Measurements in Film Cooling With Lateral Injection: Adiabatic Effectiveness Values and Temperature Fields

Temperature fields were taken in a film cooling lateral injection configuration with pitch-to-hole-diameter of 3.0. These measurements were done with a traversing thermocouple. Momentum flux ratios of 0.25, 1.0 and 2.25 were used. Results are presented as fields of dimensionless temperatures, given by θ=Tprobe-T∞Tc-T∞. Near-surface values of this quantity over an unheated surface are adiabatic effectiveness values. Streamwise evolutions of these temperature fields are documented. It is seen how with higher blowing ratio the film cooling jets tend to lift off the surface. Comparisons are made to previous data and computational results. It is verified that lateral injection yields a more uniform distribution of effectiveness immediately downstream of injection. It is shown also how interaction of adjacent film cooling jets leads to such improved uniformity. This interaction depends on the pitch to diameter ratio, P/D. In order to study the effect of this parameter, additional data with P/D = 6.0 are presented. The present thermal field data complement previous velocity field measurements taken in the same flow.

Film Cooling From Spanwise Oriented Holes in Two Staggered Rows

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

10.1115/95-gt-039 ◽

1995 ◽

Cited By ~ 3

Author(s):

Phillip M. Ligrani ◽

Anthony E. Ramsey

Keyword(s):

Film Cooling ◽

Density Ratio ◽

Flux Ratio ◽

Test Surface ◽

Spanwise Direction ◽

Transfer Coefficients ◽

Blowing Ratio ◽

Streamwise Location ◽

Adiabatic Effectiveness ◽

Adiabatic effectiveness and iso-energetic heat transfer coefficients are presented from measurements downstream of film-cooling holes inclined at 30 degrees with respect to the test surface in spanwise/normal planes. With this configuration, holes are spaced 3d apart in the spanwise direction and 4d in the streamwise direction in two staggered rows. Results are presented for an injectant to freestream density ratio near 1.0, and injection blowing ratios from 0.5 to 1.5. Spanwise-averaged adiabatic effectiveness values downstream of the spanwise/normal plane holes are significantly higher than values measured downstream of simple angle holes for x/d<25–70 (depending on blowing ratio) when compared for the same normalized streamwise location, blowing ratio, and spanwise and streamwise hole spacings. Differences are principally due to different coalescence of injectant accumulations from the two different rows of holes, as well as significantly different lift-off dependence on momentum flux ratio. Spanwise-averaged iso-energetic Stanton number ratios are somewhat higher than ones measured downstream of other simple and compound angle configurations studied. Values range between 1.0 and 1.41, increase with blowing ratio at each streamwise station, and show little variation with streamwise location for each value of blowing ratio tested.

Film Cooling From a Single Row of Holes Oriented in Spanwise/Normal Planes

10.1115/1.2841187 ◽

1997 ◽

Vol 119 (4) ◽

pp. 770-776 ◽

Cited By ~ 5

Author(s):

P. M. Ligrani ◽

A. E. Ramsey

Keyword(s):

Film Cooling ◽

Test Surface ◽

Spanwise Direction ◽

Single Row ◽

Local Maxima ◽

Blowing Ratio ◽

Streamwise Location ◽

Structure Of Flow ◽

Adiabatic Effectiveness ◽

Experimental results are presented that describe the development and structure of flow downstream of a single row of film-cooling holes inclined at 30 deg from the test surface in spanwise/normal planes. With this configuration, holes are spaced 6d apart in the spanwise direction in a single row. Results are presented for a ratio of injectant density to free-stream density near 1.0, and injection blowing ratios from 0.5 to 1.5. Compared to results measured downstream of simple angle (streamwise) oriented holes, spanwise-averaged adiabatic effectiveness values are significantly higher for the same spanwise hole spacing, normalized streamwise location x/d, and blowing ratio m when m = 1.0 and 1.5 for x/d < 80. The injectant from the spanwise/normal holes is also less likely to lift off of the test surface than injectant from simple angle holes. This is because lateral components of momentum keep higher concentrations of injectant in closer proximity to the surface. As a result, local adiabatic effectiveness values show significantly greater spanwise variations and higher local maxima at locations immediately downstream of the holes. Spanwise-averaged iso-energetic Stanton number ratios range between 1.07 and 1.26, which are significantly higher than values measured downstream of two other injection configurations (one of which is simple angle, streamwise holes) when compared at the same x/d and blowing ratio.

