Self-balancing air riding seal for a turbine
A turbine of a gas turbine engine has an air riding seal that forms a seal between a rotor and a stator of the turbine, the air riding seal including an annular piston movable in an axial direction under the influence of a pressure on one side with a pressure acting on an opposite side that self-balances the air riding seal during the steady state condition of the engine and lifts off the seal during engine transients.
1. A self-balancing air riding seal between a rotor and a stator in a turbine of a gas turbine engine comprising:
a stator of the turbine in the gas turbine engine;
an annular piston movable in an axial direction in the stator;
a rotor with a rotor sealing surface;
the annular piston having a cushion chamber that forms an air riding seal with the rotor sealing surface;
a labyrinth seal tooth extending from the annular piston and separating a first chamber from a second chamber within the stator;
a central passage within the annular piston connecting the first chamber to the cushion chamber;
an orifice connecting the central passage to the second chamber; and,
axial movement of the annular piston blocks the orifice such pressure in the first chamber is substantially equal to the pressure in the second chamber.
2. The self-balancing air riding seal of claim 1 , and further comprising:
in an engine start-up mode, the orifice is open and the annular piston is moved away from the rotor sealing surface; and,
in an engine steady-state mode, the orifice is blocked and the annular piston is moved toward the rotor sealing surface.
3. The self-balancing air riding seal of claim 1 , and further comprising:
a pressure source of pressurized gas is connected to the first chamber.
4. The self-balancing air riding seal of claim 1 , and further comprising:
a pressure supply valve connected to the second chamber to supply or to block a pressure to the second chamber.
5. The self-balancing air riding seal of claim 1 , and further comprising:
a pressure source is connected directly to the first chamber and indirectly to the second chamber thru a pressure supply valve having an open or a closed position.
6. A turbine of a gas turbine engine, the turbine comprising:
a rotor with a rotor blade extending therefrom;
a stator with a stator vane extending therefrom;
the rotor being adjacent to the stator;
an annular piston movable in an axial direction within the stator;
the annular piston having a cushion chamber that forms an air riding seal with a surface of the rotor;
the annular piston having a labyrinth tooth extending therefrom and having a first pressure surface on one side that will move the annular piston toward the surface of the rotor and a second pressure surface on an opposite side that will move the annular piston away from the surface of the rotor;
the annular piston having an axial passage connecting the first pressure surface to the cushion chamber; and,
the annular piston having a radial orifice connecting the axial passage to the second pressure surface.
7. The turbine of claim 6 , and further comprising:
the radial orifice is closed by a section of the stator at a steady state condition of the gas turbine engine; and,
the radial orifice is opened by the section of the stator at a start-up condition of the engine.
8. The turbine of claim 6 , and further comprising:
the first pressure surface is in a first pressure chamber formed by the stator; and,
the second pressure surface is in a second pressure chamber formed by the stator.
9. The turbine of claim 8 , and further comprising:
a source of pressure is continuously supplied to the first pressure chamber.
10. The turbine of claim 9 , and further comprising:
a pressure regulating valve with an open and closed position is connected to the source of pressure and the second pressure chamber.