THE DUFOUR EFFECT IN FILM COOLING EXPERIMENTS WITH FOREIGN GASES

2021 ◽  
pp. 1-17
Author(s):  
James L. Rutledge ◽  
Carol Bryant ◽  
Connor Wiese ◽  
Jacob Anthony Fischer
Keyword(s):  
Wall Temperature ◽  
Film Cooling ◽  
Leading Edge ◽  
Temperature Gradients ◽  
Coolant Temperature ◽  
Adiabatic Wall ◽  
Dufour Effect ◽  
Temperature Separation ◽  
Thermal Conductivity Model ◽  
Cooling Hole

Abstract In typical film cooling experiments, the adiabatic wall temperature may be determined from surface temperature measurements on a low thermal conductivity model in a low temperature wind tunnel. In such experiments, it is generally accepted that the adiabatic wall temperature must be bounded between the coolant temperature and the freestream recovery temperature as they represent the lowest and highest temperature introduced into the experiment. Many studies have utilized foreign gas coolants to alter the coolant properties such as density and specific heat to more appropriately simulate engine representative flows. In this paper, we show that the often ignored Dufour effect can alter the thermal physics in such an experiment from those relevant to the engine environment that we generally wish to simulate. The Dufour effect is an off-diagonal coupling of heat and mass transfer that can induce temperature gradients even in what would otherwise be isothermal experiments. These temperature gradients can result in significant errors in calibration of various experimental techniques, as well as lead to results that at first glance may appear non-physical such as adiabatic effectiveness values not bounded by zero and one. This work explores Dufour effect induced temperature separation on two common cooling flow schemes, a leading edge with compound injection through a cylindrical cooling hole, and a flat plate with axial injection through a 7-7-7 shaped cooling hole. Air, argon, carbon dioxide, helium, and nitrogen coolant were utilized due to their usage in recent film cooling studies.

Film Cooling Efficiency in the Supersonic Flow With Foreign Gas Injection

2010 ◽  
Author(s):  
A. G. Zditovets ◽  
A. I. Leontiev ◽  
U. A. Vinogradov ◽  
M. M. Strongin ◽  
A. A. Titov
Keyword(s):  
Wall Temperature ◽  
Film Cooling ◽  
Gas Injection ◽  
Supersonic Boundary Layer ◽  
Low Flow ◽  
Coolant Temperature ◽  
State University ◽  
Adiabatic Wall ◽  
Supersonic Wind Tunnel ◽  
Experimental Researches

Numerical investigation (A.I.Leontiev, V.G.Lushchik, A.E.Jakubenko «PARADOXES OF HEAT TRANSFER ON A PERMEABLE WALL») shows that adiabatic wall temperature in the region of the gas film may be lower than the injected gas (coolant) temperature. It occurs in case of foreign light-gas injection and it does not occur in case of uniform gas injection under the same conditions. This paper is devoted to the experimental investigation of this conclusion. Experimental researches have been conducted in the low flow-rate supersonic wind tunnel (Mach number of 3) located in the Institute of Mechanics of the Moscow State University. Argon was used as a primary stream, helium and argon as coolant. The coolant was blown in through the porous permeable part of a model and injected into the supersonic boundary layer. The surface temperature of the model was gained with use of the infrared scanning device ThermaCAM SC 3000. As a result following data have been obtained. It is shown in particular that the adiabatic wall temperature in the region of the gas film may be lower than the injected gas (coolant) temperature. This effect does not take place in case of uniform (air-air, argon-argon etc.) gas injection, for this effect is especially essential for gas mixtures with low values of the Prandtl number.

The Delta Phi Method of Evaluating Overall Film Cooling Performance

2016 ◽  
Vol 138 (7) ◽  
Author(s):  
James L. Rutledge ◽  
Marc D. Polanka ◽  
David G. Bogard
Keyword(s):  
Heat Flux ◽  
Wall Temperature ◽  
Film Cooling ◽  
Convective Heat Transfer Coefficient ◽  
Leading Edge ◽  
Metal Temperature ◽  
Edge Region ◽  
Adiabatic Wall ◽  
Constant Wall Temperature ◽  
Cooling Performance

