Validation of Mist/Steam Cooling CFD Model in a Horizontal Tube

2008 ◽  
Author(s):  
T. S. Dhanasekaran ◽  
Ting Wang
Keyword(s):  
Gas Turbine ◽  
Droplet Diameter ◽  
Turbulence Models ◽  
Horizontal Tube ◽  
Working Environment ◽  
Cfd Model ◽  
Wall Film ◽  
Cooling Enhancement ◽  
Steam Cooling ◽  
Uniform Droplets

Mist cooling concept has been considered for cooling turbine airfoils for many years. This concept has been proven experimentally as an effective method to significantly enhance the cooling effectiveness with several fundamental studies in the laboratory under low pressure and temperature conditions. However, it is not certain the same performance can be harnessed in the real gas turbine environment under the condition of elevated temperature, pressure, heat flux, and Reynolds number. This paper aims at validating a CFD model against experimental results in a circular tube and then applies the validated CFD model to simulate mist/steam cooling performance at elevated gas turbine working conditions. The results show that the standard k-ε and a RSM turbulence models are the best-suited model for this application. The mist with smaller droplet diameter is found achieving higher cooling enhancement than the flows with bigger droplets, while mist with a distributed droplet size matches the data slightest better than with uniform droplets. Both the wall-film and the reflect droplet boundary conditions are employed and their effects on the cooling result is not significant at the studied cases. The validated CFD model can predict the wall temperature within 2% in steam-only flow and 5% in the mist/steam flow. Applying the calibrated CFD model to the actual gas turbine working environment shows that the mist/steam cooling technique could harness an average 50–100% cooling enhancement.

Calibration of a Computational Model to Predict Mist/Steam Impinging Jets Cooling With an Application to Gas Turbine Blades

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
Ting Wang ◽  
T. S. Dhanasekaran
Keyword(s):  
Gas Turbine ◽  
Working Condition ◽  
Turbulence Models ◽  
Impinging Jet ◽  
Impinging Jets ◽  
Operating Conditions ◽  
Experimental Results ◽  
Cfd Model ◽  
Cooling Enhancement ◽  
Mist Cooling

In heavy-frame advanced turbine systems, steam is used as a coolant for turbine blade cooling. The concept of injecting mist into the impinging jets of steam was experimentally proved as an effective way of significantly enhancing the cooling effectiveness in the laboratory under low pressure and temperature conditions. However, whether or not mist/steam cooling is applicable under actual gas turbine operating conditions is still subject to further verification. Recognizing the difficulties of conducting experiments in an actual high-pressure, high-temperature working gas turbine, a simulation using a computational fluid dynamic (CFD) model calibrated with laboratory data would be an opted approach. To this end, the present study conducts a CFD model calibration against the database of two experimental cases including a slot impinging jet and three rows of staggered impinging jets. The calibrated CFD model was then used to predict the mist cooling enhancement at the elevated gas turbine working condition. Using the experimental results, the CFD model has been tuned by employing different turbulence models, computational cells, and wall y+ values. In addition, the effects of different forces (e.g., drag, thermophoretic, Brownian, and Saffman’s lift force) are also studied. None of the models is a good predictor for all the flow regions from near the stagnation region to far-field downstream of the jets. Overall speaking, both standard k-ε and Reynolds stress model (RSM) turbulence models perform better than other models. The RSM model has produced the closest results to the experimental data due to its capability of modeling the nonisotropic turbulence shear stresses in the 3D impinging jet fields. The simulated results show that the calibrated CFD model can predict the heat transfer coefficient of steam-only case within 2–5% deviations from the experimental results for all the cases. When mist is employed, the prediction of wall temperatures is within 5% for a slot jet and within 10% for three-row jets. The predicted results with 1.5% mist at the gas turbine working condition show the mist cooling enhancement of 20%, whereas in the laboratory condition, the enhancement is predicted as 80%. Increasing mist ratio to 5% increased the cooling enhancement to about 100% at the gas turbine working condition.

scholarly journals CFD Model Validation and Prediction of Mist/Steam Cooling in a 180-Degree Bend Tubes

2010 ◽  
Author(s):  
T. S. Dhanasekaran ◽  
Ting Wang
Keyword(s):  
Boundary Condition ◽  
Gas Turbine ◽  
Working Conditions ◽  
Working Condition ◽  
Cfd Simulation ◽  
Experimental Results ◽  
Cfd Model ◽  
Cooling Enhancement ◽  
Mist Cooling ◽  
Steam Cooling

