Experimental Evaluation of Thermal and Mass Transfer Techniques to Measure Adiabatic Effectiveness With Various Coolant to Freestream Property Ratios

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Connor J. Wiese ◽  
James L. Rutledge ◽  
Marc D. Polanka
Keyword(s):  
Mass Transfer ◽  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Adiabatic Wall ◽  
Thermal Methods ◽  
Turbine Cooling ◽  
Fluid Properties ◽  
Gas Turbine Cooling ◽  
Adiabatic Effectiveness

Experimentally evaluating gas turbine cooling schemes is generally prohibitive at engine conditions. Thus, researchers conduct film cooling experiments near room temperature and attempt to scale the results to engine conditions. An increasingly popular method of evaluating adiabatic effectiveness employs pressure sensitive paint (PSP) and the heat–mass transfer analogy. The suitability of mass transfer methods as a substitute for thermal methods is of interest in the present work. Much scaling work has been dedicated to the influence of the coolant-to-freestream density ratio (DR), but other fluid properties also differ between experimental and engine conditions. Most notably in the context of an examination of the ability of PSP to serve as a proxy for thermal methods are the properties that directly influence thermal transport. That is, even with an adiabatic wall, there is still heat transfer between the freestream flow and the coolant plume, and the mass transfer analogy would not be expected to account for the specific heat or thermal conductivity distributions within the flow. Using various coolant gases (air, carbon dioxide, nitrogen, and argon) and comparing with thermal experiments, the efficacy of the PSP method as a direct substitute for thermal measurements was evaluated on a cylindrical leading edge model with compound coolant injection. The results thus allow examination of how the two methods respond to different property variations. Overall, the PSP technique was found to overpredict the adiabatic effectiveness when compared to the results obtained from infrared (IR) thermography, but still reveals valuable information regarding the coolant flow.

Experimental Evaluation of Thermal and Mass Transfer Techniques to Measure Adiabatic Effectiveness With Various Coolant to Freestream Property Ratios

2017 ◽  
Author(s):  
Connor J. Wiese ◽  
James L. Rutledge ◽  
Marc D. Polanka
Keyword(s):  
Thermal Conductivity ◽  
Mass Transfer ◽  
Specific Heat ◽  
Film Cooling ◽  
Pressure Sensitive Paint ◽  
Adiabatic Wall ◽  
Thermal Methods ◽  
Pressure Sensitive ◽  
Thermal Measurements ◽  
Adiabatic Effectiveness

As gas turbine engine temperatures increase, experimentally evaluating the necessary cooling schemes becomes increasingly cost prohibitive at engine conditions. Thus, researchers conduct film cooling experiments near room temperature and attempt to scale the results to engine conditions. Although thermal measurements of film cooling adiabatic effectiveness are common, an increasingly popular method of evaluating adiabatic effectiveness employs pressure sensitive paint and the heat-mass transfer analogy. Mass transfer methods are attractive because an impermeable model can be used as an analog for a perfectly adiabatic wall; however, the mass transfer analogy is imperfect. The suitability of mass transfer methods as a substitute for thermal methods is of interest in the present work. Much scaling work has been dedicated to the influence of the coolant-to-freestream density ratio, but other fluid properties that differ between experimental and engine conditions have only been considered in more recent work. Most notably in the context of an examination of the ability of mass transfer methods to serve as a proxy for thermal methods are the properties that directly influence thermal transport — thermal conductivity and specific heat. That is, even with an adiabatic wall there is still heat transfer between the freestream flow and the coolant plume and the mass transfer analogy would not be expected to account for the specific heat or thermal conductivity distributions within the flow field. Using various coolant gases (air, carbon dioxide, nitrogen and argon) and comparing with thermal experiments, the efficacy of the pressure sensitive paint method as a direct substitute for thermal measurements was evaluated on a simulated leading edge model with compound coolant injection. The results thus allow examination of how the two methods respond to different property variations. Overall, the pressure sensitive paint technique was found to over predict the adiabatic effectiveness of a particular coolant flow when compared to the results obtained from infrared thermography, but still reveals a great deal of valuable information regarding the coolant flow structure.

