Effect of Density Ratio on Multi-Row Film Cooling Performance

2017 ◽  
Author(s):  
Michael T. Voet ◽  
Craig P. Fernandes ◽  
Zachary Little ◽  
Erik Fernandez ◽  
Jay Kapat
Keyword(s):  
Film Cooling ◽  
Momentum Flux ◽  
Velocity Ratio ◽  
Density Ratio ◽  
Diameter Ratio ◽  
Cylindrical Hole ◽  
Co2 Injection ◽  
Freestream Velocity ◽  
Blowing Ratio ◽  
Density Ratios

This study is an investigation into the effects of density ratio on the jet structure of different film cooling configurations. A simple-shaped cylindrical hole is tested at a tight spacing, which has a lateral and streamwise pitch-to-hole-diameter ratio of 7.5. Each of the holes are 3.8mm in diameter, and have a hole length-to-diameter ratio of 11.2. The holes are inclined at 20°. The cylindrical hole shapes were machined from an aluminum plate. Two different density ratios of nominally 1 and 1.5, are achieved by alternating the coolant gas between air and CO2 respectively, while maintaining a constant freestream velocity of 36.2 m/s. In order to compare cases between different densities, various ratios are independently matched for both density ratios. Blowing ratios comparisons made at 0.3 and 0.5, accompanied by comparisons of momentum flux ratio and velocity ratio at 0.1 and 0.3, respectively. Particle image velocimetry (PIV) is utilized to measure the flow field of the centerline planes of the film cooling arrays over the two density ratios. This data is then used to investigate flow interactions as coolant leaves the film cooling hole, and structure of the jet as it enters and mixes with the freestream. When comparing density ratio effects at low blowing and momentum flux ratios, increased turbulence intensities are seen closer to the surface for CO2 injection. This suggests that the overall performance of the film decreases with increasing density ratio at these low mass flux and momentum flux cases. However, when increasing blowing ratio, the higher density injection is seen to have lower levels of turbulence in the near wall region, when compared to that of the lower density fluid. This suggests that as blowing ratio increases, the higher density fluid out performs the lower density fluid. When a low constant velocity ratio is observed, the higher density fluid is seen to have decreased levels of turbulence, again suggesting that the higher density fluid out performs the low density fluid.

Numerical Investigation of Coolant-to-Mainstream Scaling Parameters With Film Cooling on Pressure and Suction Side of a Gas Turbine Blade

2017 ◽  
Author(s):  
Lingyu Zeng ◽  
Xueying Li ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Gas Turbine ◽  
Film Cooling ◽  
Momentum Flux ◽  
Velocity Ratio ◽  
Density Ratio ◽  
Flux Ratio ◽  
Suction Side ◽  
Pressure Side ◽  
Blowing Ratio ◽  
Adiabatic Effectiveness

Most experiments of blade film cooling are conducted with density ratio lower than that of turbine conditions. In order to accurately model the performance of film cooling under a high density ratio, choosing an appropriate coolant to mainstream scaling parameter is necessary. The effect of density ratio on film cooling effectiveness on the surface of a gas turbine twisted blade is investigated from a numerical point of view. One row of film holes are arranged in the pressure side and two rows in the suction side. All the film holes are cylindrical holes with a pitch to diameter ratio P/d = 8.4. The inclined angle is 30°on the pressure side and 34° on the suction side. The steady solutions are obtained by solving Reynolds-Averaged-Navier-Stokes equations with a finite volume method. The SST turbulence model coupled with γ-θ transition model is applied for the present simulations. A film cooling experiment of a turbine vane was done to validate the turbulence model. Four different density ratios (DR) from 0.97 to 2.5 are studied. To independently vary the blowing ratio (M), momentum flux ratio (I) and velocity ratio (VR) of the coolant to the mainstream, seven conditions (M varying from 0.25 to 1.6 on the pressure side and from 0.25 to 1.4 on the suction side) are simulated for each density ratio. The results indicate that the adiabatic effectiveness increases with the increase of density ratio for a certain blowing ratio or a certain momentum flux ratio. Both on the pressure side and suction side, none of the three parameters listed above can serve as a scaling parameter independent of density ratio in the full range. The velocity ratio provides a relative better collapse of the adiabatic effectiveness than M and I for larger VRs. A new parameter describing the performance of film cooling is introduced. The new parameter is found to be scaled with VR for nearly the whole range.

