Sister Holes Research Articles

Numerical Investigation on Supersonic Film Cooling Performance with Discrete Film Holes

The effect of the discrete film cooling hole type on flow characteristics and the cooling performance of supersonic film cooling are numerically studied on a flat plate. Three film hole types (cylindrical hole, merged hole, and sister hole) are evaluated. Numerical simulation is conducted under a constant mainstream Mach number and six coolant Mach numbers ranging from . The three-dimensional effects of shock impingement on the flow characteristics and cooling performance are analyzed. The flow features (especially the interaction between the jet flow and the mainstream) are illustrated. The results show that the supersonic film cooling performance is heavily affected by many factors: the shear layer developed from the detached boundary layer, the boundary-layer separation downstream of the film hole, the jet liftoff phenomenon, the kidney vortex, and the oblique shock wave impingement. Those factors, except for the shock wave impingement, are heavily affected by the discrete film hole types and coolant Mach numbers. The shock impingement is not conducive to the lateral expansion of the cooling film. There is an optimal coolant Mach number for the best film cooling effectiveness under three film hole types, and the sister hole yields the best cooling performance.

Numerical investigation of area ratio on sister hole applications at a constant exit area

A numerical study was performed to investigate the effect of the area ratio at sister hole applications on film cooling effectiveness and flow structure. Two secondary coolant holes are placed on both sides of the main hole at a lateral distance of one main hole diameter. Four different area ratios (AR = 2–5) between the main hole and sister hole were studied. A single cylindrical hole was also studied for comparison and baseline. The structured mesh was generated and realizable k-ε turbulence model with scalable wall function was used in these simulations. Blowing ratios of 0.25, 0.50, 0.80, and 1 were simulated to evaluate the effect of sister holes in practical applications. The centerline cooling effectiveness and laterally averaged cooling effectiveness are studied as well as temperature contours and streamlines at two different streamwise locations (x/D = 1 and x/D = 3). The area ratio on sister hole application has an important effect on cooling effectiveness as the sister hole exit area affects the Anti- Counter Rotating Vortex intensity (A-CRVP vorticity) and size. The positive effect of the sister hole is more pronounced with the increasing blowing ratio. Lower are ratios such as AR = 2 and AR = 3, decrease the vorticity of the CRVP around %30 which directly affects the cooling effectiveness. The results of this study showed area ratio, as well as lateral distance between main hole and sister hole centers heavily affects the cooling effectiveness, the lower area ratios are more efficient for film cooling.

Comparisons on flow characteristics and film cooling performance of cylindrical and sister holes with/without internal coolant crossflow

Simulations and comparisons on the influence of internal coolant crossflow of a novel film cooling hole design, called “sister holes”, and a baseline cylindrical hole were performed with an established turbulence model. The results show that sister holes can provide better film cooling performance than the baseline case at three blowing ratios, and as the blowing ratio increases the sister holes show significant advantages. At a high blowing ratio, the simple cylindrical hole provides very poor cooling effectiveness, since the jet penetrates into the passage flow due to the high jet velocity and the action of a counter-rotating vortex pair. Compared with the cases using a plenum feeding the film cooling holes, the cases with internal coolant crossflow show higher laterally-averaged film cooling effectiveness because deflection of the jet is caused by the crossflow.

Effects of plasma actuation and hole configuration on film cooling performance

In this paper, plasma actuators are arranged asymmetrically downstream the wall to improve film cooling performance. Effects of blowing ratio, hole configuration and applied voltage on flow characteristics and film cooling effectiveness were investigated numerically on a flat plate. Results show that highest film cooling effectiveness distribution is obtained both in the spanwise and streamwise directions under blowing ratio of 0.5. Average wall film cooling effectiveness of cylindrical hole increases by 251.9% under blowing ratio of 0.5 compared to that under blowing ratio of 1.5. The scale of the counter rotating vortex pairs (CRVP) from fan shaped hole and sister hole are significantly reduced compared to that from cylindrical hole. The console hole has an anti-counter rotating vortex pair (Anti-CRVP), which weakens the entrainment of the CRVP to the coolant air near the wall. Compared with the cylindrical hole, average wall film cooling effectivenesses for fan shaped hole, sister hole and console hole increase by 73.1%, 97.5% and 119.9%. The adherent performance of the coolant air is enhanced after applying plasma actuator. The aerodynamic actuation of the plasma results in the rebound of the fluid close to the wall at 24 kV applied voltage. Average wall film cooling effectiveness of the console hole at 12 kV applied voltage is 10.6% higher than that without plasma.

