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.

Account of Film Turbulence for Predicting Film Cooling Effectiveness in Gas Turbine Combustors

1979 ◽  
Author(s):  
G. J. Sturgess
Keyword(s):  
Gas Turbine ◽  
Film Cooling ◽  
Cooling Effectiveness ◽  
Turbine Engine ◽  
Film Cooling Effectiveness ◽  
Wide Range ◽  
Engine Combustion ◽  
Turbulence Effects ◽  
The Impact ◽  
Combustor Liner

The paper deals with a small but important part of the overall gas turbine engine combustion system and continues earlier published work on turbulence effects in film cooling to cover the case of film turbulence. Film cooling of the gas turbine combustor liner imposes certain geometric limitations on the coolant injection device. The impact of practical film injection geometry on the cooling is one of increased rates of film decay when compared to the performance from idealized injection geometries at similar injection conditions. It is important to combustor durability and life estimation to be able to predict accurately the performance obtainable from a given practical slot. The coolant film is modeled as three distinct regions, and the effects of injection slot geometry on the development of each region are described in terms of film turbulence intensity and initial circumferential non-uniformity of the injected coolant. The concept of the well-designed slot is introduced and film effectiveness is shown to be dependent on it. Only slots which can be described as well-designed are of interest in practical equipment design. A prediction procedure is provided for well-designed slots which describes growth of the film downstream of the first of the three film regions. Comparisons of predictions with measured data are made for several very different well-designed slots over a relatively wide range of injection conditions, and good agreement is shown.

Improvement of Film Cooling Effectiveness in the Gas Turbine Endwall by Use of Optimization Framework

2019 ◽  
Author(s):  
Daisuke Hata ◽  
Kazuto Kakio ◽  
Yutaka Kawata ◽  
Masahiro Miyabe
Keyword(s):  
Pressure Gradient ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Film Cooling ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Combined Cycle ◽  
Inlet Temperature ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness

Abstract Recently, the number of gas turbine combined cycle plants is rapidly increasing in substitution of nuclear power plants. The turbine inlet temperature (TIT) is constantly being increased in order to achieve higher effectiveness. Therefore, the improvement of the cooling technology for high temperature gas turbine blades is one of the most important issue to be solved. In a gas turbine, the main flow impinging at the leading edge of the turbine blade generates a so called horseshoe vortex by the interaction of its boundary layer and generated pressure gradient at the leading edge. The pressure surface leg of this horseshoe vortex crosses the passage and reaches the blade suction surface, driven by the pressure gradient existing between two consecutive blades. In addition, this pressure gradient generates a cross-flow along the endwall. This all results into a very complex flow field in proximity of the endwall. For this reason, burnouts tend to occur at a specific position in the vicinity of the leading edge. In this research, a methodology to cool the endwall of the turbine blade by means of film cooling jets from the blade surface and the endwall is proposed. The cooling performance is investigated using the transient thermography method. CFD analysis is also conducted to investigate the phenomena occurring at the endwall and calculate the film cooling effectiveness.

Account of Film Turbulence for Predicting Film Cooling Effectiveness in Gas Turbine Combustors

1980 ◽  
Vol 102 (3) ◽  
pp. 524-534 ◽  
Author(s):  
G. J. Sturgess
Keyword(s):  
Gas Turbine ◽  
Film Cooling ◽  
Cooling Effectiveness ◽  
Turbine Engine ◽  
Film Cooling Effectiveness ◽  
Wide Range ◽  
Engine Combustion ◽  
Turbulence Effects ◽  
The Impact ◽  
Combustor Liner

