This two-part paper deals with the influence of high-pressure turbine (HPT) purge flows on the aerodynamic performance of turbine center frames (TCF). Measurements were carried out in a product-representative one and a half-stage turbine test setup. Four individual purge mass flows differing in flow rate, pressure, and temperature were injected through the hub and tip, forward and aft cavities of the unshrouded HPT rotor. Two TCF designs, equipped with nonturning struts, were tested and compared. In this first part of the paper, the influence of different purge flow rates (PFR) is discussed, while in the second part of the paper, the impact of the individual hub and tip purge flows on the TCF aerodynamics is investigated. The acquired measurement data illustrate that the interaction of the ejected purge flow with the main flow enhances the secondary flow structures through the TCF duct. Depending on the PFR, the radial migration of purge air onto the strut surfaces directly impacts the loss behavior of the duct. The losses associated with the flow close to the struts and in the strut wakes are highly dependent on the relative position between the HPT vane and the strut leading edge (LE), as well as the interaction between vane wake and ejected purge flow. This first-time experimental assessment demonstrates that a reduction in the purge air requirement benefits the engine system performance by lowering the TCF total pressure loss.
This paper deals with the investigation on the acoustics of different turning mid turbine frames (TMTF) in the two-stage two-spool test turbine located at the Institute for Thermal Turbomachinery and Machine Dynamics (ITTM) of Graz University of Technology. The facility is a continuously operating cold-flow open-circuit plant which is driven by pressurized air. The flow path consists of a transonic turbine stage (HP) followed by a low pressure turbine stage made of a turning mid turbine frame (TMTF) and a counter-rotating low pressure rotor. Downstream of the low pressure turbine a measurement section is instrumented with acoustic sensors. Three TMTF setups have been investigated at engine like flow conditions. The first configuration (C1) consists of 16 highly 3D-shaped turning struts. The goal of the second design (C2) was to reduce the length of the TMTF by 10% without increasing the losses and providing comparable inflow to the LP turbine rotor. This was achieved by applying 3D-contoured endwalls at the hub. The third one (C3) is a new embedded concept for the turning mid turbine frame with two zero-lift splitters placed into the strut passages. In total 48 vanes (16 struts plus 32 splitter vanes) guide the flow from the HP rotor to the LP rotor. The comparison in terms of noise generation and propagation of the turbines is done by the microphones signal spectra, the emitted sound pressure and sound power level of each TMTF setup. Therefore the acoustic field is characterized by azimuthal and radial modes by means of a microphone array at the outer casing traversed over 360 degrees. By comparing the first two setups (C1 and C2) in terms of noise generation the propagating modes due to the HP turbine were found to be the same, while a difference of 5 dB in amplitude of the modes related to the LP turbine was found due to the different axial spacing between both setups. In the multi-splitter configuration (C3), the overall sound power level depending on the blade passing frequency (BPF) of the HP turbine is reduced by 7 dB and depending on the BPF of the LP turbine by 4 dB compared to C1, respectively. The overall effect is a reduction of the noise emission for the HP turbine due to the embedded design as well as for the LP turbine due to increasing the axial spacing between the TMTF Vanes and LP Blades on the one hand and considerably due to the embedded design on the other hand.
This paper presents the design, construction and the initial commissioning of a secondary air system, applied to a one and a half stage high pressure turbine test setup at the cold flow test facility in Graz University of Technology. The unique system can provide up to eight independent airflows to analyse engine realistic rim seals ejection or cooling injection for stator or rotor blades. This paper focuses on a specific test setup which used a total of four purge flows. These are used to purge the cavities around the high pressure turbine. While two flows enter upstream of the high pressure turbine, two enter downstream, with one flow at the inner and one at the outer wall of the flow channel, respectively. This paper primarily discusses the development and commissioning of the new facility. Initial five-hole probe measurement results are presented downstream of the high pressure turbine with and without any cooling injection. The outcomes of the first-time experiment depict the importance of the purge flow on the isentropic total to total stage efficiency.
The paper deals with the investigation of the noise generation in the two-stage two-spool test turbine located at the Institute for Thermal Turbomachinery and Machine Dynamics (ITTM) at Graz University of Technology. The facility is a continuously operating cold-flow open-circuit plant which is driven by pressurized air. The flow path is formed by a transonic turbine stage (high pressure, HP) followed by a low pressure (LP) turbine stage consisting of a turning mid turbine frame and a counter-rotating LP rotor. Downstream of the low pressure turbine the measurement section is instrumented with acoustic sensors. The acquisition system consists of a fully circumferentially traversable microphone array located at the outer casing. Two configurations of turning mid turbine frames were tested. The baseline is an intermediate turbine duct with 16 turning struts. The second one is a new embedded concept for the turning mid turbine frame with two zero-lift splitters placed in the struts' passages. In total 48 vanes (16 struts plus 32 splitter vanes) guide the flow from the HP rotor to the LP rotor. In order to determine the noise emission of both configurations the microphones signal spectra and the emitted sound power level are compared. The acoustic field is characterized by azimuthal and radial modes by means of a microphone array traversed over 360 . In the multi-splitter configuration, the overall sound power level depending on the blade passing frequency of the HP turbine is reduced by 7 dB and depending on the blade passing frequency of the LP turbine by 4 dB, respectively. The overall effect is a reduction of the acoustic emission for the turning mid turbine frame with embedded design.
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