Anti-vortex Hole Research Articles

Experimental optimization of butterfly-shaped film cooling hole configuration with a 30 degree injection angle

Film cooling is one of the external cooling techniques that is widely applied to the hot-gas path components of a gas turbine, forming a thin film of a coolant on the surface to prevent the direct convective heat transfer between combustion gas and components. The film cooling effectiveness (FCE) is significantly influenced by the geometry of the injection hole. Therefore, it is important to adjust the shape parameters in order to derive the optimal hole configuration under given flow conditions. In a previous study, a butterfly-shaped film cooling hole configuration (BSHC), which combines the advantages of fan-shaped holes and anti-vortex holes, was proposed. In this study, an investigation into the optimal shape design of the BSHC was performed using the design of experiments. The forward expansion angle, lateral expansion angle, and twisted angle were defined as design variables. Before the optimization, the effect of each design variable on local and averaged FCE was analysed. Generally, a high FCE could be obtained when the forward expansion angle was small within a range of 7⁰ - 15⁰. However, at high blowing ratios, high effectiveness was also observed even with a large forward expansion angle. Both the lateral expansion angle and the twisted angle had high FCE near the centre point, 11⁰ and 20⁰, respectively. The response surface of the overall averaged FCE was predicted using the Kriging model. The optimized BSHC under a density ratio of 2.0 and blowing ratio of 2.0 was determined and named OPT BSHC. The OPT BSHC showed 8.6 % and 10.5 % higher FCE respectively, compared to two types of the optimized fan-shaped holes that were optimized under the same conditions.

Investigation and numerical simulation on film cooling performance with an anti-vortex hole design: Influences of diameter ratio

This paper extends the development of film cooling for application to gas turbines. Three diameter ratios of secondary hole to primary hole (0.3, 0.5 and 0.7) are constructed in an anti-vortex hole design. Film cooling effectiveness values and heat transfer coefficients are measured by the Thermochromic Liquid Crystal technique. In-flow temperature fields over downstream planes oriented normal to the main flow are measured by traversing a thermocouple. Numerical simulations are made to compute details of the flow structure to describe underlying mechanisms. Three coolant-to-mainstream blowing ratios (0.5, 1.0 and 1.5) and two coolant-to-mainstream mass flow ratios (3.43% and 5.15%) are tested. The anti-vortex hole design reduces the deleterious effects of the kidney vortex pair generated at the emersion point of the coolant jet into the passage, enlarges the film coverage, and finally improves film cooling effectiveness. The anti-vortex hole with larger secondary holes usually provides higher film cooling effectiveness.

A numerical study of anti-vortex film-cooling holes designs in a 1-1/2 turbine stage using LES

The primary focus of the present study is to investigate the impact of anti-vortex holes design on the film-cooling performance in a film-cooled rotor blade model using the large eddy simulation method (LES). One row of the film holes was positioned on the pressure surface of the rotor blade. This row had three cylindrical holes (the main hole in the present study) with a diameter (D) of 4 mm and a tangential injection angle of 28 deg. Each main hole supplemented with the addition of two symmetrical side holes (anti-vortex holes), which branch out from the same main hole. Three positions for the anti-vortex side holes were considered; namely: upstream to the outlet of the main hole; in line with the main hole; and downstream of the main hole. The Reynolds number was fixed at Re = 1.92 × 105 and the speed of the rotor blade was taken to be 1800 rpm. The blowing ratio varied from 1.0 to 5.0 and the density ratio of coolant to mainstream was 2.0. Compared to the base hole, the film cooling performance of the all anti-vortex cases showed obvious improvement at all blowing ratios. The middle stream side holes and downstream side holes each demonstrated good film cooling performance at all blowing ratios, while the upstream side holes perform well only at a lower blowing ratio. The presence of side holes can restrain the CRVP (counter rotating vortex pairs) intensity of the main hole and reduce the coolant lift-off, improving the film coverage and film cooling effectiveness. The downstream side holes can perform better in reducing the CRVP intensity.

