Combined Effect of Grid Turbulence and Unsteady Wake on Film Effectiveness and Heat Transfer Coefficient of a Gas Turbine Blade With Air and CO2 Film Injection

1997 ◽  
Vol 119 (3) ◽  
pp. 594-600 ◽  
Author(s):  
S. V. Ekkad ◽  
A. B. Mehendale ◽  
J. C. Han ◽  
C. P. Lee
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blade ◽  
Leading Edge ◽  
Combined Effect ◽  
Grid Turbulence ◽  
Free Stream Turbulence ◽  
Nusselt Numbers ◽  
Unsteady Wake

Experiments were performed to study the combined effect of grid turbulence and unsteady wake on film effectiveness and heat transfer coefficient of a turbine blade model. Tests were done on a five-blade linear cascade at the chord Reynolds number of 3.0 × 105 at cascade inlet. Several combinations of turbulence grids, their locations, and unsteady wake strengths were used to generate various upstream turbulence conditions. The test blade had three rows of film holes in the leading edge region and two rows each on the pressure and suction surfaces. Air and CO2 were used as injectants. Results show that Nusselt numbers for a blade with film injection are much higher than that without film holes. An increase in mainstream turbulence level causes an increase in Nusselt numbers and a decrease in film effectiveness over most of the blade surface, for both density injectants, and at all blowing ratios. A free-stream turbulence superimposed on an unsteady wake significantly affects Nusselt numbers and film effectiveness compared with only an unsteady wake condition.

Detailed Film Cooling Measurements on a Cylindrical Leading Edge Model: Effect of Free-Stream Turbulence and Coolant Density

1997 ◽  
Author(s):  
Srinath V. Ekkad ◽  
Je-Chin Han ◽  
Hui Du
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Free Stream ◽  
Density Ratio ◽  
Leading Edge ◽  
Cylinder Surface ◽  
Free Stream Turbulence ◽  
Blowing Ratio ◽  
Nusselt Numbers

Detailed heat transfer coefficient and film effectiveness distributions are presented on a cylindrical leading edge model using a transient liquid crystal technique. Tests were done in a low speed wind tunnel on a cylindrical model in a crossflow with two rows of injection holes. Mainstream Reynolds number based on the cylinder diameter was 100,900. The two rows of injection holes were located at ±15° from stagnation. The film holes were spaced 4-hole diameters apart and were angled 30° and 90° to the surface in the spanwise and streamwise directions, respectively. Heat transfer coefficient and film effectiveness distributions are presented on only one side of the front half of the cylinder. The cylinder surface is coated with a thin layer of thermochromic liquid crystals and a transient test is run to obtain the heat transfer coefficients and film effectiveness. Air and CO2 were used as coolant to simulate coolant-to-mainstream density ratio effect. The effect of coolant blowing ratio was studied for blowing ratios of 0.4, 0.8, and 12. Results show that Nusselt numbers downstream of injection increase with an increase in blowing ratio for both coolants. Air provides highest effectiveness at blowing ratio of 0.4 and CO2 provides highest effectiveness at a blowing ratio of 0.8. Higher density coolant (CO2) provides lower Nusselt numbers at all blowing ratios compared to lower density coolant (air). An increase in free-stream turbulence has very small effect on Nusselt numbers for both coolants. However, an increase in free-stream turbulence reduces film effectiveness significantly at low blowing ratios for both coolants.

Detailed Film Cooling Measurements on a Cylindrical Leading Edge Model: Effect of Free-Stream Turbulence and Coolant Density

1998 ◽  
Vol 120 (4) ◽  
pp. 799-807 ◽  
Author(s):  
S. V. Ekkad ◽  
J. C. Han ◽  
H. Du
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Free Stream ◽  
Density Ratio ◽  
Leading Edge ◽  
Cylinder Surface ◽  
Free Stream Turbulence ◽  
Blowing Ratio ◽  
Nusselt Numbers

Detailed heat transfer coefficient and film effectiveness distributions are presented on a cylindrical leading edge model using a transient liquid crystal technique. Tests were done in a low-speed wind tunnel on a cylindrical model in a crossflow with two rows of injection holes. Mainstream Reynolds number based on the cylinder diameter was 100,900. The two rows of injection holes were located at ±15 deg from stagnation. The film holes were spaced four hole diameters apart and were angled 30 and 90 deg to the surface in the spanwise and streamwise directions, respectively. Heat transfer coefficient and film effectiveness distributions are presented on only one side of the front half of the cylinder. The cylinder surface is coated with a thin layer of thermochromic liquid crystals and a transient test is run to obtain the heat transfer coefficients and film effectiveness. Air and CO2 were used as coolant to simulate coolant-to-mainstream density ratio effect. The effect of coolant blowing ratio was studied for blowing ratios of 0.4, 0.8, and 1.2. Results show that Nusselt numbers downstream of injection increase with an increase in blowing ratio for both coolants. Air provides highest effectiveness at blowing ratio of 0.4 and CO2 provides highest effectiveness at a blowing ratio of 0.8. Higher density coolant (CO2) provides lower Nusselt numbers at all blowing ratios compared to lower density coolant (air). An increase in free-stream turbulence has very small effect on Nusselt numbers for both coolants. However, an increase in free-stream turbulence reduces film effectiveness significantly at low blowing ratios for both coolants.

