Time-Resolved Film-Cooling Flows at High and Low Density Ratios

2013 ◽  
Vol 136 (6) ◽  
Author(s):  
Molly K. Eberly ◽  
Karen A. Thole
Keyword(s):  
Film Cooling ◽  
Momentum Flux ◽  
Particle Image Velocimetry Data ◽  
Round Hole ◽  
Cooling Effectiveness ◽  
Time Resolved ◽  
Cooling Flow ◽  
Image Velocimetry ◽  
Cooling Hole ◽  
Density Ratios

Film-cooling is one of the most prevalent cooling technologies that is used for gas turbine airfoil surfaces. Numerous studies have been conducted to give the cooling effectiveness over ranges of velocity, density, mass flux, and momentum flux ratios. Few studies have reported flowfield measurements with even fewer of those providing time-resolved flowfields. This paper provides time-averaged and time-resolved particle image velocimetry data for a film-cooling flow at low and high density ratios. A generic film-cooling hole geometry with wide lateral spacing was used for this study, which was a 30 deg inclined round hole injecting along a flat plate with lateral spacing P/D = 6.7. The jet Reynolds number for flowfield testing varied from 2500 to 7000. The data indicate differences in the flowfield and turbulence characteristics for the same momentum flux ratios at the two density ratios. The time-resolved data indicate Kelvin–Helmholtz breakdown in the jet-to-freestream shear layer.

Time-Resolved Film-Cooling Flows at Low and High Density Ratios

2013 ◽  
Author(s):  
Molly K. Eberly ◽  
Karen A. Thole
Keyword(s):  
Film Cooling ◽  
Momentum Flux ◽  
Particle Image Velocimetry Data ◽  
High Density ◽  
Round Hole ◽  
Time Resolved ◽  
Cooling Flow ◽  
Image Velocimetry ◽  
Cooling Hole ◽  
Density Ratios

Film-cooling is one of the most prevalent cooling technologies that is used for gas turbine airfoil surfaces. Numerous studies have been conducted to give the cooling effectiveness over ranges of velocity, density, mass flux, and momentum flux ratios. Few studies have reported flowfield measurements with even fewer of those providing time-resolved flowfields. This paper provides time-averaged and time-resolved particle image velocimetry data for a film-cooling flow at low and high density ratios. A generic film-cooling hole geometry with wide lateral spacing was used for this study, which was a 30° inclined round hole injecting along a flat plate with lateral spacing P/D = 6.7. The jet Reynolds number for flowfield testing varied from 2500 to 7000. The data indicate differences in the flowfield and turbulence characteristics for the same momentum flux ratios at the two density ratios. The time-resolved data indicate Kelvin-Helmholtz breakdown in the jet-to-freestream shear layer.

Effect of Row Spacing on the Accuracy of Film Cooling Superposition Method

2018 ◽  
Author(s):  
Lang Wang ◽  
Xueying Li ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Film Cooling ◽  
Row Spacing ◽  
Superposition Method ◽  
Round Hole ◽  
Cooling Effectiveness ◽  
Blowing Ratio ◽  
Cooling Hole ◽  
Shaped Hole ◽  
The Difference ◽  
Density Ratios

Film cooling technique is widely used in a modern gas turbine. Many applications in hot sections require multiple film cooling rows to get better cooled. In most situation, the additive effect is computed using Sellers superposition method, but it is not accurate when the hole rows are close to each other. In this paper, row spacing between two rows of cooling hole was investigated by numerical method, which was validated by PSP results. The validation experiments are performed on flat test bench and the freestream is maintained at 25m/s. The inlet boundary conditions of numerical simulations were same with the experiment. Both round hole and shaped hole were investigated at blowing ratio M = 0.5, density ratios DR = 1.5 and row spacing S/D = 6, 10, 15, 20. It is found that the round hole results by Sellers method are similar to experiment results only at large row spacing, and the results of Sellers are always higher than experimental results. The boundary layer has a big effect on cooling effectiveness for round hole, but very little effect on shaped hole. When the row spacing increase, the difference between experiment and prediction become smaller. The vortex is the major factor to effect the accuracy of superposition method.

