Turbine Nozzle Endwall Inlet Film Cooling: The Effect of a Back-Facing Step

2003 ◽  
Author(s):  
Luzeng Zhang ◽  
Hee Koo Moon
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Mass Flow ◽  
Film Cooling ◽  
Secondary Flows ◽  
Film Cooling Effectiveness ◽  
Cooling Flow ◽  
Wall Flow ◽  
Cooling Air ◽  
Near Wall

Film cooling effectiveness was measured on a contoured endwall surface using the pressure sensitive paint (PSP) technique. A double staggered row of holes was adopted to supply cooling air in front of the nozzle leading edges. To simulate realistic engine configuration, a back-facing step was built, which was located upstream from the film injection. Nitrogen gas was used to simulate film cooling flow as a tracer gas to indicate oxygen concentration such that film effectiveness by the mass transfer analogy could be obtained. Cooling mass flow was controlled to be from 0.5% to 3.0% of the mainstream mass flow. Film effectiveness distributions were measured on the endwall surface for both smooth (baseline) and back-facing step inlet configurations. For the smooth inlet case, film effectiveness increased nonlinearly with mass flow rate, indicating a strong interference between the cooling jets and the secondary flows. At lower mass flow ratios, the secondary flow dominated the near wall flow field, resulting in a low film effectiveness value. At higher mass flow ratios, the cooling jet momentum dominated the near wall flow field, resulting in a higher film effectiveness. For the back-facing step inlet configuration, the values of film effectiveness were reduced significantly, suggesting a stronger secondary flow interaction. In addition to the comparison between the smooth and back-facing step inlet configurations, comparison to previous data by the authors on a flat endwall was also made.

Turbine Nozzle Endwall Film Cooling Study Using Pressure-Sensitive Paint

2001 ◽  
Vol 123 (4) ◽  
pp. 730-738 ◽  
Author(s):  
Luzeng J. Zhang ◽  
Ruchira Sharma Jaiswal
Keyword(s):  
Flow Field ◽  
Mass Flow ◽  
Film Cooling ◽  
Free Stream ◽  
Surface Film ◽  
Secondary Flows ◽  
Pressure Sensitive Paint ◽  
Pressure Sensitive ◽  
Wall Flow ◽  
Near Wall

Endwall surface film cooling effectiveness was measured on a turbine vane endwall surface using the pressure-sensitive paint (PSP) technique. A double staggered row of holes and a single row of discrete slots were used to supply film cooling in front of the nozzle cascade leading edges. Nitrogen gas was used to simulate film cooling flow as well as a tracer gas to indicate oxygen concentration such that film effectiveness by the mass transfer analogy could be obtained. Cooling mass flow was controlled to be 0.5 to 3.0 percent of the mainstream mass flow. The free-stream Reynolds number was about 283,000 and Mach number was about 0.11. The free-stream turbulence intensity was kept at 6.0 percent for all the tests, measured by a thermal anemometer. The PSP was calibrated at various temperatures and pressures to obtain better accuracy before being applied to the endwall surface. Film effectiveness distributions were measured on a flat endwall surface for five different mass flow rates. The film effectiveness increased nonlinearly with mass flow rate, indicating a strong interference between the cooling jets and the endwall secondary flows. At lower mass flow ratios, the secondary flow dominated the near wall flow field, resulting in a low film effectiveness. At higher mass flow ratios, the cooling jet momentum dominated the near wall flow field, resulting in a higher film effectiveness. The comparison between hole injection and slot injection was also made.

Turbine Nozzle Endwall Film Cooling Study Using Pressure Sensitive Paint

2001 ◽  
Author(s):  
Luzeng J. Zhang ◽  
Ruchira Sharma Jaiswal
Keyword(s):  
Flow Field ◽  
Mass Flow ◽  
Film Cooling ◽  
Surface Film ◽  
Secondary Flows ◽  
Hole Injection ◽  
Pressure Sensitive Paint ◽  
Pressure Sensitive ◽  
Wall Flow ◽  
Near Wall

