Development of a Turning Mid Turbine Frame With Embedded Design: Part II — Unsteady Measurements

2013 ◽  
Author(s):  
Rosario Spataro ◽  
Emil Göttlich ◽  
Davide Lengani ◽  
Christian Faustmann ◽  
Franz Heitmeir
Keyword(s):  
Flow Behavior ◽  
Fast Response ◽  
Meridional Flow ◽  
Secondary Flows ◽  
Time Resolved ◽  
University Of Technology ◽  
Baseline Case ◽  
Embedded Design ◽  
Aero Engines ◽  
Secondary Vortices

The paper, which is constituted by two parts, presents a new setup for the two-stage two-spool facility located at the Institute for Thermal Turbomachinery and Machine Dynamics (ITTM) of Graz University of Technology. The rig was designed in order to reproduce the flow behavior of a transonic turbine followed by a counter rotating low pressure stage like those in high bypass aero-engines. The meridional flow path of the machine is characterized by a diffusing S-shaped duct between the two rotors. The role of wide chord vanes placed into the mid turbine frame is to lead the flow towards the LP rotor with appropriate swirl. Experimental and numerical investigations performed on this setup over the last years showed that the wide chord struts induce large wakes and extended secondary flows at LP inlet flow. Moreover, large deterministic fluctuations of pressure, which may cause noise and blade vibrations, were observed downstream of the LP rotor. In order to minimize secondary vortices and to damp the unsteady interactions, the mid turbine frame was redesigned to locate two zero-lifting splitters into the vane passage. While in the first part paper the design process of the splitters and the time-averaged flow field were presented, in this second part the measurements performed by means of a fast response probe will support the explanation of the time-resolved field. The discussion will focus on the comparison between the baseline case (without splitters) and the embedded design.

Development of a Turning Mid Turbine Frame With Embedded Design—Part II: Unsteady Measurements

2014 ◽  
Vol 136 (7) ◽  
Author(s):  
Rosario Spataro ◽  
Emil Göttlich ◽  
Davide Lengani ◽  
Christian Faustmann ◽  
Franz Heitmeir
Keyword(s):  
Flow Behavior ◽  
Low Pressure ◽  
Fast Response ◽  
Meridional Flow ◽  
Secondary Flows ◽  
Time Resolved ◽  
University Of Technology ◽  
Embedded Design ◽  
Aero Engines ◽  
Secondary Vortices

This paper, the second of two parts, presents a new setup for the two-stage two-spool facility located at the Institute for Thermal Turbomachinery and Machine Dynamics (ITTM) of Graz University of Technology. The rig was designed to reproduce the flow behavior of a transonic turbine followed by a counter-rotating low pressure stage such as those in high bypass aero-engines. The meridional flow path of the machine is characterized by a diffusing S-shaped duct between the two rotors. The role of wide chord vanes placed into the mid turbine frame is to lead the flow towards the low pressure (LP) rotor with appropriate swirl. Experimental and numerical investigations performed on this setup showed that the wide chord struts induce large wakes and extended secondary flows at the LP inlet flow. Moreover, large deterministic fluctuations of pressure, which may cause noise and blade vibrations, were observed downstream of the LP rotor. In order to minimize secondary vortices and to damp the unsteady interactions, the mid turbine frame was redesigned to locate two zero-lift splitters into each vane passage. While in the first part of the paper the design process of the splitters and the time-averaged flow field were presented, in this second part the measurements performed by means of a fast response probe will support the explanation of the time-resolved field. The discussion will focus on the comparison between the baseline case (without splitters) and the embedded design.