Conjugate Heat Transfer and Flow Features of Single-Hole and Combined-Hole Film Cooling With Rib-Roughened Internal Passages

Abstract Internal cooling and film cooling, as two main cooling methods in modern gas turbines, work together to protect the high-temperature components of gas turbines. This paper presents the results of a computational study on cooling performance for a flat plate with both film cooling and internal cooling using a conjugate heat transfer analysis. Three internal delivery channel geometries, smooth channel, channel roughened by square ribs (SR), and channel roughened by crescent ribs (CR), are studied with two film cooling geometries, cylindrical hole, and sister holes (SS). The respective conjugate cooling performances are compared. Detailed flow and heat transfer characteristics are presented and discussed. Results show that both film cooling effectiveness and internal cooling performances are influenced by the delivery channel geometry near the hole inlets. The sink flow effects of film cooling enhance the heat transfer coefficient near the film cooling hole inlet. At the same time, film cooling performance is affected by the internal channel as the flow inside the film cooling hole is influenced by the ribs near the hole inlets. When using sister holes, ribs in the internal channels make the anti-kidney vortex structure created by sister holes more effective by changing the mass flow distribution among the three holes.

Effects of Bulk Flow Pulsations on Film Cooling with Two Sister Holes

In a triple-hole system comprising a primary hole and two sister holes, when the sister holes are positioned slightly downstream of the main hole under steady flow conditions, their jets generate an anti-counter-rotating vortex pair. Vortex interactions between the jets increase the effectiveness of adiabatic film cooling. In this study, a series of large-eddy simulations were conducted to understand how pulsations in the main flow affect film cooling in a triple hole. To understand the effects of pulsations on film cooling performance is important for better cooling design of the gas turbine engines. The numerical simulations were carried out on a flat plate geometry with a triple cylindrical hole system at 35° injection angle. The pulsations were approximately sinusoidal, and their effect on film cooling was investigated at several frequencies (2, 16, and 32 Hz) and Strouhal numbers (Sr = 0.1005, 0.8043, and 1.6085) at an average blowing ratio of 0.5. The results for the triple-hole system were compared with those for a single hole for the same amount of cooling air and the same cross-sectional area of the holes. Increasing the Strouhal number of the main flow decreased η in both systems. However, at each Strouhal number, η was higher in the triple hole. Furthermore, the triple-hole system was found to be better for film cooling than a single-hole system for higher values of the pulsation Strouhal number. Contours of time-averaged film cooling effectiveness and dimensionless temperature, instantaneous film cooling effectiveness contours on a test plate, mean velocity magnitude contours in the hole, and Q-contours for the triple holes under the application of pulsations to the flow were investigated.

Numerical investigation on the effect of sister holes on film cooling performance with Barchan-dune shaped shells

Numerical investigation on the effect of sister holes on film cooling performance with Barchan-dune shaped shells

Effects of Injection Angles and Aperture Ratios on Film Cooling Performance of Sister Holes

In this paper, to analyze the influences of the injection angles and aperture ratios (AR) of the primary hole and the side hole on the film cooling performance of a flat plate model, pressure sensitive paint (PSP) technology was used to study the forward and backward jet of a single hole and four sister holes, and a numerical simulation was supplemented to explore the flow structure of the sister holes. The sister holes had a better film cooling performance than the cylindrical hole at all blowing ratios (BR). The backward jet of the primary hole or the side hole could increase the spanwise film coverage of the sister hole. In this study, with the primary hole featuring a backward jet and the side hole featuring a forward jet, the film cooling performance was the best, 11.9 times higher than the areal mean film cooling efficiency of the cylindrical hole when AR=1 and BR=1.5. At a low blowing ratio, the counter-rotating vortex pair (CRVP) of the side hole could suppress the strength of the CRVP of the primary hole. At a high blowing ratio, when the primary hole featured a backward jet and the side hole featured a forward jet, the CRVP of the side hole had the optimal performance for suppressing the CRVP of the primary hole.

