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.

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.

Effect of the In-Hole Vortical Structures on the Cylindrical-Hole Film-Cooling Effectiveness

2020 ◽  
Author(s):  
Shubham Agarwal ◽  
Laurent Gicquel ◽  
Florent Duchaine ◽  
Nicolas Odier ◽  
Jérôme Dombard
Keyword(s):  
Film Cooling ◽  
Turbine Blades ◽  
Hairpin Vortices ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Vortical Structures ◽  
Blowing Ratio ◽  
Eddy Simulation ◽  
Control Film ◽  
Cooling Hole

Abstract Understanding the flow from a cooling hole is very important to be able to properly control film cooling of turbine blades. For this purpose, large eddy simulation (LES) investigation of the flow inside a cylindrical film cooling hole is presented in this paper. Two different geometries, with different hole metering lengths, are investigated at a blowing ratio of 0.5. The main flow structure in the hole are the hairpin vortices that originate from a shear layer formed due to flow separation near the hole entry. The comparison of these hairpin vortices in the two cases with different hole metering length is presented in detail. The results show that in case of the hole with longer length the hairpin vortices dissociate within the hole itself. In such a case a uniform flow is seen at the hole exit. However, when the hole length is significantly decreased, it is shown that these vortices exit the hole and effect the vortex structures outside the hole, thereby accounting for the reduction in film cooling effectiveness. Overall, these results bring forth one other major reason for the reduction in film cooling effectiveness with reduction in hole length, i.e. the exit of in-hole hairpin vortices into the crossflow.

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.

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.

Film Cooling Effectiveness From a Single Scaled-Up Fan-Shaped Hole: A CFD Simulation of Adiabatic and Conjugate Heat Transfer Models

2005 ◽  
Author(s):  
Mahmood Silieti ◽  
Alain J. Kassab ◽  
Eduardo Divo
Keyword(s):  
Heat Transfer ◽  
Turbulence Model ◽  
Film Cooling ◽  
Conjugate Heat Transfer ◽  
Cfd Simulation ◽  
Temperature Fields ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Hole ◽  
Transfer Models

This paper documents a computational investigation of the film cooling effectiveness of a 3-D gas turbine endwall with one fan-shaped cooling hole. The simulations were performed for adiabatic and conjugate heat transfer models. Turbulence closure was investigated using three different turbulence models; the realizable k-ε model, the SST k-ω model, as well as the v2–f turbulence model. Results were obtained for a blowing ratio of one, and a coolant-to-mainflow temperature ratio of 0.54. The simulations used a dense, high quality, O-type, hexahedral grid with three different schemes of meshing for the cooling hole: hexahedral-, hybrid-, and tetrahedral-topology grid. The computed flow/temperature fields are presented, in addition to local, two-dimensional distribution of film cooling effectiveness for the adiabatic and conjugate cases. Results are compared to experimental data in terms of centerline film cooling effectiveness downstream cooling-hole, the predictions with realizable k-ε turbulence model exhibited the best agreement especially in the region for (2 ≤ x/D ≤ 6). Also, the results show the effect of the conjugate heat transfer on the temperature (effectiveness) field in the film cooling hole region and, thus, the additional heating up of the cooling jet itself.

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).

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.

Investigations of improved cooling effectiveness for ramp film cooling with compound angle film cooling jets

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Krishna Anand Vasu Devan Nair Girija Kumari ◽  
Parammasivam Kanjikoil Mahali
Keyword(s):  
Film Cooling ◽  
Flat Surface ◽  
Flow Characteristics ◽  
Test Surface ◽  
Cooling Effectiveness ◽  
Content Type ◽  
Film Cooling Effectiveness ◽  
Ramp Test ◽  
Cooling Hole ◽  
Compound Angle

Purpose This paper aims to investigate the film cooling effectiveness (FCE) and mixing flow characteristics of the flat surface ramp model integrated with a compound angled film cooling jet. Design/methodology/approach Three-dimensional numerical simulation is performed on a flat surface ramp model with Reynolds Averaged Navier-Stokes approach using a finite volume solver. The tested model has a fixed ramp angle of 24° and a ramp width of two times the diameter of the film cooling hole. The coolant air is injected at 30° along the freestream direction. Three different film hole compound angles oriented to freestream direction at 0°, 90° and 180° were investigated for their performance on-ramp film cooling. The tested blowing ratios (BRs) are in the range of 0.9–2.0. Findings The film hole oriented at a compound angle of 180° has improved the area-averaged FCE on the ramp test surface by 86.74% at a mid-BR of 1.4% and 318.75% at higher BRs of 2.0. The 180° film hole compound angle has also produced higher local and spanwise averaged FCE on the ramp test surface. Originality/value According to the authors’ knowledge, this study is the first of its kind to investigate the ramp film cooling with a compound angle film cooling hole. The improved ramp model with a 180° film hole compound angle can be effectively applied for the end-wall surfaces of gas turbine film cooling.

Rib Turbulator Effects on Crossflow-Fed Shaped Film Cooling Holes

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Dale W. Fox ◽  
Fraser B. Jones ◽  
John W. McClintic ◽  
David G. Bogard ◽  
Thomas E. Dyson ◽  
...  
Keyword(s):  
Film Cooling ◽  
Velocity Ratio ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Smooth Channel ◽  
Cooling Hole ◽  
Film Cooling Holes ◽  
Inlet Position ◽  
The Impact

Most studies of turbine airfoil film cooling in laboratory test facilities have used relatively large plenums to feed flow into the coolant holes. However, a more realistic inlet condition for the film cooling holes is a relatively small channel. Previous studies have shown that the film cooling performance is significantly degraded when fed by perpendicular internal crossflow in a smooth channel. In this study, angled rib turbulators were installed in two geometric configurations inside the internal crossflow channel, at 45 deg and 135 deg, to assess the impact on film cooling effectiveness. Film cooling hole inlets were positioned in both prerib and postrib locations to test the effect of hole inlet position on film cooling performance. A test was performed independently varying channel velocity ratio and jet to mainstream velocity ratio. These results were compared to the film cooling performance of previously measured shaped holes fed by a smooth internal channel. The film cooling hole discharge coefficients and channel friction factors were also measured for both rib configurations with varying channel and inlet velocity ratios. Spatially averaged film cooling effectiveness is largely similar to the holes fed by the smooth internal crossflow channel, but hole-to-hole variation due to inlet position was observed.

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