An Experimental and Computational Study of the Formation of a Streamwise Shed Vortex in a Turbine Stage

2003 ◽  
Vol 125 (2) ◽  
pp. 291-297 ◽  
Author(s):  
Graham Pullan ◽  
John Denton ◽  
Michael Dunkley
Keyword(s):  
Shear Layer ◽  
Computational Study ◽  
Vortex Sheet ◽  
Surface Flow ◽  
Secondary Flows ◽  
Angle Distribution ◽  
Trailing Edge ◽  
Aircraft Wings ◽  
Yaw Angle ◽  
Stator Design

Shear layers shed by aircraft wings roll up into vortices. A similar, though far less common, phenomenon can occur in the wake of a turbomachine blade. This paper presents experimental data from a new single-stage turbine that has been commissioned at the Whittle Laboratory. Two low-aspect ratio stators have been tested with the same rotor row. Surface flow visualization illustrates the extremely strong secondary flows present in both NGV designs. These secondary flows lead to conventional passage vortices, but also to an intense vortex sheet which is shed from the trailing edge of the blades. Pneumatic probe traverses show how this sheet rolls up into a concentrated vortex in the second stator design, but not in the first. A simple numerical experiment is used to model the shear layer instability and the effects of trailing edge shape and exit yaw angle distribution are investigated. It is found that the latter has a strong influence on shear layer rollup: inhibiting the formation of a vortex downstream of NGV 1 but encouraging it behind NGV 2.

An Experimental and Computational Study of the Formation of a Streamwise Shed Vortex in a Turbine Stage

2002 ◽  
Author(s):  
Graham Pullan ◽  
John Denton ◽  
Michael Dunkley
Keyword(s):  
Shear Layer ◽  
Computational Study ◽  
Vortex Sheet ◽  
Surface Flow ◽  
Secondary Flows ◽  
Flow Visualisation ◽  
Angle Distribution ◽  
Trailing Edge ◽  
Aircraft Wings ◽  
Yaw Angle

Shear layers shed by aircraft wings roll up into vortices. A similar, though far less common, phenomenon can occur in the wake of a turbomachine blade. This paper presents experimental data from a new single stage turbine that has been commissioned at the Whittle Laboratory. Two low aspect ratio stators have been tested with the same rotor row. Surface flow visualisation illustrates the extremely strong secondary flows present in both NGV designs. These secondary flows lead to conventional passage vortices but also to an intense vortex sheet which is shed from the trailing edge of the blades. Pneumatic probe traverses show how this sheet rolls up into a concentrated vortex in the second stator design, but not in the first. A simple numerical experiment is used to model the shear layer instability and the effects of trailing edge shape and exit yaw angle distribution are investigated. It is found that the latter has a strong influence on shear layer rollup: inhibiting the formation of a vortex downstream of NGV 1 but encouraging it behind NGV 2.

Computational Study of the Risø-B1-18 Airfoil with a Hinged Flap Providing Variable Trailing Edge Geometry

2005 ◽  
Vol 29 (2) ◽  
pp. 89-113 ◽  
Author(s):  
Niels Troldborg
Keyword(s):  
Reynolds Number ◽  
Unsteady Flow ◽  
Computational Study ◽  
Turbine Blades ◽  
Aerodynamic Characteristics ◽  
Flow Conditions ◽  
Wind Turbine Blades ◽  
Trailing Edge ◽  
Edge Geometry ◽  
Fully Developed Turbulent Flow

A comprehensive computational study, in both steady and unsteady flow conditions, has been carried out to investigate the aerodynamic characteristics of the Risø-B1-18 airfoil equipped with variable trailing edge geometry as produced by a hinged flap. The function of such flaps should be to decrease fatigue-inducing oscillations on the blades. The computations were conducted using a 2D incompressible RANS solver with a k-w turbulence model under the assumption of a fully developed turbulent flow. The investigations were conducted at a Reynolds number of Re = 1.6 · 106. Calculations conducted on the baseline airfoil showed excellent agreement with measurements on the same airfoil with the same specified conditions. Furthermore, a more widespread comparison with an advanced potential theory code is presented. The influence of various key parameters, such as flap shape, flap size and oscillating frequencies, was investigated so that an optimum design can be suggested for application with wind turbine blades. It is concluded that a moderately curved flap with flap chord to airfoil curve ratio between 0.05 and 0.10 would be an optimum choice.