The paper deals with a small but important part of the overall gas turbine engine combustion system and continues earlier published work on turbulence effects in film cooling to cover the case of film turbulence. Film cooling of the gas turbine combustor liner imposes certain geometric limitations on the coolant injection device. The impact of practical film injection geometry on the cooling is one of increased rates of film decay when compared to the performance from idealized injection geometries at similar injection conditions. It is important to combustor durability and life estimation to be able to predict accurately the performance obtainable from a given practical slot. The coolant film is modeled as three distinct regions, and the effects of injection slot geometry on the development of each region are described in terms of film turbulence intensity and initial circumferential non-uniformity of the injected coolant. The concept of the well-designed slot is introduced and film effectiveness is shown to be dependent on it. Only slots which can be described as well-designed are of interest in practical equipment design. A prediction procedure is provided for well-designed slots which describes growth of the film downstream of the first of the three film regions. Comparisons of predictions with measured data are made for several very different well-designed slots over a relatively wide range of injection conditions, and good agreement is shown.

scholarly journals Computational Analysis of Surface Curvature Effect on Mist Film-Cooling Performance

2008 ◽  
Vol 130 (12) ◽  
Author(s):  
Xianchang Li ◽  
Ting Wang
Keyword(s):  
Gas Turbine ◽  
Film Cooling ◽  
Leading Edge ◽  
Operating Conditions ◽  
Curved Surfaces ◽  
Curvature Effect ◽  
Water Droplets ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Air Film

Air-film cooling has been widely employed to cool gas turbine hot components, such as combustor liners, combustor transition pieces, turbine vanes, and blades. Studies with flat surfaces show that significant enhancement of air-film cooling can be achieved by injecting water droplets with diameters of 5–10 μm into the coolant airflow. The mist/air-film cooling on curved surfaces needs to be studied further. Numerical simulation is adopted to investigate the curvature effect on mist/air-film cooling, specifically the film cooling near the leading edge and on the curved surfaces. Water droplets are injected as dispersed phase into the coolant air and thus exchange mass, momentum, and energy with the airflow. Simulations are conducted for both 2D and 3D settings at low laboratory and high operating conditions. With a nominal blowing ratio of 1.33, air-only adiabatic film-cooling effectiveness on the curved surface is lower than on a flat surface. The concave (pressure) surface has a better cooling effectiveness than the convex (suction) surface, and the leading-edge film cooling has the lowest performance due to the main flow impinging against the coolant injection. By adding 2% (weight) mist, film-cooling effectiveness can be enhanced approximately 40% at the leading edge, 60% on the concave surface, and 30% on the convex surface. The leading edge film cooling can be significantly affected by changing of the incident angle due to startup or part-load operation. The film cooling coverage could switch from the suction side to the pressure side and leave the surface of the other part unprotected by the cooling film. Under real gas turbine operating conditions at high temperature, pressure, and velocity, mist-cooling enhancement could reach up to 20% and provide a wall cooling of approximately 180 K.

Numerical Simulation on Gas Turbine Film Cooling of Curved Surface With Backward Injection

2012 ◽  
Author(s):  
Shashank Shetty ◽  
Xianchang Li ◽  
Ganesh Subbuswamy
Keyword(s):  
Numerical Simulation ◽  
Gas Turbine ◽  
Film Cooling ◽  
Gas Turbines ◽  
Turbine Blades ◽  
Operating Conditions ◽  
Strong Mixing ◽  
Inlet Temperature ◽  
Film Cooling Effectiveness ◽  
Aerodynamic Loss

Due to the unique role of gas turbine engines in power generation and aircraft propulsion, significant effort has been made to improve the gas turbine performance. As a result, the turbine inlet temperature is usually elevated to be higher than the metal melting point. Therefore, effective cooling of gas turbines is a critical task for engines’ efficiency as well as safety and lifetime. Film cooling has been used to cool the turbine blades for many years. The main issues related to film cooling are its poor coverage, aerodynamic loss, and increase of heat transfer coefficient due to strong mixing. To overcome these problems, film cooling with backward injection has been found to produce a more uniform cooling coverage under low pressure and temperature conditions and with simple cylindrical holes. Therefore, the focus of this paper is on the performance of film cooling with backward injection at gas turbine operating conditions. By applying numerical simulation, it is observed that along the centerline on both concave and convex surfaces, the film cooling effectiveness decreases with backward injection. However, cooling along the span is improved, resulting in more uniform cooling.