Large Eddy Simulation of Film Cooling with Triple Holes: Injectant Behavior and Adiabatic Film-Cooling Effectiveness

This study investigated the effect of adding two sister holes placed downstream the main hole on film cooling by employing large eddy simulation. Here, film-cooling flow fields from a triple-hole system inclined by 35° to a flat plate at blowing ratios of M = 0.5 and unity were simulated. Each sister hole supplies a cooling fluid at a flow rate that is a quarter of that for the main hole. The simulations were conducted using the Smagorinsky–Lilly model as the subgrid-scale model, and the results were compared with those for a single-hole system for the same amount of total cooling air and same cross-sectional area of the holes. Relative to the single-hole system, the spanwise-averaged film-cooling effectiveness in the triple-hole configuration at M = 1.0 increased by as much as 345%. The subsequent proper orthogonal decomposition analysis showed that the kinetic energy of a counter-rotating vortex pair in the triple-hole system dropped by 30–40% relative to that of the single-hole system. This indicates that the additional sister holes promoted the suppression of the mixing of the coolant jet with the mainstream flow, thus keeping the temperature of the latter low. Cross-sectional views of the root-mean-square temperature contours were also analyzed; with the results confirming that the effect of the sister holes on the jet trajectory greatly contributes in promoting film-cooling effectiveness as compared to the effect of the reduced mixing.

Improving adiabatic film-cooling effectiveness spanwise and lateral directions by combining BDSR and anti-vortex designs

In the present study, a numerical investigation was conducted to enhance the film cooling efficiency by using anti-vortex designs. Four configurations are considered in this paper, which are the configuration with the streamwise cylindrical injection, the case with an upstream Barchan dune shape ramp (BDSR), the case with sister holes and the configuration that combine the Barchan dune shape with sister holes. The effects of a blowing ration (M = 0.5, 0.85, 1.0 and 1.5) on the film cooling effectiveness are considered. The validation shows good agreement and almost all flow structures are well reproduced by the RANS computation. Results show that the Barchan dune shapes with sister holes have an influence on thermal and flow structures, this configuration substantially augments the film cooling efficiency.

A GMDH-type neural network model for predicting the effect of sister hole parameters on the film cooling effectiveness over a turbine blade

In this paper, a three-dimensional numerical analysis was employed to investigate the flow and thermal fields over a leading edge of AGTB-B1 high-pressure turbine blade. The effect of different parameters on the film cooling was studied. The computational methodology includes the use of a structured, non-uniform hexahedral grid consisting of the main flow channel, the coolant delivery tube and the feeding plenum. The SIMPLEC algorithm was implemented for pressure–velocity coupling. Computations were carried out for the following range of film cooling parameters: lateral position of sister holes 3, 3.5 and 4.75 mm; lateral angle of sister holes of − 8°, 0° and 8°; blowing ratio of 0.7, 1.1 and 1.5; and diameter of injection hole of 2, 2.5 and 3. Adiabatic effectiveness was used as a criterion to judge the performance of film cooling. The results show a good agreement compared with previous experimental and numerical data. Finally, the GMDH-type neural network was successfully employed for modeling and presenting a correlation for film cooling effectiveness as a function of effective parameters.

Numerical investigation on the effect of Sister Holes on film cooling performance with Barchan-dune shaped shells

The film cooling is the traditional and efficient technique that is used to adopt the turbine cooling process, a new configuration that combines sister holes with Barchan-dune shaped shells (SH-BDS) is used in this study to improve the film cooling effectiveness laterally and at spanwise direction. The investigations are performed for high blowing ratios, M = 1 and 1.5. Three-dimensional Reynolds Averaged Navier-Stokes (RANS) equations with the RNG k-e model are solved to simulate and analysis the thermal behaviour of this new configuration. The validation shows good agreement and almost all flow structures are well reproduced. It is found that the new configuration provides a significant change in the film cooling effectiveness results. Moreover, the counter-rotating vortex pairs structure (CRV) is nearly vanished. From this contribution, it is well demonstrated that this new technique (SH-BDS) has a great influence on the cooling process of the turbine and hence on its effective functioning.

