SNUBBERED BLADES WITH IMPROVED FLUTTER RESISTANCE
A bladed rotor system ( 10 ) for a turbomachine includes a row of blades ( 14 ) mounted on a rotor disc ( 12 ). Each blade ( 14 ) includes an airfoil ( 16 ) with a mid-span snubber ( 30 ). The row of blades ( 14 ) includes first (H) and second (L) sets of blades ( 14 ). The blades ( 14 ) of the second set (L) are distinguished from the blades ( 14 ) of the first set (H) by a geometry of the snubber ( 30 ) that is unique to the respective set (H, L). In particular, the snubbers ( 30 ) of the second set (L) are attached to the respective airfoils ( 16 ) at a different span-wise height than that of the snubbers ( 30 ) of the first set (H). Thereby the natural frequency of a blade ( 14 ) in the second set (L) differs from the natural frequency of a blade ( 14 ) in the first set (H) by a predetermined amount. Blades ( 14 ) of the first set (H) and the second set (L) are positioned alternately in the row of blades ( 14 ), to provide a frequency mistuning to stabilize flutter of the blades ( 14 ).
1 . A bladed rotor system ( 10 ) for a turbomachine, comprising:
a circumferential row of blades ( 14 ) mounted on a rotor disc ( 12 ), each blade ( 14 ) comprising:
an airfoil ( 16 ) extending span-wise along a radial direction from a root portion ( 18 ) to an airfoil tip ( 20 ); and
a circumferentially extending snubber ( 30 ) attached to the airfoil ( 16 ) at a mid-span region of the airfoil ( 16 ),
wherein in operation, snubbers ( 30 ) of adjacent blades ( 14 ) abut circumferentially,
wherein the row of blades ( 14 ) comprises a first set (H) of blades ( 14 ) and a second set (L) of blades ( 14 ), wherein the blades ( 14 ) of the second set (L) are distinguished from the blades ( 14 ) of the first set (H) by a geometry of the snubber ( 30 ) that is unique to the respective set (H, L), in which:
the snubbers ( 30 ) of the second set (L) are attached to the respective airfoils ( 16 ) at a different span-wise height than that of the snubbers ( 30 ) of the first set (H), whereby the natural frequency of a blade ( 14 ) in the second set (L) differs from the natural frequency of a blade ( 14 ) in the first set (H) by a predetermined amount,
wherein blades ( 14 ) of the first set (H) and the second set (L) are positioned alternately in the row of blades ( 14 ), to provide a frequency mistuning to stabilize flutter of the blades ( 14 ).
2 . The bladed rotor system ( 10 ) according to claim 1 , wherein the airfoils ( 16 ) in the first (H) and second (L) set having substantially identical cross-sectional geometry about a rotation axis ( 22 ).
3 . The bladed rotor system ( 10 ) according to claim 1 , wherein a free length (r e2 ) of the airfoils ( 16 ) in the second set (L) is larger than a free length (r e1 ) of the airfoils ( 16 ) in the first set (H),
the free length (r e1 , r e2 ) of an airfoil ( 16 ) being defined as a radial distance between the airfoil tip ( 20 ) and a point of attachment ( 34 ) of the airfoil ( 16 ) with the associated snubber ( 30 ).
4 . The bladed rotor system ( 10 ) according to claim 3 , wherein each snubber ( 30 ) comprises a pressure side snubber portion ( 30 a ) extending from a pressure side ( 2 ) of the respective airfoil ( 16 ) and a suction side snubber portion ( 30 b ) extending from a suction side ( 4 ) of the respective airfoil ( 16 ),
wherein the pressure side snubber portion ( 30 a ) and the suction side snubber portion ( 30 b ) of the snubbers ( 30 ) in the second set (L) are oriented differently than the pressure side snubber portion ( 30 a ) and the suction side snubber portion ( 30 b ) of the snubbers ( 30 ) in the first set (H), such that snubbers ( 30 ) of adjacent blades ( 14 ) of the row of blades meet at a constant radial height (r r ).
5 . The bladed rotor system ( 10 ) according to claim 4 , wherein
the pressure side snubber portion ( 30 a ) and the suction side snubber portion ( 30 b ) of each snubber ( 30 ) in the first set (H) extends radially inwardly from said point of attachment ( 34 ), and
the pressure side snubber portion ( 30 a ) and the suction side snubber portion ( 30 b ) of each snubber ( 30 ) in the second set (L) extends radially outwardly from said point of attachment ( 34 ).
