scholarly journals Density Ratio Effects on the Cooling Performances of a Combustor Liner Cooled by a Combined Slot/Effusion System

2012 ◽  
Author(s):  
A. Andreini ◽  
G. Caciolli ◽  
B. Facchini ◽  
L. Tarchi ◽  
D. Coutandin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Working Conditions ◽  
Cooling System ◽  
Velocity Ratio ◽  
Density Ratio ◽  
Perforated Plate ◽  
Flow Parameters ◽  
Adiabatic Effectiveness ◽  
Combustor Liner ◽  
Effects Of Density

The aim of the present study is to investigate the effects of density ratio between coolant and mainflow on a real engine cooling scheme of a combustor liner. Measurements of heat transfer coefficient and adiabatic effectiveness were performed by means of a steady-state Thermochromic Liquid Crystals (TLC) technique; experimental results were used to estimate, through a 1D thermal procedure (Therm1d), the Net Heat Flux Reduction and the overall effectiveness in realistic engine working conditions. In order to reproduce a representative value of combustor coolant to mainstream density ratio, tests were carried out feeding the cooling system with carbon dioxide (CO2), while air was used in the main channel; to highlight the effects of density ratio and, as a consequence, to distinguish between the influence of blowing ratio and velocity ratio, tests were replicated using air both as coolant and mainstream and results were compared. The experimental analysis was performed on a test article replicating a slot injection and an effusion array with a central large dilution hole. Test section consists of a rectangular cross-section duct and a flat perforated plate provided with 272 holes arranged in 29 staggered rows (d = 1.65 mm, α = 30°, L/d = 5.5). Furthermore a dilution hole (D = 18.75 mm) is located at the 14th row; both effusion and dilution holes are fed by a channel replicating a combustor annulus. The rig allows to control mainstream and coolant flow parameters, especially in terms of Reynolds number of mainstream and effusion holes. Located upstream the first effusion row, a 6.0 mm high slot ensures the protection of the very first region of the liner. Experiments were carried out imposing several values of effusion blowing and velocity ratios within a range of typical modern engine working conditions (BReff/VReff = 1.5; 3.0; 5.0; 7.0) and keeping constant slot flow parameters (BRsl ≈ 1.5). Results point out the influence of density ratio on film cooling performance, suggesting that velocity ratio is the driving parameter for the heat transfer phenomena; concerning the effectiveness, results show that the adiabatic effectiveness is less sensitive to the cooling flow parameters, especially at the higher blowing/velocity ratios.

scholarly journals Experimental Evaluation of the Density Ratio Effects on the Cooling Performance of a Combined Slot/Effusion Combustor Cooling System

2013 ◽  
Vol 2013 ◽  
pp. 1-14 ◽  
Author(s):  
Antonio Andreini ◽  
Gianluca Caciolli ◽  
Bruno Facchini ◽  
Lorenzo Tarchi
Keyword(s):  
Heat Transfer ◽  
Working Conditions ◽  
Film Cooling ◽  
Cooling System ◽  
Velocity Ratio ◽  
Density Ratio ◽  
Cooling Performance ◽  
Engine Cooling ◽  
Flow Parameters ◽  
Adiabatic Effectiveness

The purpose of this study is to investigate the effects of coolant-to-mainstream density ratio on a real engine cooling scheme of a combustor liner composed of a slot injection and an effusion array with a central dilution hole. Measurements of heat transfer coefficient and adiabatic effectiveness were performed by means of steady-state thermochromic liquid crystals technique; experimental results were used to estimate, through a 1D thermal procedure, the Net Heat Flux Reduction and the overall effectiveness in realistic engine working conditions. To reproduce a representative value of combustor coolant-to-mainstream density ratio, tests were carried out feeding the cooling system with carbon dioxide, while air was used in the main channel; to highlight the effects of density ratio, tests were replicated using air both as coolant and as mainstream and results were compared. Experiments were carried out imposing values of effusion blowing and velocity ratios within a range of typical modern engine working conditions. Results point out the influence of density ratio on film cooling performance, suggesting that velocity ratio is the driving parameter for the heat transfer phenomena; on the other hand, the adiabatic effectiveness is less sensitive to the cooling flow parameters, especially at the higher blowing/velocity ratios.