Adiabatic Film Cooling Effectiveness Measurements Throughout Multirow Film Cooling Arrays

10.1115/1.4035520 ◽

2017 ◽

Vol 139 (10) ◽

Cited By ~ 7

Author(s):

Greg Natsui ◽

Zachary Little ◽

Jayanta S. Kapat ◽

Jason E. Dees

Keyword(s):

Boundary Layer ◽

Film Cooling ◽

Density Ratio ◽

Diameter Ratio ◽

Test Surface ◽

Cooling Effectiveness ◽

Film Cooling Effectiveness ◽

Blowing Ratio ◽

First Case ◽

Adiabatic film cooling effectiveness measurements are obtained using pressure-sensitive paint (PSP) on a flat film cooled surface. The effects of blowing ratio and hole spacing are investigated for four multirow arrays comprised of eight rows containing 52 holes of 3.8 mm diameter with 20 deg inclination angles and hole length-to-diameter ratio of 11.2. The four arrays investigated have two different hole-to-hole spacings composed of cylindrical and diffuser holes. For the first case, lateral and streamwise pitches are 7.5 times the diameter. For the second case, pitch-to-diameter ratio is 14 in lateral direction and 10 in the streamwise direction. The holes are in a staggered arrangement. Adiabatic effectiveness measurements are taken for a blowing ratio range of 0.3–1.2 and a density ratio of 1.5, with CO2 injected as the coolant. A thorough boundary layer analysis is presented, and data were taken using hotwire anemometry with air injection, with boundary layer, and turbulence measurements taken at multiple locations in order to characterize the boundary layer. Local effectiveness, laterally averaged effectiveness, boundary layer thickness, momentum thickness, turbulence intensity, and turbulence length scale are presented. For the cylindrical holes, at the first row of injection, the film jets are still attached at a blowing ratio of 0.3. By a blowing ratio of 0.5, the jet is observed to lift off, and then impinge back onto the test surface. At a blowing ratio of 1.2, the jets lift off, but reattach much further downstream, spreading the coolant further along the test surface. A thorough uncertainty analysis has been conducted in order to fully understand the presented measurements and any shortcomings of the measurement technique. The maximum uncertainty of effectiveness and blowing ratio is 0.02 counts of effectiveness and 3%, respectively.

Effect of In-Hole Roughness on Film Cooling From a Shaped Hole

Volume 5C: Heat Transfer ◽

10.1115/gt2016-56978 ◽

2016 ◽

Cited By ~ 2

Author(s):

Robert P. Schroeder ◽

Karen A. Thole

Keyword(s):

Film Cooling ◽

Thermal Field ◽

Core Flow ◽

Blowing Ratio ◽

Cooling Hole ◽

Flow Through ◽

Shaped Hole ◽

Adiabatic Effectiveness ◽

Cool Gas ◽

Interior Walls

While much is known about how macro-geometry of shaped holes affects their ability to successfully cool gas turbine components, little is known about the influence of surface roughness on cooling hole interior walls. For this study a baseline shaped hole was tested with various configurations of in-hole roughness. Adiabatic effectiveness measurements at blowing ratios up to three showed that in-hole roughness caused decreased adiabatic effectiveness relative to smooth holes. Decreases in area-averaged effectiveness grew more severe with larger roughness size and with higher blowing ratios for a given roughness. Decreases of more than 60% were measured at a blowing ratio of three for the largest roughness values. Thermal field and flowfield measurements showed that in-hole roughness caused increased velocity of core flow through the hole, which increased the jet penetration height and turbulence intensity resulting in increased mixing between coolant and the mainstream. Effectiveness reductions due to roughness were also observed when roughness was isolated to only the diffused outlet of holes, and when the mainstream was highly turbulent.

Effect of In-Hole Roughness on Film Cooling From a Shaped Hole

10.1115/1.4034847 ◽

2016 ◽

Vol 139 (3) ◽

Cited By ~ 6

Author(s):

Robert P. Schroeder ◽

Karen A. Thole

Keyword(s):

Film Cooling ◽

Thermal Field ◽

Core Flow ◽

Blowing Ratio ◽

Cooling Hole ◽

Flow Through ◽

Shaped Hole ◽

Adiabatic Effectiveness ◽

Cool Gas ◽

Interior Walls

While much is known about how macrogeometry of shaped holes affects their ability to successfully cool gas turbine components, little is known about the influence of surface roughness on cooling hole interior walls. For this study, a baseline-shaped hole was tested with various configurations of in-hole roughness. Adiabatic effectiveness measurements at blowing ratios up to 3 showed that the in-hole roughness caused decreased adiabatic effectiveness relative to smooth holes. Decreases in area-averaged effectiveness grew more severe with larger roughness size and with higher blowing ratios for a given roughness. Decreases of more than 60% were measured at a blowing ratio of 3 for the largest roughness values. Thermal field and flowfield measurements showed that in-hole roughness caused increased velocity of core flow through the hole, which increased the jet penetration height and turbulence intensity resulting in an increased mixing between the coolant and the mainstream. Effectiveness reductions due to roughness were also observed when roughness was isolated to only the diffused outlet of holes, and when the mainstream was highly turbulent.