An Investigation of the Effects of Film Cooling in a High-Pressure Aeroengine Turbine Stage

2005 ◽  
Author(s):  
Kam S. Chana ◽  
Mary A. Hilditch ◽  
James Anderson
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Phase Iii ◽  
Cooling Effectiveness ◽  
Aerodynamic Efficiency ◽  
Cooling Flow ◽  
External Cooling ◽  
Improved Design ◽  
Density Ratios ◽  
Cooling Air

Cooling is required to enable the turbine components to survive and have acceptable life in the very high gas temperatures occurring in modern engines. The cooling air is bled from the compression system, with typically about 15% of the core flow being diverted in military engines and about 20% in civil turbofans. Cooling benefits engine specific thrust and efficiency by allowing higher cycle temperatures to be employed, but the bleed air imposes cycle penalties and also reduces the aerodynamic efficiency of the turbine blading, typically by 2–4%. Cooling research aims to develop and validate improved design methodologies that give maximum cooling effectiveness for minimum cooling flow. This paper documents external cooling research undertaken in the Isentropic Light Piston Facility at QinetiQ as part of a European collaborative programme on turbine aerodynamics and heat transfer. In Phase I, neither the ngv nor the rotor was cooled; cooling was added to the ngv only for Phase II, and to the rotor and ngv in Phase III. Coolant blowing rates and density ratios were also varied in the experiments. This paper describes the ILPF and summarises the results of this systematic programme, paying particular attention to the variation in aerofoil heat transfer with changing coolant conditions, and the effects coolant ejection has on the aerofoil’s aerodynamic performance.

Large Eddy Simulations on Fan Shaped Film Cooling Hole with Upstream Boundary Layer Turbulence Effect Generated by Trip Strip

2021 ◽  
pp. 1-37
Author(s):  
Young Seok Kang ◽  
Sangook Jun ◽  
Dong-Ho Rhee
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Film Cooling ◽  
Main Flow ◽  
Large Eddy Simulations ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Flow ◽  
Large Eddy ◽  
Cooling Hole

Abstract Large eddy simulations on the well-known 7-7-7 fan shaped cooling hole were carried out. Like using a trip strip to create turbulent boundary layer in practical experiments, trip strips with different configurations were placed upstream of the cooling hole to investigate incoming turbulent boundary layer effect on the film cooling flow behavior. Without the trip, horseshoe vortex generated by laminar boundary layer induced laterally discharging cooling flow in the lateral direction. Meanwhile, the induced cooling flow formed high film cooling effectiveness region around the film cooling hole. When the incoming boundary flow was turbulent, laterally discharged cooling flow was influenced by the turbulent boundary layer to dissipate to the main flow and resultant high effectiveness region disappeared. Depending on the trip configuration, quantitative characteristics of boundary layer such as turbulent intensity, momentum thickness and shape factor were strongly affected. Some trip configurations resulted in fully developed turbulent boundary layer just before leading edge of the film cooling hole. In such cases, distribution of the film cooling effectiveness showed a reasonable agreement with available experimental data where the quantitative properties of the turbulent boundary layer were similar. However, when the trip was located too close to the film cooling hole, the separated and reattached flow did not develop into the stabilized turbulent boundary layer. Then strong turbulence intensity in the main flow boundary layer stimulated break down of the cooling flow vortex structure and early dissipation to the main flow. It resulted in restricted film cooling flow coverage.

Large Eddy Simulations on Fan Shaped Film Cooling Hole With Various Inlet Turbulence Generation Methods

2020 ◽  
Author(s):  
Young Seok Kang ◽  
Sangook Jun ◽  
Dong-Ho Rhee
Keyword(s):  
Vortex Structure ◽  
Film Cooling ◽  
Main Flow ◽  
Large Eddy Simulations ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Flow ◽  
Large Eddy ◽  
Cooling Hole ◽  
Turbulence Generation

