scholarly journals Some Effects of Coolant Density on Film Cooling Effectiveness

1993 ◽  
Author(s):  
Ian S. Gartshore ◽  
Marthe Salcudean ◽  
Y. Barnea ◽  
K. Zhang ◽  
F. Aghadsi
Keyword(s):  
Mass Flow ◽  
Film Cooling ◽  
Flux Ratio ◽  
Leading Edge ◽  
Cooling Effectiveness ◽  
Stagnation Line ◽  
Film Cooling Effectiveness ◽  
Flame Ionization ◽  
Tunnel Model ◽  
Large Wind

Experiments have been conducted on a large wind tunnel model of the leading edge region of a turbine blade. The model had a semi-circular leading edge in which four rows of holes were symmetrically placed about the stagnation line, two at ±15° and two at ±44°. Air and alternatively CO2 were injected from the coolant holes after contamination with a known small percentage of propane. Using a flame ionization detector and the mass transfer analogy, the film cooling effectiveness was measured at various overall mass flow ratios and at various streamwise locations for each coolant type. The division of coolant flow rate from the two rows of holes was found to be more unequal for CO2 than for air, an effect which is predicted from a simple analysis of the coolant/free stream interaction and the hole discharge coefficient. This has practical implications for actual turbine operation since earlier cut-off of the coolant from the front row of holes, due to density differences, could have disastrous effects on the blade. This effect also further complicates any attempt to identify overall trends of coolant density on performance. It is not possible to conclude that air or CO2 coolant has a higher film cooling effectiveness, although, in general, air appears better close to the first row of holes, and CO2 better at some distance downstream of both rows. Based on the measurements, the effects of mass flow ratio, momentum flux ratio, relative hole placement in each row, and spanwise versus streamwise injection are discussed in the paper.

An Experimental Study of Film Cooling Effectiveness Near the Leading Edge of a Turbine Blade

1994 ◽  
Vol 116 (1) ◽  
pp. 71-79 ◽  
Author(s):  
M. Salcudean ◽  
I. Gartshore ◽  
K. Zhang ◽  
I. McLean
Keyword(s):  
Turbine Blade ◽  
Mass Flow ◽  
Film Cooling ◽  
Leading Edge ◽  
Cooling Effectiveness ◽  
Stagnation Line ◽  
Film Cooling Effectiveness ◽  
Flame Ionization ◽  
Blade Model ◽  
Flow Division

A flame ionization technique based on the heat/mass transfer analogy has been used in an experimental investigation of film cooling effectiveness. The measurements were made over the surface of a turbine blade model composed of a semi-cylindrical leading edge bonded to a flat after-body. The secondary flow was injected into the boundary layer through four rows of holes located at ±15 and ±44 deg about the stagnation line of the leading edge. These holes, of diameter d, had a 30 deg spanwise inclination and a 4d spanwise spacing. Adjacent rows of holes were staggered by 2d, and perfect geometry symmetry was maintained across the stagnation line. Discharge coefficients and flow division between the 15 and 44 deg rows of holes have also been measured. The strong pressure gradient near the leading edge produces a strongly nonuniform flow division between the first (± 15 deg) and the second (± 44 deg) row of holes at low overall mass flow ratios. This produced a total cutoff of the coolant from the first row of holes at mass flow ratios lower than approximately 0.4, leaving the leading edge unprotected near the stagnation line. Streamwise and spanwise plots of effectiveness show that the best effectiveness values are obtained in a very narrow range of mass flux ratios near 0.4 where there is also considerable sensitivity to changes in Reynolds number. The effectiveness values deteriorate abruptly with decreasing mass flow ratios, and substantially with increasing mass flow ratios. Therefore, it was concluded that the cooling arrangement investigated has poor characteristics, and some suggestions are made for alternate designs.

