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 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.

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.

Experimental Investigation of Single Roughness Element Effects on Supersonic Boundary Layer Transition

2014 ◽  
Author(s):  
Henny Bottini ◽  
Bayindir H. Saracoglu ◽  
Guillermo Paniagua
Keyword(s):  
Boundary Layer ◽  
Wall Temperature ◽  
Roughness Element ◽  
Pressure Fluctuations ◽  
Supersonic Boundary Layer ◽  
Boundary Layer Transition ◽  
Adiabatic Wall ◽  
Layer Transition ◽  
Temperature And Pressure ◽  
Unsteady Effects

Predicting the characteristics of a transitional boundary layer remains an open challenge in supersonic flow fields. An experimental campaign to understand the effects of a single roughness element on a supersonic laminar boundary layer was designed. Two Mach numbers were tested, 1.6 and 2.3, including two roughness heights, 0.1 mm and 1 mm, over a flat plate. Steady and unsteady wall temperature and pressure levels were recorded to interpret the influence of the wake of the roughness. Heat flux and adiabatic wall temperature trends, temperature and pressure fluctuations RMS trends and time evolution of spectral content were reported. The initial wall temperature was varied during the wall temperature measurements and the resulting steady and unsteady effects on the roughness wake were investigated.

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 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.

Film Cooling Effectiveness for Injection from Multirow Holes

1979 ◽  
Vol 101 (1) ◽  
pp. 101-108 ◽  
Author(s):  
M. Sasaki ◽  
K. Takahara ◽  
T. Kumagai ◽  
M. Hamano
Keyword(s):  
Pressure Gradient ◽  
Wall Temperature ◽  
Film Cooling ◽  
Infrared Camera ◽  
Superposition Model ◽  
Adiabatic Wall ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Temperature Distributions

Experimental results are presented for film cooling effectiveness with injection from both a single row and multiple rows of holes with spanwise hole-to-hole spacings of three hole diameters. In the multi-row cases, the injection holes were arranged in staggered patterns with streamwise row-to-row spacings of five or ten hole diameters. Adiabatic wall temperature distributions near and downstream of injection holes were well visualized using a scanning infrared camera. The effect of mainstream pressure gradient was partially included. The additive nature of multi-row film cooling was demonstrated experimentally, in agreement with the Sellers superposition model.

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.

scholarly journals Experimental study of the adiabatic wall temperature of a cylinder in a supersonic cross flow

2021 ◽  
Vol 2039 (1) ◽  
pp. 012029
Author(s):  
S S Popovich ◽  
N A Kiselev ◽  
A G Zditovets ◽  
Y A Vinogradov
Keyword(s):  
Experimental Study ◽  
Wall Temperature ◽  
High Speed ◽  
Cross Flow ◽  
Maximum Temperature ◽  
Thermal Imager ◽  
State University ◽  
Adiabatic Wall ◽  
Speed Flow ◽  
Total Temperature

Abstract The results of an experimental study of the adiabatic wall temperature for a supersonic air flow across the cylinder are presented. The temperature was measured contactlessly using an InfraTEC ImageIR 8855 thermal imager through a ZnSe infrared illuminator. The freestream Mach number was 3.0, input flow total temperature was 295 K, and the total pressure 615 kPa. The Reynolds number calculated from the cylinder diameter (30 mm) was about 106. It is shown that it is possible in principle to determine the high-speed flow total temperature by defining the maximum temperature of a cylindrical probe at the front critical point. Thermograms of the wall temperature distribution along the profile of the cylinder were obtained. The research was performed at the experimental facilities of the Institute of Mechanics of Lomonosov Moscow State University.

A Transient Infrared Thermography Method for Simultaneous Film Cooling Effectiveness and Heat Transfer Coefficient Measurements From a Single Test

2004 ◽  
Vol 126 (4) ◽  
pp. 597-603 ◽  
Author(s):  
Srinath V. Ekkad ◽  
Shichuan Ou ◽  
Richard B. Rivir
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Transfer Coefficient ◽  
Infrared Thermography ◽  
Wall Temperature ◽  
Film Cooling ◽  
Initial Model ◽  
Adiabatic Wall ◽  
The Heat Transfer Coefficient

In film cooling situations, there is a need to determine both local adiabatic wall temperature and heat transfer coefficient to fully assess the local heat flux into the surface. Typical film cooling situations are termed three temperature problems where the complex interaction between the jets and mainstream dictates the surface temperature. The coolant temperature is much cooler than the mainstream resulting in a mixed temperature in the film region downstream of injection. An infrared thermography technique using a transient surface temperature acquisition is described which determines both the heat transfer coefficient and film effectiveness (nondimensional adiabatic wall temperature) from a single test. Hot mainstream and cooler air injected through discrete holes are imposed suddenly on an ambient temperature surface and the wall temperature response is captured using infrared thermography. The wall temperature and the known mainstream and coolant temperatures are used to determine the two unknowns (the heat transfer coefficient and film effectiveness) at every point on the test surface. The advantage of this technique over existing techniques is the ability to obtain the information using a single transient test. Transient liquid crystal techniques have been one of the standard techniques for determining h and η for turbine film cooling for several years. Liquid crystal techniques do not account for nonuniform initial model temperatures while the transient IR technique measures the entire initial model distribution. The transient liquid crystal technique is very sensitive to the angle of illumination and view while the IR technique is not. The IR technique is more robust in being able to take measurements over a wider temperature range which improves the accuracy of h and η. The IR requires less intensive calibration than liquid crystal techniques. Results are presented for film cooling downstream of a single hole on a turbine blade leading edge model.

Analysis of Film Cooling and Full-Coverage Film Cooling of Gas Turbine Blades

1984 ◽  
Vol 106 (1) ◽  
pp. 206-213 ◽  
Author(s):  
E. R. G. Eckert
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Solid Surface ◽  
Wall Temperature ◽  
Film Cooling ◽  
Turbine Blades ◽  
Adiabatic Wall ◽  
Gas Turbine Blades ◽  
Full Coverage ◽  
Cooling Air

Film cooling has become a standard method for the protection of the skin of gas turbine blades against the influence of the hot gas stream. The cooling air is usually injected into the boundary layer covering the skin through one or two rows of holes. A calculation method to predict heat transfer to the skin of a film cooled wall based on two parameters—the film effectiveness and a heat transfer coefficient defined with the adiabatic wall temperature—has been widely accepted. More recently, those sections of a turbine blade skin requiring intensive cooling are covered over its entire area with holes through which cooling air is ejected. A different method to predict the temperature of this section by this “full coverage film cooling” has been proposed which is based on two different parameters θ and K. The air used for the cooling of the perforated section of the skin also provides protection to a solid section located downstream in the normal film cooling process. The two methods are reviewed, and it is discussed under what conditions and in which way results obtained with one method can be transformed to the parameters used in the other one. Published data [8, 9] are used to calculate film cooling effectiveness values and Stanton numbers based on the adiabatic wall temperature for a perforated wall and a solid surface downstream of 11 rows of holes with coolant injection. The results demonstrate the advantage of this method which has been shown in previous experiments with ejection through one or two rows of holes, for film cooling of a solid surface. For full-coverage film cooling, there is still the advantage that a heat transfer coefficient defined with the adiabatic wall temperature is independent of temperature difference within the restrictions imposed by the superposition model.

Sign in / Sign up

Export Citation Format

Share Document