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

Flow structures and thermal field with modulated jet near the semi-circular leading edge

10.1177/0957650919873172 ◽

2019 ◽

Vol 234 (5) ◽

pp. 594-610

Author(s):

S Sarkar

Keyword(s):

Coherent Structures ◽

Film Cooling ◽

Thermal Field ◽

Cross Flow ◽

Leading Edge ◽

Constant Thickness ◽

Simplified Approach ◽

Blowing Ratio ◽

Eddy Simulation ◽

Influence of external modulation on unsteady flow and heat transfer near the leading edge of a constant thickness aerofoil has been described through large eddy simulation. This is a simplified approach to study film cooling activities near the leading edge of a turbine blade. Discrete jets, which are forced at a Strouhal number (St) of 0.37 with an averaged blowing ratio of unity, are ejected normally from a series of film cooling holes to a separated boundary layer. The results are compared against the corresponding steady injection. Larger coherent structures appear for a forced jet with an augmented vortex dynamics resulting in high jet lift-off, earlier break down, enhanced mixing with the cross flow and dilution of coolant layer. Resolved hairpins, which are the signature of coherent structures, illustrate that the vorticity and thermal field are highly correlated. Furthermore, evolution of hairpins and their advection control scalar transport and mixing. In brief, the modulation of coolant jet near the leading edge appears not beneficial for the combination of blowing ratio and frequency considered here.

Adiabatic Film Cooling Effectiveness Measurements Throughout Multi-Row Film Cooling Arrays

Volume 5C: Heat Transfer ◽

10.1115/gt2016-56183 ◽

2016 ◽

Author(s):

Greg Natsui ◽

Zachary Little ◽

Jay Kapat ◽

Anthony Socotch ◽

Anquan Wang ◽

...

Keyword(s):

Boundary Layer ◽

Film Cooling ◽

Density Ratio ◽

Diameter Ratio ◽

Test Surface ◽

Cooling Effectiveness ◽

Film Cooling Effectiveness ◽

Blowing Ratio ◽

First Case ◽

Adiabatic film cooling effectiveness measurements are obtained using pressure-sensitive paint (PSP) on a flat film cooled surface. The effects of blowing ratio and hole spacing are investigated for four multi-row arrays comprised of 8 rows containing 52 holes of 3.8 mm diameter with 20° inclination angles and hole length-to-diameter ratio of 11.2. The four arrays investigated have two different hole-to-hole spacings composed of cylindrical and diffuser holes. For the first case, lateral and streamwise pitches are 7.5 times the diameter. For the second case, pitch-to-diameter ratio is 14 in lateral direction and 10 in the streamwise direction. The holes are in a staggered arrangement. Adiabatic effectiveness measurements are taken for a blowing ratio range of 0.3 to 1.2 and a density ratio of 1.5, with CO2 injected as the coolant. A thorough boundary layer analysis is presented, and data was taken using hotwire anemometry with air injection, with boundary layer and turbulence measurements taken at multiple locations in order to characterize the boundary layer. Local effectiveness, laterally averaged effectiveness, boundary layer thickness, momentum thickness, turbulence intensity and turbulence length scale are presented. For the cylindrical holes, at the first row of injection, the film jets are still attached at a blowing ratio of 0.3. By a blowing ratio of 0.5, the jet is observed to lift off, and then impinge back onto the test surface. At a blowing ratio of 1.2, the jets lift off, but reattach much further downstream, spreading the coolant further along the test surface. A thorough uncertainty analysis has been conducted in order to fully understand the presented measurements and any shortcomings of the measurement technique. The maximum uncertainty of effectiveness and blowing ratio is 0.02 counts of effectiveness and 3 percent respectively.

The Effect of Area Ratio Change Via Increased Hole Length for Shaped Film Cooling Holes With Constant Expansion Angles

10.1115/1.4038871 ◽

2018 ◽

Vol 140 (5) ◽

Cited By ~ 8

Author(s):

Shane Haydt ◽

Stephen Lynch ◽

Scott Lewis

Keyword(s):