Leading Edge Film Cooling of a Turbine Blade Model Through Single and Double Row Injection: Effects of Coolant Density

1994 ◽  
Author(s):  
M. Salcudean ◽  
I. Gartshore ◽  
K. Zhang ◽  
Y. Barnea
Keyword(s):  
Turbine Blade ◽  
Mass Flow ◽  
Film Cooling ◽  
Leading Edge ◽  
Spanwise Direction ◽  
Double Row ◽  
Cooling Effectiveness ◽  
Stagnation Line ◽  
Film Cooling Effectiveness ◽  
Staggered Arrangement

Experiments have been conducted on a large model of a turbine blade. Attention has been focussed on the leading edge region, which has a semi-circular shape and four rows of film cooling holes positioned symmetrically about the stagnation line. The cooling holes were oriented in a spanwise direction with an inclination of 30° to the surface, and had streamwise locations of ±15° and ±44° from the stagnation line. Film cooling effectiveness was measured using a heat/mass analogy. Single row cooling from the holes at 15° and 44° showed similar patterns: spanwise averaged effectiveness which rises from zero at zero coolant mass flow to a maximum value η* at some value of mass flow ratio M*, then drops to low values of η at higher M. The trends can be quantitatively explained from simple momentum considerations for either air or CO2 as the coolant gas. Close to the holes, air provides higher η values for small M. At higher M, particularly farther downstream, the CO2 may be superior. The use of an appropriately defined momentum ratio G collapses the data from both holes using either CO2 or air as coolant onto a single curve. For η*, the value of G for all data is about 0.1. Double row cooling with air as coolant shows that the relative stagger of the two rows is an important parameter. Holes in line with each other in successive rows can provide improvements in spanwise averaged film cooling effectiveness of as much as 100% over the common staggered arrangement. This improvement is due to the interaction between coolant from rows one and two, which tends to provide complete coverage of the downstream surface when the rows are placed correctly with respect to each other.

Leading Edge Film Cooling: Computations and Experiments Including Density Effects

1996 ◽  
Author(s):  
Pingfan He ◽  
Dragos Licu ◽  
Martha Salcudean ◽  
Ian S. Gartshore
Keyword(s):  
Experimental Data ◽  
Film Cooling ◽  
Stokes Equations ◽  
Leading Edge ◽  
Variable Density ◽  
Navier Stokes ◽  
Cooling Effectiveness ◽  
Stagnation Line ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio

The effect of varying coolant density on film cooling effectiveness for a turbine blade-model was numerically investigated and compared with experimental data. This model had a semi-circular leading edge with four rows of laterally-inclined film cooling orifices positioned symmetrically about the stagnation line. A curvilinear coordinate-based CFD code was developed and used for the numerical investigation. The code used a domain segmentation strategy in conjunction with general curvilinear grids to model the complex blade configuration. A multigrid method was used to accelerate the convergence rate. The time-averaged, variable-density, Navier-Stokes equations together with the energy or scalar equation were solved. Turbulence closure was attained by the standard k–ε model with a near-wall k model. Either air or CO2 was used as coolant in three cases of injection through single rows and alternatively staggered double raws of holes. Two different blowing rates were investigated in each case and compared with experimental data. The experimental results were obtained using a wind tunnel model, and the mass/heat analogy was used to determine the film cooling effectiveness. The higher density of the carbon dioxide coolant (approximately 1.5 times the density of air) in the isothermal mass injection experiments, was used to simulate the effects of injection of a colder air in the corresponding adiabatic heat transfer situation. Good agreement between calculated and measured film cooling effectiveness was found for low blowing ratio M ≤ 0.5 and the effect of density was not significant. At higher blowing ratio M > 1 the calculations consistently overpredict the measured values of film cooling effectiveness.