Developement of a Turning Mid Turbine Frame With Embedded Design: Part I — Design and Steady Measurements

2013 ◽  
Author(s):  
Rosario Spataro ◽  
Emil Göttlich ◽  
Davide Lengani ◽  
Christian Faustmann ◽  
Franz Heitmeir
Keyword(s):  
Flow Behavior ◽  
Low Pressure ◽  
Meridional Flow ◽  
Secondary Flows ◽  
Time Resolved ◽  
Embedded Design ◽  
Oil Flow ◽  
Field Uniformity ◽  
Flow Gradients ◽  
Lp Turbine

The paper presents a new setup for the two-stage two-spool facility located at the Institute for Thermal Turbomachinery and Machine Dynamics (ITTM) of Graz University of Technology. The rig was designed in order to simulate the flow behavior of a transonic turbine followed by a counter rotating low pressure stage like the spools of a modern high bypass aero engine. The meridional flow path of the machine is characterized by a diffusing S-shaped duct between the two rotors. The role of turning struts placed into the mid turbine frame is to lead the flow towards the LP rotor with appropriate swirl. Experimental and numerical investigations performed on the setup over the last years, which were used as baseline for this paper, showed that wide chord vanes induce large wakes and extended secondary flows at the LP rotor inlet flow. Moreover, unsteady interactions between the two turbines were observed downstream of the LP rotor. In order to increase the uniformity and to decrease the unsteady content of the flow at the inlet of the LP rotor, the mid turbine frame was redesigned with two zero-lifting splitters embedded into the strut passage. In this first part paper the design process of the splitters and its critical points are presented, while the time-averaged field is discussed by means of five-hole probe measurements and oil flow visualizations. The comparison between the baseline case and the embedded design configuration shows that the new design is able to reduce the flow gradients downstream of the turning struts, providing a more suitable inlet condition for the low pressure rotor. The improvement in the flow field uniformity is also observed downstream of the turbine and it is consequently reflected in an enhancement of the LP turbine performance. In the second part of this paper the influence of the embedded design on the time-resolved field is investigated.

Development of a Turning Mid Turbine Frame With Embedded Design—Part I: Design and Steady Measurements

2014 ◽  
Vol 136 (7) ◽  
Author(s):  
Rosario Spataro ◽  
Emil Göttlich ◽  
Davide Lengani ◽  
Christian Faustmann ◽  
Franz Heitmeir
Keyword(s):  
Flow Behavior ◽  
Low Pressure ◽  
Meridional Flow ◽  
Secondary Flows ◽  
Time Resolved ◽  
Embedded Design ◽  
Oil Flow ◽  
Field Uniformity ◽  
Flow Gradients ◽  
Lp Turbine

The paper presents a new setup for the two-stage two-spool facility located at the Institute for Thermal Turbomachinery and Machine Dynamics (ITTM) of Graz University of Technology. The rig was designed in order to simulate the flow behavior of a transonic turbine followed by a counter-rotating low pressure (LP) stage like the spools of a modern high bypass aeroengine. The meridional flow path of the machine is characterized by a diffusing S-shaped duct between the two rotors. The role of turning struts placed into the mid turbine frame is to lead the flow towards the LP rotor with appropriate swirl. Experimental and numerical investigations performed on the setup over the last years, which were used as baseline for this paper, showed that wide chord vanes induce large wakes and extended secondary flows at the LP rotor inlet flow. Moreover, unsteady interactions between the two turbines were observed downstream of the LP rotor. In order to increase the uniformity and to decrease the unsteady content of the flow at the inlet of the LP rotor, the mid turbine frame was redesigned with two zero-lifting splitters embedded into the strut passage. In this first part of the paper the design process of the splitters and its critical points are presented, while the time-averaged field is discussed by means of five-hole probe measurements and oil flow visualizations. The comparison between the baseline case and the embedded design configuration shows that the new design is able to reduce the flow gradients downstream of the turning struts, providing a more suitable inlet condition for the low pressure rotor. The improvement in the flow field uniformity is also observed downstream of the turbine and it is, consequently, reflected in an enhancement of the LP turbine performance. In the second part of this paper the influence of the embedded design on the time-resolved field is investigated.

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

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
O. Schennach ◽  
J. Woisetschläger ◽  
B. Paradiso ◽  
G. Persico ◽  
P. Gaetani
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Fast Response ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Time Resolved ◽  
Flow Angle ◽  
Aerodynamic Pressure ◽  
Velocity Flow ◽  
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.