Abstract Large eddy simulations on well-known 7-7-7 fan shaped cooling hole have been carried out. Film cooling methods are generally applied to high pressure turbine, of which flow condition is extremely turbulent because high pressure turbines are generally located downstream combustor in gas turbines. However, different to RANS simulations, implementing turbulence at the main flow inlet is not simple in LES. For this reason, several numerical techniques have been devised to give turbulence information at the inlet boundary condition in LES. In this study, rectangular turbulator was located in front of the cooling hole to generate turbulent boundary flow in the main flow. Another method used in this study is transient table method to simulate turbulent flow at the main flow inlet. Without turbulent velocity components in approaching flow, laterally discharged cooling flow touches wall while it forms a vortex structure. Then high film cooling effectiveness region around the cooling hole appears. In the meanwhile, when approaching flow is turbulent, the laterally discharged cooling flow no more forms vortex structure and dissipated to the main flow and resultant high effectiveness region disappears. Both turbulence generation methods showed that turbulent intensity of the main flow affects effective range of the cooling flow and resultant film cooling effectiveness distributions. Also high turbulence intensity of the main flow stimulates early break down of the vortex structure coming out of the cooling hole and its dissipation to the main flow. It means high turbulent intensity restricts film cooling flow coverage. Another lesson from the study is that vortex generated from the cooling hole, its development and dissipation to the main flow, have an important role to understand film cooling effectiveness distributions around the cooling hole.

Numerical Study on Effects of Density Ratio on Film Cooling Flow Structure and Film Cooling Effectiveness

2017 ◽  
Author(s):  
Eiji Sakai ◽  
Toshihiko Takahashi
Keyword(s):  
Shear Layer ◽  
Film Cooling ◽  
Numerical Study ◽  
Density Ratio ◽  
Hairpin Vortices ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Flow ◽  
High Density Ratio ◽  
Cooling Hole

To understand film cooling flow fields on a gas turbine blade, this paper reports a series of large-eddy simulations of an inclined round jet issuing into a crossflow. Simulations were performed at constant momentum ratio conditions, IR = 0.25, 0.5, 1.0 and Reynolds number, Re = 15,300, based on the crossflow velocity and the film cooling hole diameter. Density ratio, DR, is changed from 1.0 to 2.0, and effects of the density ratio on vortical structures around the film cooling hole exit and film cooling effectiveness are investigated. The results showed that the vortical structure of the ejected jet drastically changes with varying density ratio. When the density ratio is comparatively small, hairpin vortices are formed downstream of the hole exit. On the contrary, when the density ratio is comparatively high, the formation of the hairpin vortices is suppressed and jet shear layer vortices are formed on side edges of the cooling jet. The jet shear layer vortices conveys the coolant air to the wall surface. As a result, higher film cooling effectiveness is obtained at comparatively high density ratio conditions compared to comparatively low density ratio conditions. Additional simulations were performed to discuss a possibility of an improvement in the film cooling effectiveness by controlling the formation of the jet shear layer vortices.

Application of S-PIV for Investigation of Round and Shaped Film Cooling Holes at High Density Ratios

2016 ◽  
Author(s):  
Travis B. Watson ◽  
Sara Nahang-Toudeshki ◽  
Lesley M. Wright ◽  
Daniel C. Crites ◽  
Mark C. Morris ◽  
...  
Keyword(s):  
Film Cooling ◽  
High Speed ◽  
Density Ratio ◽  
High Density ◽  
Round Hole ◽  
Turbine Engine ◽  
Flow Vorticity ◽  
Cooling Hole ◽  
Shaped Hole ◽  
Density Ratios

