Academic literature on the topic 'Counter-Rotating Vortex Pair (CRVP)'

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.

Investigation of the classical and pulsating jet in crossflow (JICF) at a low Reynolds number (Re = 100) has been performed by the LES method based on varied velocity ratios (r= 1~4). Time-averaged particle trajectories are compared in the classical and pulsating JICF. The formation mechanism and the corresponding flow characteristics for the counter-rotating vortex pair (CRVP) have been analyzed. An unexpected “vortex tail” has been found in the JICF at higher velocity ratio due to the enhanced interactions indicated by the increased jet momentum among the CRVP, upright vortices, and shear layers. The analysis of time-averaged longitudinal vorticity including a coupling mechanism between vortices has been performed. The returning streamlines appear in the pulsating JICF, and two extra converging points emerge near the nozzle of the jet at different Strouhal numbers. The temperature profiles based on the iso-surface for the classical and pulsating JICF have been obtained computationally and analyzed in detail.

Two air entrainment mechanisms driven by vortex instability are reported in the unstable relaxation of a horizontal shear layer below a free surface. This flow is experimentally investigated by means of planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) coupled with surface profilometry. PLIF identifies counter-rotating vortex pairs (CRVP) emanating from the surface following the growth of high steepness two-dimensional millimetre-size waves for Reynolds and Weber numbers based on the momentum thickness of 177 to 222 and 7.59 to 13.9, respectively. High spatio-temporal resolution PIV reveals the role of surface-generated vorticity and flow separation in the highly curved trough of the waves on the injection of a CRVP. Air bubbles are entrapped in the wake of these CRVPs at Reynolds number above 190. PIV data and spanwise PLIF images show two initiation mechanisms: primary vortex instability modulating the spanwise location where the flow separates, resulting in the pinch off of an air ligament, and secondary vortex instability turning a CRVP into$\unicode[STIX]{x1D6FA}$-shaped loops pulling the surface down. Instability wavelengths agree with linear stability analysis, and models for these new air entrainment mechanisms are proposed.

Direct numerical simulation has been performed to study flow interactions in multiple jets in cross-flow. Configurations considered are twin jets side-by-side and triple jets in tandem. Computations are carried out at the jet to cross-flow velocity ratio of 2.5 and the Reynolds number 225 based on the free-stream quantities and the jet width D . For twin jets, results show that in the vicinity of jet exits, the merging of two counter rotating vortex pairs (CRVP) is strongly dependent on the gap of two jets. Downstream in the far-field, a large single CRVP dominates. The simulation is in qualitatively good agreement with the experimental findings by other researchers. For triple jets, more complicated flow structures are revealed, in which a total of three vortex pairs has been identified, but none of them is dominating. The observations of complex flow structure could assistant relevant industrial applications.

A large eddy simulation (LES) was performed for film cooling in the gas turbine blade involving spanwise injection angles (orientation angles). For a streamwise coolant injection angle (inclination angle) of 35°, the effects of the orientation angle were compared considering a simple angle of 0° and 30°. Two ratios of the coolant to main flow mass flux (blowing ratio) of 0.5 and 1.0 were considered and the experimental conditions of Jung and Lee (2000) were adopted for the geometry and flow conditions. Moreover, a Reynolds averaged Navier–Stokes simulation (RANS) was performed to understand the characteristics of the turbulence models compared to those in the LES and experiments. In the RANS, three turbulence models were compared, namely, the realizable k-ε, k-ω shear stress transport, and Reynolds stress models. The temperature field and flow fields predicted through the RANS were similar to those obtained through the experiment and LES. Nevertheless, at a simple angle, the point at which the counter-rotating vortex pair (CRVP) collided on the wall and rose was different from that in the experiment and LES. Under the compound angle, the point at which the CRVP changed to a single vortex was different from that in the LES. The adiabatic film cooling effectiveness could not be accurately determined through the RANS but was well reflected by the LES, even under the compound angle. The reattachment of the injectant at a blowing ratio of 1.0 was better predicted by the RANS at the compound angle than at the simple angle. The temperature fluctuation was predicted to decrease slightly when the injectant was supplied at a compound angle.

