O. Schennach

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

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

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.

Three Dimensional Clocking Effects in a One and a Half Stage Transonic Turbine

This paper presents an experimental investigation of the flow field in a high-pressure transonic turbine with a downstream vane row (1.5 stage machine) concerning the airfoil indexing. The objective is a detailed analysis of the three-dimensional aerodynamics of the second vane for different clocking positions. To give an overview of the time-averaged flow field, five-hole probe measurements were performed upstream and downstream of the second stator. Furthermore in these planes additional unsteady measurements were carried out with laser Doppler velocimetry in order to record rotor phase-resolved velocity, flow angle, and turbulence distributions at two different clocking positions. In the planes upstream of the second vane, the time-resolved pressure field has been measured by means of a fast response aerodynamic pressure probe. This paper shows that the secondary flows of the second vane are significantly modified by the different clocking positions, in connection with the first vane modulation of the rotor secondary flows. An analysis of the performance of the second vane is also carried out, and a 0.6% variation in the second vane loss coefficient has been recorded among the different clocking positions.

Blade Row Interaction in a One and a Half Stage Transonic Turbine Focusing on Three Dimensional Effects: Part I—Stator-Rotor Interaction

The unsteady and fully three-dimensional aerodynamics of HP turbines represent a relevant research branch for future aero-engine design. When stator-rotor interaction mechanisms and clocking effects are of concern, advanced measurement techniques as well as unsteady CFD codes are required. An extensive study on this topic was carried out in a one and a half stage transonic turbine operating at Graz University of Technology. Two steady and unsteady measurement techniques (Laser Doppler Velocimetry and a Fast Response Aerodynamic Pressure Probe) and an unsteady 3D CFD code were applied to the problem. In this paper, the 1st vane – rotor interaction is presented and discussed in detail to provide the basis for the analysis of the rotor – 2nd vane and the vane-vane interactions. The rotor-exit flowfield is mainly characterized by the wake, the hub passage vortex, the tip leakage vortex and the trailing edge shocks. All the flow structures except the tip leakage flow are strongly influenced by the first vane; in particular the main source of blade row interaction is the first vane trailing edge shock, that periodically alters the rotor trailing edge shock and the rotor hub passage vortex. The comparison with the CFD assesses the interpretation of the flow physics, and supports the identification of the first stator effects at the second stator inlet. A discussion on the stage performance is also provided.© 2008 ASME

Experimental and Numerical Flow Visualization in a Transonic Turbine

This paper focuses on the visualization of both experimental and numerical results and presents research in a highly-loaded cold-flow transonic turbine under continuous and engine-representative conditions. Special focus was placed on blade row interaction at app. 10600 rpm. While the first step was the investigation of a single stage machine (stator-rotor), the second step extended the test rig to a one-and-a-half stage configuration (stator-rotor-stator). Measurements were carried out in the transonic test turbine at Graz University of Technology using Particle-Image-Velocimetry and Laser-Doppler-Anemometry. The main results of these experiments are discussed and compared to numerical simulations.

Blade Row Interaction in a One and a Half Stage Transonic Turbine Focusing on Three Dimensional Effects: Part II — Clocking Effects

The paper presents an experimental investigation of the flow field in a high-pressure transonic turbine with a downstream vane row (1.5 stage machine) concerning the airfoil indexing. The objective is a detailed analysis of the three dimensional flow field downstream of the high pressure turbine for different vane clocking positions. To give an overview of the time averaged flow field, measurements by means of a pneumatic five hole probe were performed upstream and downstream of the second stator. Furthermore in this planes additional unsteady measurements were carried out with Laser Doppler Velocimetry in order to record rotor phase resolved velocity, flow angle and turbulence distributions at two different clocking positions. In the measurement plane upstream the second vane the time resolved pressure field has been analyzed by means of a Fast Response Aerodynamic Pressure Probe. The paper shows that the secondary flows of the second vane are significantly modified for different clocking positions, in connection with the first vane modulation of the rotor secondary flows. An analysis of the performance of the second vane is also carried out.Copyright

The Effect of Vane Clocking on the Unsteady Flowfield 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 equipped with fast response pressure transducers to record the instantaneous surface pressure for 20 different clocking positions at midspan.Copyright

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 1st vane to 2nd vane positions (clocking positions) for measurements downstream of the 2nd vane row and two different clocking positions for measurements upstream of the 2nd vane row. The paper shows that different clocking positions have a significant influence on the flow field downstream of the 2nd vane row. Furthermore different measurement lines upstream of the 2nd vane row indicate that clocking has nearly no influence on the flow field close to the rotor exit.Copyright