scholarly journals Scaling Flat-Plate, Low-Temperature Adiabatic Effectiveness Results Using the Advective Capacity Ratio

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Jacob P. Fischer ◽  
Luke J. McNamara ◽  
James L. Rutledge ◽  
Marc D. Polanka
Keyword(s):  
Low Temperature ◽  
Specific Heat ◽  
Flat Plate ◽  
Film Cooling ◽  
Velocity Ratio ◽  
Density Ratio ◽  
Flux Ratio ◽  
Capacity Ratio ◽  
Extreme Property ◽  
Adiabatic Effectiveness

Abstract Design of film-cooled engine components requires the ability to predict behavior at engine conditions through low-temperature testing. The adiabatic effectiveness, η, is one indicator film cooling performance. An experiment to measure η in a low-temperature experiment requires appropriate selection of the coolant flowrate. The mass flux ratio, M, is usually used in lieu of the velocity ratio to account for the fact that the coolant density is larger than that of the hot freestream at engine conditions. Numerous studies have evaluated the ability of M to scale η with mixed results. The momentum flux ratio, I, is an alternative also found to have mixed success, leading some to recommend matching the density ratio to allow simultaneous matching of M and I. Nevertheless, inconsistent results in the literature regarding the efficacy of these coolant flowrate parameters to scale the density ratio suggest other properties also play a role. Experiments were performed to measure η on a flat plate with a 7-7-7-shaped hole. Various coolant gases were used to give a large range of property variations. We show that a relatively new coolant flowrate parameter that accounts for density and specific heat, the advective capacity ratio, far exceeds the ability of either M or I to provide matched η between the various coolant gases that exhibit extreme property differences. With the specific heat of coolant in an engine significantly lower than that of the freestream, advective capacity ratio (ACR) is appropriate for scaling η with non-separating coolant flow.

Scaling Flat Plate, Low Temperature Adiabatic Effectiveness Results Using the Advective Capacity Ratio

2019 ◽  
Author(s):  
Jacob P. Fischer ◽  
James L. Rutledge ◽  
Luke J. McNamara ◽  
Marc D. Polanka
Keyword(s):  
Low Temperature ◽  
Specific Heat ◽  
Flat Plate ◽  
Flow Rate ◽  
Density Ratio ◽  
Flux Ratio ◽  
Coolant Flow ◽  
Coolant Flow Rate ◽  
Rate Parameter ◽  
Adiabatic Effectiveness

Abstract Effective design of film cooled engine components requires the ability to predict behavior at engine conditions. This is commonly accomplished through low temperature testing on scaled up geometries. The adiabatic effectiveness, η, is one indicator of the performance of a film cooling scheme. Performing an experiment to measure η in a low temperature wind tunnel requires appropriate selection of the coolant flow rate. Perhaps the most common flow rate parameter that is used to characterize the coolant flow relative to the freestream is the mass flux ratio, or blowing ratio, M. This is usually used in lieu of the velocity ratio to account for the fact that the density of the coolant is typically much larger than that of the hot freestream gas. Numerous studies have taken place evaluating the ability of M to properly scale the effects of density ratio and its performance has produced mixed results. The momentum flux ratio, I, is an alternative that is also found to have mixed success, leading some to recommend matching the density ratio to allow simultaneous matching of M and I. Nevertheless, widely varying results in the literature regarding the efficacy of these coolant flow rate parameters to scale the density ratio suggests there may be other largely ignored effects playing a role in the thermal physics. In the present work, thermal experiments were performed to measure adiabatic effectiveness on a flat plate with a single 7-7-7 shaped hole. Various coolant gases were used to give a large range of thermodynamic property variations. It is shown that a relatively new coolant flow rate parameter that accounts for not only density variations but also specific heat variations, the advective capacity ratio (ACR), far exceeds the ability of either M or I to provide matched adiabatic effectiveness between the various coolant gases that exhibit extreme property differences. Particularly considering that the specific heat of the coolant in an engine is significantly lower than the specific heat of the freestream gas, ACR is shown to be appropriate for characterizing non-separating coolant flow situations.

