The Effect of Temperature Ratios on the Film Cooling Process

1983 ◽  
Vol 105 (3) ◽  
pp. 615-620 ◽  
Author(s):  
P. J. Loftus ◽  
T. V. Jones
Keyword(s):  
Heat Transfer ◽  
Wind Tunnel ◽  
Wall Temperature ◽  
Film Cooling ◽  
Systematic Investigation ◽  
Effect Of Temperature ◽  
Temperature Ratio ◽  
Cooling Process ◽  
Principle Of Superposition ◽  
Injection Process

Film cooling experiments have been conducted at conditions which realistically simulate the gas turbine environment. Heat transfer has been measured using a short duration wind tunnel. Mainstream injection and wall temperatures have been varied independently in order to conduct a systematic investigation of the injection process. A model of the film cooling process based on the principle of superposition is used to interpret the experimental results. The effect of gas to wall temperature ratio on heat transfer to an uncooled plate has also been investigated.

An Experimental Study of Turbine Vane Heat Transfer With Leading Edge and Downstream Film Cooling

1990 ◽  
Vol 112 (3) ◽  
pp. 477-487 ◽  
Author(s):  
N. V. Nirmalan ◽  
L. D. Hylton
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Pressure Ratio ◽  
Leading Edge ◽  
External Heat ◽  
Gas Temperature ◽  
Temperature Ratio ◽  
External Heat Transfer ◽  
Turbine Vane

This paper presents the effects of downstream film cooling, with and without leading edge showerhead film cooling, on turbine vane external heat transfer. Steady-state experimental measurements were made in a three-vane, linear, two-dimensional cascade. The principal independent parameters—Mach number, Reynolds number, turbulence, wall-to-gas temperature ratio, coolant-to-gas temperature ratio, and coolant-to-gas pressure ratio—were maintained over ranges consistent with actual engine conditions. The test matrix was structured to provide an assessment of the independent influence of parameters of interest, namely, exit Mach number, exit Reynolds number, coolant-to-gas temperature ratio, and coolant-to-gas pressure ratio. The vane external heat transfer data obtained in this program indicate that considerable cooling benefits can be achieved by utilizing downstream film cooling. The downstream film cooling process was shown to be a complex interaction of two competing mechanisms. The thermal dilution effect, associated with the injection of relatively cold fluid, results in a decrease in the heat transfer to the airfoil. Conversely, the turbulence augmentation, produced by the injection process, results in increased heat transfer to the airfoil. The data presented in this paper illustrate the interaction of these variables and should provide the airfoil designer and computational analyst with the information required to improve heat transfer design capabilities for film-cooled turbine airfoils.

Effect of Temperature Ratio on Jet Array Impingement Heat Transfer

2007 ◽  
Author(s):  
Matt Goodro ◽  
Jongmyung Park ◽  
Phil Ligrani ◽  
Mike Fox ◽  
Hee-Koo Moon
Keyword(s):  
Heat Transfer ◽  
Turbulent Transport ◽  
Velocity Ratio ◽  
Impinging Jets ◽  
Effect Of Temperature ◽  
Temperature Ratio ◽  
Target Plate ◽  
Plate Temperature ◽  
Fluid Properties ◽  
Effects Of Temperature

Considered are the effects of temperature ratio on the heat transfer from an array of jets impinging on a flat plate. At constant Reynolds number of 18000, and constant Mach number of 0.2, different ratios of target plate temperature to jet temperature are employed. The spacing between holes in the streamwise direction X is 8D, and the spanwise spacing between holes in a given streamwise row Y is also 8D. The target plate is located 3D away from the impingement hole exits. Experimental results show that local, line-averaged, and spatially-averaged Nusselt numbers decrease as the Tw/Tj temperature ratio increases. This is believed to be due to the effects of temperature-dependent fluid properties, as they affect local and global turbulent transport in the flow field created by the array of impinging jets. The effect of temperature ratio on crossflow-to-jet mass velocity ratio and discharge coefficients are also examined.

scholarly journals Systematic Investigation on Conjugate Heat Transfer Rates of Film Cooling Configurations

