scholarly journals METHOD FOR DETERMINING ADIABATIC FILM EFFECTIVENESS IN PRESENCE OF THERMAL BOUNDARY LAYER

2021 ◽  
pp. 1-20
Author(s):  
James Parker ◽  
Thomas Povey
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
Thermal Boundary Layer ◽  
Complex Function ◽  
Mixing Layer ◽  
Inlet Temperature ◽  
Gas Temperature ◽  
Point Of Interest ◽  
The Difference ◽  
Processing Techniques

Abstract In this paper we present a new method for determining adiabatic film effectiveness in film-cooling experiments with non-uniform inlet temperature distributions, in particular the situation of an inlet thermal boundary layer. This might arise in a quasi-steady experiment due to loss of heat from the mainstream flow to the inlet contraction walls, for example. In this situation the thermal boundary layer would be time varying. Adiabatic film effectiveness is generally normalised by the difference between mainstream and coolant gas temperatures. Most importantly these temperatures are generally assumed to be spatially—and, possibly temporally—uniform at the system inlet. In experiments with non-uniform inlet temperature, the relevant hot-gas temperature for a particular point of interest on a surface is not easily determined, being a complex function of both the inlet temperature profile and the flow-field between the inlet and the point of interest. In this situation, adiabatic film effectiveness cannot be uniquely defined using conventional processing techniques. We solve this problem by introducing the concept of equivalent mainstream effectiveness, a non-dimensional temperature for the mainstream that can be used to represent the thermal boundary layer profile at the inlet plane, or the effective temperature of the mainstream gas—which we refer to as the equivalent mainstream temperature—entrained into the mixing layer affecting the wall temperature at a particular point of interest.

The Effects of Conjugate Heat Transfer on the Thermal Field Above a Film Cooled Wall

2011 ◽  
Author(s):  
Jason E. Dees ◽  
David G. Bogard ◽  
Gustavo A. Ledezma ◽  
Gregory M. Laskowski
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Wall Temperature ◽  
Film Cooling ◽  
Thermal Boundary Layer ◽  
Heat Transfer Analysis ◽  
Gas Temperature ◽  
Adiabatic Wall ◽  
Thermal Fields ◽  
Conducting Wall

Common gas turbine heat transfer analysis methods rely on the assumption that the driving temperature for heat transfer to a film cooled wall can be approximated by the adiabatic wall temperature. This assumption implies that the gas temperature above a film cooled adiabatic wall is representative of the overlying gas temperature on a film cooled conducting wall. This assumption has never been evaluated experimentally. In order for the adiabatic wall temperature as driving temperature for heat transfer assumption to be valid, the developing thermal boundary layer that exists above a conducting wall must not significantly affect the overriding gas temperature. In this paper, thermal fields above conducting and adiabatic walls of identical geometry and at the same experimental conditions were measured. These measurements allow for a direct comparison of the thermal fields above each wall in order to determine the validity of the adiabatic wall temperature as driving temperature for heat transfer assumption. In cases where the film cooling jet was detached, a very clear effect of the developing thermal boundary layer on the gas temperature above the wall was measured. In this case, the temperatures above the wall were clearly not well represented by the adiabatic wall temperature. For cases where the film cooling jet remained attached, differences in the thermal fields above the adiabatic and conducting wall were small, indicating a very thin thermal boundary layer existed beneath the coolant jet.

On the Momentum and Thermal Structures of Turbulent Spots in a Favorable Pressure Gradient

2005 ◽  
Vol 128 (4) ◽  
pp. 689-698 ◽  
Author(s):  
T. P. Chong ◽  
S. Zhong
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Pressure Gradient ◽  
Velocity Component ◽  
Thermal Boundary Layer ◽  
Temperature Fluctuations ◽  
Turbulent Spots ◽  
Zone Length ◽  
Favorable Pressure Gradient ◽  
The Difference