To achieve higher efficiency target of the advanced turbine systems, the closed-loop steam cooling scheme is employed to cool the airfoil. It is proven from the experimental results at laboratory working conditions that injecting mist into steam can significantly augment the heat transfer in the turbine blades with several fundamental studies. The mist cooling technique has to be tested at gas turbine working conditions before implementation. Realizing the fact that conducting experiment at gas turbine working condition would be expensive and time consuming, the computational simulation is performed to get a preliminary evaluation on the potential success of mist cooling at gas turbine working conditions. The present investigation aims at validating a CFD model against experimental results in a 180-degree tube bend and applying the model to predict the mist/steam cooling performance at gas turbine working conditions. The results show that the CFD model can predict the wall temperature within 8% of experimental steam-only flow and 16% of mist/steam flow condition. Five turbulence models have been employed and their results are compared. Inclusion of radiation into CFD model causes noticeable increase in accuracy of prediction. The reflect Discrete Phase Model (DPM) wall boundary condition predicts better than the wall-film boundary condition. The CFD simulation identifies that mist impingement over outer wall is the cause for maximum mist cooling enhancement at 45° of bend portion. The computed results also reveals the phenomenon of mist secondary flow interaction at bend portion, adding the mist cooling enhancement at the inner wall. The validated CFD simulation predicts that average of 100% mist cooling enhancement can be achieved by injecting 5% mist at elevated GT working condition.

scholarly journals Simulation of Mist Film Cooling at Gas Turbine Operating Conditions

2006 ◽  
Author(s):  
Ting Wang ◽  
Xianchang Li
Keyword(s):  
Gas Turbine ◽  
Film Cooling ◽  
Water Mist ◽  
Operating Conditions ◽  
Round Hole ◽  
Adiabatic Wall ◽  
Cooling Enhancement ◽  
Temperature And Pressure ◽  
Uniform Droplets ◽  
Air Film

Air film cooling has been successfully used to cool gas turbine hot sections for the last half century. A promising technology is proposed to enhance air film cooling with water mist injection. Numerical simulations have shown that injecting a small amount of water droplets into the cooling air improves film-cooling performance significantly. However, previous studies were conducted at conditions of low Reynolds number, temperature, and pressure to allow comparisons with experimental data. As a continuous effort to develop a realistic mist film cooling scheme, this paper focuses on simulating mist film cooling under typical gas turbine operating conditions of high temperature and pressure. The mainstream flow is at 15 atm with a temperature of 1561K. Both 2-D and 3-D cases are considered with different hole geometries on a flat surface, including a 2-D slot, a simple round hole, a compound-angle hole, and fan-shaped holes. The results show that 10%–20% mist (based on the coolant mass flow rate) achieves 5%–10% cooling enhancement and provides an additional 30–68K adiabatic wall temperature reduction. Uniform droplets of 5 to 20 μm are used. The droplet trajectories indicate the droplets tend to move away from the wall, which results in a lower cooling enhancement than under low pressure and temperature conditions. The commercial software Fluent (v. 6.2.16) is adopted in this study, and the standard k-ε model with enhanced wall treatment is adopted as the turbulence model.

Model Verification of Mist/Steam Cooling With Jet Impingement Onto a Concave Surface and Prediction at Elevated Operating Conditions

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Ting Wang ◽  
T. S. Dhanasekaran
Keyword(s):  
Jet Impingement ◽  
Elevated Pressure ◽  
Operating Conditions ◽  
Model Verification ◽  
Concave Surface ◽  
Cfd Model ◽  
Cooling Performance ◽  
Cooling Enhancement ◽  
Mist Cooling ◽  
Steam Cooling

Internal mist/steam blade cooling technology is proposed for advanced gas turbine systems that use the closed-loop steam cooling scheme. Previous experiments on mist/steam heat transfer with a 2D slot jet impingement onto a concave surface showed cooling enhancement of up to 200% at the stagnation point by injecting approximately 0.5% of mist under low temperature and pressure laboratory conditions. Realizing the difficulty in conducting experiments at elevated pressure and temperature working conditions, computational fluid dynamics (CFD) simulation becomes an opted approach to predict the potential applicability of the mist/steam cooling technique at real GT operating conditions. In this study, the CFD model is first validated within 3% and 6% deviations from experimental results for the flows of steam-only and mist/steam flow cases, respectively. The validated CFD model is then used to simulate a row of multiple holes impinging jet onto a concave surface under elevated pressure, temperature, and Reynolds number conditions. The predicted results show an off-center cooling enhancement with a local maximum of 100% at s/d=2 and an average cooling enhancement of about 50%. The mist cooling scheme is predicted to work better on a concave surface than on the flat surface. The extent of wall jet and the size of 3D recirculation zones are identified as a major influencing parameter on the curvature effect on mist cooling performance. The mist enhancement from a slot jet is more pronounced than a row of round jets. The effects of wall heat flux and mist ratio on mist cooling performance are also investigated in this study.