Combined Effect of Slot Injection, Effusion Array and Dilution Hole on the Cooling Performance of a Real Combustor Liner

2009 ◽  
Author(s):  
Alberto Ceccherini ◽  
Bruno Facchini ◽  
Lorenzo Tarchi ◽  
Lorenzo Toni ◽  
Daniele Coutandin
Keyword(s):  
Rectangular Cross Section ◽  
Velocity Ratio ◽  
Perforated Plate ◽  
Cross Flow ◽  
Engine Cooling ◽  
Flow Parameters ◽  
Fluid Network ◽  
Local Protection ◽  
Definition Of ◽  
Combustor Liner

Due to the higher cooling requirements of novel combustor liners a comprehensive understanding of the phenomena concerning the interaction of hot gases with different coolant flows plays a major role in the definition of a well performing liner. An experimental analysis of a real engine cooling scheme was performed on a test article replicating a slot injection and an effusion array with a central large dilution hole. Test section consists of a rectangular cross-section duct and a flat perforated plate with 272 holes arranged in 29 staggered rows (d = 1.65 mm, Sx/d = 7.6, Sy/d = 6, L/d = 5.5, α = 30 deg); a dilution hole (D = 18.75 mm) is located at the 14th row. Both effusion and dilution holes are fed by a channel replicating combustor annulus, that allows to control cold gas side cross-flow parameters. Upstream the first effusion row, a 6.0 mm high slot ensure the protection of the very first region of the liner. Final aim was the measurement of adiabatic effectiveness of the cooling scheme by means of a steady-state Thermochromic Liquid Crystals (TLC) technique, considering the combined effects of slot, effusion and dilution holes. Experiments were carried out imposing three different effusion velocity ratios typical of modern engine working conditions (VReff = 3, 5, 7) and keeping constant slot flow parameters (VRsl = 1.1). CFD RANS calculations were also performed with the aim of better understanding interactions between coolant exiting from the slot and injected by effusion cooling rows. Numerical analysis revealed a large dependency on effusion velocity ratio. An in-house one-dimensional fluid network solver was finally used to compare experimental and numerical results with the ones predicted by correlations and then quantify the possibility of giving predictions. Both CFD and experimental results reveal that slot protection is reduced in the first rows by coolant injected with such high velocity ratios; nevertheless effusion, though in penetration regime, guarantees a significant effectiveness level in the more downstream region. Dilution hole alters the effectiveness growth rate, moreover leading to local protection lowering just after its injection.

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.

Flow Field and Heat Transfer Characteristics in an Impingement/Effusion Cooling System for Combustor Liner

2005 ◽  
Author(s):  
Quanhong Xu ◽  
Chi Zhang ◽  
Yuzhen Lin ◽  
Gaoen Liu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Flow Field ◽  
Transfer Coefficient ◽  
Cooling System ◽  
Impingement Jet ◽  
Impingement Heat Transfer ◽  
Double Skin ◽  
Combustor Liner ◽  
Effusion Hole

The present study is conducted to investigate the characteristics of the flow field and heat transfer in an impingement/effusion cooling scheme for gas turbine combustor liner. It is designed to provide an insight, through the study of the flow field, into the physical mechanisms responsible for the enhanced impingement heat transfer near the effusion hole entrance. In this impingement/effusion cooling scheme, the angle between the impingement hole and effusion hole and the wall surface are 90 deg and 30 deg respectively. The square arrays of impingement/effusion holes are used with equal numbers of holes offset half a pitch relative to each plate so that an impingement jet is located on the center of each four effusion holes and vice versa. The flow field of the double skin wall space is described by the way of Particle Image Velocimetry (PIV). Two kinds of target plates, with and without effusion holes, are used in the impingement heat transfer study. Through changing the impingement Reynolds and the impingement gap, the change of the impingement heat transfer coefficient on the target plates is investigated. The impingement heat transfer test results show that the impingement heat transfer is enhanced near the entrance of the effusion holes, which could fully explain the feature of the impingement heat transfer coefficient on the target plate.

High-Resolution Film Cooling Effectiveness Measurements of Axial Holes Embedded in a Transverse Trench With Various Trench Configurations

2006 ◽  
Vol 129 (2) ◽  
pp. 294-302 ◽  
Author(s):  
Scot K. Waye ◽  
David G. Bogard
Keyword(s):  
High Resolution ◽  
Film Cooling ◽  
Density Ratio ◽  
Field Measurements ◽  
Suction Side ◽  
Lateral Spreading ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Flow Parameters ◽  
Adiabatic Effectiveness