Hot section turbine engine components are often cooled through the use of a cool film of air on the component wall. The source of the air used for film cooling comes from the compressor of the gas turbine engine and may be 800°C, or more, cooler than the hot gas path air. The temperature differential between the hot mainstream gas and the film coolant results in a large difference in density between the two gases. In order to investigate the effect of high density ratios on film cooling performance, a traditional, round hole (θ = 30°) and a laidback, fan shaped hole (θ = 30°, α = γ = 10°) were observed using Stereo-Particle Image Velocimetry (S-PIV). Flowfield measurements were performed on various planes downstream of the film cooling hole (x/d = 0, 1, 3 and 10 for the round hole and x/d = 0, 3, and 10 for the shaped hole). At each location the coolant-to-mainstream interaction was captured at multiple density ratios (DR = 1, 2, 3, 4) and blowing ratios (M = 0.5, 1.0, 1.5). Using S-PIV, the three-dimensional flow field was measured. Distributions of the flow vorticity were derived from the high speed velocity measurements taken during S-PIV testing. For the simple angle, round holes, the results show at the elevated density ratios, the coolant spreads laterally near the hole; while at DR = 1, the coolant trace is limited to the width of the film cooling hole. Furthermore, as the cooling jet exits from the round hole, the vorticity within the jet is very strong, leading to increased mixing with the mainstream. However, as the density ratio increases (at a given blowing ratio), this mixing was reduced. For a given flow condition, the rotation was reduced with the jet exiting the shaped hole (compared to the round hole), and this led to enhanced protection on the surface. While investigating both round and shaped holes, it was shown the S-PIV method is a valuable tool to observe and quantify the jet–to–mainstream interactions near the film cooled surface.

Film Cooling Effectiveness Improvements Using a Nondiffusing Oval Hole

2015 ◽  
Vol 138 (4) ◽  
Author(s):  
Emin Issakhanian ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Film Cooling ◽  
Measurement Techniques ◽  
Round Hole ◽  
Blade Surface ◽  
Mean Velocity ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
Shaped Hole ◽  
Film Cooling Holes

The need for improvements in film cooling effectiveness over traditional cylindrical film cooling holes has led to varied shaped hole and sister hole designs of increasing complexity. This paper presents a simpler shaped hole design which shows improved film cooling effectiveness over both cylindrical holes and diffusing fan-shaped holes without the geometric complexity of the latter. Magnetic resonance imaging measurement techniques are used to reveal the coupled 3D velocity and coolant mixing from film cooling holes which are of a constant oval cross section as opposed to round. The oval-shaped hole yielded an area-averaged adiabatic effectiveness twice that of the diffusing fan-shaped hole tested. Three component mean velocity measurements within the channel and cooling hole showed the flow features and vorticity fields which explain the improved performance of the oval-shaped hole. As compared to the round hole, the oval hole leads to a more complex vorticity field, which reduces the strength of the main counter-rotating vortex pair (CVP). The CVP acts to lift the coolant away from the turbine blade surface, and thus strongly reduces the film cooling effectiveness. The weaker vortices allow the coolant to stay closer to the blade surface and to remain relatively unmixed with the main flow over a longer distance. Thus, the oval-shaped film cooling hole provides a simpler solution for improving film cooling effectiveness beyond circular hole and diffusing hole designs.

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.

Film Cooling Effectiveness From Two-Row of Compound Angled Cylindrical Holes Using PSP Technique

2018 ◽  
Author(s):  
Nian Wang ◽  
Mingjie Zhang ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Free Stream Turbulence ◽  
Cooling Hole ◽  
Cylindrical Holes ◽  
Inclined Angle ◽  
Density Ratios

This study investigates the combined effects of blowing ratio and density ratio on flat plate film cooling effectiveness from two-row of compound angled cylindrical holes. Two arrangements of two-row compound angled cylindrical holes are tested: the first row and second row are oriented in staggered but same compound angled direction (β = +45° for the first row, +45° for the second row); the first row and second row are oriented in inline but opposite direction (β = +45° for the first row, −45° for the second row). Each cooling hole is 4 mm in diameter with an inclined angle 30°. The streamwise distance between the two rows is fixed at 4d and the spanwise pitch between the two holes (p) is 4d, 6d, and 8d, respectively. The experiments are performed at four blowing ratios (M = 0.5, 1.0, 1.5, 2.0) and three density ratios (DR = 1.0, 1.5, 2.0). The free stream turbulence intensity is kept at 6%. Detailed film cooling effectiveness distributions are obtained using the steady state pressure-sensitive paint (PSP) technique. The detailed film cooling effectiveness contours are presented and the spanwise averaged film effectiveness results are compared over the range of flow parameters. Film cooling effectiveness correlations are developed for both inline and staggered compound angled cylindrical holes. The results provide baseline information for the flat plate film cooling analysis with two-row of compound angled cylindrical holes.

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