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

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.

The Influence of Turbulence and Reynolds Number on Slot Film Cooling Over the Downstream Pressure Surface

Volume 5B: Heat Transfer ◽

10.1115/gt2019-90508 ◽

2019 ◽

Author(s):

L. W. Soma ◽

F. E. Ames ◽

S. Acharya

Keyword(s):

Flow Field ◽

Film Cooling ◽

Thermal Stresses ◽

Surface Film ◽

Leading Edge ◽

Internal Cooling ◽

Pressure Surface ◽

Density Ratios ◽

Slot Film Cooling

Abstract Pressure surface film cooling from discrete holes can often be challenging due to higher than optimum coolant to surface pressure ratios, effects of high levels of flow field turbulence, and the potential for clogging. Double wall cooling methods can be designed to collect spent cooling air and distribute the film cooling downstream through a slot. Incremental impingement is a new internal cooling method designed for cooling the leading edge region and pressure surface. Internally, incremental impingement includes high solidity pedestals to conduct heat and transmit thermal stresses due to temperature variations between cold and hot side surfaces. Subsequently, the flow is collected downstream from the last row of pedestals and discharged through a slot. Experimental and computational research from mesh slots, which have dense arrays of pedestals upstream from the discharge, and slots downstream from high solidity pedestal arrays have shown that turbulence and vorticity generated inside a film cooling plenum can have a significant impact on downstream film cooling. This impact of plenum flow disturbances is in addition to the film cooling dissipation caused by external flow field turbulence. Incremental impingement, in addition to high solidity pedestals, has impingement jets integrated behind the last row of pedestals which may cause further disruption to the film discharge and flow field interaction. The present measurements document the film cooling effectiveness distributions downstream from a slot located at 62% arc along the pressure surface of a vane. The plenum has been designed to include high solidity pedestals and impingement jets consistent with an incremental impingement geometry. Blowing ratios of 0.4, 0.7 and 1.0 have been investigated at vane exit chord Reynolds numbers of 500,000, 1,000,000 and 2,000,000 at density ratios a little over 1. These conditions have been run at 5 independent turbulence levels ranging from 0.7% to over 17%. The results provide a consistent picture of pressure surface slot film cooling downstream from incremental impingement.

Computational analysis of span-wise hole locations on fluid flow and film cooling of internal channels with crescent ribs

International Journal of Numerical Methods for Heat &amp Fluid Flow ◽

10.1108/hff-09-2018-0474 ◽

2019 ◽

Vol 29 (8) ◽

pp. 2728-2753

Author(s):

Guohua Zhang ◽

Xueting Liu ◽

Bengt Ake Sundén ◽

Gongnan Xie

Keyword(s):

Film Cooling ◽

Cross Flow ◽

Side Wall ◽

Target Surface ◽

Internal Cooling ◽

Cooling Performance ◽

Content Type ◽

Blowing Ratio ◽

Cooling Air

Purpose This study aims to clarify the mechanism of film hole location at the span-wise direction of an internal cooling channel with crescent ribs on the adiabatic film cooling performance, three configurations are designed to observe the effects of the distance between the center of the ellipse and the side wall(Case 1, l = w/2, Case 2, l = w/3 and for Case 3, l = w/4). Design/methodology/approach Numerical simulations are conducted under two blowing ratios (i.e. 0.5 and 1) and a fixed cross-flow Reynolds number (Rec = 100,000) with a verified turbulence model. Findings It is shown that at low blowing ratio, reducing the distance increases the film cooling effectiveness but keeps the trend of the effectiveness unchanged, while at high blowing ratio, the characteristic is a little bit different in the range of 0 = x/D = 10. Research limitations/implications These features could be explained by the fact that shrinking the distance between the hole and side wall induces a much smaller reserved region and vortex downstream the ribs and a lower resistance for cooling air entering the film hole. Furthermore, the spiral flow inside the hole is impaired. Originality/value As a result, the kidney-shaped vortices originating from the jet flow are weakened, and the target surface can be well covered, resulting in an enhancement of the adiabatic film cooling performance.