Film-Cooling Performance of Anti-Vortex Hole on a Flat Plate

2011 ◽  
Author(s):  
Diganta P. Narzary ◽  
Christopher LeBlanc ◽  
Srinath Ekkad
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Poor Performance ◽  
Diameter Ratio ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Density Ratios

Film cooling performance of two hole geometries is evaluated on a flat plate surface with steady-state IR (infrared thermography) technique. The base geometry is a simple cylindrical hole design inclined at 30° from the surface with pitch-to-diameter ratio of 3.0. The second geometry is an anti-vortex design where the two side holes, also of the same diameter, branch out from the root at 15° angle. The pitch-to-diameter ratio is 6.0 between the main holes. The mainstream Reynolds number is 3110 based on the coolant hole diameter. Two secondary fluids — air and carbon-dioxide — were used to study the effects of coolant-to-mainstream density ratio (DR = 0.95 and 1.45) on film cooling effectiveness. Several blowing ratios in the range 0.5 –4.0 were investigated independently at the two density ratios. Results indicate significant improvement in effectiveness with anti-vortex holes compared to cylindrical holes at all the blowing ratios studied. At any given blowing ratio, the anti-vortex hole design uses 50% less coolant and provides at least 30–40% higher cooling effectiveness. The use of relatively dense secondary fluid improves effectiveness immediately downstream of the anti-vortex holes but leads to poor performance downstream.

Effect of Breakout Angle on Tripod Injection Hole Geometries on Flat Plate Film Cooling

2012 ◽  
Author(s):  
Christopher LeBlanc ◽  
Sridharan Ramesh ◽  
Srinath Ekkad ◽  
Mary Anne Alvin
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Diameter Ratio ◽  
Cylindrical Hole ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Shaped Hole ◽  
Jet Interactions ◽  
Density Ratios

In this study, effect of breakout angle of side holes from the main hole in a tripod hole design on film cooling performance is evaluated on a flat plate surface with steady-state IR (infrared thermography) technique. The designs are compared a cylindrical hole design inclined at 30° from the surface with pitch-to-diameter ratio of 3.0 and a shaped hole design, which is identical to the cylindrical hole design with the addition of adding a 10° flare and laydown to the exit on the mainstream surface. The two tripod hole designs are one where the two side holes, also of the same diameter, branch from the root at a 15° angle while maintaining the same 30° inclination as the cylindrical and shaped designs witha pitch-to-diameter ratio between the main holes for this design is 6.0. The other tripod hole design is a modified tripod hole design that increases the branch angle to 30°, which has the added effect of increasing the pitch-to-diameter ratio between the main holes to 7.5. Two secondary fluids — air and carbon-dioxide — were used to study the effects of coolant-to-mainstream density ratio (DR = 0.95 and 1.45) on film cooling effectiveness. Several blowing ratios in the range 0.5–4.0 were investigated independently at the two density ratios. Results show that the tripod hole design provides similar film cooling effectiveness as the shaped hole case with overall reduced coolant usage. Increasing the breakout angle from 15° to 30° reduces overall cooling effectiveness but increases jet-to-jet interactions.

Density Ratio Effects on the Flow Field Emanating From Cylindrical Effusion and Trenched Film Cooling Holes

2014 ◽  
Author(s):  
Peter Schreivogel ◽  
Bernhard Kröss ◽  
Michael Pfitzner
Keyword(s):  
Flow Field ◽  
Film Cooling ◽  
Recirculation Zone ◽  
Velocity Ratio ◽  
Density Ratio ◽  
Piv Measurements ◽  
Blowing Ratio ◽  
Density Ratios ◽  
Film Cooling Holes ◽  
Cooling Air