Film cooling designs are often evaluated experimentally and characterized in terms of their spatial distributions of adiabatic effectiveness, η, which is the nondimensionalized form of the adiabatic wall temperature, Taw. Additionally, film cooling may alter the convective heat transfer coefficient with the possibility of an increase in h that offsets the benefits of reduced Taw. It is therefore necessary to combine these two effects to give some measure of the benefit of film cooling. The most frequently used method is the net heat flux reduction (NHFR), which gives the fractional reduction in heat flux that accompanies film cooling for the hypothetical case of constant wall temperature. NHFR is imperfect in part due to the fact that this assumption does not account for the primary purpose of film cooling—to reduce the metal temperature to an acceptable level. In the present work, we present an alternative method of evaluating film cooling performance that yields the reduction in metal temperature, or in the nondimensional sense, an increase in ϕ that would be predicted with film cooling. This Δϕ approach is then applied using experimentally obtained η and h/h0 values on a simulated turbine blade leading edge region. The delta-phi approach agrees well with the legacy NHFR technique in terms of the binary question of whether the film cooling is beneficial or detrimental, but provides greater insight into the temperature reduction that a film cooling design would provide an actual turbine component. For example, instead of giving an area-averaged NHFR = 0.67 (indicating a 67% reduction in heat flux through film cooling) on the leading edge region with M = 0.5, the Δϕ approach indicates an increase in ϕ of 0.061 (or a 61 K surface temperature decrease with a notional value of T∞ −Tc = 1000 K). Alternatively, the technique may be applied to predict the maximum allowable increase in T∞ against which a film cooling scheme could protect.

The Delta Phi Method of Evaluating Overall Film Cooling Performance

2015 ◽  
Author(s):  
James L. Rutledge ◽  
Marc D. Polanka ◽  
David G. Bogard
Keyword(s):  
Heat Flux ◽  
Wall Temperature ◽  
Film Cooling ◽  
Convective Heat Transfer Coefficient ◽  
Leading Edge ◽  
Metal Temperature ◽  
Edge Region ◽  
Adiabatic Wall ◽  
Constant Wall Temperature ◽  
Cooling Performance

Film cooling designs are often evaluated experimentally and characterized in terms of their spatial distributions of adiabatic effectiveness, η, which is the nondimensionalized form of the adiabatic wall temperature, Taw. Additionally, film cooling may alter the convective heat transfer coefficient with the possibility of an increase in h that offsets the benefits of reduced Taw. It is therefore necessary to combine these two effects to give some measure of the benefit of film cooling. The most frequently used method is the net heat flux reduction, which gives the fractional reduction in heat flux that accompanies film cooling for the hypothetical case of constant wall temperature. NHFR is imperfect in part due to the fact that this assumption does not account for the primary purpose of film cooling — to reduce the metal temperature to an acceptable level. In the present work we present an alternative method of evaluating film cooling performance that yields the reduction in metal temperature, or in the nondimensional sense, an increase in ϕ that would be predicted with film cooling. This Δϕ approach is then applied using experimentally obtained η and h/h0 values on a simulated turbine blade leading edge region. The delta-phi approach agrees well with the legacy NHFR technique in terms of the binary question of whether the film cooling is beneficial or detrimental, but provides greater insight into the temperature reduction that a film cooling design would provide an actual turbine component. For example, instead of giving an area-averaged NHFR = 0.67 (indicating a 67% reduction in heat flux through film cooling) on the leading edge region with M = 0.5, the Δϕ approach indicates an increase in ϕ of 0.061 (or a 61 K surface temperature decrease with a notional value of T∞ - Tc = 1000 K). Alternatively, the technique may be applied to predict the maximum allowable increase in T∞ against which a film cooling scheme could protect.

scholarly journals Adiabatic Wall Effectiveness Measurements of Film-Cooling Holes With Expanded Exits

1997 ◽  
Author(s):  
M. Gritsch ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Mach Number ◽  
Film Cooling ◽  
Thermal Protection ◽  
Lateral Spreading ◽  
Cylindrical Hole ◽  
Adiabatic Wall ◽  
Camera System ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole

