Rotor-Tip Leakage: Part I—Basic Methodology

1982 ◽  
Vol 104 (1) ◽  
pp. 154-161 ◽  
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.

Aerodynamic Performance of Blade Tip End-Plates Designed for Low-Noise Operation in Axial Flow Fans

2009 ◽  
Vol 131 (8) ◽  
Author(s):  
Alessandro Corsini ◽  
Franco Rispoli ◽  
A. G. Sheard
Keyword(s):  
Flow Behavior ◽  
Acoustic Emissions ◽  
Axial Flow ◽  
Low Noise ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Blade Tip ◽  
Tip Leakage Flows

This study assesses the effectiveness of modified blade-tip configurations in achieving passive noise control in industrial fans. The concepts developed here, which are based on the addition of end-plates at the fan-blade tip, are shown to have a beneficial effect on the fan aeroacoustic signature as a result of the changes they induce in tip-leakage-flow behavior. The aerodynamic merits of the proposed blade-tip concepts are investigated by experimental and computational studies in a fully ducted configuration. The flow mechanisms in the blade-tip region are correlated with the specific end-plate design features, and their role in the creation of overall acoustic emissions is clarified. The tip-leakage flows of the fans are analyzed in terms of vortex structure, chordwise leakage flow, and loading distribution. Rotor losses are also investigated. The modifications to blade-tip geometry are found to have marked effects on the multiple vortex behaviors of leakage flow as a result of changes in the near-wall fluid flow paths on both blade surfaces. The improvements in rotor efficiency are assessed and correlated with the control of tip-leakage flows produced by the modified tip end-plates.

Blade Tip Shape Optimization for Enhanced Turbine Aerothermal Performance

2013 ◽  
Author(s):  
C. De Maesschalck ◽  
S. Lavagnoli ◽  
G. Paniagua
Keyword(s):  
Leakage Flow ◽  
Optimization Strategy ◽  
Flow Conditions ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Turbine Efficiency ◽  
Gap Flow ◽  
Blade Tip ◽  
Tip Leakage Flows

In high-speed unshrouded turbines tip leakage flows generate large aerodynamic losses and intense unsteady thermal loads over the rotor blade tip and casing. The stage loading and rotational speeds are steadily increased to achieve higher turbine efficiency, and hence the overtip leakage flow may exceed the transonic regime. However, conventional blade tip geometries are not designed to cope with supersonic tip flow velocities. A great potential lays in the modification and optimization of the blade tip shape as a means to control the tip leakage flow aerodynamics, limit the entropy production in the overtip gap, manage the heat load distribution over the blade tip and improve the turbine efficiency at high stage loading coefficients. The present paper develops an optimization strategy to produce a set of blade tip profiles with enhanced aerothermal performance for a number of tip gap flow conditions. The tip clearance flow was numerically simulated through two-dimensional compressible Reynolds-Averaged Navier-Stokes (RANS) calculations that reproduce an idealized overtip flow along streamlines. A multi-objective optimization tool, based on differential evolution combined with surrogate models (artificial neural networks), was used to obtain optimized 2D tip profiles with reduced aerodynamic losses and minimum heat transfer variations and mean levels over the blade tip and casing. Optimized tip shapes were obtained for relevant tip gap flow conditions in terms of blade thickness to tip gap height ratios (between 5 and 25), and blade pressure loads (from subsonic to supersonic tip leakage flow regimes) imposing fixed inlet conditions. We demonstrated that tip geometries which perform superior in subsonic conditions are not optimal for supersonic tip gap flows. Prime tip profiles exist depending on the tip flow conditions. The numerical study yielded a deeper insight on the physics of tip leakage flows of unshrouded rotors with arbitrary tip shapes, providing the necessary knowledge to guide the design and optimization strategy of a full blade tip surface in a real 3D turbine environment.