The present paper investigates density ratio effects on the flow field of cylindrical hole effusion and trench film cooling. An extensive parametric study of varying blowing rates (M = 1; 2; 4; 6), momentum (I = 1; 2; 8; 16) and velocity ratios (VR = 0.5; 1; 2) was carried out at three different density ratios (DR = 1.33; 1.6; 2). All cases were simulated using the realizable k-ε turbulence model with enhanced wall treatment. The mainstream boundary conditions were kept constant, while the coolant mass flow and temperature were varied. Additional 2D PIV measurements in streamwise planes and planes parallel to the wall were carried out in a heated, closed loop wind tunnel with an injection of cryogenically cooled air. For constant momentum ratios, the jet core trajectories for both configurations were almost independent from the density ratio. In case of a constant blowing ratio, the jet penetration decreased with the density ratio, while it increased for a constant velocity ratio. Downstream of the trench a large recirculation zone is visible. Furthermore, cooling air is forced out of the trench in the midplane between two cooling holes.

scholarly journals Theory of Non-Dimensional Groups in Film Effectiveness Studies

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Francesco Ornano ◽  
Thomas Povey
Keyword(s):  
Heat Capacity ◽  
Physical Interpretation ◽  
Film Cooling ◽  
Gas Turbines ◽  
Momentum Flux ◽  
Density Ratio ◽  
Flux Ratio ◽  
Cooling Performance ◽  
Momentum Flux Ratio ◽  
Blowing Ratio

Abstract The desire to improve gas turbines has led to a significant body of research concerning film cooling optimization. The open literature contains many studies considering the impact on film cooling performance of both geometrical factors (hole shape, hole separation, hole inclination, row separation, etc.) and physical influences (effect of density ratio (DR), momentum flux ratio, etc.). Film cooling performance (typically film effectiveness, under either adiabatic or diabatic conditions) is almost universally presented as a function of one or more of three commonly used non-dimensional groups: blowing—or local mass flux—ratio, density ratio, and momentum flux ratio. Despite the abundance of papers in this field, there is some confusion in the literature about the best way of presenting such data. Indeed, the very existence of a discussion on this topic points to lack of clarity. In fact, the three non-dimensional groups in common use (blowing ratio (BR), density ratio, and momentum flux ratio) are not entirely independent of each other making aspects of this discussion rather meaningless, and there is at least one further independent group of significance that is rarely discussed in the literature (specific heat capacity flux ratio). The purpose of this paper is to bring clarity to this issue of correct scaling of film cooling data. We show that the film effectiveness is a function of 11 (additional) non-dimensional groups. Of these, seven can be regarded as boundary conditions for the main flow path and should be matched where complete similarity is required. The remaining four non-dimensional groups relate specifically to the introduction of film cooling. These can be cast in numerous ways, but we show that the following forms allow clear physical interpretation: the momentum flux ratio, the blowing ratio, the temperature ratio (TR), and the heat capacity flux ratio. Two of these parameters are in common use, a third is rarely discussed, and the fourth is not discussed in the literature. To understand the physical mechanisms that lead to each of these groups being independently important for scaling, we isolate the contribution of each to the overall thermal field with a parametric numerical study using 3D Reynolds-averaged Navier–Stokes (RANS) and large eddy simulations (LES). The results and physical interpretation are discussed.

The Influence of Coolant Supply Geometry on Film Coolant Exit Flow and Surface Adiabatic Effectiveness

1997 ◽  
Author(s):  
Steven W. Burd ◽  
Terrence W. Simon
Keyword(s):  
Turbulence Intensity ◽  
Film Cooling ◽  
Velocity Ratio ◽  
Turbine Engines ◽  
Freestream Velocity ◽  
Cooling Flow ◽  
Adiabatic Effectiveness ◽  
Density Ratios ◽  
Film Cooling Holes ◽  
Counter Current