Endwall surface film cooling effectiveness was measured on a turbine vane endwall surface using the pressure sensitive paint (PSP) technique. A double staggered row of holes and a single row of discrete slots were used to supply film cooling in front of the nozzle cascade leading edges. Nitrogen gas was used to simulate film cooling flow as well as a tracer gas to indicate oxygen concentration such that film effectiveness by the mass transfer analogy could be obtained. Cooling mass flow was controlled to be 0.5 to 3.0% of the mainstream mass flow. The freestream Reynolds number was about 283000 and Mach number was about 0.11. The freestream turbulence intensity was kept at 6.0% for all the tests, measured by a thermal anemometer. The PSP was calibrated at various temperatures and pressures to obtain better accuracy before being applied to the endwall surface. Film effectiveness distributions were measured on a flat endwall surface for five different mass flow rates. The film effectiveness increased nonlinearly with mass flow rate, indicating a strong interference between the cooling jets and the endwall secondary flows. At lower mass flow ratios, the secondary flow dominated the near wall flow field, resulting in a low film effectiveness. At higher mass flow ratios, the cooling jet momentum dominated the near wall flow field, resulting in a higher film effectiveness. The comparison between hole injection and slot injection was also made.

Single and Multiple Row Endwall Film-Cooling of a Highly Loaded First Turbine Vane With Variation of Loading

2013 ◽  
Vol 136 (6) ◽  
Author(s):  
Martin Kunze ◽  
Konrad Vogeler ◽  
Michael Crawford ◽  
Glenn Brown
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Film Cooling ◽  
Wall Material ◽  
Measured Temperature ◽  
Single Row ◽  
Wall Flow ◽  
Endwall Film Cooling ◽  
Highly Loaded ◽  
Near Wall

This paper reports endwall film-cooling investigations with single and multiple rows of fan-shaped film holes using temperature-sensitive paint (TSP). The experiments are carried out in a six-bladed linear cascade based on the geometry of a highly loaded gas turbine first vane. The film effectiveness performance of the cooling rows is investigated under the influence of enhanced near-wall secondary flow. Tests are conducted at three different loading conditions changing the profile incidence. Film-cooling injection is established at elevated coolant density ratios of 1.4 using heated carbon dioxide. Due to the finite thermal conductivity of the wall material, the heat conduction effects observed in the measured temperature fields are assessed by a newly developed data analysis based on a finite element thermal analysis and tracking algorithms along CFD-computed near-wall surface streamlines. The results showed that the coolant trajectories are visibly influenced revealing the intense interaction between the film jets and the near-wall flow field. These effects are certainly enhanced with higher incidence leading to increased streamwise coolant consumption and reduced wall coverage. At the cascade inlet, the film-cooling injection is significantly affected by the near-wall flow field showing distinct over- and undercooled regions. Due to the enhanced deflection and mixing of the film jets injected from a single row, area-averaged film effectiveness and wall coverage decreases about 9 and 11%, respectively. With adding more cooling holes to this endwall area, the influence of the enhanced secondary flow becomes more pronounced. Hence, larger reduction in film effectiveness of 23% and wall coverage with 28% is observed. For single row injection at the airfoil pressure side, the stronger secondary flow motion with intensified streamwise mixing leads to a visibly decreased endwall coverage ratio of about 38% and maximum flow path reduction of about 41%. In this case, film effectiveness is found to be reduced up to 47% due to the small amount of coolant injected through this row. This effect is significantly smaller when more cooling rows are added showing an almost constant cooling performance for all incidence cases.

Effects of Slot Bleed Injection Over a Contoured Endwall on Nozzle Guide Vane Cooling Performance: Part I — Flow Field Measurements

2000 ◽  
Author(s):  
Steven W. Burd ◽  
Terrence W. Simon
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Large Scale ◽  
Secondary Flows ◽  
Cooling Flow ◽  
Nozzle Guide ◽  
Aerodynamic Losses