Comparison of RANS and DES Modeling Against Measurements of Leading Edge Film Cooling on a First-Stage Vane

2016 ◽  
Author(s):  
S. Ravelli ◽  
G. Barigozzi
Keyword(s):  
Film Cooling ◽  
Guide Vane ◽  
Leading Edge ◽  
Spanwise Direction ◽  
Intensity Level ◽  
Edge Region ◽  
Cooling Effectiveness ◽  
Stagnation Line ◽  
Film Cooling Effectiveness ◽  
Adiabatic Effectiveness

The performance of a showerhead arrangement of film cooling in the leading edge region of a first stage nozzle guide vane was experimentally and numerically evaluated. A six-vane linear cascade was tested at an isentropic exit Mach number of Ma2s = 0.42, with a high inlet turbulence intensity level of 9%. The showerhead cooling scheme consists of four staggered rows of cylindrical holes evenly distributed around the stagnation line, angled at 45° towards the tip. The blowing ratios tested are BR = 2.0, 3.0 and 4.0. Adiabatic film cooling effectiveness distributions on the vane surface around the leading edge region were measured by means of Thermochromic Liquid Crystals technique. Since the experimental contours of adiabatic effectiveness showed that there is no periodicity across the span, the CFD calculations were conducted by simulating the whole vane. Within the RANS framework, the very widely used Realizable k-ε (Rke) and the Shear Stress Transport k-ω (SST) turbulence models were chosen for simulating the effect of the BR on the surface distribution of adiabatic effectiveness. The turbulence model which provided the most accurate steady prediction, i.e. Rke, was selected for running Detached Eddy Simulation at the intermediate value of BR = 3. Fluctuations of the local temperature were computed by DES, due to the vortex structures within the shear layers between the main flow and the coolant jets. Moreover, mixing was enhanced both in the wall-normal and spanwise direction, compared to RANS modeling. DES roughly halved the prediction error of laterally averaged film cooling effectiveness on the suction side of the leading edge. However, neither DES nor RANS provided the expected decay of effectiveness progressing downstream along the pressure side, with 15% overestimation of ηav at s/C =0.2.

Experimental Study on Film Cooling Effectiveness of Blade with Chevron Shaped Holes under Wake Influence

2021 ◽  
pp. 1-20
Author(s):  
Jichen Li ◽  
Hui Ren Zhu ◽  
Cun Liang Liu ◽  
Lin Ye ◽  
Zhou Daoen
Keyword(s):  
Mass Flux ◽  
Film Cooling ◽  
Gas Turbines ◽  
Flux Ratio ◽  
Leading Edge ◽  
High Mass ◽  
Suction Surface ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Pressure Surface

Abstract Gas turbines have been widely used. With the continuous improvement of the performance of gas turbines, the turbine inlet temperature has greatly exceeded the heat resistance limit of the turbine blade material, so advanced cooling technology is required. The film cooling effectiveness distribution over the blade under the effect of wake was obtained by Pressure Sensitive Paint (PSP) technique. The test blade has 5 rows of chevron film holes on the pressure side, 3 rows of cylindrical film holes on the leading edge and 3 rows of chevron film holes on the suction side. The mainstream Reynolds number is 130,000 based on the blade chord length, and the mainstream turbulence intensity is 2.7%. The upstream wake was simulated by the spoken-wheel type wake generator. The film cooling effectiveness was measured at three wake Strouhal numbers (0, 0.12 and 0.36) and three mass flux ratios (MFR1, MFR2 and MFR3). The results show that the increase of mass flux ratio leads a decrease of the film cooling effectiveness on the suction surface. In the wake condition, the effect of mass flux ratio is weakened. Wake leads a marked decrease of the film cooling effectiveness over most blade surface except for the surface near leading edge on the pressure surface. In the high mass flux ratio condition, the effect of wake on the film cooling effectiveness is weakened on the suction surface and strengthened on the pressure surface.