Effect of Rotation on a Gas Turbine Blade Internal Cooling System: Numerical Investigation

2016 ◽  
Author(s):  
E. Burberi ◽  
D. Massini ◽  
L. Cocchi ◽  
L. Mazzei ◽  
A. Andreini ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Flow Field ◽  
Transfer Coefficient ◽  
Numerical Investigation ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Cooling System ◽  
Leading Edge ◽  
Internal Cooling

Increasing turbine inlet temperature is one of the main strategies used to accomplish the demands of increased performance of modern gas turbines. As a consequence, optimization of the cooling system is of paramount importance in gas turbine development. Leading edge represents a critical part of cooled nozzles and blades, given the presence of the hot gases stagnation point and the unfavourable geometry for cooling. This paper reports the results of a numerical investigation aimed at assessing the rotation effects on the heat transfer distribution in a realistic leading edge internal cooling system of a high pressure gas turbine blade. The numerical investigation was carried out in order to support and to allow an in-depth understanding of the results obtained in a parallel experimental campaign. The model is composed of a trapezoidal feeding channel which provides air to the cold bridge system by means of three large racetrack-shaped holes, generating coolant impingement on the internal concave leading edge surface, whereas four big fins assure the jets confinement. Air is then extracted through 4 rows of 6 holes reproducing the external cooling system composed of shower-head and film cooling holes. Experiments were performed in static and rotating conditions replicating the typical range of jet Reynolds number (Rej) from 10000 to 40000 and Rotation number (Roj) up to 0.05, for three crossflow cases representative of the working condition that can be found at blade tip, midspan and hub, respectively. Experimental results in terms of flow field measurements on several internal planes and heat transfer coefficient on the LE internal surface have been performed on two analogous experimental campaigns at University of Udine and University of Florence respectively. Hybrid RANS-LES models were used for the simulations, such as Scale Adaptive Simulation (SAS) and Detached Eddy Simulation (DES), given their ability to resolve the complex flow field associated with jet impingement. Numerical flow field results are reported in terms of both jet velocity profiles and 2D vector plots on symmetry and transversal internal planes, while the heat transfer coefficient distributions are presented as detailed 2D maps together with radial and tangential averaged Nusselt number profiles. A fairly good agreement with experimental measurements is observed, which represent a validation of the adopted computational model. As a consequence, the computed aerodynamic and thermal fields also allow an in-depth interpretation of the experimental results.

Film Cooling Parameter Waveforms on a Turbine Blade Leading Edge Model With Oscillating Stagnation Line

2016 ◽  
Vol 138 (7) ◽  
Author(s):  
James L. Rutledge ◽  
Tylor C. Rathsack ◽  
Matthew T. Van Voorhis ◽  
Marc D. Polanka
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blade ◽  
Film Cooling ◽  
Leading Edge ◽  
Stagnation Line ◽  
Inverse Heat Transfer ◽  
Adiabatic Effectiveness ◽  
Blade Leading Edge

It is necessary to understand how film cooling influences the external convective boundary condition involving both the adiabatic wall temperature and the heat transfer coefficient in order to predict the thermal durability of a gas turbine hot gas path component. Most studies in the past have considered only steady flow, but studies of the unsteadiness naturally present in turbine flow have become more prevalent. One source of unsteadiness is wake passage from upstream components which can cause fluctuations in the stagnation location on turbine airfoils. This in turn causes unsteadiness in the behavior of the leading edge coolant jets and thus fluctuations in both the adiabatic effectiveness and heat transfer coefficient. The dynamics of h and η are now quantifiable with modern inverse heat transfer methods and nonintrusive infrared thermography. The present study involved the application of a novel inverse heat transfer methodology to determine time-resolved adiabatic effectiveness and heat transfer coefficient waveforms on a simulated turbine blade leading edge with an oscillating stagnation position. The leading edge geometry was simulated with a circular cylinder with a coolant hole located 21.5 deg downstream from the leading edge stagnation line, angled 20 deg to the surface and 90 deg to the streamwise direction. The coolant plume is shown to shift in response to the stagnation line movement. These oscillations thus influence the film cooling coverage, and the time-averaged benefit of film cooling is influenced by the oscillation.