Adiabatic film cooling effectiveness of axial holes embedded within a transverse trench on the suction side of a turbine vane was investigated. High-resolution two-dimensional data obtained from infrared thermography and corrected for local conduction provided spatial adiabatic effectiveness data. Flow parameters of blowing ratio, density ratio, and turbulence intensity were independently varied. In addition to a baseline geometry, nine trench configurations were tested, all with a depth of 1∕2 hole diameter, with varying widths, and with perpendicular and inclined trench walls. A perpendicular trench wall at the very downstream edge of the coolant hole was found to be the key trench characteristic that yielded much improved adiabatic effectiveness performance. This configuration increased adiabatic effectiveness up to 100% near the hole and 40% downstream. All other trench configurations had little effect on the adiabatic effectiveness. Thermal field measurements confirmed that the improved adiabatic effectiveness that occurred for a narrow trench with perpendicular walls was due to a lateral spreading of the coolant and reduced coolant jet separation. The cooling levels exhibited by these particular geometries are comparable to shaped holes, but much easier and cheaper to manufacture.

Influence of Entrance Geometry on Heat Transfer in Narrow Rectangular Cooling Channels (AR = 4:1) With Angled Ribs

2003 ◽  
Author(s):  
Lesley M. Wright ◽  
Eungsuk Lee ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Rotation Number ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Transfer Enhancement ◽  
Cooling Channels ◽  
Flow Parameters ◽  
Smooth Channel ◽  
Mainstream Flow ◽  
Sudden Contraction

The effect of entrance geometry on the heat transfer in rotating, narrow rectangular cooling channels is investigated in this study. Both smooth channels and channels with angled ribs are considered with three different entrance conditions: fully developed, sudden contraction, partial sudden contraction. The rectangular channel has as aspect ratio of 4:1, and it is oriented at 135° with respect to the plane of rotation. In the test section with angled ribs, the ribs are angled at 45° to the mainstream flow. The rib height-to-hydraulic diameter ratio (e/Dh) is 0.078, and the rib pitch-to-height ratio (P/e) is 10. The range of flow parameters includes Reynolds number (Re = 5000–40000), rotation number (Ro = 0.0–0.302), and inlet coolant-to-wall density ratio (Δρ/ρ = 0.12). The heat transfer at the entrance of the heated portion of the smooth channel is significantly enhanced with the sudden contraction and partial sudden contraction entrances. In the smooth rotating channels, the effect of the entrance geometry is also present; however, as the rotation number increases, the effect of the entrance geometry decreases. It was also found in this study that the sudden and partial sudden contraction entrances provide higher heat transfer enhancement than the fully developed entrance through the first 3 to 4 hydraulic diameters of the channels with angled ribs. Again, the effect of the entrance geometry is greater in the stationary channels with angled ribs than the rotating channels with ribs. In both stationary and rotating channels, the influence of the entrance geometry on the heat transfer is more apparent in the smooth channels than in the ribbed channels.

scholarly journals Effects on Heat Transfer Coefficient and Adiabatic Effectiveness in Combined Backside and Film Cooling With Short-Hole Geometry

2019 ◽  
Author(s):  
Renzo La Rosa ◽  
Jaideep Pandit ◽  
Wing Ng ◽  
Brett Barker
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Density Ratio ◽  
Transfer Model ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Adiabatic Effectiveness

Abstract Heat transfer experiments were done on a flat plate to study the effect of internal counter-flow backside cooling on adiabatic film cooling effectiveness and heat transfer coefficient. In addition, the effects of density ratio (DR), blowing ratio (BR), diagonal length over diameter (L/D) ratio, and Reynolds number were studied using this new configuration. The results are compared to a conventional plenum fed case. Data were collected up to X/D = 23 where X = 0 at the holes, an S/D = 1.65 and L/D = 1 and 2. Testing was done at low L/D ratios since short holes are normally found in double wall cooling applications in turbine components. A DR of 2 was used in order to simulate engine-like conditions and this was compared to a DR of 0.92 since relevant research is done at similar low DR. The BR range of 0.5 to 1.5 was chosen to simulate turbine conditions as well. In addition, previous research shows that peak effectiveness is found within this range. Infrared (IR) thermography was used to capture temperature contours on the surface of interest and the images were calibrated using a thermocouple and data analyzed through MATLAB software. A heated secondary fluid was used as ‘coolant’ in the present study. A steady state heat transfer model was used to perform the data reduction procedure. Results show that backside cooling configuration has a higher adiabatic film cooling effectiveness when compared to plenum fed configurations at the same conditions. In addition, the trend for effectiveness with varying BR is reversed when compared with traditional plenum fed cases. Yarn flow visualization tests show that flow exiting the holes in the backside cooling configuration is significantly different when compared to flow exiting the plenum fed holes. We hypothesize that backside cooling configuration has flow exiting the holes in various directions, including laterally, and behaving similar to slot film cooling, explaining the differences in trends. Increasing DR at constant BR shows an increase in adiabatic effectiveness and HTC in both backside cooling and plenum fed configurations due to the decreased momentum of the coolant, making film attachment to the surface more probable. The effects of L/D ratio in this study were negligible since both ratios used were small. This shows that the coolant flow is still underdeveloped at both L/D ratios. The study also showed that increasing turbulence through increasing Reynolds number decreased adiabatic effectiveness.

