An Experimental Study of Mist/Air Film Cooling On a Flat Plate With Application to Gas Turbine Airfoils—Part II: Two-Phase Flow Measurements and Droplet Dynamics

2014 ◽  
Vol 136 (7) ◽  
Author(s):  
Lei Zhao ◽  
Ting Wang
Keyword(s):  
Film Cooling ◽  
Flow Behavior ◽  
Droplet Size Distribution ◽  
Main Flow ◽  
Reynolds Stresses ◽  
Two Phase ◽  
Flow Measurements ◽  
Cooling Effectiveness ◽  
Droplet Dynamics ◽  
Air Film

A phase Doppler particle analyzer (PDPA) system is employed to measure the two-phase mist flow behavior including flow velocity field, droplet size distribution, droplet dynamics, and turbulence characteristics. Based on the droplet measurements made through PDPA, a projected profile describing how the air-mist coolant jet flow spreads and eventually blends into the hot main flow is proposed. This proposed profile is found to be well supported by the measurement results of the turbulent Reynolds stresses. The coolant film envelope is identified with shear layers characterized by higher magnitudes of turbulent Reynolds stresses. In addition, the separation between the mist droplet layer and the coolant air film is identified through the droplet measurements—large droplets penetrate through the air coolant film layer and travel further into the main flow. With the proposed air-mist film profile, the heat transfer results on the wall presented in Part I are re-examined and more in-depth physics is revealed. It is found that the location of the optimum cooling effectiveness coincides with the point where the air-mist coolant stream starts to bend back towards the surface. Thus, the data suggests that the “bending back” film pattern is critical in keeping the mist droplets close to the surface, which improves the cooling effectiveness for mist cooling.

An Experimental Study of Mist/Air Film Cooling on a Flat Plate With Application to Gas Turbine Airfoils: Part 2 — Two-Phase Flow Measurements and Droplet Dynamics

2013 ◽  
Author(s):  
Lei Zhao ◽  
Ting Wang
Keyword(s):  
Film Cooling ◽  
Flow Behavior ◽  
Droplet Size Distribution ◽  
Main Flow ◽  
Reynolds Stresses ◽  
Two Phase ◽  
Flow Measurements ◽  
Cooling Effectiveness ◽  
Droplet Dynamics ◽  
Air Film

A Phase Doppler Particle Analyzer (PDPA) system is employed to measure the two-phase mist flow behavior including flow velocity field, droplet size distribution, droplet dynamics, and turbulence characteristics. Based on the droplet measurements made through PDPA, a projected profile describing how the air-mist coolant jet flow spreads and eventually blends into the hot main flow is proposed. This proposed profile is found to be well supported by the measurement results of the turbulent Reynolds stresses. The coolant film envelope is identified with shear layers characterized by higher magnitudes of turbulent Reynolds stresses. In addition, the separation between the mist droplet layer and the coolant air film is identified through the droplet measurements — large droplets penetrate through the air coolant film layer and travel further into the main flow. With the proposed air-mist film profile, the heat transfer results on the wall presented in Part 1 are re-examined and more in-depth physics is revealed. It is found that the location of optimum cooling effectiveness is coincided with the point where the air-mist coolant stream starts to bend back towards the surface. Thus, the data suggests that the “bending back” film pattern is critical in keeping the mist droplets close to the surface, which improves the cooling effectiveness for mist cooling.

An Experimental Study of Mist/Air Film Cooling With Fan-Shaped Holes on an Extended Flat Plate: Part 2 — Two-Phase Flow Measurements and Droplet Dynamics

2014 ◽  
Author(s):  
Reda Ragab ◽  
Ting Wang
Keyword(s):  
Flow Behavior ◽  
Droplet Size Distribution ◽  
Data Rate ◽  
Main Flow ◽  
Shear Stresses ◽  
Two Phase ◽  
Lateral Direction ◽  
Flow Measurements ◽  
Droplet Dynamics ◽  
Film Layer

A Phase Doppler Particle Analyzer (PDPA) system is employed to measure the two-phase mist flow behavior including flow velocity field, droplet size distribution, droplet dynamics, and turbulence characteristics. Based on the droplet measurements made through PDPA, a projected profile describing how the air-mist coolant jet flow spreads and eventually blends into the hot main flow is prescribed for both cylindrical and fan-shaped holes. The mist film layer consists of a typical coolant film layer and a wider droplet layer. The droplet layer is identified by a wedge-shaped enclosure prescribed by the data rate (droplet number per second) distribution. The apex of the enclosure, depicting by the maximum data rate, roughly indicating the core region of the coolant film. The upper boundary of the film layer, characterized by active mixing with the main flow, is found to be close to relatively high values of local Reynolds shear stresses. Thanks to higher inertia possessed by larger droplets (>20 μm in diameter) at the injection hole, the larger droplets tend to shoot across the coolant layer, resulting in a wider droplet layer than the cooling film layer. With the prescribed coolant film and droplet layer profiles, the heat transfer results on the wall presented in Part 1 are reexamined. The 3-D droplet measurements show that the droplets injected from the fan-shaped holes tend to spread wider in lateral direction than cylinder holes and accumulate at the location where the neighboring coolant film layers meet. This flow and droplet behavior explains the higher cooling performance as well as mist-enhancement occurs between the fan-shaped cooling holes, rather than along the hole’s centerline as demonstrated in the case using the cylindrical holes.