6 . The bladed rotor system ( 10 ) according to claim 5 , wherein the pressure side snubber portion ( 30 a ) and the suction side snubber portion ( 30 b ) of each snubber ( 30 ) in each of the first (H) and second (L) sets extends radially inwardly or outwardly from said point of attachment ( 34 ) along a linear profile.
7 . The bladed rotor system ( 10 ) according to claim 5 , wherein
the pressure side snubber portion ( 30 a ) and the suction side snubber portion ( 30 b ) of each snubber ( 30 ) in the first set (H) is curved radially inward from said point of attachment ( 34 ), and
the pressure side snubber portion ( 30 a ) and the suction side snubber portion ( 30 b ) of each snubber ( 30 ) in the second set (L) is curved radially outward from said point of attachment ( 34 ).
8 . The bladed rotor system ( 10 ) according to claim 1 , wherein the snubbers ( 30 ) in the first set (H) and the second set (L) have the same mean radial thickness.
9 . A blade ( 14 ) for a row of blades in a turbomachine, the blade ( 14 ) comprising:
an airfoil ( 16 ) extending span-wise along a radial direction from a root portion ( 18 ) to an airfoil tip ( 20 ); and
a circumferentially extending snubber ( 30 ) attached to the airfoil ( 16 ) at a mid-span region of the airfoil,
wherein the blade ( 14 ) is designed to be identical to a first set (H) of blades ( 14 ) or a second set (L) of blades ( 14 ) in the row,
wherein the blades ( 14 ) of the second set (L) are distinguished from the blades ( 14 ) of the first set (H) by a geometry of the snubber ( 30 ) that is unique to the respective set (H, L), in which:
the snubbers ( 30 ) of the second set (L) are attached to the respective airfoils ( 16 ) at a different span-wise height than that of the snubbers ( 30 ) of the first set (H), whereby the natural frequency of a blade ( 14 ) in the second set (L) differs from the natural frequency of a blade ( 14 ) in the first set (H) by a predetermined amount,
wherein blades ( 14 ) of the first set (H) and the second set (L) are positioned alternately in the row of blades ( 14 ), to provide a frequency mistuning to stabilize flutter of the blades ( 14 ).
10 . The blade ( 14 ) according to claim 9 , wherein the snubber ( 30 ) comprises a pressure side snubber portion ( 30 a ) extending from a pressure side ( 2 ) of the airfoil ( 16 ) and a suction side snubber portion ( 30 b ) extending from a suction side ( 4 ) of the airfoil ( 16 ), and
wherein the pressure side snubber portion ( 30 a ) and the suction side snubber portion ( 30 b ) of the snubber extend radially outwardly from a point of attachment ( 34 ) of the airfoil ( 16 ) to the snubber ( 30 ).
11 . The blade ( 14 ) according to claim 10 , wherein the pressure side snubber portion ( 30 a ) and the suction side snubber portion ( 30 b ) of the snubber ( 30 ) extend radially outwardly from said point of attachment ( 34 ) along a straight profile.
12 . The blade ( 14 ) according to claim 10 , wherein the pressure side snubber portion ( 30 a ) and the suction side snubber portion ( 30 b ) of the snubber ( 30 ) curve outward from said point of attachment ( 34 ).
13 . The blade ( 14 ) according to claim 9 , wherein the snubber ( 30 ) comprises a pressure side snubber portion ( 30 a ) extending from a pressure side ( 2 ) of the airfoil ( 16 ) and a suction side snubber portion ( 30 b ) extending from a suction side ( 4 ) of the airfoil ( 16 ), and
wherein the pressure side snubber portion ( 30 a ) and the suction side snubber portion ( 30 b ) of the snubber ( 30 ) extend radially inwardly from a point of attachment ( 34 ) of the airfoil ( 16 ) to the snubber ( 30 ).
14 . The blade ( 14 ) according to claim 13 , wherein the pressure side snubber portion ( 30 a ) and the suction side snubber portion ( 30 b ) of the snubber ( 30 ) extend radially inwardly from said point of attachment ( 34 ) along a straight profile.
15 . The blade ( 14 ) according to claim 13 , wherein the pressure side snubber portion ( 30 a ) and the suction side snubber portion ( 30 b ) of the snubber ( 30 ) curve inward from said point of attachment ( 34 ).