Numerical Study of Film Cooling Enhancement in Gas Turbine Combustor Liner

2008 ◽  
Author(s):  
Ganesh Subbuswamy ◽  
Xianchang Li
Keyword(s):  
Gas Turbine ◽  
Film Cooling ◽  
Structural Integrity ◽  
Numerical Study ◽  
Current Work ◽  
Working Fluid ◽  
Large Temperature ◽  
Film Cooling Effectiveness ◽  
Hot Air ◽  
Combustor Liner

Combustion chamber or combustor is one of the hottest parts of a gas turbine. Liner is where the actual flame occurs in a combustor and thus, the hottest part of the combustor. The temperature of working fluid inside a liner is about 1200 to 2000K. Because of the hot fluid, the liner is heated up to a temperature almost impossible for the material to withstand. Although the mechanical stresses experienced by the combustor liner are within acceptable limits, high temperatures and large temperature gradients affect the structural integrity of its components, which makes the liner a very critical component of a gas turbine in structural and thermal designs. Film cooling is a traditional method of cooling the inner surface of liner. In film cooling for a combustor, axial holes are drilled along the surface of the liner at discrete locations, through which cold air is injected axially into the liner to provide a film of cool air that prevents direct contact of hot air, and thus, protects the inner wall surface. The film is destroyed in the downstream to the flow because of mixing of cool and hot air. Though this method provides an acceptable cooling, there is a compromise with the increased net benefits of the gas turbine. Therefore, there is a need for new cooling techniques or enhancing the techniques available. The current work is a numerical simulation of film cooling in a model combustor. The effect of coolant injection angles and blowing ratios on film cooling effectiveness is studied. One innovative method, cooling with mist injection, is explored to enhance the performance of film cooling. The effect of droplet size and mist concentration, which can affect the performance of the mist injection, is also analyzed. Fluent, a commercial CFD software, is used in the current work for numerical simulations.

scholarly journals Computational Analysis of Surface Curvature Effect on Mist Film Cooling Performance

2007 ◽  
Author(s):  
Xianchang Li ◽  
Ting Wang
Keyword(s):  
Gas Turbine ◽  
Film Cooling ◽  
Convex Surface ◽  
Leading Edge ◽  
Operating Conditions ◽  
Curvature Effect ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Enhancement ◽  
Air Film

Air film cooling has been widely employed to cool gas turbine hot components such as combustor liners, combustor transition pieces, turbine vanes and blades. Enhancing air film cooling by injecting mist with tiny water droplets with diameters of 5–10μm has been studied in the past on flat surfaces. This paper focuses on computationally investigating the curvature effect on mist/air film cooling enhancement, specifically for film cooling near the leading edge and on the curved surfaces. Numerical simulations are conducted for both 2-D and 3-D settings at low and high operating conditions. The results show, with a nominal blowing ratio of 1.33, air-only adiabatic film cooling effectiveness on the curved surface is less than on a flat surface. The concave (pressure) surface has a better cooling effectiveness than the convex (suction) surface, and the leading edge film cooling has the lowest performance due to main flow impinging against the coolant injection. By adding 2% (weight) mist, film cooling effectiveness can be enhanced approximately 40% at the leading edge, 60% on the concave surface, and 30% on the convex surface. The leading edge film cooling can be significantly affected by changing of the incident angle due to startup or part-load operation. The film cooling coverage could switch from the suction side to the pressure side and leave the surface of the other part unprotected by the cooling film. Under real gas turbine operating conditions at high temperature, pressure, and velocity, mist cooling enhancement could achieve 20% and provides a wall cooling of approximately 180K.