Effects of diameter ratio and inclination angle on flow and heat transfer characteristics of sister holes film cooling

In order to investigate the flow and heat transfer characteristics of sister holes cooling method, sister holes cooling structures have been applied on a flat plate with four primary to sister hole diameter ratios and three inclination angles under three blowing ratios. Single cylindrical hole film cooling structure is also established as a benchmark structure. The numerical results of the single cylindrical hole case and one sister holes case are validated with the experimental results available in literatures. The tangential velocity vectors and total vorticity distributions are studied and compared. The spanwise averaged film cooling effectiveness and the adiabatic temperature contours are studied and compared. Results show that the development of the kidney vortex induced by primary hole is impeded by the sister hole induced kidney vortex and thus the film cooling performance is promoted. The blowing ratio and diameter ratio heavily affect the flow and heat transfer characteristics of sister holes cooling cases, the influence of the inclination angle is much smaller. In this paper, the best film cooling performance of sister holes cooling cases is obtained under the smallest diameter ratio.

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.

Influence of hole geometry on film cooling effectiveness for a constant exit flow area

Film cooling is an effective method which can protect the surface from the high temperature environment. Most previous studies have used the same mass flux ratio with different coolant exit flow area for different holes. A better comparison of the film cooling effectiveness would keep the coolant mass flow rate and exit area the same. The present study investigated the effect of hole geometry on the film cooling effectiveness for a constant film cooling exit flow area experimentally and numerically. Four kinds of film cooling holes, the cylindrical hole, the fan-shaped hole, the double jet holes and the hole with sister holes were studied with blowing ratio varied from 0.3 to 1.5. In the experiment, plate surface temperature was measured by an infrared camera and the main flow and coolant flow temperature were measured by thermocouples. To investigate the flow characters, numerical calculation using RNG k−ε turbulence model was performed. Protected wall temperature, film cooling effectiveness and coolant flow stream lines were studied to illustrate the difference between the coolant jets from the four kinds of hole geometries. The results show that film cooling with the other three kinds of holes have an obvious advantage compared to the cylindrical hole. The reason is that for the cylindrical hole, the coolant flow forms a strong vortex pair in the main flow which pulls the hot main flow underneath the coolant flow to lift the coolant jet from the wall, so the cooling effectiveness is very low. For the other three kinds of holes, the mixing between the main flow and the coolant jet forms a complex vortex structure which keeps the coolant jet on the wall, thus improves the cooling effectiveness.

Design of sister hole arrangements to reduce kidney vortex for film cooling enhancement

In this study, we investigated whether vortex control of forward and backward injection jets with different vortex strengths contributed to enhanced film cooling effectiveness. Various hole arrangements, composed of primary and sister holes, were used to control vortex strengths and vortex interactions between film cooling jets. Numerical simulations were conducted to obtain and analyze the flow characteristics and film cooling effectiveness of six sister hole arrangements, composed of forward and backward injection holes, for blowing ratios of 1 and 2. Hole arrangements with backward injection holes showed improved film cooling effectiveness and laterally wide coverage of film cooling jets. Hole arrangements with forward injection primary holes and backward injection sister holes showed coverage of the entire surface by the film cooling jets, due to the backward injection jets from sister holes and the formation of outward vortexes. Additionally, the other hole arrangement, consisting of forward injection sister holes in the first row and backward injection primary holes in the second row, produced an anti-kidney vortex and improved film cooling effectiveness at high blowing ratios.

Effect of rotation on a downstream sister holes film cooling performance in a flat plate model

Using the Thermochromic Liquid Crystal (TLC) technique, one downstream sister holes and one base round hole were investigated experimentally to study the effect of rotation on film cooling performance on a flat plate test model. Blowing ratios of 0.3, 0.5, 1.0, 1.5, 2.0 and 2.5 were studied. Density ratio of the cooling air to hot air was 1.05. The mainstream Reynolds number (ReD) was 3400, and 4 rotation speeds of 200, 400, 600 and 800rpm were applied on both the pressure side (PS) and suction side (SS). Under rotation, the film cooling performance of the downstream sister holes improved clearly at blowing ratio M=0.3–2.5, both on the PS and SS. For both the base hole and downstream sister holes, the film trajectory showed a distinct centrifugal deflection on the SS, with lower film cooling effectiveness than that on the PS. On the PS, the rotation number had a clear effect on film cooling performance, which increased first and then decreased with increased rotation speeds and reached the highest value at 600rpm.