Film cooling and secondary flows are major contributors to aerodynamic losses in turbine passages. This is particularly true in low aspect ratio nozzle guide vanes where secondary flows can occupy a large portion of the passage flow field. To reduce losses, advanced cooling concepts and secondary flow control techniques must be considered. To this end, combustor bleed cooling flows introduced through an inclined slot upstream of the airfoils in a nozzle passage were experimentally investigated. Testing was performed in a large-scale, high-pressure turbine nozzle cascade comprised of three airfoils between one contoured and one flat endwall. Flow was delivered to this cascade with high-level (∼9%), large-scale turbulence at a Reynolds number based on inlet velocity and true chord length of 350,000. Combustor bleed cooling flow was injected through the contoured endwall upstream of the contouring at bleed-to-core mass flow rate ratios ranging from 0 to 6%. Measurements with triple-sensor, hot-film anemometry characterize the flow field distributions within the cascade. Total and static pressure measurements document aerodynamic losses. The influences of bleed mass flow rate on flow field mean streamwise and cross-stream velocities, turbulence distributions, and aerodynamic losses are discussed. Secondary flow features are also described through these measurements. Notably, this study shows that combustor bleed cooling flow imposes no aerodynamic penalty. This is atypical of schemes where coolant is introduced within the passage for the purpose of endwall cooling. Also, instead of being adversely affected by secondary flows, this type of cooling is able to reduce secondary flow effects.

Turbine Nozzle Endwall Inlet Film Cooling: The Effect of a Back-Facing Step and Velocity Ratio

2004 ◽  
Author(s):  
Luzeng Zhang ◽  
Hee Koo Moon
Keyword(s):  
Mass Flow ◽  
Film Cooling ◽  
Velocity Ratio ◽  
Secondary Flows ◽  
Tracer Gas ◽  
Nitrogen Gas ◽  
Cooling Flow ◽  
Pressure Sensitive ◽  
Jet Velocity ◽  
Cooling Air

Endwall inlet film cooling serves two purposes: to suppress the secondary flows and to provide effective cooling. To optimize endwall inlet film cooling, the combined effects of a back facing step and jet velocity ratio were studied in a warm cascade simulating realistic engine conditions. Film effectiveness distribution was measured on a nozzle endwall surface using the pressure sensitive paint (PSP) technique. A double staggered row of holes was used to supply cooling air in front of the nozzle leading edges. Changing the diameter of the film injection hole varied the velocity ratio and the back-facing step was designed to simulate the discontinuity of the nozzle inlet to the combustor exit cone. Nitrogen gas was used to simulate cooling flow as well as a tracer gas to indicate oxygen concentration such that film effectiveness by the mass transfer analogy could be obtained. Cooling mass flow was controlled to be from 0.5% to 3.0% of the mainstream mass flow. The film effectiveness distribution was locally measured for each of the cooling mass flows. It was demonstrated that by optimizing the jet velocity ratio the adverse effect of the back-facing step could be reduced, particularly for the range of mass flow practical in design. The pattern of the film effectiveness distribution suggested the opposite effect of the film injection and the back-facing step on the secondary flows, while one suppresses and the other enhances it.

Aero-Thermal Performance of Purge Flow in Turbine Cascade Endwall Cooling

2012 ◽  
Vol 229-231 ◽  
pp. 737-741 ◽  
Author(s):  
W. Ghopa Wan Aizon ◽  
Kenichi Funazaki
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Secondary Flow ◽  
Film Cooling ◽  
Gas Turbines ◽  
Thermal Stresses ◽  
Secondary Flows ◽  
Inlet Temperature ◽  
Turbine Cascade ◽  
Film Cooling Effectiveness

The endwall and blade film cooling systems are the typical solution adopted within gas turbines to allow further increase of turbine inlet temperature, avoiding critical material thermal stresses. Due to complex secondary flow field in the blade passage, endwallis more difficult to cool than blade surfaces. In the matter of fact, in endwall film cooling studies, it is necessary to investigate the interaction between coolant air and the secondary flow. In present study, the flow field of high-pressure turbine cascade has been investigated by 5-holes pitot tube to reveal the secondary flows behavior under the influenced of purge flows while the heat transfer measurement was conducted bythermochromic liquid crystal (TLC). Experimental has significantly captured theaerodynamics effect of purge flowat blade downstream close to the endwall region. Furthermore, TLC measurement illustrated that the film cooling effectiveness and heat transfer coefficient contours were strongly influenced by the secondary flow on the endwall.