Experimental hot-wire anemometry and thermocouple measurements are taken to document the sensitivity which film cooling performance has to the hole length and the geometry of the plenum which supplies cooling flow to the holes. This sensitivity is described in terms of the effects these geometric features have on hole-exit velocity and turbulence intensity distributions and on adiabatic effectiveness values on the surface downstream. These measurements were taken under high freestream turbulence intensity (12%) conditions, representative of operating gas turbine engines. Coolant is supplied to the film cooling holes by means of (1) an unrestricted plenum, (2) a plenum which restricts the flow approaching the holes, forcing it to flow co-current with the freestream, and (3) a plenum which forces the flow to approach the holes counter-current with the freestream. Short-hole (L/D = 2.3) and long-hole (L/D = 7.0) comparisons are made. The geometry has a single row of film cooling holes with 35°-inclined streamwise injection. The film cooling flow is supplied at the same temperature as that of the freestream for hole-exit measurements and 10°C above the freestream temperature for adiabatic effectiveness measurements, yielding density ratios in the range 0.96–1.0. Two coolant-to-freestream velocity ratios, 0.5 and 1.0, are investigated. The results document the effects of (1) supply plenum geometry, (2) velocity ratio, and (3) hole L/D.

Influence of Coolant Density on Turbine Blade Film-Cooling With Compound-Angle Shaped Holes

2012 ◽  
Author(s):  
Kevin Liu ◽  
Shang-Feng Yang ◽  
Je-Chin Han
Keyword(s):  
Film Cooling ◽  
Momentum Flux ◽  
Density Ratio ◽  
Flux Ratio ◽  
Suction Side ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Shaped Hole ◽  
Compound Angle

Adiabatic film-cooling effectiveness is examined systematically on a typical high pressure turbine blade by varying three critical flow parameters: coolant blowing ratio, coolant-to-mainstream density ratio, and freestream turbulence intensity. Three average coolant blowing ratios 1.0, 1.5, and 2.0; three coolant density ratios 1.0, 1.5, and 2.0; two turbulence intensities 4.2% and 10.5%, are chosen for this study. Conduction-free pressure sensitive paint (PSP) technique is used to measure film-cooling effectiveness. Three foreign gases — N2 for low density, CO2 for medium density, and a mixture of SF6 and Argon for high density are selected to study the effect of coolant density. The test blade features 45° compound-angle shaped holes on the suction side and pressure side, and 3 rows of 30° radial-angle cylindrical holes around the leading edge region. The inlet and the exit Mach number are 0.27 and 0.44, respectively. Reynolds number based on the exit velocity and blade axial chord length is 750,000. Results reveal that the PSP is a powerful technique capable of producing clear and detailed film effectiveness contours with diverse foreign gases. As blowing ratio exceeds the optimum value, it induces more mixing of coolant and mainstream. Thus film-cooling effectiveness reduces. Greater coolant-to-mainstream density ratio results in lower coolant-to-mainstream momentum and prevents coolant to lift-off; as a result, film-cooling increases. Higher freestream turbulence causes effectiveness to drop everywhere except in the region downstream of suction side. Results are also correlated with momentum flux ratio and compared with previous studies. It shows that compound shaped hole has the greatest optimum momentum flux ratio, and then followed by axial shaped hole, compound cylindrical hole, and axial cylindrical hole.

Film Cooling Effectiveness Distributions on a Flat Plate With a Double Hole Geometry Using PSP

2011 ◽  
Author(s):  
Lesley M. Wright ◽  
Evan L. Martin
Keyword(s):  
Flat Plate ◽  
Film Cooling ◽  
Surface Film ◽  
Density Ratio ◽  
Cooling Effectiveness ◽  
Freestream Velocity ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Blowing Ratio ◽  
Hole Geometry

Detailed film cooling effectiveness distributions are obtained on a flat plate using the pressure sensitive paint (PSP) technique. The effects of average blowing ratio (M = 0.25–1.0) and coolant – to – mainstream density ratio (DR = 1.0–1.4) are evaluated in a low speed wind tunnel with a freestream velocity of 8.5 m/s and a freestream turbulence intensity of 6.8%. The coolant – to – mainstream density ratio is varied by using either nitrogen (DR = 1.0) or argon (DR = 1.4) as the coolant gases. The double hole geometry consists of a row of simple angle (θ = 35°), cylindrical holes coupled with one row of compound angle holes (θ = 45°, β = 50°). With the selected geometry, the compound holes effectively weaken the counter rotating vortex pair formed within the traditional simple angle hole. Therefore, the surface film cooling effectiveness is increased compared to a single row of simple angle film cooling holes. While increasing the blowing ratio decreases the film cooling effectiveness, the severity of the film cooling effectiveness reduction is less than with the single row of holes.

