Rotor-Tip Leakage: Part II — Design Optimization Through Viscous Analysis and Experiment

Blade tip losses represent a major efficiency penalty in a turbine rotor. These losses are presently controlled by maintaining close tolerances on tip clearances. This two-part paper outlines a new methodology for predicting and minimizing tip flows, and focuses on the control of tip leakage through minimization of the discharge coefficient to control the normal leakage flow component. Minimization of the discharge coefficient was achieved through viscous analysis and was supported by discharge-rig testing. The analysis for the discharge cross-flow used a stream function-vorticity formulation. Support testing was conducted with a newly developed water table discharge rig in which tip-coolant discharge could also be simulated. Experimental and numerical tip-leakage results are presented on a discharge coefficient parameter for five different tip configurations. In addition, numerical studies were conducted for stationary and rotating blades with and without tip coolant injection.

Rotor-Tip Leakage: Part II—Design Optimization Through Viscous Analysis and Experiment

Journal of Engineering for Power ◽

10.1115/1.3227245 ◽

1982 ◽

Vol 104 (1) ◽

pp. 162-169 ◽

Cited By ~ 21

Author(s):

A. R. Wadia ◽

T. C. Booth

Keyword(s):

Stream Function ◽

Discharge Coefficient ◽

Cross Flow ◽

Turbine Rotor ◽

Leakage Flow ◽

Tip Leakage ◽

Rotating Blades ◽

Numerical Studies ◽

Coolant Injection ◽

Volume 1: Aircraft Engine; Marine; Turbomachinery; Microturbines and Small Turbomachinery ◽

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

10.1115/97-gt-421 ◽

1997 ◽

Cited By ~ 3

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 ◽

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.

Characteristics of Tip Leakage Flow of the Turbine Blade With Cutback Squealer and Coolant Injection

Volume 7: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2010-22566 ◽

2010 ◽

Author(s):

Jianhua Wang ◽

Yalin Liu ◽

Xiaochun Wang ◽

Zhineng Du ◽

Shijie Yang

Keyword(s):

Turbine Blade ◽

Film Cooling ◽

Flow Characteristics ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Coolant Injection ◽

Blade Tip ◽

Film Cooling Holes ◽

Numerical Program

Experimental and numerical investigations of the tip leakage flow characteristics between turbine blade tip and stator wall (shroud) were conducted by a particle image velocimetry (PIV) system and the commercially available software CFX 11.0. A three-time scaled profile of the GE-E3 blade was used as specimen. Two rows of cylindrical film-cooling holes with 1.5mm diameter were arranged in the blade tip. One row with 5 holes was placed in pressure side just below the groove floor, and the other with 11 holes was equidistantly arranged on the tip along the mid camber line. To exhibit the generation and movement of leakage vortex, and to compare the coolant injection effects from different rows, several typical velocity profiles were captured by the PIV system. The experimental results were used as a data source to validate the turbulence model and numerical program. To better understand the mixing characteristics of the coolant injected from different rows with the leakage flow, the fluid fields of the leakage vortex and coolant flow were simulated, and the leakage mass rates from the blade tip in different coolant injection cases and different gaps were quantitatively estimated by the validated numerical program.

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

Volume 2C: Turbomachinery ◽

10.1115/gt2014-26390 ◽

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 ◽

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.

Rotor-Tip Leakage: Part I—Basic Methodology

Journal of Engineering for Power ◽

10.1115/1.3227244 ◽

1982 ◽

Vol 104 (1) ◽

pp. 154-161 ◽

Cited By ~ 76

Author(s):

T. C. Booth ◽

P. R. Dodge ◽

H. K. Hepworth

Keyword(s):

Discharge Coefficient ◽

Tangential Velocity ◽

Turbine Rotor ◽

Normal Velocity ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Leakage Flows ◽

