Unsteady Flow Interactions Within the Inlet Cavity of a Turbine Rotor Tip Labyrinth Seal

2003 ◽  
Vol 127 (4) ◽  
pp. 679-688 ◽  
Author(s):  
A. Pfau ◽  
J. Schlienger ◽  
D. Rusch ◽  
A. I. Kalfas ◽  
R. S. Abhari
Keyword(s):  
Three Dimensional ◽  
Cavity Flow ◽  
Fast Response ◽  
Labyrinth Seal ◽  
Turbine Rotor ◽  
Major Effect ◽  
Main Flow ◽  
Toroidal Vortex ◽  
Head Diameter ◽  
Flow Interactions

This paper focuses on the flow within the inlet cavity of a turbine rotor tip labyrinth seal of a two stage axial research turbine. Highly resolved, steady and unsteady three-dimensional flow data are presented. The probes used here are a miniature five-hole probe of 0.9 mm head diameter and the novel virtual four sensor fast response aerodynamic probe (FRAP) with a head diameter of 0.84mm. The cavity flow itself is not only a loss producing area due to mixing and vortex stretching, it also adversely affects the following rotor passage through the fluid that is spilled into the main flow. The associated fluctuating mass flow has a relatively low total pressure and results in a negative incidence to the rotor tip blade profile section. The dominating kinematic flow feature in the region between cavity and main flow is a toroidal vortex, which is swirling at high circumferential velocity. It is fed by strong shear and end wall fluid from the pressure side of the stator passage. The static pressure field interaction between the moving rotor leading edges and the stator trailing edges is one driving force of the cavity flow. It forces the toroidal vortex to be stretched in space and time. A comprehensive flow model including the drivers of this toroidal vortex is proposed. This labyrinth seal configuration results in about 1.6% turbine efficiency reduction. This is the first in a series of papers focusing on turbine loss mechanisms in shrouded axial turbines. Additional measurements have been made with variations in seal clearance gap. Initial indications show that variation in the gap has a major effect on flow structures and turbine loss.

Unsteady Flow Interactions Within the Inlet Cavity of a Turbine Rotor Tip Labyrinth Seal

2003 ◽  
Author(s):  
A. Pfau ◽  
J. Schlienger ◽  
D. Rusch ◽  
A. I. Kalfas ◽  
R. S. Abhari
Keyword(s):  
Cavity Flow ◽  
Fast Response ◽  
Labyrinth Seal ◽  
Turbine Rotor ◽  
Major Effect ◽  
Main Flow ◽  
Toroidal Vortex ◽  
Head Diameter ◽  
Flow Interactions ◽  
Axial Turbines

This paper focuses on the flow within the inlet cavity of a turbine rotor tip labyrinth seal of a 2 stage axial research turbine. Highly resolved, steady and unsteady 3-dimensional flow data are presented. The probes used here are a miniature 5 hole probe of 0.9mm head diameter and the novel virtual four sensor fast response aerodynamic probe (FRAP) with a head diameter of 0.84mm. The cavity flow itself is not only a loss producing area due to mixing and vortex stretching, it also adversely affects the following rotor passage through the fluid that is spilled into the main flow. The associated fluctuating mass flow has a relatively low total pressure and results in a negative incidence to the rotor tip blade profile section. The dominating kinematic flow feature in the region between cavity and main flow is a toroidal vortex, which is swirling at high circumferential velocity. It is fed by strong shear and end wall fluid from the pressure side of the stator passage. The static pressure field interaction between the moving rotor leading edges and the stator trailing edges is one driving force of the cavity flow. It forces the toroidal vortex to be stretched in space and time. A comprehensive flow model including the drivers of this toroidal vortex is proposed. This labyrinth seal configuration results in about 1.6% turbine efficiency reduction. This is the first in a series of papers focussing on turbine loss mechanisms in shrouded axial turbines. Additional measurements have been made with variations in seal clearance gap. Initial indications show that variation in the gap has a major effect on flow structures and turbine loss.

Flow Interaction From the Exit Cavity of an Axial Turbine Blade Row Labyrinth Seal

2000 ◽  
Author(s):  
A. Pfau ◽  
M. Treiber ◽  
M. Sell ◽  
G. Gyarmathy
Keyword(s):  
Channel Wall ◽  
Wall Motion ◽  
Cavity Flow ◽  
Labyrinth Seal ◽  
Turbine Rotor ◽  
Main Channel ◽  
Axial Turbine ◽  
Pressure Mapping ◽  
Blade Row ◽  
Classical Picture

The structure of labyrinth cavity flow has been experimentally investigated in a three fin axial turbine labyrinth seal (four cavities). The geometry corresponds to a generic steam turbine rotor shroud. The relative wall motion has not been modeled. The measurements were made with specially developed low-blockage pneumatic probes and extensive wall pressure mapping. Instead of the classical picture of a circumferentially uniform leakage sheet exiting from the last labyrinth clearance, entering the channel, and uniformly spreading over the downstream channel wall, the results reveal uneven flow and the existence of high circumferential velocity within the entire exit cavity. The circumferential momentum is brought into the cavity by swirling fluid from the main channel. This fluid penetrates the cavity and breaks up the leakage sheet into individual jets spaced according to the blade passages. This gives rise to strong local cross flows that may also considerably disturb the performance of a downstream blade row.

