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.

Requirements and Limitations of Controlling Turbine Tip Shroud Cavity Flow Mixing With Bladelets on Rotating Shroud

2015 ◽  
Author(s):  
Timothy R. Palmer ◽  
Choon S. Tan ◽  
Matthew Montgomery ◽  
Anthony Malandra ◽  
David Little ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Cavity Flow ◽  
Efficiency Gain ◽  
Turbine Stage ◽  
Loss Mechanism ◽  
Inlet Flow ◽  
Flow Asymmetry ◽  
Low Reynolds ◽  
Tip Shroud

A potential means of significantly reducing the cavity exit mixing loss, a dominant primary loss mechanism in turbine tip shroud cavity flow, is assessed. The operational constraints on the turbine stage dictate that losses may only be mitigated through configuration changes within the cavity. A configuration, known herein as the Hybrid Blade, features a shrouded main blade with a row of high aspect ratio bladelets affixed to the rotating shroud is formulated and shown to nearly eliminate the cavity exit mixing loss. However the Hybrid Blade configuration incurs a penalty associated with bladelet low Reynolds number effects, cavity inlet flow asymmetry introduced by the scalloped shroud, and a resulting mismatch with the upstream vane as well as downstream diffuser. This penalty offsets the efficiency gain from mitigating cavity exit mixing loss. For the Hybrid Blade system, it can thus be inferred that the turbine stage and the diffuser need to be reconfigured to accommodate the modified tip shroud, and the bladelets redesigned for low Reynolds number operation and cavity inlet flow asymmetry to achieve an overall benefit.

Quantifying Loss Mechanisms in Turbine Tip Shroud Cavity Flows

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Timothy R. Palmer ◽  
Choon S. Tan ◽  
Humberto Zuniga ◽  
David Little ◽  
Matthew Montgomery ◽  
...  
Keyword(s):  
Functional Dependence ◽  
Main Flow ◽  
Leakage Flow ◽  
Recirculating Flow ◽  
Velocity Magnitude ◽  
Toroidal Vortices ◽  
Flow Features ◽  
The Difference ◽  
Gap Height ◽  
Tip Shroud

Numerical calculations, steady as well as unsteady, of flow in a turbine stage with a tip shroud cavity elucidate that the loss-generating flow features consist of tip seal leakage jet, the interaction of cavity exit flow with main flow, the partially recirculating cavity inlet flow interaction with vane wakes, and injection of leakage flow into the shroud cavity. The first two flow features, namely, the tip seal leakage flow and mixing of cavity exit flow with main flow, dominate while the injection of leakage flow plays an indirect role in affecting the loss generation associated with cavity exit flow. The tip shroud cavity flow essentially consists of a system of toroidal vortices, the configuration of which is set by the cavity geometry and changes when subject to unsteady vane–rotor interaction. The role which the toroidal vortices play in setting the cavity inlet recirculating flow pattern and loss generation is delineated. It is suggested that there exists a link between the inlet cavity sizing and the toroidal vortical structure. The computed results appear to indicate that the main flow path approximately perceives the presence of the tip shroud cavity as a sink–source pair; as such a flow model based on this approximation is formulated. Loss variations with tip gap height and leakage flow injection are assessed. Results show that the expected loss due to mixing has a functional dependence on the square of the difference in their velocity magnitude and swirl. The tip seal leakage jet loss scales approximately linearly with the corrected mass flow rate per unit area over the range of tip gaps investigated.

Influence of Stator-Rotor Interaction on the Aerothermal Performance of Recess Blade Tips

2008 ◽  
Author(s):  
Bob Mischo ◽  
Andre´ Burdet ◽  
Reza S. Abhari
Keyword(s):  
Nusselt Number ◽  
Steady State ◽  
Flow Field ◽  
Heat Load ◽  
Design Procedure ◽  
Leading Edge ◽  
Cavity Flow ◽  
Turbine Stage ◽  
Beneficial Effects ◽  
Time Average

This paper investigates the influence of stator-rotor interaction on the stage performance of three blade tip geometries. A reference flat tip is used to assess two different recess blade geometries. The study is made in the context of the realistic turbine stage configuration provided by the ETHZ 1.5 stage LISA turbine research facility. This numerical investigation describes the details of unsteady recess cavity flow structure and confirms the beneficial effects of the improved recess geometry over the flat tip and the nominal recess design both in terms of stage efficiency and tip heat load. The tip flow field obtained from the improved recess design combines the advantages of a nominal recess design (aerodynamic sealing) and the flat tip configuration. The turbine stage capacity is almost unchanged between the flat tip and the improved recess tip cases, which simplifies the design procedure when using the improved recess design. Overall heat load in the improved recess case is reduced by 26% compared to the flat tip and by 12% compared to the nominal recess. A key finding of this study is the difference in effects of the upstream stator wake on the recess cavity flow. Where cavity flow in the nominal design is only moderately influenced, the improved recess cavity flow shows enhanced flow unsteadiness. The tip Nusselt number from a purely steady state prediction in the nominal recess case is nearly identical to the time-average prediction. The improved design shows a 6% difference between steady state and time average tip Nusselt number. This is due to the strong influence of the wake passing on the recess cavity flow. In fact, the wake enhances a small flow difference at the leading edge of the recess cavity between the nominal and improved recess cavities, which results in a completely different flow field further downstream in the recess cavity.

