Investigation of a Novel Secondary Flow Feature in a Turbine Cascade With End Wall Profiling

2004 ◽  
Author(s):  
Grant Ingram ◽  
David Gregory-Smith ◽  
Neil Harvey
Keyword(s):  
Secondary Flow ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Unexpected Result ◽  
Full Potential ◽  
Flow Angle ◽  
Passage Vortex ◽  
Flow Feature ◽  
New Feature ◽  
End Wall

A novel secondary flow feature, previously unreported for turbine blading as far as the authors are aware, has been discovered. It has been found that it is possible to separate part of the inlet boundary layer on the blade row end wall as it is being over-turned and rolled up into the passage vortex. This flow feature has been discovered during a continuing investigation into the aerodynamic effects of non-axisymmetric end wall profiling. Previous work, using the low speed linear cascade at Durham University, has shown the potential of end wall profiling for reducing secondary losses. The latest study, the results of which are described here, was undertaken to determine the limits of what end wall profiling can achieve. The flow has been investigated in detail with pressure probe traversing and surface flow visualization. This has found that the inlet boundary locally separates, on the early suction side of the passage, generating significant extra loss which feeds directly into the core of the passage vortex. The presence of this new feature gives rise to the unexpected result that the secondary flow, as determined by the exit flow angle deviations and levels of secondary kinetic energy, can be reduced while at the same time the loss is increased. CFD was found to calculate the secondary flows moderately well compared with measurements. However, CFD did not predict this new feature, nor the increase in loss it caused. It is concluded that the application of non-axisymmetric end wall profiling, although it has been shown to be highly beneficial, can give rise to adverse features that current CFD tools are unable to predict. Improvements to CFD capability are required in order to be able to avoid such features, and obtain the full potential of end wall profiling.

Investigation of a Novel Secondary Flow Feature in a Turbine Cascade With End Wall Profiling

2005 ◽  
Vol 127 (1) ◽  
pp. 209-214 ◽  
Author(s):  
Grant Ingram ◽  
David Gregory-Smith ◽  
Neil Harvey
Keyword(s):  
Secondary Flow ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Unexpected Result ◽  
Full Potential ◽  
Flow Angle ◽  
Passage Vortex ◽  
Flow Feature ◽  
New Feature ◽  
End Wall

A novel secondary flow feature, previously unreported for turbine blading as far as the authors are aware, has been discovered. It has been found that it is possible to separate part of the inlet boundary layer on the blade row end wall as it is being over-turned and rolled up into the passage vortex. This flow feature has been discovered during a continuing investigation into the aerodynamic effects of non-axisymmetric end wall profiling. Previous work, using the low speed linear cascade at Durham University, has shown the potential of end wall profiling for reducing secondary losses. The latest study, the results of which are described here, was undertaken to determine the limits of what end wall profiling can achieve. The flow has been investigated in detail with pressure probe traversing and surface flow visualization. This has found that the inlet boundary locally separates, on the early suction side of the passage, generating significant extra loss which feeds directly into the core of the passage vortex. The presence of this new feature gives rise to the unexpected result that the secondary flow, as determined by the exit flow angle deviations and levels of secondary kinetic energy, can be reduced while at the same time the loss is increased. CFD was found to calculate the secondary flows moderately well compared with measurements. However, CFD did not predict this new feature, nor the increase in loss it caused. It is concluded that the application of non-axisymmetric end wall profiling, although it has been shown to be highly beneficial, can give rise to adverse features that current CFD tools are unable to predict. Improvements to CFD capability are required in order to be able to avoid such features, and obtain the full potential of end wall profiling.

scholarly journals Nonaxisymmetric Turbine End Wall Design: Part II—Experimental Validation

1999 ◽  
Vol 122 (2) ◽  
pp. 286-293 ◽  
Author(s):  
J. C. Hartland ◽  
D. G. Gregory-Smith ◽  
N. W. Harvey ◽  
M. G. Rose
Keyword(s):  
Secondary Flow ◽  
Three Dimensional ◽  
Design System ◽  
Flow Angle ◽  
Linear Cascade ◽  
Pressure Distributions ◽  
Turbine Performance ◽  
Passage Vortex ◽  
Blade Row ◽  
End Wall

The Durham Linear Cascade has been redesigned with the nonaxisymmetric profiled end wall described in the first part of this paper, with the aim of reducing the effects of secondary flow. The design intent was to reduce the passage vortex strength and to produce a more uniform exit flow angle profile in the radial direction with less overturning at the wall. The new end wall has been tested in the linear cascade and a comprehensive set of measurements taken. These include traverses of the flow field at a number of axial planes and surface static pressure distributions on the end wall. Detailed comparisons have been made with the CFD design predictions, and also for the results with a planar end wall. In this way an improved understanding of the effects of end wall profiling has been obtained. The experimental results generally agree with the design predictions, showing a reduction in the strength of the secondary flow at the exit and a more uniform flow angle profile. In a turbine stage these effects would be expected to improve the performance of any downstream blade row. There is also a reduction in the overall loss, which was not given by the CFD design predictions. Areas where there are discrepancies between the CFD calculations and measurement are likely to be due to the turbulence model used. Conclusions for how the three-dimensional linear design system should be used to define end wall geometries for improved turbine performance are presented. [S0889-504X(00)01002-3]

scholarly journals Numerical Study of Purge and Secondary Flows in a Low Pressure Turbine