Flow Evolution Through a Turning Mid Turbine Frame With Embedded Design

2014 ◽  
Author(s):  
Pascal Bader ◽  
Wolfgang Sanz ◽  
Rosario Spataro ◽  
Emil Göttlich
Keyword(s):  
Decisive Role ◽  
Low Pressure ◽  
Pressure Stage ◽  
University Of Technology ◽  
Embedded Design ◽  
High Pressure Stage ◽  
Flow Evolution ◽  
Aero Engines ◽  
Insight Into ◽  
Engine Size

The paper discusses the time-averaged flow of a new concept turbine transition duct placed in a two-stage counter-rotating test turbine located at the Institute for Thermal Turbomachinery and Machine Dynamics of Graz University of Technology. As a possible architecture for the turbine transition duct of future engines, the structural vanes carrying the bearing loadings can be integrated with the first low pressure vane row in one aerodynamically optimized wide-chord vane. Such architecture is also called Turning Mid Turbine Frame (TMTF). In order to increase the flow uniformity and to decrease the unsteady content of the flow at the inlet of the LP rotor, a baseline TMTF was redesigned embedding two splitter vanes into the strut passage. The discussion on the flow field is based on numerical results obtained by a CFD code and validated by aerodynamic measurements. The flow structures moving from the outlet of the transonic high pressure stage are observed propagating towards the low pressure stage. In particular the splitter vanes are seen playing a major role in suppressing the big structures generated by the struts. On the other hand new losses are introduced by the splitter structures. Such structures play a decisive role in the overall component performance and therefore their effect should be properly understood in the design phase. This work provides a deep insight into the flow physics of TMTF designed with an embedded concept for next generation aero-engines. This configuration is seen to be a promising architecture in order to compact the engine size while keeping the components performance high.

Improving Efficiency of a High Work Turbine Using Non-Axisymmetric Endwalls: Part II—Time-Resolved Flow Physics

2008 ◽  
Author(s):  
P. Schuepbach ◽  
R. S. Abhari ◽  
M. G. Rose ◽  
T. Germain ◽  
I. Raab ◽  
...  
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Guide Vane ◽  
Axial Flow ◽  
Fast Response ◽  
Secondary Flows ◽  
Streamwise Vorticity ◽  
Time Resolved ◽  
Flow Physics ◽  
High Work

This paper is the second part of a two part paper that reports on the improvement of efficiency of a one-and-half stage high work axial flow turbine. The first part covered the design of the endwall profiling as well as a comparison with steady probe data, this part covers the analysis of the time-resolved flow physics. The focus is on the time-resolved flow physics that lead to a total-to-total stage efficiency improvement of Δηtt = 1.0% ± 0.4%. The investigated geometry is a model of a high work (Δh/U2 = 2.36), axial shroudless HP turbine. The time-resolved measurements have been acquired upstream and downstream of the rotor using a Fast Response Aerodynamic Probe (FRAP). The paper contains a detailed analysis of the secondary flow field that is changed between the axisymmetric and the non-axisymmetric endwall profiling cases. The flowfield at exit of the first stator is improved considerably due to non-axisymmetric endwall profiling and results in reduced secondary flow and a reduction of loss at both hub and tip, as well as a reduced trailing shed vorticity. The rotor has reduced losses and a reduction of secondary flows mainly at the hub. At the rotor exit the flow field with non-axisymmetric endwalls is more homogenous due to the reduction of secondary flows in the two rows upstream of the measurement plane. This confirms that non-axisymmetric endwall profiling is an effective tool for reducing secondary losses in axial turbines. Using a frozen flow assumption the time-resolved data is used to estimate the axial velocity gradients, which are then used to evaluate the streamwise vorticity and dissipation. The non-axisymmetric endwall profiling of the first nozzle guide vane show reductions of dissipation and streamwise vorticity due to reduced trailing shed vorticity. This smaller vorticity explains the reduction of loss at mid-span, which is shown in the first part of the two part paper. This leads to the conclusion that non-axisymmetric endwall profiling also has the potential of reducing trailing shed vorticity.