This paper presents detailed measurements of the film-cooling effectiveness for three single, scaled-up film-cooling hole geometries. The hole geometries investigated include a cylindrical hole and two holes with a diffuser shaped exit portion (i.e. a fanshaped and a laidback fanshaped hole). The flow conditions considered are the crossflow Mach number at the hole entrance side (up to 0.6), the crossflow Mach number at the hole exit side (up to 1.2), and the blowing ratio (up to 2). The coolant-to-mainflow temperature ratio is kept constant at 0.54. The measurements are performed by means of an infrared camera system which provides a two-dimensional distribution of the film-cooling effectiveness in the nearfield of the cooling hole down to x/D = 10. As compared to the cylindrical hole, both expanded holes show significantly improved thermal protection of the surface downstream of the ejection location, particularly at high blowing ratios. The laidback fanshaped hole provides a better lateral spreading of the ejected coolant than the fanshaped hole which leads to higher laterally averaged film-cooling effectiveness. Coolant passage crossflow Mach number and orientation strongly affect the flowfield of the jet being ejected from the hole and, therefore, have an important impact on film-cooling performance.

Effects of Double Wall Cooling Configuration and Conditions on Performance of Full-Coverage Effusion Cooling

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Nathan Rogers ◽  
Zhong Ren ◽  
Warren Buzzard ◽  
Brian Sweeney ◽  
Nathan Tinker ◽  
...  
Keyword(s):  
Film Cooling ◽  
Cross Flow ◽  
Hole Array ◽  
Adiabatic Wall ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Full Coverage ◽  
Cooling Hole ◽  
Double Wall

Experimental results are presented for a double wall cooling arrangement which simulates a portion of a combustor liner of a gas turbine engine. The results are collected using a new experimental facility designed to test full-coverage film cooling and impingement cooling effectiveness using either cross flow, impingement, or a combination of both to supply the film cooling flow. The present experiment primarily deals with cross flow supplied full-coverage film cooling for a sparse film cooling hole array that has not been previously tested. Data are provided for turbulent film cooling, contraction ratio of 1, blowing ratios ranging from 2.7 to 7.5, coolant Reynolds numbers based on film cooling hole diameter of about 5000–20,000, and mainstream temperature step during transient tests of 14 °C. The film cooling hole array consists of a film cooling hole diameter of 6.4 mm with nondimensional streamwise (X/de) and spanwise (Y/de) film cooling hole spacing of 15 and 4, respectively. The film cooling holes are streamwise inclined at an angle of 25 deg with respect to the test plate surface and have adjacent streamwise rows staggered with respect to each other. Data illustrating the effects of blowing ratio on adiabatic film cooling effectiveness and heat transfer coefficient are presented. For the arrangement and conditions considered, heat transfer coefficients generally increase with streamwise development and increase with increasing blowing ratio. The adiabatic film cooling effectiveness is determined from measurements of adiabatic wall temperature, coolant stagnation temperature, and mainstream recovery temperature. The adiabatic wall temperature and the adiabatic film cooling effectiveness generally decrease and increase, respectively, with streamwise position, and generally decrease and increase, respectively, as blowing ratio becomes larger.

Bump and Trench Modifications to Film-Cooling Holes at the Vane-Endwall Junction

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
N. Sundaram ◽  
K. A. Thole
Keyword(s):  
Film Cooling ◽  
Large Scale ◽  
Leading Edge ◽  
High Heat ◽  
Junction Region ◽  
High Heat Transfer ◽  
Turbine Vane ◽  
Cooling Hole ◽  
Adiabatic Effectiveness ◽  
Film Cooling Holes

The endwall of a first-stage vane experiences high heat transfer and low adiabatic effectiveness levels because of high turbine operating temperatures and formation of leading edge vortices. These vortices lift the coolant off the endwall and pull the hot mainstream gases toward it. The region of focus for this study is the vane-endwall junction region near the stagnation location where cooling is very difficult. Two different film-cooling hole modifications, namely, trenches and bumps, were evaluated to improve the cooling in the leading edge region. This study uses a large-scale turbine vane cascade with a single row of axial film-cooling holes at the leading edge of the vane endwall. Individual hole trenches and row trenches were placed along the complete row of film-cooling holes. Two-dimensional semi-elliptically shaped bumps were also evaluated by placing the bumps upstream and downstream of the film-cooling row. Tests were carried out for different trench depths and bump heights under varying blowing ratios. The results indicated that a row trench placed along the row of film-cooling holes showed a greater enhancement in adiabatic effectiveness levels when compared to individual hole trenches and bumps. All geometries considered produced an overall improvement to adiabatic effectiveness levels.