Component Identification ◽

Blade Tip ◽

Tip Leakage Flows

Blade tip losses represent a major efficiency penalty in a turbine rotor. These losses are presently controlled by maintaining close tolerances on tip clearances. This two-part paper outlines a new methodology for predicting and minimizing tip leakage flows. Part I of the paper describes a series of experiments and analyses which indicated a predominantly inviscid nature of tip leakage flow. The experiments were conducted on a series of three water flow rigs in which leakage quantities were measured over simulated blade tips. As a result of the experiments, a simple tip-leakage model is proposed that treats the normal velocity component in terms of discharge coefficient and conserves the tangential velocity (momentum) component. Identification of tip leakage controlled by a normal discharge coefficient suggests an optimum tip-treatment configuration may be designed through discharge testing of candidate configurations. A preliminary design optimization was conducted on the simple discharge rigs, and the results were evaluated on the water table cascade rig and on a turbine stage.

Investigation of Turbine Cascade Blades With Part-Span Sweep With an Open End

Volume 6A: Turbomachinery ◽

10.1115/gt2013-95314 ◽

2013 ◽

Author(s):

Rachel Trehan ◽

Bhaskar Roy

Keyword(s):

Flow Rate ◽

Cross Flow ◽

Turbine Rotor ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Turbine Rotor Blade ◽

Pressure Losses ◽

Tip Leakage ◽

Mainstream Flow ◽

The Impact

The present paper focuses on a low-speed computational investigation into the application of backward sweep for application on a typical low-pressure turbine rotor blade. A quasi-two-dimensional linear cascade using T106 profile, was investigated using flow solver Star-CCM+®. Three backward-swept tip modifications (axial sweep, tangential sweep, and a combination of both) have been applied to the baseline profile from 90%–100% span, the rest of the 90% of the blade remained straight and orthogonal to the cascade mainstream flow. The blade stacking axis near the tip was shifted away from the mainstream flow for all three sweep configurations at 15°, 30°, and 45° from the blade axis plane. The impact on pressure losses, tip blade loading, and reduction of tip leakage flow and associated vortices has been analyzed. As the leakage vortex increases in size, causing enhanced blockage to the passage flow, rotor work extraction capability decreases. The application of backward sweep to the blade tip increases the tip cross flow rate, but reduces the turbulent kinetic energy (TKE) across the tip gap. The reduction of TKE of the leakage flow, results in a smaller and less intense tip leakage vortex even though the cross flow rate increases. Minimizing the leakage vortex size and intensity reduces total pressure losses and thereby improves rotor efficiency.

Investigation of Leakage Flow and Heat Transfer in a Gas Turbine Blade Tip With Emphasis on the Effect of Rotation

Volume 4: Heat Transfer, Parts A and B ◽

10.1115/gt2008-51215 ◽

2008 ◽

Author(s):

Dianliang Yang ◽

Xiaobing Yu ◽

Zhenping Feng

Keyword(s):

Heat Transfer ◽

Relative Motion ◽

Turbulence Models ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Blade Height ◽

Tip Leakage ◽

Flow And Heat Transfer ◽

Blade Rotation ◽

In this paper, numerical methods have been applied to the investigation of the effect of rotation on the blade tip leakage flow and heat transfer. Using the first stage rotor blade of GE-E3 engine high pressure turbine, both flat tip and squealer tip have been studied. The tip gap height is 1% of the blade height, and the groove depth of the squealer tip is 2% of the blade height. Heat transfer coefficient on tip surface obtained by using different turbulence models was compared with experimental results. And the grid independence study was carried out by using the Richardson extrapolation method. The effect of the blade rotation was studied in the following cases: 1) blade domain is rotating and shroud is stationary; 2) blade domain is stationary and shroud is rotating; and 3) both blade domain and shroud are stationary. In this approach, the effects of the relative motion of the endwall, the centrifugal force and the Coriolis force can be investigated respectively. By comparing the results of the three cases discussed, the effects of the blade rotation on tip leakage flow and heat transfer are revealed. It indicated that the main effect of the rotation on the tip leakage flow and heat transfer is resulted from the relative motion of the shroud, especially for the squealer tip blade.

