Florian Schönleitner

Comparison of the Aerodynamics of Acoustically Designed EGVs and a State-of-the-Art EGV

Within previous EU projects, possible modifications to the engine architecture have been investigated, that would allow for an optimised aerodynamic or acoustic design of the exit guide vanes (EGV) of the turbine exit casing (TEC). However, the engine weight should not be increased and the aerodynamic performance must be at least the same.This paper compares a state-of-the art TEC (reference TEC) with typical EGVs with an acoustically optimised TEC configuration for the engine operating point approach. It is shown that a reduction in sound power level for the fundamental tone (1 blade passing frequency) for this acoustically important operating point can be achieved. It is also shown that the weight of the acoustically optimised EGVs (only bladings considered) is almost equal to the Reference TEC, but a reduction in engine length can be achieved.Measurements were conducted in the subsonic test turbine facility (STTF) at the Institute for Thermal Turbomachinery and Machine Dynamics, Graz University of Technology. The inlet guide vanes, the low pressure turbine (LPT) stage, and the EGVs have been designed by MTU Aero Engines.© 2014 ASME

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.

Comparison of the Experimental Results Between a 2D EGV Cascade Test and a Rig Test Under Engine Representative Conditions

Today the exit guide vanes (EGV) of the turbine exit casing (TEC) of a bypass-engine have to fulfill three major functions. Firstly, they have to support the rear bearing of an aero engine and to provide space to lead through different supply lines, secondly the engine mount is supported and therefore they have to be rigid and large in thickness. Thirdly, the EGVs have to reduce swirl of the last stage LPT (carrying the aerodynamic load) in order to transform it into thrust for highest propulsive efficiency. Further, if available they have to provide the correct flow field for the following component e.g. a mixer as used in low by-pass ratio engines. Such a state-of-the-art EGV is subject to a 2D cascade test performed at the Institute for Fluid Mechanics at Technical University Braunschweig and a rig test performed at the Institute for Thermal Turbomachinery at Graz University of Technology. This work presents the differences in the results between these two tests due to three dimensional effects such as incoming wakes, turbulence and radial variations in swirl, total pressure and yaw angle over the passage height.Copyright

Comparison of numerical forced response predictions with experimental results obtained in a subsonic test turbine facility

In order to achieve the ACARE targets regarding reduction of emissions it is essential to reduce fuel consumption drastically. Reducing engine weight is supporting this target and one option to reduce weight is to reduce the overall engine length (shorter shafts, nacelle). However, to achieve a reduction of engine length the spacing between stator and rotor can be minimised, thus changing rotor blade excitation. Related to the axial spacing, a number of excitation mechanisms in respect to the rotor blading have to be considered already during the design process. Based on these facts several setups have been investigated at different engine relevant operating points and axial spacing between stator and rotor in the subsonic test turbine facility for aerodynamic, acoustic, and aeroelastic investigations (STTF-AAAI) at the Institute for Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. In order to avoid upstream effects of supporting struts, these struts are far downstream of the stage which is under investigation. In this paper the capability to predict forced response vibrations of selected rotor blades is evaluated with experimental results for two different axial gaps between rotor blade and stator vane row. The investigation is done for engine relevant operating conditions. For rotor blade vibration measurements a novel telemetry system in combination with strain gauges is applied. The stage was modelled using the software package ANSYS. Flow fields up and downstream of the turbine stage are analysed and visualised for two axial gaps and compared to the forced response of the blading. Detailed structural dynamic investigations show critical modes during operation which are identified by the telemetry measurements as well. Finally, the influence of the axial spacing regarding the rotor blade excitation and vibration can be elaborated and is prepared to get a better understanding of basic mechanism. The paper shows that reducing axial spacing is a promising option when reducing engine weight. However, prediction of forced response vibrations is still challenging due to the variety of unknown parameters of a real life engine such as coupling stiffness, damping, blade mass, etc.

On the influence of a five-hole-probe on the vibration characteristics of a low pressure turbine rotor while performing aerodynamic measurements

For many reasons it is essential to know and assess the flow field and its characteristics upand downstream of a turbine stage. For these purpose measurements are conducted in test rigs such as the STTF-AAAI (subsonic test turbine facility for aerodynamic, acoustic, and aeroelastic investigations) at the Institute for Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. A low pressure turbine is operated in engine relevant operating conditions. The turbine is experienced high mechanical loads and is excited to vibrate (forced response). In the rotor design process forced response predictions and structural assessments are performed. However, it is not common to include instrumentation (e.g. total pressure and temperature rakes, five-hole-probes, fast response aerodynamic pressure probes) in these forced response predictions. But, these measurement devices are essential and therefore this paper investigates the influence of such an instrumentation onto the vibrational behaviour of a low pressure turbine rotor of the STTF-AAAI. Several vibration measurements at distinct circumferential and radial positions of the five-hole-probe in the flow channel are conducted. These measurement results are compared to measurements performed without a five-hole-probe in the flow channel. A clear influence of the five-hole-probe on the vibration level is shown.

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.