Measurements of Secondary Losses in a Turbine Cascade With the Implementation of Nonaxisymmetric Endwall Contouring

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
D. C. Knezevici ◽  
S. A. Sjolander ◽  
T. J. Praisner ◽  
E. Allen-Bradley ◽  
E. A. Grover
Keyword(s):  
Kinetic Energy ◽  
Axial Flow ◽  
Surface Flow ◽  
Secondary Flows ◽  
Test Facility ◽  
Suction Surface ◽  
Blade Passage ◽  
Low Pressure Turbine ◽  
Endwall Contouring ◽  
Pressure And Velocity Measurements

An approach to endwall contouring has been developed with the goal of reducing secondary losses in highly loaded axial flow turbines. The present paper describes an experimental assessment of the performance of the contouring approach implemented in a low-speed linear cascade test facility. The study examines the secondary flows of a cascade composed of Pratt & Whitney PAKB airfoils. This airfoil has been used extensively in low-pressure turbine research, and the present work adds intrapassage pressure and velocity measurements to the existing database. The cascade was tested at design incidence and at an inlet Reynolds number of 126,000 based on inlet midspan velocity and axial chord. Quantitative results include seven-hole pneumatic probe pressure measurements downstream of the cascade to assess blade row losses and detailed seven-hole probe measurements within the blade passage to track the progression of flow structures. Qualitative results take the form of oil surface flow visualization on the endwall and blade suction surface. The application of endwall contouring resulted in lower secondary losses and a reduction in secondary kinetic energy associated with pitchwise flow near the endwall and spanwise flow up the suction surface within the blade passage. The mechanism of loss reduction is discussed in regard to the reduction in secondary kinetic energy.

Lift Control Using MEMS-Based Moving Trailing-Edge Tabs

2002 ◽  
Author(s):  
C. P. van Dam ◽  
C. Bauer ◽  
D. T. Yen Nakafuji
Keyword(s):  
Lift Coefficient ◽  
Aerodynamic Characteristics ◽  
Trailing Edge ◽  
Aircraft Wings ◽  
Lifting Surface ◽  
Lifting Surfaces ◽  
Lift Control

Micro-electro-mechanical (MEM) translational tabs are introduced for active lift control on aircraft. These tabs are mounted near the trailing edge of lifting surfaces such as aircraft wings and tails, deploy approximately normal to the surface, and have a maximum deployment height on the order of one percent of the section chord. Deployment of the tab effectively changes the sectional camber, thereby changing the aerodynamic characteristics of a lifting surface. Tabs with said deployment height generate a change in the section lift coefficient of approximately ±0.3. The microtab design and the techniques used to fabricate and test the tabs are presented.

Aero-Thermal Investigation of a Rib-Roughened Trailing Edge Channel With Crossing-Jets: Part I—Flow Field Analysis

2008 ◽  
Author(s):  
Alessandro Armellini ◽  
Filippo Coletti ◽  
Tony Arts ◽  
Christophe Scholtes
Keyword(s):  
Flow Field ◽  
Computational Study ◽  
Three Dimensional ◽  
Side Wall ◽  
Field Analysis ◽  
Trailing Edge ◽  
Present Contribution ◽  
Numerical Predictions ◽  
Flow Features ◽  
Rib Roughened

The present contribution addresses the aero-thermal experimental and computational study of a trapezoidal cross-section model simulating a trailing edge cooling cavity with one rib-roughened wall. The flow is fed through tilted slots on one side wall and exits through straight slots on the opposite side wall. The flow field aerodynamics is investigated in part I of the paper. The reference Reynolds number is defined at the entrance of the test section and set at 67500 for all the experiments. A qualitative flow model is deduced from surface-streamline flow visualizations. Two-dimensional Particle Image Velocimetry measurements are performed in several planes around mid-span of the channel and recombined to visualize and quantify three-dimensional flow features. The jets issued from the tilted slots are characterized and the jet-rib interaction is analyzed. Attention is drawn to the motion of the flow deflected by the rib-roughened wall and impinging on the opposite smooth wall. The experimental results are compared with the numerical predictions obtained from the finite volume, RANS solver CEDRE.

Turbine Nozzle Endwall Phantom Cooling With Compound Angled Pressure Side Injection

2018 ◽  
Author(s):  
Kevin Liu ◽  
Hongzhou Xu ◽  
Michael Fox
Keyword(s):  
Film Cooling ◽  
High Speed ◽  
Axial Direction ◽  
Secondary Flows ◽  
Test Case ◽  
Pressure Side ◽  
Complex Flow ◽  
Trailing Edge ◽  
Cooling Effectiveness ◽  
Extended Area

