Sabine Bauinger

The effect of airfoil clocking on noise generation and propagation in a two shaft test turbine

The paper deals with the investigation on the acoustics in a two-stage two-spool test turbine located at the Institute for Thermal Turbomachinery and Machine Dynamics (ITTM) of Graz University of Technology regarding six distinct relative positions between the HP stator and the struts of a Turning Mid Turbine Frame (TMTF). The facility is a continuously operating cold-flow open-circuit plant which is driven by pressurized air and which allows the acoustic measurements to be performed at engine relevant flow conditions (Mach number similarity). The flow path consists of a transonic turbine stage (HP) followed by a low pressure turbine stage consisting of the turning mid turbine frame (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. 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 for six stator-stator clocking positions. The aim of these analyses was to find an ideal vane-vane position where sound emissions can be reduced compared to other positions and thereby finding a quite simple possibility for making aero engines more quiet respectively reducing the amplitudes of certain modes which not only influence acoustics but can also have a big impact on the aeroelastics of an aero engine. 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 a circumferentially traversable microphone array located at the outer casing. The acoustic field was characterized by azimuthal and radial modes determined by traversing the microphone array over 360 degrees and therefore the emitted sound power levels at certain significant radial modes are compared for different vane-vane positions.

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.

Experimental Determination of the Effectiveness of a Sound Absorbing Turbine Exit Casing

This work presents results from experimental investigations conducted in the subsonic test turbine facility for aerodynamic, acoustic, and aeroelastic investigations at Graz University of Technology. The experiments have been performed for the acoustically relevant operating point approach under engine relevant conditions. The sound absorbing exit guide vanes of the turbine exit casing have been designed as Helmholtz resonators with a resonance frequency according to the blade passing frequency of an aero design point. In order to prove the effectiveness of that exit guide vanes acoustic measurements and modal decomposition have been performed and the sound power per azimuthal mode was calculated and compared with results of a conventional hard wall exit guide vane of aerodynamic design. It is shown that the sound power level can be reduced significantly by about 23 dB. However, the losses are increased dramatically.

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.

Impact Of Different Shroud Configurations On Leakage Flow Of a LP Rotor

For this work, different shroud configurations of a LP turbine rotor and their influence on the tip leakage flow as well as on the main passage flow were experimentally and numerically investigated. The basic configuration of the LP rotor consists of a shroud with two straight sealing fins. Based on foregoing investigations in the basic setup, the geometry of the shroud was altered by drilling radially through the shroud in each rotor passage. The bore is located near the pressure side of the blade between the two sealing fins. The basic idea is to produce an aerodynamic blockage effect inside the shroud cavity and therefore reduce the cavity flow. The time-resolved measurement data from measurements with a Fast Response Aerodynamic Pressure Probe (FRAPP) downstream of the LP rotor is compared to results from CFD calculations. During the investigations it was found, that the radial bore not only influences the tip region downstream of the LP rotor, but also causes changes of the flow field close to the hub.

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

Impact of Passive Tip-Injection on Tip-Leakage Flow in Axial Low Pressure Turbine Stage

In addition to geometrical modifications of the blade tip for reducing tip-leakage mass flow rate the method of passive tip-injection serves as an aerodynamic resistance towards the tip-leakage flow. The impact of this method has been investigated thoroughly at unshrouded blades in linear cascades. Furthermore combinations of shrouded blades with passive tip-injection have been investigated analytically as well as via numerical simulations for incompressible flow in linear cascades. The objective of this paper is to consider a real uncooled low pressure turbine stage with shrouded blades and to investigate the effect of passive tip-injection on various operational characteristics. CFD calculations have been carried out in a rotational frame taking into consideration compressible flow and serve for evaluating the method of passive tip-injection in the given turbine stage. Experimental data obtained from the machine without tip-injection serve as boundary conditions for the CFD calculations.Copyright