2016 ◽  
Author(s):  
J. Cui ◽  
P. G. Tucker
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Secondary Flows ◽  
Generation Rate ◽  
Suction Surface ◽  
Flow Angle ◽  
Blade Passage ◽  
Angle Deviation ◽  
Passage Vortex ◽  
Purge Flow

The secondary flow increases the loss and changes the flow incidence in the downstream blade row. To prevent hot gases from entering disk cavities, purge flows are injected into the mainstream in a real aero-engine. The interaction between purge flows and the mainstream usually induces aerodynamic losses. The endwall loss is also affected by shedding wakes and secondary flow from upstream rows. Using a series of eddy-resolving simulations, this paper aims to improve the understanding of the interaction between purge flows, incoming secondary flows along with shedding wakes and mainstream flows on the endwall within a stator passage. It is found that for a blade with an aspect ratio of 2.2, a purge flow with a 1% leakage rate increases loss generation within the blade passage by around 10%. The incoming wakes and secondary flows increase the loss generation further by around 20%. The purge flow pushes the passage vortex further away from the endwall and increases the exit flow angle deviation. However, the maximum exit flow angle deviation is reduced after introducing incoming wakes and secondary flows. The loss generation rate is calculated using the mean flow kinetic energy equation. Two regions with high loss generation rate are identified within the blade passage: the corner region and the region where passage vortex interacts with the boundary layer on the suction surface. Loss generation rate increases dramatically after the separated boundary layer transitions. Since the endwall flow energizes the boundary layer and triggers earlier transition on the suction surface, the loss generation rate close to the endwall at the trailing edge is suppressed.

scholarly journals Numerical Study of Purge and Secondary Flows in a Low-Pressure Turbine

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Jiahuan Cui ◽  
Paul Tucker
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Secondary Flows ◽  
Generation Rate ◽  
Suction Surface ◽  
Flow Angle ◽  
Blade Passage ◽  
Angle Deviation ◽  
Passage Vortex ◽  
Purge Flow

The secondary flow increases the loss and changes the flow incidence in the downstream blade row. To prevent hot gases from entering disk cavities, purge flows are injected into the mainstream in a real aero-engine. The interaction between purge flows and the mainstream usually induces aerodynamic losses. The endwall loss is also affected by shedding wakes and secondary flow from upstream rows. Using a series of eddy-resolving simulations, this paper aims to improve the understanding of the interaction between purge flows, incoming secondary flows along with shedding wakes, and mainstream flows on the endwall within a stator passage. It is found that for a blade with an aspect ratio of 2.2, a purge flow with a 1% leakage rate increases loss generation within the blade passage by around 10%. The incoming wakes and secondary flows increase the loss generation further by around 20%. The purge flow pushes the passage vortex further away from the endwall and increases the exit flow angle deviation. However, the maximum exit flow angle deviation is reduced after introducing incoming wakes and secondary flows. The loss generation rate is calculated using the mean flow kinetic energy equation. Two regions with high loss generation rate are identified within the blade passage: the corner region and the region where passage vortex interacts with the boundary layer on the suction surface. Loss generation rate increases dramatically after the separated boundary layer transitions. Since the endwall flow energizes the boundary layer and triggers earlier transition on the suction surface, the loss generation rate close to the endwall at the trailing edge (TE) is suppressed.

Influence of Unsteady Wakes on the Secondary Flows in the Linear T106 Turbine Cascade

2016 ◽  
Author(s):  
Ilker Kirik ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Secondary Flow ◽  
High Speed ◽  
Base Flow ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Hot Wire ◽  
Flow Angle ◽  
Secondary Flow Field

