Effect of Vortex Generators on Film Cooling Effectiveness

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
S. Sarkar ◽  
Ganesh Ranakoti
Keyword(s):  
Film Cooling ◽  
Near Field ◽  
Density Ratio ◽  
Protective Layer ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Cooling Effectiveness ◽  
Freestream Velocity ◽  
Film Cooling Effectiveness ◽  
Lift Off

Film cooling is often adopted, where coolant jets are ejected to form a protective layer on the surface against the hot combustor gases. The bending of jets in crossflow results in counter rotating vortex pair (CRVP), which is a cause for high jet lift-off and poor film cooling effectiveness in the near field. There are efforts to mitigate this detrimental effect of CRVP, and thus, to improve the film cooling performance. In the present study, the effects of both downwash and upwash type of vortex generator (VG) on film cooling are numerically analyzed. A series of discrete holes on a flat plate with 35 deg streamwise orientation and connected to a common delivery plenum is used here, where the vortex generators are placed upstream of the holes. The blowing ratio and the density ratio are considered as 0.5 and 1.2, respectively, with a Reynolds number based on freestream velocity and diameter of hole being 15,885. The computations are performed by ANSYS fluent 13.0 using k–ε realizable turbulence model. The results show that vortices generated by downwash vortex generator (DWVG) counteracts the effect of CRVP preventing the jet lift-off, which results in increased effectiveness in streamwise as well as in spanwise directions. However, upwash vortex generator (UWVG) augments the effect of CRVP, resulting in poor performance of film cooling.

Effect of Vortex Generators on Film Cooling Effectiveness

2015 ◽  
Author(s):  
S. Sarkar ◽  
Ganesh Ranakoti
Keyword(s):  
Film Cooling ◽  
Near Field ◽  
Density Ratio ◽  
Protective Layer ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Stream Velocity ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Lift Off

Film cooling is often adopted, where coolant jets are ejected to form a protective layer on the surface against the hot combustor gases. The bending of jets in crossflow results in Counter Rotating Vortex Pair (CRVP), which is a cause for high jet lift-off and poor film cooling effectiveness in the near field. There are efforts to mitigate this detrimental effect of CRVP and thus to improve the film cooling performance. In the present study, the effects of both downwash and upwash type of vortex generator on film cooling are numerically analysed. A series of discrete holes on a flat plate with 35° streamwise orientation and connected to a common delivery plenum is used here, where the vortex generators are placed upstream of the holes. The blowing ratio and the density ratio are considered as 0.5 and 1.2 respectively with a Reynolds number based on free-stream velocity and diameter of hole being 15885. The computations are performed by ANSYS Fluent 13.0 using k-ε realizable turbulence model. The results show that vortices generated by downwash vortex generator (DWVG) counteracts the effect of CRVP preventing the jet lift-off, which results in increased effectiveness in streamwise as well as in spanwise directions. However, upwash vortex generator (UWVG) augments the effect of CRVP, resulting in poor performance of film cooling.

Turbine Vane Endwall Film Cooling From Cross-Row Configuration With Simulated Upstream Leakage Flow

2017 ◽  
Author(s):  
Nafiz H. K. Chowdhury ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han ◽  
Luzeng Zhang ◽  
Hee-Koo Moon
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Companion Paper ◽  
Leakage Flow ◽  
Blow Down ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Free Stream Turbulence ◽  
Lift Off ◽  
Endwall Cooling

The performance of a full coverage film cooling configuration called cross-row (CR) configuration including upstream inlet leakage flow was studied by measuring the adiabatic film cooling effectiveness distribution using PSP technique. Experiments were conducted in a blow-down wind tunnel cascade facility at the isentropic exit Mach number of 0.5 corresponding to inlet Reynolds number of 3.8 × 105, based on axial chord length. A free-stream turbulence level was generated as high as 19% with a length scale of 1.7 cm at the inlet. The results are presented as two-dimensional adiabatic film cooling effectiveness distributions on the endwall surface with corresponding spanwise averaged distributions. The focus of this study is to investigate the effect of coolant-to-mainstream mass flow ratio (MFR) and density ratio (DR) on the proposed endwall cooling design. Initially, increased MFR for the endwall cooling and upstream leakage levels up the local adiabatic cooling effectiveness and yields relatively uniform coverage on the entire endwall. However, in either case, highest MFR does not provide any improvement as endwall cooling suffered from the jet lift-off and leakage coolant coverage restricted by the downstream near-wall flow field. Results also indicated a density ratio of 1.5 provides the best performance. Finally, a fair comparison is made with another design called axial-row (AR) configuration from a companion paper.