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.

Thermal Performance Intensification of Car Radiator using SiO2/Water and ZnO/Water Nanofluids

2021 ◽  
pp. 1-25
Author(s):  
Hussein Maghrabie ◽  
Hamouda Mousa
Keyword(s):  
Heat Transfer ◽  
Working Conditions ◽  
Flow Rate ◽  
Thermal Performance ◽  
Cooling System ◽  
Volume Flow Rate ◽  
Volume Flow ◽  
Coolant Temperature ◽  
Inlet Temperature ◽  
The Impact

Abstract Recent progress in nanotechnology has lead to a revolution in the automotive cooling system. In the present work, enhancement of car radiator thermal performance was investigated using different nanofluids named SiO2/water, ZnO/water nanofluids as cooling mediums. The present study mainly aims to investigate the impact of (5 wt.%) from SiO2 and ZnO nanoparticles (NPs) dispersed in water based on car radiator heat transfer with spherical and hexagonal morphology, respectively. The experiments were performed in two working conditions of the nanofluids i.e coolant temperature and volume flow rate, moreover the present results were compared with the previous studies. The experimental working conditions were set at coolant inlet temperature (tc,i) ranged from 45 oC to 80 oC and the coolant volume flow rate (V) ranged from 3.5 lit/min to 6.5 lit/min. The experimental results show that the hexagonal ZnO/water nanofluid was superior towards enhancement of car radiator thermal performance comparing to that of SiO2 NPs. Additionally, at 6.5 lit/min and 45 °C, the enhancements of car radiator effectiveness due to using SiO2 and ZnO based water nanofluids and compared with that for the based water were 13.9% and 16%, respectively. The present study used the multiple regression analysis (MRA) and hence empirical correlations are suggested to estimate the overall heat transfer coefficient (U) for all coolants as functions of volume flow rate (V) and the coolant inlet temperature (tc,i) with a maximum STDEV of ± 1.85%.

Influence of Entrance Geometry on Heat Transfer in Rotating Rectangular Cooling Channels (AR=4:1) With Angled Ribs

2005 ◽  
Vol 127 (4) ◽  
pp. 378-387 ◽  
Author(s):  
Lesley M. Wright ◽  
Wen-Lung Fu ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Rotation Number ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Transfer Enhancement ◽  
Cooling Channels ◽  
Flow Parameters ◽  
Smooth Channel ◽  
Mainstream Flow ◽  
Sudden Contraction

The effect of entrance geometry on the heat transfer in rotating, narrow rectangular cooling channels is investigated in this study. Both smooth channels and channels with angled ribs are considered with three different entrance conditions: fully developed, sudden contraction, and partial sudden contraction. The rectangular channel has as aspect ratio of 4:1, and it is oriented at 135° with respect to the plane of rotation. In the test section with angled ribs, the ribs are angled at 45° to the mainstream flow. The rib height-to-hydraulic diameter ratio e/Dh is 0.078, and the rib pitch-to-height ratio P/e is 10. The range of flow parameters includes Reynolds number (Re=5000–40,000), rotation number (Ro=0.0–0.302), and inlet coolant-to-wall density ratio (Δρ/ρ=0.12). The heat transfer at the entrance of the heated portion of the smooth channel is significantly enhanced with the sudden contraction and partial sudden contraction entrances. In the smooth rotating channels, the effect of the entrance geometry is also present; however, as the rotation number increases, the effect of the entrance geometry decreases. It was also found in this study that the sudden and partial sudden contraction entrances provide higher heat transfer enhancement than the fully developed entrance through the first three to four hydraulic diameters of the channels with angled ribs. Again, the effect of the entrance geometry is greater in the stationary channels with angled ribs than the rotating channels with ribs. In both stationary and rotating channels, the influence of the entrance geometry on the heat transfer is more apparent in the smooth channels than in the ribbed channels.

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