Experimental and Numerical Investigation Into the Unsteady Interaction of Labyrinth Seal Leakage Flow and Main Flow in a 1.5-Stage Axial Turbine

2004 ◽  
Author(s):  
A. Giboni ◽  
K. Wolter ◽  
J. R. Menter ◽  
H. Pfost
Keyword(s):  
Secondary Flow ◽  
Three Dimensional ◽  
Labyrinth Seal ◽  
Main Flow ◽  
Navier Stokes ◽  
Experimental Program ◽  
Leakage Flow ◽  
Axial Turbine ◽  
Flow Phenomena ◽  
Grid Points

This paper presents the results of experimental and numerical investigations into the flow in a 1.5-stage low-speed axial turbine with a straight labyrinth seal on the rotor shroud. The paper focuses on the time dependent interaction between the leakage flow and the main flow. The experimental program consists of time accurate measurements of the three-dimensional properties of the main flow. The region of the entering leakage flow downstream of the rotor trailing edge was of special interest. The measurements were carried out using pneumatic five-hole probes and three dimensional hot-wire probes at the design operating point of the turbine. The measurement planes behind the three blade rows extend over one pitch from the shroud to the casing. The complex three-dimensional flow field is mapped in great detail by 1,008 points per measurement plane. The time-accurate experimental data of the three measurement planes was compared with the results of unsteady, numerical simulations of the turbine flow. The 3D-Navier-Stokes Solver CFX-TASCflow was used. The experimental and numerical results correspond well and allow detailed analysis of the mixing process. As demonstrated in this paper, the leakage flow causes strong fluctuations of the secondary flow behind the rotor and the second stator. Above all, the high number of numerical grid points reveals both the secondary flow phenomena and the vortex structures of the mixing zone. The time-dependence of both position and intensity of the vortices is shown. The development of the important leakage vortex is illustrated and explained. The paper shows that even at realistic clearance heights the leakage flow gives rise to negative incidence of considerable parts of the downstream stator which causes the flow to separate. Thus, labyrinth seal leakage flow should be taken properly into account in the design or optimization process of turbomachinery.

Interaction of Labyrinth Seal Leakage Flow and Main Flow in an Axial Turbine

2003 ◽  
Author(s):  
A. Giboni ◽  
J. R. Menter ◽  
P. Peters ◽  
K. Wolter ◽  
H. Pfost ◽  
...  
Keyword(s):  
Secondary Flow ◽  
Three Dimensional ◽  
Labyrinth Seal ◽  
Main Flow ◽  
Experimental Program ◽  
Leakage Flow ◽  
Axial Turbine ◽  
Measurement Plane ◽  
Flow Phenomena ◽  
Operating Points

This paper presents the results of an experimental investigation into the flow in a 1.5-stage low-speed axial turbine with a straight labyrinth seal on the rotor shroud. The paper focuses on the interaction between the leakage flow and the main flow. The experimental program consists of measurements of the three-dimensional properties of the main flow downstream of the rotor trailing edge after the re-injection of the leakage flow. The measurements were carried out using pneumatic five-hole probes and three dimensional hot-wire probes at different operating points of the turbine. The measurement plane behind the rotor extends over one pitch from the shroud to the casing, with the complex three-dimensional flow field being mapped in great detail by 1,008 measurement points. As demonstrated in this paper, the entering leakage flow not only introduces mixing losses but also predominates the secondary flow behind the rotor and the second stator. The experimental data show that even at realistic clearance heights the leakage flow gives rise to negative incidence of considerable parts of the downstream stator which causes the flow to separate. Thus, labyrinth seal leakage flow should be taken properly into account in the design or optimisation process of turbomachinery. The high number of measurement points allows detailed analysis of the secondary flow phenomena and of the vortex structures. The time-dependence of the position and the intensity of the vortices is shown and the influence of the turbine’s operating point is presented.