Computational Investigation of Film Cooling from Cylindrical and Row Trenched Cooling Holes near the Combustor End Wall

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.554.225 ◽

2014 ◽

Vol 554 ◽

pp. 225-229 ◽

Author(s):

Nor Azwadi Che Sidik ◽

Kianpour Ehsan

Keyword(s):

Film Cooling ◽

Surface Film ◽

Three Dimensional ◽

Navier Stokes ◽

Internal Cooling ◽

Cooling Performance ◽

Turbine Engine ◽

Blowing Ratio ◽

Three Dimensional Representation

This study was accomplished in order to investigate the effects of cylindrical and row trenched cooling holes with alignment angle of 0 degree and 90 degree at blowing ratio, BR = 3.18 on the film cooling performance adjacent to the endwall surface of a combustor simulator. In this research a three dimensional representation of Pratt and Whitney gas turbine engine was simulated and analyzed with a commercial finite volume package FLUENT 6.2. The current study has been performed with Reynolds-averaged Navier-Stokes turbulence model (RANS) on internal cooling passages. This combustor simulator combined the interaction of two rows of dilution jets, which were staggered in the stream wise direction and aligned in the span wise direction, with that of film cooling along the combustor liner walls. The findings of the study declared that with using the row trenched holes near the endwall surface, film cooling effectiveness is doubled compared to the cooling performance of baseline case.

Analyzes of Film Cooling from Cylindrical and Row Trenched Holes with Alignment Angle of 90 Degrees at Low Blowing Ratio

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.695.376 ◽

2014 ◽

Vol 695 ◽

pp. 376-379 ◽

Author(s):

Kianpour Ehsan ◽

Nor Azwadi Che Sidik

Keyword(s):

Film Cooling ◽

Surface Film ◽

Three Dimensional ◽

Internal Cooling ◽

Wall Surface ◽

Cooling Effectiveness ◽

Blowing Ratio ◽

Alignment Angle ◽

End Wall

The current study was conducted to analyze the effects of cylindrical and row trenched cooling holes with alignment angle of 90 degrees at blowing ratio, BR = 1.25 on the film cooling effectiveness near the end wall surface of a combustor simulator. In the current research a three dimensional representation of Pratt and Whitney gas turbine engine was simulated and analyzed with a commercial finite volume package FLUENT 6.2.26. This study has been performed with Reynolds-averaged Navier-Stokes turbulence model (RANS) on internal cooling passages. This combustor simulator combined the interaction of two rows of dilution jets, which were staggered in the stream wise direction and aligned in the span wise arrangement, with that of film cooling along the combustor liner walls. The findings of the study declared that with using the row trenched holes near the end wall surface, film cooling effectiveness is increased three times compared to the cooling performance of baseline case.

Influence of Unsteady Wake With Trailing Edge Coolant Ejection on Turbine Blade Film Cooling

Journal of Turbomachinery ◽

10.1115/1.4004883 ◽

2012 ◽

Vol 134 (6) ◽

Cited By ~ 8

Author(s):

Shiou-Jiuan Li ◽

Akhilesh P. Rallabandi ◽

Je-Chin Han

Keyword(s):

