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.

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.

Unsteady Aerodynamics of a Low Aspect Ratio Turbine Stage: Modeling Issues and Flow Physics

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
G. Persico ◽  
A. Mora ◽  
P. Gaetani ◽  
M. Savini
Keyword(s):  
Aspect Ratio ◽  
Coming Out ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Fast Response ◽  
Operating Conditions ◽  
Pressure Probe ◽  
Turbine Stage ◽  
Time Resolved ◽  
Low Aspect Ratio

In this paper the three-dimensional unsteady aerodynamics of a low aspect ratio, high pressure turbine stage are studied. In particular, the results of fully unsteady three-dimensional numerical simulations, performed with ANSYS-CFX, are critically evaluated against experimental data. Measurements were carried out with a novel three-dimensional fast-response pressure probe in the closed-loop test rig of the Laboratorio di Fluidodinamica delle Macchine of the Politecnico di Milano. An analysis is first reported about the strategy to limit the CPU and memory requirements while performing three-dimensional simulations of blade row interaction when the rotor and stator blade numbers are prime to each other. What emerges as the best choice is to simulate the unsteady behavior of the rotor alone by applying the stator outlet flow field as a rotating inlet boundary condition (scaled on the rotor blade pitch). Thanks to the reliability of the numerical model, a detailed analysis of the physical mechanisms acting inside the rotor channel is performed. Two operating conditions at different vane incidence are considered, in a configuration where the effects of the vortex-blade interaction are highlighted. Different vane incidence angles lead to different size, position, and strength of secondary vortices coming out from the stator, thus promoting different interaction processes in the subsequent rotor channel. However some general trends can be recognized in the vortex-blade interaction: the sense of rotation and the spanwise position of the incoming vortices play a crucial role on the dynamics of the rotor vortices, determining both the time-mean and the time-resolved characteristics of the secondary field at the exit of the stage.

Transonic Turbine Stage Heat Transfer Investigation in Presence of Strong Shocks

2007 ◽  
Author(s):  
A. de la Loma ◽  
G. Paniagua ◽  
D. Verrastro ◽  
P. Adami
Keyword(s):  
Heat Transfer ◽  
Rotor Blade ◽  
Turbine Stage ◽  
Test Rig ◽  
Unsteady Heat Transfer ◽  
Tube Test ◽  
Stator Blade ◽  
Transonic Turbine ◽  
Aero Engines ◽  
Layered Thin Film

This paper reports the external convective heat transfer distribution of a modern single-stage transonic turbine together with the physical interpretation of the different shock interaction mechanisms. The measurements have been performed in the compression tube test rig of the von Karman Institute using single and double-layered thin film gauges. The three pressure ratios tested are representative of those encountered in actual aero-engines, with M2, is ranging from 1.07 to 1.25 and a Reynolds number of about 106. Three different rotor blade heights (15%, 50% and 85%) and the stator blade at mid-span have been investigated. The measurements highlight the destabilizing effect of the vane left running shock on the rotor boundary layer. The stator unsteady heat transfer is dominated by the fluctuating right running vane trailing edge shock at the blade passing frequency.

Unsteady Aerodynamics of a Low Aspect Ratio Turbine Stage: Modeling Issues and Flow Physics

2010 ◽  
Author(s):  
G. Persico ◽  
A. Mora ◽  
P. Gaetani ◽  
M. Savini
Keyword(s):  
Aspect Ratio ◽  
Coming Out ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Fast Response ◽  
Pressure Probe ◽  
Turbine Stage ◽  
Aerodynamic Pressure ◽  
Low Aspect Ratio

In this paper the three-dimensional unsteady aerodynamics of a low aspect ratio, high pressure turbine stage is studied. Fully unsteady, three-dimensional numerical simulations are performed using the commercial code ANSYS-CFX The numerical model is critically evaluated against experimental data. Measurements were performed with a three-dimensional fast-response aerodynamic pressure probe in the closed-loop test rig operating in the Laboratorio di Fluidodinamica delle Macchine of the Politecnico di Milano (Italy). An analysis is first reported about the strategy to reduce the CPU and memory requirements while performing three-dimensional simulations of stator-rotor interaction in actual turbomachinery. What emerges as the best choice, at least for subsonic stages, is to simulate the unsteady behaviour of the rotor blade row alone by applying the stator outlet flow field as rotating inlet boundary condition. When measurements are available upstream of the rotor the best representation of the experimental results downstream of the stage is achieved. The agreement with the experiments achieved at the rotor exit makes the CFD simulation a key-tool for the comprehension and the interpretation of the physical mechanisms acting inside the rotor channel (often difficult to achieve using experiments only). Numerical investigations have been carried out by varying the incidence at the vane entrance. Different vane incidence angles lead to different size, position, and strength of secondary vortices coming out from the stator. The configuration is chosen is such a way to isolate the effects of the vortex-blade interaction. Results show that some general trends can be recognized in the vortex-blade interaction. The sense of rotation and the spanwise position of the incoming vortices play a crucial role on their interaction with the rotor vortices, thus determining both the time-mean and the time-resolved characteristics of the stage-exit secondary field.