This paper represents the results from an experimental investigation of the flow physics behind the difference in the transition zone length indicated by the momentum boundary layer and thermal boundary layer parameters observed on the suction surfaces of gas turbine blades. The experiments were carried out on turbulent spots created artificially in an otherwise laminar boundary layer developing over a heated flat plate in a zero pressure gradient and a favorable pressure gradient. A specially designed miniature triple wire probe was used to measure the streamwise velocity component U, transverse velocity component V and temperature T simultaneously during the passage of the spots. In this paper, the general characteristics of the ensemble-averaged velocity and temperature perturbations, rms fluctuations, and the second moment turbulent quantities are discussed and the influence of favorable pressure gradient on these parameters is examined. When a favorable pressure gradient is present, unlike in the velocity boundary layer where significant velocity fluctuations and Reynolds shear stress occur both on the plane of symmetry and the spanwise periphery, high temperature fluctuations (and turbulent heat fluxes) are confined in the plane of symmetry. The difference in the levels of velocity/temperature fluctuations at these two locations gives an indication of the effectiveness of momentum/heat transfer across the span of the spots. The results of this study indicate that the heat transfer within a spot is inhibited more than that of the momentum transfer at the presence of a favorable pressure gradient. This phenomenon is expected to slow down the development of a transitional thermal boundary layer, leading to a longer transitional zone length indicated by the heat transfer parameters as reported in the literature.

Superposition Characteristics of Full Coverage Film Cooling With Various Blowing Ratio and Row Number

2019 ◽  
Author(s):  
Lang Wang ◽  
Xueying Li ◽  
Weihong Li ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
Jet Flow ◽  
Inlet Temperature ◽  
Superposition Method ◽  
Turbine Blade Cooling ◽  
Blowing Ratio ◽  
Blade Cooling ◽  
Full Coverage ◽  
Accuracy Of Prediction

Abstract Effusion cooling is the next step in gas turbine blade cooling to get the higher turbine inlet temperature, but the interaction between the front jet flow and the rear jet flow still need to be studied. In this paper, the effect of row number and blowing ratio are studied experimentally by PSP and numerically by RANS. One to five rows of staggered cooling holes were investigated with blowing ratio 0.5, 1.0 and 1.5. It is found that the income boundary layer helps the rear rows penetrate deeper to the main flow at low blowing ratio M = 0.5, the cooling performance become worse for single row. The performance at high blowing ratio M = 1.5 for row 3–5 is nearly not effected by income boundary layer due to blowing off. Finally, a corrected equation based on Sellers superposition method for full coverage film cooling is realized, which could explain the “fully developed level” and improve the accuracy of prediction of full coverage film cooling.

scholarly journals Combustor Flame Radiation and Wall Temperatures for #2 Distillate and a Coal Derived Liquid Fuel

1982 ◽  
Author(s):  
R. J. Kuznar ◽  
E. W. Tobery ◽  
A. Cohn
Keyword(s):  
Heat Flux ◽  
Film Cooling ◽  
Liquid Fuel ◽  
Gas Temperature ◽  
Flame Radiation ◽  
Flame Heat Flux ◽  
Primary Zone ◽  
The Difference ◽  
Process Measurements ◽  
Cooling Air

Flame radiation measurements were made in the primary zone of a film cooled gas turbine combustor, while burning #2 distillate (13 percent H) and a coal derived liquid fuel (8.7 percent H), from the SRC II process. Measurements from three circumferentially located radiometers indicate an average increase in flame heat flux of 55 percent, during combustion of the SRC II blend. Individual radiometer readings measured an increase ranging from 52 to 60 percent. Analytical predictions of the average combustor metal temperature, for the SRC II blend, cannot be explained by the increase in flame heat flux alone. If the same temperature of hot gases which mix in with film cooling air is used for both fuels then the calculated temperatures for SRC II fuel would be higher than those measured. Therefore, a lower value for hot gas temperature is required for the SRC II fuel case. This difference is attributed to the difference inflame shape between the two fuels.

Numerical Study of Mist Film Cooling in Combustor at Operating Conditions

2009 ◽  
Author(s):  
Srinivasa Rao Para ◽  
Xianchang Li ◽  
Ganesh Subbuswamy
Keyword(s):  
Gas Turbine ◽  
Film Cooling ◽  
Numerical Study ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Gas Temperature ◽  
Cooling Effectiveness ◽  
Wall Functions ◽  
Film Cooling Effectiveness ◽  
Combustor Liner

To improve the gas turbine thermal performance, apart from using a high compression ratio, the turbine inlet temperature must be increased. Therefore, the gas temperature inside the combustion chamber needs to be maintained at a very high level. Hence, cooling of the combustor liner becomes critical. Among all the cooling techniques, film cooling has been successfully applied to cool the combustor liner. In film cooling, coolant air is introduced through discrete holes and forms a thin film between the hot gases and the inner surface of the liner, so that the inner wall can be protected from overheating. The film will be destroyed in the downstream flow because of mixing of hot and cold gases. The present work focuses on numerical study of film cooling under operating conditions, i.e., high temperature and pressure. The effect of coolant injection angles and blowing ratios on film cooling effectiveness is studied. A promising technology, cooling with mist injection, is studied under operating conditions. The effect of droplet size and mist concentration is also analyzed. The results of this study indicate that the film cooling effectiveness can increase ∼11% at gas turbine operating conditions with mist injection of 2% coolant air when droplets of 10μm and a blowing ratio of 1.0 are applied. The cooling performance can be further improved by higher mist concentration. The commercial CFD software, Fluent 6.3.26, is used in this study and the standard k-ε model with enhanced wall functions is adopted as the turbulence model.