Film Cooling ◽

Gas Turbines ◽

Area Ratio ◽

Navier Stokes ◽

Lateral Expansion ◽

Blowing Ratio ◽

Expansion Angle ◽

Adiabatic Effectiveness ◽

Lift Off ◽

Film Cooling Holes

Shaped film cooling holes are used as a cooling technology in gas turbines to reduce metal temperatures and improve durability, and they generally consist of a small metering section connected to a diffuser that expands in one or more directions. The area ratio (AR) of these holes is defined as the area at the exit of the diffuser, divided by the area at the metering section. A larger AR increases the diffusion of the coolant momentum, leading to lower average momentum of the coolant jet at the exit of the hole and generally better cooling performance. Cooling holes with larger ARs are also more tolerant of high blowing ratio conditions, and the increased coolant diffusion typically better prevents jet lift-off from occurring. Higher ARs have traditionally been accomplished by increasing the expansion angle of the diffuser while keeping the overall length of the hole constant. The present study maintains the diffuser expansion angles and instead increases the length of the diffuser, which results in longer holes. Various ARs have been examined for two shaped holes: one with forward and lateral expansion angles of 7 deg (7-7-7 hole) and one with forward and lateral expansion angles of 12 deg (12-12-12 hole). Each hole shape was tested at numerous blowing ratios to capture trends across various flow rates. Adiabatic effectiveness measurements indicate that for the baseline 7-7-7 hole, a larger AR provides higher effectiveness, especially at higher blowing ratios. Measurements also indicate that for the 12-12-12 hole, a larger AR performs better at high blowing ratios but the hole experiences ingestion at low blowing ratios. Steady Reynolds-averaged Navier–Stokes simulations did not accurately predict the levels of adiabatic effectiveness, but did predict the trend of improving effectiveness with increasing AR for both hole shapes. Flowfield measurements with particle image velocimetry (PIV) were also performed at one downstream plane for a low and high AR case, and the results indicate an expected decrease in jet velocity due to a larger diffuser.

The Effect of Freestream Turbulence on Film Cooling Adiabatic Effectiveness

Volume 3: Turbo Expo 2002, Parts A and B ◽

10.1115/gt2002-30172 ◽

2002 ◽

Cited By ~ 1

Author(s):

James E. Mayhew ◽

James W. Baughn ◽

Aaron R. Byerley

Keyword(s):

Flat Plate ◽

Film Cooling ◽

Density Ratio ◽

Main Flow ◽

Freestream Turbulence ◽

Coverage Area ◽

Liquid Crystal Thermography ◽

Blowing Ratio ◽

Adiabatic Effectiveness ◽

Cooling Air

The film-cooling performance of a flat plate in the presence of low and high freestream turbulence is investigated using liquid crystal thermography. High-resolution distributions of the adiabatic effectiveness are determined over the film-cooled surface of the flat plate using the hue method and image processing. Three blowing rates are investigated for a model with three straight holes spaced three diameters apart, with density ratio near unity. High freestream turbulence is shown to increase the area-averaged effectiveness at high blowing rates, but decrease it at low blowing rates. At low blowing ratio, freestream turbulence clearly reduces the coverage area of the cooling air due to increased mixing with the main flow. However, at high blowing ratio, when much of the jet has lifted off in the low turbulence case, high freestream turbulence turns its increased mixing into an asset, entraining some of the coolant that penetrates into the main flow and mixing it with the air near the surface.

Film Cooling From Novel Sister Shaped Single-Holes

Volume 5B: Heat Transfer ◽

10.1115/gt2014-25971 ◽

2014 ◽

Cited By ~ 5

Author(s):

Siavash Khajehhasani ◽

Bassam Jubran

Keyword(s):

Film Cooling ◽

Three Dimensional ◽

Lateral Spreading ◽

Navier Stokes ◽

The Novel ◽

Cooling Performance ◽

Film Cooling Effectiveness ◽

Blowing Ratio ◽

Shaped Hole ◽

A numerical investigation of the film cooling performance from novel sister shaped single-holes (SSSH) is presented in this paper and the obtained results are compared with a single cylindrical hole, a forward diffused shaped hole, as well as discrete sister holes. Three types of the novel sister shaped single-hole schemes namely downstream, upstream and up/downstream SSSH, are designed based on merging the discrete sister holes to the primary hole in order to reduce the jet lift-off effect and increase the lateral spreading of the coolant on the blade surface as well as a reduction in the amount of coolant in comparison with discrete sister holes. 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 upstream SSSH demonstrates similar film cooling performance to that of the forward diffused shaped hole for the low blowing ratio of 0.5. While it performs more efficiently at M = 1, where the centerline and laterally averaged effectiveness results improved by 70% and 17%, respectively. On the other hand, the downstream and up/downstream SSSH schemes show a considerable improvement in film cooling performance in terms of obtaining higher film cooling effectiveness and less jet lift-off effect as compared with the single cylindrical and forward diffused shaped holes for both blowing ratios of M = 0.5 and 1. For example, the laterally averaged effectiveness for the downstream SSSH configuration shows an improvement of approximately 57% and 110% on average as compared to the forward diffused shaped hole for blowing ratios of 0.5 and 1, respectively.