Three-Dimensional Velocity Measurements of Film Cooling Flow Under Favorable Pressure Gradient

2012 ◽  
Author(s):  
Filippo Coletti ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Pressure Gradient ◽  
Film Cooling ◽  
Flow Direction ◽  
Three Dimensional ◽  
Vortex Pair ◽  
Strong Impact ◽  
Cooling Flow ◽  
Magnetic Resonance Velocimetry ◽  
Favorable Pressure Gradient ◽  
Streamwise Pressure Gradient

This paper addresses the effect of a favorable streamwise pressure gradient on the velocity field of a single-hole film cooling configuration, operating at unity blowing ratio. The hole is circular and inclined at 30 degrees with respect to the main flow direction. Magnetic Resonance Velocimetry is used to obtain the full three-dimensional field for a baseline configuration with negligible streamwise pressure gradient and for a configuration with favorable streamwise pressure gradient. In the latter case the acceleration parameter is K = 4.8·10−6, which is representative of the conditions along the pressure side of a turbine airfoil. The experiments are performed in water. The velocity and vorticity distributions highlight the strong impact of the favorable pressure gradient on the development of the counter-rotating vortex pair which dominates the dynamics of the film cooling flow. The accelerating flow drives the vortex pair towards the wall, while the increased stretching of the vortices augments their circulation. Both effects contribute to bring the counter-rotating vortices closer to each other. They also persist much further in space with respect to the zero-pressure-gradient case. Implications for the film cooling performance are discussed.

Aerodynamic Analysis of Film Cooling Jet Under Different Main Stream Pressure Gradient

2015 ◽  
Author(s):  
Yanmin Qin ◽  
Hong Yin ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Film Cooling ◽  
Loss Coefficient ◽  
Spanwise Direction ◽  
Main Stream ◽  
Aerodynamic Loss ◽  
Favorable Pressure Gradient ◽  
Streamwise Pressure Gradient ◽  
Compound Angle

Streamwise pressure gradient is an important characteristic of the turbine flow and compound angle film cooling is a sufficient way to improve cooling performance. Both experimental and numerical studies are carried out to investigate the effect of streamwise pressure gradient and film cooling hole compound angle on aerodynamic loss of film cooling. Stronger mainstream favorable pressure gradient leads to a larger discharge coefficient. The effect of momentum supplement of the coolant jet with large blowing ratios is significant when pressure loss coefficient is investigated. Kinetic loss coefficient considering the kinetic energy of the coolant jet is used to investigate the overall aerodynamic loss of film cooling. The kinetic loss coefficient increases with blowing ratio. Favorable pressure gradient decreases the loss coefficient. The boundary layer is quite thick for adverse and moderate favorable pressure gradient case that the coolant jet remains within the boundary layer which increases the mixing loss. The kinetic loss coefficient of compound angle film cooling is about 40% higher than the axial hole. This is due to the dissipation of the momentum component in the spanwise direction and the stronger shearing between the single large vortex formed by the compound angle injection with the main flow.

Pitfalls of Fan-Shaped Hole Design: Insights From Experimental Measurement of In-Hole Flow Through MRV

2017 ◽  
Author(s):  
Emin Issakhanian ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Film Cooling ◽  
Vortex Pair ◽  
Cooling Effectiveness ◽  
Cooling Flow ◽  
Magnetic Resonance Velocimetry ◽  
Cooling Hole ◽  
Good Improvement ◽  
Flow Through ◽  
Shaped Hole ◽  
Lift Off

Film cooling jets from discrete round holes are very susceptible to jet lift-off which reduces surface effectiveness. Since the experiments of Goldstein et al. (1974), shaped holes have become prominent for improved coolant coverage. Fan-shaped holes are the most common design and have shown good improvement over round holes. However, fan-shaped holes introduce additional parameters to the already complex task of modeling cooling effectiveness. This study presents velocity and vorticity fields measured using high-resolution magnetic resonance velocimetry (MRV) to study three different fan-shaped hole geome tries at two blowing ratios. Because MRV does not require line of sight, it provides otherwise hard to obtain experimental data of the flow within the film cooling hole in addition to the mainflow measurements. By allowing measurement within the cooling hole, MRV shows how poor choice of diffuser start point and angle can be detrimental to film cooling if overall hole length and cooling flow velocity are not properly accounted for in the design. The downstream effect of these choices on the jet height and counter-rotating vortex pair is also observed.