Time-Resolved Numerical Investigation of the Interaction of Labyrinth Seal Leakage and Main-Flow in a 1.5-Stage LP Turbine

2011 ◽  
Author(s):  
Marc H.-O. Biester ◽  
Lasse Mueller ◽  
Joerg R. Seume ◽  
Yavuz Guendogdu
Keyword(s):  
Turbine Blades ◽  
Three Dimensional ◽  
Vortex Pair ◽  
Labyrinth Seal ◽  
Main Flow ◽  
Leakage Flow ◽  
Labyrinth Seals ◽  
Time Resolved ◽  
Lp Turbine ◽  
German Aerospace

In axial turbomachinery such as low pressure turbines, shrouded airfoils with labyrinth seals are commonly used. Among different sealing options, labyrinth seals in particular are characterized by long term durability and high sealing efficiency. Since a leakage flow is inevitable, a thorough understanding of how the leakage flow exits the cavities, its interaction with the main flow, and the induction of losses is necessary. In order to take into account unsteady effects, three-dimensional time resolved RANS computations of a 1.5 stage LPT rig in its design operating point are conducted. To capture effects in the boundary layer, a low Reynolds approach is used at the blade surface as well as on the hub and tip surfaces. To match the real geometry of the turbine blades, fillets have been modeled. Simulations were performed using the TRACE solver developed by the German Aerospace Center (DLR). The investigation shows how cavity flows have a significant influence on the main-flow aerodynamics and the loss generation. Steady and unsteady results with full spatially discretized cavities show a significant decrease of isentropic efficiency compared to simulations without cavities. The efficiency drop for the steady and time-averaged cavity computations can be explained with intensified secondary flow. The time resolved calculation shows a strong non-uniformity of the leakage flux depending on the instantaneous circumferential position of the up- and downstream blades. The time dependent ingress of cavity leakage results in the formation of a counter-rotating vortex pair. In terms of the influence on the main flow, it is shown that the interaction is limited to the end walls with almost no influence on the midspan flow.

Effects of Shroud Asymmetry on the Turbine Tip Shroud Cavity Flow Field

2015 ◽  
Author(s):  
Timothy R. Palmer ◽  
Choon S. Tan ◽  
Matthew Montgomery ◽  
Anthony Malandra ◽  
David Little ◽  
...  
Keyword(s):  
Flow Field ◽  
Cavity Flow ◽  
Main Flow ◽  
Toroidal Vortex ◽  
Turbine Stage ◽  
Numerical Computations ◽  
Velocity Difference ◽  
Inlet Flow ◽  
Toroidal Vortices ◽  
Tip Shroud

The effects of shroud asymmetry (known as a scalloped shroud) on loss generation and stage performance are assessed by numerical computations, steady as well as unsteady, in a turbine stage with tip shroud cavity. Introducing shroud asymmetry leads to cavity mixing at higher flow velocities with larger velocity difference, hence higher loss relative to a baseline axisymmetric shroud. Shroud asymmetry alters the system of toroidal vortices which characterizes tip shroud cavity flow. Specifically, the asymmetry downstream of the tip seal prevents the formation of two large, continuous toroidal vortex cores. Instead, several small, discrete cores are formed immediately downstream of the tip seal due to the onset of mixing with the main flow. Unsteady vane-rotor-shroud interaction results in a redistribution of vorticity in the cavity inlet. Compatibility requirement between main flow and cavity flow provides quantitative limits on the existence of the cavity inlet vortex as well as explains why the cavity inlet flow field looks the way it does and not otherwise.

Tip Leakage/Main Flow Interactions in Multi-Stage HP Turbines With Short-Height Blading

2004 ◽  
Author(s):  
Piotr Lampart ◽  
Sergey Yershov ◽  
Andrey Rusanov ◽  
Mariusz Szymaniak
Keyword(s):  
Labyrinth Seal ◽  
Main Flow ◽  
Rotor Blades ◽  
Navier Stokes ◽  
Blade Passage ◽  
Tip Leakage ◽  
Multi Stage ◽  
Flow Interactions ◽  
Sst Turbulence Model ◽  
Downstream Flow

Interaction of the main flow with tip leakage over shrouded rotor blades in a multi-stage turbine is studied numerically. The flow in blade-to-blade channels is computed with the aid of a 3D Navier-Stokes solver FlowER with the Menter SST turbulence model. In this paper, the labyrinth seals are not computed but the numerical scheme is modified to include the source/sink-type boundary conditions at places at the endwalls referring to design locations of injection of leakage flows into, or their extraction from, the blade-to-blade passage. Without considering complete labyrinth seal geometries, the tip leakage jet is represented by its flow rate and direction at re-entry to the blade-to-blade passage, as if referring to the performance of a range of different labyrinth seal arrangements. The effect of direction of tip leakage re-entry on the downstream flow and efficiency of the turbine stage (stage group) is studied. The calculation method is validated on a model air stator/rotor turbine.

