Numerical and Experimental Analysis of the Effects of Non-Axisymmetric Contoured Stator Endwalls in an Axial Turbine

2010 ◽  
Author(s):  
Thorsten Poehler ◽  
Jochen Gier ◽  
Peter Jeschke
Keyword(s):  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Experimental Investigations ◽  
Time Interval ◽  
Axial Turbine ◽  
Passage Vortex ◽  
Unsteady Rans ◽  
Endwall Contouring ◽  
Inlet Conditions

Numerical and experimental investigations have been performed to determine the effects of non-axisymmetric stator endwall contouring on the efficiency of an axial turbine stage. The influences of the contoured endwalls on the secondary flows in the stator and the rotor have been analyzed by conducting steady and unsteady RANS simulations as well as measurements in the 1.5-stage axial cold air turbine test rig of the Institute of Jet Propulsion and Turbomachinery. Both numerical and experimental results show an aerodynamic improvement of efficiency and secondary kinetic energy through non-axisymmetric endwall contouring. The non-axisymmetric endwall contour induces a vortex, which separates the pressure side leg of the horseshoe vortex from the passage vortex resulting in redistributed and reduced secondary flows. The modified secondary flow pattern increases the torque of the rotor blade in the hub region as a consequence of improved inlet conditions for the rotor as well as a reduction of the time interval the secondary flows are convected through the rotor passage within. Concerning the shroud region the endwall contour had no significant impact on the efficiency as a consequence of a dominating tip clearance vortex system.

Experimental Investigations of Tip Clearance Flow and its Influence on Secondary Flows in a 1-1/2 Stage Axial Turbine

2000 ◽  
Author(s):  
B. Stephan ◽  
H. E. Gallus ◽  
R. Niehuis
Keyword(s):  
Flow Field ◽  
Flow Behavior ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Radial Clearance ◽  
Experimental Investigations ◽  
Axial Turbine ◽  
Tip Clearance Flow ◽  
Clearance Flow ◽  
Flow Phenomena

A multistage turbomachine has inherently unsteady flow fields due to the relative motion between rotor and stator airfoils, which lead to viscous and inviscid interactions between the blade rows. Additionally, the radial clearance between casing and rotor strongly influences the 3D flow field and the loss generation in turbomachines. The objective of the presented study is to investigate the effects of tip clearance on secondary flow phenomena and, in consequence, on the performance of a 1-1/2 stage axial turbine. The low aspect ratio of the blades and their prismatic design leads to a high degree of secondary flows and three-dimensionality. Extended measurements of the flow field behind each blade row with pneumatic and hotwire probes have been conducted for three different tip clearances. Experimental results reveal significant change of flow behavior and turbine performance with increasing tip clearance.

The Application of Non-Axisymmetric Endwall Contouring in a Single Stage, Rotating Turbine

2009 ◽  
Author(s):  
Glen Snedden ◽  
Dwain Dunn ◽  
Grant Ingram ◽  
David Gregory-Smith
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Pressure Gradient ◽  
Full Scale ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Detailed Understanding ◽  
Low Speed ◽  
Endwall Contouring ◽  
Probe Measurements

As turbine manufacturers strive to develop machines that are more efficient, one area of focus has been the control of secondary flows. To a large extent these methods have been developed through the use of computational fluid dynamics and detailed measurements in linear and annular cascades and proven in full scale engine tests. This study utilises 5-hole probe measurements in a low speed, model turbine in conjunction with computational fluid dynamics to gain a more detailed understanding of the influence of a generic endwall design on the structure of secondary flows within the rotor. This work is aimed at understanding the influence of such endwalls on the structure of secondary flows in the presence of inlet skew, unsteadiness and rotational forces. Results indicate a 0.4% improvement in rotor efficiency as a result of the application of the generic non-axisymmetric endwall contouring. CFD results indicate a clear weakening of the cross passage pressure gradient, but there are also indications that custom endwalls could further improve the gains. Evidence of the influence of endwall contouring on tip clearance flows is also presented.

