A Computational Study of Tip Desensitization in Axial Flow Turbines: Part 2 — Turbine Rotor Simulations With Modified Tip Shapes

2004 ◽  
Author(s):  
James A. Tallman
Keyword(s):  
Mass Flow ◽  
Computational Study ◽  
Three Dimensional ◽  
Axial Flow ◽  
Numerical Procedure ◽  
Suction Side ◽  
Turbine Rotor ◽  
Leakage Flow ◽  
Side Edge ◽  
Blade Tip

This study used Computational Fluid Dynamics (CFD) to investigate modified turbine blade tip shapes as a means of reducing the leakage flow and vortex. The subject of this study was the single-stage experimental turbine facility at Penn State University, with scaled three-dimensional geometry representative of a modern high-pressure stage. To validate the numerical procedure, the rotor flowfield was first computed with no modification to the tip, and the results compared with measurements of the flowfield. The flow was then predicted for a variety of different tip shapes: first with coarse grids for screening purposes and then with more refined grids for final verification of preferred tip geometries. Part 2 of this two-part paper focuses on flow-field predictions with modified blade tip geometries, and the corresponding comparisons with the baseline, flat-tip solutions presented in Part 1. Fifteen different tip shapes were computed using the ADPAC CFD Solver and moderately sized grids (720,000 nodes). These modified tip shapes incorporated different combinations of blade tip edge rounding and squealer cavities, both square and rounded, as means of reducing the leakage flow and vortex. Rounding of the suction side edge of the blade tip resulted in a considerable reduction in the size and strength of the leakage vortex, while rounding of the pressure side edge of the blade tip significantly increased the mass flow rate through the gap. Rounded squealer cavities acted to reduce the mass flow through the gap and proved advantageous over traditional, square squealer cavities. The presence of a square squealer cavity without edge rounding showed no aerodynamic advantage over a flat tip. Final computations of two preferred tip shapes were then carried out using more refined grids (7.2 million nodes). The final, refined grid computations reconfirmed a reduction in the leakage flow and vortex, as well as their associated losses.

Three-Dimensional Navier-Stokes Analysis of Turbine Rotor and Tip-Leakage Flowfield

1997 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Three Dimensional ◽  
Turbine Rotor ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Mean Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

The 3-D viscous flowfield in the rotor passage of a single-stage turbine, including the tip-leakage flow, is computed using a Navier-Stokes procedure. A grid-generation code has been developed to obtain embedded H grids inside the rotor tip gap. The blade tip geometry is accurately modeled without any “pinching”. Chien’s low-Reynolds-number k-ε model is employed for turbulence closure. Both the mean-flow and turbulence transport equations are integrated in time using a four-stage Runge-Kutta scheme. The computational results for the entire turbine rotor flow, particularly the tip-leakage flow and the secondary flows, are interpreted and compared with available data. The predictions for major features of the flowfield are found to be in good agreement with the data. Complicated interactions between the tip-clearance flows and the secondary flows are examined in detail. The effects of endwall rotation on the development and interaction of secondary and tip-leakage vortices are also analyzed.

Numerical Simulation of Effects of Tip Geometry on the Performance of an Axial Compressor

2012 ◽  
Author(s):  
Hongwei Ma ◽  
Jun Zhang
Keyword(s):  
Mass Flow ◽  
Tangential Force ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Leading Edge ◽  
Suction Side ◽  
Leakage Flow ◽  
Base Line ◽  
Compressor Rotor ◽  
Blade Tip

The purpose of this paper is to investigate numerically the effects of the tip geometry on the performance of an axial compressor rotor. There are three case studies which are compared with the base line tip geometry. 1) baseline (flat tip); 2) Cavity (tip with a cavity); 3) SSQA (suction side squealer tip) and 4) SSQB (modified suction side squealer tip). The case of SSQB is a combination of suction side squealer tip and the cavity tip. From leading edge to 10% chord, the tip has a cavity. From 10% chord to trailing edge, the tip has a suction side squealer. The numerical results of 2) show that the cavity tip leads to lower leakage mass flow and greater loss in tip gap and the rotor passage. The loading near the blade tip is lower than the baseline, thus the tangential force of the blade is lower. It leads to lower pressure rise than the baseline. The performance of the compressor for the tip with cavity is worse than the baseline. The results of 3) show that the higher curvature of the suction side squealer increases the loading of the blade and the tangential blade force. With the suction side squealer tip, the leakage flow experiences two vena contractor thus the mass of the leakage flow is reduced which is benefit for the performance of the compressor. The loss in the tip gap is lower than baseline. The performance is better than the baseline with greater pressure rise of the rotor, smaller leakage mass flow and lower averaged loss. For the case the SSQB, the leakage mass flow is lower than the SSQA and the loss in the tip gap and the rotor passage is greater than SSQA. The performance of the case of the SSQB is worse than the case of SSQA.