A Numerical Study on the Characteristics of How Heat and Cooling Transfer on the Leading Edge of a Film-Cooling Blade

2011 ◽  
Vol 383-390 ◽  
pp. 3963-3968
Author(s):  
Shao Hua Li ◽  
Li Mei Du ◽  
Wen Hua Dong ◽  
Ling Zhang
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Numerical Study ◽  
Leading Edge ◽  
Suction Side ◽  
Pressure Side ◽  
Cooling Effectiveness ◽  
Stagnation Line ◽  
Film Cooling Effectiveness ◽  
Pressure Surface

In this paper, a numerical simulation was performed to investigate heat transferring characteristics on the leading edge of a blade with three rows of holes of film-cooling using Realizable k- model. Three rows of holes were located on the suction side leading edge stagnation line and the pressure surface. The difference of the cooling efficiency and the heat transfer of the three rows of holes on the suction side and pressure side were analyzed; the heat transfer and film cooling effectiveness distribution in the region of leading edge are expounded under different momentum rations.The results show that under the same condition, the cooling effectiveness on the pressure side is more obvious than the suction side, but the heat transfer is better on the suction side than the pressure side. The stronger momentum rations are more effective cooling than the heat transfer system.

Assessment of Steady State PSP and Transient Ir Measurement Techniques for Leading Edge Film Cooling

2005 ◽  
Author(s):  
Zhihong Gao ◽  
Lesley M. Wright ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Film Cooling ◽  
Measurement Techniques ◽  
Turbine Blades ◽  
Leading Edge ◽  
Cooling Effectiveness ◽  
Stagnation Line ◽  
Film Cooling Effectiveness ◽  
Film Cooling Holes

Film cooling is commonly used on the leading edge of turbine blades to protect the blade surface from hot mainstream gases in the turbine. Obtaining detailed film cooling effectiveness distributions on the leading edge can be challenging. This paper considers two measurement techniques which can be applied to the leading edge (modeled by a cylinder) to obtain detailed distributions of the film effectiveness. A steady state pressure sensitive paint (PSP) technique and a transient infrared (IR) thermography technique are used to obtain detailed film cooling effectiveness distributions on the cylinder. The cylinder, 7.62 cm in diameter, is placed in a low speed wind tunnel, with the mainstream flow having a Reynolds number of 100,900 (based on the cylinder diameter). The cylinder has two rows of film cooling holes located at ±15° from the cylinder’s stagnation line. The pitch-to-diameter ratio of the film holes is 4, and holes are inclined 30° in spanwise direction. PSP continues to show promise for film cooling effectiveness measurements. Detailed distributions can be obtained near the film cooling holes because this technique relies on mass transfer rather than heat transfer. In order to reduce the error caused by conduction in heat transfer experiments, transient measurement techniques are favorable. Transient IR measurements are taken, and film cooling effectiveness is determined on the cylinder’s surface. Although the effect of conduction is reduced with the transient IR technique (compared to a steady state heat transfer experiment), heat conduction through the cylinder has not been eliminated (or even minimized). Without correction, the results obtained from transient heat transfer experiments must be used cautiously. For this reason, PSP is developing a niche within the gas turbine community for detailed film cooling effectiveness measurements.

Experimental Investigation of Film Cooling Effectiveness for a New Shaped Hole at the Leading Edge

2010 ◽  
Author(s):  
T. Elnady ◽  
I. Hassan ◽  
L. Kadem ◽  
T. Lucas
Keyword(s):  
Experimental Investigation ◽  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Suction Side ◽  
Local Cooling ◽  
Cooling Effectiveness ◽  
Stagnation Line ◽  
Film Cooling Effectiveness ◽  
Lift Off

