Uncertainty Quantification Analysis of Back Facing Steps Film Cooling Configurations

2018 ◽  
Author(s):  
Eiji Sakai ◽  
Meng Bai ◽  
Richard Ahlfeld ◽  
Francesco Montomoli
Keyword(s):  
Uncertainty Quantification ◽  
Film Cooling ◽  
Lateral Spreading ◽  
Step Height ◽  
Stream Velocity ◽  
Main Stream ◽  
Stochastic Variation ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole

This paper compares two back step film-cooling configurations under an uncertainty quantification framework. An important limit of such configurations is their reliability under geometrical variations, which is taken into account in this study. For the back step configurations, a straight and a curved step is used. Detached eddy simulations with k-ω turbulence model are performed using OpenFOAM ver. 4.0. The Reynolds number is based on the main stream velocity and film cooling hole diameter, d, and is Re = 15,300. The investigated step heights are 0.5d and 0.75d, and the blowing ratios, BR, are 0.5 and 1.0. The straight and the curved steps are found to enhance lateral spreading of coolant flow, resulting in higher film cooling effectiveness compared to the baseline case without the step at comparatively higher BR conditions. The curved step shows better performance than the straight one in particular from BR = 1.0 upwards with the step height of 0.5d. At lower BR with lower H/d, and at higher BR with higher H/d, deterministic simulations are not able to identify the best performer. However when the performance of the two configurations is evaluated considering the stochastic variation of step height and the cooling condition, the benefit of the curved step becomes clear. In particular, the curved step shows better mean performance and has a higher probability to achieve a better performance than the other one. The uncertainty in the film cooling effectiveness caused by the uncertainty of the step height and the BR is investigated using Sparse Approximation of Moment-Based Arbitrary polynomial chaos (SAMBA).

scholarly journals Adiabatic Wall Effectiveness Measurements of Film-Cooling Holes With Expanded Exits

1997 ◽  
Author(s):  
M. Gritsch ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Mach Number ◽  
Film Cooling ◽  
Thermal Protection ◽  
Lateral Spreading ◽  
Cylindrical Hole ◽  
Adiabatic Wall ◽  
Camera System ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole

This paper presents detailed measurements of the film-cooling effectiveness for three single, scaled-up film-cooling hole geometries. The hole geometries investigated include a cylindrical hole and two holes with a diffuser shaped exit portion (i.e. a fanshaped and a laidback fanshaped hole). The flow conditions considered are the crossflow Mach number at the hole entrance side (up to 0.6), the crossflow Mach number at the hole exit side (up to 1.2), and the blowing ratio (up to 2). The coolant-to-mainflow temperature ratio is kept constant at 0.54. The measurements are performed by means of an infrared camera system which provides a two-dimensional distribution of the film-cooling effectiveness in the nearfield of the cooling hole down to x/D = 10. As compared to the cylindrical hole, both expanded holes show significantly improved thermal protection of the surface downstream of the ejection location, particularly at high blowing ratios. The laidback fanshaped hole provides a better lateral spreading of the ejected coolant than the fanshaped hole which leads to higher laterally averaged film-cooling effectiveness. Coolant passage crossflow Mach number and orientation strongly affect the flowfield of the jet being ejected from the hole and, therefore, have an important impact on film-cooling performance.

Experimental Investigations on Aero-Thermal Interaction of Film Cooling Air Ejected From Multiple Shallow Angle Cooling Holes: Effect of Freestream Turbulence

2013 ◽  
Author(s):  
Kamil Abdullah ◽  
Ken-ichi Funazaki
Keyword(s):  
Flow Field ◽  
Film Cooling ◽  
Lateral Spreading ◽  
Test Model ◽  
Thermal Interaction ◽  
Freestream Turbulence ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Test Models ◽  
Cooling Hole

The objective of the present study is to investigate the aero-thermal interaction of the secondary air injected from multiple shallow angled film cooling holes. The focus is on the influence of freestream turbulence on the film cooling effectiveness and secondary flow field. For the experiments, infrared thermography and Laser Doppler Velocimetry (LDV) were employed. The experiments were conducted at a Reynolds number based on the hole diameter, ReD = 6200 at blowing ratio, BR = 1.0 and 2.0. Two flat plate test models; TMA and TMG, have been considered, which involved twenty cylindrical holes constituting a matrix composed of four rows with five holes in each row. The cooling holes for both test models were inclined at 20° in the streamwise direction with the lateral pitch, Pz = 6D for TMA and 3D for TMG. Two different freestream turbulence levels have been considered for both the aerodynamic and thermal investigations. The results of LDV show two distinct dynamics for each test model which influence the flow field differently. Consequently, the thermal field produced a distinctive film cooling effectiveness distribution of each test model. Higher freestream turbulence level enhances the mixing in the vicinity of the vortical structure thus deterring the film cooling effectiveness just downstream of the cooling hole but aids to lateral spreading of the coolant further downstream of the cooling hole, providing greater film effectiveness coverage.