Effects of Streamwise Pressure Gradient and Convex Curvature on Film Cooling Effectiveness

2014 ◽  
Author(s):  
Yanmin Qin ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Pressure Gradient ◽  
Film Cooling ◽  
Main Stream ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Flat Wall ◽  
Favorable Pressure Gradient ◽  
Convex Wall ◽  
Cooling Hole ◽  
Streamwise Pressure Gradient

The effects of streamwise pressure gradient and convex wall curvature on film cooling effectiveness are investigated using PSP technology. Film cooling under five different main stream pressure gradients on both flat and convex wall is examined. The cooling hole has an inclined angle of 30° and no compound angle with a hole length of L/D = 4. The convex wall has a constant radius of r/D = 30. Numerical simulations are also conducted to gain more flow field information. For the flat wall case, film cooling effectiveness is higher with greater favorable pressure gradient for low blowing ratios. While for high blowing ratio cases, cooling effectiveness doesn’t vary much with streamwise pressure gradient. Film cooling effectiveness is increased significantly on convex wall compared with flat wall for M<0.5. The effect of streamwise pressure gradient is greater on convex wall and becomes unneglectable. The influence of streamwise pressure gradient and convex wall curvature is conjugated and should be discussed together. For all blowing ratios, film cooling effectiveness is apparently higher for larger mainstream favorable pressure gradient on convex wall.

Building Block Experiments in Discrete Hole Film Cooling

2015 ◽  
Author(s):  
Kevin J. Ryan ◽  
Filippo Coletti ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Building Block ◽  
Film Cooling ◽  
Three Dimensional ◽  
Vortex Pair ◽  
Mean Velocity ◽  
Jet Trajectory ◽  
Dominant Feature ◽  
Cooling Hole

This paper reports a series of building block experiments for discrete hole film cooling. Seven different configurations, including variations in injection wall curvature, mainstream pressure gradient, and boundary layer thickness are measured for a round film cooling hole, inclined 30 degrees at injection, and operated at a blowing ratio of unity. Full three dimensional, three component velocity fields and scalar coolant concentration fields are acquired using Magnetic Resonance Imaging (MRI) techniques. The results show the effect of varying the mainstream condition on the mean coolant concentration distribution and mean velocity field, including the counter-rotating vortex pair (CVP), a dominant feature of jet in crossflow type flows. The present study focuses on an analysis of the building block configurations only possible with full three dimensional velocity and concentration fields. Several scalar parameters including normalized perimeter, jet trajectory, maximum coolant concentration, and coolant concentration spread are extracted from the collected data and compared across the different configurations. The results indicate that the pressure gradient variations have the strongest effect on the calculated quantities, the boundary layer slightly less, and the curvature very little.

scholarly journals The Design of an Improved Endwall Film-Cooling Configuration

1998 ◽  
Author(s):  
S. Friedrichs ◽  
H. P. Hodson ◽  
W. N. Dawes
Keyword(s):  
Secondary Flow ◽  
Film Cooling ◽  
Large Scale ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Aerodynamic Loss ◽  
Cooling Flow ◽  
High Static Pressure ◽  
Endwall Film Cooling ◽  
Aerodynamic Losses

The endwall film-cooling cooling configuration investigated by Friedrichs et al. (1996, 1997) had in principle sufficient cooling flow for the endwall, but in practice, the redistribution of this coolant by secondary flows left large endwall areas uncooled. This paper describes the attempt to improve upon this datum cooling configuration by redistributing the available coolant to provide a better coolant coverage on the endwall surface, whilst keeping the associated aerodynamic losses small. The design of the new, improved cooling configuration was based on the understanding of endwall film-cooling described by Friedrichs et al. (1996, 1997). Computational fluid dynamics were used to predict the basic flow and pressure field without coolant ejection. Using this as a basis, the above described understanding was used to place cooling holes so that they would provide the necessary cooling coverage at minimal aerodynamic penalty. The simple analytical modelling developed in Friedrichs et al. (1997) was then used to check that the coolant consumption and the increase in aerodynamic loss lay within the limits of the design goal. The improved cooling configuration was tested experimentally in a large scale, low speed linear cascade. An analysis of the results shows that the redesign of the cooling configuration has been successful in achieving an improved coolant coverage with lower aerodynamic losses, whilst using the same amount of coolant as in the datum cooling configuration. The improved cooling configuration has reconfirmed conclusions from Friedrichs et al. (1996, 1997); firstly, coolant ejection downstream of the three-dimensional separation lines on the endwall does not change the secondary flow structures; secondly, placement of holes in regions of high static pressure helps reduce the aerodynamic penalties of platform coolant ejection; finally, taking account of secondary flow can improve the design of endwall film-cooling configurations.

A CFD-Based Parametric Study on Modification of Discrete Sister Holes Location for the Film Cooling Flow

2014 ◽  
Author(s):  
Siavash Khajehhasani ◽  
Bassam Jubran
Keyword(s):  
Film Cooling ◽  
Numerical Study ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Base Case ◽  
Spanwise Direction ◽  
Cooling Performance ◽  
Cooling Flow ◽  
Lift Off ◽  
The Individual