Flow Interaction From the Exit Cavity of an Axial Turbine Blade Row Labyrinth Seal

2000 ◽  
Vol 123 (2) ◽  
pp. 342-352 ◽  
Author(s):  
A. Pfau ◽  
M. Treiber ◽  
M. Sell ◽  
G. Gyarmathy
Keyword(s):  
Channel Wall ◽  
Wall Motion ◽  
Cavity Flow ◽  
Labyrinth Seal ◽  
Turbine Rotor ◽  
Main Channel ◽  
Axial Turbine ◽  
Pressure Mapping ◽  
Blade Row ◽  
Classical Picture

The structure of labyrinth cavity flow has been experimentally investigated in a three fin axial turbine labyrinth seal (four cavities). The geometry corresponds to a generic steam turbine rotor shroud. The relative wall motion has not been modeled. The measurements were made with specially developed low-blockage pneumatic probes and extensive wall pressure mapping. Instead of the classical picture of a circumferentially uniform leakage sheet exiting from the last labyrinth clearance, entering the channel, and uniformly spreading over the downstream channel wall, the results reveal uneven flow and the existence of high circumferential velocity within the entire exit cavity. The circumferential momentum is brought into the cavity by swirling fluid from the main channel. This fluid penetrates the cavity and breaks up the leakage sheet into individual jets spaced according to the blade passages. This gives rise to strong local cross flows that may also considerably disturb the performance of a downstream blade row.

Multistage Aspects and Unsteady Effects of Stator and Rotor Clocking in an Axial Turbine With Low Aspect Ratio Blading

2005 ◽  
Vol 128 (1) ◽  
pp. 11-22 ◽  
Author(s):  
T. Behr ◽  
L. Porreca ◽  
T. Mokulys ◽  
A. I. Kalfas ◽  
R. S. Abhari
Keyword(s):  
Aspect Ratio ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Fast Response ◽  
Test Case ◽  
Systematic Analysis ◽  
Number Count ◽  
Low Aspect Ratio ◽  
Multi Stage ◽  
Flow Interactions

This paper presents the outcome of a recent study in clocking-related flow features and multistage effects occurring in high-pressure turbine blade geometries. The current investigation deals with an experimentally based systematic analysis of the effects of both stator-stator and rotor-rotor clocking. Due to the low aspect ratio of the turbine geometry, the flow field is strongly three-dimensional and is dominated by secondary flow structures. The investigation aims to identify the flow interactions involved and the associated effects on performance improvement or degradation. Consequently a three-dimensional numerical analysis has been undertaken to provide the numerical background to the test case considered. The experimental studies were performed in a two-stage axial research turbine facility. The turbine provides a realistic multi-stage environment, in which both stator blade rows and the two rotors can be clocked relative to each other. All blade rows have the same blade number count, which tends to amplify clocking effects. Unsteady and steady measurements were obtained in the second stage using fast response aerodynamic probes and miniature pneumatic five-hole probes. The current comprehensive investigation has shown that multistage and unsteady flow effects of stator and rotor clocking in low aspect ratio turbines are combined in a nonlinear fashion caused by axial and radial redistribution of low energy fluid. The integral result of clocking on stage efficiency is compensated by competing loss generating mechanisms across the span.

Multistage Aspects and Unsteady Effects of Stator and Rotor Clocking in an Axial Turbine With Low Aspect Ratio Blading

2004 ◽  
Author(s):  
T. Behr ◽  
L. Porreca ◽  
T. Mokulys ◽  
A. I. Kalfas ◽  
R. S. Abhari
Keyword(s):  
Aspect Ratio ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Fast Response ◽  
Test Case ◽  
Systematic Analysis ◽  
Number Count ◽  
Low Aspect Ratio ◽  
Multi Stage ◽  
Flow Interactions

This paper presents the outcome of a recent study in clocking-related flow features and multistage effects occurring in high-pressure turbine blade geometries. The current investigation deals with an experimentally based systematic analysis of the effects of both stator-stator and rotor-rotor clocking. Due to the low aspect ratio of the turbine geometry, the flow field is strongly three-dimensional and is dominated by secondary flow structures. The investigation aims to identify the flow interactions involved and the associated effects on performance improvement or degradation. Consequently a three-dimensional numerical analysis has been undertaken to provide the numerical background to the test case considered. The experimental studies were performed in a two-stage axial research turbine facility. The turbine provides a realistic multi-stage environment, in which both stator blade rows and the two rotors can be clocked relative to each other. All blade rows have the same blade number count, which tends to amplify clocking effects. Unsteady and steady measurements were obtained in the second stage using fast response aerodynamic probes (FRAP) and miniature pneumatic 5-hole probes. The current comprehensive investigation has shown that multistage and unsteady flow effects of stator and rotor clocking in low aspect ratio turbines are combined in a nonlinear fashion caused by axial and radial redistribution of low energy fluid. The integral result of clocking on stage efficiency is compensated by competing loss generating mechanisms across the span.

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