Effect of Blowing Ratio in the Near-Stagnation Region of a Three-Row Leading Edge Film Cooling Geometry Using Large Eddy Simulations

2009 ◽  
Author(s):  
Sai Shrinivas Sreedharan ◽  
Danesh K. Tafti
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Large Eddy Simulations ◽  
Stagnation Region ◽  
Stagnation Line ◽  
Blowing Ratio ◽  
Large Eddy ◽  
Adiabatic Effectiveness ◽  
Compound Angle

Computational studies are carried out using Large Eddy Simulations (LES) to investigate the effect of coolant to mainstream blowing ratio in a leading edge region of a film cooled vane. The three row leading edge vane geometry is modeled as a symmetric semi-cylinder with a flat afterbody. One row of coolant holes is located along the stagnation line and the other two rows of coolant holes are located at ±21.3° from the stagnation line. The coolant is injected at 45° to the vane surface with 90° compound angle injection. The coolant to mainstream density ratio is set to unity and the freestream Reynolds number based on leading edge diameter is 32000. Blowing ratios (B.R.) of 0.5, 1.0, 1.5, and 2.0 are investigated. It is found that the stagnation cooling jets penetrate much further into the mainstream, both in the normal and lateral directions, than the off-stagnation jets for all blowing ratios. Jet dilution is characterized by turbulent diffusion and entrainment. The strength of both mechanisms increases with blowing ratio. The adiabatic effectiveness in the stagnation region initially increases with blowing ratio but then generally decreases as the blowing ratio increases further. Immediately downstream of off-stagnation injection, the adiabatic effectiveness is highest at B.R. = 0.5. However, further downstream the larger mass of coolant injected at higher blowing ratios, in spite of the larger jet penetration and dilution, increases the effectiveness with blowing ratio.

Scaling of Performance for Varying Density Ratio Coolants on an Airfoil With Strong Curvature and Pressure Gradient Effects

2000 ◽  
Author(s):  
Marcia I. Ethridge ◽  
J. Michael Cutbirth ◽  
David G. Bogard
Keyword(s):  
Pressure Gradient ◽  
Film Cooling ◽  
Density Ratio ◽  
Flux Ratio ◽  
Leading Edge ◽  
Suction Side ◽  
Cooling Performance ◽  
Injection Angle ◽  
Adiabatic Effectiveness ◽  
Strong Curvature

An experimental study was conducted to investigate the film cooling performance on the suction side of a first stage turbine vane. Tests were conducted on a nine times scale vane model at density ratios of DR = 1.1 and 1.6 over a range of blowing conditions, 0.2 ≤ M ≤ 1.5 and 0.05 ≤ I ≤ 1.2. Two different mainstream turbulence intensity levels, Tu∞ = 0.5% and 20%, were also investigated. The row of coolant holes studied was located in a position of both strong curvature and strong favorable pressure gradient. In addition, its performance was isolated by blocking the leading edge showerhead coolant holes. Adiabatic effectiveness measurements were made using an infrared camera to map the surface temperature distribution. The results indicate that film cooling performance was greatly enhanced over holes with a similar 50° injection angle on a flat plate. Overall, adiabatic effectiveness scaled with mass flux ratio for low blowing conditions and with momentum flux ratio for high blowing conditions. However, for M < 0.5 there was a higher rate of decay for the low density ratio data. High mainstream turbulence had little effect at low blowing ratios, but degraded performance at higher blowing ratios.

Investigation of Various Parametric Influences on Leading Edge Film Cooling

1997 ◽  
Author(s):  
Michael W. Cruse ◽  
Ushio M. Yuki ◽  
David G. Bogard
Keyword(s):  
Film Cooling ◽  
Large Scale ◽  
Free Stream ◽  
Density Ratio ◽  
Leading Edge ◽  
Line Position ◽  
Stagnation Line ◽  
Free Stream Turbulence ◽  
Adiabatic Effectiveness ◽  
Density Ratios

Film cooling adiabatic effectiveness of a simulated turbine airfoil leading edge was studied experimentally. The leading edge had two rows of holes, one at nominally the stagnation line position and the second a few hole diameters downstream. Hole positions at the leading edge, and inclination of the holes with respect to the surface, were different than typically used in previous studies, but were representative of current design practice. Various leading edge film cooling parameters were investigated including stagnation line position, free-stream turbulence level, leading edge geometry, and coolant to mainstream density ratio. Large density ratios were obtained by cooling the injected coolant to very low temperatures. Large scale, high level free-stream turbulence (Tu = 20%) was generated using a specially developed cross-jet turbulence generator. An infrared camera system was used to obtain well resolved surface temperature distributions around the coolant holes and across the leading edge. Results from the experiments showed considerably higher optimum blowing ratios than found in previous studies. The stagnation line position was found to be important in influencing the direction of coolant flow from the first row of holes. High free-stream turbulence levels were found to greatly decrease adiabatic effectiveness at low blowing ratios (M = 1.0), but had little effect at high blowing ratios (M = 2.0 and 2.5). Adiabatic effectiveness distributions were very similar for circular and elliptical leading edges. Experiments conducted at coolant to mainstream density ratios of 1.1 and 1.8 showed distinctly different flow characteristics in the stagnation line region for the different density ratio coolants.