Cooling of the turbine nozzle endwall is challenging due to its complex flow field involving strong secondary flows. Increasingly-effective cooling schemes are required to meet the higher turbine inlet temperatures required by today’s gas turbine applications. Therefore, in order to cool the endwall surface near the pressure side of the airfoil and the trailing edge extended area, the spent cooling air from the airfoil film cooling and pressure side discharge slots, referred to as “phantom cooling” is utilized. This paper studies the effect of compound angled pressure side injection on nozzle endwall surface. The measurements were conducted in a high speed linear cascade, which consists of three nozzle vanes and four flow passages. Two nozzle test models with a similar film cooling design were investigated, one with an axial pressure side film cooling row and trailing edge slots; the other with the same cooling features but with compound angled injection, aiming at the test endwall. Phantom cooling effectiveness on the endwall was measured using a Pressure Sensitive Paint (PSP) technique through the mass transfer analogy. Two-dimensional phantom cooling effectiveness distributions on the endwall surface are presented for four MFR (Mass Flow Ratio) values in each test case. Then the phantom cooling effectiveness distributions are pitchwise-averaged along the axial direction and comparisons were made to show the effect of the compound angled injection. The results indicated that the endwall phantom cooling effectiveness increases with the MFR significantly. A compound angle of the pressure side slots also enhanced the endwall phantom cooling significantly. For combined injections, the phantom cooling effectiveness is much higher than the pressure side slots injection only in the endwall downstream extended area.

The Aerodynamics of Trailing-Edge-Cooled Transonic Turbine Blades: Part 2 — Theoretical and Computational Approach

1997 ◽  
Author(s):  
Mathias Deckers ◽  
John D. Denton
Keyword(s):  
Transonic Flow ◽  
Theoretical Study ◽  
Computational Study ◽  
Control Volume ◽  
Turbine Blades ◽  
Computational Approach ◽  
Trailing Edge ◽  
Time Marching ◽  
Transonic Turbine ◽  
Volume Method

A theoretical and computational study into the aerodynamics of trailing-edge-cooled transonic turbine blades is described in this part of the paper. The theoretical study shows that, for unstaggered blades with coolant ejection, the base pressure and overall loss can be determined exactly by a simple control volume analysis. This theory suggests that a thick, cooled trailing edge with a wide slot can be more efficient than a thin, solid trailing edge. An existing time-marching finite volume method is adapted to calculate the transonic flow with trailing edge coolant ejection on a structured, quasi-orthogonal mesh. Good overall agreement between the present method, inviscid and viscous, and experimental evidence is obtained.

scholarly journals Effects of a Curved Trailing Edge on Growth of a Compressible Shear Layer-Comparison between Single and Double Shear Layers-

2005 ◽  
Vol 53 (620) ◽  
pp. 408-413
Author(s):  
Mikiya Araki ◽  
Jun Osaka ◽  
Osamu Imamura ◽  
Mitsuhiro Tsue ◽  
Michikata Kono
Keyword(s):  
Shear Layer ◽  
Shear Layers ◽  
Trailing Edge ◽  
Double Shear

Nonaxisymmetric Convection in Stationary Gas Tungsten Arc Weld Pools

1997 ◽  
Vol 119 (1) ◽  
pp. 164-172 ◽  
Author(s):  
Y. Joshi ◽  
P. Dutta ◽  
P. E. Schupp ◽  
D. Espinosa
Keyword(s):  
Computational Study ◽  
Numerical Models ◽  
Three Dimensional ◽  
Pulsed Laser ◽  
Surface Flow ◽  
Rotational Flow ◽  
Visualization System ◽  
Gas Tungsten Arc ◽  
Laser Visualization ◽  
Weld Pools

Observations of surface flow patterns of steel and aluminum GTAW pools have been made using a pulsed laser visualization system. The weld pool convection is found to be three-dimensional, with the azimuthal circulation depending on the location of the clamp with respect to the torch. Oscillation of steel pools and undulating motion in aluminum weld pools are also observed even with steady process parameters. Current axisymmetric numerical models are unable to explain such phenomena. A three-dimensional computational study is carried out in this study to explain the rotational flow in aluminum weld pools.

Production and Development of Secondary Flows and Losses Within a Three Dimensional Turbine Stator Cascade

1985 ◽  
Author(s):  
A. Yamamoto ◽  
R. Yanagi
Keyword(s):  
Three Dimensional ◽  
Quantitative Information ◽  
Secondary Flows ◽  
Suction Surface ◽  
Trailing Edge ◽  
Loss Mechanism ◽  
Flow Measurements ◽  
Aerodynamic Loss ◽  
Vortical Flows ◽  
Turbine Stator

Using five-hole pitot tubes, detailed flow measurements were made before, within and after a low-speed three-dimensional turbine stator blade row to obtain quantitative information on the aerodynamic loss mechanism. Qualitative flow visualization tests and endwall static pressure measurements were also made. An analysis of the tests revealed that many vortical flows promote loss generation. Within a large part of the cascade, a major loss process could be explained simply as the migration of boundary layer low energy fluids from surrounding walls (endwalls and blade surfaces) to the blade suction surface near the trailing edge. On the other hand, complexity exists after the cascade and in the vortical flows near the trailing edge. The strong trailing shedding vortices affect upstream flow fields within the cascade. Detailed flow surveys within the cascade under the effects of blade tip leakage flows are also included.

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