An experimental investigation has been performed to study the film cooling of a smooth expansion exit at the leading edge of a gas turbine vane. A two-dimensional cascade has been employed to measure the cooling performance of the proposed expansion using a transient Thermochromatic Liquid Crystal technique. One row of cylindrical holes, located on the stagnation line, is investigated with two expansion levels at the hole exit, 2d and 4d, in addition to the standard cylindrical exit. The air is injected at 0° and 30° inclination angles with the mainstream direction at four blowing ratios ranging from 1 and 2 and a 0.9 density ratio. The Mach number and the Reynolds number based on the cascade exit velocity and the axial chord are 0.23 and 1.4E5, respectively. The detailed local cooling effectiveness over both the pressure side and the suction side are presented in addition to the lateral-averaged cooling effectiveness. The proposed expansion enhances the coolant distribution over the leading edge, particularly over the suction side. The cooling effectiveness increases with the increase of the blowing ratio due to the decrease in the jet lift-off, hence higher cooling capacity is provided. The complete confrontation between both streams on the 0° inclination angle causes a strong dispersion to the coolant, yielding a significant reduction in the effectiveness.

Experimental Study on Film Cooling Effectiveness of Blade With Chevron Shaped Holes Under Wake Influence

2020 ◽  
Author(s):  
Ji-Chen Li ◽  
Hui-Ren Zhu ◽  
Da-Wei Chen ◽  
Dao-En Zhou
Keyword(s):  
Mass Flux ◽  
Film Cooling ◽  
Gas Turbines ◽  
Flux Ratio ◽  
Leading Edge ◽  
High Mass ◽  
Suction Surface ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Pressure Surface

Abstract Gas turbines have been widely used. With the continuous improvement of the performance of gas turbines, the turbine inlet temperature has greatly exceeded the heat resistance limit of the turbine blade material, so advanced cooling technology is required. The film cooling effectiveness distribution over the blade under the effect of wake was obtained by Pressure Sensitive Paint (PSP) technique. The test blade has 5 rows of chevron film holes on the pressure side, 3 rows of cylindrical film holes on the leading edge and 3 rows of chevron film holes on the suction side. The mainstream Reynolds number is 130,000 based on the blade chord length, and the mainstream turbulence intensity is 2.7%. The upstream wake was simulated by the spoken-wheel type wake generator. The film cooling effectiveness was measured at three wake Strouhal numbers (0, 0.12 and 0.36) and three mass flux ratios (MFR1, MFR2 and MFR3). The results show that the increase of mass flux ratio leads a decrease of the film cooling effectiveness on the suction surface. In the wake condition, the effect of mass flux ratio is weakened. Wake leads a marked decrease of the film cooling effectiveness over most blade surface except for the surface near leading edge on the pressure surface. In the high mass flux ratio condition, the effect of wake on the film cooling effectiveness is weakened on the suction surface and strengthened on the pressure surface.

Experiment Study of Simulated Effect of Rotor Stator Interaction: Effect of Axial Spacing and Rotor Blade Film Cooling Air Injection Ratio

2011 ◽  
Author(s):  
Murari Sridhar ◽  
B. V. S. S. S. Prasad ◽  
N. Sitaram
Keyword(s):  
Mass Flow ◽  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Main Flow ◽  
Air Injection ◽  
Blade Surface ◽  
Trailing Edge ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness

The effect of inlet wake and air injection on blade surface temperature distribution is experimentally determined in the present paper. A flat plate with smoothly curved leading edge and a symmetric beveled trailing edge is used to produce inlet wake. Experiments are performed on a seven-airfoil linear cascade in a low speed wind tunnel at the chord Reynolds number of 5.3×105. Three blades in the middle of the cascade are provided with multiple rows of air injection holes on both pressure surface and suction surface. The distance between the trailing edge of the wake plate and leading edge of the cascade blade is kept at three axial locations, i.e. 0.25, 0.35 and 0.5 (all measured in terms of percent blade chord), at seven transverse locations for each axial location. The detailed temperature distributions on the blade surface are measured using “T-Type” thermocouples connected to a data logger. The results are obtained in terms of film cooling effectiveness for a density ratio (between the hot fluid through air injection holes and cold main flow fluid) of 1.1 and injection mass flow rates of 1.1, 2.5, 3.0 and 5.0 percent of main flow. A significant change in the film cooling effectiveness is observed with increase in the injection mass flow rate and change in the axial spacing.

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