An Experimental Study of Mist/Air Film Cooling With Fan-Shaped Holes on an Extended Flat Plate—Part II: Two-Phase Flow Measurements and Droplet Dynamics

2017 ◽  
Vol 140 (4) ◽  
Author(s):  
Reda Ragab ◽  
Ting Wang
Keyword(s):  
Flow Behavior ◽  
Data Rate ◽  
Main Flow ◽  
Shear Stresses ◽  
Two Phase ◽  
Flow Measurements ◽  
Droplet Dynamics ◽  
Mist Flow ◽  
Film Layer ◽  
Upper Boundary

A phase Doppler particle analyzer (PDPA) system is employed to measure the two-phase mist flow behavior including flow velocity field, droplet size distribution, droplet dynamics, and turbulence characteristics. Based on the droplet measurements made through PDPA, a projected profile describing how the air–mist coolant jet flow spreads and eventually blends into the hot main flow is prescribed for both cylindrical and fan-shaped holes. The mist film layer consists of two layers: a typical coolant film layer (cooling air containing the majority of the droplets) and a wider droplet layer containing droplets outside the film layer. Thanks to the higher inertia possessed by larger droplets (>20 μm in diameter) at the injection hole, the larger droplets tend to shoot across the coolant film layer, resulting in a wider droplet layer than the coolant film layer. The wider droplet layer boundaries are detected by measuring the droplet data rate (droplet number per second) distribution, and it is identified by a wedge-shaped enclosure prescribed by the data rate distribution curve. The coolant film layer is prescribed by its core and its upper boundary. The apex of the data rate curve, depicted by the maximum data rate, roughly indicates the core region of the coolant film layer. The upper boundary of the coolant film layer, characterized by active mixing with the main flow, is found to be close to relatively high values of local Reynolds shear stresses. With the results of PDPA measurements and the prescribed coolant film and droplet layer profiles, the heat transfer results on the wall presented in Part I are re-examined, and the fundamental mist-flow physics are analyzed. The three-dimensional (3D) droplet measurements show that the droplets injected from the fan-shaped holes tend to spread wider in lateral direction than cylinder holes and accumulate at the location where the neighboring coolant film layers meet. This flow and droplet behavior explain the higher cooling performance as well as mist-enhancement occurs between the fan-shaped cooling holes, rather than along the hole's centerline as demonstrated in the case using the cylindrical holes.

Flow and Heat Transfer Analysis of Mist-Film Cooling on a Flat Plate

2017 ◽  
Author(s):  
Anjali Dwivedi ◽  
Ankit Verma ◽  
S. Sarkar
Keyword(s):  
Flat Plate ◽  
Latent Heat ◽  
Film Cooling ◽  
Thermal Stresses ◽  
Density Ratio ◽  
Heat Transfer Analysis ◽  
Main Stream ◽  
Two Phase ◽  
Maximum Enhancement ◽  
Cooling Effectiveness

Film cooling is one of the preferred methods for effective cooling of a gas turbine that forms a protective layer between hot flue gases and blade surface. This paper investigates the interaction of mist in the secondary flow and physics indicating the upper limit of mist concentration. Numerical simulations are performed on a flat plate having a series of discrete holes with 35 degree streamwise orientation and the holes are connected to a common delivery plenum chamber. The blowing ratio, density ratio and Reynolds number based on freestream and hole diameter (D) are 0.5, 1.2 and 15885 respectively. A two-phase mist consisting of finely dispersed water droplets of 10 micron in an airstream is introduced as the coolant from these holes. The latent heat absorbed by the evaporating droplets significantly reduces the sensible heat of the main stream, providing heat sinks that result in enhanced cooling effectiveness. The coupling between the two-phases is modelled through the interaction terms in the transport equations. Computations are performed by ANSYS Fluent 15.0 using k-ε realizable model. The results illustrate insight of complex transport phenomena associated with the mist of varying concentration from 2% to 7%. It has been observed that the maximum enhancement of cooling effectiveness reaches 43% at X/D = 10 for 2% mist by mass with an average enhancement of 26.5%. For 3% mist, the maximum enhancement becomes 80% at X/D = 16 with the average cooling enhancement of 43%. Mist concentrations 5% and beyond trend to increase average cooling because of more absorption of latent heat by droplets, but its trajectories shift towards wall, detrimental to the blade due to corrosion effect and thermal stresses.