Modeling the heat transfer characteristics of highly turbulent flow in gas turbine film cooling is important for providing better insights and engineering solutions to the film cooling problem. This study proposes a modified detached eddy simulation (DES) model for better film cooling simulations. First, spatially varying anisotropic eddy viscosity is found from the results of the large eddy simulation (LES) of film cooling. Then the correlation for eddy viscosity anisotropy ratio has been established based on the LES results and is proposed as the modification approach for the DES model. The modified DES model has been tested for the near-field film cooling simulations under different blowing ratios. Detailed comparisons of the centerline and 2D film cooling effectiveness indicate that the modified DES model enhances the spanwise spreading of the temperature field. The DES model leads to deviations of 62.4%, 39.8%, and 33.5% from the experimental centerline effectiveness under blowing ratios of 0.5, 1.0, and 1.5, respectively, while the modified DES reduces the deviations to 51.5%, 26.7%, and 28.9%. The modified DES model provides a promising approach for film cooling numerical simulations. It embraces the advantage of LES in resolving detailed vortical structure dynamics with a moderate computational cost. It also significantly improves the original DES model on the spanwise counter rotating vortex pair (CRVP) spreading, mixing, and effectiveness prediction.

An experimental study to identify the structures present in a jet in crossflow has been carried out at a jet-to-crossflow velocity ratio U/Ucf = 3.8 and Reynolds number Re = UcfD/v = 6600. The hot-wire velocity data measured with a rake of eight X-wires at x/D = 5 and 15 and flow visualizations using planar laser-induced fluorescence (PLIF) confirm that the well-established pair of counter-rotating vortices is a feature of the mean field and that the upright, tornado-like or Fric's vortices that are shed to the leeward side of the jet are connected to the jet flow at the core. The counter-rotating vortex pair is strongly modulated by a coherent velocity field that, in fact, is as important as the mean velocity field. Three different structures – folded vortex rings, horseshoe vortices and handle-type structures – contribute to this coherent field. The new handle-like structures identified in the current study link the boundary layer vorticity with the counter-rotating vortex pair through the upright tornado-like vortices. They are responsible for the modulation and meandering of the counter-rotating vortex pair observed both in video recordings of visualizations and in the instantaneous velocity field. These results corroborate that the genesis of the dominant counter-rotating vortex pair strongly depends on the high pressure gradients that develop in the region near the jet exit, both inside and outside the nozzle.