Experimental Investigation of the Upstream Effect of Different Low Pressure Turbine Exit Guide Vane Designs on Rotor Blade Vibration

Exit guide vanes of turbine exit casings are designed to meet aerodynamic, structural and acoustic criteria. New low pressure turbine architectures of aero engines try to optimize components weight in order to decrease the fuel consumption and reduce noise emissions. For this purpose different designs of turbine exit guide vanes (TEGV) exist which vary geometry as well as the number of vanes in the casing. In the subsonic test turbine facility at the Institute for Thermal Turbomachinery and Machine Dynamics of Graz University of Technology, which represents a 1 ½ low pressure turbine stage, the upstream effect of these innovative turbine exit casings (TEC) designs is under investigation. Up to now the influence of the turbine exit casing in relation to the aerodynamic vibration excitation of the rotor blading is not well known. For rotor blade vibration measurements a telemetry system in combination with strain gauges is applied. The present paper is a report of blade vibration measurements within a rotating system in the area of low pressure turbines under engine relevant operating conditions. Within the test phase different turbine exit casings are under investigation at two different operating points (OP). These turbine exit casings represent different design goals, e.g. aerodynamically optimization was performed to reduce losses at the aero design point or an acoustically optimization was done to reduce noise emission at the operating point approach. All these different design intents lead to a changed upstream effect, thus changing rotor blade vibrations. To identify parameters affecting blade vibration attention is paid to aerodynamic measurements as well. Selected results of steady and unsteady flow field measurements are analyzed to draw conclusions. The upstream effect of different turbine exit casings can be quantified at OP1. Depending on the vane number both the potential effect of the TEGV increase and the upstream effect as well. Aerodynamic as well as acoustic improvements as wanted with H-TEC and inverse-cut-off TEC lead to unfavorable conditions and higher blade loading in comparison to the referenced TEC. OP2 provides additional information of downstream effects. Due to the stator vane number the rotor blading is excited in its 4th eigenfrequency. The comparison between all investigated turbine exit casings with respect to the referenced configuration provides a basis for numerical code validation and future developments.© 2016 ASME

Acoustic Comparison of Different Turbine Exit Guide Vane Designs - Part 1: Design Philosophy and Numerical Predictions

In a number of publications of the past years, the authors have presented detailed descriptions of the STTF acoustic turbine test facility at the Graz University of Technology and highlighted its importance for tool validation and technology verification. In this context, multiple configurations have been designed and tested at the cold flow LPT rig and their results with respect to aerodynamics and acoustics have been published. The present paper completes this approach by summarizing the results of a selected number of acoustic design modifications to the Turbine Exit Guide Vane (TEGV) in a comparative way and complementing it with an aerodynamically motivated design optimization. In total, a number of four TEGV designs will be presented and discussed with respect to the respective design objectives, effects on noise generation as well as scattering effects within the LPT (and TEGV) control volume, and noise reduction potential. Within this paper, the corresponding numerical predictions by the MTU in-house LEE code Lin3d will be presented. In addition, in a companion paper also to be presented at the 21st AIAA/ CEAS Aeroacoustics Conference, the experimental results of the four different TEGV designs will be assessed in detail. In addition to the modal acoustic measurements, also several aerodynamic results will be discussed.

Modal Characterization, Strain Gauge Setup and 1-Way FSI of a Low Pressure Turbine Rotor Blading

New designs of low pressure turbines show optimized geometries of stator and rotor blading as well as reduced axial spacing between stator and rotor due to the main target of saving weight which is directly related to the fuel consumption of the aero engine. An important step during the realization process is to investigate altered excitation mechanism. For this purpose aero elastic investigations will be performed at the test rig of Graz University of Technology. In general for a serious prediction of vibration characteristics under operating conditions of any structure a detailed knowledge of the dynamic behavior is essential. In preparation of upcoming strain gauge vibration measurements in combination with a telemetry system of the low pressure turbine rotor blading, modal characteristics as well as a realistic estimation of blade deformation are mandatory. Within this paper different methods of evaluating modal characteristic numerical as well as experimental such as impact hammer and shaker tests, respectively are presented. Numerical investigations show different models and mathematical contact formulation and should provide a better understanding for using correct contact models additionally. When comparing numerical with experimental results a prediction of an optimal strain gauge setup for vibration measurements as well as a simplified numerical model for further aero elastic investigations, such as fluid structure interaction analysis (FSI), complete previous investigations. In order to set up the telemetry system the knowledge of blade deformation at operating conditions is of particular importance. Therefore finally in this paper a 1-way FSI coupling is presented.Copyright

Comparison of a State of the Art and a High Stage Loading Rotor

This paper presents measurement results of a 1½ stage LPT test rig at Graz University of Technology incorporating two different rotor geometries: one with a regular blade loading and a second rotor with a highly loaded blade geometry. The test rig was designed in cooperation with MTU Aero Engines and represents the last 1.5 stages of a commercial aero engine. Considerable efforts were put on the adjustment of all relevant model parameters (Mach number, blade count ratio, airfoil aspect ratio, blade loading, etc.) to reproduce the full scale LPT situation. The rig diameter is approximately half of that of a commercial aero engine LPT. The number of blades and vanes for the two investigated stages as well as the pressure ratio and power output are identical, resulting in a decrease in rotational speed of the HSL rotor. Measurement data from a fast response pressure probe (FRAPP) is used to compare the flow fields of the two different stages.The effect of the different stage designs can be seen when comparing the exit flow fields. The highly loaded stage shows a more pronounced tip leakage vortex compared to the datum stage. The highly loaded stage shows wider wakes with a lower total pressure deficit. The fluctuations of total pressure within the flow field are directly related to the upstream wake. If the measurement position is located within a stator wake, the fluctuations are significantly smaller than out of the wake.Copyright