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.

Influence of Different Rim Widths and Blowing Ratios on Film Cooling Characteristics for a Blade Tip

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Jin Wang ◽  
Bengt Sundén ◽  
Min Zeng ◽  
Qiu-wang Wang
Keyword(s):  
Heat Transfer ◽  
Numerical Simulations ◽  
Film Cooling ◽  
Three Dimensional ◽  
Suction Side ◽  
Leakage Flow ◽  
Pressure Side ◽  
Tip Leakage Flow ◽  
Blade Tip ◽  
Film Cooling Holes

Three-dimensional simulations of the squealer tip on the GE-E3 blade with eight film cooling holes were carried out. The effect of the rim width and the blowing ratio on the blade tip flow and cooling performance were revealed. Numerical simulations were performed to predict the leakage flow and the tip heat transfer with the k–ɛ model. For the squealer tip, the depth of the cavity is fixed but the rim width varies to form a wide cavity, which can decrease the coolant momentum and the tip leakage flow velocity. This cavity contributes to the improvement of the cooling effect in the tip zone. To investigate the influence on the tip heat transfer by the rim width, numerical simulations were performed as a two-part study: (1) unequal rim width study on the pressure side and the suction side and (2) equal rim width study with rim widths of 0.58%, 1.16%, and 1.74% of the axial chord (0.5 mm, 1 mm, and 1.5 mm, respectively) on both the pressure side rim and the suction side rim. With different rim widths, the effect of different global blowing ratios, i.e., M = 0.5, 1.0 and 1.5, was investigated. It is found that the total heat transfer rate is increasing and the heat transfer rates on the rim surface (RS) rapidly ascend with increasing rim width.

Reduction of Tip Clearance Losses in an Axial Turbine by Shaped Design of the Blade Tip Region

2007 ◽  
Author(s):  
K. Kusterer ◽  
N. Moritz ◽  
D. Bohn ◽  
T. Sugimoto ◽  
R. Tanaka
Keyword(s):  
Numerical Investigation ◽  
Mass Flow ◽  
Suction Side ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Pressure Side ◽  
Aerodynamic Efficiency ◽  
Blade Tip ◽  
Radial Gap ◽  
Tip Clearance Vortex

Secondary flows and leakage flows lead to complex vortex structures in the flow field inside the passages of the vanes and blades in turbo machines. These result in aerodynamic losses and, thus, reduced efficiency. One of the major vortex structures is the tip clearance vortex, which is generated on the airfoil’s suction side due to the leakage flow through the tip clearance, e.g. between rotating blades and casing. This leakage flow is induced by the pressure difference between pressure and suction side. The tip clearance vortex intensity strongly depends on the amount of tip clearance leakage. Thus, the reduction of this leakage mass flow increases the aerodynamic efficiency of a turbo-machine. In gas turbines, two ways are commonly used to influence the tip leakage flow: contouring of the radial gap either at blade tip or endwall, or changing the blade tip geometry by application of squealers or winglets on the blade tip. In this paper, a numerical investigation on the principle physics of a specific blade tip design is presented. On the pressure side the blades are extended in the tip region comparable to winglets (“hook-shaped”). With this change, the structures of the flow entering the gap between blade tip and casing are influenced to achieve a reduction of the mass flow in the radial gap. In this approach, the contour of the blade on the pressure side surface is shaped smoothly so that only a low increase of the local stresses should be expected and the blade is manufactured in one part. Furthermore, the height of the tip clearance is not affected. The new blade tip design is applied to 2nd and 3rd blade of the axial turbine in a test configuration of a KHI industrial gas turbine. Thus, a multi-stage numerical approach has been selected for the numerical investigation. The numerical model includes the flow path, vanes and blades of the 2nd and 3rd stage. The mixing plane technique is used to couple the blocks computed in stationary system of reference and rotating system of reference. The aerodynamic efficiency of the new designed blade tip in the two-stage arrangement is compared to the original design. It shows that a slight increase can be achieved in the static polytropic efficiency of the turbine configuration. The influence of the new design on the flow structures in the tip clearance region of the blades is analysed in detail to explain the mechanisms that cause the efficiency increase.

