Flutter inhibiting intake for gas turbine propulsion system
Disclosed is flutter damper including a first cavity having a radially inner side in fluid communication with a flow path, and a second cavity having a radially inner side in fluid communication with a radially outer side of the first cavity, and the flutter damper having an impedance characteristic at one or more target frequencies defined as f target =f S,ND +Ω·ND wherein f S,ND is a resonance frequency corresponding to a structural mode of a rotating component, ND is a nodal diameter count of the structural mode, and Ω is a rotational speed of the rotating component, and wherein the flutter damper has the following impedance characteristic at the one or more targeted frequencies R ≥2ρ c −3ρ c≤X ≤−0.6ρ c wherein R is the real part of the impedance characteristic, X is the imaginary part of the impedance characteristic, ρ is air density, and c is speed of sound.
1. An acoustic liner for a nacelle inlet of a gas turbine engine, comprising:
a flutter damper comprising:
a circumferential array of chambers disposed about the acoustic liner, wherein a flutter dampening volume includes a volume of the circumferential array and a volume of the acoustic liner, each of the chambers including:
a first cavity having a radially inner side in fluid communication with a flow path, the first cavity extending rapidly outwardly from the acoustic liner, and a second cavity having a radially inner side in fluid communication with a radially outer side of the first cavity, the second cavity having an arcuate profile and a larger volume than the first cavity; and
the flutter damper having an impedance characteristic at one or more target frequencies defined as:
f target =f S,ND +Ω·ND
wherein
f S,ND is a resonance frequency corresponding to a structural mode of a rotating component;
ND is a nodal diameter count of the structural mode; and
Ω is a rotational speed of the rotating component; and
wherein the flutter damper has the following impedance characteristic at the one or more targeted frequencies:
R≥2ρc
−3 ρc≤X≤− 0.6 ρc
wherein R is the real part of the impedance characteristic, X is the imaginary part of the impedance characteristic, ρ is air density, and c is speed of sound.
2. The liner of claim 1 , wherein the rotating component is a fan blade, and the targeted frequencies include:
f S,ND =frequency of first or second bending mode of fan with ND nodal diameters
1≤ND≤3
Ω Mreltip=0.85 ≤Ω≤Ω Mreltip=1.2
wherein Mreltip is a relative Mach number for a radial outer tip of the fan blade, and the bending mode is a vibrational mode of the fan blade.
3. The liner of claim 2 , wherein at the one or more target frequencies:
0.0143
≤
Vf
target
Sc
≤
0.165
wherein V is a combined volume of the first and second cavities, and S is an entrance area to the second cavity.
4. The liner of claim 3 , wherein the first cavity and the flow path surface fluidly communicate through a first perforated surface, and the first cavity and second cavity fluidly communicate through a second perforated surface.
5. The liner of claim 4 , wherein the first cavity contains a cellular structure.
6. The liner of claim 5 , wherein the first cavity has a smaller volume than the second cavity.
7. The liner of claim 5 , wherein the first cavity is an acoustic liner for a propulsion system.
8. A gas turbine propulsion system, comprising:
a nacelle;
an acoustic liner for a nacelle inlet of the nacelle;
a flutter damper for a rotating component secured in the nacelle and disposed proximate a flow path, the flutter damper comprising:
a circumferential array of chambers disposed about the acoustic liner, wherein a flutter dampening volume includes a volume of the circumferential array and a volume of the acoustic liner, each of the chambers including:
a first cavity having a radially inner side in fluid communication with a flow path, the first cavity extending radically outwardly from the acoustic liner, and a second cavity having a radially inner side in fluid communication with a radially outer side of the first cavity, the second cavity having an arcuate profile and a larger volume than the first cavity; and
the flutter damper having an impedance characteristic at one or more target frequencies defined as:
f target =f S,ND +Ω·ND
wherein
f S,ND is a resonance frequency corresponding to a structural mode of a rotating component;
ND is a nodal diameter count of the structural mode; and
Ω is a rotational speed of the rotating component; and
wherein the flutter damper has the following impedance characteristic at the one or more targeted frequencies:
R≥2ρc
−3 ρc≤X≤− 0.6 ρc
wherein R is the real part of the impedance characteristic, X is the imaginary part of the impedance characteristic, ρ is air density, and c is speed of sound.
9. The gas turbine propulsion system of claim 8 , wherein the rotating component is a fan blade, and the targeted frequencies include:
f S,ND =frequency of first or second bending mode of fan with ND nodal diameters
1≤ND≤3
Ω Mreltip=0.85 ≤Ω≤Ω Mreltip=1.2
wherein Mreltip is a relative Mach number for a radial outer tip of the fan blade, and the bending mode is a vibrational mode of the fan blade.
10. The gas turbine propulsion system of claim 9 , wherein at the one or more target frequencies:
0.0143
≤
Vf
target
Sc
≤
0.165
wherein V is a combined volume of the first and second cavities, and S is an entrance area to the second cavity.
11. The gas turbine propulsion system of claim 10 , wherein the first cavity and the flow path surface fluidly communicate through a first perforated surface, and the first cavity and second cavity fluidly communicate through a second perforated surface.
12. The gas turbine propulsion system of claim 11 , wherein the first cavity contains a cellular structure.
13. The gas turbine propulsion system of claim 10 , wherein the first cavity has a smaller volume than the second cavity.
14. The gas turbine propulsion system of claim 10 , wherein the first cavity is an acoustic liner for a propulsion system.
15. A method of providing flutter damping to a gas turbine engine, comprising:
passing a flow over a flutter damper of an acoustic liner for a nacelle inlet of a nacelle, the flutter damper having a circumferential array of chambers disposed about the acoustic liner, wherein a flutter dampening volume includes a volume of the circumferential array and a volume of the acoustic liner, each of the chambers including: a first cavity with a radially inner side in fluid communication with a flow path surface, the first cavity extending radially outwardly from the acoustic liner, and a second cavity having a radially inner side in fluid communication with a radially outer side of the first cavity, the second cavity having an arcuate profile and a larger volume than the first cavity; and
dampening flutter for a rotating component disposed in a flow path with the flutter damper at one or more target frequencies defined as:
f target =f S,ND +Ω·ND
wherein f S,ND is a resonance frequency corresponding to a structural mode of the rotating component, ND is a nodal diameter count of the structural mode, and Ω is a rotational speed of the rotating component; and
wherein the flutter damper has the following impedance characteristic at the one or more targeted frequencies:
R≥2ρc
−3 ρc≤X≤− 0.6 ρc
wherein R is the real part of the impedance characteristic, X is the imaginary part of the impedance characteristic, ρ is air density, and c is speed of sound.
16. The method of claim 15 , wherein the rotating component is a fan blade, and the targeted frequencies include:
f S,ND frequency of first or second bending mode of fan with ND nodal diameters
1≤ND≤3
Ω Mreltip=0.85 ≤Ω≤Ω Mreltip=1.2
wherein Mreltip is a relative Mach number for a radial outer tip of the fan blade, and the bending mode is a vibrational mode of the fan blade.