Film Cooling Heat Transfer with High Free Stream Turbulence.

1995 ◽  
Author(s):  
John J. Schauer ◽  
David J. Pestian
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Free Stream ◽  
Free Stream Turbulence

Effusion-Cooling Performance at Gas Turbine Combustor Representative Flow Conditions

2012 ◽  
Author(s):  
Vinod U. Kakade ◽  
Steven J. Thorpe ◽  
Miklós Gerendás
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Free Stream ◽  
Flow Conditions ◽  
Cooling Performance ◽  
Free Stream Turbulence ◽  
High Turbulence ◽  
Adiabatic Effectiveness

The thermal management of aero gas turbine engine combustion systems commonly employs effusion-cooling in combination with various cold-side convective cooling schemes. The combustor liner incorporates many small holes which are usually set in staggered arrays and at a shallow angle to the cooled surface; relatively cold compressor delivery air is then allowed to flow through these holes to provide the full-coverage film-cooling effect. The efficient design of such systems requires robust correlations of film-cooling effectiveness and heat transfer coefficient at a range of aero-thermal conditions, and the use of appropriately validated computational models. However, the flow conditions within a combustor are characterised by particularly high turbulence levels and relatively large length scales. The experimental evidence for performance of effusion-cooling under such flow conditions is currently sparse. The work reported here is aimed at quantifying typical effusion-cooling performance at a range of combustor relevant free-stream conditions (high turbulence), and also to assess the importance of modeling the coolant to free-stream density ratio. Details of a new laboratory wind-tunnel facility for the investigation of film-cooling at high turbulence levels are reported. For a typical combustor effusion geometry that uses cylindrical holes, spatially resolved measurements of adiabatic effectiveness, heat transfer coefficient and net heat flux reduction are presented for a range of blowing ratios (0.48 to 2), free-stream turbulence conditions (4 and 22%) and density ratios (0.97 and 1.47). The measurements reveal that elevated free-stream turbulence impacts on both the adiabatic effectiveness and heat transfer coefficient, although this is dependent upon the blowing ratio being employed and particularly the extent to which the coolant jets detach from the surface. At low blowing ratios the presence of high turbulence levels causes increased lateral spreading of the coolant adjacent to the injection points, but more rapid degradation in the downstream direction. At high blowing ratios, high turbulence levels cause a modest increase in effectiveness due to turbulent transport of the detached coolant fluid. Additionally, the augmentation of heat transfer coefficient caused by the coolant injection is seen to be increased at high free-stream turbulence levels.

Effects of Free-Stream Turbulence and Surface Roughness on Film Cooling

1996 ◽  
Author(s):  
Donald L. Schmidt ◽  
David G. Bogard
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Momentum Flux ◽  
Free Stream ◽  
Cooling Performance ◽  
Free Stream Turbulence ◽  
Adiabatic Effectiveness

A flat plate test section was used to study how high free-stream turbulence with large turbulence length scales, representative of the turbine environment, affect the film cooling adiabatic effectiveness and heat transfer coefficient for a round hole film cooling geometry. This study also examined cooling performance with combined high free-stream turbulence and a rough surface which simulated the roughness representative of an in-service turbine. The injection was from a single row of film cooling holes with injection angle of 30°. The density ratio of the injectant to the mainstream was 2.0 for the adiabatic effectiveness tests, and 1.0 for the heat transfer coefficient tests. Streamwise and lateral distributions of adiabatic effectiveness and heat transfer coefficients were obtained at locations from 2 to 90 hole diameters downstream. At small to moderate momentum flux ratios, which would normally be considered optimum blowing conditions, high free-stream turbulence dramatically decreased adiabatic effectiveness. However, at large momentum flux ratios, conditions for which the film cooling jet would normally be detached, high free-stream turbulence caused an increase in adiabatic effectiveness. The combination of high free-stream turbulence with surface roughness resulted in an increase in adiabatic effectiveness relative to the smooth wall with high free-stream turbulence. Heat transfer rates were relatively unaffected by a film cooling injection. The key result from this study was a substantial increase in the momentum flux ratios for maximum film cooling performance which occurred for high free-stream turbulence and surface roughness conditions which are more representative of actual turbine conditions.

Numerical Approach at Flat Plate for Predicting the Film Cooling Effectiveness Part A: Effect Blowing Ratio

2018 ◽  
Vol 16 ◽  
pp. 30-44 ◽  
Author(s):  
Farouk Kebir ◽  
Azzeddine Khorsi
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Film Cooling ◽  
Thermal Stresses ◽  
Free Stream ◽  
Turbine Blades ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Free Stream Turbulence ◽  
Blowing Ratio

Film cooling is vital for gas turbine blades to protect them from thermal stresses and high temperatures due to the hot gas flow in the blade surface. Film cooling is applied to almost all external surfaces associated with aerodynamic profiles that are exposed to hot combustion gases such as main bodies, end-walls, blade tips and leading edges. In a review of the literature, it was found that there are strong effects of free-stream turbulence, surface curvature and hole shape on film cooling performance also blowing ratio. The performance of the film cooling is difficult to predict due to the inherent complex flow fields along the surfaces of the airfoil components in the turbine engines. From all what we introducing the film cooling is reviewed through a discussion of the analyses methodologies, a physical description, and the various influences on film-cooling performance. Initially Computational analysis was done on a flat plate with hole inclined at 55° to the surface plate. This study focuses on the efficient computation of film cooling flows with three blowing ratio. The numerical results show the effectiveness cooling and heat transfer behavior with increasing injection blowing ratio M (0.5, 1, and 1.5). The influence of increased blade film cooling can be assessed via the values of Nusselt number in terms of reduced heat transfer to the blade. Predictions of film effectiveness are compared with experimental results for a circular jet at blowing ratios ranging from 0.5, 1.0 and 1.5. The present results are obtained at a free stream turbulence of 10%, which are the typical conditions upstream of the effectiveness is generally lower for a large stream-wise angle of 55°.