Numerical Investigation of Coolant-to-Mainstream Scaling Parameters With Film Cooling on Pressure and Suction Side of a Gas Turbine Blade

2017 ◽  
Author(s):  
Lingyu Zeng ◽  
Xueying Li ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Gas Turbine ◽  
Film Cooling ◽  
Momentum Flux ◽  
Velocity Ratio ◽  
Density Ratio ◽  
Flux Ratio ◽  
Suction Side ◽  
Pressure Side ◽  
Blowing Ratio ◽  
Adiabatic Effectiveness

Most experiments of blade film cooling are conducted with density ratio lower than that of turbine conditions. In order to accurately model the performance of film cooling under a high density ratio, choosing an appropriate coolant to mainstream scaling parameter is necessary. The effect of density ratio on film cooling effectiveness on the surface of a gas turbine twisted blade is investigated from a numerical point of view. One row of film holes are arranged in the pressure side and two rows in the suction side. All the film holes are cylindrical holes with a pitch to diameter ratio P/d = 8.4. The inclined angle is 30°on the pressure side and 34° on the suction side. The steady solutions are obtained by solving Reynolds-Averaged-Navier-Stokes equations with a finite volume method. The SST turbulence model coupled with γ-θ transition model is applied for the present simulations. A film cooling experiment of a turbine vane was done to validate the turbulence model. Four different density ratios (DR) from 0.97 to 2.5 are studied. To independently vary the blowing ratio (M), momentum flux ratio (I) and velocity ratio (VR) of the coolant to the mainstream, seven conditions (M varying from 0.25 to 1.6 on the pressure side and from 0.25 to 1.4 on the suction side) are simulated for each density ratio. The results indicate that the adiabatic effectiveness increases with the increase of density ratio for a certain blowing ratio or a certain momentum flux ratio. Both on the pressure side and suction side, none of the three parameters listed above can serve as a scaling parameter independent of density ratio in the full range. The velocity ratio provides a relative better collapse of the adiabatic effectiveness than M and I for larger VRs. A new parameter describing the performance of film cooling is introduced. The new parameter is found to be scaled with VR for nearly the whole range.

Computational Fluid Dynamics Evaluations of Film Cooling Flow Scaling Between Engine and Experimental Conditions

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
James L. Rutledge ◽  
Marc D. Polanka ◽  
Nathan J. Greiner
Keyword(s):  
Low Temperature ◽  
Film Cooling ◽  
Momentum Flux ◽  
Room Temperature ◽  
Density Ratio ◽  
Flux Ratio ◽  
Experimental Conditions ◽  
Cold Air ◽  
Momentum Flux Ratio ◽  
Adiabatic Effectiveness

The hostile turbine environment requires testing film cooling designs in wind tunnels that allow for appropriate instrumentation and optical access, but at temperatures much lower than in the hot section of an engine. Low-temperature experimental techniques may involve methods to elevate the coolant to freestream density ratio to match or approximately match engine conditions. These methods include the use of CO2 or cold air for the coolant while room temperature air is used for the freestream. However, the density is not the only fluid property to differ between typical wind tunnel experiments so uncertainty remains regarding which of these methods best provide scaled film cooling performance. Furthermore, matching of both the freestream and coolant Reynolds numbers is generally impossible when either mass flux ratio or momentum flux ratio is matched. A computational simulation of a film cooled leading edge geometry at high-temperature engine conditions was conducted to establish a baseline condition to be matched at simulated low-temperature experimental conditions with a 10× scale model. Matching was performed with three common coolants used in low-temperature film cooling experiments—room temperature air, CO2, and cold air. Results indicate that matched momentum flux ratio is the most appropriate for approximating adiabatic effectiveness for the case of room temperature air coolant, but matching the density ratio through either CO2 or cold coolant also has utility. Cold air was particularly beneficial, surpassing the ability of CO2 to match adiabatic effectiveness at the engine condition, even when CO2 perfectly matches the density ratio.