scholarly journals The Design of an Improved Endwall Film-Cooling Configuration

1998 ◽  
Author(s):  
S. Friedrichs ◽  
H. P. Hodson ◽  
W. N. Dawes
Keyword(s):  
Secondary Flow ◽  
Film Cooling ◽  
Large Scale ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Aerodynamic Loss ◽  
Cooling Flow ◽  
High Static Pressure ◽  
Endwall Film Cooling ◽  
Aerodynamic Losses

The endwall film-cooling cooling configuration investigated by Friedrichs et al. (1996, 1997) had in principle sufficient cooling flow for the endwall, but in practice, the redistribution of this coolant by secondary flows left large endwall areas uncooled. This paper describes the attempt to improve upon this datum cooling configuration by redistributing the available coolant to provide a better coolant coverage on the endwall surface, whilst keeping the associated aerodynamic losses small. The design of the new, improved cooling configuration was based on the understanding of endwall film-cooling described by Friedrichs et al. (1996, 1997). Computational fluid dynamics were used to predict the basic flow and pressure field without coolant ejection. Using this as a basis, the above described understanding was used to place cooling holes so that they would provide the necessary cooling coverage at minimal aerodynamic penalty. The simple analytical modelling developed in Friedrichs et al. (1997) was then used to check that the coolant consumption and the increase in aerodynamic loss lay within the limits of the design goal. The improved cooling configuration was tested experimentally in a large scale, low speed linear cascade. An analysis of the results shows that the redesign of the cooling configuration has been successful in achieving an improved coolant coverage with lower aerodynamic losses, whilst using the same amount of coolant as in the datum cooling configuration. The improved cooling configuration has reconfirmed conclusions from Friedrichs et al. (1996, 1997); firstly, coolant ejection downstream of the three-dimensional separation lines on the endwall does not change the secondary flow structures; secondly, placement of holes in regions of high static pressure helps reduce the aerodynamic penalties of platform coolant ejection; finally, taking account of secondary flow can improve the design of endwall film-cooling configurations.

The Influence of Turbulence and Reynolds Number on Multiple Slot Film Cooling Over the Suction Surface

2020 ◽  
Author(s):  
L. W. Soma ◽  
F. E. Ames ◽  
S. Acharya
Keyword(s):  
Film Cooling ◽  
Surface Film ◽  
Secondary Flows ◽  
Internal Cooling ◽  
Suction Surface ◽  
Film Cooling Effectiveness ◽  
Cooling Method ◽  
Cooling Section ◽  
Slot Film Cooling ◽  
Cooling Air

Abstract Developing robust film cooling protection on the suction surface of a vane is critical to managing the high heat loads which exist there. Suction surface film cooling often produces high levels of film cooling but can be influenced by secondary flows and some dissipation due to free-stream turbulence. Directly downstream from suction surface film cooling, heat loads are often significantly mitigated and internal cooling levels can be modest. One thermodynamically efficient way to cool the suction surface of a vane is with a counter cooling scheme. This combined internal/external cooling method moves cooling air in a direction opposite to the external flow through an internal convection array. The coolant is then discharged upstream where the high level of film cooling can offset the reduced cooling potential of the spent cooling air. The present suction surface film cooling arrangement combines a slot film cooling discharge on the near suction surface from an incremental impingement cooling method with a second from a counter cooling section. A second counter cooling section is added further downstream on the suction surface. The internal cooling plenums replicate the geometry of the cooling methods to ensure the fluid dynamics of the flow discharging from the slots are representative of the actual internal cooling geometry. These film cooling flows have been tested at blowing ratios of 0.5 and 1.0 for the initial slot and blowing ratios of 0.15 and 0.3 for the two downstream slots. The measurements have been taken at exit chord Reynolds numbers of 500,000, 1,000,000, and 2,000,000 with inlet turbulence levels ranging from 0.7% to 12.6%. Film cooling effectiveness measurements were acquired using both thermocouples and infrared thermography. The infrared thermography shows the influence of secondary flows on film cooling coverage near the suction surface endwall junction. The film cooling effectiveness results at varied blowing ratios, turbulence levels and Reynolds numbers document the impact of these major variables on suction surface slot film cooling. The results provide a consistent picture of the slot film cooling for the present three slot arrangement on the suction surface and they support the development of an advanced double wall cooling method.

