Mainstream Turbulence Intensity Research Articles

Film-Cooling Effectiveness on a Turbine Blade Platform With Various Hole Shapes and Layouts

Abstract This paper reports a film-cooling effectiveness experiment on a turbine blade platform that combines two film hole shapes with three layouts. A linear cascade using the pressure-sensitive paint (PSP) technique was employed to measure the adiabatic film effectiveness and discharge coefficients. Three film hole layouts, including two double-row layouts and one dispersed layout, were designed based on the platform configurations. One double-row layout arranges both rows of holes on the pressure side. Another double-row layout arranges one row on the pressure side and one row on the suction side. The dispersed layout was designed with streamwise multirows using the same number of holes. A fan-shaped hole and a diffusion slot hole were tested and compared. The experiments were conducted at a mainstream Reynolds number of 7 × 105, a mainstream turbulence intensity of 3.6%, and a coolant-to-mainstream density ratio of 1.5. The blowing ratio ranged from 0.5 to 2.5. The results demonstrated that regardless of the hole shape, the dispersed layout performed better than the two double-row layouts. However, the effects of the layout on the film effectiveness and discharge coefficients are smaller for the diffusion slot hole. In the three layouts, the film effectiveness of the diffusion slot holes is remarkably greater than that of the fan-shaped holes, and the superiority increases as the blowing ratio increases. In contrast, the superiority of the diffusion slot hole in double-row layouts surpasses that of a dispersed layout.

Effect of Inlet Geometry on Film-Cooling Effectiveness from Shaped Holes

Modern gas turbine engines require a sophisticated cooling system design to achieve higher power output and efficiency. This study investigates the potential effect of noncylindrical inlet geometries on the performance of laid-back, fan-shaped film-cooling holes using the pressure-sensitive paint measurement technique on a flat plate. On the basis of a common pattern of outlet geometry, racetrack-shaped inlet geometries with aspect ratios of 2:1 and 4:1 were tested along with traditional cylindrical inlets. The coolant flow conditions range from M = 0.3–1.5 and DR = 1 and 2. The mainstream turbulence intensity is held at 6%. Test results show that the shaped inlets provide a higher area-averaged film-cooling effectiveness over the cylindrical inlet using the same amount of coolant. For the 2:1 inlet, an advantage of 20% higher effectiveness could be maintained for DR = 1, while for DR = 2 this advantage is reduced to 10%. For the 4:1 inlet, when the coolant momentum flux ratio I < 0.5, a similar or slightly higher improvement can be obtained, but when I > 1, the advantage diminishes with the growing I to approximately 5%, at I = 2.25. Regarding discharge coefficients, the 2:1 inlet geometry is similar to the cylindrical inlet. For the 4:1 inlet, it is 2–5% lower or nearly equivalent.

TPIV Experimental Investigation of Film Coolant-to-Mainstream Interaction From Shaped Cooling Holes With Various Inlet Geometries

Abstract In this investigation, multiple sets of time-averaged tomographic particle imaging velocimetry measurements are completed for laid-back, fan-shaped film cooling holes with “racetrack” shaped inlets. Traditional 10-10-10, laid-back, fan-shaped holes are inclined 30 deg to the mainstream flow on a flat plate. The inlet cross section varies from round to two elongated racetrack shapes. The cross-sectional area and the outlet-to-inlet area ratio for all the geometries are held constant. The flat plate is installed in a low-speed wind tunnel with a mainstream turbulence intensity of 8% and an average velocity of 21.6 m/s. The blowing ratios of the film jets range from 0.6 to 1.5 and the density ratio is 1. The Reynolds number of the cooling jet varies from 2600 to 8400. The characteristics of the resulting flowfield are coupled with the detailed film cooling effectiveness distributions. It can be noted from the results that the counter-rotating vortex pair generated by the 2:1 inlet is the closest to the surface and weakest in strength, likely caused by the minimum peak jet momentum of the three. The Reynolds stresses downstream of the 2:1 and 4:1 inlets are significantly lower than those downstream of the shaped hole with a round inlet. An inverse relation between volumetric turbulence accumulation (TA), and surface effectiveness (η), can be correlated for the blowing ratios considered. The turbulence accumulation term can thus be used to evaluate the performance of a film cooling hole design with flowfield data.