A Simple Method for the Prediction of Wall Temperatures in Gas Turbines

1978 ◽  
Author(s):  
D. Kretschmer ◽  
J. Odgers
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Gas Temperature ◽  
Empirical Formulas ◽  
Simple Method ◽  
Hot Gas ◽  
Manufacturing Tolerances ◽  
Factor Governing

The cited method predicts wall temperatures generally within an accuracy of ± 6 percent, The biggest single factor governing the wall temperature is shown to be the hot gas temperature. Other factors discussed are the effects of changes in inlet temperature, fuel types, the geometry of the film cooling devices and manufacturing tolerances. Empirical formulas are given for the prediction of effective temperatures within the various combustor zones. Some comparisons are made between predictions and measurements of wall temperatures over a range of operating conditions.

Experimental and CFD Studies of NGV Endwall Cooling

2013 ◽  
Author(s):  
Mitra Thomas ◽  
Benjamin Kirollos ◽  
Dougal Jackson ◽  
Thomas Povey
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
Large Scale ◽  
Guide Vane ◽  
Complex Nature ◽  
Outlet Temperature ◽  
Double Row ◽  
The Difference ◽  
Layer Flow ◽  
Nozzle Guide

For engines operating at high turbine entry temperatures it is increasingly important to cool the high pressure nozzle guide vane (HP NGV) endwalls. This is particularly so for low NOx combustors operating with flatter outlet temperature distributions. Double-row arrangements of film/ballistic cooling holes upstream of the NGV passage have been employed in production engines. Optimisation of such systems is non-trivial, however, due to the complex nature of the flow in the endwall region. Previous studies have reported that strong cross passage pressure gradients lead to migration of coolant flow and boundary layer flow within the passage. In addition the vane potential field effects lead to non-uniform blowing ratios for holes upstream of the vanes. It has also been reported that inlet total pressure and turbulence profiles have a significant effect on the development of the film cooling layer. In this study, endwall film cooling flows are studied experimentally in a large-scale low-speed cascade tunnel with engine-realistic combustor geometry and turbulence profiles. At very low blowing ratios mild cross-passage migration effects are observed. At higher blowing ratios more realistic of the engine situation no cross-passage migration is observed. This finding is somewhat contrary to the classical view of endwall secondary flow, which is presented as significant at the scale of the vane passage by several authors. The difference arises in part because of the thinning of the boundary layer due to strong acceleration in the vane inlet contraction. The findings are further supported by CFD simulations. Methods of improving conventional double-row systems to offer improved cooling of the endwall are also discussed.

Experimental and Numerical Investigations of the Heat Transfer and Flow Field in a Trailing Edge Cooling Geometry: Part 1 — Experimental Study With IR Thermography and PIV

2015 ◽  
Author(s):  
Guanghua Wang ◽  
Jordi Estevadeordal ◽  
James DeLancey ◽  
Jeremy Bailey ◽  
James Kopriva ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Gas Turbines ◽  
Density Ratio ◽  
Field Measurements ◽  
Open Loop ◽  
Inlet Temperature ◽  
Gas Temperature ◽  
Trailing Edge ◽  
Ir Camera

Airfoil Trailing Edge (TE) cooling is critical for turbine blade and nozzle lifing and safety. Gas turbines overall efficiency enhancement requires further increasing of the turbine inlet temperature and decreasing of cooling flow usage. This requires more advanced TE designs to meet the inherent conflicting requirements. Aerodynamic requirements of thin TE, particularly in jet engines, lead to Pressure Side (PS) cutback of the TE with a span-wise slot forming uniform cooling film over the cutback/floor region. This study focused on the PS cutback TE film effectiveness and flow field measurements of a standard geometry with t/s=0.9. The measurements were conducted in a subsonic open loop wind tunnel with a generic setup to cover different TE running conditions. IR camera is used to measure the TE coupon surface temperature distribution. The test conditions are characterized by a constant main flow Mach number with constant gas temperature. CO2 at constant temperature is used as the coolant to reach the realistic blowing ratio and density ratio. Inlet boundary layer is measured by the Particle Image Velocimerty (PIV) to characterize the TE flow conditions and study the underlying flow physics. The experimental data for 2D wall contours and laterally-averaged profiles of adiabatic film effectiveness, velocity vector field and boundary layer profiles were discussed. These data will be used to provide inlet boundary conditions and validate CFD simulations in Part 2.