Effect of film hole geometry and blowing ratio on film cooling performance

In this paper, four kinds of film holes (cylindrical hole, fan-shaped hole, anti-vortex hole and sister hole) are experimentally and numerically studied to investigate the effect of hole geometry and blowing ratio on film cooling performance and flow structure. The blowing ratio ranges from 0.3 to 2.0, the density ratio is 1.065 and the mainstream Reynolds number is 38664. In the experiment, the steady-state Thermochromic Liquid Crystal (TLC) is applied to obtain the film cooling effectiveness. The numerical investigation is performed to analyze the flow structure and counter-rotating vortex pair (CRVP) intensity. Experimental results show that the sister hole demonstrates best cooling performance with blowing ratio from 0.3 to 1.5. The sister hole provides better cooling performance than anti-vortex hole. While the fan-shaped hole performs better at high blowing ratios and it achieves best at blowing ratio of 2.0. Numerical simulation indicates that for the anti-vortex hole and sister hole, the application of side holes can decrease the main hole CRVP intensity and weaken the mixing between the main hole CRVP and mainstream, which increases cooling performance. The coolant interaction between side holes and main hole of the sister hole is stronger than that of the anti-vortex hole.

Film-Cooling Effectiveness of Antivortex Holes at Three Different Mainstream Turbulence Levels

The effects of mainstream turbulence intensity on the film-cooling effectiveness of antivortex film-cooling holes were experimentally investigated. Four film-cooling hole configurations and three mainstream turbulence intensities (1, 6.5, and 16) were tested. The primary film-cooling hole had a 30 deg angle with respect to the mainstream flow, and the angles between the primary and auxiliary holes of the antivortex holes were 0, 15, and 30 deg, respectively. The film-cooling effectiveness was measured using pressure-sensitive paint technique. The particle image velocimetry measurement results showed that the coolant from the antivortex film-cooling hole stayed closer to the endwall than that for the cylindrical hole case. The film-cooling effectiveness for the antivortex hole cases was higher than that for the cylindrical hole case for all blowing ratios. For the antivortex hole cases, the coolant-covered area generally increased as the blowing ratio increased. For the high mainstream turbulence intensity case, the higher blowing ratio cases showed greater film-cooling effectiveness due to the dragdown of the coolant. Among the tested configurations, the 15 deg antivortex hole case showed the best film-cooling performance at all blowing ratios and turbulence intensities.

Film Cooling Performance of Tripod Antivortex Injection Holes Over the Pressure and Suction Surfaces of a Nozzle Guide Vane

Film cooling performance of the antivortex (AV) hole has been well documented for a flat plate. The goal of this study is to evaluate the same over an airfoil at three different locations: leading edge suction and pressure surface and midchord suction surface. The airfoil is a scaled up first stage vane from GE E3 engine and is mounted on a low-speed linear cascade wind tunnel. Steady-state infrared (IR) technique was employed to measure the adiabatic film cooling effectiveness. The study has been divided into two parts: the initial part focuses on the performance of the antivortex tripod hole compared to the cylindrical (CY) hole on the leading edge. Effects of blowing ratio (BR) and density ratio (DR) on the performance of cooling holes are studied here. Results show that the tripod hole clearly provides higher film cooling effectiveness than the baseline cylindrical hole case with overall reduced coolant usage on the both pressure and suction sides of the airfoil. The second part of the study focuses on evaluating the performance on the midchord suction surface. While the hole designs studied in the first part were retained as baseline cases, two additional geometries were also tested. These include cylindrical and tripod holes with shaped (SH) exits. Film cooling effectiveness was found at four different blowing ratios. 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.

Numerical Study on the Effects of Freestream Turbulence on Antivortex Film Cooling Design at High Blowing Ratio

An advanced, high-effectiveness film cooling design, the antivortex hole (AVH) has been investigated by several research groups and shown to mitigate or counter the vorticity generated by conventional holes and increase film effectiveness at high blowing ratios and low freestream turbulence levels. The effects of increased turbulence on an AVH geometry were previously investigated in a preliminary steady computational fluid dynamics (CFD) study by Hunley et al. on the film effectiveness and net heat flux reduction (NHFR) at high blowing ratio. The current paper presents the results of an extended numerical parametric study, which attempts to separate the effects of turbulence intensity and length scale on film cooling performance of the AVH concept at high blowing ratio (2.0) and density ratio (2.0). In this extended study, steady Reynolds-averaged Navier–Stokes (RANS) analysis was performed with turbulence intensities of 5, 10, and 20% and length scales based on cooling hole diameter of Λx/dm = 1, 3, and 6. Increasing turbulence intensity was shown to increase the centerline, span-averaged, and area-averaged adiabatic film cooling effectiveness and NHFR. Larger turbulent length scales in the steady RANS analysis were shown to have little to no effect on the centerline, span-averaged, and area-averaged adiabatic film cooling effectiveness and NHFR at lower turbulence levels, but moderate effect at the highest turbulence levels investigated. Heat transfer results were in good agreement with the findings from adiabatic cases from previous work. Unsteady RANS results also provided supplementary flow visualization for the AVH film cooling flow under varying turbulence levels.