Scaling Considerations for Thermal and Pressure-Sensitive Paint Methods Used to Determine Adiabatic Effectiveness

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Luke J. McNamara ◽  
Jacob P. Fischer ◽  
James L. Rutledge ◽  
Marc D. Polanka
Keyword(s):  
Mass Transfer ◽  
Film Cooling ◽  
Heat Mass Transfer ◽  
Measurement Techniques ◽  
Flux Ratio ◽  
Experimental Methods ◽  
Thermal Methods ◽  
Film Cooling Effectiveness ◽  
Pressure Sensitive ◽  
Adiabatic Effectiveness

Abstract To be representative of engine conditions, a measurement of film cooling behavior with an experiment must involve matching certain nondimensional parameters, such as freestream Reynolds number. However, the coolant flowrate must also be scaled between the experiments and engine conditions to accurately predict film cooling effectiveness. This process is complicated by gas property variation with temperature. Additionally, selection of the appropriate coolant flowrate parameter to scale from low to high temperatures is a topic of continued uncertainty. Furthermore, experiments are commonly conducted using thermal measurement techniques with infrared thermography (IR), but the use of pressure-sensitive paints (PSPs) implementing the heat-mass transfer analogy is also common. Thus, the question arises of how the adiabatic effectiveness distributions compare between mass transfer experimental methods and thermal experimental methods and whether these two methods are sensitive to coolant flowrate parameters in different ways. In this study, a thermal technique with IR was compared with a heat-mass transfer method with a PSP on a flat plate model with a 7-7-7 film cooling hole. While adiabatic effectiveness is best scaled by accounting for specific heats with the advective capacity ratio (ACR) using thermal techniques, results revealed that PSP measurements are scaled best with the mass flux ratio (M). The difference in these methods has significant implications for engine designers that rely on PSP experimental data to predict engine thermal behavior as PSP is fundamentally not sensitive to the same relevant physical mechanisms to which thermal methods are sensitive.

NUMERICAL ASSESSMENT OF DENSITY RATIO AND MAINSTREAM TURBULENCE EFFECTS ON LEADING EDGE FILM COOLING: HEAT AND MASS TRANSFER METHODS

2021 ◽  
pp. 1-29
Author(s):  
Silvia Ravelli ◽  
Hamed Abdeh ◽  
Giovanna Barigozzi
Keyword(s):  
Mass Transfer ◽  
Film Cooling ◽  
Transport Model ◽  
Density Ratio ◽  
Flux Ratio ◽  
Leading Edge ◽  
Operating Conditions ◽  
Thermal Method ◽  
Detached Eddy Simulation ◽  
Experimental Database

Abstract Within the context of leading edge film cooling in a high-pressure turbine vane, the present study is a step forward towards modelling showerhead performance for a baseline geometry (namely 4 staggered rows of cylindrical holes) at engine like conditions, starting from a previous investigation, at low speed flow (exit isentropic Mach number of Ma2is = 0.2), low inlet turbulence intensity of Tu1 = 1.6% and density ratio of DR ∼ 1. Those operating conditions, dictated by experimental constraints, were essential to validate results from delayed detached-eddy simulation (DDES) against off-the-wall measurements of velocity, vorticity and turbulent fluctuations, for the coolant-to-mainstream blowing ratio of BR = 3 (momentum flux ratio of I = 9). Here, the potential of DDES is exploited to predict the aero-thermal features of the flow in the leading edge region at larger density ratio (DR ∼ 1.5) and turbulent mainstream (Tu1 = 13%), while matching either BR or I. The experimental database contains surface measurements of film cooling adiabatic effectiveness obtained by using the pressure sensitive paint (PSP) technique. DDES predictions were computed by means of the species transport model (i.e. mass transfer), for comparison against the conventional thermal method, based on creating a temperature differential between the mainstream and the coolant (i.e. heat transfer). The simulated film cooling performance was found to depend on the method used, thus suggesting that other parameters than DR, BR, I and Tu1 should be taken into account when the goal is matching engine-like conditions.

