scholarly journals Film Cooling Effectiveness Predictions for Short Holes Fed by a Narrow Plenum

1999 ◽  
Author(s):  
C. A. Hale ◽  
S. Ramadhyani ◽  
M. W. Plesniak
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Film Cooling ◽  
Turbulence Models ◽  
Boundary Layer Separation ◽  
Cooling Effectiveness ◽  
Wall Functions ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Film Cooling Holes

This study evaluates the ability of available turbulence models in the commercial software FLUENT to predict film cooling effectiveness for a single row of short (L / D = 2.91). film cooling holes fed by a narrow plenum (H / D = 1). The results are compared to experimental data obtained by the present investigators. The study concentrates on the near-hole region for the geometry being studied experimentally by the present investigators. The results of the study indicate that the use of wall functions to predict film cooling effectiveness in the near-hole region is inappropriate due to the boundary layer separation in that region. Also, the ability of the Reynolds Stress turbulence model to better predict spanwise spreading of the jet indicates the need for anisotropic turbulnce model capabilities to better predict film cooling effectiveness.

Effect of Unheated Starting Lengths on Film Cooling Experiments

2006 ◽  
Vol 128 (3) ◽  
pp. 579-588 ◽  
Author(s):  
Sarah M. Coulthard ◽  
Ralph J. Volino ◽  
Karen A. Flack
Keyword(s):  
Film Cooling ◽  
Infrared Camera ◽  
Stanton Number ◽  
Flow Structures ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Heat Transfer Coefficients ◽  
Film Cooling Holes

The effect of an unheated starting length upstream of a row of film cooling holes was studied experimentally to determine its effect on heat transfer coefficients downstream of the holes. Cases with a single row of cylindrical film cooling holes inclined at 35deg to the surface of a flat plate were considered at blowing ratios of 0.25, 0.5, 1.0, and 1.5. For each case, experiments were conducted to determine the film-cooling effectiveness and the Stanton number distributions in cases with the surface upstream of the holes heated and unheated. Measurements were made using an infrared camera, thermocouples, and hot and cold-wire anemometry. Ratios were computed of the Stanton number with film cooling (Stf) to corresponding Stanton numbers in cases without film cooling (Sto), but the same surface heating conditions. Contours of these ratios were qualitatively the same regardless of the upstream heating conditions, but the ratios were larger for the cases with a heating starting length. Differences were most pronounced just downstream of the holes and for the lower blowing rate cases. Even 12 diameters downstream of the holes, the Stanton number ratios were 10–15% higher with a heated starting length. At higher blowing rates the differences between the heated and unheated starting length cases were not significant. The differences in Stanton number distributions are related to jet flow structures, which vary with blowing rate.

Film Cooling Effectiveness for Short Film Cooling Holes Fed by a Narrow Plenum

1999 ◽  
Vol 122 (3) ◽  
pp. 553-557 ◽  
Author(s):  
C. A. Hale ◽  
M. W. Plesniak ◽  
S. Ramadhyani
Keyword(s):  
Film Cooling ◽  
Short Film ◽  
Injection Hole ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Hole Geometry ◽  
Thin Walled ◽  
Film Cooling Holes

The adiabatic, steady-state liquid crystal technique was used to measure surface adiabatic film cooling effectiveness values in the near-hole region X/D<10. A parametric study was conducted for a single row of short holes L/D⩽3 fed by a narrow plenum H/D=1. Film cooling effectiveness values are presented and compared for various L/D ratios (0.66 to 3.0), three different blowing ratios (0.5, 1.0, and 1.5), two different plenum feed configurations (co-flow and counterflow), and two different injection angles (35 and 90 deg). Injection hole geometry and plenum feed direction were found to affect short hole film cooling performance significantly. Under certain conditions, similar or improved coverage was achieved with 90 deg holes compared with 35 deg holes. This result has important implications for manufacturing of thin-walled film-cooled blades or vanes. [S0889-504X(00)00603-6]

Comparison of Four Different Two-Equation Models of Turbulence in Predicting Film Cooling Performance

2006 ◽  
Author(s):  
Jawad S. Hassan ◽  
Savas Yavuzkurt
Keyword(s):  
Experimental Data ◽  
Film Cooling ◽  
Turbulence Models ◽  
Accurate Solution ◽  
Diameter Ratio ◽  
Lateral Direction ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Free Stream Turbulence ◽  
Blowing Ratio