Combined effects of blowing ratio and mist diameter with mainstream turbulence intensity in mist-assisted film cooling

Advanced cooling techniques are essential in modern gas turbines to improve the efficiency of the Brayton cycle by raising the turbine inlet temperature. Mist-assisted film cooling offers an innovative solution for cooling high-temperature gas turbine blades. When mist particles with various momenta are injected through the cooling holes, the interplay between mainstream turbulence intensity (Tu) and mist momentum plays a crucial role in mist-assisted film cooling under high Tu conditions. Hence, this numerical study investigates the relationship between mainstream Tu and mist characteristics for the first time, considering the blowing ratio and mist diameter as controlling parameters. Film effectiveness and particle distribution statistics are analysed to understand their correlation. The results demonstrate that mist-assisted film effectiveness follows the trend of air-only film cooling with varying blowing ratios and Tu; however, the magnitude is amplified. The influence of the mist diameter on film effectiveness is determined by the surface-area-to-volume ratio and Stokes number. These factors impact the sensitivity of particles to Tu and subsequently affect film effectiveness. This study provides a novel quantitative analysis of the combined effect of mainstream Tu and mist on film cooling effectiveness, revealing the correlation between mist and mainstream parameters.HighlightsCombined effect of mainstream turbulence intensity (Tu) and mist characteristics is investigated.High mainstream Tu significantly increases the cooling enhancement induced by mist.Mist-assisted film cooling exhibits similar trends to varying mainstream Tu and blowing ratio.Mist diameter significantly influences the response to Tu, governed by surface-area-to-volume ratio and Stokes number.Small particles demonstrate the highest cooling effectiveness and variation by Tu.

Experimental Investigation of Effusion Film Cooling on a Cylindrical Leading Edge Model

Abstract Effusion film cooling is effective for cooling high-temperature turbine blades because it requires less coolant and produces a more uniform temperature distribution than conventional film cooling. Effusion cooling for a cylindrical model representing the leading edge of a gas turbine blade was investigated. The experiment was performed in a low-speed wind tunnel at a Reynolds number of 100,000. Pressure-sensitive paint was used to measure the adiabatic film cooling effectiveness. Additive manufacturing was used to fabricate a porous structure on the test cylinder for effusion cooling. Both simple and compound angles were used for cooling injection. The effects of streamwise and spanwise hole spacings, turbulence intensities (1% and 8.7%), and blowing ratios (0.075, 0.15, 0.3, and 0.6) were studied at a fixed density ratio of 1. The effusion hole diameter was 0.1 cm, and the spanwise hole pitch-to-diameter ratio was either 2 or 4. Compared with conventional film cooing, effusion cooling achieved a higher cooling effectiveness and produced a better coolant coverage. Increasing the streamwise spacing noticeably reduced the cooling effectiveness for the simple-angle design due to film lift-off; the compound-angle designs thus achieved higher effectiveness. The simple-angle holes were more sensitive to changes in the mainstream turbulence intensity; increases in the turbulence intensity promoted the mixing of the coolant with the mainstream. Moreover, effusion cooling was more resistant to coolant lift-off at high blowing ratios.

Film Cooling Effectiveness on Pressure Surface and Suction Surface of Turbine Guide Vane With Diffusion Slot Holes

