows through the bleed path under negative pressurization, but the working fluid does not actively flow through the bleed path by positive pressurization pushed from the inlet toward the outlet from some external pressurizing device or from a path open to the pressure surface.
13. The rotor of claim 12, wherein the bleed path is located radially outward of a circumferential axis bisecting the blade, and the inlet is a slot extending in a generally radial direction along the blade.
14. The rotor of claim 12, wherein the outlet is located in at least one of the suction surface or the trailing surface, and is located radially inward of a radially outermost tip of the blade.
15. The rotor of claim 12, wherein the rotor is at least one of an aircraft propeller, a marine propeller, a helicopter rotor, a turbine engine rotor, or a windmill impeller.
16. A rotor blade comprising:
- a root region;
- a tip region disposed radially outwardly of the root region;
- a leading surface extending between the root and tip regions;
- a trailing surface extending between the root and tip regions;
- a pressure surface extending between the root and tip regions and the leading and trailing surfaces;
- a suction surface extending between the root and tip regions and the leading and trailing surfaces; and
- a bleed path opening to the suction surface and including: an inlet in the suction surface to receive working fluid on the suction surface; a conduit in communication with the inlet to convey the working fluid from the inlet toward the tip region; and an outlet in communication with the conduit and disposed radially outwardly of the inlet to exhaust the working fluid out of the blade.
17. The rotor blade of claim 16, wherein the bleed path is configured such that working fluid flows through the bleed path under centrifugal pumping forces when the blade rotates, to passively bleed working fluid from the suction surface, and such that the working fluid passively flows through the bleed path under negative pressurization, but the working fluid does not actively flow through the bleed path by positive pressurization from some external pressurizing device or from a path open to the pressure surface.
18. The rotor blade of claim 16, wherein the bleed path is located radially outward of a circumferential axis bisecting the blade, and the inlet is a slot extending in a generally radial direction along the blade.
19. The rotor blade of claim 16, wherein the outlet is located in at least one of the suction surface or the trailing surface, and is located radially inward of a radially outermost tip of the blade.
20. The rotor blade of claim 16, wherein the rotor blade is a working member of at least one of an aircraft propeller, a marine propeller, a helicopter rotor, a turbine engine rotor, or a windmill impeller.
Type: Application
Filed: May 28, 2010
Publication Date: Dec 1, 2011
Applicant: Lockheed Martin Corporation (Bethesda, MD)
Inventors: Brett W. Denner (Fort Worth, TX), Neal D. Domel (Aledo, TX)
Application Number: 12/790,091
International Classification: F01D 5/18 (20060101);