Blade Tip Shape Optimization for Enhanced Turbine Aerothermal Performance

2013 ◽  
Vol 136 (4) ◽  
Author(s):  
C. De Maesschalck ◽  
S. Lavagnoli ◽  
G. Paniagua
Keyword(s):  
Leakage Flow ◽  
Optimization Strategy ◽  
Flow Conditions ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Turbine Efficiency ◽  
Gap Flow ◽  
Blade Tip ◽  
Tip Leakage Flows

In high-speed, unshrouded turbines, tip leakage flows generate large aerodynamic losses and intense unsteady thermal loads over the rotor blade tip and casing. The stage-loading and rotational speeds are steadily increased to achieve higher turbine efficiency, and hence, the overtip leakage flow may exceed the transonic regime. However, conventional blade tip geometries are not designed to cope with supersonic tip flow velocities. A great potential lies in the modification and optimization of the blade tip shape as a means to control the tip leakage flow aerodynamics, limit the entropy production in the overtip gap, manage the heat-load distribution over the blade tip, and improve the turbine efficiency at high-stage loading coefficients. The present paper develops an optimization strategy to produce a set of blade tip profiles with enhanced aerothermal performance for a number of tip gap flow conditions. The tip clearance flow was numerically simulated through two-dimensional compressible Reynolds-averaged Navier–Stokes (RANS) calculations that reproduce an idealized overtip flow along streamlines. A multiobjective optimization tool, based on differential evolution combined with surrogate models (artificial neural networks), was used to obtain optimized 2D tip profiles with reduced aerodynamic losses and minimum heat transfer variations and mean levels over the blade tip and casing. Optimized tip shapes were obtained for relevant tip gap flow conditions in terms of blade thickness to tip gap height ratios (between 5 and 25) and blade pressure loads (from subsonic to supersonic tip leakage flow regimes), imposing fixed inlet conditions. We demonstrated that tip geometries that perform superior in subsonic conditions are not optimal for supersonic tip gap flows. Prime tip profiles exist, depending on the tip flow conditions. The numerical study yielded a deeper insight on the physics of tip leakage flows of unshrouded rotors with arbitrary tip shapes, providing the necessary knowledge to guide the design and optimization strategy of a full blade tip surface in a real 3D turbine environment.

Flow Structures in the Tip Region for a Transonic Compressor Rotor

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Juan Du ◽  
Feng Lin ◽  
Jingyi Chen ◽  
Chaoqun Nie ◽  
Christoph Biela
Keyword(s):  
Numerical Simulations ◽  
Reference Frame ◽  
Three Dimensional ◽  
Flow Structures ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Three Dimensional Flow ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Tip Leakage Flows

Numerical simulations are carried out to investigate flow structures in the tip region for an axial transonic rotor, with careful comparisons with the experimental results. The calculated performance curve and two-dimensional (2D) flow structures observed at casing, such as the shock wave, the expansion wave around the leading edge, and the tip leakage flow at peak efficiency and near-stall points, are all captured by simulation results, which agree with the experimental data well. An in-depth analysis of three-dimensional flow structures reveals three features: (1) there exists an interface between the incoming main flow and the tip leakage flow, (2) in this rotor the tip leakage flows along the blade chord can be divided into at least two parts according to the blade loading distribution, and (3) each part plays a different role on the stall inception mechanism in the leakage flow dominated region. A model of three-dimensional flow structures of tip leakage flow is thus proposed accordingly. In the second half of this paper, the unsteady features of the tip leakage flows, which emerge at the operating points close to stall, are presented and validated with experiment observations. The numerical results in the rotor relative reference frame are first converted to the casing absolute reference frame before compared with the measurements in experiments. It is found that the main frequency components of simulation at absolute reference frame match well with those measured in the experiments. The mechanism of the unsteadiness and its significance to stability enhancement design are then discussed based on the details of the flow field obtained through numerical simulations.