Numerical study of ceramic catalytic turbine technology for emission reduction during vehicle warm-up

2021 ◽  
pp. 146808742110360
Author(s):  
Leilei Wang ◽  
Xu Tan ◽  
Harold Sun ◽  
Abraham Engeda ◽  
Hongjuan Hou ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Catalytic Reaction ◽  
Gasoline Engine ◽  
Numerical Study ◽  
Moving Average ◽  
Inlet Temperature ◽  
Gas Temperature ◽  
Turbine Inlet Temperature ◽  
Warm Up ◽  
Turbine Inlet

Ceramic Catalytic Turbine (CCT) Technology is expected to become an important means to reduce vehicle emissions, especially during engine warm-up. In this paper, catalytic reaction was numerically simulated in 3D for a CCT on a gasoline engine during the warm-up period. The results showed that turbulence in the turbine promotes catalytic activity; CCT starts to significantly affect exhaust pollution since turbine inlet temperature of 550 K; the conversion efficiency of harmful gas in exhaust rises sharply when turbine inlet reaches 575–625 K; when the inlet temperature is about 720 K, the conversion efficiencies of C3H6, CO, and NO reach 23.7%, 21.1%, and 15.5%, respectively. Meanwhile the gas temperature is increased by about 30 K at turbine outlet. In addition, during the process of numerical modeling and calculation, it is found that minor change in boundary layer thickness has a negligible impact on the simulation. However, an extremely thin boundary layer will cause computational divergence. The intensity of catalytic reaction can influence the convergence of numerical calculation, while the moving average of the catalytic reaction with the turbine inlet temperature, in return, can reveal the catalytic light-off process.

scholarly journals Determination of active and reactive thermal resistance of one-layer building envelopes

Vestnik MGSU ◽  
2020 ◽  
pp. 1126-1134
Author(s):  
Tatiana A. Musorina ◽  
Mikhail R. Petrichenko ◽  
Darya D. Zaborova ◽  
Olga S. Gamayunova
Keyword(s):  
Boundary Layer ◽  
Thermal Resistance ◽  
Thermal Boundary Layer ◽  
Individual Characteristics ◽  
Building Envelope ◽  
Heat Output ◽  
Total Resistance ◽  
Temperature Differential ◽  
Active Resistance ◽  
The Difference

Introduction. The subject of the study is the individual characteristics of a 0.51 m thick external single-layer building envelope made of solid ceramic bricks. The paper focuses on the heat engineering parameters of the wall, namely, the calculation of active and reactive thermal resistances. We determine the differences between the two types of resistances. We also provide an example of calculating the thermal boundary layer in which all temperature fluctuations occur and determining the amount of heat absorbed and released by the envelope. Materials and methods. We give consideration to taking into account the two components of thermal resistance based on wave functions — thermal and temperature waves. Active thermal resistance is determined at any point of the building envelope with a fixed time value t (stationary heat transfer mode). The coordinate is recorded when determining total resistance. To calculate the thickness of the envelope thermal boundary layer, the temperature differential from −30 to 40 °С outside the premises is considered, the temperature inside the premises is assumed to be 18 °С. The temperature differential value is calculated from the ratio of the difference between current temperatures and the initial value. The required heat quantity and heat output are calculated using standard thermal physics formulas. Results. The difference between active and reactive thermal resistances, which together make up total thermal resistance, was proved. Active resistance is always 1.57 times less than total resistance. In this case, the active resistance will drop as the temperature differential decreases, and will increase when the outside temperature is higher than the temperature inside the premise. The thermal boundary layer thickness is always less than half of the envelope thickness. Conclusions. Using this method, it is sufficient to calculate the active thermal resistance of the building envelope to determine the remaining values. In addition, the greater the temperature differential, the thicker the temperature boundary layer, i.e. all temperature changes occur only in this layer while the rest of the envelope functions as a thermal accumulator. When the outside ambient temperature drops, all accumulated heat will be transferred into the premise. Such an envelope can be used to heat the premise or to direct this heat to various envelope elements.

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