Airfoil with dynamic stall control by oscillatory forcing
AssigneeRamot University Authority for Applied Research and Industrial Development Ltd.
InventorsIsrael Wygnanski, David Greenblatt, Avi Seifert
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Abstract
A method for inhibiting dynamic stall of an airfoil by causing a fluid to flow out of at least one location on the airfoil. This location may be anywhere on the airfoil; but if the location is within one-quarter of the airfoil chord from the leading edge and the fluid flow has non-zero net mass flux, then the fluid flow is modulated at a frequency described by a Strouhal ratio greater than one.
Claims35
A method for inhibiting dynamic stall of an airfoil having a leading edge and a trailing edge that define a chord therebetween, as the airfoil executes a pitching motion at a frequency of airfoil oscillation, comprising a step selected from the group consisting of:
- (a) causing a fluid to flow through at least one location on the airfoil within about one quarter of the chord from the leading edge, said flow being with a zero net mass flux;
- (b) causing a fluid to flow through at least one location on the airfoil within about one quarter of the chord from the leading edge, said flow being with a non-zero net mass flux and modulated at a first frequency of oscillatory forcing described by a Strouhal ratio greater than about one;
- and
- (c) causing said fluid to flow through at least one location on the airfoil beyond about one quarter of the chord from the leading edge.
A method for inhibiting dynamic stall in an airfoil having a surface, the airfoil moving through a medium and executing a pitching motion at a frequency of airfoil oscillations the method comprising the step of establishing an oscillation in said medium adjacent to at least one location on said surface of the airfoil, said oscillation being modulated at a frequency of oscillatory forcing described by a Strouhal ratio greater than about one.
A rotary wing aircraft, for motion through a medium, comprising an airfoil that includes:
- (a) an upper surface;
- (b) a lower surface, said upper surface and said lower surface meeting at a leading edge and at a trailing edge, said upper surface and said lower surface defining between them an interior, said leading edge and said trailing edge defining between them a chord;
- (c) at least one aperture in a location selected from the group consisting of:
- (i) locations in said upper surface beyond about one quarter of said chord from said leading edge,
- (ii) locations in said lower surface beyond about one quarter of said chord from said leading edge, and
- (iii) locations along said trailing edge;
- and
- (d) a mechanism for causing oscillatory flow of a fluid between said medium and said interior via said at least one aperture at a Strouhal ratio greater than about one.
A rotary wing aircraft for motion through a medium, comprising an airfoil that includes:
- (a) an upper surface;
- (b) a lower surface, said upper surface and lower surface meeting at a leading edge and at a trailing edge, said upper surface and said lower surface defining between them an interior, said leading edge and said trailing edge defining between them a chord, each of said upper surface and said lower surface having a certain shape;
- and
- (c) a mechanism for oscillating a portion of the medium adjacent to at least one location selected from the group consisting of:
- (i) locations in said upper surface,
- (ii) locations in said lower surface,
- (iii) locations along said leading edge, and
- (iv) locations along said trailing edge,
- wherein said mechanism oscillates at a Strouhal ratio greater than about one.
A rotary wing aircraft, for motion through a medium, comprising an airfoil that includes:
- (a) an upper surface;
- (b) a lower surface, said upper surface and said lower surface meeting at a leading edge and at a trailing edge, said upper surface and said lower surface defining between them an interior, said leading edge and said trailing edge defining between them a chord;
- (c) at least one aperture in a location selected from the group consisting of:
- (i) locations in said upper surface within about one quarter of said chord from said leading edge,
- (ii) locations in said lower surface within about one quarter of said chord from said leading edge, and
- (iii) locations along said leading edge;
- and
- (d) a mechanism for causing a fluid to flow between said medium and said interior via said at least one aperture, said flow being with a non-zero net mass flux and modulated at a first frequency of oscillatory forcing described by a Strouhal ratio greater than about one.
A rotary wing aircraft, for motion through a medium, comprising an airfoil that includes:
- (a) an upper surface;
- (b) a lower surface, said upper surface and said lower surface meeting at a leading edge and at a trailing edge, said upper surface and said lower surface defining between them an interior, said leading edge and said trailing edge defining between them a chord;
- (c) at least one aperture in a location selected from the group consisting of:
- (i) locations in said upper surface between said leading edge and said trailing edge,
- (ii) locations in said upper surface between said leading edge and said trailing edge,
- (iii) locations along said leading edge, and
- (iv) locations along said trailing edge;
- and
- (d) a mechanism for causing oscillatory flow of a fluid between said medium and said interior via said at least one aperture at a Strouhal ratio greater than about one.
Dependencies are inferred from the claim text.