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.

scholarly journals The Effect of Blade Tip Geometry on the Tip Leakage Flow in Axial Turbine Cascades

1991 ◽  
Author(s):  
F. J. G. Heyes ◽  
H. P. Hodson ◽  
G. M. Dailey
Keyword(s):  
Discharge Coefficient ◽  
Suction Side ◽  
Generation Process ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip ◽  
Overall Performance ◽  
Turbine Cascades ◽  
Made In ◽  
Blade Tip Geometry

The phenomenon of tip leakage has been studied in two linear cascades of turbine blades.The investigation includes an examination of the performance of the cascades with a variety of tip geometries. The effects of using plain tips, suction side squealers and pressure side squealers are reported. Traverses of the exit flow field were made in order to determine the overall performance. A method of calculating the tip discharge coefficients for squealer geometries is put forward. In linking the tip discharge coefficient and cascade losses a procedure for predicting the relative performance of tip geometries is developed. The model is used to examine the results obtained using the different tip treatments and to highlight the important aspects of the loss generation process.

Controlling Leakage Flows Over a Rotor Blade Tip Using Air-Curtain Injection: Part II — Rotor Casing Film Cooling

2019 ◽  
Author(s):  
Qiang Zhao ◽  
Xing Yang ◽  
Zhao Liu ◽  
Zhenping Feng ◽  
Terrence W. Simon
Keyword(s):  
Film Cooling ◽  
Leading Edge ◽  
Cooling Effectiveness ◽  
Air Curtain ◽  
Film Cooling Effectiveness ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Blade Tip ◽  
Tip Injection ◽  
Tip Leakage Flows

Abstract In modern gas turbine engines, the rotor casing region experiences high thermal loads due to complex flow structures and aerothermal effects. Thus, casing cooling is one of essential measures to ensure turbine service lifetime and performance. However, studies on heat transfer and cooling over the rotor casing with tip leakage flows are limited in the open literature during the past decades. The present work aims at controlling leakage flows over the blade tip and decreasing heat loads on the rotor casing. A novel approach proposed in a companion paper (GT2019-90232) is adopted in this paper as Part II by introducing an air-curtain injection from the rotor casing through a pair of inclined rows of discrete holes positioned in the range of 30% and 50% axial chord downstream of the blade leading edge in the casing. This air-curtain injection approach is applied to flat and recessed tips with and without tip injection to evaluate its sealing capability on tip leakage flows and film cooling effectiveness on the casing for two injection ratios of 0.7% and 1.0%. In this paper, Reynolds-averaged Navier-Stokes (RANS) simulations with Shear Stress Transport (SST) k-ω turbulence model and γ-Reθ transition model, which are validated with relevant experimental data, are performed to investigate tip leakage flows and film cooling effectiveness on the casing in a single-stage, high-pressure gas turbine engine. Results show that casing injection can reduce tip leakage mass flow effectively by changing the development and migration of tip leakage mass flows, especially when the recessed tip is applied. Adding tip injection would further reduces the tip leakage. The casing injection also provides an excellent cooling effect on the casing across rotor middle chord through trailing edge regions. In the presence of the recessed tip, coolant spreads out well on the rotor tip and the casing surfaces, resulting in better film cooling effectiveness on the casing over rotor tip leading edge. In addition, the tip injection could provide an extra cooling effect in some other regions of the casing.

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

1981 ◽  
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 ◽  
Blade Tip

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.

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.

scholarly journals Shock Formation in Overexpanded Tip Leakage Flow

1992 ◽  
Author(s):  
John Moore ◽  
Kevin M. Elward
Keyword(s):  
Rectangular Channel ◽  
Tip Clearance ◽  
Gas Flows ◽  
Shock Formation ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Hydraulic Analogy ◽  
Tip Leakage Flows ◽  
Turbine Design

Shock formation due to overexpansion of supersonic flow at the inlet to the tip clearance gap of a turbomachine has been studied. The flow was modelled on a water table using a sharp-edged rectangular channel. The flow exhibited an oblique hydraulic jump starting on the channel sidewall near the channel entrance. This flow was analyzed using hydraulic theory. The results suggest a model for the formation of the jump. The hydraulic analogy between free surface water flows and compressible gas flows is used to predict the location and strength of oblique shocks in analogous tip leakage flows. Features of the flow development are found to be similar to those of compressible flow in sharp-edged orifices. Possible implications of the results for high-temperature gas turbine design are considered.

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