The present work extends previous investigations on the secondary flows around a steady and unsteady base flow to detailed time-averaged and time-resolved flow field measurements up- and downstream of the cascade. As a representative of modern low pressure turbine rotors of moderate aerodynamic loading, the LPT cascade T106 with parallel sidewalls was chosen for these investigations. Previous investigations have shown that the intensity of secondary flows in the endwall region within a first test set-up was fairly low due to the thin endwall boundary layer at the inlet of the cascade which impeded to study the influence of periodically incoming wakes on the temporal development of the secondary flow field. For that reason a new test-up was built providing a thicker inlet boundary. Measurements have been performed in the High-Speed Cascade Wind Tunnel of the University of the Federal Armed Forces Munich under realistic Mach and Reynolds numbers. In order to simulate real turbomachinery situtations, a wake generator is installed generating temporally representative wakes in the inlet plane of the cascade by a moving bar system. The inlet conditions were determined using a hot wire and a Pitot probe. Detailed measurements of the three-dimensional flow field were carried out downstream of the cascade with a triple hot wire probe, a conventional five hole pressure probe, and a dynamic pressure probe equipped with a single Kulite sensor. All measurements were performed with and without moving bars. Based on previous investigations, a pitch of the moving bars of 40 mm and a circumferential speed of 20 m/s was chosen as the configuration with the highest influence on the secondary flow field. It is shown that the intended increase of the inlet boundary layer was achieved by putting plates on top of each other in the inlet plane endwalls. This leads to more pronounced secondary flow parameters in the spanwise distribution of the pitchwise averaged secondary flow angle (Δβ2,sec) and the secondary losses (ζ2,sec).

scholarly journals The Secondary Flow Field of a Turbine Cascade With 3D Airfoil Design and Endwall Contouring at Off-Design Incidence

1999 ◽  
Author(s):  
Arno Duden ◽  
Leonhard Fottner
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
High Speed ◽  
Secondary Flows ◽  
Turbine Cascade ◽  
Flow Angle ◽  
Radial Extent ◽  
Endwall Contouring ◽  
End Wall ◽  
Secondary Flow Field

A highly loaded turbine cascade with prismatic airfoils and straight endwalls was redesigned with the objective of reducing the secondary flow by applying end wall contouring and 3D airfoil design in the endwall regions. When tested at design conditions the flow field showed distinct improvements. The radial extent of the secondary flows was reduced and a decrease in secondary losses was observed (Duden et al., 1998). As an extension of this investigation, the effects of positive and negative incidence on the performance of the redesigned cascade have been evaluated and compared to the original cascade. The investigations were carried out in a high speed cascade wind tunnel. At negative incidence the redesigned cascade was observed to reduce the radial variation of the circumferential exit flow angle but to increase the magnitude of the secondary losses. At positive incidence, in comparison to the flowfield in the reference cascade, the radial extent of the secondary flows and the magnitude of the secondary losses were greatly reduced. The benefits provided by the 3D airfoil design and endwall contouring were even more obvious at positive incidence than at the design conditions.

Investigation of Non-Axisymmetric Endwall Contouring and 3D Airfoil Design in a 1.5 Stage Axial Turbine: Part I — Design and Novel Numerical Analysis Method

2014 ◽  
Author(s):  
Thorsten Poehler ◽  
Jens Niewoehner ◽  
Peter Jeschke ◽  
Yavuz Guendogdu
Keyword(s):  
Numerical Analysis ◽  
Secondary Flow ◽  
Flow Pattern ◽  
Target Function ◽  
Secondary Flows ◽  
Unexpected Result ◽  
Flow Angle ◽  
Endwall Contouring ◽  
The Impact ◽  
Stage Efficiency

This paper presents the results of the analysis of different 3D designs for the first stator and the rotor of a 1.5-stage turbine test rig. A tangential endwall contouring for the hub and the shroud, a bowed profile stacking, and a combination of those have been designed for the first stator. In addition a tangential endwall contouring has been designed for the hub of the unshrouded rotor. Part I of this two-part paper deals with the design process and the numerical analysis of the results. All designs have been optimized with the stage efficiency as the target function. For the design of the 3D stator vanes, the optimization led to an unexpected result: The secondary flow vortex strength increased. However, the secondary flow pattern has been rearranged and the exit flow angle has been homogenized. Although the stator losses increased, the stage efficiency also increased. Thus, a reduction of the rotor losses overcompensated the higher stator losses. In order to understand how the 3D vanes affect the stator secondary flow pattern, a detailed analysis of vortex stretching and vortex dissipation is presented here. With this approach, the various impacts of the 3D designs on the secondary flow vortices’ strength can be quantified. In addition, the potential theory effect of the self-induced velocity is introduced here in order to explain the effects of a tangential endwall contouring on the trajectory of the pressure side leg of the horseshoe vortex. At the authors’ knowledge, both approaches are new for the analysis of turbine secondary flows. The impact of the stronger but rearranged stator secondary flow on the rotor secondary loss development is analyzed by means of unsteady simulations. The results show that the rotor secondary flow can be effectively reduced through a proper stator secondary flow pattern. In part II of this paper, the analysis of extensive experimental results validates and supplements the numerical analysis.