Overall Effectiveness and Flowfield Measurements for an Endwall With Nonaxisymmetric Contouring

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Amy Mensch ◽  
Karen A. Thole
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Transfer Model ◽  
Internal Cooling ◽  
Blowing Ratio ◽  
Passage Vortex ◽  
Endwall Contouring ◽  
Overall Effectiveness

Endwall contouring is a technique used to reduce the strength and development of three-dimensional secondary flows in a turbine vane or blade passage in a gas turbine. The secondary flows locally affect the external heat transfer, particularly on the endwall surface. The combination of external and internal convective heat transfer, along with solid conduction, determines component temperatures, which affect the service life of turbine components. A conjugate heat transfer model is used to measure the nondimensional external surface temperature, known as overall effectiveness, of an endwall with nonaxisymmetric contouring. The endwall cooling methods include internal impingement cooling and external film cooling. Measured values of overall effectiveness show that endwall contouring reduces the effectiveness of impingement alone, but increases the effectiveness of film cooling alone. Given the combined case of both impingement and film cooling, the laterally averaged overall effectiveness is not significantly changed between the flat and the contoured endwalls. Flowfield measurements indicate that the size and location of the passage vortex changes as film cooling is added and as the blowing ratio increases. Because endwall contouring can produce local effects on internal cooling and film cooling performance, the implications for heat transfer should be considered in endwall contour designs.

Numerical and Experimental Investigations on Endwall Contouring in a Four-Stage Turbine

2001 ◽  
Author(s):  
Dieter E. Bonn ◽  
Harald Funke ◽  
Norbert Sürken ◽  
Franz Kreitmeier
Keyword(s):  
Flow Field ◽  
Flow Analysis ◽  
Numerical Results ◽  
Secondary Flows ◽  
Experimental Investigations ◽  
Maximum Deviation ◽  
Reference Case ◽  
Geometric Configurations ◽  
Endwall Contouring ◽  
Aerodynamic Losses

Secondary flows and leakage flows create complex vortex structures in the 3-D flow field of a turbine stage. Aerodynamic losses are the consequence. Reducing the aerodynamic losses by endwall contouring is subject of an actual investigation of the flow field in a 4-stage test turbine with repeating stages. Numerical 4-stage simulations are performed for a reference case of a turbine without endwall modifications and two different geometric configurations with endwall contouring. The numerical results for the reference case are compared to corresponding experimental investigations. Both, the experiment and the CFD focus on the stage exit flow field of the second, the third and the fourth stage of the actual four stage turbine. The 3-D flow field is calculated by application of a steady 3-D Navier-Stokes code. The numerical results of an arc-like endwall contouring at the casing are presented a) with a maximum deviation from the reference contour in the axial gap within the stages (“arc contour”) and b) with a maximum deviation in the axial gap between the stages (“off-set arc contour”). The results show a significant influence of the bumps on the blade’s profile pressure distribution near the radial gap, the leakage flow and the radial pressure field. A detailed secondary flow analysis shows the influence of the different endwall contours on the leakage vortex development. Finally, the aerodynamic efficiencies of the geometric configurations are compared. It is predicted that the off-set arc contour has a remarkable positive influence on the machine’s performance.

Numerical Simulation of Tip Leakage Flows in Axial Flow Turbines, With Emphasis on Flow Physics: Part I — Effect of Tip Clearance Height

2000 ◽  
Author(s):  
J. Tallman ◽  
B. Lakshminarayana
Keyword(s):  
Mass Flow ◽  
Axial Flow ◽  
Numerical Procedure ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Flow Physics ◽  
Tip Leakage ◽  
Inlet Conditions