Combined Effect of Free-Stream Turbulence and Unsteady Wake on Heat Transfer Coefficients From a Gas Turbine Blade

1995 ◽  
Vol 117 (2) ◽  
pp. 296-302 ◽  
Author(s):  
L. Zhang ◽  
J.-C. Han
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Combined Effect ◽  
Transfer Coefficients ◽  
Free Stream Turbulence ◽  
Heat Transfer Coefficients ◽  
Unsteady Wake ◽  
Turbulence Grid

The combined effect of free-stream turbulence and unsteady wakes on turbine blade surface heat transfer was studied. The experiments used a five-blade linear cascade in a low-speed wind tunnel facility. A turbulence grid and spoked-wheel type wake generator produced the free-stream turbulence and unsteady wakes. The mainstream Reynolds numbers based on the cascade inlet mean velocity and blade chord length were 100,000, 200,000, and 300,000. Results show that the blade time-averaged heat transfer coefficient depends on the mean turbulence intensity, regardless of whether this mean turbulence intensity is from unsteady wake only, turbulence grid only, or a wake and grid combination. The higher mean turbulence promotes earlier boundary layer transition and causes much higher heat transfer coefficients on the suction surface. It also significantly enhances the heat transfer coefficients on the pressure surface. The unsteady wake greatly affects blade heat transfer for low oncoming free-stream turbulence; however, the wake effect diminishes for high oncoming turbulence. The free-stream turbulence also strongly affects blade heat transfer for a low wake passing frequency, but the oncoming turbulence effect diminishes for a high unsteady wake condition.

Heat Transfer Boundary Condition Waveforms on a Turbine Blade Leading Edge With Unsteady Film Cooling

2013 ◽  
Author(s):  
James L. Rutledge
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blade ◽  
Film Cooling ◽  
Leading Edge ◽  
Adiabatic Wall ◽  
Time Resolved ◽  
Stagnation Line ◽  
Adiabatic Effectiveness

It is necessary to understand how film cooling both reduces the adiabatic wall temperature and influences the heat transfer coefficient in order to predict the net heat flux to a gas turbine hot gas path component. Although a great number of studies have considered steady film cooling flows, the influence of film cooling unsteadiness has only recently been considered. Unsteadiness in the freestream flow or the coolant flow can cause fluctuations in both the adiabatic effectiveness and heat transfer coefficient, the dynamics of which have been difficult to measure. In previous studies, only time averaged effects have been measured. The present study has determined time resolved adiabatic effectiveness and heat transfer coefficient waveforms using a novel inverse heat transfer methodology. Unsteady film cooling was examined on the leading edge region of a circular cylinder simulating the leading edge of a turbine blade. Unsteady interactions between h and η, were examined near a coolant hole located 21.5° downstream from the leading edge stagnation line, angled 20° to the surface and 90° to the streamwise direction. The coolant plume is shown to shift back and forth as the jet’s momentum fluctuates. Increasing freestream turbulence was found to both reduce η, and the amplitude of the η waveforms.

scholarly journals Effect of Film Injection Location on Local Heat Transfer Coefficient on a Gas Turbine Blade

1998 ◽  
Vol 4 (3) ◽  
pp. 163-174
Author(s):  
Anant B. Mehendale ◽  
H. Wanda Jiang ◽  
Srinath V. Ekkad ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blade ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Nusselt Numbers ◽  
High Turbulence ◽  
Blade Model ◽  
Injection Location

Experiments were performed to study the effect of film hole location on local heat transfer coefficient distribution of a turbine blade model with air or CO2 film injection to simulate coolant density effect. Tests were performed on a five blade linear cascade at the chord Reynolds number of3×105at cascade inlet. The test blade had three rows of film holes in the leading edge region and two rows each on the pressure and suction surfaces. Film hole locations were varied by leaving the desired ones open and plugging the rest. A combination of turbulence grid and unsteady wake was used to generate upstream high turbulence condition. Results indicate that film injection by itself causes a substantial increase in Nusselt numbers over a blade model without film holes. An increase in mainstream turbulence intensity causes an increase in Nusselt numbers over most of the blade surface, for both coolants, and at all blowing ratios. Film injection promotes an earlier boundary layer transition on the suction surface and the onset of transition depends on the film injection location; but at high turbulence levels, transition location is almost independent of film injection location.