Experimental investigation of the influence of freestream turbulence on an anti-vortex film cooling hole

Film cooling is used in gas turbines to thermally protect combustor and turbine hot section components by creating a layer of relatively cooler air to insulate the components from the hot freestream gases. This relatively cooler air is taken from upstream in the compressor section at a loss to the engine efficiency and therefore must be used as effectively as possible. A novel anti-vortex hole (AVH) geometry has been investigated experimentally through a transient infrared thermography technique to study the film cooling effectiveness and heat transfer coefficient by varying blowing ratio and freestream turbulence intensity. The AVH geometry is designed with two secondary holes stemming from a main cooling hole that attempts to diffuse the coolant jet and mitigate the vorticity produced by conventional straight holes. The AVH geometry data collected showed improved cooling performance at low freestream turbulence intensities compared to conventional straight holes. Three turbulence intensities of 1, 7.5, and 11.7% were investigated for the AVH geometry at blowing ratios of 0.5, 1.0, 1.5, and 2.0 for a total of twelve different conditions. Results showed that higher freestream turbulence conditions were beneficial to the performance of the AVH. Increasing the blowing ratio at all turbulence levels also improved film cooling effectiveness, both span-averaged and on the centerline. The highest performing case was at a turbulence intensity of 7.5% and a blowing ratio of 2.0. The 11.7% cases outperformed the 1% cases, but it appears that at the 11.7% cases the higher freestream turbulence reduces the performance of the secondary holes compared to the 7.5% case. Increasing the blowing ratio and turbulence intensity will result in a higher heat transfer coefficient, which must be taken into account for future designs and overall reduction of heat load.

PSP를 이용한 15°반와류 홀과 30-7-7 팬형상 홀의 막냉각 효율 비교 연구

PSP를 이용한 15^°반와류 홀과 30-7-7 팬형상 홀의 막냉각 효율 비교 연구

Flow Visualization of Multi-Hole Film-Cooling Flow under Varying Freestream Turbulence Levels

A flat plate film cooling flow from a multi-exit hole configuration has been numerically simulated using both steady and unsteady Reynolds Averaged Navier Stokes (RANS and URANS) Computational Fluid Dynamics (CFD) formulations. This multi-exit hole concept, the Anti-Vortex Hole (AVH), has been developed and studied by previous research groups and shown to mitigate or counter the vorticity generated by conventional holes resulting in a more attached film cooling layer and higher film cooling effectiveness. The film cooling jets interaction with the free stream flow is a long studied area in gas turbine heat transfer. The present study numerically simulates the jet interaction with the multi-exit hole concept at a high blowing ratio (M = 2.0) and density ratio (DR = 2.0) in order to provide a more detailed, graphical explanation of the improvement in film cooling effectiveness. This paper presents a numerical study of the flow visualization of the interaction of film cooling jets with a subsonic crossflow. The contour plots of adiabatic cooling effectiveness were used to compare the multi-exit hole and conventional single hole configurations. The vortex structures in the flow were analyzed by URANS formulations and the effect of these vortices on the cooling effectiveness was investigated together with the coolant jet lift-off predictions. Quasi-Instantaneous Temperature Isosurface plots are used in the investigations of the effect of turbulence intensity on the cooling effectiveness and coolant jet coverage. The effect of varying turbulence intensity was investigated when analyzing the jets’ interaction with the cross flow and the corresponding temperatures at the wall. The results show that as the turbulence intensity is increased, the cooling flow will stay more attached to the wall and have more pronounced lateral spreading far downstream of the cooling holes.

