Development of a Turning Mid Turbine Frame With Embedded Design: Part II — Unsteady Measurements

Abstract

The paper, which is constituted by two parts, presents a new setup for the two-stage two-spool facility located at the Institute for Thermal Turbomachinery and Machine Dynamics (ITTM) of Graz University of Technology. The rig was designed in order to reproduce the flow behavior of a transonic turbine followed by a counter rotating low pressure stage like those in high bypass aero-engines. The meridional flow path of the machine is characterized by a diffusing S-shaped duct between the two rotors. The role of wide chord vanes placed into the mid turbine frame is to lead the flow towards the LP rotor with appropriate swirl. Experimental and numerical investigations performed on this setup over the last years showed that the wide chord struts induce large wakes and extended secondary flows at LP inlet flow. Moreover, large deterministic fluctuations of pressure, which may cause noise and blade vibrations, were observed downstream of the LP rotor. In order to minimize secondary vortices and to damp the unsteady interactions, the mid turbine frame was redesigned to locate two zero-lifting splitters into the vane passage. While in the first part paper the design process of the splitters and the time-averaged flow field were presented, in this second part the measurements performed by means of a fast response probe will support the explanation of the time-resolved field. The discussion will focus on the comparison between the baseline case (without splitters) and the embedded design.

On the acoustics of a turning mid turbine frame with embedded design in a two-stage test-turbine

“…Since the noise generated by the HP turbine is the same for both TMTF setups in terms of an input source, these modes generated by the interactions including the HP stator describe the noise reducing impact of the additional splitter vanes in setup C3. This is in good accordance with the unsteady investigations done by Spataro et al., 3 where measurements upstream the LP rotor showed a more uniformly distributed flow field for the TMTF setup C3. Due to the reduced pressure fluctuations in the presence of the splitters, the intensity of the rotor interaction with the wakes of the TMTF struts is considerably lowered.…”

“…For more details on the design and aerodynamics of this setup the reader can refer to Spataro et al. 2,3

Figure 1.Meridional and blade-to-blade section of the two-spool facility: (a) baseline configuration with TMTF C1; (b) embedded design C3 with two additional splitter vanes between the bulky TMTF struts. HP: high pressure; LP: low pressure.

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“…A baseline setup without splitters was redesigned embedding two zero-lift splitters in the strut passage in order to minimize secondary vortices and to damp the rotor-rotor interaction. The design process and the results of the aerodynamic measurements on the setup with splitters can be found in Spataro et al 2,3 The measurement took place in the transonic test turbine facility (TTTF). The facility is a continuously operating cold-flow open-circuit plant which is driven by pressurized air.…”

Progress in Experimental Research of Turbine Aeroacoustics

“…In the assumed ideal case of the splitter setup, mode m = − 8 should not be there. However, as observed by Spataro et al [22,23] the unsteady effects induced by strut and splitter vane wakes differ considerably downstream of the LP rotor. The modes generated due to the interaction of the 48 LP vanes with the LP blades may be predicted when the modes are scattered at the 16 struts (e.g.…”

“…The high sound pressure level at the BP F LP may be due to the effect of "shifting" modes towards lower orders and not necessarily to an enhanced unsteady interaction. Unsteady measurements by means of a fast response aerodynamic pressure probe downstream of the LP rotor reported in Spataro et al [23] revealed that the unsteady pressure fluctuations, evaluated for the LP rotor phase, are of comparable order of magnitude for both setups.…”