The capabilities of four two-equation turbulence models in predicting film cooling effectiveness were investigated and their limitations as well as relative performance are presented. The four turbulence models are the standard, RNG, and realizable k-ε models as well as the standard k-ω model all found in the FLUENT CFD code. In all four models, the enhanced wall treatment has been used to resolve the flow near solid boundaries. A systematic approach has been followed in the computational setup to insure grid-independence and accurate solution that reflects the true capabilities of the turbulence models. Exact geometrical and flow-field replicas of an experimental study on discrete-jet film cooling were generated and used in FLUENT. A pitch-to-diameter ratio of 3.04, injection length-to-diameter ratio of 4.6 and density ratios of 0.92 and 0.97 were some of the parameters used in the film cooling analysis. Furthermore, the study covered two levels of blowing ratio (M = 0.5 and 1.5) at an environment of low free-stream turbulence intensity (Tu = 0.1%). The standard k-ε model had the most consistent performance among all considered turbulence models and the best centerline film cooling effectiveness predictions with the results deviating from experimental data by only ±10% and about 20–60% for the low (M = 0.5) and high (M = 1.5) blowing ratio cases, respectively. However, centerline side-view and surface top-view contours of non-dimensional temperature for the standard k-ε cases revealed that the good results for film cooling effectiveness η compared to the experimental data were due to a combination of an over-prediction of jet penetration in the normal direction with an under-prediction of jet spread in the lateral direction. The standard k-ω model completely failed to produce any results that were meaningful with under-predictions of η that ranged between 80 and 85% for the low blowing ratio case and over-predictions of about 200% for the high blowing ratio case. Even though the RNG and realizable models showed to have better predicted the jet spread in the lateral direction compared to the standard k-ε model, there were some aspects of the flow, such as levels of turbulence generated by cross-flow and jet interaction, that were not realistic resulting in errors in the η prediction that ranged from −10% to +80% for the M = 0.5 case and from −80% to +70% for the M = 1.5 case. As a result of this study at this point it was concluded that the standard k-ε model have the most promising potential among the two-equation models considered. It was chosen as the best candidate for further improvement for the simulation of film cooling flows.

Effects of Orientation Angles on Film Cooling Over a Flat Plate: Boundary Layer Temperature Distributions and Adiabatic Film Cooling Effectiveness

1999 ◽  
Vol 122 (1) ◽  
pp. 153-160 ◽  
Author(s):  
In Sung Jung ◽  
Joon Sik Lee
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
Plate Boundary ◽  
Orientation Angle ◽  
Thermochromic Liquid Crystal ◽  
Test Plate ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Temperature Distributions ◽  
Film Cooling Holes

Presented are experimental results describing the effects of orientation angle of film cooling holes on boundary layer temperature distributions and film cooling effectiveness. Film flow data were obtained from a row of five film cooling holes on a flat test plate. The inclination angle of the hole was fixed at 35 deg and four orientation angles of 0, 30, 60, and 90 deg were investigated. The velocity ratios surveyed were 0.5, 1.0, and 2.0. The boundary layer temperature distributions were measured at three downstream locations using 1μm platinum wire. Detailed adiabatic film cooling effectiveness distributions were measured using thermochromic liquid crystal. Results show that the increased lateral momentum in the case of large orientation angle injection strongly affects boundary layer temperature distributions. Temperature distribution characteristics are, in general, explained in the context of the interactions between injectant and free-stream fluid and between injectants issuing from adjacent holes. The adiabatic film cooling effectiveness distributions are discussed in connection with the boundary layer temperature distributions. Spanwise-averaged effectiveness distributions and space-averaged effectiveness distributions are also presented with respect to the velocity ratios and the orientation angles. [S0889-504X(00)01701-3]

Experimental and Numerical Film Effectiveness Downstream a Row of Compound Angle Film Holes

2003 ◽  
Author(s):  
A. Khanicheh ◽  
M. E. Taslim
Keyword(s):  
High Temperature ◽  
Film Cooling ◽  
Computational Study ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Cooling Hole ◽  
Cylindrical Holes ◽  
Film Cooling Holes ◽  
Compound Angle