2005 ◽  
Vol 2005 (3) ◽  
pp. 211-220 ◽  
Author(s):  
Dieter Bohn ◽  
Jing Ren ◽  
Karsten Kusterer
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Conjugate Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Systematic Investigation ◽  
Transfer Condition ◽  
Film Cooling Effectiveness ◽  
Conjugate Calculation

For the determination of the film-cooling heat transfer, the design of a turbine blade relies on the conventional determination of the adiabatic film-cooling effectiveness and heat transfer conditions for test configurations. Thus, additional influences by the interaction of fluid flow and heat transfer and influences by additional convective heat transfer cannot be taken into account with sufficient accuracy. Within this paper, calculations of a film-cooled duct wall and a film-cooled real blade with application of the adiabatic and a conjugate heat transfer condition have been performed for different configurations. It can be shown that the application of the conjugate calculation method comprises the influence of heat transfer within the cooling film. The local heat transfer rate varies significantly depending on the local position.

Effect of Temperature Ratio on Jet Impingement Heat Transfer in Active Clearance Control Systems

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Riccardo Da Soghe ◽  
Cosimo Bianchini ◽  
Jacopo D’Errico ◽  
Lorenzo Tarchi
Keyword(s):  
Heat Transfer ◽  
Jet Impingement ◽  
Effect Of Temperature ◽  
Internal Cooling ◽  
Temperature Ratio ◽  
Present Contribution ◽  
Wide Range ◽  
Depth Analysis ◽  
The Impact ◽  
Clearance Control

Impinging jet arrays are typically used to cool several gas turbine parts. Some examples of such applications can be found in the internal cooling of high-pressure turbine airfoils or in the turbine blade tip clearances control of aero-engines. The effect of the wall-to-jets temperature ratio (TR) on heat transfer is generally neglected by the correlations available in the open literature. In the present contribution, the impact of the temperature ratio on the heat transfer for a real engine active clearance control system is analyzed by means of validated computational fluid dynamics (CFD) computations. At different jets Reynolds number and considering several impingement array arrangements, a wide range of target wall-to-jets temperature ratio is accounted for. Computational results prove that both local and averaged Nusselt numbers reduce with increasing. An in-depth analysis of the numerical data shows that the last mentioned evidence is motivated by both the heat transfer incurring between the spent coolant flow and the fresh jets and the variation of gas properties with temperature through the boundary layer. A scaling procedure, based on the TR power law, was proposed to estimate the Nusselt number at different wall temperature levels necessary to correct available open-literature correlations, typically developed with small temperature differences, for real engine applications.

Numerical Study on Flow and Heat Transfer Characteristics of Swirl Cooling on Leading Edge Model of Gas Turbine Blade

2011 ◽  
Author(s):  
Zhao Liu ◽  
Zhenping Feng ◽  
Liming Song
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Wall Temperature ◽  
Leading Edge ◽  
Circular Pipe ◽  
Temperature Ratio ◽  
Cooling Passage ◽  
Tangential Inlet

In this paper a numerical simulation is performed to predict the swirl cooling on internal leading edge cooling passage model. The relative performances of four kinds of turbulence models including the standard κ-ε model, the RNG κ-ε model, the standard κ-ω model and the SST κ-ω model in the simulation of the swirl flow by tangential inlet jets in a circular pipe are compared with available experimental data. The results show that SST κ-ω model is the best one based on simulation accuracy. Then the SST κ-ω model is adopted for the present simulation. A circular pipe with a single rectangular tangential inlet jet or with two rectangular tangential inlet jets is adopted to investigate the swirl cooling and its effectiveness. The influence of the Reynolds number and the inlet to wall temperature ratio are investigated. The results indicate that the heat transfer coefficient on the swirl chamber increases with the increase of Reynolds number, and increases with the decrease of the inlet to wall temperature ratio. The swirl pipe with two tangential inlets could get a heat transfer enhancement of about three times to that of the nonswirling pipe, while swirl pipe with one tangential inlet could get a heat transfer coefficient 38% higher than that of the nonswirling pipe.

scholarly journals An Investigation of Treating Adiabatic Wall Temperature as the Driving Temperature in Film Cooling Studies