Overall Cooling Effectiveness Characteristic and Influence Mechanism on an Endwall With Film Cooling and Impingement

2015 ◽  
Author(s):  
Mingfei Li ◽  
Xueying Li ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Internal Heat ◽  
Main Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
One Dimensional ◽  
Influence Mechanism ◽  
Endwall Cooling ◽  
Internal Heat Transfer

The cooling system is required to ensure gas turbine can work at high temperature, which has exceeded the material limitation. An endwall cooling test rig was built up to conduct the endwall cooling research. A detailed work was done for analyzing characteristics of endwall heat transfer and discussing the multi-parameter influence mechanism of overall cooling effectiveness. The main flow side heat transfer coefficient, adiabatic film cooling effectiveness and overall cooling effectiveness were measured in the experiments. The effects of coolant mass flowrate ratio (MFR) were considered through the measurement. In order to analyze how each of the parameters works on overall cooling effectiveness, a one-dimensional correlation was developed. The results showed that obvious enhancement could be found in cooling effectiveness by increasing coolant MFR, and the film jet can be easily attached to the surface after the acceleration of the main flow in the nozzle channel. Comparing with film cooling effectiveness, overall cooling effectiveness distribution is more uniform, which is due to the influence of internal cooling. The verified one-dimensional analysis method showed that the improvement in film cooling would be most efficient to heighten overall cooling effectiveness. The improvement in film cooling would be more efficient when film cooling effectiveness is in high level than in low level. However, the enhancement of internal heat transfer is more efficient when internal heat transfer coefficient is low.

Film Cooling on Highly Loaded Blades With Main Flow Separation—Part I: Heat Transfer

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Reinaldo A. Gomes ◽  
Reinhard Niehuis
Keyword(s):  
Heat Transfer ◽  
Flow Separation ◽  
Film Cooling ◽  
Separation Bubble ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Main Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness

Film cooling experiments were run at the high speed cascade wind tunnel of the University of the Federal Armed Forces Munich. The investigations were carried out with a linear cascade of highly loaded turbine blades. The main objectives of the tests were to assess the film cooling effectiveness and the heat transfer in zones with main flow separation. Therefore, the blades were designed to force the flow to detach on the pressure side shortly downstream of the leading edge and reattach at about half of the axial chord. In this zone, film cooling rows are placed among others for a reduction of the size of the separation bubble. The analyzed region on the blade is critical due to the high heat transfer present at the leading edge and at the reattachment line after the main flow separation. Film cooling can contribute to a reduction of the size of the separation bubble reducing aerodynamic losses, however, in general, it increases heat transfer due to turbulent mixing. The reduction of the size of the separation bubble might also be twofold, since it acts like a thermal insulator on the blade and reducing the size of the bubble might lead to a stronger heating of the blade. Film cooling should, therefore, take both into account: first, a proper protection of the surface and second, reducing aerodynamic losses, diminishing the extension of the main flow separation. While experimental results of the adiabatic film cooling effectiveness were shown in previous publications, the local heat transfer is analyzed in this paper. Emphasis is also placed upon analyzing, in detail, the flow separation process. Furthermore, the tests comprise the analysis of the effect of different outlet Mach and Reynolds numbers and film cooling. In part two of this paper, the overall film cooling effectiveness is addressed. Local heat transfer is still difficult to predict with modern numerical tools and this is especially true for complex flows with flow separation. Some numerical results with the Reynolds averaged Navier-Stokes (RANS) and large eddy simulation (LES) show the capability of a commercial solver in predicting the heat transfer.

Correlation of Film Cooling Effectiveness From Thermographic Measurements at Engine Like Conditions

2002 ◽  
Author(s):  
S. Baldauf ◽  
M. Scheurlen ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Film Cooling ◽  
Radiation Effects ◽  
Flow Behavior ◽  
Density Ratio ◽  
Geometrical Parameters ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Jet Interaction ◽  
New Correlation ◽  
Large Matrix