Model Verification of Mist/Steam Cooling With Jet Impingement Onto a Concave Surface and Prediction at Elevated Operating Condition

2010 ◽  
Author(s):  
Ting Wang ◽  
T. S. Dhanasekaran
Keyword(s):  
Jet Impingement ◽  
Elevated Pressure ◽  
Operating Conditions ◽  
Model Verification ◽  
Concave Surface ◽  
Cfd Model ◽  
Cooling Performance ◽  
Cooling Enhancement ◽  
Mist Cooling ◽  
Steam Cooling

Internal mist/steam blade cooling technology is proposed for advanced gas turbine systems that use the closed-loop steam cooling scheme. Previous experiments on mist/steam heat transfer with a 2-D slot jet impingement onto a concave surface showed cooling enhancement of up to 200% at the stagnation point by injecting approximately 0.5% of mist under low temperature and pressure laboratory conditions. Realizing the difficultly in conducting experiments at elevated pressure and temperature working conditions, CFD simulation becomes an opted approach to predict the potential applicability of the mist/steam cooling technique at real GT operating conditions. In this study, the CFD model is first validated within 3% and 6% deviation from experimental results for the flows of steam only and mist/steam flow cases, respectively. The validated CFD model is then used to simulate a row of multiple holes impinging jet onto a concave surface under elevated pressure, temperature, and Reynolds number condition. The predicted results show an off-center cooling enhancement with a local maximum of 200% at s/d = 2 and an average cooling enhancement of about 150%. The mist cooling scheme is predicted to work better on a concave surface than on the flat surface. The extent of wall jet and the size of 3-D recirculation zones are identified as a major influencing parameter on the curvature effect on mist cooling performance. The mist enhancement from a slot jet is more pronounced than a row of round jets. The effects of wall heat flux and mist ratio on mist cooling performance are also investigated in this study.

Calibration of CFD Model for Mist/Steam Impinging Jets Cooling

2008 ◽  
Author(s):  
Ting Wang ◽  
T. S. Dhanasekaran
Keyword(s):  
Gas Turbine ◽  
Isotropic Turbulence ◽  
Laboratory Data ◽  
Turbulence Models ◽  
Impinging Jet ◽  
Impinging Jets ◽  
Operating Conditions ◽  
Experimental Results ◽  
Shear Stresses ◽  
Cfd Model

In the heavy-frame advanced turbine systems, steam is used as a coolant for turbine blade cooling. The concept of injecting mist into the impinging jets of steam was experimentally proved as an effective way of significantly enhancing the cooling effectiveness in the laboratory under low pressure and temperature conditions. However, whether mist/steam cooling is applicable under actual gas turbine operating conditions is still subject to further verification. Recognizing the difficulties of conducting experiments in an actual high-pressure, high-temperature working gas turbine, a simulation using a CFD model calibrated with laboratory data would be an opted approach. To this end, the present study conducts a CFD model calibration against the database of two experimental cases including a slot impinging jet and three rows of staggered impinging jets. Using the experimental results, the CFD model has been tuned by employing different turbulence models, computational cells, wall y+ values, and selection of near-wall functions. In addition, the effect of different forces (e.g. drag, thermophoretic, Brownian, and Saffman’s lift force) are also studied. None of the models are good predictors for all the flow regions from near the stagnation region to far-field downstream of the jets. Overall speaking, both the standard k-ε and RSM turbulence models perform better than other models. The RSM model has produced the closest results to the experimental data due to its capability of modeling the non-isotropic turbulence shear stresses in the 3-D impinging jet fields. For the 3-D flow fields, the nearest element from the wall must be set to approximately unity (y+ ≈ 1) to capture the correct flow structure. The simulated results showed that the calibrated CFD model could predict the heat transfer coefficient of steam-only case within 2 to 5% deviations from the experimental results for all the cases. When mist is employed, the prediction of wall temperatures is within 5% for a slot jet and within 10% for three-row jets.