Le refroidissement par film froid des aubes des turbines aéronautiques d’avion est utilisé depuis quelques décennies pour augmenter la température d'entrée de la turbine (TIT) et ainsi augmenter la poussée, et également pour prolonger la durée de vie de l'aube de turbine. Les normes d'émission strictes des polluants encouragent l'amélioration de l'efficacité globale de la turbine et donc l’optimisation du processus de refroidissement par film. C’est une technique par convection forcée dans laquelle un jet froid est injecté à travers des trous discrets à la surface de l'aube de turbine de manière à former une couche d'air frais sur la surface de l'aube protégeant efficacement l'aube des flux à très haute température résultant de la combustion. Ce principe peut être étudié académiquement comme un jet débouchant dans un écoulement transverse. Cet écoulement est très complexe parce que de nombreuses structures cohérentes turbulentes se développent et interagissent les unes avec les autres. L'un des systèmes de tourbillons les plus importants est la paire de tourbillons contra-rotatifs (CRVP) résultant des contraintes de cisaillement qui se développent dans la couche de mélange supérieure entre le jet débouchant et le jet principal. La courbure du jet débouchant le long de la direction du flux transversal intensifie le développement du CRVP qui augmente ainsi le mélange entre les deux écoulements, ce qui réduit l'efficacité du film de refroidissement. Par conséquent, dans cette étude, une organisation spatiale de trous auxiliaires est étudiée expérimentalement et numériquement pour réduire l'intensité de l’influence du CRVP, ce qui contribue finalement à augmenter l'efficacité du refroidissement du film adiabatique. Les trous auxiliaires, placés en amont du trou principal, permettent de réduire l'intensité du CRVP issu du trou principal du fait de la diminution des contraintes de cisaillement subies par le jet issu du trou principal. Dans cette thèse, une méthode numérique basée sur des simulations RANS utilisant le modèle de turbulence k-ω SST a été utilisée pour optimiser l’organisation spatiale des trous auxiliaires et pour avoir une compréhension préliminaire de ces interactions de structures cohérentes. Une étude détaillée de la structure instationnaire de l'écoulement a également été réalisée à l'aide de la simulation aux grandes échelles L.E.S. Pour étudier expérimentalement les champs de température dans le fluide, une métrologie de mesure de température a été spécialement développée : la thermométrie utilisant le rapport d’intensités spectrales d’émission de phosphorescence du ZnO à l’aide d’une seule caméra intensifiée. Cette technique permet la mesure de la température instantanée et moyenne de manière non intrusive. Une analyse détaillée des propriétés d'émission du luminophore ZnO excitée par un laser à 266 nm est décrite. Une procédure d'étalonnage a été développée et testée dans une cavité Rayleigh-Bénard remplie d’eau. Ensuite, cette procédure a été mise en œuvre sur le nouveau banc d'essai BATH pour étudier expérimentalement le film de refroidissement dimensionné par la simulation RANS pour trois taux de soufflage. L'analyse des résultats expérimentaux et numériques aide à identifier les structures cohérentes clés, conduisant à une meilleure compréhension des phénomènes physiques mis en jeu et à appréhender l'augmentation de l'efficacité de refroidissement du film dans le système de trous auxiliaires par rapport à un trou cylindrique simple classique
Film cooling of aircraft gas turbine blades has been in use since a few decades now to improve the Turbine Inlet Temperature (TIT) and to extend the lifetime of the turbine blade. Additionally, stringent emission norms stipulate the improvement of overall efficiency of the gas turbine engine and hence the need to improve film cooling process. Film cooling is a technique where a cold jet is injected through discrete holes on the surface of the turbine blade, so as to form a layer of cool air over the surface of the blade, effectively protecting the blade from high temperature crossflows arising from the combustion chamber. This problem can be viewed as a Jet In Cross-Flow (JICF) phenomena where the interaction of the crossflow with a jet injected perpendicular or at an angle creates a system of vortices. One of the most important vortex systems in this arrangement is the Counter Rotating Vortex Pair arising from the shear forces at the sides of the ejecting jet with the crossflow primarily. The bending of the jet along the direction of the crossflow promotes the CRVP to ingest hot crossflow into the jet stream which reduces the effectiveness of the film cooling system. Hence, in this study, an auxiliary hole system is studied experimentally and numerically to reduce the intensity and the height of the CRVP which eventually helps in an augmented adiabatic film cooling effectiveness. The auxiliary holes placed upstream of the main film cooling hole reduces the intensity of the main hole CRVP due to the reduction in the shear forces experienced by the jet emanating from the main hole. In this thesis numerical analysis through RANS study using k-ω SST turbulence model to have a preliminary understanding of the auxiliary hole system and a detailed understanding of the flow structure using Large Eddy Simulation are performed. The highlight of this work is the development of single camera phosphor thermometry using the spectral intensity ratio method. This technique allows the measurement of the instantaneous and mean flow temperature non-intrusively. A detailed analysis of the emission properties of ZnO phosphor upon excitation by a 266nm laser is described. A calibration procedure for the intensity ratio method is defined and it is tested using a Rayleigh-Bénard natural convection process. This phosphor thermometry procedure with the validated code is implemented on the new BATH test Rig to study film cooling arrangements. Three different configurations are tested for their aero-thermal characteristics at penetration blowing ratio regime. Analysis of the experimental and numerical results help in identifying key vortex structures, leading to the better understanding of reasons for the augmentation of film cooling effectiveness in the auxiliary hole system compared to a classical simple cylindrical hole

Three-dimensional large-eddy simulations (LES) of single and multiple jets in cross-flow (JICF) were conducted using the 19-bit Lattice Boltzmann Equation (LBE) method coupled with a conventional Navier-Stokes (NS) finite-volume scheme. In this coupled LBE-NS approach, the LBE-LES was employed to simulate the flow inside jet nozzles, while the NS-LES was used to simulate the cross-flow. The key application area was to study the micro-blowing technique (MBT) for drag control similar to recent experiments at NASA/GRC. A single jet in the cross-flow case was used for validation purposes, and results were compared with experimental data and full LBE-LES simulation. Good agreement with data was obtained. Transient analysis of flow structures was performed to investigate the contribution of flow structures to the counter-rotating vortex pair (CRVP) formation. It was found that both spanwise roller (at the lee side of the jet) and streamwise vortices (at the jet-side) contribute to the generation of the CRVP. Span-wise roller at the corner of the jet experiences high spanwise vortex compression as well as high streamwise vortex stretch. As a result, they get realigned, mix with the jet-side streamwise vortices, and eventually generate the CRVP. Furthermore, acoustic pulses were used to test the proper information exchange from the LBE domain to the NS domain, and vice-versa. Subsequently, MBT over a flat plate with porosity of 25 percent was simulated using nine jets in a compressible cross-flow at a Mach number of 0.4. Three cases with injection ratios of 0.003, 0.02 and 0.07 were conducted to investigate how the blowing rate impacts skin friction. It is shown that MBT suppressed the near-wall vortices and reduced the skin friction by up to 50 percent. This is in good agreement with experimental data.

