Propulsion device having unducted counter-rotating and coaxial rotors
View Patent ↗A propulsion device including an unducted upstream propeller and a counter-rotating and coaxial downstream propeller. At least one blade of the upstream propeller is configured to generate a corotating secondary vortex for acting upstream of the downstream propeller to destabilize a blade tip vortex of the same at least one blade.
1. A propeller blade comprising:
a plurality of blade sections stacked in a radial direction over a height h between a blade root and a blade tip, each blade section extending between a leading edge and a trailing edge, and between a pressure side and a suction side;
wherein the leading edge presents negative sweep at the blade root, positive sweep at the blade tip, and between the negative sweep and the positive sweep, a convex portion at a radial position z v at a distance lying in a range of 0.2×h to 0.4×h from the blade root,
each blade section presenting a chord of function C(z) for which a derivative dC/dz presents a first local maximum between the blade root and the position z v , a local minimum between the position z v and a radial position z t lying at a distance in a range of 0.7×h to 0.8×h from the blade root, and a second local maximum between the position z t and the blade tip.
2. A blade root according to claim 1 , wherein each blade section presents an offset along a tangential direction towards the suction side in application of a function y g (z) for which a derivative dy g /dz presents a local maximum and a local minimum between the position z t and the blade tip.
3. A propulsive device comprising:
an unducted upstream propeller and a counter-rotating and coaxial downstream propeller, wherein the upstream propeller includes at least one propeller blade according to claim 1 so that a secondary vortex corotating with a blade tip vortex of the of at least one propeller blade destabilizes the blade tip vortex upstream from the downstream propeller.
4. A method of eliminating interaction noise between an unducted upstream propeller and a counter-rotating and coaxial downstream propeller, wherein at least one blade of the upstream propeller includes a plurality of blade sections stacked along a radial axis over a height h between a blade root and a blade tip, each blade section extending between a leading edge and a trailing edge, and between a pressure side and a suction side,
the leading edge of the blade presenting a negative sweep at the blade root, a positive sweep at the blade tip, and between the negative sweep and the positive sweep, a convex portion presenting a radial position z v at a distance lying in a range of 0.2×h to 0.4×h from the blade root;
each blade section presenting, between the leading edge and the trailing edge, a chord of function C(z) for which a derivative dC/dz presents a first local maximum between the blade root and the position z v , a local minimum between the position z v and a radial position z t lying at a distance in a range of 0.7×h to 0.8×h from the blade root, and a second local maximum between the position z t and the blade tip, the method comprising:
destabilizing a blade tip vortex of at least one propeller blade of the upstream propeller upstream from the downstream propeller by a corotating secondary vortex generated by the at least one propeller blade.
5. A method according to claim 4 , wherein each blade section presents an offset along a tangential axis towards the suction side in application of a function y g (z) having a derivative dy g /dz that presents a local maximum and a local minimum between the position z t and the blade tip.