Experimental Flow Field Investigations of Nozzle Film Cooling Scheme on a Flat Plate Using Stereo PIV

2013 ◽  
Author(s):  
Yingjie Zheng ◽  
Ibrahim Hassan
Keyword(s):  
Flow Field ◽  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Cylindrical Hole ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Field Investigations ◽  
Nozzle Hole

This paper presents experimental flow field investigations of a film cooling scheme, referred to as nozzle scheme, on a flat plate using stereo PIV. The nozzle scheme has a cylindrical hole and internal obstacles to change the velocity distribution near the hole exit and hence the jet-mainstream interaction. Counter-rotating vortex pair (CRVP) is known to be one of the detrimental effects that affect the film cooling effectiveness. Previous CFD simulations demonstrated nozzle hole’s capability of reducing CRVP strength and enhancing film cooling effectiveness in comparison with a normal cylindrical hole. The present study examines the nozzle hole flow filed experimentally at blowing ratio ranged from 0.5 to 2.0 and compares with cylindrical hole. The experiments were conducted in a low-speed wind tunnel with a mainstream Reynolds number of 115,000 and the density ratio was 1.0 during all the investigations. The experimental results show that nozzle hole reduces streamwise vorticity of CRVP by an average of 55% at low blowing ratio, and 34%–40% at high blowing ratios. The velocity field and vorticity field of nozzle jet are compared with cylindrical jet. The result reveals that the nozzle jet forms a round bulk in contrast to the kidney shape jet core in cylindrical hole case. In addition, it is found that CRVP strength may not be a primary contributor to the jet lift-off.

Adiabatic Film Cooling Effectiveness Measurements Throughout Multirow Film Cooling Arrays

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Greg Natsui ◽  
Zachary Little ◽  
Jayanta S. Kapat ◽  
Jason E. Dees
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
Density Ratio ◽  
Diameter Ratio ◽  
Test Surface ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
First Case ◽  
Lift Off

Adiabatic film cooling effectiveness measurements are obtained using pressure-sensitive paint (PSP) on a flat film cooled surface. The effects of blowing ratio and hole spacing are investigated for four multirow arrays comprised of eight rows containing 52 holes of 3.8 mm diameter with 20 deg inclination angles and hole length-to-diameter ratio of 11.2. The four arrays investigated have two different hole-to-hole spacings composed of cylindrical and diffuser holes. For the first case, lateral and streamwise pitches are 7.5 times the diameter. For the second case, pitch-to-diameter ratio is 14 in lateral direction and 10 in the streamwise direction. The holes are in a staggered arrangement. Adiabatic effectiveness measurements are taken for a blowing ratio range of 0.3–1.2 and a density ratio of 1.5, with CO2 injected as the coolant. A thorough boundary layer analysis is presented, and data were taken using hotwire anemometry with air injection, with boundary layer, and turbulence measurements taken at multiple locations in order to characterize the boundary layer. Local effectiveness, laterally averaged effectiveness, boundary layer thickness, momentum thickness, turbulence intensity, and turbulence length scale are presented. For the cylindrical holes, at the first row of injection, the film jets are still attached at a blowing ratio of 0.3. By a blowing ratio of 0.5, the jet is observed to lift off, and then impinge back onto the test surface. At a blowing ratio of 1.2, the jets lift off, but reattach much further downstream, spreading the coolant further along the test surface. A thorough uncertainty analysis has been conducted in order to fully understand the presented measurements and any shortcomings of the measurement technique. The maximum uncertainty of effectiveness and blowing ratio is 0.02 counts of effectiveness and 3%, respectively.

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