Film Cooling ◽

Surface Film ◽

Turbine Rotor ◽

Suction Surface ◽

Trailing Edge ◽

Cooling Effectiveness ◽

Turbine Rotor Blade ◽

Blowing Ratio ◽

Unsteady Wake

Detailed film cooling effectiveness distributions along a modeled turbine rotor blade under the combined effects of an upstream trailing edge unsteady wake with coolant ejection are presented using the pressure sensitive paint (PSP) mass transfer analogy method. The experiment is conducted in a low speed wind tunnel facility with a five blade linear cascade. The exit Reynolds number based on the axial chord is 370,000. Unsteady wakes and trailing edge coolant jets are produced by a spoked wheel-type wake generator with hollow rods equipped with several coolant ejections from holes. The coolant-to-mainstream density ratios for both the blade and trailing edge coolant ejection range from 1.5 to 2.0 for simulating realistic engine conditions. Blade blowing ratio studies are 0.5 and 1.0 on the suction surface and 1.0 and 2.0 on the pressure surface. The trailing edge jet blowing ratio and Strouhal numbers are 1.0 and 0.12, respectively. The results show that the unsteady wake reduces the overall film cooling effectiveness. However, the unsteady wake with trailing edge coolant ejection enhances the overall effectiveness. The results also show that the overall filming cooling effectiveness increases by using heavier coolant for trailing edge ejection and for blade surface film cooling.

Tripod Hole Geometry Performance for a Vane Suction Surface Near Throat Location

Volume 3B: Heat Transfer ◽

10.1115/gt2013-94459 ◽

2013 ◽

Author(s):

Sridharan Ramesh ◽

Chris LeBlanc ◽

Srinath V. Ekkad ◽

Mary Anne Alvin

Keyword(s):

Film Cooling ◽

Suction Side ◽

Suction Surface ◽

Cooling Effectiveness ◽

Throat Region ◽

Blowing Ratio ◽

Hole Geometry ◽

Film Cooling Holes ◽

Cooling Air

Film cooling performance depends strongly on the hole exit geometry, blowing ratio, and hole location. The goal of this study is to evaluate film cooling geometries that can provide better protection over the suction surface of the airfoil beyond the throat region. This study compares the performance of standard cylindrical; fan-shaped (10° flare/laidback); tripod hole geometry (15° breakout angle); and tripod holes with shaped exits (5° flare on 15° tripod). Film cooling holes are located just upstream of the throat region on the suction side of an airfoil. The airfoil is a scaled up first stage vane from GE E3 engine and is mounted on a low speed linear cascade wind tunnel. A range of blowing ratios from 0.5 to 2.0 was covered for a cylindrical hole, while ensuring all other hole geometries run under similar mass flow rate conditions. Steady state IR (Infra-Red) technique was employed to measure adiabatic film cooling effectiveness. Results show that the tripod holes with and without shaped exits provide much higher film effectiveness than cylindrical and slightly higher effectiveness than shaped exit holes using 50% lesser cooling air while operating at the same blowing ratios. Effectiveness values up to 0.2–0.25 are seen 40-hole diameters downstream for the tripod hole configurations thus providing cooling in the important trailing edge portion of the airfoil.

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

Volume 5: Turbo Expo 2003, Parts A and B ◽

10.1115/gt2003-38319 ◽

2003 ◽

Cited By ~ 22

Author(s):

Luzeng Zhang ◽

Hee Koo Moon

Keyword(s):

Flow Field ◽

Secondary Flow ◽

Mass Flow ◽

Film Cooling ◽

Secondary Flows ◽

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.

Influence of Unsteady Wake With Trailing Edge Coolant Ejection on Turbine Blade Film Cooling

Volume 5: Heat Transfer, Parts A and B ◽

10.1115/gt2011-45925 ◽

2011 ◽

Author(s):

Shiou-Jiuan Li ◽

Akhilesh P. Rallabandi ◽

Je-Chin Han

Keyword(s):