A fundamental investigation on a key vortical structure in film cooling flow, which is called counter-rotating vortex pair (CRVP), has been performed. Traditionally, the coolant’s momentum flux ratio is thought as the most critical parameter on film cooling effectiveness, which is the index of film cooling performance, and this performance is also influenced notably by CRVP. About the sources of CRVP, the in-tube vortex, the in-tube boundary layer vorticity, the jet/mainstream interaction effect, alone or combined, are proposed as the main source in the literature. A numerical approach was applied in present study. By simulating a general inclined cylindrical cooling hole on a flat plate (the baseline case), the CRVP was visualized as well as the in-tube vortex. Another case, which is identical with the baseline except the boundary condition of the in-tube wall was set as free-slip to isolate its boundary layer effect, was simulated for comparing. Their comparisons have clarified that the jet/mainstream interaction is the only essential source of CRVP. Through further analyzing its mechanism, CRVP was found to be a pair of x direction (mainstream wise direction) vortices. Hence, the velocity gradients -v/z and w/y were the promoters of CRVP. Applying this mechanism, a new scheme named nozzle scheme was designed to control the CRVP intensity and isolate the overall momentum flux ratio Iov, a parameter used in literature. Analysis of the effects of CRVP intensity and momentum flux ratio on film cooling effectiveness has demonstrated that the CRVP intensity, instead of the momentum flux ratio, was the most critical factor governing the film cooling performance.

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.

Abstract The performance of a simple slot is perfect, but it does not have structural integrity. A new advanced cooling scheme with perfect performance and practical structural integrity is presented. Based on the crucial effect of the counter-rotating vortex pair (CRVP) on the film cooling effectiveness (η), the new scheme is composed of a comb-like structure and a blind slot, in which the comb structure maintains the mechanical strength, and the blind slot is intended to eliminate the CRVP and produce a smooth coolant film. The new scheme is investigated experimentally with the transient thermochromic liquid crystal (TLC) technique. Two classic geometries, the cylindrical hole and the simple slot, were also measured. The agreement of their results with the published data validated the present experimental facilities. The experimental results of the Comb scheme demonstrated that, with practical structural integrity, the new scheme has perfect performance, which bears comparison with the simple slot. Consequently, the success of the Comb scheme proved the crucial CRVP effect on η.

Abstract The adiabatic film cooling effectiveness behind a single row of circular holes fed by internal crossflow was measured by fast-response pressure-sensitive paint technique. During the experiment, the coolant flow was discharged from the coolant holes via either plenum or crossflow channel. The test model has a row of circular holes with 3D spacing, 6.5D entry length, and 35° inclination angle. Two blowing ratios (M = 0.40 and 0.80) were tested with a density ratio of 0.97. A numerical steady-state RANS simulation, using SST k-ω and Realizable k-ε turbulence models, was conducted to understand the internal crossflow behaviors. The unsteadiness caused by the flow structures (counter-rotating vortex pair (CRVP) and horseshoe vortex) was quantified by the root mean square and the cross-correlations. In addition, the proper orthogonal decomposition was used to identify the large-scale unsteady coherent structures and their contributions. The fluctuations of the crossflow feed were asymmetric, which were significantly weaker compared with the plenum case. The CRVP, as the most significant coherent structures, were demonstrated to play the main role in the unsteadiness of the crossflow feed.