A pressure-correction based, 3D Navier-Stokes CFD code was used to simulate the effects of turbine parameters on the tip leakage flow and vortex in a linear turbine cascade to understand the detailed flow physics. A baseline case simulation of a cascade was first conducted in order to validate the numerical procedure with experimental measurements. The effects of realistic tip clearance spacing, inlet conditions, and relative endwall motion were then sequentially simulated, while maintaining previously modified parameters. With each additional simulation, a detailed comparison of the leakage flow’s direction, pressure gradient, and mass flow, as well as the leakage vortex and its roll-up, size, losses, location, and interaction with other flow features, was conducted. Part I of this two-part paper series focuses on the effect of reduced tip clearance height on the leakage flow and vortex. Reduced tip clearance resulted in less mass flow through the gap, a smaller leakage vortex, and less aerothermal losses in both the gap and the vortex. The shearing of the leakage jet and passage flow to which leakage vortex roll-up is usually attributed to was not observed in any of the simulations. Alternative explanations of the leakage vortex’s roll-up are presented. Additional secondary flows that were seen near the casing were also discussed. A more thorough thesis on the research presented in this paper can be found at the World Wide Web address http://navier.aero.psu.edu/∼jat.

Numerical Simulation of Tip Leakage Flows in Axial Flow Turbines, With Emphasis on Flow Physics: Part II—Effect of Outer Casing Relative Motion

2000 ◽  
Vol 123 (2) ◽  
pp. 324-333 ◽  
Author(s):  
J. Tallman ◽  
B. Lakshminarayana
Keyword(s):  
Mass Flow ◽  
Relative Motion ◽  
Numerical Procedure ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Flow Physics ◽  
Tip Leakage ◽  
Inlet Conditions

A pressure-correction based, 3D Navier-Stokes CFD code was used to simulate the effects of turbine parameters on the tip leakage flow and vortex in a linear turbine cascade to understand the detailed flow physics. A baseline case simulation of a cascade was first conducted in order to validate the numerical procedure with experimental measurements. The effects of realistic tip clearance spacing, inlet conditions, and relative endwall motion were then sequentially simulated, while maintaining previously modified parameters. With each additional simulation, a detailed comparison of the leakage flow’s direction, pressure gradient, and mass flow, as well as the leakage vortex and its roll-up, size, losses, location, and interaction with other flow features, was conducted. Part II of this two-part paper series focuses on the effect of relative motion of the outer casing on the leakage flow and vortex development. Casing relative motion results in less mass flow through the gap and a smaller leakage vortex. The structure of the aerothermal losses in the passage change dramatically when the outer casing motion was incorporated, but the total losses in the passage remained very similar. Additional secondary flows that are seen near the casing are also discussed.

Numerical Simulation of Tip Leakage Flows in Axial Flow Turbines, With Emphasis on Flow Physics: Part II — Effect of Outer Casing Relative Motion

2000 ◽  
Author(s):  
J. Tallman ◽  
B. Lakshminarayana
Keyword(s):  
Mass Flow ◽  
Relative Motion ◽  
Numerical Procedure ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Flow Physics ◽  
Tip Leakage ◽  
Inlet Conditions

A pressure-correction based, 3D Navier-Stokes CFD code was used to simulate the effects of turbine parameters on the tip leakage flow and vortex in a linear turbine cascade to understand the detailed flow physics. A baseline case simulation of a cascade was first conducted in order to validate the numerical procedure with experimental measurements. The effects of realistic tip clearance spacing, inlet conditions, and relative endwall motion were then sequentially simulated, while maintaining previously modified parameters. With each additional simulation, a detailed comparison of the leakage flow’s direction, pressure gradient, and mass flow, as well as the leakage vortex and its roll-up, size, losses, location, and interaction with other flow features, was conducted. Part II of this two-part paper series focuses on the effect of relative motion of the outer casing on the leakage flow and vortex development. Casing relative motion resulted in less mass flow through the gap and a smaller leakage vortex. The structure of the aerothermal losses in the passage changed dramatically when the outer casing motion was incorporated, but the total losses in the passage remained very similar. Additional secondary flows that were seen near the casing are also discussed. A more thorough thesis on the research presented in this paper can be found at the World Wide Web address http://navier.aero.psu.edu/∼jat.

