Stefan Zerobin

Noise generation and propagation for different turning mid turbine frame setups in a two shaft test turbine

The paper deals with the investigation on the acoustics of two 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 consisting of a TMTF and a counter-rotating low pressure rotor. Compared to the setup within the EU-Project DREAM, the rig was upgraded by fully circumferentially traversable measurement sections at the inlet of the TMTF as well as downstream of the LP turbine. The two TMTF setups have been investigated at engine like flow conditions. The first configuration consists of 16 highly 3D-shaped turning struts. The goal of the second design was to reduce the length of the TMTF by 10% without increasing the losses and providing the same inflow to the LP turbine rotor. This was achieved by applying 3D-contoured endwalls at the hub. Due to the fact that noise becomes more and more an issue, acoustic measurements were carried out downstream of the low pressure turbine at three different operating conditions representative for approach, cutback and sideline. In order to evaluate the noise emission of the turbine, the outflow duct of the facility was instrumented with a new acoustic measurement setup which uses traversable microphone arrays. Therefore, the emitted sound pressure level and the microphones’ spectra are compared for both configurations. The acoustic field was characterized by azimuthal and radial modes determined by traversing the microphone array over 360 degrees. By comparing the two setups in terms of noise generation, the propagating modes due to the HP turbine were found to be at the same level, while an increase of up to 9 dB in amplitude of the modes related to the LP turbine was found in the 10% shorter setup. This is in good accordance with previous studies, where reducing the distance between stator and rotor of a LPT increases the emitted sound.

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

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.

Acoustic Comparison of Different Turbine Exit Guide Vane Designs Part 2: Experimental Analysis

In this paper the sound power levels of three different designs of turbine exit guide vanes (TEGV) of turbine exit casings are compared with a standard design of an TEGV. The comparison is made with respect to the LPT for the acoustically relevant operating point approach. Additionally a rough loss estimation is also given in this paper. It is shown that the acoustically optimised TEC reduces the sound power level of the main interacion modes by about 14 dB while the aeroynamically optimised TEC even increases the sound power level by 2 dB. All three TEGV designs show higher aerodynamic losses for this off design point (approach). The measurements have been conducted in the subsonic test turbine facility at the Institute for Thermal Turbomachinery and Machine Dynamics, Graz University of Technology.

Impact of Individual High-Pressure Turbine Rotor Purge Flows on Turbine Center Frame Aerodynamics

This paper presents an experimental study of the impact of individual high-pressure turbine purge flows on the main flow in a downstream turbine center frame duct. Measurements were carried out in a product-representative one and a half stage turbine test setup, installed in the Transonic Test Turbine Facility at Graz University of Technology. The rig allows testing at engine-relevant flow conditions, matching Mach, Reynolds, and Strouhal number at the inlet of the turbine center frame. The reference case features four purge flows differing in flow rate, pressure, and temperature, injected through the hub and tip, forward and aft cavities of the high-pressure turbine rotor. To investigate the impact of each individual cooling flow on the flow evolution in the turbine center frame, the different purge flows were switched off one-by-one while holding the other three purge flow conditions. In total, this approach led to six different test conditions when including the reference case and the case without any purge flow ejection. Detailed measurements were carried out at the turbine center frame duct inlet and outlet for all six conditions and the post-processed results show that switching off one of the rotor case purge flows leads to an improved duct performance. In contrast, the duct exit flow is dominated by high pressure loss regions if the forward rotor hub purge flow is turned off. Without the aft rotor hub purge flow, a reduction in duct pressure loss is determined. The purge flows from the rotor aft cavities are demonstrated to play a particularly important role for the turbine center frame aerodynamic performance. In summary, this paper provides a first-time assessment of the impact of four different purge flows on the flow field and loss generation mechanisms in a state-of-the-art turbine center frame configuration. The outcomes of this work indicate that a high-pressure turbine purge flow reduction generally benefits turbine center frame performance. However, the forward rotor hub purge flow actually stabilizes the flow in the turbine center frame duct and reducing this purge flow can penalize turbine center frame performance. These particular high-pressure turbine/turbine center frame interactions should be taken into account whenever high-pressure turbine purge flow reductions are pursued.Copyright

Influence of Operational Geometry Changes on Turbine Acoustics

Due to the fact that noise emitted by aero engines became a very important issue especially during the last few years, acoustic measurements were carried out downstream of the low-pressure turbine in a two-stage two-spool test turbine. The aim of these analyses was to determine the influence of small geometry changes in the flow path of the rig under engine-relevant conditions, which usually occur during the operation of an engine. These geometry changes include steps in the flow path and different rotor tip gaps, both generated by a non-uniform warming of different parts of the engine. In order to evaluate the noise emissions, the outflow duct downstream of the second rotor was instrumented with an acoustic measurement section, which uses a circumferentially traversable microphone array located at the outer endwall. The acoustic field is characterized by azimuthal modes gained by traversing the microphone array over 360 degrees. Therefore, the spectra and emitted sound pressure levels are compared regarding different geometry changes.

Development And Commissioning Of A Purge Flow System In A Two Spool Test Facility

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.

Influence of Measurement Grid Resolution on Duct Loss Evaluation

The present paper deals with the influence of the measurement grid resolution, used for positioning five-hole-probes, on the evaluation of the aerodynamic flow field in a newly designed one-and-a-half stage test turbine. In particular, five-hole-probe data taken under engine realistic conditions downstream of the high pressure rotor at the inlet and outlet of an intermediate turbine duct is used to generate the corresponding flow fields with various measurement grid resolutions. The effect of reducing circumferential and radial grid points is discussed in terms of total pressure loss and total measurement time. In addition, the effect of extrapolating the radial total pressure distribution to the static pressures at the endwalls is demonstrated. Consequently, this paper provides estimates of the error generated by a low measurement grid resolution and proposes a time-efficient adaptive measurement grid which accurately captures the flow field without jeopardizing the quality of the obtained data.

Turbine Noise Reduction: Axial Spacing and Embedded Design

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.Copyright