Quantifying Loss Mechanisms in Turbine Tip Shroud Cavity Flows

2014 ◽  
Author(s):  
Timothy R. Palmer ◽  
Choon S. Tan ◽  
Humberto Zuniga ◽  
David Little ◽  
Matthew Montgomery ◽  
...  
Keyword(s):  
Functional Dependence ◽  
Main Flow ◽  
Leakage Flow ◽  
Recirculating Flow ◽  
Velocity Magnitude ◽  
Toroidal Vortices ◽  
Flow Features ◽  
The Difference ◽  
Gap Height ◽  
Tip Shroud

Numerical calculations, steady as well as unsteady, of flow in a turbine stage with a tip shroud cavity elucidate that the loss generating flow features consist of tip seal leakage jet, the interaction of cavity exit flow with main flow, the partially recirculating cavity inlet flow interaction with vane wakes, and injection of leakage flow into the shroud cavity. The first two flow features, namely the tip seal leakage flow and mixing of cavity exit flow with main flow, dominate while the injection of leakage flow plays an indirect role in affecting the loss generation associated with cavity exit flow. The tip shroud cavity flow essentially consists of a system of toroidal vortices, the configuration of which is set by the cavity geometry and changes when subject to unsteady vane-rotor interaction. The role which the toroidal vortices play in setting the cavity inlet recirculating flow pattern and loss generation is delineated. It is suggested that there exists a link between the inlet cavity sizing and the toroidal vortical structure. The computed results appear to indicate that the main flow path approximately perceives the presence of the tip shroud cavity as a doublet; as such a flow model based on this approximation is formulated. Loss variations with tip gap height and leakage flow injection are assessed. Results show that the expected loss due to mixing has a functional dependence on the square of the difference in their velocity magnitude and swirl. The tip seal leakage jet loss scales approximately linearly with the corrected mass flow rate per unit area over the range of tip gaps investigated.

Influence of Stator-Rotor Interaction on the Aerothermal Performance of Recess Blade Tips

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Bob Mischo ◽  
André Burdet ◽  
Reza S. Abhari
Keyword(s):  
Nusselt Number ◽  
Steady State ◽  
Flow Field ◽  
Heat Load ◽  
Design Procedure ◽  
Leading Edge ◽  
Cavity Flow ◽  
Turbine Stage ◽  
Beneficial Effects ◽  
Time Average

This paper investigates the influence of stator-rotor interaction on the stage performance of three blade tip geometries. A reference flat tip is used to assess two different recess blade geometries. The study is made in the context of the realistic turbine stage configuration provided by the ETHZ 1.5-stage LISA turbine research facility. This numerical investigation describes the details of unsteady recess cavity flow structure and confirms the beneficial effects of the improved recess geometry over the flat tip and the nominal recess design both in terms of stage efficiency and tip heat load. The tip flow field obtained from the improved recess design combines the advantages of a nominal recess design (aerodynamic sealing) and the flat tip configuration. The turbine stage capacity is almost unchanged between the flat tip and the improved recess tip cases, which simplifies the design procedure when using the improved recess design. The overall heat load in the improved recess case is reduced by 26% compared with the flat tip and by 14% compared with the nominal recess. A key finding of this study is the difference in effects of the upstream stator wake on the recess cavity flow. Where cavity flow in the nominal design is only moderately influenced, the improved recess cavity flow shows enhanced flow unsteadiness. The tip Nusselt number from a purely steady-state prediction in the nominal recess case is nearly identical to the time-average prediction. The improved design shows a 6% difference between steady-state and time-average tip Nusselt number. This is due to the strong influence of the wake passing on the recess cavity flow. In fact, the wake enhances a small flow difference at the leading edge of the recess cavity between the nominal and improved recess cavities, which results in a completely different flow field further downstream in the recess cavity.

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.

On the Effect of Volute Tongue Design on Radial Turbine Performance

2012 ◽  
Author(s):  
Jan F. Suhrmann ◽  
Dieter Peitsch ◽  
Marc Gugau ◽  
Tom Heuer
Keyword(s):  
Flow Field ◽  
Gas Turbines ◽  
Preliminary Design ◽  
Turbine Stage ◽  
Turbine Wheel ◽  
Inlet Flow ◽  
Flow Angle ◽  
Flow Parameters ◽  
Radial Turbine ◽  
The One

