Claims
- 1. An apparatus for providing propulsive force by increasing the velocity of a fluid working medium, the apparatus comprising:
a rotatable impeller including a plurality of lifting elements spaced from each other, wherein each said lifting element has an airfoil cross-section that provides lift as the fluid working medium travels relative thereto; and a device for directing the fluid working medium into an inlet of said impeller, wherein said device varies a parameter of the flow relative to each said lifting element in repeating cycles to cause said apparatus to generate a predetermined acoustic signature characterized by predetermined acoustic energy levels in the fluid at given locations relative to said apparatus.
- 2. An apparatus as in claim 1, wherein said impeller comprises an axial flow impeller and said lifting elements comprise a plurality of impeller blades arranged around a hub capable of rotating on an axis.
- 3. An apparatus as in claim 2, wherein said device varies the parameter such that a far field acoustic sound power generated by the apparatus is minimized.
- 4. An apparatus as in claim 2, wherein said device provides a predetermined acoustic signature by varying the parameter such that selected sound frequencies generated by the apparatus in the fluid are canceled and other selected sound frequencies generated by the apparatus in the fluid are enhanced.
- 5. An apparatus as in claim 4, wherein the predetermined acoustic signature mimics another sound source and thereby enables the apparatus to act as an acoustic decoy.
- 6. An apparatus as in claim 2, wherein:
said device comprises a stator with a plurality of stator blades arranged around said axis upstream of said impeller; and said parameter is a flow angle at which the flow is directed to said impeller, each said stator blade being oriented at a predetermined turning angle for circumferentially varying said flow angle above and below an angle of attack at which each said lifting element experiences steady-state stall.
- 7. An apparatus as in claim 2, wherein:
said device includes a second axial flow impeller having a plurality of impeller blades arranged around said hub, said second impeller being upstream of said first-mentioned impeller and mounted for rotation on said axis in a direction opposite the direction of rotation of said first impeller; and said parameter is a flow angle at which the flow is directed to said first impeller, each said blade of said second impeller being oriented at a predetermined turning angle for circumferentially varying said flow angle above and below an angle of attack at which each said lifting element experiences steady-state stall.
- 8. An apparatus as in claim 1, further comprising an axial flow device, wherein:
said lifting elements are arranged in a first cascade around a hub capable of rotating on an axis; said device includes a second plurality of lifting elements having an airfoil cross-section arranged in a second cascade around said hub; and said airfoils in said second cascade have at least one predetermined geometric property for controlling the parameter by varying circumferentially or radially or both from element to element, said property including at least one of lifting element pitch, cross-sectional thickness, camber distribution, chord length, and element-to-element spacing.
- 9. An apparatus as in claim 8, wherein:
said first cascade includes a first axial flow impeller; said second cascade includes at least one of (i) a stator with a plurality of stationary blades and (ii) a second axial flow impeller having a plurality of impeller blades mounted for rotation on said axis in a direction opposite the direction of rotation of said first impeller; and the parameter is a flow angle at which the flow is directed to said first impeller, each said blade of said second cascade being oriented at a predetermined exit angle for circumferentially varying said flow angle to cause the flow relative to each lifting element to begin to separate from the lifting element and then reattach thereto during each cycle.
- 10. An apparatus as in claim 9, wherein:
said first-mentioned axial flow impeller comprises a propeller for generating thrust used to propel a body through said fluid; and said geometric property cyclically varies in a predetermined manner to minimize variations in thrust in the direction of said axis.
- 11. An apparatus as in claim 10, wherein:
said propeller comprises 2MJ blades, M being an integer greater than 1 and J being an integer greater than or equal to 1; and said second cascade introduces M cyclical variations in said flow angle around the circumference of said impeller.
- 12. A method of optimizing the acoustic energy signature generated by a propulsor that increases the velocity of a fluid working medium to provide a predetermined propulsive force by rotating an impeller having a plurality of lifting elements spaced from each other, the method comprising the steps of:
varying a parameter of the flow relative to each said lifting element in repeating cycles to cause the propulsor to generate a predetermined acoustic signature characterized by predetermined acoustic energy levels in the fluid at given locations spaced from the propulsor; and choosing values of the parameter that cause the flow relative to each lifting element to begin to separate from the lifting element and then reattach thereto during each cycle to increase the propulsive force generated by the impeller at a given rotational speed, thereby permitting generation of the predetermined thrust at a reduced rotational speed.
- 13. A method as in claim 12, wherein the parameter is at least one of the magnitude of the velocity of the flow entering said inlet of said cascade, the direction of the velocity of the flow entering said inlet of said cascade, and the swirl in the flow entering said inlet of said cascade.
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of application Ser. No. 10/627,851, filed Jul. 25, 2003, which claims the benefit of U.S. provisional application No. 60/425,282, filed Nov. 12, 2002, and U.S. provisional application No. 60/429,351, filed Nov. 27, 2002. This application claims the benefit of U.S. provisional application No. 60/425,303, filed Nov. 12, 2002. All four of these related applications are incorporated herein by reference.
STATEMENT REGARDING GOVERNMENT RIGHTS
[0002] This invention was made with Government support under contract number N00014-02-M-0210 awarded by the U.S. Navy. The Government has certain rights in the invention.
Provisional Applications (3)
|
Number |
Date |
Country |
|
60425282 |
Nov 2002 |
US |
|
60429351 |
Nov 2002 |
US |
|
60425303 |
Nov 2002 |
US |
Continuation in Parts (1)
|
Number |
Date |
Country |
Parent |
10627851 |
Jul 2003 |
US |
Child |
10702272 |
Nov 2003 |
US |