Bump and Trench Modifications to Film-Cooling Holes at the Vane Endwall Junction

2007 ◽  
Author(s):  
N. Sundaram ◽  
K. A. Thole
Keyword(s):  
Film Cooling ◽  
Large Scale ◽  
Leading Edge ◽  
High Heat ◽  
Junction Region ◽  
High Heat Transfer ◽  
Turbine Vane ◽  
Cooling Hole ◽  
Adiabatic Effectiveness ◽  
Film Cooling Holes

The endwall of a first stage vane experiences high heat transfer and low adiabatic effectiveness levels because of high turbine operating temperatures and formation of leading edge vortices. These vortices lift the coolant off the endwall and pull the hot mainstream gases towards it. The region of focus for this study is the vane-endwall junction region near the stagnation location where cooling is very difficult. Two different film-cooling hole modifications, namely trenches and bumps, were evaluated to improve the cooling in the leading edge region. This study uses a large-scale turbine vane cascade with a single row of axial film-cooling holes at the leading edge of the vane endwall. Individual hole trenches and row trenches were placed along the complete row of film-cooling holes. Two-dimensional semi-elliptically shaped bumps were also evaluated by placing the bumps upstream and downstream of the film-cooling row. Tests were carried out for different trench depths and bump heights under varying blowing ratios. The results indicated that a row trench placed along the row of film-cooling holes showed a greater enhancement in adiabatic effectiveness levels when compared to individual hole trenches and bumps. All geometries considered produced an overall improvement to adiabatic effectiveness levels.

Effects of Surface Deposition, Hole Blockage, and Thermal Barrier Coating Spallation on Vane Endwall Film Cooling

2006 ◽  
Vol 129 (3) ◽  
pp. 599-607 ◽  
Author(s):  
N. Sundaram ◽  
K. A. Thole
Keyword(s):  
Thermal Barrier Coating ◽  
Film Cooling ◽  
Gas Turbines ◽  
Large Scale ◽  
Leading Edge ◽  
Thermal Barrier ◽  
Cooling Effectiveness ◽  
Barrier Coating ◽  
Cooling Hole ◽  
Alternate Fuels

With the increase in usage of gas turbines for power generation and given that natural gas resources continue to be depleted, it has become increasingly important to search for alternate fuels. One source of alternate fuels is coal derived synthetic fuels. Coal derived fuels, however, contain traces of ash and other contaminants that can deposit on vane and turbine surfaces affecting their heat transfer through reduced film cooling. The endwall of a first stage vane is one such region that can be susceptible to depositions from these contaminants. This study uses a large-scale turbine vane cascade in which the following effects on film cooling adiabatic effectiveness were investigated in the endwall region: the effect of near-hole deposition, the effect of partial film cooling hole blockage, and the effect of spallation of a thermal barrier coating. The results indicated that deposits near the hole exit can sometimes improve the cooling effectiveness at the leading edge, but with increased deposition heights the cooling deteriorates. Partial hole blockage studies revealed that the cooling effectiveness deteriorates with increases in the number of blocked holes. Spallation studies showed that for a spalled endwall surface downstream of the leading edge cooling row, cooling effectiveness worsened with an increase in blowing ratio.

The Effectiveness of Film Cooling With Three-Dimensional Slot Geometries

1971 ◽  
Vol 93 (4) ◽  
pp. 425-430 ◽  
Author(s):  
M. N. R. Nina ◽  
J. H. Whitelaw
Keyword(s):  
Gas Turbine ◽  
Wall Temperature ◽  
Film Cooling ◽  
Mass Velocity ◽  
Three Dimensional ◽  
Area Ratio ◽  
Hole Injection ◽  
Open Area ◽  
Adiabatic Wall

The paper describes measurements of adiabatic wall temperature downstream of discrete hole injection slots for a range of parameters relevant to gas turbine practice. The influence of open-area-ratio, slot-lip-length and slot-lip-thickness is determined for tangential holes and a range of mass velocity ratios, 0.3 < m < 2.0, and downstream distances up to 40 equivalent slot heights; similar measurements are reported downstream of three-dimensional splash cooling geometries. In all, 13 different three-dimensional configurations are investigated and permit conclusions to be drawn as to the significance of the parameters investigated. The measurements clearly demonstrate the need for a thin and long slot lip and for a large value of open area ratio.

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