This paper presents experimental flow field investigations of a film cooling scheme, referred to as nozzle scheme, on a flat plate using stereo PIV. The nozzle scheme has a cylindrical hole and internal obstacles to change the velocity distribution near the hole exit and hence the jet-mainstream interaction. Counter-rotating vortex pair (CRVP) is known to be one of the detrimental effects that affect the film cooling effectiveness. Previous CFD simulations demonstrated nozzle hole’s capability of reducing CRVP strength and enhancing film cooling effectiveness in comparison with a normal cylindrical hole. The present study examines the nozzle hole flow filed experimentally at blowing ratio ranged from 0.5 to 2.0 and compares with cylindrical hole. The experiments were conducted in a low-speed wind tunnel with a mainstream Reynolds number of 115,000 and the density ratio was 1.0 during all the investigations. The experimental results show that nozzle hole reduces streamwise vorticity of CRVP by an average of 55% at low blowing ratio, and 34%–40% at high blowing ratios. The velocity field and vorticity field of nozzle jet are compared with cylindrical jet. The result reveals that the nozzle jet forms a round bulk in contrast to the kidney shape jet core in cylindrical hole case. In addition, it is found that CRVP strength may not be a primary contributor to the jet lift-off.

A new advanced film cooling scheme, named high-aspect-ratio holes has been proposed. Four configurations were designed, and numerically simulated under density ratio of 2 and different blowing ratios. All configurations demonstrate extremely high film cooling effectiveness values, some are as high as the so-called perfect performance, while their mechanical strength are similar to the conventional schemes. The new scheme exhibits two traits distinctive from the conventional geometries: Its film cooling effectiveness is much higher than the coverage ratio (t/P), and the high film cooling effectiveness is obtained under strong counter-rotating vortex pair (CRVP). It has been found that, in the new scheme, along with the aspect ratio value increase, the CRVP move away from the coolant-mainstream interface, and the coolant laterally expands in the vicinity of the exit. Consequently, a continuous coolant film would occur near the trailing edge position if aspect ratio is high enough. The approach of high-aspect-ratio holes could be used to design the highest film cooling performance geometries.

Film cooling holes are a well-established cooling technique used in gas turbines to keep component metal temperatures in an acceptable range. A streamwise-oriented film cooling hole creates a symmetric counter-rotating vortex pair (CRVP) due to the jet interaction with the crossflow. As the orientation of the film cooling hole is incrementally misaligned with the streamwise direction (known as a compound angle), one of the vortices in the CRVP gains strength at the expense of the other until there is a single streamwise vortex that dominates the flowfield. This vortex diffuses the coolant jet and impinges hot gas onto the surface, which can augment heat transfer coefficients in a region uncovered by coolant. Although this has been well studied for cylindrical holes, there is less understanding about the nature of this phenomenon for shaped holes, which are intended to diffuse coolant laterally to minimize flowfield interaction. In the present study, particle image velocimetry (PIV) was used to measure the flowfield of compound angled shaped film cooling holes at several downstream planes normal to the streamwise direction. Five compound angled 7-7-7 holes were tested, from a streamwise oriented hole (0° compound angle) to a 60° compound angle hole, in increments of 15°. All cases were tested at a density ratio of 1.0 and blowing ratios ranging from 1.0 to 4.0. Experimental data shows that the circulation increases as compound angle increases because the flowfield transitions from a CRVP to a single streamwise vortex. For large compound angles, the streamwise vortex lifts the core of the jet off of the surface, isolating the coolant from the endwall. Measurements also indicate hole-to-hole interaction downstream for cases with high blowing ratio and large compound angle. Flowfield results are compared with adiabatic effectiveness results from a companion study in order to explain hole-to-hole interaction trends.

Abstract To study the effect of blockage on the film cooling performance, film cooling plate models with cylindrical hole, compound hole, and fan-shaped hole under the all-round blockage, leading-edge blockage, and trailing-edge blockage were established respectively. The anti-blockage performance of three kinds of the hole was compared. The result shows that the cooling performance of cylindrical holes is the worst due to the appearance of counter-rotating vortex pair (CRVP) under blockage. The cooling effectiveness decreases with the increase of the blockage ratio. With the re-attachment effect, the cooling effectiveness of downstream increases by 11% on the contrary. The cooling effectiveness of the compound hole decreases obviously with the all-round and trailing-edge blockages, meanwhile, the peak cooling effectiveness and the coolant coverage area decrease. However, the cooling effectiveness increases by 15% when the leading-edge is blocked. For fan-shaped hole, the change of velocity gradient affects the development of the anti-CRVP, which disappears under the all-round blockage and reduces the cooling effectiveness greatly. The change of cooling performance of leading-edge and trailing-edge is very slight no more than 5%. In conclusion, the fan-shaped hole shows the best anti-blockage capability under the trailing-edge blockage condition and the all-round blockage condition with a high blow ratio, while the compound hole performs better in other conditions.