Transport of Entropy Waves Within a High Pressure Turbine Stage

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Paolo Gaetani ◽  
Giacomo Persico
Keyword(s):  
Outer Part ◽  
Axial Direction ◽  
Fast Response ◽  
Turbine Stage ◽  
Time Resolved ◽  
Aerodynamic Pressure ◽  
Thermal Phenomenon ◽  
Unsteady Interaction ◽  
Stator Blade ◽  
Aero Engines

This paper presents the results of an experimental study on the transport of entropy waves within a research turbine stage, representative of the key aero-thermal phenomenon featuring the combustor-turbine interaction in aero-engines. The entropy waves are injected upstream of the turbine by a dedicated entropy wave generator (EWG) and are released in axial direction; they feature circular shape with peak amplitude in the center and exhibit sinusoidal-like temporal evolution over the whole wave area. The maximum over-temperature amounts to 7% of the undisturbed flow, while the frequency is 30 Hz. The entropy waves are released in four azimuthal positions upstream of the stage, so to simulate four different burner-to-stator blade clocking. Time-resolved temperature measurements were performed with fast microthermocouples (FTC); the flow and the pressure field upstream and downstream of the stator and the rotor was measured with five-hole pneumatic probes and fast-response aerodynamic pressure probes. The entropy waves are observed to undergo a relevant attenuation throughout their transport within the stator blade row, but they remain clearly visible at the stator exit and retain their dynamic characteristics. In particular, the total temperature distribution appears severely altered by burner-stator clocking position. At the stage exit, the entropy waves loose their coherence, appearing spread in the azimuthal direction to almost cover the entire pitch in the outer part of the channel, while being more localized below midspan. Despite the severe and unsteady interaction of the entropy waves within the rotor, they retain their original dynamic character. A comparison with measurements performed by injecting steady hot streaks is finally reported, remarking both differences and affinities. As a relevant conclusion, it is experimentally shown that entropy waves can be proficiently simulated by considering a succession of hot streaks of different amplitude.

Effect of Hot Streak Migration on Unsteady Blade Row Interaction in an Axial Turbine

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
P. Jenny ◽  
C. Lenherr ◽  
R. S. Abhari ◽  
A. Kalfas
Keyword(s):  
Hot Spot ◽  
Fast Response ◽  
Secondary Flows ◽  
Inlet Temperature ◽  
Time Resolved ◽  
Axial Turbine ◽  
Blade Row ◽  
Hot Streak ◽  
The Impact ◽  
Blade Row Interaction

This paper presents an experimental study of the effect of unsteady blade row interaction on the migration of hot streaks in an axial turbine. The hot streaks can cause localized hot spots on the blade surfaces in a high-pressure turbine, leading to high heat loads and potentially catastrophic failure of the blades. An improved understanding of the effect of unsteady blade row interaction on an inlet temperature distortion is of crucial importance. The impact of hot streaks on the aerodynamic performance of a turbine stage is also not well understood. In the current experiment, the influence of hot streaks on a highly loaded 1.5-stage unshrouded model axial turbine is studied. A hot streak generator has been developed specifically for this project to introduce hot streaks that match the dimensional parameters of real engines. The temperature profile, spanwise position, circumferential position, and cross-section shape of the hot streak can be independently varied. The recently developed ETH Zurich two-sensor high temperature (260 °C) fast response aerodynamic probe (FRAP) technique and the fast response entropy. Probe (FENT) systems are used in this experimental campaign. Time resolved measurements of the unsteady pressure, temperature, and entropy are made at the NGV inlet and between the rotor and stator blade rows. From the nozzle guide vane inlet to outlet the measurements show a reduction in the maximum relative entropy difference between the free stream and the hot spot of 30% for the highest temperature gases in the core of the hot streak, indicating a region of heat loss. Time resolved flow field measurements at the rotor exit based on both measurement methods showed the hot gases traveling towards the hub and tip casing on the blade pressure side and interacting with secondary flows such as the hub passage vortex.

