Andreas Marn

Shorten the Intermediate Turbine Duct Length by Applying an Integrated Concept

The demand of further increased bypass ratio of aero engines will lead to low pressure turbines with larger diameters, which rotate at lower speed. Therefore, it is necessary to guide the flow leaving the high pressure turbine to the low pressure turbine at larger diameters minimizing the losses and providing an adequate flow at the low pressure (LP)-turbine inlet. Due to costs and weight, this intermediate turbine duct has to be as short as possible. This would lead to an aggressive (high diffusion) s-shaped duct geometry. It is possible to shorten the duct simply by reducing the length but the risk of separation is rising and losses increase. Another approach to shorten the duct and thus the engine length is to apply a so called integrated concept. These are novel concepts where the struts, mounted in the transition duct, replace the usually following LP-vane row. This configuration should replace the first LP-vane row from a front bearing engine architecture where the vane needs a big area to hold bearing services. That means the rotor is located directly downstream of the strut. This means that the struts have to provide the downstream blade row with undisturbed inflow with suitable flow angle and Mach number. Therefore, the (lifting) strut has a distinct three-dimensional design in the more downstream part, while in the more upstream part, it has to be cylindrical to be able to lead through supply lines. In spite of the longer chord compared with the base design, this struts have a thickness to chord ratio of 18%. To apply this concept, a compromise must be found between the number of struts (weight), vibration, noise, and occurring flow disturbances due to the secondary flows and losses. The struts and the outer duct wall have been designed by Industria de Turbopropulsores. The inner duct was kept the same as for the base line configuration (designed by Motoren und Turbinen Union). The aim of the design was to have similar duct outflow conditions (exit flow angle and radial mass flow distribution) as the base design with which it is compared in this paper. This base design consists of a single transonic high pressure (HP)-turbine stage, an aggressive s-shaped intermediate turbine duct, and a LP-vane row. Both designs used the same HP-turbine and were run in the continuously operating Transonic Test Turbine Facility at Graz University of Technology under the same engine representative inlet conditions. The flow field upstream and downstream the LP-vane and the strut, respectively, has been investigated by means of five hole probes. A rough estimation of the overall duct loss is given as well as the upper and lower weight reduction limit for the integrated concept.

The Influence of Blade Tip Gap Variation on the Flow Through an Aggressive S-Shaped Intermediate Turbine Duct Downstream a Transonic Turbine Stage: Part II — Time-Resolved Results and Surface Flow

The demand of further increased bypass ratio of aero engines will lead to low pressure turbines with larger diameters rotating at lower speed. Therefore it is necessary to guide the flow leaving the high pressure turbine to the low pressure turbine at larger diameter without any separation or flow disturbances. Due to costs and weight this intermediate turbine duct has to be as short as possible leading to aggressive (high diffusion) S-shaped duct geometries. To investigate the influence of the blade tip gap size on such a nonseparating high diffusion duct flow a detailed test arrangement under engine representative conditions is necessary. Therefore the continuously operating Transonic Test Turbine Facility (TTTF) at Graz University of Technology has been adapted: An high diffusion intermediate duct is arranged downstream of a HP turbine stage providing an exit Mach number of about 0.6 and a swirl angle of −15 degrees. A LP vane row is located at the end of the duct and represents the counter rotating low pressure turbine at larger diameter. In order to determine the influence of the blade tip gap size on the flow through such an S-shaped turbine duct measurements were performed with two different tip gap sizes, 0.8 mm and 1.3 mm. The aerodynamic design was done by MTU Aero Engines. While Part I describes the investigation by means of five hole probes with thermo couples, boundary layer rakes and static pressure tappings Part II uses Laser-Doppler-Velocimetry (LDV) for measurements at duct inlet directly downstream the HP blades to obtain unsteady information about the inflow and to quantify the differences between the two tip gaps. Additionally oil-film visualization was used to discuss the surface flow at the outer and inner wall of the duct. A comparison with a numerical simulation is also given. This work is part of the EU-project AIDA (Aggressive Intermediate Duct Aerodynamics, Contract: AST3-CT-2003-502836).© 2007 ASME