Aero-Thermal Investigations of Tip Leakage Flow In Axial Flow Turbines: Part II — Effect of Relative Casing Motion

2007 ◽  
Author(s):  
S. K. Krishnababu ◽  
W. N. Dawes ◽  
H. P. Hodson ◽  
G. D. Lock ◽  
J. Hannis ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Numerical Study ◽  
Axial Flow ◽  
Suction Side ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Suction Surface ◽  
Average Heat ◽  
Tip Leakage

A numerical study has been performed to investigate the effect of casing motion on the tip leakage flow and heat transfer characteristics in unshrouded axial flow turbines. The relative motion between the blade tip and the casing was simulated by moving the casing in a direction from the suction side to the pressure side of the stationary blade. Baseline flat tip geometry and squealer type geometries namely double squealer or cavity and suction side squealer were considered at a clearance gap of 1.6%C. The computations were performed using a single blade with periodic boundary conditions imposed along the boundaries in the pitchwise direction. Turbulence was modelled using the SST k-ω model. The flow conditions correspond to an exit Reynolds number of 2.3×105. The results were compared with those obtained without the relative casing motion reported in part I of this paper. In general, the effect of relative casing motion was to decrease the tip leakage mass flow and the average heat transfer to the tip due to the decrease in leakage flow velocity caused by a drop in driving pressure difference. Compared to the computations with stationary casing, in the case of all the three geometries considered, the average heat transfer to the suction surface of the blade was found to be larger in the case of the computations with relative casing motion. At a larger clearance gap of 2.8%C, in case of flat tip, while the tip leakage mass flow decreased due to relative casing motion only a smaller change in the average heat transfer to the tip and the suction surface of the blade was noticed.

Aerothermal Investigations of Tip Leakage Flow in Axial Flow Turbines—Part II: Effect of Relative Casing Motion

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
S. K. Krishnababu ◽  
W. N. Dawes ◽  
H. P. Hodson ◽  
G. D. Lock ◽  
J. Hannis ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Axial Flow ◽  
Suction Side ◽  
Leakage Flow ◽  
Base Line ◽  
Tip Leakage Flow ◽  
Suction Surface ◽  
Average Heat ◽  
Tip Leakage

A numerical study has been performed to investigate the effect of casing motion on the tip leakage flow and heat transfer characteristics in unshrouded axial flow turbines. The relative motion between the blade tip and the casing was simulated by moving the casing in a direction from the suction side to the pressure side of the stationary blade. Base line flat tip geometry and squealer type geometries, namely, double squealer or cavity and suction side squealer, were considered at a clearance gap of 1.6%C. The computations were performed using a single blade with periodic boundary conditions imposed along the boundaries in the pitchwise direction. Turbulence was modeled using the shear stress transport k-ω model. The flow conditions correspond to an exit Reynolds number of 2.3×105. The results were compared to those obtained without the relative casing motion reported in Part I of this paper. In general, the effect of relative casing motion was to decrease the tip leakage mass flow and the average heat transfer to the tip due to the decrease in leakage flow velocity caused by a drop in driving pressure difference. Compared to the computations with stationary casing, in the case of all the three geometries considered, the average heat transfer to the suction surface of the blade was found to be larger in the case of the computations with relative casing motion. At a larger clearance gap of 2.8%C, in case of a flat tip, while the tip leakage mass flow decreased due to relative casing motion, only a smaller change in the average heat transfer to the tip and the suction surface of the blade was noticed.