High component lifetimes of modern gas turbines can be achieved by cooling the airfoils effectively. Film cooling is commonly employed on the airfoils and other engine hot section surfaces in order to protect them from the high thermal stress fields created by exposure to combustion gases. Complex geometries as well as optimized cooling considerations often dictate the use of compound-angled film cooling hole. In the present experimental and computational study, the effects that two different compound angle film cooling hole injection configurations have on film cooling effectiveness are investigated. Film cooling effectiveness measurements have been made downstream of a single row of compound angle cylindrical holes with a diameter of 7.5 mm, and a single row of compound angle, diffuser-shaped holes with an inlet diameter of 7.5 mm. The cylindrical holes were inclined (α=25°) with respect to the coverage surface and were oriented perpendicular to the high-temperature airflow direction. The diffuser-shaped holes had a compound angle of 45 degrees with respect to the high temperature air flow direction and, similar to the cylindrical film holes, a 25-deg angle with the coverage surface. Both geometries were tested over a blowing ratio range of 0.7 to 4.0. Surface temperatures were measured along four longitudinal rows of thermocouples covering the downstream area between two adjacent holes. The results showed that the best overall protection over the widest range of blowing ratios was provided by the diffuser-shaped film cooling holes. Compared with the cylindrical hole results, the diffuser-shaped expansion holes produced higher film cooling effectiveness downstream of the film cooling holes, particularly at high blowing ratios. The increased cross sectional area at the shaped hole exit compared to that of the cylindrical hole lead to a reduction of the mean velocity, thus the reduction of the momentum flux of the jet exiting the hole. Therefore, the penetration of the jet into the main flow was reduced, resulting in an increased cooling effectiveness. A commercially available CFD software package was used to study film cooling effectiveness downstream of the row of holes. Comparisons between the experimentally measured and numerically calculated film effectiveness distributions showed that the computed results are in reasonable agreement with the measured results. Therefore, CFD can be considered as a viable tool to predict the cooling performance of different film cooling configurations in a parametric study. A more realistic turbulence model, possibly adopting a two-layer model that incorporates boundary layer anisotropy, in the computational study may improve the predicted results.

Film Cooling Effectiveness for Short Film Cooling Holes Fed by a Narrow Plenum

1999 ◽  
Author(s):  
C. A. Hale ◽  
M. W. Plesniak ◽  
S. Ramadhyani
Keyword(s):  
Film Cooling ◽  
Short Film ◽  
Injection Hole ◽  
Counter Flow ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Thin Walled ◽  
Film Cooling Holes

The adiabatic, steady-state liquid crystal technique was used to measure surface adiabatic film cooling effectiveness values in the near-hole region (X / D < 10). A parametric study was conducted for a single row of short holes (L / D ≤ 3) fed by a narrow plenum (H / D = 1). Film cooling effectiveness values are presented and compared for various L / D ratios (0.66 to 3.0), three different blowing ratios (0.5, 1.0, and 1.5), two different plenum feed configurations (co-flow and counter flow), and two different injection angles (35° and 90°). Injection hole geometery and plenum feed direction were found to significantly affect short hole film cooling performance. Under certain conditions, comparable or improved coverage was achieved with 90° holes as with 35° holes. This result has important implications for manufacturing of thin-walled film-cooled blades or vanes.

Effect of Unheated Starting Lengths on Film Cooling Experiments

2005 ◽  
Author(s):  
Sarah M. Coulthard ◽  
Ralph J. Volino ◽  
Karen A. Flack
Keyword(s):  
Film Cooling ◽  
Infrared Camera ◽  
Stanton Number ◽  
Flow Structures ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Heat Transfer Coefficients ◽  
Film Cooling Holes

The effect of an unheated starting length upstream of a row of film cooling holes was studied experimentally to determine its effect on heat transfer coefficients downstream of the holes. Cases with a single row of cylindrical film cooling holes inclined at 35 degrees to the surface of a flat plate were considered at blowing ratios of 0.25, 0.5, 1.0 and 1.5. For each case experiments were conducted to determine the film cooling effectiveness and the Stanton number distributions in cases with the surface upstream of the holes heated and unheated. Measurements were made using an infrared camera, thermocouples, and hot and cold wire anemometry. Ratios were computed of the Stanton number with film cooling (Stf) to corresponding Stanton numbers in cases without film cooling (Sto) but the same surface heating conditions. Contours of these ratios were qualitatively the same regardless of the upstream heating conditions, but the ratios were larger for the cases with a heating starting length. Differences were most pronounced just downstream of the holes and for the lower blowing rate cases. Even 12 diameters downstream of the holes the Stanton number ratios were 10 to 15% higher with a heated starting length. The differences in Stanton number distributions are related to jet flow structures which vary with blowing rate.