Unsteady Wake and Coolant Density Effects on Turbine Blade Film Cooling Using PSP Technique

2010 ◽  
Author(s):  
Akhilesh P. Rallabandi ◽  
Shiou-Jiuan Li ◽  
Je-Chin Han
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Suction Side ◽  
Suction Surface ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Unsteady Wake ◽  
Lift Off ◽  
Film Cooling Holes

The effect of an unsteady stator wake (simulated by wake rods mounted on a spoke wheel wake generator) on the modeled rotor blade is studied using the Pressure Sensitive Paint (PSP) mass transfer analogy method. Emphasis of the current study is on the mid-span region of the blade. The flow is in the low Mach number (incompressible) regime. The suction (convex) side has simple angled cylindrical film-cooling holes; the pressure (concave) side has compound angled cylindrical film cooling holes. The blade also has radial shower-head leading edge film cooling holes. Strouhal numbers studied range from 0 to 0.36; the exit Reynolds Number based on the axial chord is 530,000. Blowing ratios range from 0.5 to 2.0 on the suction side; 0.5 to 4.0 on the pressure side. Density ratios studied range from 1.0 to 2.5, to simulate actual engine conditions. The convex suction surface experiences film-cooling jet lift-off at higher blowing ratios, resulting in low effectiveness values. The film coolant is found to reattach downstream on the concave pressure surface, increasing effectiveness at higher blowing ratios. Results show deterioration in film cooling effectiveness due to increased local turbulence caused by the unsteady wake, especially on the suction side. Results also show a monotonic increase in film-cooling effectiveness on increasing the coolant to mainstream density ratio.

Combined Effects of Freestream Pressure Gradient and Density Ratio on the Film Cooling Effectiveness of Round and Shaped Holes on a Flat Plate

2016 ◽  
Author(s):  
Kyle R. Vinton ◽  
Travis B. Watson ◽  
Lesley M. Wright ◽  
Daniel C. Crites ◽  
Mark C. Morris ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Flat Plate ◽  
Film Cooling ◽  
Density Ratio ◽  
Round Hole ◽  
Combined Effects ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Lift Off

The combined effects of a favorable, mainstream pressure gradient and coolant-to-mainstream density ratio have been investigated. Detailed film cooling effectiveness distributions have been obtained on a flat plate with either cylindrical (θ = 30°) or laidback, fan-shaped holes (θ = 30°, β = γ = 10°) using the pressure sensitive paint (PSP) technique. In a low speed wind tunnel, both non-accelerating and accelerating flows were considered while the density ratio varied from 1–4. In addition, the effect of blowing ratio was considered, with this ratio varying from 0.5 to 1.5. The film produced by the shaped hole outperformed the round hole under the presence of a favorable pressure gradient for all blowing and density ratios. At the lowest blowing ratio, in the absence of freestream acceleration, the round holes outperformed the shaped holes. However, as the blowing ratio increases, the shaped holes prevent lift-off of the coolant and offer enhanced protection. The effectiveness afforded by both the cylindrical and shaped holes, with and without freestream acceleration, increased with density ratio.

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.

Improved Film Cooling Effectiveness by Placing a Vortex Generator Downstream of Each Hole

2008 ◽  
Author(s):  
David L. Rigby ◽  
James D. Heidmann
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Three Dimensional ◽  
Vortex Generator ◽  
Vortex Pair ◽  
Navier Stokes ◽  
Dramatic Improvement ◽  
Freestream Velocity ◽  
Film Cooling Effectiveness ◽  
Cooling Hole

Calculations are presented demonstrating the effect of placing a delta vortex generator downstream of a film cooling hole. The effects of blowing ratio, density ratio, and spanwise pitch are included in the study. Flow over a flat plate with film cooling holes oriented at a 30 degree angle was investigated. The Reynolds numbers based on the freestream velocity and the hole diameter was 11,300. The simulation was performed using the Glenn-HT code, a full three-dimensional Navier-Stokes solver using the Wilcox k-ω turbulence model. A structured multi-block grid was used with approximately one million cells, and average y+ values on the order of unity. Local and span averaged effectiveness are presented. Analysis and visualization of the flow are presented as well as a discussion on the mechanisms which contribute to the dramatic improvement in effectiveness. The results demonstrate that the delta vortex generator was able to annihilate the up-wash vortex pair produced by the film hole and produce a down-wash pair downstream.