Adiabatic film cooling effectiveness on a flat plate surface downstream of a row of cylindrical holes is investigated. Highly resolved two dimensional surface data were measured by means of infrared thermography and carefully corrected for local conduction and radiation effects [1]. These locally acquired data are laterally averaged to give the streamwise distributions of the effectiveness. An independent variation of the flow parameters blowing rate, density ratio, and turbulence intensity as well as the geometrical parameters streamwise ejection angle and hole spacing is examined. The influences of these parameters on the laterally effectiveness is discussed and interpreted with the help of surface distributions of effectiveness and heat transfer coefficients presented in earlier publications [1, 2]. Besides the known jet in cross-flow behavior of coolant ejected from discrete holes, these data demonstrate the effect of adjacent jet interaction and its impact on jet lift-off and adiabatic effectiveness. In utilizing this large matrix of measurements the effect of single parameters and their interactions are correlated. The important scaling parameters of the effectiveness are shaped out during the correlation process and are discussed. The resulting new correlation is designed to yield the quantitatively correct effectiveness as a result of the interplay of the jet in crossflow behavior and the adjacent jet interaction. It is built modularly to allow for future inclusion of additional parameters. The new correlation is valid without any exception within the full region of interest, reaching from the point of the ejection to far downstream, for all combinations of flow and geometry parameters.

Correlation of Film-Cooling Effectiveness From Thermographic Measurements at Enginelike Conditions

2002 ◽  
Vol 124 (4) ◽  
pp. 686-698 ◽  
Author(s):  
S. Baldauf ◽  
M. Scheurlen ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Film Cooling ◽  
Radiation Effects ◽  
Flow Behavior ◽  
Density Ratio ◽  
Geometrical Parameters ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Jet Interaction ◽  
New Correlation ◽  
Large Matrix

Adiabatic film-cooling effectiveness on a flat plate surface downstream of a row of cylindrical holes is investigated. Highly resolved two-dimensional surface data were measured by means of infrared thermography and carefully corrected for local conduction and radiation effects. These locally acquired data are laterally averaged to give the streamwise distributions of the effectiveness. An independent variation of the flow parameters blowing rate, density ratio, and turbulence intensity as well as the geometrical parameters streamwise ejection angle and hole spacing is examined. The influences of these parameters on the lateral effectiveness is discussed and interpreted with the help of surface distributions of effectiveness and heat transfer coefficients presented in earlier publications. Besides the known jet in cross-flow behavior of coolant ejected from discrete holes, these data demonstrate the effect of adjacent jet interaction and its impact on jet lift-off and adiabatic effectiveness. In utilizing this large matrix of measurements the effect of single parameters and their interactions are correlated. The important scaling parameters of the effectiveness are shaped out during the correlation process and are discussed. The resulting new correlation is designed to yield the quantitatively correct effectiveness as a result of the interplay of the jet in crossflow behavior and the adjacent jet interaction. It is built modularly to allow for future inclusion of additional parameters. The new correlation is valid without any exception within the full region of interest, reaching from the point of the ejection to far downstream, for all combinations of flow and geometry parameters.

Flow Dynamics and Film Cooling Effectiveness on a Non-Axisymmetric Contour Endwall in a Two-Dimensional Cascade Passage

2009 ◽  
Author(s):  
Gazi I. Mahmood ◽  
Ross Gustafson ◽  
Sumanta Acharya
Keyword(s):  
Temperature Field ◽  
Flow Field ◽  
Film Cooling ◽  
Free Stream ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Flow ◽  
Blowing Ratio

The measured flow field and temperature field near a three-dimensional asymmetric contour endwall employed in a linear blade cascade are presented with and without film-cooling flow on the endwall. Flow field temperature and Nusselt number distributions along the asymmetric endwall with wall heating and no film-cooling flow are also reported to show local high heat transfer region on the endwall and justify the locations of the coolant holes. Adiabatic film-cooling effectiveness along the endwall is then measured to indicate the local effects of the coolant jets. The near endwall flow field and temperature field provide the coolant flow behavior and the interaction of coolant jets with the boundary layer flow. Thus, the local film-cooling effectiveness can be explained with the coolant jet trajectories. The measurements are obtained at the Reynolds number of 2.30×105 based on blade actual chord and inlet velocity, coolant-to-free stream temperature ratio of 0.93, and coolant-to-free stream density ratio of 1.06. The cascade employs the hub side blade section and passage geometry of the first stage rotor of GE-E3 turbine engine. The contour endwall profile is employed on the bottom endwall only in the cascade. The blowing ratio of the film-cooling flow varies from 1.0 to 2.4 from 71 discrete cylindrical holes located in the contour endwall. The three-dimensional profile of the endwall varies in height in both the pitchwise and axial directions. The flow field is quantified with the streamwise vorticity and turbulent intensity, pitchwise static pressure difference, flow yaw angle, and pitchwise velocity. Both the flow field and temperature data indicate that the coolant jets cover more distance in the pitchwise and axial direction in the passage as the blowing ratio increases. Thus, the local and average film-cooling effectiveness increase with the blowing ratio.

Sign in / Sign up

Export Citation Format

Share Document