Effect of Active Modulation of Through-Casing Coolant Injection on Turbine Efficiency

Volume 2A: Turbomachinery ◽

10.1115/gt2017-64705 ◽

2017 ◽

Cited By ~ 1

Author(s):

Brian M. T. Tang ◽

Marko Bacic ◽

Peter T. Ireland

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Total Pressure ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Turbine Efficiency ◽

Coolant Injection ◽

Cooling Air

This paper presents a computational investigation into the impact of cooling air injected through the stationary over-tip turbine casing on overall turbine efficiency. The high work axial flow turbine is representative of the high pressure turbine of a civil aviation turbofan engine. The effect of active modulation of the cooling air is assessed, as well as that of the injection locations. The influence of the through-casing coolant injection on the turbine blade over-tip leakage flow and the associated secondary flow features are examined. Transient (unsteady) sliding mesh simulations of a one turbine stage rotor-stator domain are performed using periodic boundary conditions. Cooling air configurations with a constant total pressure air supply, constant mass flow rate and actively controlled total pressure supply are assessed for a single geometric arrangement of cooling holes. The effects of both the mass flow rate of cooling air and the location of its injection relative to the turbine rotor blade are examined. The results show that all of the assessed cooling configurations provided a benefit to turbine row efficiency of between 0.2 and 0.4 percentage points. The passive and constant mass flow rate configurations reduced the over-tip leakage flow, but did so in an inefficient manner, with decreasing efficiency observed with increasing injection mass flow rate beyond 0.6% of the mainstream flow, despite the over-tip leakage mass flow rate continuing to reduce. By contrast, the active total pressure controlled injection provided a more efficient manner of controlling this leakage flow, as it permitted a redistribution of cooling air, allowing it to be applied in the regions close to the suction side of the blade tip which more directly reduced over-tip leakage flow rates and hence improved efficiency. Cooling air injected close to the pressure side of the rotor blade was less effective at controlling the leakage flow, and was associated with increased aerodynamic loss in the passage vortex.

A Summary of the Cooled Turbine Blade Tip Heat Transfer and Film Effectiveness Investigations Performed by Dr. D. E. Metzger

Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/94-gt-167 ◽

1994 ◽

Author(s):

Y. W. Kim ◽

W. Abdel-Messeh ◽

J. P. Downs ◽

F. O. Soechting ◽

G. D. Steuber ◽

...

Keyword(s):

Heat Transfer ◽

Turbine Blade ◽

Film Cooling ◽

Convection Heat Transfer ◽

Secondary Flows ◽

Test Surface ◽

Leakage Flow ◽

Test Technique ◽

Coolant Injection ◽

The clearance gap between the stationary outer air seal and blade tips of an axial turbine allows a clearance gap leakage flow to be driven through the gap by the pressure-to-suction side pressure difference. The presence of strong secondary flows on the pressure side of the airfoil tends to deliver air from the hottest regions of the mainstream to the clearance gap. The blade tip region, particularly near the trailing edge, is very difficult to cool adequately with blade internal coolant flow. In this case, film cooling injection directly onto the blade tip region can be used in an attempt to directly reduce the heat transfer rates from the hot gases in the clearance gap to the blade tip. The present paper is intended as a memorial tribute to the late Professor Darryl E. Metzger who has made significant contributions in this particular area over the past decade. A summary of this work is made to present the results of his more recent experimental work that has been performed to investigate the effects of film coolant injection on convection heat transfer to the turbine blade tip for a variety of tip shapes and coolant injection configurations. Experiments are conducted with blade tip models that are stationary relative to the simulated outer air seal based on the result of earlier works that found the leakage flow to be mainly a pressure-driven flow which is related strongly to the airfoil pressure loading distribution and only weakly, if at all, to the relative motion between blade tip and shroud. Both heat transfer and film effectiveness are measured locally over the test surface using a transient thermal liquid crystal test technique with a computer vision data acquisition and reduction system for various combinations of clearance heights, clearance flow Reynolds numbers, and film flow rates with different coolant injection configurations. The present results reveal a strong dependency of film cooling performance on the choice of the coolant supply hole shapes and injection locations for a given tip geometry.

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

Volume 6: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2008-50085 ◽

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%.