The effect of hole length to diameter ratio on flat plate film cooling effectiveness and flow structures of axial and compound angle hole is investigated by large eddy simulation (LES). Film cooling simulations are performed for three blowing ratios (M) ranging from 0.4 to 1.2, three hole length-to-diameter ratios (L/D) from 0.5 to 5 and two compound angle (β: 0°, 45°). The prediction accuracy is validated by the reported hydrodynamic data and present film effectiveness data measured by pressure sensitive paint (PSP). Results indicate that discrete hole with L = 0.5 show highest film cooling effectiveness regardless of compound angle. Round hole generally shows an increasing trend as L increases from 2 to 5, while compound angle hole shows a complex trend concerning with blowing ratios and length to diameter ratios. This is associated with the fact that length-to-diameter ratio influences the in-tube flow behavior, formation of Kelvin-Helmholtz (K-H) structures, and development of single asymmetric main vortex (SAMV). Scalar field transportation features are investigated to clarify how different vortex structures affect the temperature distribution and the film cooling effectiveness. It is also demonstrated that the counter rotating vortex pair (CRVP) which is observed in the time-averaged flow field of axial hole is originated in different vortex structures with varying blowing ratios and length to diameter ratios.

Abstract Discrete hole film cooling has been commonly used as an effective cooling technique to protect gas turbine blades from hot gas. There have been numerous investigations on the cylindrical hole and shaped hole, but few experimental investigations on the cooling mechanism of the novel film holes with side holes (anti-vortex hole and sister hole) are available. This paper presents an experimental and numerical investigation to study the film cooling performance and flow structure of four kinds of film holes (cylindrical hole, fan-shaped hole, anti-vortex hole and sister hole) on the flat plate. The film holes have the same main hole diameter of 4mm and the same inclination angle of 45°. The adiabatic film cooling effectiveness is obtained by the steady-state Thermochromic Liquid Crystal (TLC). The flow visualization experiment and numerical investigation are performed to investigate the flow structure and counter-rotating vortex pair (CRVP) intensity. The smoke is selected as the tracer particle in the flow visualization experiment. The mainstream Reynolds number is 2900, the blowing ratio ranges from 0.3 to 2.0, and the density ratio of coolant to mainstream is 1.065. Experimental results show that compared with the cylindrical hole, the film cooling performance of the anti-vortex hole and sister hole shows significant improvement at all blowing ratios. The sister hole can achieve the best cooling performance at blowing ratios of 0.3 to 1.5. The fan-shaped hole only performs well at high blowing ratios and it performs best at the blowing ratio of 2.0. Flow visualization experiment and numerical investigation reveal that the anti-vortex hole and sister hole can decrease the CRVP intensity of the main hole and suppress the coolant lift-off because of side holes, which increases the film coverage and cooling effectiveness. For the sister hole, the side holes are parallel to the main hole, but for the anti-vortex hole, there are lateral angles between them. The coolant interaction between the side holes and main hole of the sister hole is stronger than that of the anti-vortex hole. Therefore, the sister hole provides better film cooling performance than the anti-vortex hole.

A companion experimental and numerical study was conducted of the performance of a row of 5 sweeping jet (SJ) film cooling holes consisting of conventional curved fluidic oscillators with an aspect ratio (AR) of unity and a hole spacing of P/D = 8.5. Adiabatic film effectiveness (η), thermal field (θ), convective heat transfer coefficient (h) and discharge coefficient (CD) were measured at two different freestream turbulence levels (Tu = 0.4% and 10.1%) and four blowing ratios (M = 0.98, 1.97, 2.94 and 3.96) at a density ratio (DR) of 1.04 and hole Reynolds number of ReD = 2800. Adiabatic film effectiveness and thermal field data were also acquired for a baseline 777-shaped hole. The sweeping jet film cooling hole showed significant improvement in cooling effectiveness in the lateral direction due to the sweeping action of the fluidic oscillator. An unsteady RANS simulation was performed to evaluate the flow field at the exit of the hole. Time resolved flow fields revealed two alternating streamwise vortices at all blowing ratios. The sense of rotation of these alternating vortices is opposite to the traditional counter rotating vortex pair (CRVP) found in a ‘jet in crossflow’ and serves to spread the film coolant laterally.