Film Cooling Performance of the Embedded Holes in Trenches With Compound Angles

2010 ◽  
Author(s):  
Jia Li ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Film Cooling ◽  
Free Stream ◽  
Lateral Spreading ◽  
Stream Velocity ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Axial Ejection ◽  
Cooling Air ◽  
Compound Angle

Film cooling performance for a row of cylindrical holes can be enhanced by embedding the row in a suitable transverse slot. The compound angle of the holes can even more affects the cooling performance at downstream of the injections. In this study the cooling performance of the embedded holes in transverse trenches with different compound angles are explored both by pressure sensitive paint (PSP) experiment technology and RANS algorithm. A film cooling test rig was built up in Tsinghua University, which contains an accelerating free stream section to model the surface of a turbine airfoil. The PSP technology is applied in the tests to obtain the film cooling effectiveness. The experiments are performed for a single mainstream Reynolds number based on free-stream velocity and film hole diameter of 4000. Considering three compound angles, 0°, 45° and 90°, and with or without transverse trenches. All six cases are tested at three different coolant-to-mainstream blowing ratios of 0.5, 1.0, and 1.5. Meanwhile, the test cases are numerically simulated based on RANS with k-ε turbulence model to show the detail of the flow patterns. Both the experimental and numerical results show that the adiabatic film effectiveness is relative insensitive to the blowing ratio in the case of holes with trenches. Moreover, it could be improved with a more uniform spanwise distribution. It is mainly due to the blockage of the ejected coolant at the downstream edge of the trench, which forces a portion of the cooling air to spread laterally within the trench prior to issuing onto the upper surface. Both 45° and 90° compound angles can further enhance the film cooling effectiveness over the axial ejection, this is mainly due to the lateral momentum component of the ejection. A lateral passage vortex is formed inside the trench which strengthens the lateral spreading of the jets. The 45° compound angle gives a higher film cooling effectiveness overall.

Adiabatic Wall Effectiveness Measurements of Film-Cooling Holes With Expanded Exits

1998 ◽  
Vol 120 (3) ◽  
pp. 549-556 ◽  
Author(s):  
M. Gritsch ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Mach Number ◽  
Film Cooling ◽  
Thermal Protection ◽  
Lateral Spreading ◽  
Cylindrical Hole ◽  
Camera System ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
Shaped Hole

This paper presents detailed measurements of the film-cooling effectiveness for three single, scaled-up film-cooling hole geometries. The hole geometries investigated include a cylindrical hole and two holes with a diffuser-shaped exit portion (i.e., a fan-shaped and a laid-back fan-shaped hole). The flow conditions considered are the crossflow Mach number at the hole entrance side (up to 0.6), the crossflow Mach number at the hole exit side (up to 1.2), and the blowing ratio (up to 2). The coolant-to-mainflow temperature ratio is kept constant at 0.54. The measurements are performed by means of an infrared camera system, which provides a two-dimensional distribution of the film-cooling effectiveness in the near field of the cooling hole down to x/D = 10. As compared to the cylindrical hole, both expanded holes show significantly improved thermal protection of the surface downstream of the ejection location, particularly at high blowing ratios. The laidback fan-shaped hole provides a better lateral spreading of the ejected coolant than the fan-shaped hole, which leads to higher laterally averaged film-cooling effectiveness. Coolant passage cross-flow Mach number and orientation strongly affect the flowfield of the jet being ejected from the hole and, therefore, have an important impact on film-cooling performance.

scholarly journals Influence of Internal Flow on Film Cooling Effectiveness

1999 ◽  
Author(s):  
Günter Wilfert ◽  
Stefan Wolff
Keyword(s):  
Film Cooling ◽  
Cross Flow ◽  
Vortex Generator ◽  
Internal Flow ◽  
Main Stream ◽  
Thermochromic Liquid Crystal ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
Inlet Conditions

Film cooling experiments were conducted to investigate the effects of internal flow conditions and plenum geometry on the film cooling effectiveness. The film cooling measurements show a strong influence of the coolant inlet conditions on film cooling performance. The present experiments were carried out on a flat plate with a row of cylindrical holes oriented at 30 degrees with respect to a constant-velocity external flow, systematically varying the plenum geometry and blowing rates (0.5≤M≤1.25). Adiabatic film cooling measurements using the multiple narrow-banded Thermochromic Liquid Crystal-technique (TLC) were carried out simulating a flow parallel to the main stream flow with and without cross flow at the coolant hole entry compared with a standard plenum configuration. An impingement in front of the cooling hole entry with and without cross flow was also investigated. For all parallel flow configurations ribs were installed at the top and bottom coolant channel wall. As the hole length-to-diameter ratio has an influence on the film cooling effectiveness, the wall thickness has also been varied. In order to optimise the benefit of the geometry effects with ribs, a vortex generator was designed and tested. Results from these experiments show in a region 5≤X/D≤80 downstream of the coolant injection location differences in adiabatic film cooling effectiveness between +5% and +65% compared with a standard plenum configuration.