A numerical investigation of film cooling performance through variations in the location of discrete sister holes

In the present paper, a numerical parametric study on the effects of the discrete sister holes’ location on film cooling performance is carried out. The location of the up/downstream combination of the sister holes has been changed individually in the streamwise and spanwise directions. These include five new locations in each direction. The simulations are performed using three-dimensional Reynolds Averaged Navier-Stokes (RANS) analysis with the realizable k–ε model combined with the standard wall function. Simulations are performed for low and high blowing ratios, where the low blowing ratios are represented by M=0.2 and 0.5, and the high blowing ratios by M=1.0 and 1.5. It is found that the streamwise variations in the location of the sister holes do not provide a significant change in the adiabatic film cooling effectiveness results. On the other hand, the effectiveness results are considerably improved for the spanwise variations. For example, the laterally averaged effectiveness results for a case where the sister holes were positioned at the spanwise location of z/D=±1 is increased about 78% and 49% as compared to the base case (z/D=±0.75) for the blowing ratios of 1 and 1.5, respectively. Moreover, as a result of the anti-counter rotating vortices generated from the sister holes and the repositioning of the sister holes, the jet lift-off effect has considerably decreased and more volume of coolant is distributed in the spanwise direction.

Film Cooling Effectiveness Improvements Using a Nondiffusing Oval Hole

The need for improvements in film cooling effectiveness over traditional cylindrical film cooling holes has led to varied shaped hole and sister hole designs of increasing complexity. This paper presents a simpler shaped hole design which shows improved film cooling effectiveness over both cylindrical holes and diffusing fan-shaped holes without the geometric complexity of the latter. Magnetic resonance imaging measurement techniques are used to reveal the coupled 3D velocity and coolant mixing from film cooling holes which are of a constant oval cross section as opposed to round. The oval-shaped hole yielded an area-averaged adiabatic effectiveness twice that of the diffusing fan-shaped hole tested. Three component mean velocity measurements within the channel and cooling hole showed the flow features and vorticity fields which explain the improved performance of the oval-shaped hole. As compared to the round hole, the oval hole leads to a more complex vorticity field, which reduces the strength of the main counter-rotating vortex pair (CVP). The CVP acts to lift the coolant away from the turbine blade surface, and thus strongly reduces the film cooling effectiveness. The weaker vortices allow the coolant to stay closer to the blade surface and to remain relatively unmixed with the main flow over a longer distance. Thus, the oval-shaped film cooling hole provides a simpler solution for improving film cooling effectiveness beyond circular hole and diffusing hole designs.

Effects of side hole position and blowing ratio on sister hole film cooling performance in a flat plate

Three kinds of sister hole and one single cylindrical hole were experimentally studied in order to analyze the effects of side hole position and blowing ratio on film cooling performance in a flat plate model by applying Thermochromic Liquid Crystal (TLC) technique. The blowing ratio varied from 0.3 to 2.5 and the density ratio of coolant to mainstream was 1.05. The Reynolds number based on the velocity of mainstream and the diameter of the main hole was fixed at 3400. Compared to the base hole, the film cooling performance of all sister holes showed obvious improvement at all blowing ratios. The middle stream sister hole and downstream sister hole each demonstrated good film cooling performance at all blowing ratios, while the upstream sister hole performs well only at a lower blowing ratio. A numerical calculation is also performed to better analyze the experimental results and determine the relationships among CRVP intensity, flow structure, and film cooling effectiveness at a low blowing ratio of M = 0.5 and high blowing ratio of M = 2.0. The presence of side holes can restrain the CRVP intensity of the main hole and reduce the coolant lift-off, improving the film coverage and film cooling effectiveness. The downstream sister hole can perform best in reducing the CRVP intensity.