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Highly efficient turbine exhaust diffuser cannot be designed without taking into account the unsteady interactions with the last rotating row of the turbine.Former investigations described in the literature show a very high poten- tial compared to that of other parts of turbomachines for improving the diffuser.A scale model of a typical gas turbine exhaust diffuser is investigated experimentally.To investigate the influence of rotating wakes,measure- ments without a spoke wheel as well as measurements with a variable-speed rotating cylindrical spoke wheel with 2 mm-or 10 mm-spokes simulating turbine rotor wakes were made.Miniaturized 3-hole pneumatic probes as well as a 2D-Laser-Doppler-Velocimeter (LDV) were used to investigate velocity profiles.122 static pressure tapings were used to measure several axial and circumferential static pressure distributions.Without a spoke-wheel the annular diffuser separates at the shroud for all swirl configurations.For the measurements with the 2 mm spoke wheel,the separating diffuser was unstable while keeping the test rig operating parameters constant.For a non-rotating 10 mm spoke wheel and at rotational speeds less than 1,000 rpm,the annular diffuser separated at the shroud.In- creasing the rotational speed of the 10ram spoke wheel,flow did not separate at the shroud and much higher pressure recovery than without spoke wheel has achieved.
Highly efficient turbine exhaust diffuser can not be designed without taking into account the unsteady interactions with the last rotating row of the turbine. Former investigations described in the literature show a very high poten- tial compared to that of other parts of turbomachines for improving the diffuser. A scale model of a typical gas turbine exhaust diffuser is investigated experimentally. To investigate the influence of rotating wakes, measure-ments without a spoke wheel as well as measurements with a variable-speed rotating cylindrical spoke wheel with 2 mm-or 10 mm- spokes simulating turbine rotor wakes were made. Miniaturized 3-hole pneumatic probes as well as a 2D-Laser-Doppler-Velocimeter (LDV) were used to investigate velocity profiles. 122 static pressure tapings were used to measure several axial and circumferential static pressure distributions .Without a spoke-wheel the annular diffuser separates at the shroud for all swirl configurations.For the measurements with the 2 mm spoke wheel, the separating diffuser was unstable while keeping the test rig operating parameters constant. For a non-rotating 10 mm spoke wheel and at rotational speeds less than 1,000 rpm, the annular diffuser separated at the shroud.In- creasing the rotational speed of the 10ram spoke wheel, flow did not separate at the shroud and much higher pressure recovery than without spoke wheel has achieved.