Behavior of a Coolant Film With Two Rows of Holes Along the Pressure Side of a High-Pressure Nozzle Guide Vane

1990 ◽  
Vol 112 (3) ◽  
pp. 512-520 ◽  
Author(s):  
T. Arts ◽  
A. E. Bourguignon
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Film Cooling ◽  
Free Stream ◽  
Guide Vane ◽  
Internal Flow ◽  
Pressure Side ◽  
Free Stream Turbulence ◽  
Nozzle Guide Vane ◽  
Nozzle Guide

The purpose of this paper is to quantify the influence on external convective heat transfer of a coolant film whose position varies along the pressure side of a high-pressure turbine nozzle guide vane. The measurements were performed in the short-duration Isentropic Light Piston Compression Tube facility of the von Karman Institute. The effects of external and internal flow are considered in terms of Mach number, Reynolds number, free-stream turbulence intensity, blowing rate, and coolant to free-stream temperature ratio. The way to evaluate these results in terms of film cooling efficiency and heat transfer coefficient is finally discussed.

Numerical Validation of Heat Transfer Characteristics for Shower Head Film Cooled Turbine Vane

2012 ◽  
Author(s):  
Reddaiah Vishnumolakala ◽  
Jong S. Liu ◽  
Sridhar Murari ◽  
Ramakumar Bommisetty
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Free Stream ◽  
Cooling Systems ◽  
Free Stream Turbulence ◽  
Heat Transfer Behavior ◽  
Transfer Behavior ◽  
Exit Mach Number

In modern gas turbines, film cooling is one of the widely used external cooling techniques for turbine vanes and blades. The turbine airfoil leading edge, which is highly loaded thermally, is currently protected from the hot gas by film cooling schemes, so called showerhead cooling. Flow field in film cooling is very complex and detailed knowledge of heat transfer rates and metal temperatures are required while designing these cooling systems. Computational Fluid Dynamics (CFD) is gaining popularity for modeling these complex cooling systems. However, the application of CFD depends on its accuracy and reliability. This requires the CFD code to be validated with laboratory measurements to ensure its predictive capacity. In this regard, a project has been taken to validate the commercially available CFD code for predicting the blade heat transfer characteristics with shower head film cooling. The validation is accomplished with the test results of Ames [5]. C3X vanes were used for their four vane cascade test facility. The showerhead array used consists of 5 rows of 20° spanwise slanted holes. Experiments were carried out with lower (1%) and higher (12%) turbulence intensities. Results of metal temperatures and heat transfer coefficients were reported. The objective of this study is to validate and calibrate a commercially available CFD code, against the available test data [5] and to understand the relationship between complex flow fields and heat transfer behavior. STAR-CCM+ is used for model generation, mesh generation and solution. Polyhedral elements with prism layers around the wall surfaces are generated. Three turbulence models, Durbin’s v2f model, Menter SST and SST transition models are explored in this study. Simulations are performed for two turbulence intensities available. Typical flow parameters such as blade surface heat transfer coefficient (HTC), surface temperatures and the location of flow transition are compared. Results were compared for two typical cascade exit Mach number conditions such as 0.2 and 0.7, which represents subsonic and transonic conditions respectively. Except in suction side transition region, numerically simulated heat transfer coefficient and Stanton number matched well with test data. Vane wall temperature contours were presented to understand the heat transfer behavior. The heat transfer behavior was numerically investigated for realistic exit Mach numbers. Sensitivity study for two inlet free stream turbulence intensities and three inlet free stream turbulence length scales are performed for realistic exit Mach number and reported heat transfer coefficient and Stanton number.

Simulation of the Near-Field Region of Film Cooling Jets Using RANS and Hybrid URANS/LES Models

2014 ◽  
Author(s):  
Hosein Foroutan ◽  
Savas Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Free Stream ◽  
Near Field ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Field Region ◽  
Detached Eddy Simulation ◽  
Film Cooling Effectiveness ◽  
Free Stream Turbulence

This paper investigates the flow field and heat transfer in the near-field region of film cooling jets through numerical simulations using RANS and hybrid URANS/LES models. Detailed simulations of flow and thermal fields of a single row of film cooling cylindrical holes with 30° inline injection on a flat plate are obtained for low (M = 0.5) and high (M = 1.5) blowing ratios under high free stream turbulence (10%). The realizable k-ε model is used within the RANS framework and a realizable k-ε-based detached eddy simulation (DES) is used as a hybrid URANS/LES model. Both models are used together with the two-layer zonal model for near-wall simulations. Steady and time-averaged unsteady film cooling effectiveness obtained using these models in ANSYS-FLUENT are compared with available experimental data. It is shown that hybrid URANS/LES models (DES in the present paper) predict more mixing both in the wall-normal and spanwise directions compared to RANS models, while unsteady asymmetric vortical structures of the flow can also be captured. The turbulent heat flux components predicted by the DES model are higher than those obtained by the RANS simulations, resulting in enhanced turbulent heat transfer between the jet and mainstream, and consequently better predictions of the effectiveness. Furthermore, the unsteady physics of jet and crossflow interactions and the jet lift-off under high free stream turbulence is studied using the present DES results.

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