Effects of a Wake on Turbine Blade Heat Transfer in a Transonic Cascade

1997 ◽  
Author(s):  
James H. Hale ◽  
Thomas E. Diller ◽  
Wing F. Ng
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blade ◽  
Leading Edge ◽  
Suction Surface ◽  
Maximum Increase ◽  
Pressure Surface ◽  
Transonic Cascade

The effects of a wake generated by a stationary upstream strut on surface beat transfer to turbine blades were measured experimentally in a heated, transonic cascade tunnel. Five pitchwise locations of the upstream strut were tested, while maintaining a constant axial distance between the strut and the leading edge plane of the cascade. Time-resolved unsteady heat flux measurements were made with Heat Flux Microsensors (HFM) at three positions on the suction surface and one position on the pressure surface. In addition, hot-wire surveys were taken along the leading edge plane of the cascade to document the disturbance generated by the upstream strut. Results from the hot-wire surveys show that with the strut placed upstream and near the stagnation point of the turbine blade, the turbulence intensity in the wake was as high as 50%. This high level of turbulence intensity was due to the coupling of the strut wake with the potential flow around the blunt leading edge of the turbine blade. A strong influence on the heat transfer coefficient was seen from the relative pitchwise position of the strut with respect to the leading edge of the test blades. For the suction surface, the maximum increase in average heat transfer coefficient occurred when the upstream strut was placed near the stagnation point of the blade. The heat transfer coefficients were increased by 15, 20, and 10% for the gages located on 10, 22, and 50% chord positions of the suction surface, respectively, compared to the baseline case of no strut. For the pressure side, results show the maximum increase in heat transfer coefficient occurred when the upstream strut was placed along the pitchline near the middle of the blade passage. At 30% chord position on the pressure surface, the heat transfer coefficient was increased by 25 %. Attempts to correlate these increases in mean heat transfer with integral values of the measured unsteadiness of the flow or heat flux were not successful.

scholarly journals CFD Predictions of Heat Transfer Coefficient Augmentation on a Simulated Film Cooled Turbine Blade Leading Edge

2012 ◽  
Author(s):  
Gwennaël Beirnaert-Chartrel ◽  
David G. Bogard
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blade ◽  
Turbulence Model ◽  
Density Ratio ◽  
Experimental Studies ◽  
Leading Edge ◽  
The Heat Transfer Coefficient ◽  
Blade Leading Edge

Many experimental studies of the augmentation of the heat transfer coefficients due to film cooling jet injection have been done with the coolant at mainstream temperature because this improves the accuracy of the measurements. However, for typical engine conditions the coolant is generally much colder than the mainstream with a significantly higher density. It is generally presumed that the density of the coolant has negligible effect on the augmentation of the heat transfer coefficient due to coolant injection. In this study, the effects of coolant density on heat transfer coefficient augmentation were studied computationally. The focus was on a simulation of a turbine blade leading edge where augmentation of the heat transfer coefficient can be as much as factor of two. The realizable k-ε turbulence model (RKE) and Shear Stress Transport k-ω turbulence model (SST) were used in these computational simulations. The RKE computations completed at a unity density ratio were found to be similar to previous experimental measurements, whereas SST computations exhibited significant discrepancies. Simulations with coolant density ratios varying from 1.0 to 1.5 showed that heat transfer coefficient augmentation can be simulated using unity density ratio jets, but only when scaled with the momentum flux ratio of the coolant jets.

Film Cooling Parameter Waveforms on a Turbine Blade Leading Edge Model With Oscillating Stagnation Line

2015 ◽  
Author(s):  
James L. Rutledge ◽  
Tylor C. Rathsack ◽  
Matthew T. Van Voorhis ◽  
Marc D. Polanka
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blade ◽  
Film Cooling ◽  
Leading Edge ◽  
Stagnation Line ◽  
Inverse Heat Transfer ◽  
Adiabatic Effectiveness ◽  
Blade Leading Edge

It is necessary to understand how film cooling influences the external convective boundary condition involving both the adiabatic wall temperature and the heat transfer coefficient in order to predict the thermal durability of a gas turbine hot gas path component. Most studies in the past have considered only steady flow, but studies of the unsteadiness naturally present in turbine flow have become more prevalent. One source of unsteadiness is wake passage from upstream components which can cause fluctuations in the stagnation location on turbine airfoils. This in turn causes unsteadiness in the behavior of the leading edge coolant jets and thus fluctuations in both the adiabatic effectiveness and heat transfer coefficient. The dynamics of h and η are now quantifiable with modern inverse heat transfer methods and non-intrusive infrared thermography. The present study involved the application of a novel inverse heat transfer methodology to determine time resolved adiabatic effectiveness and heat transfer coefficient waveforms on a simulated turbine blade leading edge with an oscillating stagnation position. The leading edge geometry was simulated with a circular cylinder with a coolant hole located 21.5° downstream from the leading edge stagnation line, angled 20° to the surface and 90° to the streamwise direction. The coolant plume is shown to shift in response to the stagnation line movement. These oscillations thus influence the film cooling coverage and the time-averaged benefit of film cooling is influenced by the oscillation.

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