2011 ◽  
Author(s):  
Lei Zhao ◽  
Ting Wang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Wall Temperature ◽  
Film Cooling ◽  
Injection Hole ◽  
Adiabatic Wall ◽  
Temperature Potential ◽  
Driving Potential

In film cooling heat transfer analysis, one of the core concepts is to deem film cooled adiabatic wall temperature (Taw) as the driving potential for the actual heat flux over the film-cooled surface. Theoretically, the concept of treating Taw as the driving temperature potential is drawn from compressible flow theory when viscous dissipation becomes the heat source near the wall and creates higher wall temperature than in the flowing gas. But in conditions where viscous dissipation is negligible, which is common in experiments under laboratory conditions, the heat source is not from near the wall but from the main hot gas stream; therefore, the concept of treating the adiabatic wall temperature as the driving potential is subjected to examination. To help investigate the role that Taw plays, a series of computational simulations are conducted under typical film cooling conditions over a conjugate wall with internal flow cooling. The result and analysis support the validity of this concept to be used in the film cooling by showing that Taw is indeed the driving temperature potential on the hypothetical zero wall thickness condition, ie. Taw is always higher than Tw with underneath (or internal) cooling and the adiabatic film heat transfer coefficient (haf) is always positive. However, in the conjugate wall cases, Taw is not always higher than wall temperature (Tw), and therefore, Taw does not always play the role as the driving potential. Reversed heat transfer through the airfoil wall from downstream to upstream is possible, and this reversed heat flow will make Tw > Taw in the near injection hole region. Yet evidence supports that Taw can be used to correctly predict the heat flux direction and always result in a positive adiabatic heat transfer coefficient (haf). The results further suggest that two different test walls are recommended for conducting film cooling experiments: a low thermal conductivity material should be used for obtaining accurate Taw and a relative high thermal conductivity material be used for conjugate cooling experiment. Insulating a high-conductivity wall will result in Taw distribution that will not provide correct heat flux or haf values near the injection hole.

Effect of Temperature Ratio on Jet Array Impingement Heat Transfer

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Matt Goodro ◽  
Jongmyung Park ◽  
Phil Ligrani ◽  
Mike Fox ◽  
Hee-Koo Moon
Keyword(s):  
Heat Transfer ◽  
Turbulent Transport ◽  
Velocity Ratio ◽  
Impinging Jets ◽  
Effect Of Temperature ◽  
Temperature Ratio ◽  
Target Plate ◽  
Plate Temperature ◽  
Fluid Properties ◽  
Effects Of Temperature

This paper consider the effects of temperature ratio on the heat transfer from an array of jets impinging on a flat plate. At a constant Reynolds number of 18,000 and a constant Mach number of 0.2, different ratios of target plate temperature to jet temperature are employed. The spacing between holes in the streamwise direction X is 8D, and the spanwise spacing between holes in a given streamwise row Y is also 8D. The target plate is located 3D away from the impingement hole exits. Experimental results show that local, line-averaged, and spatially averaged Nusselt numbers decrease as the Twa∕Tj temperature ratio increases. This is believed to be due to the effects of temperature-dependent fluid properties, as they affect local and global turbulent transport in the flow field created by the array of impinging jets. The effect of temperature ratio on crossflow-to-jet mass velocity ratio and discharge coefficients is also examined.

Effect of Variable Properties Within a Boundary Layer With Large Freestream to Wall Temperature Differences

2013 ◽  
Author(s):  
Nathan J. Greiner ◽  
Marc D. Polanka ◽  
Jacob R. Robertson ◽  
James L. Rutledge
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Wall Temperature ◽  
Film Cooling ◽  
Linear Trend ◽  
Linear Method ◽  
Ratio Method ◽  
Variable Properties ◽  
Adiabatic Wall ◽  
Constant Property