Film Cooling ◽

Surface Film ◽

Turbine Rotor ◽

Suction Surface ◽

Trailing Edge ◽

Cooling Effectiveness ◽

Turbine Rotor Blade ◽

Pressure Surface ◽

Unsteady Wake

Detailed film cooling effectiveness distributions along a modeled turbine rotor blade under combined effects of upstream trailing edge unsteady wake with coolant ejection are presented using the pressure sensitive paint (PSP) mass transfer analogy method. The experiment is conducted in a low speed wind tunnel facility with a five blade linear cascade. The exit Reynolds number based on the axial chord is 370,000. Unsteady wakes and trailing edge coolant jets are produced by a spoked wheel-type wake generator with hollow rods equipped with several coolant ejections from holes. The coolant-to-mainstream density ratios for both blade and trailing edge coolant ejection range from 1.5 to 2.0 for simulating realistic engine conditions. Blade blowing ratios studied are 0.5 and 1.0 on Suction surface and 1.0 and 2.0 on Pressure surface. Trailing edge jet blowing ratio and Strouhal number are 1.0 and 0.12, respectively. Results show the unsteady wake reduces overall film cooling effectiveness. However, the unsteady wake with trailing edge coolant ejection enhances overall effectiveness. Results also show that the overall filming cooling effectiveness increases by using heavier coolant for trailing edge ejection as well as for blade surface film cooling.

Turbine Nozzle Film Cooling Study Using the Pressure Sensitive Paint (PSP) Technique

Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/99-gt-196 ◽

1999 ◽

Cited By ~ 17

Author(s):

Luzeng Zhang ◽

Michael Baltz ◽

Ram Pudupatty ◽

Michael Fox

Keyword(s):

Reynolds Number ◽

Mach Number ◽

Film Cooling ◽

High Speed ◽

Surface Film ◽

Pressure Sensitive Paint ◽

Suction Surface ◽

Cooling Effectiveness ◽

Pressure Sensitive

The use of pressure sensitive paint (PSP) to measure film cooling effectiveness on a turbine nozzle surface was demonstrated in a high speed wind tunnel. Film cooling effectiveness was measured from a single row of holes located on a turbine vane suction surface with a shaped exit. 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. Three blowing ratios were studied for each of the five freestream conditions: a reference condition, a reduced and an increased Reynolds number condition, and a reduced and an increased Mach number condition. The freestream turbulence intensity was kept at 12.0% for all the tests. The PSP was calibrated at various temperatures and pressures to obtain better accuracy before being applied to the airfoil surface. The film effectiveness increased with blowing ratio for all the freestream conditions. The effects of secondary flow and freestream Mach number and Reynolds number on turbine nozzle suction surface film cooling are also discussed.

Experimental and Numerical Investigations of Shock-Film Cooling Interaction on a Turbine Blade With Fan-Shaped Cooling Holes

Journal of Thermal Science and Engineering Applications ◽

10.1115/1.4031465 ◽

2015 ◽

Vol 7 (4) ◽

Cited By ~ 3

Author(s):

S. Xue ◽

A. Arisi ◽

W. Ng

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Pressure Gradient ◽

Transfer Coefficient ◽

Film Cooling ◽

Secondary Flows ◽

Suction Surface ◽

Cooling Effectiveness ◽

Near Surface ◽

Film Cooling Effectiveness

This paper presents the findings of an experimental and numerical investigation on the shock effect on heat transfer coefficient and film-cooling effectiveness. In this study, coolant was injected on the blade surface through a fan-shaped hole in a transonic cascade. The experimental results indicate that on the film-cooled suction surface of the blade, the shock from the adjacent blade impinging on the suction surface causes the film-cooling effectiveness to drop quickly by 18%, and then stay at a low level downstream of the shock. The shock also causes the local heat transfer coefficient to decrease rapidly by 25%, but then rise back up immediately after the shock. The results from the numerical study supported the film-cooling effectiveness and heat transfer coefficient trends that were observed in the experiment. A detailed analysis of the numerical results reveals that the rapid change of the film-cooling effectiveness is due to the near surface secondary flows, which push the hot mainstream air toward the injection centerline and lifts the low temperature core away from the surface. This secondary flow is a result of a spanwise pressure gradient. The drop in heat transfer coefficient is caused by a boundary layer separation bubble which results from an adverse streamwise pressure gradient at the shock position.