Investigation of Nonaxisymmetric Endwall Contouring and Three-Dimensional Airfoil Design in a 1.5-Stage Axial Turbine—Part I: Design and Novel Numerical Analysis Method

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Thorsten Poehler ◽  
Jens Niewoehner ◽  
Peter Jeschke ◽  
Yavuz Guendogdu
Keyword(s):  
Numerical Analysis ◽  
Secondary Flow ◽  
Flow Pattern ◽  
Target Function ◽  
Secondary Flows ◽  
Unexpected Result ◽  
Angle Distribution ◽  
Flow Angle ◽  
Endwall Contouring ◽  
The Impact

This paper presents the results of the analysis of different 3D designs for the first stator and the rotor of a 1.5-stage turbine test rig. A tangential endwall contouring for the hub and the shroud, a bowed profile stacking, and a combination of those have been designed for the first stator. In addition, a tangential endwall contouring has been designed for the hub of the unshrouded rotor. Part I of this two-part paper deals with the design process and the numerical analysis of the results. All designs have been optimized using the stage efficiency as target function. For the design of the 3D stator vanes, the optimization led to an unexpected result: The secondary flow vortex strength increased. However, the secondary flow pattern is rearranged by the 3D-designing, leading to a smoother radial exit flow angle distribution. A subsequent reduction of the rotor losses overcompensates the higher stator losses. In order to understand how the 3D vanes affect the stator secondary flow pattern, a detailed analysis of vortex stretching and vortex dissipation is presented in this paper. With this approach, the various impacts of the 3D designs on the secondary flow vortices' strength can be quantified. In addition, the potential theory effect of the self-induced velocity is introduced here in order to explain the effects of a tangential endwall contouring on the trajectory of the pressure side leg of the horseshoe vortex (HVps). To the best of our knowledge, both approaches are new for the analysis of turbine secondary flows. The impact of the stronger but rearranged stator secondary flow on the rotor secondary loss development is analyzed by means of unsteady simulations. The results show that the rotor secondary flow can be effectively reduced through a proper stator secondary flow pattern. In Part II of this paper, the analysis of extensive experimental results validates and supplements the numerical analysis.

scholarly journals Non-Axisymmetric Turbine End Wall Design: Part II — Experimental Validation

1999 ◽  
Author(s):  
J. C. Hartland ◽  
D. G. Gregory-Smith ◽  
N. W. Harvey ◽  
M. G. Rose
Keyword(s):  
Secondary Flow ◽  
Three Dimensional ◽  
Design System ◽  
Flow Angle ◽  
Linear Cascade ◽  
Pressure Distributions ◽  
Turbine Performance ◽  
Passage Vortex ◽  
Blade Row ◽  
End Wall

The Durham Linear Cascade has been redesigned with the non-axisymmetric profiled end wall described in the first part of this paper, with the aim of reducing the effects of secondary flow. The design intent was to reduce the passage vortex strength and to produce a more uniform exit flow angle profile in the radial direction with less over turning at the wall. The new end wall has been tested in the linear cascade and a comprehensive set of measurements taken. These include traverses of the flow field at a number of axial planes and surface static pressure distributions on the end wall. Detailed comparisons have been made with the CFD design predictions, and also for the results with a planar end wall. In this way an improved understanding of the effects of end wall profiling has been obtained. The experimental results generally agree with the design predictions, showing a reduction in the strength of the secondary flow at the exit and a more uniform flow angle profile. In a turbine stage these effects would be expected to improve the performance of any downstream blade row. There is also a reduction in the overall loss, which was not given by the CFD design predictions. Areas where there are discrepancies between the CFD calculations and measurement are likely to be due to the turbulence model used. Conclusions for how the three-dimensional linear design system should be used to define end wall geometries for improved turbine performance are presented.

scholarly journals Incidence Angle and Pitch-Chord Effects on Secondary Flows Downstream of a Turbine Cascade

1992 ◽  
Author(s):  
A. Perdichizzi ◽  
V. Dossena
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Incidence Angle ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Turbine Cascade ◽  
Oil Flow ◽  
Secondary Velocity ◽  
Secondary Flow Field

This paper describes the results of an experimental investigation of the three-dimensional flow downstream of a linear turbine cascade at off-design conditions. The tests have been carried out for five incidence angles from −60 to +35 degrees, and for three pitch-chord ratios: s/c = 0.58,0.73,0.87. Data include blade pressure distributions, oil flow visualizations, and pressure probe measurements. The secondary flow field has been obtained by traversing a miniature five hole probe in a plane located at 50% of an axial chord downstream of the trailing edge. The distributions of local energy loss coefficients, together with vorticity and secondary velocity plots show in detail how much the secondary flow field is modified both by incidence and cascade solidity variations. The level of secondary vorticity and the intensity of the crossflow at the endwall have been found to be strictly related to the blade loading occurring in the blade entrance region. Heavy changes occur in the spanwise distributions of the pitch averaged loss and of the deviation angle, when incidence or pitch-chord ratio is varied.

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