Numerical Investigation of Rotation Effects on Anti-vortex Film-Cooling Holes

The anti-vortex film-cooling technique under rotating conditions is investigated using large eddy simulation (LES) due to its complex mixture between the main stream flow, film-cooling flow, and the flow through the anti-vortex holes. The film-cooling was enhanced by placing two small injection holes (anti-vortex holes) just downstream of the main cooling hole in order to modify the approaching boundary layer flow and its interaction with the film-cooling jet. A geometry of a single row of rectangular holes inclined normally on a flat plate is used as the baseline case. The finite volume method and the unsteady SIMPLE algorithm were applied on a non-uniform staggered grid. The simulations were performed for four different values of rotation number (Ro) of 0.0, 0.03021, 0.06042, and 0.12084 and a jet Reynolds number of 4,700. Three different values of velocity ratio (coolant jets / main jet velocity), namely 0.5, 1, and 1.5, were studied. One position of the anti-vortex holes is investigated with density ratio (coolant density / main stream density), namely 1.04. The present simulation is carried out using an in-house FORTRAN code. Numerical calculations of flow field and film-cooling effectiveness are validated with reported LES results. It was shown that the rotational speed is the dominant factor in determining the cooling effectiveness level. The jet footprint of the anti-vortex is broader than for the single jet case and increases as Ro increases. Furthermore, it was also found that the anti-vortex technique used in this study reduces the mixing of the main stream and the coolant jets and improves the film-cooling effectiveness using the same amount of coolant fluid as was used in the case of a single jet. It was also shown that the anti-vortex holes create reverse vortices against the main vortices that are created by the main hole. These reverse vortices help to keep the coolant jet flow near the wall.

Effect of Angle between the Primary and Auxiliary Holes of an Anti-vortex Film Cooling Hole

In this paper, weanalytically investigated the effect of the angle between primary and auxiliary film cooling holes of an anti-vortex hole on the film cooling effectiveness. The effect of blowing ratio and the mainstream turbulence intensity were also considered. A commercial software, CFX was utilized and the RNG k-ɛ turbulence model was selected as the turbulence model for the analysis. The angle between primary and auxiliary hole was varied from 0 to 75 degrees and the blowing ratio was ranged from 0.25 to 2.0. Four different mainstream turbulence intensities were also considered. Results showed that the anti-vortex film cooling holes performed better than the cylindrical hole. Also, the film cooling effectiveness for the anti-vortex holes were strongly affected by the angle between primary and auxiliary holes of the anti-vortex film cooling hole and the mainstream turbulence intensity.

Parametric Study on Anti-Vortex Film Cooling Hole Arrangements

Film cooling has been extensively used to provide thermal protection for the external surface of the gas turbine blades. Numerous number of film cooling holes designs and arrangements have been introduced. The main motivation of these designs and arrangements are to reduce the lift-off effect cause by the counter rotating vortices (CRVP) produce by cylindrical cooling hole. One of the efforts is the introduction of newly found anti-vortex film cooling design. The present study focuses on anti-vortex holes arrangement consists of a main hole and pair of smaller holes. All three holes share a common inlet with the outlet of the smaller holes varies base on it relative position towards the main hole. Three anti-vortex holes arrangements have been considered; downstream anti-vortex hole arrangement (DAV), lateral anti-vortex hole arrangement (LAV), and upstream anti-vortex hole arrangement (UAV). In addition, a single hole (SH) film cooling has also been considered as the baseline. The investigation make used of ANSYS CFX software ver. 14. The investigations are made through Reynolds Average Navier Stokes analyses with the application of shear k-ε turbulence model. The results show that the anti-vortex designs produce significant improvement in term of film cooling effectiveness and distribution. The LAV arrangement shows the best film cooling effectiveness distribution among all considered cases and is consistent for all blowing ratios (BR). The results also unveil the formation of new vortex pair on both side of the primary hole CRVP. Interaction between the new vortices and the main CRVP structure reduce the lift off explaining the increased lateral film effectiveness.

반와류 홀의 각도가 평판의 막냉각 효율에 미치는 영향 연구

In this paper, the experimental study was carried to investigate the effect of angle of the anti-vortex holes on the film cooling effectiveness on a flat plate. The pressure sensitive paint technique was applied to measure the film cooling effectiveness. Two anti-vortex hole angles of 0 ° and 15 ° with respect to the primary hole were considered, and the simple cylindrical hole case was also tested. The blowing ratio based on the cylindrical hole was 0.5 and the same flow rate was kept for all anti-vortex hole cases. Results showed that the film cooling effectiveness for the anti-vortex hole cases were much higher than that of the cylindrical case. Among the anti-vortex hole cases, 15° angle anti-vortex hole case showed higher film cooling effectiveness than that by the 0° angle anti-vortex hole case.