With an increasing need for gas turbines with rather low flow rates in many industrial applications, e.g. decentralized power generation, aircrafts or automotive turbochargers, the development of small size radial turbines becomes more and more important. A major step in the development of a radial turbine stage is the preliminary design, which is the definition of basic geometrical features and the calculation of general turbine flow parameters at the design point and within the operating range. These are mainly the rotational speed, the expansion ratio, the flow rate and in particular the expected turbine efficiency. In a radial turbine stage, the volute component delivers the flow to the rotor wheel and according to the geometrical form it defines major flow parameters like the mass flow parameter or the absolute rotor inlet flow angle. Amongst others, the way the flow enters the turbine wheel represents one of the most important loss generating factors. Thus, on the one hand an approach is necessary for the calculation of the optimum rotor inlet flow angle, in order to avoid dispensable losses due to secondary flow in the turbine wheel region. On the other hand, the volute tongue generates flow non-uniformity which has an effect on the overall circumferential averaged rotor inlet flow angle. Furthermore, the local flow pattern downstream of the volute tongue can generate suboptimal flow conditions for the turbine wheel. Hussain and Bhinder [1] measured the flow field at the outlet of a vaneless volute at different circumferential positions and detected a variation of the outlet angle of about Δα = 10°. The authors conclusion was, that the influence on the stage performance of flow non-uniformity generated by the volute could exceed the one of pressure losses through the volute. In this paper, the effect of different geometrical volute parameters on the flow condition especially at the turbine wheel inlet area is investigated. Experimental data of the influence of different volute tongue geometries on the flow field is difficult to generate. Hence, comprehensive numerical investigations are made using steady 3D-CFD calculations of the turbine volute as well as calculations of complete turbine stages including a turbine wheel geometry. Based on the numerical results, a design guideline is developed to estimate the influence of the geometric volute parameters on the flow and to raise the quality of the preliminary design process.

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.

scholarly journals Manifold reduction techniques for the comparison of crank angle-resolved particle image velocimetry (PIV) data and Reynolds-averaged Navier-Stokes (RANS) simulations in a spark ignition direct injection (SIDI) engine

2021 ◽  
pp. 146808742110131
Author(s):  
Xiaohang Fang ◽  
Li Shen ◽  
Christopher Willman ◽  
Rachel Magnanon ◽  
Giuseppe Virelli ◽  
...  
Keyword(s):  
Flow Field ◽  
Particle Image ◽  
Direct Injection ◽  
Linear Manifold ◽  
Main Flow ◽  
Navier Stokes ◽  
Reduction Techniques ◽  
Image Velocimetry ◽  
Manifold Reduction ◽  
Relevance Index

In this article, different manifold reduction techniques are implemented for the post-processing of Particle Image Velocimetry (PIV) images from a Spark Ignition Direct Injection (SIDI) engine. The methods are proposed to help make a more objective comparison between Reynolds-averaged Navier-Stokes (RANS) simulations and PIV experiments when Cycle-to-Cycle Variations (CCV) are present in the flow field. The two different methods used here are based on Singular Value Decomposition (SVD) principles where Proper Orthogonal Decomposition (POD) and Kernel Principal Component Analysis (KPCA) are used for representing linear and non-linear manifold reduction techniques. To the authors’ best knowledge, this is the first time a non-linear manifold reduction technique, such as KPCA, has ever been used in the study of in-cylinder flow fields. Both qualitative and quantitative studies are given to show the capability of each method in validating the simulation and incorporating CCV for each engine cycle. Traditional Relevance Index (RI) and two other previously developed novel indexes: the Weighted Relevance Index (WRI) and the Weighted Magnitude Index (WMI), are used for the quantitative study. The results indicate that both POD and KPCA show improvements in capturing the main flow field features compared to ensemble-averaged PIV experimental data and single cycle experimental flow fields while capturing CCV. Both methods present similar quantitative accuracy when using the three indexes. However, challenges were highlighted in the POD method for the selection of the number of POD modes needed for a representative reconstruction. When the flow field region presents a Gaussian distribution, the KPCA method is seen to provide a more objective numerical process as the reconstructed flow field will see convergence with an increasing number of modes due to its usage of Gaussian properties. No additional criterion is needed to determine how to reconstruct the main flow field feature. Using KPCA can, therefore, reduce the amount of analysis needed in the process of extracting the main flow field while incorporating CCV.

scholarly journals Influence of Seal Cavity Leakage Flow on Compressor Performance Investigated with a Circumferentially Averaged Method

2021 ◽  
Vol 11 (2) ◽  
pp. 780
Author(s):  
Dong Liang ◽  
Xingmin Gui ◽  
Donghai Jin
Keyword(s):  
Flow Field ◽  
Pressure Ratio ◽  
Interaction Mechanism ◽  
Main Flow ◽  
Leakage Flow ◽  
Destructive Effect ◽  
Through Flow ◽  
Compressor Performance ◽  
Overall Performance ◽  
Flow Blockage

In order to investigate the effect of seal cavity leakage flow on a compressor’s performance and the interaction mechanism between the leakage flow and the main flow, a one-stage compressor with a cavity under the shrouded stator was numerically simulated using an inhouse circumferentially averaged through flow program. The leakage flow from the shrouded stator cavity was calculated simultaneously with main flow in an integrated manner. The results indicate that the seal cavity leakage flow has a significant impact on the overall performance of the compressor. For a leakage of 0.2% of incoming flow, the decrease in the total pressure ratio was 2% and the reduction of efficiency was 1.9 points. Spanwise distribution of the flow field variables of the shrouded stator shows that the leakage flow leads to an increased flow blockage near the hub, resulting in drop of stator performance, as well as a certain destructive effect on the flow field of the main passage.

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