Influence of Water Droplet Size and Temperature on Wet Compression

2007 ◽  
Author(s):  
M. Bianchi ◽  
F. Melino ◽  
A. Peretto ◽  
P. R. Spina ◽  
S. Ingistov
Keyword(s):  
Gas Turbine ◽  
Water Droplet ◽  
Droplet Diameter ◽  
Axial Compressor ◽  
Combined Cycle ◽  
Water Evaporation ◽  
Air Cooling ◽  
Compression Process ◽  
Two Phase ◽  
Wet Compression

In the last years, among all different gas turbine inlet air cooling techniques, an increasing attention to fogging approach is dedicated. The various fogging strategies seem to be a good solution to improve gas turbine or combined cycle produced power with low initial investment cost and less installation downtime. In particular, overspray fogging and interstage injection involve two-phase flow consideration and water evaporation during compression process (also known as wet compression). According to the Author’s knowledge, the field of wet compression is not completely studied and understood. In the present paper, all the principal aspects of wet compression and in particular the influence of injected water droplet diameter and surface temperature, and their effect on gas turbine performance and on the behavior of the axial compressor (change in axial compressor performance map due to the water injection, redistribution of stage load, etc.) are analyzed by using a calculation code, named IN.FO.G.T.E. (INterstage FOgging Gas Turbine Evaluation), developed and validated by the Authors.

Compressor Performance and Operability in Swirl Distortion

2010 ◽  
Author(s):  
Yogi Sheoran ◽  
Bruce Bouldin ◽  
P. Murali Krishnan
Keyword(s):  
Gas Turbine ◽  
Complex Geometry ◽  
Full Range ◽  
Axial Compressor ◽  
Cfd Model ◽  
Generator System ◽  
Sliding Mesh ◽  
Wide Range ◽  
Compressor Performance ◽  
The Impact

Inlet swirl distortion has become a major area of concern in the gas turbine engine community. Gas turbine engines are increasingly installed with more complicated and tortuous inlet systems, like those found on embedded installations on Unmanned Aerial Vehicles (UAVs). These inlet systems can produce complex swirl patterns in addition to total pressure distortion. The effect of swirl distortion on engine or compressor performance and operability must be evaluated. The gas turbine community is developing methodologies to measure and characterize swirl distortion. There is a strong need to develop a database containing the impact of a range of swirl distortion patterns on a compressor performance and operability. A recent paper presented by the authors described a versatile swirl distortion generator system that produced a wide range of swirl distortion patterns of a prescribed strength, including bulk swirl, twin swirl and offset swirl. The design of these swirl generators greatly improved the understanding of the formation of swirl. The next step of this process is to understand the effect of swirl on compressor performance. A previously published paper by the authors used parallel compressor analysis to map out different speed lines that resulted from different types of swirl distortion. For the study described in this paper, a computational fluid dynamics (CFD) model is used to couple upstream swirl generator geometry to a single stage of an axial compressor in order to generate a family of compressor speed lines. The complex geometry of the analyzed swirl generators requires that the full 360° compressor be included in the CFD model. A full compressor can be modeled several ways in a CFD analysis, including sliding mesh and frozen rotor techniques. For a single operating condition, a study was conducted using both of these techniques to determine the best method given the large size of the CFD model and the number of data points that needed to be run to generate speed lines. This study compared the CFD results for the undistorted compressor at 100% speed to comparable test data. Results of this study indicated that the frozen rotor approach provided just as accurate results as the sliding mesh but with a greatly reduced cycle time. Once the CFD approach was calibrated, the same techniques were used to determine compressor performance and operability when a full range of swirl distortion patterns were generated by upstream swirl generators. The compressor speed line shift due to co-rotating and counter-rotating bulk swirl resulted in a predictable performance and operability shift. Of particular importance is the compressor performance and operability resulting from an exposure to a set of paired swirl distortions. The CFD generated speed lines follow similar trends to those produced by parallel compressor analysis.

Thermodynamic Evaluation of Gas Turbine Cogeneration Cycles: Part II—Complex Cycle Analysis

1987 ◽  
Vol 109 (1) ◽  
pp. 8-15 ◽  
Author(s):  
I. G. Rice
Keyword(s):  
Gas Turbine ◽  
Heat Balance ◽  
Steam Injection ◽  
Balance Method ◽  
Visual Perspective ◽  
Thermodynamic Evaluation ◽  
The Future ◽  
Steam Cooling ◽  
The Heat Balance ◽  
Regenerative Cycle

Complex open gas turbine cycles are analyzed by applying the heat balance method presented in Part I of this paper. Reheating, intercooling, regeneration, steam injection, and steam cooling are evaluated graphically to give a visual perspective of what takes place in terms of the overall heat balance when such complexities are introduced to the cycle. An example of a viable, new, intercooled regenerative cycle is given. A second example of a prototype reheat gas turbine is also included. The overall approach using the heat balance method can be applied to various cogeneration configurations when considering the more complex cycles of the future.

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