Numerical Analysis of Heat Transfer and Flow of Stator Duct Models

This paper describes the analysis of the fluid flow in the stator ducts of a hydrogenerator using computational fluid dynamics. The main objective is to define permissible simplifications of the model in order to speed up the simulation. Therefore, the rotor-stator interaction is significant and needs to be taken under consideration. The software package ANSYS CFX supports two possibilities to connect these two reference models for steady-state simulations, the Frozen Rotor and the Stage model. Their differences are shown on a couple of parameters comparing these completely different reference models. Another important aspect pointed out in this paper is a comparison of the fluid flow and the heat transfer along one of the stator ducts. Last but not least, a quality and sensitivity study has been accomplished. The dependence of the computed wall heat transfer coefficient on the quality of the mesh near the wall is illustrated. Furthermore, the differences obtained lead to two particular turbulence models with different near-wall treatments, both of which have been applied.

The Influence of Blade Tip Gap Variation on the Flow Through an Aggressive S-Shaped Intermediate Turbine Duct Downstream a Transonic Turbine Stage: Part I — Time-Averaged Results

The demand of further increased bypass ratio of aero engines will lead to low pressure turbines with larger diameters which rotate at lower speed. Therefore, it is necessary to guide the flow leaving the high pressure turbine to the low pressure turbine at a larger diameter without any loss generating separation or flow disturbances. Due to costs and weight this intermediate turbine duct has to be as short as possible. This leads to an aggressive (high diffusion) s-shaped duct geometry. To investigate the influence of the blade tip gap size of such a nonseparating high diffusion duct flow a detailed test arrangement under engine representative conditions is necessary. Therefore, the continuously operating Transonic Test Turbine Facility (TTTF) at Graz University of Technology has been adapted: A high diffusion intermediate duct is arranged downstream a HP turbine stage providing an exit Mach number of about 0.6 and a swirl angle of 15 degrees (counter swirl). An LP vane row is located at the end of the duct and represents the counter rotating low pressure turbine at larger diameter. In order to determine the influence of the blade tip gap size on the flow through such an s-shaped turbine duct measurements were conducted with two different tip gap sizes, 1.5% span (0.8mm) and 2.4% span. (1.3mm). The aerodynamic design of the HP vane, the HP turbine, the duct and the LP vane was done by MTU Aero Engines. The investigation was conducted by means of five-hole-probes with thermocouples, boundary layer rakes and static pressure taps at the inner and outer wall along the duct at several circumferential positions. Five-hole-probe measurements were done in five planes within the duct and in two planes downstream of the LP vane. A rough estimation of the duct loss is given at the end of the paper. Part II of this work deals with two-component Laser-Doppler Velocimeter (LDV) measurements at duct inlet directly downstream the HP blade to obtain unsteady information about the inflow. Additionally, oil film visualisation was used to get information about the surface flow at the outer and inner wall of the duct.Copyright

Numerical Investigation of the Effect of Tip Leakage Flow on an Aggressive S-Shaped Intermediate Turbine Duct