Downstream Vortex Generators to Enhance Film-Cooling Effectiveness

2020 ◽  
Author(s):  
Chien-Shing Lee ◽  
Kenneth M. Bryden ◽  
Tom I-P. Shih
Keyword(s):  
Film Cooling ◽  
Cfd Simulation ◽  
Lateral Spreading ◽  
Vortex Generators ◽  
Shape Parameters ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Vortical Structures ◽  
Simulation Based ◽  
Cooling Hole

Abstract CFD simulation based on steady RANS were performed to assess the usefulness of adding a pair of “downstream” vortex generators (VGs) to improve the effectiveness of film cooling a flat plate through one row of inclined holes. Each VG in the pair is a rectangular plate with span S, chord C, and thickness t that is oriented at +45 or −45 degrees with respect to a plane that passes through the center of the film-cooling hole and placed at a distance D downstream of the hole, where D is the hole diameter. The separation between the VGs in the pair is smallest at their leading edges (0.72D) so that the VGs form a V-shape. Parameters studied include: S/D = 0.0, 0.25, 0.5, 1.0; C/D = 0.0, 0.2, 0.4; and blowing ratios of BR = 0.5, 1.0, and 2.0. Results obtained show “downstream” VGs can significantly increase lateral spreading of the film-cooling jet and thereby greatly improve film-cooling effectiveness. Results obtained also show the effects of S/D, C/D, and BR on adiabatic effectiveness, pressure loss, and vortical structures formed.

Study of an Optimized Trench Film Cooling Configuration Using Scale Adaptive Simulation and Infrared Thermography

2014 ◽  
Author(s):  
Peter Schreivogel ◽  
Bernhard Kröss ◽  
Michael Pfitzner
Keyword(s):  
Infrared Thermography ◽  
Film Cooling ◽  
Lateral Spreading ◽  
Spatial Average ◽  
Hexahedral Mesh ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
Cooling Air ◽  
Trench Width

In the present paper, a narrow, angled trench layout is proposed and numerically optimized. In the optimization process the trench width and depth as well as the edge contour were varied. For each design, the optimizer automatically created the geometry and a structured hexahedral mesh. Then, six blowing ratios from M = 1 to 6 were evaluated based on RANS computations. The spatial average and the standard deviation of the film cooling effectiveness served as objective variables for the optimizer. One novel configuration was studied in more detail and compared to a trench with a depth of 0.75 hole diameters D and a cooling hole angle of α = 30 deg. For both configurations unsteady simulations using the hybrid SAS turbulence model were carried out and validated against infrared thermography measurements of the adiabatic film cooling effectiveness. The match between SAS and experiment is improved compared to RANS computations with the realizable k-ε-model. The optimized configuration yields a significant improvement of the film cooling performance. The swept shape of the trench promotes the lateral spreading of the coolant, while the decreased trench width reduces the mixing of cooling air and hot free-stream gas in the region between the cooling holes.

scholarly journals Effect of main stream turbulence on the film cooling effectiveness of a circular and a fan-shaped film cooling hole

2020 ◽  
Vol 7 (4) ◽  
pp. 20-00176-20-00176
Author(s):  
Kenichiro TAKEISHI ◽  
Yutaka ODA ◽  
Shohei MORI ◽  
Robert KREWINKEL
Keyword(s):  
Film Cooling ◽  
Main Stream ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole

Effects of Streamwise Pressure Gradient and Convex Curvature on Film Cooling Effectiveness

2014 ◽  
Author(s):  
Yanmin Qin ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Pressure Gradient ◽  
Film Cooling ◽  
Main Stream ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Flat Wall ◽  
Favorable Pressure Gradient ◽  
Convex Wall ◽  
Cooling Hole ◽  
Streamwise Pressure Gradient

The effects of streamwise pressure gradient and convex wall curvature on film cooling effectiveness are investigated using PSP technology. Film cooling under five different main stream pressure gradients on both flat and convex wall is examined. The cooling hole has an inclined angle of 30° and no compound angle with a hole length of L/D = 4. The convex wall has a constant radius of r/D = 30. Numerical simulations are also conducted to gain more flow field information. For the flat wall case, film cooling effectiveness is higher with greater favorable pressure gradient for low blowing ratios. While for high blowing ratio cases, cooling effectiveness doesn’t vary much with streamwise pressure gradient. Film cooling effectiveness is increased significantly on convex wall compared with flat wall for M<0.5. The effect of streamwise pressure gradient is greater on convex wall and becomes unneglectable. The influence of streamwise pressure gradient and convex wall curvature is conjugated and should be discussed together. For all blowing ratios, film cooling effectiveness is apparently higher for larger mainstream favorable pressure gradient on convex wall.

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