Experimental Investigation of Coolant-to-Mainstream Scaling Parameters With Cylindrical and Shaped Film Cooling Holes

2015 ◽  
Author(s):  
Joshua B. Anderson ◽  
Emily J. Boyd ◽  
David G. Bogard
Keyword(s):  
Film Cooling ◽  
Velocity Ratio ◽  
Density Ratio ◽  
Flux Ratio ◽  
Experimental Film ◽  
Single Row ◽  
Blowing Ratio ◽  
Scaling Parameters ◽  
Dimensional Parameters ◽  
Adiabatic Effectiveness

The performance of film cooling designs is typically quantified by the adiabatic effectiveness, with results presented in terms of non-dimensional parameters such as the blowing ratio, momentum flux ratio, or velocity ratio of the coolant to the overflowing mainstream gas. In order to appropriately model experimental film cooling designs, the correct coolant flow parameter should be selected. In this work, a single row of axial round holes and shaped holes were placed in a flat plate and tested within a recirculating wind tunnel at low speeds and temperatures. Mainstream turbulence intensity and boundary layer thickness were set similar to expected engine conditions. The density ratio of the coolant was varied from 1.2 to 1.6 in order to independently vary the parameters listed above, which were tested at six different conditions for each density ratio. High-resolution IR thermography was used to measure adiabatic effectiveness downstream of the single row of cooling holes. The results indicate that adiabatic effectiveness performance of cylindrical and shaped holes are scaled most effectively using velocity ratio, providing much more accurate results then when the blowing ratio is used.

Effects of Velocity Ratio on Trends in Film-Cooling Adiabatic Effectiveness and Turbulence

2019 ◽  
Author(s):  
Zachary T. Stratton ◽  
Tom I.-P. Shih
Keyword(s):  
Heat Flux ◽  
Film Cooling ◽  
Velocity Ratio ◽  
Density Ratio ◽  
Flux Ratio ◽  
Turbulence Models ◽  
Absolute Difference ◽  
Turbulent Heat ◽  
Reynolds Stresses ◽  
Adiabatic Effectiveness

Abstract For film-cooling of a flat plate with cooling jets issuing from round holes, turbulent mixing has been shown to scale with the velocity ratio (VR). In this paper, large-eddy simulations (LES) were performed to investigate the effect of varying blowing ratio (BR = 0.5 – 1.3), density ratio (DR = 1.1 – 2.1), and momentum-flux ratio (MR = 0.2–0.8) on adiabatic effectiveness and turbulence, while keeping the VR fixed at 0.46 and 0.63. Simulations based on Reynolds-Averaged Navier-Stokes (RANS) equations with the realizable k-ϵ and shear-stress transport k-ω models were also performed. The LES results show that separation and spreading of the film-cooling jet increase as BR, DR, and MR increase while VR remains constant. For a given VR, the LES predicts an absolute difference between the minimum adiabatic effectiveness of the lowest and highest MRs to be 2 to 5 times greater than those predicted by RANS. This is because RANS with either model cannot respond appropriately to changes in MR. However, RANS can correctly predict that adiabatic effectiveness decreases as VR increases. The LES results show the turbulent kinetic energy and Reynolds stresses near the film-cooling hole to change considerably with MRs at a constant VR, while turbulent heat flux changes negligibly. This suggests that while improved turbulence models for heat flux can improve RANS prediction of spreading, capturing trends, however, requires improved modeling of the Reynolds stresses.

CFD Evaluations of Film Cooling Flow Scaling Between Engine and Experimental Conditions

2016 ◽  
Author(s):  
James L. Rutledge ◽  
Marc D. Polanka ◽  
Nathan J. Greiner
Keyword(s):  
Low Temperature ◽  
Film Cooling ◽  
Momentum Flux ◽  
Room Temperature ◽  
Density Ratio ◽  
Flux Ratio ◽  
Experimental Conditions ◽  
Cold Air ◽  
Momentum Flux Ratio ◽  
Adiabatic Effectiveness