Simulations of Film Cooling Flow Structure and Heat Transfer in the Near Field of Cooling Jets With a Modified DES Model

2019 ◽  
Author(s):  
Feiyan Yu ◽  
Savas Yavuzkurt
Keyword(s):  
Experimental Data ◽  
Film Cooling ◽  
Near Field ◽  
Density Ratio ◽  
Spanwise Direction ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Single Hole ◽  
Film Cooling Holes ◽  
Des Model

Abstract Simulations of film cooling in the near field (x/D &lt; 15) of coolant jets on a flat plate are carried out with detached eddy simulation (DES) and modified DES models. The time-averaged unsteady film cooling effectiveness is compared with experimental data. Both models use two-layer zonal model for near-wall treatment. The near field critical turbulent flow behaviors such as mainstream entrainment, spanwise spreading of counter rotating vortex pair (CRVP), and vortical structure evolutions are predicted and analyzed by DES and modified DES in this study. Modified DES model differs from the DES by implementing an increased eddy viscosity in the spanwise direction to enhance spanwise-diffusion of film cooling jets. Detailed comparisons of DES and modified DES modeling results are made under density ratios of 2.0, 1.6, 1.2 and blowing ratio of 1.0 for a single hole. Modified DES model predicts a wider spanwise spreading of temperature field and film cooling effectiveness. In a comparison of spanwise-averaged film cooling effectiveness with experimental data, DES and modified DES models predict 14.8% and 10.4% deviations under density ratio of 2.0. For density ratio of 1.2, the DES and modified DES results deviate from data 24.5% and 14.7% respectively. Then simulation of film cooling with a three hole domain is also carried out. Instantaneous effectiveness results show that the jets from nearby film cooling holes start to interact with each other before x/D &lt; 10. When the interactions of flow from film cooling holes next to each other are strong, simulations using several cooling holes are meaningful and the current study shows the difference of multi hole and single hole simulations.

A Film-Cooling Correlation for Shaped Holes on a Flat-Plate Surface

2008 ◽  
Author(s):  
Will F. Colban ◽  
Karen A. Thole ◽  
David Bogard
Keyword(s):  
Experimental Data ◽  
Flat Plate ◽  
Film Cooling ◽  
Empirical Correlation ◽  
Cooling Effectiveness ◽  
Physical Relationship ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Current Correlation ◽  
Film Cooling Holes

A common method of optimizing coolant performance in gas turbine engines is through the use of shaped film-cooling holes. Despite widespread use of shaped holes, existing correlations for predicting performance are limited to narrow ranges of parameters. This study extends the prediction capability for shaped holes through the development of a physics-based empirical correlation for predicting laterally-averaged film-cooling effectiveness on a flat plate downstream of a row of shaped film-cooling holes. Existing data was used to determine the physical relationship between film-cooling effectiveness and several parameters, including; blowing ratio, hole coverage ratio, area ratio, and hole spacing. Those relationships were then incorporated into the skeleton form of an empirical correlation, using results from the literature to determine coefficients for the correlation. Predictions from the current correlation, as well as existing shaped hole correlations and a cylindrical hole correlation were compared to the existing experimental data. Results show that the current physics-based correlation yields a significant improvement in predictive capability, by expanding the valid parameter range and improving agreement with experimental data. Particularly significant is the inclusion of higher blowing ratio conditions (up to M = 2.5) into the current correlation, whereas the existing correlations worked adequately only at lower blowing ratios (M ≈ 0.5).

A Film-Cooling Correlation for Shaped Holes on a Flat-Plate Surface

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Will F. Colban ◽  
Karen A. Thole ◽  
David Bogard
Keyword(s):  
Experimental Data ◽  
Flat Plate ◽  
Film Cooling ◽  
Empirical Correlation ◽  
Cooling Effectiveness ◽  
Physical Relationship ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Current Correlation ◽  
Film Cooling Holes

A common method of optimizing coolant performance in gas turbine engines is through the use of shaped film-cooling holes. Despite widespread use of shaped holes, existing correlations for predicting performance are limited to narrow ranges of parameters. This study extends the prediction capability for shaped holes through the development of a physics-based empirical correlation for predicting laterally averaged film-cooling effectiveness on a flat-plate downstream of a row of shaped film-cooling holes. Existing data were used to determine the physical relationship between film-cooling effectiveness and several parameters, including blowing ratio, hole coverage ratio, area ratio, and hole spacing. Those relationships were then incorporated into the skeleton form of an empirical correlation, using results from the literature to determine coefficients for the correlation. Predictions from the current correlation, as well as existing shaped-hole correlations and a cylindrical hole correlation, were compared with the existing experimental data. Results show that the current physics-based correlation yields a significant improvement in predictive capability, by expanding the valid parameter range and improving agreement with experimental data. Particularly significant is the inclusion of higher blowing ratio conditions (up to M=2.5) into the current correlation, whereas the existing correlations worked adequately only at lower blowing ratios (M≈0.5).

Sign in / Sign up

Export Citation Format

Share Document