The demand of a further increased bypass ratio of aero engines will lead to low pressure turbines with larger diameters which rotate at lower speed. Therefore, it is necessary to guide the flow leaving the high pressure turbine to the low pressure turbine at a larger diameter without any loss generating separation or flow disturbances. Due to costs and weight this intermediate turbine duct has to be as short as possible. This leads to an aggressive (high diffusion) S-shaped duct geometry. In order to investigate the influence of the blade tip gap height of a preceding rotor on such a high-diffusion duct flow a detailed measurement campaign in the Transonic Test Turbine Facility at Graz University of Technology has been performed. A high diffusion intermediate duct is arranged downstream a high-pressure turbine stage providing an exit Mach number of about 0.6 and a swirl angle of −15 degrees (counter swirl). A low-pressure vane row is located at the end of the duct and represents the counter rotating low pressure turbine at larger diameter. At the ASME 2007, results of these investigations were presented for two different tip gap heights of 1.5% span (0.8 mm) and 2.4% span (1.3 mm). In order to better understand the flow phenomena observed in the intermediate duct a detailed numerical study is conducted. The unsteady flow through the whole configuration is simulated for both gap heights as well as for a rotor with zero gap height. The unsteady data are compared at the stage exit and inside the duct to study the flow physics. The calculation of the zero gap height configuration allows to determine the influence of the tip leakage flow of the preceding rotor on the intermediate turbine duct. It turns out that for this aggressive duct the tip leakage flow has a very positive effect on the pressure recovery.Copyright

The Effect of Vane Clocking on the Unsteady Flow Field in a One-and-a-Half Stage Transonic Turbine

The current paper presents the results of numerical and experimental clocking investigations performed in a high-pressure transonic turbine with a downstream vane row. The objective was a detailed analysis of shock and wake interactions in such a 1.5-stage machine while clocking the vanes. Therefore, a transient 3D Navier-Stokes calculation was done for two clocking positions, and the three-dimensional results are compared with laser-Doppler-velocimetry measurements at midspan. Additionally, the second vane was eauipped with fast response pressure transducers to record the instantaneous surface pressure for 20 different clocking positions at midspan.

Experimental Investigations of Clocking in a One-and-a-Half-Stage Transonic Turbine Using Laser Doppler Velocimetry and a Fast Response Aerodynamic Pressure Probe

The current paper presents experimental clocking investigations of the flow field in midspan in a high-pressure transonic turbine with a downstream vane row (1.5 stage machine). Laser-Doppler-velocimetry measurements were carried out in order to record rotor phase resolved velocity, flow angle, and turbulence distributions upstream and downstream of the second vane row at several different vane-vane positions. Additionally, a fast-response aerodynamic pressure probe was used to get the total pressure distribution downstream of the second vane row for the same positions. Altogether, the measurements were performed for ten different first vane to second vane positions (clocking positions) for measurements downstream of the second vane row and two different clocking positions for measurements upstream of the second vane row. The paper shows that different clocking positions have a significant influence on the flow field downstream of the second vane row. Furthermore, different measurement lines upstream of the second vane row indicate that clocking has nearly no influence on the flow field close to the rotor exit.

EXPERIMENTAL INVESTIGATION OF THE NOISE GENERATION AND PROPAGATION FOR DIFFERENT TURNING MID TURBINE FRAME SETUPS IN A TWO-STAGE TWO-SPOOL 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 rig went into operation within the EU-project DREAM, where the target was to investigate the aerodynamics of interturbine flow ducts. The facility is a continuously operating cold-flow open-circuit plant which is driven by pressurized air. The flow path contains a transonic turbine stage (HP) followed by a low pressure turbine stage consisting of a turning mid turbine frame and a counter-rotating LP-rotor.Downstream of the low pressure turbine a measurement section is instrumented with acoustic sensors. The acquisition system consists of a fully circumferentially traversable microphone array located at the outer casing, while at the hub endwall a stationary flush mounted microphone is placed as a reference.Additionally a new embedded concept for the turning mid turbine frame was tested. Here, two zero-lift splitters were located into the vane passage.In order to evaluate the noise emission of the turbine the facility was instrumented with a new acoustic measurement setup which is presented in the paper. Therefore the emitted sound pressure level and the microphones signal spectra are compared for both configurations. The acoustic field was characterized by azimuthal modes by means of a microphone array traversed over 360 degrees.In the multisplitter configuration, the propagating modes due to the HP turbine are found suppressed by 5 dB, while the increase in amplitude of the modes related to the LP turbine is negligible. The overall effect is a reduction of the acoustic emission for the turning mid turbine frame with embedded design.Copyright

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.

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