Parametric Study of Showerhead Film Cooling Performance on a Gas Turbine Blade

2014 ◽  
Author(s):  
G. Urquiza ◽  
J. O. Davalos ◽  
J. C. Garcia ◽  
L. Castro ◽  
J. A. Rodríguez ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Turbine Blade ◽  
Film Cooling ◽  
Operating Conditions ◽  
Geometrical Parameters ◽  
Blade Surface ◽  
Gas Turbine Blade ◽  
Gas Temperature ◽  
Cooling Effectiveness ◽  
Blade Geometry

Gas turbine power and efficiency have direct relation with inlet gas temperature. However, high gas temperature could cause thermal damage to gas turbine blade material. Gas turbine blade could be cooled using the so-called film cooling technique which is necessary to ensure blade material integrity. In film cooling, air from compressor is injected through internal blade ducts. The air leaves the internal ducts through holes placed on blade surface, creating a cooling film on the blade surface. Operating conditions and hole geometrical factors can influence the cooling effectiveness. Several investigations have been conducted related to film cooling in order to study its behavior under different conditions. Due to its complexity, many studies replace blade geometry for flat plates. A better approximation to realistic results could be obtained by modeling the blade geometry with cooling holes. In this work, influence of geometrical parameters on cooling effectiveness under different operating conditions, like blowing ratio and angular velocity, is studied by means of numerical analysis using a commercial CFD code. The object of study is a typical showerhead configuration at mid-span of the tested blade, with three rows of cooling holes. In order to reduce computational cost, an algorithm was implemented to generate blade geometries and grids, performing numerical analyses and computing results in an automatic way, based on selected parameters. The algorithm could be used in optimization process to reduce the effort used in the construction geometries. The results show the effects of change geometrical parameters on cooling effectiveness. Additionally, changes on cooling flow direction are observed at high angular velocities.

Computational Study of Mist Assisted Film Cooling on a Flat Plate

2019 ◽  
Author(s):  
Mallikarjuna Rao Pabbi Setty ◽  
B. V. S. S. S. Prasad
Keyword(s):  
Gas Turbine ◽  
Film Cooling ◽  
Computational Study ◽  
Operating Conditions ◽  
Main Stream ◽  
Air Cooling ◽  
Water Droplets ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Air

Abstract Previous investigation [1, 2] proposed that an introduction of water droplets into the film cooling air significantly improves the effectiveness of gas turbine blade. In order to allow comparison with experimental data, all the previous studies were confined to laboratory conditions. However, under typical gas turbine operating conditions temperature difference between the main stream flow (1561 K) and the coolant air (644 K) is approximately 917 K. The aim of this study is to numerically investigate the performance of mist assisted film cooling under the typical operating conditions of the gas turbine. Results showed the value of mist assisted film cooling effectiveness are greater than pure air cooling. Trajectories of droplets show that the water droplets vaporize faster. Typical percentage enhancement of the mist assisted film cooling effectiveness is 16% when the cooling air contains 6% mist with droplet diameter of one micron.

scholarly journals A Study on the Effect of Angle in Diffused Hole Film Cooling Effectiveness at Different Blowing Ratios

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Nishant Gandhi ◽  
Suresh Sivan
Keyword(s):  
Gas Turbine ◽  
Film Cooling ◽  
Cylindrical Hole ◽  
Inlet Temperature ◽  
Turbine Inlet Temperature ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Turbine Inlet ◽  
Grid Independence

AbstractHigher the turbine inlet temperature of a gas turbine, higher will be the efficiency, however the increase in the turbine inlet temperature is limited to the materials and the cooling strategies employed. This article presents a study on the effect of blowing ratio on film cooling effectiveness for a cylindrical hole and a diffused hole at different angles. The analysis was done for blowing ratios of 0.5, 1.0, 1.5 and 2.0 while the angle in the diffused hole was varied as 5°, 10° and 15°. A grid independence study was performed and the simulation was validated. The results of cylindrical and different angles of diffused holes were compared. For a cylindrical hole as well as diffused hole, a blowing ratio of 1.0 was found to have an optimal effectiveness. The diffused hole was found to improve the near hole and downstream effectiveness at higher blowing ratios.

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