Improved Film Cooling Effectiveness With a Round Film Cooling Hole Embedded in a Contoured Crater

2014 ◽  
Author(s):  
Prasad Kalghatgi ◽  
Sumanta Acharya
Keyword(s):  
Film Cooling ◽  
Free Stream ◽  
Near Field ◽  
Density Ratio ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Field Development ◽  
Eddy Simulation ◽  
Baseline Case ◽  
Cooling Hole

Studies of film cooling holes embedded in craters and trenches have shown significant improvements in the film cooling performance. In this paper a new design of a round film cooling hole embedded in a contoured crater is proposed for improved film cooling effectiveness over existing crater designs. The proposed design of the contour aims to generate a pair of vortices that counter and diminish the near-field development of the main kidney-pair vortex generated by the flm cooling jet. With a weakened kidney-pair vortex, the coolant jet is expected to stay closer to the wall, reduce mixing, and therefore increase cooling effectiveness. In the present study, the performance of the proposed contoured crater design is evaluated for depth between 0.2D and 0.75D. A round film cooling hole with a 35° inclined short delivery tube (l/D = 1.75), free stream Reynolds number ReD = 16000 and density ratio of coolant to free stream fluid ρj/ρ∞ = 2.0 is used as the baseline case. Hydrodynamic and thermal fields for all cases are investigated numerically using large eddy simulation technique. The baseline case results are validated with published experimental data. The performance of the new crater design for various crater depths and blowing ratios are compared with the baseline case. Results are also compared with other reported crater designs with similar flow conditions and crater depth. Performance improvement in cooling effectiveness of over 100% of the corresponding baseline case is observed for the contoured crater.

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.

Improved Film Cooling Effectiveness With a Round Film Cooling Hole Embedded in a Contoured Crater

2015 ◽  
Vol 137 (10) ◽  
Author(s):  
Prasad Kalghatgi ◽  
Sumanta Acharya
Keyword(s):  
Film Cooling ◽  
Near Field ◽  
Density Ratio ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Field Development ◽  
Eddy Simulation ◽  
Baseline Case ◽  
Cooling Hole ◽  
Film Cooling Holes

Studies of film cooling holes embedded in craters and trenches have shown significant improvements in the film cooling performance. In this paper, a new design of a round film cooling hole embedded in a contoured crater is proposed for improved film cooling effectiveness over existing crater designs. The proposed design of the contour aims to generate a pair of vortices that counter and diminish the near-field development of the main kidney-pair vortex generated by the film cooling jet. With a weakened kidney-pair vortex, the coolant jet is expected to stay closer to the wall, reduce mixing, and therefore increase cooling effectiveness. In the present study, the performance of the proposed contoured crater design is evaluated for depth between 0.2D and 0.75D. A round film cooling hole with a 35 deg inclined short delivery tube (l/D = 1.75), freestream Reynolds number ReD = 16,000, and density ratio of coolant to freestream fluid ρj/ρ∞ = 2.0 is used as the baseline case. Hydrodynamic and thermal fields for all cases are investigated numerically using large eddy simulation (LES) technique. The baseline case results are validated with published experimental data. The performance of the new crater design for various crater depths and blowing ratios are compared with the baseline case. Results are also compared with other reported crater designs with similar flow conditions and crater depth. Performance improvement in cooling effectiveness of over 100% of the corresponding baseline case is observed for the contoured crater.

A Comparative Study of Film Cooling Effectiveness on a Flat Plate With Adiabatic and Conjugate Conditions for Different Hole Shapes

2012 ◽  
Author(s):  
P. M. Dileep Chandran ◽  
Paresh Halder ◽  
Rajesh Kumar Panda ◽  
B. V. S. S. S. Prasad
Keyword(s):  
Film Cooling ◽  
Computational Study ◽  
Density Ratio ◽  
Cross Flow ◽  
Complex Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Significant Difference ◽  
Sst Turbulence Model ◽  
Lift Off

A computational study is carried out for comparison of the effectiveness of film cooling through holes of different shapes: cylindrical, shaped, trenched cylindrical and trenched shaped hole. Both adiabatic and conjugate wall thermal condition with various blowing ratios (0.6 to 1.4) are considered for the investigation. The coolant-to-mainstream density ratio and temperature ratio are maintained at 1.6 and 0.625 respectively. The κ-ω SST turbulence model is used for computation. The complex flow structures within the film hole, the exit and in the interaction zone of jet with cross flow are reported. Among the configurations studied, the shaped and trenched shaped holes have shown smaller jet lift off and uniform coolant coverage in both lateral and streamwise directions. Further, the results showed a significant difference in the indicated values of centerline surface temperature and effectiveness with the adiabatic and the conjugate conditions; the conjugate values being much lower but more uniform.

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