A numerical study on the effects of sister holes locations on film cooling performance is presented. This includes the change of the location of the individual discrete sister holes in the streamwise and spanwise directions, where each one of these directions includes 9 different locations, The simulations are performed using three-dimensional Reynolds-Averaged Navier Stokes analysis with the realizable k–ε model combined with the standard wall function. The variation of the sister holes in the streamwise direction provides similar film cooling performance as the base case for both blowing ratios of 0.5 and 1. On the other hand, the spanwise variation of the sister holes’ location has a more prominent effect on the effectiveness. In some cases, as a result of the anti-vortices generated from the sister holes and the repositioning of the sister holes in the spanwise direction, the jet lift-off effect notably decreases and more volume of coolant is distributed in the spanwise direction.

scholarly journals Bulk Flow Pulsations and Film Cooling: Flow Structure Just Downstream of the Holes

1997 ◽  
Vol 119 (3) ◽  
pp. 568-573 ◽  
Author(s):  
P. M. Ligrani ◽  
R. Gong ◽  
J. M. Cuthrell
Keyword(s):  
Film Cooling ◽  
Static Pressure ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Bulk Flow ◽  
Shear Stresses ◽  
Pressure Pulsations ◽  
Mean Velocity ◽  
Cooling Flow ◽  
Flow Pulsations

Experimental results are presented that describe the effects of bulk flow pulsations on film cooling from a single row of simple angle film cooling holes. The pulsations are in the form of sinusoidal variations of static pressure and streamwise velocity. Such pulsations are important in turbine studies because: (i) Static pressure pulsations result in significant periodic variations of film cooling flow rates, coverage, and trajectories, and (ii) static pressure pulsations occur near blade surfaces in operating engines from potential flow interactions between moving blade rows and from families of passing shock waves. Distributions of ensemble-averaged and time-averaged Reynolds stress tensor components are investigated just downstream of the holes along with distributions of all three mean velocity components. Important changes are evident in all measured quantities. In particular, maximum Reynolds shear stresses −2u′υ′/u∞2 are lower in regions containing the largest film concentrations because the strong shear layer produced by the injectant is more three dimensional, larger in extent, and oscillates its position from the wall with time.

Implicit LES for Shaped-Hole Film Cooling Flow

2017 ◽  
Author(s):  
Todd A. Oliver ◽  
Joshua B. Anderson ◽  
David G. Bogard ◽  
Robert D. Moser ◽  
Gregory Laskowski
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Vortex Pair ◽  
Cooling Flow ◽  
Blowing Ratio ◽  
Eddy Simulation ◽  
Mean Temperature ◽  
Cooling Hole ◽  
The Mean ◽  
Adiabatic Effectiveness

Results of a recent joint experimental and computational investigation of the flow through a plenum-fed 7-7-7 shaped film cooling hole are presented. In particular, we compare the measured adiabatic effectiveness and mean temperature against implicit large eddy simulation (iLES) for blowing ratio approximately 2, density ratio 1.6, and Reynolds number 6000. The results overall show reasonable agreement between the iLES and the experimental results for the adiabatic effectiveness and gross features of the mean temperature field. Notable discrepancies include the centerline adiabatic effectiveness near the hole, where the iLES under-predicts the measurements by Δη ≈ 0.05, and the near-wall temperature, where the simulation results show features not present in the measurements. After showing this comparison, the iLES results are used to examine features that were not measured in the experiments, including the in-hole flow and the dominant fluxes in the mean internal energy equation downstream of the hole. Key findings include that the flow near the entrance to the hole is highly turbulent and that there is a large region of backflow near the exit of the hole. Further, the well-known counter-rotating vortex pair downstream of the hole is observed. Finally, the typical gradient diffusion hypothesis for the Reynolds heat flux is evaluated and found to be incorrect.

Computational Predictions of Heat Transfer and Film-Cooling for a Turbine Blade With Nonaxisymmetric Endwall Contouring

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Stephen P. Lynch ◽  
Karen A. Thole ◽  
Atul Kohli ◽  
Christopher Lehane
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Film Cooling ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Turbine Engine ◽  
Cooling Flow ◽  
Endwall Contouring ◽  
Dynamics Simulations ◽  
Endwall Film Cooling

Three-dimensional contouring of the compressor and turbine endwalls in a gas turbine engine has been shown to be an effective method of reducing aerodynamic losses by mitigating the strength of the complex vortical structures generated at the endwall. Reductions in endwall heat transfer in the turbine have been also previously measured and reported in literature. In this study, computational fluid dynamics simulations of a turbine blade with and without nonaxisymmetric endwall contouring were compared to experimental measurements of the exit flowfield, endwall heat transfer, and endwall film-cooling. Secondary kinetic energy at the cascade exit was closely predicted with a simulation using the SST k-ω turbulence model. Endwall heat transfer was overpredicted in the passage for both the SST k-ω and realizable k-ε turbulence models, but heat transfer augmentation for a nonaxisymmetric contour relative to a flat endwall showed fair agreement to the experiment. Measured and predicted film-cooling results indicated that the nonaxisymmetric contouring limits the spread of film-cooling flow over the endwall depending on the interaction of the film with the contour geometry.

Sign in / Sign up

Export Citation Format

Share Document