반와류 홀의 형상 변화가 막냉각 효율에 미치는 영향

A parametric study on anti-vortex holes for turbine blade cooling was investigated numerically. Three-dimensional Reynolds-averaged Navier-Stokes equations and shear stress transport turbulence model were used for analysis of anti-vortex film cooling. Validation of numerical results was carried out comparing with experimental data. The cooling performance of anti-vortex holes was assessed by two geometric variables, the ratio of diameters of holes and the lateral distances between the primary hole and anti-vortex hole at blowing ratios of 0.5 and 1.0. The results showed that the spatially-averaged film-cooling effectiveness increases as the ratio of the diameters increases and the distance between the primary hole and anti-vortex hole decreases.

Film-Cooling Performance of Antivortex Hole on a Flat Plate

Improved film cooling performance and coolant flow usage have a significant effect on overall engine performance. In the current study, film cooling performance of an improved antivortex or tripod hole geometry is evaluated on a flat plate surface with steady-state IR (infrared thermography) technique and compared to traditional baseline geometry. The baseline geometry is a simple cylindrical hole design inclined at 30 deg from the surface with pitch-to-diameter ratio of 3.0. The proposed improvement is a tripod design where the two side holes, also of the same diameter, branch out from the root of the main hole at 15 deg angle with a larger pitch-to-diameter ratio of 6.0 between the main holes. The third geometry studied is the same tripod design embedded in a trench to enhance two-dimensional film performance. The mainstream Reynolds number is 3110 based on the coolant hole inlet 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 the tripod holes compared to cylindrical holes at all the blowing ratios studied. The trenched design shows improved effectiveness in the trench region and reduced effectiveness in the downstream region. At any given blowing ratio, the tripod hole designs use 50% less coolant and provide at least 30%–40% overall averaged higher cooling effectiveness. The use of relatively dense secondary fluid improves effectiveness immediately downstream of the antivortex holes but leads to poor performance downstream.

Effect of Pressure Gradient on Film Cooling From Holes Supplemented by Anti-Vortex Holes

An experimental test rig is constructed to study the effect of pressure gradient on different configurations of the anti-vortex film cooling technique. This technique depends on adding a pair of cylindrical anti-vortex holes branching out from the main cylindrical film cooling holes to mitigate the effect of kidney vortices that causes the jet to lift off. Four different values of velocity ratios (VR), (Coolant Jet Velocity/Main Stream Velocity) namely VR=0.5, 1.0, 1.5, and 2.0, are studied with three different positions of anti-vortex holes. A single row of 30o angled holes on a flat surface, under zero pressure gradient along the downstream test surface, is taken as a baseline case. The numerical study is carried out using FLUENT commercial code using the k-e model. The density ratio is taken in consideration. Numerical results are first compared with experimental values of temperatures and film cooling effectiveness and the comparisons verified the numerical model. Both of experimental and numerical studies show that the new technique improves the film cooling effectiveness.The numerical velocity vectors in the boundary layer region showed that the anti-vortex holes create reverse vortices against the main vortices that are created by the main hole. These reverse vortices help in keeping the coolant jet flow near the surface. The adverse pressure gradient decreases the film cooling effectiveness while the presence of favorable pressure gradient increases the film cooling effectiveness.

Film Cooling From a Row of Holes Supplemented With Antivortex Holes

The primary focus of this paper is to study the film cooling performance for a row of cylindrical holes each supplemented with two symmetrical antivortex holes, which branch out from the main holes. The antivortex design was originally developed at NASA-Glenn Research Center by James Heidmann, coauthor of this paper. This “antivortex” design is unique in that it requires only easily machinable round holes, unlike shaped film cooling holes and other advanced concepts. The hole design is intended to counteract the detrimental vorticity associated with standard circular cross-section film cooling holes. The geometry and orientation of the antivortex holes greatly affect the cooling performance downstream, which is thoroughly investigated. By performing experiments at a single mainstream Reynolds number of 9683 based on the freestream velocity and film hole diameter at four different coolant-to-mainstream blowing ratios of 0.5, 1, 1.5, and 2 and using the transient IR thermography technique, detailed film cooling effectiveness and heat transfer coefficients are obtained simultaneously from a single test. When the antivortex holes are nearer the primary film cooling holes and are developing from the base of the primary holes, better film cooling is accomplished as compared to other antivortex hole orientations. When the antivortex holes are laid back in the upstream region, film cooling diminishes considerably. Although an enhancement in heat transfer coefficient is seen in cases with high film cooling effectiveness, the overall heat flux ratio as compared to standard cylindrical holes is much lower. Thus cases with antivortex holes placed near the main holes certainly show promising results.