Performance Improvement of a Heavy Duty GT: Adiabatic Effectiveness Measurements on First Stage Vanes in Representative Engine Conditions

2014 ◽  
Author(s):  
Luca Andrei ◽  
Bruno Facchini ◽  
Gianluca Caciolli ◽  
Alessio Picchi ◽  
Lorenzo Tarchi ◽  
...  
Keyword(s):  
High Pressure ◽  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Inlet Temperature ◽  
Internal Cooling ◽  
Heavy Duty ◽  
Creep Failure ◽  
Film Cooling Effectiveness ◽  
Adiabatic Effectiveness

Nowadays total inlet temperature of gas turbine is far above the permissible metal temperature; as a consequence, advanced cooling techniques must be applied to protect from thermal stress and to reduce the risk of creep failure, oxidation and corrosion of components located in the high pressure stages, such as first vane. Film cooling has been widely used to control temperature of high temperature and high pressure vanes. In a film cooled vane the air taken from last compressor stages is ejected through discrete holes to provide a cold layer between hot mainstream and turbine components. A comprehensive understanding of phenomena concerning the complex interaction of hot gases with coolant flows in a vane passage plays a major role in the definition of a well performing film cooling scheme. The aim of this study is the measurement of adiabatic effectiveness on the first stage vane of a heavy duty GT by means of coolant concentration technique based on Pressure Sensitive Paint (PSP). The investigation of coolant distribution on airfoils and platforms was done in order to make feasible possible optimizations and to validate numerical design tools. The experimental analysis was performed on a static test article replicating an annular sector made up of two cooled airfoils and three passages. An actual first stage vane (scale 1:1) with complete internal cooling scheme has been tested at different coolant conditions and imposing two values of density ratio (DR = 1.0;1.5). Film protection was generated by a showerhead on the leading edge and by cylindrical holes on pressure and suction side and on the platforms; finally a cutback with elongated pedestals was employed for the protection of the pressure side trailing edge. Results, reported in terms of detailed 2D maps of film cooling effectiveness and averaged trends, point out the effect of coolant-to-mainstream mass ratio and density ratio. Beyond the results obtained in this specific vane geometry, the use of PSP was proven to be a promising technique for direct measurements on real geometries: as a matter of fact, the opportunity to get detailed results of pressure and adiabatic effectiveness distributions is of outstanding importance for the design and optimization of vanes and blades cooling systems.

Heat Transfer Boundary Condition Waveforms on a Turbine Blade Leading Edge With Unsteady Film Cooling

2013 ◽  
Author(s):  
James L. Rutledge
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blade ◽  
Film Cooling ◽  
Leading Edge ◽  
Adiabatic Wall ◽  
Time Resolved ◽  
Stagnation Line ◽  
Adiabatic Effectiveness

It is necessary to understand how film cooling both reduces the adiabatic wall temperature and influences the heat transfer coefficient in order to predict the net heat flux to a gas turbine hot gas path component. Although a great number of studies have considered steady film cooling flows, the influence of film cooling unsteadiness has only recently been considered. Unsteadiness in the freestream flow or the coolant flow can cause fluctuations in both the adiabatic effectiveness and heat transfer coefficient, the dynamics of which have been difficult to measure. In previous studies, only time averaged effects have been measured. The present study has determined time resolved adiabatic effectiveness and heat transfer coefficient waveforms using a novel inverse heat transfer methodology. Unsteady film cooling was examined on the leading edge region of a circular cylinder simulating the leading edge of a turbine blade. Unsteady interactions between h and η, were examined near a coolant hole located 21.5° downstream from the leading edge stagnation line, angled 20° to the surface and 90° to the streamwise direction. The coolant plume is shown to shift back and forth as the jet’s momentum fluctuates. Increasing freestream turbulence was found to both reduce η, and the amplitude of the η waveforms.

The Effects of Specific Heat and Viscosity on Film Cooling Behavior

2021 ◽  
pp. 1-25
Author(s):  
Connor Wiese ◽  
James L. Rutledge
Keyword(s):  
Thermal Conductivity ◽  
Specific Heat ◽  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Cooling Effectiveness ◽  
Ratio Effect ◽  
Cooling Hole ◽  
Cooling Behavior ◽  
Adiabatic Effectiveness

Abstract For many years, there has been interest in evaluating the effect of density differences between the coolant and the freestream in terms of the cooling effectiveness. Numerous experiments have been conducted with different cooling gases or different temperature gases to evaluate the effect of the density ratio. With little agreement on the best way to scale the density ratio effect, it has become commonplace for some researchers to insist upon matching the density ratio for experimental work. Unfortunately, the density is not the only property that differs between the various coolant gases used in experiments, and it is certainly not the only property difference between the coolant and the freestream in actual engines. In the present work, we isolate some of these effects through film cooling experiments with carefully selected and conditioned coolant gases at near identical densities but exhibiting other property differences. Most significantly, coolant specific heat varied, but subtle viscosity and thermal conductivity effects were present. Through measurements of the adiabatic effectiveness from a film cooling hole on a leading edge model, we are able to show that the specific heat effect is just as important as the density effect, providing more evidence that effects in prior research attributed to density differences, are actually a combination of density and other property differences.

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