Experimental Investigation of Secondary Flow Structure in a Blade Passage With and Without Leading Edge Fillets

2006 ◽  
Vol 129 (3) ◽  
pp. 253-262 ◽  
Author(s):  
G. I. Mahmood ◽  
S. Acharya
Keyword(s):  
Cross Section ◽  
Pressure Loss ◽  
Leading Edge ◽  
Suction Side ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Blade Passage ◽  
Pressure Loss Coefficient ◽  
Passage Vortex ◽  
Loss Coefficients

Velocity and pressure measurements are presented for a blade passage with and without leading edge contouring in a low speed linear cascade. The contouring is achieved through fillets placed at the junction of the leading edge and the endwall. Two fillet shapes, one with a linear streamwise cross-section (fillet 1) and the other with a parabolic cross-section (fillet 2), are examined. Measurements are taken at a constant Reynolds number of 233,000 based on the blade chord and the inlet velocity. Data presented at different axial planes include the pressure loss coefficient, axial vorticity, velocity vectors, and yaw and pitch angles. In the early stages of the development of the secondary flows, the fillets are seen to reduce the size and strength of the suction-side leg of the horseshoe vortex with associated reductions in the pressure loss coefficients and pitch angles. Further downstream, the total pressure loss coefficients and vorticity show that the fillets lift the passage vortex higher above the endwall and move it closer to the suction side in the passage. Near the trailing edge of the passage, the size and strength of the passage vortex is smaller with the fillets, and the corresponding reductions in pressure loss coefficients extend beyond the mid-span of the blade. While both fillets reduce pressure loss coefficients and vorticity, fillet 1 (linear fillet profile) appears to exhibit greater reductions in pressure loss coefficients and pitch angles.

The Performance of a Low Speed One and a Half Stage Axial Turbine With Varying Rotor Tip Clearance and Tip Gap Geometry

1994 ◽  
Author(s):  
G. Morphis ◽  
J. P. Bindon
Keyword(s):  
Secondary Flows ◽  
Tip Clearance ◽  
Surprising Result ◽  
Loss Mechanism ◽  
Axial Turbine ◽  
Low Speed ◽  
Tip Leakage ◽  
Second Stage ◽  
Gap Flow ◽  
Flow Loss

The performance of a low speed axial turbine followed by a second stage nozzle is measured with particular reference to the understanding of tip clearance effects in a real machine and to possible benefits of streamlined low loss rotor tips. A radiused pressure edge was found to improve the performance of b single stage and of a one and a half stage turbine at the small tip clearance levels for which the radius was selected. This is in contrast to cascade results where mixing loss reduced the benefits of such tips. Clearance gap flow appears therefore to be just like other turbine flow where the loss mechanism of separation must be avoided. Loss formation within and downstream of a rotor are more complex than previously realized and do not obey the simple rules that have been used to design for minimum tip clearance loss. For example, approximately 48% of the tip leakage mass flow within a rotor appears to be a flat wall jet rather than a wrapped up vortex. The second stage nozzle efficiency was found to be significantly higher than for the first stage and to even increase with tip clearance. This is a surprising result since it means that not only is there a reduction in secondary flow loss but also that rotor leakage and rotor secondary flows do not generate downstream mixing loss.

Interaction Mechanisms Between Tip Leakage Flow and the Passage Vortex in a Linear Turbine Rotor Cascade

1988 ◽  
Vol 110 (3) ◽  
pp. 329-338 ◽  
Author(s):  
A. Yamamoto
Keyword(s):  
Three Dimensional ◽  
Turbine Rotor ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Passage Vortex ◽  
Generation Mechanisms ◽  
Downstream Flow

In order to study the loss generation mechanisms due to the tip-leakage flow in turbine rotor passages, extensive traverse measurements were made of the three-dimensional flows in a low-speed linear cascade for various tip-clearance sizes and for various cascade inlet flow angles (or incidences). Effects of the leakage flow on the cascade downstream flow fields and interactions between the leakage flow and the passage vortices are discussed in detail based on the traverse measurements and flow-visualization tests in terms of secondary flows and the associated losses. Other traverses were also performed of the tip-casing endwall flows both inside and outside the tip-clearance gap using a micro five-hole pitot tube to reveal the axial development of the interaction throughout the cascade passage. Overall loss characteristics of the present high-turning cascade with blunt leading and trailing edges are obtained and compared with those predicted by the Ainley–Mathieson method.

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