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.

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.

Tip Leakage Flow in Radial Inflow Rotor of a Microturbine With Varying Blade-Shroud Clearance

2007 ◽  
Author(s):  
Qinghua Deng ◽  
Jiufang Niu ◽  
Zhenping Feng
Keyword(s):  
Three Dimensional ◽  
Flow Simulation ◽  
Turbine Rotor ◽  
Tip Clearance ◽  
Transverse Mass ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Clearance Flow

In this paper, tip clearance flow in a radial inflow turbine rotor under the stage environment is investigated using a three-dimensional viscous flow simulation with three different blade-shroud gap heights of 1%, 2% and 3% of the local span. The results indicate that more relative casing motion increases the scraping effect on tip leakage flow at the rotor entrance. Also, the scraping flow can dominate the whole tip clearance at the rotor entrance when the velocity is high enough at the rotor tip diameter. Regardless of the transverse mass flow rates of the three tip clearances, the results strongly exhibit the characteristics of linearity when the relative meridional length S is greater than 40%. According to the analysis of leakage flow fields in the tip clearance, measures such as a circumference slot, axial slot, or honeycomb are proposed to be applied and placed at the shroud surface over the exducer of the rotor for effectively reducing the transverse flow.

Numerical Simulation of Tip Clearance Control in Axial Turbine Rotor: Part 2—Passive Control of Five Different Tip Platforms

2008 ◽  
Author(s):  
Wei Li ◽  
Wei-Yang Qiao ◽  
Kai-Fu Xu ◽  
Hua-Ling Luo
Keyword(s):  
Flow Control ◽  
Passive Control ◽  
Suction Side ◽  
Turbine Rotor ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Clearance Flow

The tip leakage flow has significant effects on turbine in loss production, aerodynamic efficiency, etc. Then it’s important to minimize these effects for a better performance by adopting corresponding flow control. The active turbine tip clearance flow control with injection from the tip platform is given in Part-1 of this paper. This paper is Part-2 of the two-part papers focusing on the effect of five different passive turbine tip clearance flow control methods on the tip clearance flow physics, which consists of a partial suction side squealer tip (Partial SS Squealer), a double squealer tip (Double Side Squealer), a pressure side tip shelf with inclined squealer tip on a double squealer tip (Improved PS Squealer), a tip platform extension edge in pressure side (PS Extension) and in suction side (SS Extension) respectively. Combined with the turbine rotor and the numerical method mentioned in Part 1, the effects of passive turbine tip clearance flow controls on the tip clearance flow were sequentially simulated. The detailed tip clearance flow fields with different squealer rims were described with the streamline and the velocity vector in various planes parallel to the tip platform or normal to the tip leakage vortex core. Accordingly, the mechanisms of five passive controls were put in evidence; the effects of the passive controls on the turbine efficiency and the tip clearance flow field were highlighted. The results show that the secondary flow loss near the outer casing including the tip leakage flow and the casing boundary layer can be reduced in all the five passive control methods. Comparing the active control with the passive control, the effect brought by the active injection control on the tip leakage flow is evident. The turbine rotor efficiency could be increased via the rational passive turbine tip clearance flow control. The Improved PS Squealer had the best effect on turbine rotor efficiency, and it increased by 0.215%.

scholarly journals Entropy Analysis of the Flat Tip Leakage Flow with Delayed Detached Eddy Simulation

Entropy ◽  
2018 ◽  
Vol 21 (1) ◽  
pp. 21 ◽  
Author(s):  
Hui Li ◽  
Xinrong Su ◽  
Xin Yuan
Keyword(s):  
Tip Clearance ◽  
Flow Structures ◽  
Leakage Flow ◽  
Detached Eddy Simulation ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Passage Vortex ◽  
Unsteady Effects

In unshrouded turbine rotors, the tip leakage vortices develop and interact with the passage vortices. Such complex leakage flow causes the major loss in the turbine stage. Due to the complex turbulence characteristics of the tip leakage flow, the widely used Reynolds Averaged Navier–Stokes (RANS) approach may fail to accurately predict the multi-scale turbulent flow and the related loss. In order to effectively improve the turbine efficiency, more insights into the loss mechanism are required. In this work, a Delayed Detached Eddy Simulation (DDES) study is conducted to simulate the flow inside a high pressure turbine blade, with emphasis on the tip region. DDES results are in good agreement with the experiment, and the comparison with RANS results verifies the advantages of DDES in resolving detailed flow structures of leakage flow, and also in capturing the complex turbulence characteristics. The snapshot Proper Orthogonal Decomposition (POD) method is used to extract the dominant flow features. The flow structures and the distribution of turbulent kinetic energy reveal the development of leakage flow and its interaction with the secondary flow. Meanwhile, it is found that the separation bubble (SB) is formed in tip clearance. The strong interactions between tip leakage vortex (TLV) and the up passage vortex (UPV) are the main source of unsteady effects which significantly enhance the turbulence intensity. Based on the DDES results, loss analysis of tip leakage flow is conducted based on entropy generation rates. It is found that the viscous dissipation loss is much stronger than heat transfer loss. The largest local loss occurs in the tip clearance, and the interaction between the leakage vortex and up passage vortex promotes the loss generation. The tip leakage flow vortex weakens the strength of up passage vortex, and loss of up passage flow is reduced. Comparing steady and unsteady effects to flow field, we found that unsteady effects of tip leakage flow have a large influence on flow loss distribution which cannot be ignored. To sum up, the current DDES study about the tip leakage flow provides helpful information about the loss generation mechanism and may guide the design of low-loss blade tip.