The Dynamics of the Vorticity Field in a Low Solidity Axial Turbine

2008 ◽  
Author(s):  
K. G. Barmpalias ◽  
A. I. Kalfas ◽  
N. Chokani ◽  
R. S. Abhari
Keyword(s):  
Current Trend ◽  
Three Dimensional ◽  
Fast Response ◽  
Secondary Flows ◽  
Vorticity Field ◽  
Time Resolved ◽  
Axial Turbine ◽  
Unsteady Interaction ◽  
Vorticity Transport ◽  
Highly Loaded

A current trend in turbomachinery design is the use of low solidity axial turbines that can generate a given power with fewer blades. However, due to the higher turning of the flow, relative to a high solidity turbine, there is an increase in secondary flows and their associated losses. In order to increase the efficiency of these more highly loaded stages, an improved understanding of the mechanisms related to the development, evolution and unsteady interaction of the secondary flows is required. An experimental investigation of the unsteady vorticity field in highly loaded stages of a research turbine is presented here. The research turbine facility is equipped with a two-stage axial turbine that is representative of the high-pressure section of a steam turbine. Steady and unsteady area measurements are performed, with the use of miniature pneumatic and fast response aerodynamic probes, in closely spaced planes at the exits of each blade row. In addition to the 3D total pressure flowfield, the multi-plane measurements allow the full three-dimensional time-resolved vorticity and velocity fields to be determined. These measurements are then used to describe the development, evolution and unsteady interaction of the secondary flows and loss generation. Particular emphasis is given to the vortex stretching term of the vorticity transport equation, which gives new insight into the vortex tilting and stretching that is associated with the secondary loss generation.

Effect of Hot Streak Migration on Unsteady Blade Row Interaction in an Axial Turbine

2010 ◽  
Author(s):  
P. Jenny ◽  
C. Lenherr ◽  
A. Kalfas ◽  
R. S. Abhari
Keyword(s):  
Hot Spot ◽  
Fast Response ◽  
Secondary Flows ◽  
Inlet Temperature ◽  
Time Resolved ◽  
Axial Turbine ◽  
Blade Row ◽  
Hot Streak ◽  
The Impact ◽  
Blade Row Interaction

This paper presents an experimental study of the effect of unsteady blade row interaction on the migration of hot streaks in an axial turbine. The hot streaks can cause localised hot spots on the blade surfaces in a high-pressure turbine, leading to high heat loads and potentially catastrophic failure of the blades. An improved understanding of the effect of unsteady blade row interaction on an inlet temperature distortion is of crucial importance. The impact of hot streaks on the aerodynamic performance of a turbine stage is also not well understood. In the current experiment, the influence of hot streaks on a highly loaded one-and-half-stage unshrouded model axial turbine is studied. A hot streak generator has been developed specifically for this project to introduce hot streaks that match the dimensional parameters of real engines. The temperature profile, spanwise position, circumferential position and cross-section shape of the hot streak can be independently varied. The recently developed ETH Zurich 2-sensor high temperature (260°C) Fast Response Aerodynamic Probe (FRAP) technique and the Fast Response Entropy Probe (FENT) systems are used in this experimental campaign. Time resolved measurements of the unsteady pressure, temperature and entropy are made at the NGV inlet and between the rotor and stator blade rows. From the nozzle guide vane inlet to outlet the measurements show a reduction in the maximum relative entropy difference between the free stream and the hot spot of 30% for the highest temperature gases in the core of the hot streak, indicating a region of heat loss. Time resolved flow field measurements at the rotor exit based on both measurement methods showed the hot gases travelling towards the hub and tip casing on the blade pressure side and interacting with secondary flows such as the hub passage vortex.

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