The hostile turbine environment requires that film cooling designs are tested in wind tunnels that allow for appropriate instrumentation and optical access, but at temperatures much lower than in the hot section of an engine. Low temperature experimental techniques may involve methods to elevate the coolant to freestream density ratio to match or approximately match engine conditions. These methods include the use of CO2 or cold air for the coolant while room temperature air is used for the freestream. However, density is not the only fluid property to differ between typical wind tunnel experiments so uncertainty remains regarding which of these methods is best suited to provide scaled film cooling performance. Furthermore, precise matching of both the freestream and coolant Reynolds numbers is generally impossible when either mass flux ratio or momentum flux ratio is matched. A computational simulation of an engine scale film cooled leading edge geometry at high temperature engine conditions was conducted to establish a baseline condition to be matched at simulated low temperature experimental conditions with a 10x scale model. Matching was performed with three common coolant types used in low temperature film cooling experiments — room temperature air, CO2, and cold air to match density ratio. Results indicate that matched momentum flux ratio is the most appropriate for matching adiabatic effectiveness for the case of room temperature air coolant, but also matching density ratio through either CO2 or cold coolant has utility. Cold air was particularly beneficial, surpassing the ability of CO2 to match adiabatic effectiveness at the engine condition, even when CO2 perfectly matches density ratio.

The Effect of Freestream Turbulence on Film Cooling Adiabatic Effectiveness

2002 ◽  
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.

scholarly journals Film Cooling From Spanwise Oriented Holes in Two Staggered Rows

1995 ◽  
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 ◽  
Lift Off

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.

scholarly journals Effects of Crossflow in an Internal-Cooling Channel on Film Cooling of a Flat Plate Through Compound-Angle Holes

2015 ◽  
Author(s):  
Zachary T. Stratton ◽  
Tom I-P. Shih ◽  
Gregory M. Laskowski ◽  
Brian Barr ◽  
Robert Briggs
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Gas Flow ◽  
Density Ratio ◽  
Internal Cooling ◽  
Cfd Simulations ◽  
Hot Gas ◽  
Adiabatic Effectiveness ◽  
Cooling Passage ◽  
Internal Cooling Passage

CFD simulations were performed to study the film cooling of a flat plate from one row of compound-angles holes fed by an internal-cooling passage that is perpendicular to the hot-gas flow. Parameters examined include direction of flow in the internal cooling passage and blowing ratios of 0.5, 1.0, and 1.5 with the coolant-to-hot-gas density ratio kept at 1.5. This CFD study is based on steady RANS with the shear-stress transport (SST) and realizable k-ε turbulence models. To understand the effects of unsteadiness in the flow, one case was studied by using large-eddy simulation (LES). Results obtained showed an unsteady vortical structure forms inside the hole, causing a side-to-side shedding of the coolant jet. Values of adiabatic effectiveness predicted by CFD simulations were compared with the experimentally measured values. Steady RANS was found to be inconsistent in its ability to predict adiabatic effectiveness with relative error ranging for 10% to over 100%. LES was able to predict adiabatic effectiveness with reasonable accuracy.

Scaling of Performance for Varying Density Ratio Coolants on an Airfoil With Strong Curvature and Pressure Gradient Effects

2000 ◽  
Author(s):  
Marcia I. Ethridge ◽  
J. Michael Cutbirth ◽  
David G. Bogard
Keyword(s):  
Pressure Gradient ◽  
Film Cooling ◽  
Density Ratio ◽  
Flux Ratio ◽  
Leading Edge ◽  
Suction Side ◽  
Cooling Performance ◽  
Injection Angle ◽  
Adiabatic Effectiveness ◽  
Strong Curvature

An experimental study was conducted to investigate the film cooling performance on the suction side of a first stage turbine vane. Tests were conducted on a nine times scale vane model at density ratios of DR = 1.1 and 1.6 over a range of blowing conditions, 0.2 ≤ M ≤ 1.5 and 0.05 ≤ I ≤ 1.2. Two different mainstream turbulence intensity levels, Tu∞ = 0.5% and 20%, were also investigated. The row of coolant holes studied was located in a position of both strong curvature and strong favorable pressure gradient. In addition, its performance was isolated by blocking the leading edge showerhead coolant holes. Adiabatic effectiveness measurements were made using an infrared camera to map the surface temperature distribution. The results indicate that film cooling performance was greatly enhanced over holes with a similar 50° injection angle on a flat plate. Overall, adiabatic effectiveness scaled with mass flux ratio for low blowing conditions and with momentum flux ratio for high blowing conditions. However, for M < 0.5 there was a higher rate of decay for the low density ratio data. High mainstream turbulence had little effect at low blowing ratios, but degraded performance at higher blowing ratios.

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