scholarly journals Computation of Flow Past a Turbine Blade With and Without Tip Clearance

1991 ◽  
Author(s):  
W. R. Briley ◽  
D. V. Roscoe ◽  
H. J. Gibeling ◽  
R. C. Buggeln ◽  
J. S. Sabnis ◽  
...  
Keyword(s):  
Stokes Equations ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Turbine Rotor ◽  
Tip Clearance ◽  
Navier Stokes ◽  
Main Stream ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Gas Generator

Three-dimensional solutions of the ensemble-averaged Navier-Stokes equations have been computed for a high-turning turbine rotor passage, both with and without tip clearance effects. The geometry is Pratt & Whitney’s preliminary design for the Generic Gas Generator Turbine (GGGT), having an axial chord of 0.5 inch and turning angle of about 160 degrees. The solutions match the design Reynolds number of 3x 106/inch and design inflow/outflow distributions of flow quantities. The grid contains 627,000 points, including 20 radial points in the clearance gap of 0.015 inch, and has a minimum spacing of 10−4 inch adjacent to all surfaces. The solutions account for relative motion of the blade and shroud surfaces and include a backstep on the shroud. Computed results are presented which show the general flow behavior, especially near the tip clearance and backstep regions. The results are generally consistent with experimental observations for other geometries having thinner blades and smaller turning angles. The leakage flow includes some fluid originally in the freestream at 91 percent span. Downstream, the leakage flow behaves as a wall jet directed at 100 degrees to the main stream, with total pressure and temperature higher than the freestream. Radial distributions of circumferentially-averaged flow quantities are compared for solutions with and without tip leakage flow. Two-dimensional solutions are also presented for the mid-span blade geometry for design and off-design inflow angles.

Active Tip Clearance Flow Control for an Axial-Flow Turbine Rotor Using Ring-Type Plasma Actuators

2014 ◽  
Author(s):  
Takayuki Matsunuma ◽  
Takehiko Segawa
Keyword(s):  
Flat Plate ◽  
Turbine Rotor ◽  
Plasma Actuator ◽  
Tip Clearance ◽  
Plasma Actuators ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Ring Type ◽  
Tip Leakage ◽  
Blade Tip

Tip leakage flow through the small gap between the blade tip and the casing wall in turbomachinery reduces the aerodynamic performance of the blade. New ring-type dielectric barrier discharge (DBD) plasma actuators have been developed to facilitate active control of the tip leakage flow of a turbine rotor. In the present study, the ring-type plasma actuators consisted of metallic wires coated with insulation material, mounted in an insulator embedded in the tip casing wall. For the fundamental experiments using a flat plate and a single airfoil with tip clearance, particle image velocimetry (PIV) was used to obtain two-dimensional velocity field measurements near the plate and blade tip regions. From flat plate experiments in a static flow field, it was confirmed that the operation of the plasma actuator generates an upward flow at the corner between the blade tip and the casing wall, and this forms a perpendicular obstacle to the tip leakage flow. In flat plate experiments on tip leakage flow in a wind tunnel, the forcibly-induced tip leakage flow was successfully dissipated by means of the plasma actuator flow control. In single airfoil experiments, the tip leakage flow was also reduced by the plasma actuator. In annular turbine rotor experiments, the plasma emission at the blade tip and its motion with blade rotation were determined. Single-element hot-wire anemometry was used to measure the turbulence intensity distributions at the turbine rotor exit. The amplitude of input voltage for the plasma actuator was varied from ±3.0 to ±6.0 kV. The high turbulence intensity region created by the tip leakage flow was reduced with an increase in the input voltage of the plasma actuator.

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.

PIV Maps of Tip Leakage and Secondary Flow Fields on a Low Speed Turbine Blade Cascade With Moving Endwall

2005 ◽  
Author(s):  
P. Palafox ◽  
M. L. G. Oldfield ◽  
J. E. LaGraff ◽  
T. V. Jones
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Field Measurements ◽  
Turbine Rotor ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Low Speed ◽  
Tip Leakage

New, detailed flow field measurements are presented for a very large low-speed cascade representative of a high-pressure turbine rotor blade with turning of 110 degrees and blade chord of 1.0 m. Data was obtained for tip leakage and passage secondary flow at a Reynolds number of 4.0 × 105, based on exit velocity and blade axial chord. Tip clearance levels ranged from 0% to 1.68% of blade span (0% to 3% of blade chord). Particle Image Velocimetry (PIV) was used to obtain flow field maps of several planes parallel to the tip surface within the tip gap, and adjacent passage flow. Vector maps were also obtained for planes normal to the tip surface in the direction of the tip leakage flow. Secondary flow was measured at planes normal to the blade exit angle at locations upstream and downstream of the trailing edge. The interaction between the tip leakage vortex and passage vortex is clearly defined, revealing the dominant effect of the tip leakage flow on the tip endwall secondary flow. The relative motion between the casing and the blade tip was simulated using a motor-driven moving belt system. A reduction in the magnitude of the under-tip flow near the endwall due to the moving wall is observed and the effect on the tip leakage vortex examined.

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.

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