Transport of Entropy Waves Within a HP Turbine Stage

2018 ◽  
Author(s):  
Paolo Gaetani ◽  
Giacomo Persico
Keyword(s):  
Experimental Study ◽  
High Pressure ◽  
Gas Turbine ◽  
Main Flow ◽  
Streamwise Direction ◽  
Turbine Stage ◽  
Time Resolved ◽  
Blade Row ◽  
Stator Blade ◽  
The Waves

This paper presents the results of an experimental study on the transport of entropy waves, representative of those generated by gas turbine burners, within an un-cooled high-pressure gas turbine stage. The prescribed entropy waves were injected in streamwise direction featuring a 7% over-temperature with respect to the main flow at the stage inlet, with a frequency of 30 Hz. The entropy waves are injected in four different circumferential positions with respect to the stator blade. Detailed time-resolved temperature measurements as well as aerodynamic measurements upstream and downstream of the blade rows were performed. Measurements showed a relevant attenuation of the entropy waves throughout their transport within the stator blade row. The temperature distribution resulted in a severe alteration depending on the injection position. Downstream of the rotor, the waves spread over the pitch above midspan and are more concentrated at the hub. Finally, a comparison with measurements performed with conventional steady hot streaks is also reported, remarking both differences and affinities. As a relevant conclusion, it is experimentally shown that entropy waves can be proficiently simulated by considering a number of hot streaks of different amplitude.

Time-Resolved Measurements of the Unsteady Flow Field in a Single Stage Low Pressure Axial Compressor

2013 ◽  
Author(s):  
J. Sans ◽  
G. Dell’Era ◽  
J. Desset ◽  
J.-F. Brouckaert ◽  
S. Hiernaux
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Axial Compressor ◽  
Low Pressure ◽  
Fast Response ◽  
Single Stage ◽  
Time Resolved ◽  
Flow Angle ◽  
Aerodynamic Pressure ◽  
Time Resolved Measurements

The experimental investigation of the unsteady flow field in a highly loaded single stage low pressure axial compressor, also called a booster, is presented in this paper. The compressor design is representative of an advanced direct drive turbofan booster. Tests were performed on different speed lines at choke, design, and near stall, in the VKI-R4 closed loop compressor test rig. The rotor casing was instrumented with fast response pressure transducers to perform a detailed survey of the tip flow features. Simultaneous time-resolved measurements with fast response aerodynamic pressure probes were performed by radial and circumferential traverses to map the unsteady flow field at rotor and stator exit. The originality of this paper also resides in the fact that unsteady flow angle data are presented as the probe was used in a virtual 3-hole mode. The casing measurements allow to map the direction and extension of the tip leakage vortex. The flow path measurements show its extension at the exit of the rotor blade passage and its evolution as throttling is increased towards the compressor stability limit. The results are presented in terms of periodic and random fluctuations. These experimental results are combined to provide a three-dimensional view of the experimental flow field. They are discussed and compared to CFD simulations, showing that, in some regions, important features are not captured by the numerical model. In particular, the presence of a second wake has been observed in the unsteady yaw angle map at rotor exit. This uncommon feature is currently under further investigation.

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.

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.

Experimental Investigation of the Unsteady Flow Field Downstream of a Counter-Rotating Two-Spool Turbine Rig

2012 ◽  
Author(s):  
Davide Lengani ◽  
Cornelia Santner ◽  
Rosario Spataro ◽  
Berardo Paradiso ◽  
Emil Göttlich
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Unsteady Flow ◽  
Fast Response ◽  
Secondary Flows ◽  
Operating Conditions ◽  
Pressure Probe ◽  
Time Resolved ◽  
Flow Angle ◽  
Aerodynamic Pressure

The paper presents an experimental investigation of the unsteady flow field in the two-spool counter-rotating transonic turbine at Graz University of Technology. The test setup consists of a high pressure (HP) stage, a diffusing mid turbine frame with turning struts (TMTF) and a shrouded low pressure (LP) rotor. The two rotors are mounted on mechanically independent shafts in order to provide engine-representative operating conditions. The rig was designed in cooperation with MTU Aero Engines and Volvo Aero within the EU project DREAM (ValiDation of Radical Engine Architecture SysteMs). A two-sensor fast response aerodynamic pressure probe (2S-FRAP) has been employed to provide time-resolved aerodynamic area traverses downstream of the LP turbine. Such measurement allows estimating the total deterministic unsteadiness transported through the duct. In particular, it has been possible to isolate the structures induced by each rotor by means of the encoders mounted on the two shafts. A global ensemble averaged field, which takes into account the rotor-rotor interactions, is also provided. The time resolved distributions of the flow quantities are then discussed in details. The perturbations due to the HP rotor in terms of velocity and flow angle are negligible in this downstream plane. Indeed, the largest fluctuations of velocity are due to the TMTF-LP rotor interaction, they occur in the wake and secondary flows of the TMTF. Large fluctuations of static and total pressure are instead due to both rotors to the same extent.

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.

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