Modern aviation combustors run at high fuel-air ratios to achieve high turbine inlet temperatures and higher turbine efficiencies. To maximize turbine durability in such extreme temperatures, the blades are fitted with film cooling schemes to form a layer of cool air between the blade and the hot core flow. Two terms that are utilized to evaluate a cooling scheme are the heat transfer coefficient (h) and the local driving temperature, namely, the adiabatic wall temperature (Taw). The literature presents a method for calculating these two parameters by assuming the heat flux (q) is proportional to the difference in freestream and wall temperatures (T∞ − Tw). Several researchers have shown the viability of this approach by altering the wall temperature over a finite range in low temperature environment. A linear trend ensues where the slope is h and the q = 0 intercept is adiabatic wall temperature. This technique has proven valuable since constant h is known to be a valid assumption for constant property flow. The current study explores the validity of this assumption by analytically predicting and experimentally measuring the h and q at high T∞ and low Tw characteristic of a modern combustor. Both a reference temperature method and temperature ratio method were applied to model the effects of variable properties within the boundary layer. To explore the linearity of the heat transfer with driving temperature, the analysis determined the apparent h and Taw which would be measured over small ranges of Tw by the linear method discussed in the literature. This study shows that, over large Tw ranges, property variations play a significant role. It is also shown that the linear trend technique is valid even at high temperature conditions but only when used in small temperature ranges. Finally, this investigation shows that the apparent Taw used in the linear convective heat transfer assumption is a valid driving temperature over small ranges of Tw but cannot always be interpreted literally as the temperature where q(Taw) = 0.

Effect of Temperature Ratio on Jet Impingement Heat Transfer in Active Clearance Control Systems

2018 ◽  
Author(s):  
Riccardo Da Soghe ◽  
Cosimo Bianchini ◽  
Jacopo D’Errico ◽  
Lorenzo Tarchi
Keyword(s):  
Heat Transfer ◽  
Jet Impingement ◽  
Effect Of Temperature ◽  
Internal Cooling ◽  
Temperature Ratio ◽  
Present Contribution ◽  
Wide Range ◽  
Depth Analysis ◽  
The Impact ◽  
Clearance Control

Impinging jet arrays are typically used to cool several gas turbine parts. Some examples of such applications can be found in the internal cooling of high pressure turbine airfoils or in the turbine blade tip clearances control of aero-engines. The effect of wall-to-jets temperature ratio on heat transfer is generally neglected by the correlations available in the open literature. In present contribution, the impact of the temperature ratio on the heat transfer for a real engine Active Clearance Control system, is analyzed by means of validated CFD computations. At different jets Reynolds number and considering several impingement array arrangements, a wide range of target wall-to-jets temperature ratio (TR) is accounted for. Computational results prove that both local and averaged Nusselt numbers reduce with increasing temperature ratios. An in-depth analysis of the numerical data show that the last mentioned evidence is motivated by both the heat transfer incurring between the spent coolant flow and the fresh jets and the variation of gas properties with temperature through the boundary layer. A scaling procedure, based on TR power law, was proposed to estimate the Nusselt number at different wall temperature levels necessary to correct available open-literature correlations, typically developed with small temperature differences, for real engine applications.

Prediction of Heat Transfer Characteristics for Discrete Hole Film Cooling for Turbine Blade Applications

1990 ◽  
Vol 112 (3) ◽  
pp. 504-511 ◽  
Author(s):  
D. K. Tafti ◽  
S. Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Film Cooling ◽  
Three Dimensional ◽  
Hole Injection ◽  
Two Dimensional ◽  
Transfer Coefficients ◽  
Film Cooling Effectiveness ◽  
Injection Process ◽  
Prediction Scheme

A two-dimensional injection model is used with a two-dimensional low Reynolds number k-ε model boundary layer code. The three-dimensional effects of the discrete hole injection process are introduced in the two-dimensional prediction scheme through an “entrainment fraction” (Υ). An established correlation between Υ and the injection parameters obtained in a previous paper is used to predict the film cooling effectiveness (η) and heat transfer coefficients for multirow injection, injection into a laminar boundary layer, and finally injection on convex curved surfaces. Predictions of η are in good agreement with experimental data for most of the cases tested. Predictions of Stanton numbers defined by St(0) and St(l) are good for low injection ratios (M) but as M increases the values are underpredicted. In spite of some shortcomings, in the authors’ opinion the present two-dimensional prediction scheme is one of the most comprehensive developed so far. It is seen that the entrainment fraction Υ is quite universal in its application to two-dimensional predictions of the discrete hole film cooling process.

Sign in / Sign up

Export Citation Format

Share Document