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.

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.

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.

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.

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.

Experimental Investigations of Pressure Drop in the Combustion Chamber of Gas Turbine

1989 ◽  
Author(s):  
Marek Dzida ◽  
Krzysztof Kosowski
Keyword(s):  
Pressure Drop ◽  
Combustion Chamber ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Experimental Results ◽  
Experimental Investigations ◽  
Relative Pressure ◽  
Wide Range ◽  
Few Data

In bibliography we can find many methods of determining pressure drop in the combustion chambers of gas turbines, but there is only very few data of experimental results. This article presents the experimental investigations of pressure drop in the combustion chamber over a wide range of part-load performances (from minimal power up to take-off power). Our research was carried out on an aircraft gas turbine of small output. The experimental results have proved that relative pressure drop changes with respect to fuel flow over the whole range of operating conditions. The results were then compared with theoretical methods.

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.

Experimental study of physical mechanisms in the control of supersonic impinging jets using microjets

2008 ◽  
Vol 613 ◽  
pp. 55-83 ◽  
Author(s):  
FARRUKH S. ALVI ◽  
HUADONG LOU ◽  
CHIANG SHIH ◽  
RAJAN KUMAR
Keyword(s):  
Shear Layer ◽  
Nozzle Exit ◽  
Feedback Loop ◽  
Large Scale ◽  
Impinging Jet ◽  
Impinging Jets ◽  
Operating Conditions ◽  
Jet Flows ◽  
Streamwise Vorticity ◽  
Control Approach

Supersonic impinging jet(s) inherently produce a highly unsteady flow field. The occurrence of such flows leads to many adverse effects for short take-off and vertical landing (STOVL) aircraft such as: a significant increase in the noise level, very high unsteady loads on nearby structures and an appreciable loss in lift during hover. In prior studies, we have demonstrated that arrays of microjets, appropriately placed near the nozzle exit, effectively disrupt the feedback loop inherent in impinging jet flows. In these studies, the effectiveness of the control was found to be strongly dependent on a number of geometric and flow parameters, such as the impingement plane distance, microjet orientation and jet operating conditions. In this paper, the effects of some of these parameters that appear to determine control efficiency are examined and some of the fundamental mechanisms behind this control approach are explored. Through comprehensive two- and three-component velocity (and vorticity) field measurements it has been clearly demonstrated that the activation of microjets leads to a local thickening of the jet shear layer, near the nozzle exit, making it more stable and less receptive to disturbances. Furthermore, microjets generate strong streamwise vorticity in the form of well-organized, counter-rotating vortex pairs. This increase in streamwise vorticity is concomitant with a reduction in the azimuthal vorticity of the primary jet. Based on these results and a simplified analysis of vorticity transport, it is suggested that the generation of these streamwise vortices is mainly a result of the redirection of the azimuthal vorticity by vorticity tilting and stretching mechanisms. The emergence of these longitudinal structures weakens the large-scale axisymmetric structures in the jet shear layer while introducing substantial three-dimensionality into the flow. Together, these factors lead to the attenuation of the feedback loop and a significant reduction of flow unsteadiness.

Conjugate heat transfer simulation of turbine blade high efficiency cooling method with mist injection

2014 ◽  
Vol 228 (15) ◽  
pp. 2738-2749 ◽  
Author(s):  
Yuting Jiang ◽  
Qun Zheng ◽  
Guoqiang Yue ◽  
Ping Dong ◽  
Jie Gao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Conjugate Heat Transfer ◽  
High Efficiency ◽  
Turbulence Models ◽  
Operating Conditions ◽  
Cooling Performance ◽  
Convective Cooling ◽  
Mist Cooling ◽  
The Impact

The idea of utilizing a finely dispersed water-in-air mixture has been proven to be a feasible technique to produce very high cooling rates. The accuracy of numerical simulation program for conjugate heat transfer methodology is verified with the Mark II transonic high pressure turbine stator which is cooled by internal convection through radial round pipes, and different turbulence models and transition models are employed to analyze the influence on results. On the basis of it, the mist cooling is simulated under typical gas turbine operating conditions for internal convective cooling to discuss the improvement of cooling performance. Though the results indicate that mist cooling can decrease the temperature of boundary layer without impact on the temperature of the mainstream and the thickness of boundary layer, the cooling capacity is limited by inadequate evaporation of mist. Considering the distribution of thermal stress and mist evaporation, a compound cooling blade of film cooling with trailing edge ejection is acquired which is modified from the blade of Mark II internal convective cooling; the effects of various parameters including mist concentration and mist diameter on the improvement of cooling performance are investigated, meanwhile the impact of curvature on cooling efficiency and mist trajectory is analyzed finally.

Application of an Object-Oriented CFD Code to Heat Transfer Analysis

2008 ◽  
Author(s):  
Luca Mangani ◽  
A. Andreini
Keyword(s):  
Heat Transfer ◽  
Turbulence Models ◽  
Lateral Spreading ◽  
Impinging Jets ◽  
Experimental Results ◽  
Heat Transfer Analysis ◽  
Specific Class ◽  
Turbine Cooling ◽  
Numerical Predictions ◽  
High Flexibility

This paper is aimed at showing the performances obtained with an open-source CFD code for heat transfer predictions after the addiction of specific modules. The development steps to make this code suitable for such simulations are described in order to point out its potentiality as a customizable CFD tool, appropriate for both academic and industrial research. The C++ library, named OpenFOAM, offers specific class and polyhedral finite volume operators thought for continuum mechanics simulations as well as built-in solvers and utilities. To make it robust, fast and reliable for RANS heat transfer predictions it was indeed necessary to implement additional submodules. The package coded by the authors within the OpenFOAM environment includes a suitable algorithm for compressible steady-state analysis. A SIMPLE like algorithm was specifically developed to extend the operability field to a wider range of Mach numbers. A set of Low-Reynolds eddy-viscosity turbulence models, chosen amongst the best performing in wall bounded flows, were developed. In addition an algebraic anisotropic correction, to increase jets lateral spreading, and an automatic wall treatment, to obtain mesh independence, were added. The results presented cover several types of flows amongst the most typical for turbomachinery and combustor gas turbine cooling devices. Impinging jets were investigated as well as film and effusion cooling flows, both in single and multi-hole configuration. Numerical predictions for wall effectiveness and wall heat transfer coefficient were tested against standard literature and in-house set-up experimental results. The numerical predictions obtained proves to be in-line with the equivalent models of commercial CFD packages obtaining a general good agreement with the experimental results. Moreover during the tests OpenFOAM code has shown a good accuracy and robustness, as well as an high flexibility in the implementation of user-defined submodules.

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