Nekomimi Film Cooling Holes Configuration Under Conjugate Heat Transfer Conditions

2014 ◽  
Author(s):  
Karsten Kusterer ◽  
Nurettin Tekin ◽  
Tobias Wüllner ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Secondary Flow ◽  
Flow Structure ◽  
Film Cooling ◽  
Conjugate Heat Transfer ◽  
Cooling Effectiveness ◽  
Cooling Flow ◽  
Secondary Flow Structure ◽  
Cooling Air

In modern gas turbines, the film cooling technology is essential for the protection of the hot parts, in particular of the first stage vanes and blades of the turbine, against the hot gases from the combustion process in order to reach an acceptable life span of the components. As the cooling air is usually extracted from the compressor, the reduction of the cooling effort would directly result in increased thermal efficiency of the gas turbine. Understanding of the fundamental physics of film cooling is necessary for the improvement of the state-of-the-art. Thus, huge research efforts by industry as well as research organizations have been undertaken to establish high efficient film cooling technologies. Today it is common knowledge that film cooling effectiveness degradation is caused by secondary flows inside the cooling jets, i.e. the Counter-Rotating Vortices (CRV) or sometimes also called kidney-vortices, which induce a lift-off of the jet. Further understanding of the secondary flow development inside the jet and how this could be influenced, has led to hole configurations, which can induce Anti-Counter-Rotating Vortices (ACRV) in the cooling jets. As a result, the cooling air remains close to the wall and is additionally distributed flatly along the surface. Beside different other technologies, the NEKOMIMI cooling technology is a promising approach to establish the desired ACRVs. It consists of a combination of two holes in just one configuration so that the air is distributed mainly on two cooling air streaks following the special shape of the generated geometry. The NEKOMIMI configuration and two conventional cooling hole configurations (cylindrical and shaped holes) has been investigated numerically under adiabatic and conjugate heat transfer conditions. The influence of the conjugate heat transfer on the secondary flow structure has been analysed. In conjugate heat transfer calculations, it cannot directly derived from the surface temperature distribution if the reached cooling effectiveness values are due to the improved hole configuration with improved secondary flow structure or due to the heat conduction in the material. Therefore, a methodology has been developed, to distinguish between cooling effectiveness due to heat conduction in the material and film cooling flow over the surface. The numerical results shows that for the NEKOMIMI configuration, 77% of the reached overall cooling effectiveness is due to film cooling with improved flow structure in the secondary flow (ACRV) and 23% due to heat conduction in the material. For the cylindrical hole configuration, 10% of the reached overall cooling effectiveness is due to the film cooling flow structure and 90% due to heat conduction in the material.

Improved Trench Film Cooling With Shaped Trench Outlets

2011 ◽  
Author(s):  
Habeeb Idowu Oguntade ◽  
Gordon E. Andrews ◽  
Alan Burns ◽  
Derek B. Ingham ◽  
Mohammed Pourkashanian
Keyword(s):  
Mass Flow ◽  
Film Cooling ◽  
Cross Flow ◽  
Trailing Edge ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Vertical Slot ◽  
Superior Surface ◽  
Cooling Air ◽  
Computational Predictions

This paper presents the influence of the shaped trailing edge of trench outlets on film cooling effectiveness and aerodynamics. A 90° outlet wall to a trench will give a vertical slot jet into the cross flow and it was considered that improvements in the cooling effectiveness would occur if the trailing edge of the trench outlet was bevelled or filleted. CFD approach was used for these investigations which started with the predictions of the conventional sharp edged trench outlet for two experimental geometries. The computational predictions for the conventional sharp edged trench outlet were shown to have good agreement with the experimental data for two experimental geometries. The shaped trailing edge of the trench outlet was predicted to improve the film cooling effectiveness. The bevelled and filleted trench outlets were predicted to further suppress vertical jet momentum and give a Coanda effect that allowed the cooling air to attach to the downstream wall surface with a better transverse spread of the coolant film. The new trench outlet geometries would allow a reduction in film cooling mass flow rate for the same cooling effectiveness. Also, it was predicted that reducing the coolant mass flow per hole and increasing the number of holes gave, for the same total coolant mass flow, a much superior surface averaged cooling effectiveness for the same cooled surface area.

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