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.

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.

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.

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.

Effect of an Axially Tilted Variable Stator Vane Platform on Penny Cavity and Main Flow

2021 ◽  
Author(s):  
Johannes Janssen ◽  
Daniel Pohl ◽  
Peter Jeschke ◽  
Alexander Halcoussis ◽  
Rainer Hain ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Flow Region ◽  
Cavity Flow ◽  
Main Flow ◽  
Pressure Probe ◽  
Stator Vane ◽  
Cfd Analyses ◽  
Annular Cascade ◽  
The Impact ◽  
Variable Stator

Abstract This paper presents the impact of an axially tilted variable stator vane platform on penny cavity flow and passage flow, with the aid of both optical and pneumatic measurements in an annular cascade wind tunnel as well as steady CFD analyses. Variable stator vanes (VSVs) in axial compressors require a clearance from the endwalls. This means that penny cavities around the vane platform are inevitable. Production and assembly deviations can result in a vane platform which is tilted about the circumferential axis. Due to this deformation, backward facing steps occur on the platform edge. Penny cavity and main flow in geometries with and without platform tilting were compared in an annular cascade wind tunnel, which comprises a single row of 30 VSVs. Detailed particle image velocimetry (PIV) measurements were conducted inside the penny cavity and in the vane passage. Steady pressure and velocity data was obtained by two-dimensional multi-hole pressure probe traverses in the inflow and the outflow. Furthermore, pneumatic measurements were carried out using pressure taps inside the penny cavity. Additionally, oil flow visualization was conducted on the airfoil, hub, and penny cavity surfaces. Steady CFD simulations with boundary conditions, according to the measurements, have been benchmarked against experimental data. The results show that tilting the VSV platform reduces the mass flow into and out of the penny cavity. By decreasing penny cavity leakage, platform tilting also affects the passage flow where it leads to a reduced turbulence level and total pressure loss in the leakage flow region. In summary, the paper demonstrates the influence of penny platform tilting on cavity flow and passage flow and provides new insights into the mechanisms of penny cavity-associated losses.

Interaction of Shroud Leakage Flow and Main Flow in a Three-Stage LP Turbine

2003 ◽  
Vol 127 (4) ◽  
pp. 649-658 ◽  
Author(s):  
Jochen Gier ◽  
Bertram Stubert ◽  
Bernard Brouillet ◽  
Laurent de Vito
Keyword(s):  
Main Flow ◽  
Secondary Flows ◽  
Test Facility ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Jet Engines ◽  
Flow Interactions ◽  
Lp Turbine ◽  
The Impact ◽  
The Ideal

Endwall losses significantly contribute to the overall losses in modern turbomachinery, especially when aerodynamic airfoil load and pressure ratios are increased. In turbines with shrouded airfoils a large portion of these losses are generated by the leakage flow across the shroud clearance. Generally the related losses can be grouped into losses of the leakage flow itself and losses caused by the interaction with the main flow in subsequent airfoil rows. In order to reduce the impact of the leakage flow and shroud design related losses a thorough understanding of the leakage losses and especially of the losses connected to enhancing secondary flows and other main flow interactions has to be understood. Therefore, a three stage LP turbine typical for jet engines is being investigated. For the three-stage test turbine 3D Navier-Stokes computations are performed simulating the turbine including the entire shroud cavity geometry in comparison with computations in the ideal flow path. Numerical results compare favorably against measurements carried out at the high altitude test facility at Stuttgart University. The differences of the simulations with and without shroud cavities are analyzed for several points of operation and a very detailed quantitative loss breakdown is presented.

Influence of Honeycomb Rubbing on the Labyrinth Seal Performance

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Daniel Frączek ◽  
Włodzimierz Wróblewski ◽  
Krzysztof Bochon
Keyword(s):  
Aircraft Engine ◽  
Labyrinth Seal ◽  
Turbine Rotor ◽  
Geometrical Model ◽  
Computational Effort ◽  
Radial Clearance ◽  
Leakage Flow ◽  
Leakage Flows ◽  
Full Structure ◽  
Sst Turbulence Model

The aircraft engine operates in various conditions. In consequence, the design of seals must take account of the seal clearance changes and the risk of rubbing. A small radial clearance of the rotor tip seal leads to the honeycomb rubbing in take-off conditions, and the leakage flow may increase in cruise conditions. The aim of this study is to compare two honeycomb seal configurations of the low-pressure gas turbine rotor. In the first configuration, the clearance is small and rubbing occurs. In the second,—the fins of the seal are shorter to eliminate rubbing. It is assumed that the real clearance in both configurations is the same. A study of the honeycomb geometrical model is performed to reduce the computational effort. The problem is investigated numerically using the RANS equations and the two-equation k–ω SST turbulence model. The honeycomb full structure is taken into consideration to show details of the fluid flow. Main parameters of the clearance and leakage flows are compared and discussed for the rotor different axial positions. An assessment of the leakage flow through the seal variants could support the design process.

Investigation of Cavity Flow Using Fast-Response Pressure-Sensitive Paint

AIAA Journal ◽  
2014 ◽  
Vol 52 (11) ◽  
pp. 2462-2470 ◽  
Author(s):  
W. Flaherty ◽  
Todd M. Reedy ◽  
Gregory S. Elliott ◽  
J. M. Austin ◽  
Ryan F. Schmit ◽  
...  
Keyword(s):  
Cavity Flow ◽  
Fast Response ◽  
Pressure Sensitive Paint ◽  
Pressure Sensitive ◽  
Response Pressure

Influence of Labyrinth Seal Leakage on Centrifugal Compressor Performance

2009 ◽  
Author(s):  
Bob Mischo ◽  
Beat Ribi ◽  
Christof Seebass-Linggi ◽  
Sebastiano Mauri
Keyword(s):  
Centrifugal Compressor ◽  
Leading Edge ◽  
Suction Side ◽  
Labyrinth Seal ◽  
Main Flow ◽  
Low Flow ◽  
Leakage Flow ◽  
Multi Stage ◽  
Compressor Impeller ◽  
Rotating Impeller

The focus of this paper lies on the leakage flow across the shroud of a centrifugal compressor impeller. It is common practice to use shrouded impellers in multi stage compressors featuring a single shaft. The rotating impeller then has to be sealed against the higher pressure in the downstream diffuser by means of labyrinths. The relative amount of leakage is higher for stages designed for low flow, meaning that the associated losses gain in relevance. In addition to this loss source, the injection of the leakage flow has a serious influence on the main flow in a region where it is prone to separation, i.e. at the suction side of the impeller blades close to the shroud, where the highest relative velocities are found. The present paper discusses the numerical results of several geometrical arrangements where the leakage flow was mixed with the main flow in different ways. The distance between the location of injection and the leading edge of the impeller as well as the orientation of the injected flow showed a distinct influence on the performance of the entire stage, mainly on stability.

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