A Computational Study of Tip Desensitization in Axial Flow Turbines: Part 1 — Baseline Turbine Computations and Comparisons With Measurement

2004 ◽  
Author(s):  
James A. Tallman
Keyword(s):  
Turbulence Modeling ◽  
Stokes Equations ◽  
Computational Study ◽  
Three Dimensional ◽  
Axial Flow ◽  
Numerical Procedure ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Penn State ◽  
High Pressure Stage

This study used Computational Fluid Dynamics (CFD) to investigate modified turbine blade tip shapes as a means of reducing the leakage flow and vortex. The subject of this study was the single-stage experimental turbine facility at Penn State University, with scaled three-dimensional geometry representative of a modern high-pressure stage. To validate the numerical procedure, the rotor flowfield was first computed with no modification to the tip, and the results compared with measurements of the flowfield. The flow was then predicted for a variety of different tip shapes: first with coarse grids for screening purposes and then with more refined grids for final verification of preferred tip geometries. Part 1 of this two-part paper focuses on the turbine case description, numerical procedure, baseline flat-tip computations, and comparison of the baseline results with measurement. A Runge-Kutta time-marching CFD solver (ADPAC) was used to solve the Reynolds-Averaged Navier-Stokes equations. Two-equation turbulence modeling with low Reynolds number adjustments was used for closure. The baseline rotor flowfield was computed twice: with a moderately sized mesh (720,000 nodes) and also with a much more refined mesh (7.2 million nodes). Both solutions showed good agreement with previously taken measurements of the rotor flowfield, including five-hole probe measurements of the velocity and total pressure inside the passage, as well as pressure measurements on the blade and casing surfaces.

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

2000 ◽  
Vol 123 (2) ◽  
pp. 314-323 ◽  
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 focuses on the effect of reduced tip clearance height on the leakage flow and vortex. Reduced tip clearance results 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 is not observed in any of the simulations. Alternative explanations of the leakage vortex’s roll-up are presented. Additional secondary flows that are seen near the casing are also discussed.

The Three Dimensional Flow Structure and Turbulence in the Tip Region of an Axial Flow Compressor

2015 ◽  
Author(s):  
David Tan ◽  
Yuanchao Li ◽  
Huang Chen ◽  
Ian Wilkes ◽  
Joseph Katz
Keyword(s):  
Refractive Index ◽  
Shear Layer ◽  
Flow Rate ◽  
Three Dimensional ◽  
Axial Flow ◽  
Leading Edge ◽  
Suction Side ◽  
Streamwise Velocity ◽  
Leakage Flow ◽  
Single Structure

Continuing preliminary data submitted last year, this paper focuses on effect of operation point on the structure of a tip leakage vortex (TLV) in compressor-like settings. Experiments are being performed at the Johns Hopkins University refractive index-matched facility. The transparent acrylic blades of the one and a half stage compressor have the same geometry, but lower aspect ratio as the inlet guide vanes and the first stage of the Low Speed Axial Compressor facility at NASA Glenn. The refractive index of the liquid, an aqueous NaI solution is matched with that of the blades and transparent casing, facilitating unobstructed stereo-PIV measurements. As the flow rate is reduced close to stall conditions, the leakage flow is confined to rotor chordwise sections further towards the leading edge, and the TLV rollup occurs further upstream, and more radially inward. However, as the leakage flow stops in the aft part of the passage, the near-stall TLV migrates faster to the PS side of the next blade. Instantaneous realizations demonstrate that the TLV consists of multiple interlaced vortices and never rolls up into a single structure, but when phased-averaged, it appears as single structure. The circumferential velocity peak is located radially inward of the mean vorticity center. Turbulent kinetic energy (TKE) is high in the TLV center, in the shear layer connecting the suction side (SS) corner to the TLV feeding vorticity into it, as well as in the region of flow separation on the endwall casing where the leakage flow meets the passage flow. The normal and shear Reynolds stress demonstrate high inhomogeneity and anisotropy, with the streamwise velocity fluctuations being the largest contributor to TKE. The dominant inplane contributors to TKE production rate involve contraction in the region of endwall casing separation and near the SS tip corner, and shear production in the shear layer. Fragmentation and rapid growth of the TLV occurs at mid passage, moving upstream with decreasing flow rate.

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