Abstract This paper investigated the film-cooling effectiveness of diffusion slot holes in a turbine nozzle guide vane. The pressure-sensitive paint measurement technique was employed to obtain the film-cooling effectiveness at a density ratio of DR = 1.5. The mainstream Reynolds number based on the axial chord length and the exit velocity was 6 × 105. The mainstream turbulence intensity was approximately 3.7%. Three diffusion slot hole geometries with cross-sectional aspect ratios (ASs) of 2.3, 3.4, and 4.9 were tested and compared with a typical fan-shaped hole. The experiments were performed at three typical hole row locations on the pressure surface (PS) and suction surface (SS). The average blowing ratios varied from M = 0.5 to 2.5. The results showed that throughout the blowing ratio range, on the PS, a substantially higher film-cooling effectiveness than the fan-shaped hole is always obtained from the diffusion slot hole with a large aspect ratio (AS = 4.9); on the SS, the diffusion slot hole with a small AS (AS = 2.3). The influence of hole row positioning is inconsistent for diffusion slot holes with different ASs. The diffusion slot hole is less affected by the PS when the AS is moderate and less affected by the SS when the AS is large. The film-cooling effectiveness of the diffusion slot holes is basically the lowest where the PS has a maximum concave curvature and the highest where the SS has a large favorable pressure gradient.

Coupling of Volumetric Flowfield and Surface Effectiveness Measurements for Flat-Plate Film Cooling With Cylindrical Holes Using Tomographic Particle Image Velocimetry and Pressure-Sensitive Paint

AbstractIn this study, a series of time-averaged tomographic particle image velocimetry (TPIV) measurements are completed for simple angle, cylindrical film cooling holes on a flat plate with an inclination angle of 30 deg and a diameter of 4 mm. The flat plate is installed in a low-speed wind tunnel with a mainstream turbulence intensity of Tu=8% and an average velocity of 21.6 m/s. The blowing ratios of the jet range from M = 0.3 to M = 1.5, and the density ratio of the jet is fixed at DR = 1. The Reynolds number of the cooling jet varies from 1700 to 8400. The repeatability and accuracy of the tomographic particle imaging velocimetry (TPIV) measurements are compared against the results obtained by other flowfield measurement techniques. The results of the TPIV measurements are presented in velocity and vorticity iso-surface distributions in 3D, as well as 2D planar slices of velocity, vorticity, turbulence intensity, and Reynolds Stress distributions within the measurement volume. The characteristics of the flowfield are coupled with the detailed film cooling effectiveness distribution obtained using the pressure-sensitive paint (PSP) technique. An inverse relation among volumetric turbulence accumulation (TA) and surface film effectiveness, η, can be correlated.

Effects of Mainstream Velocity and Turbulence Intensity on the Sweeping Jet and Film Composite Cooling

The jet always sweeps to the leftmost and rightmost points in the sweeping jet and film composite cooling (SJF) process, resulting in a different coolant flow in each film hole. The film can not easily cover the outer surface evenly under the scouring of the mainstream. This work presents a case study to analyze the effects of two mainstream variables on the film areodynamic and cooling performance of the SJF. Three different mainstream velocities (Vm= 10 m/s, 50 m/s, 90 m/s) and three different mainstream turbulence intensities (Tu = 1%, 10%, 20%) are discussed. Results indicate that the increase of mainstream velocity yields to better film attachment. When the mainstream velocity increases from 10 m/s to 50 m/s, the overall cooling effectiveness and total pressure loss coefficient are reduced by 17.68% and 98.60%, respectively. When the mainstream velocity increases from 50 m/s to 90 m/s, the overall cooling effectiveness and total pressure loss coefficient are almost unchanged. The effect of turbulence intensity on the overall cooling effectiveness and total pressure loss coefficient are relatively small. The increase of mainstream turbulence intensity enhances the disturbance of the mainstream to the coolant from the middle film holes, and the distribution of adiabatic film cooling effectiveness is more uneven when the mainstream turbulence intensity is raised to 10% and 20%. In the research scope of present work, the flow structure, total pressure loss coefficient and overall cooling effectiveness are the most expected under the conditions of lower turbulence intensity and higher mainstream velocity (Tu = 1%, Vm= 90 m/s).

Effect of inflow conditions on transonic turbine airfoil limit loading

To better understand airfoil limit loading and the effect inflow conditions have on local efficiency, a computational fluid dynamic investigation was performed for four different transonic turbine airfoils under sub-critical, critical, and supercritical conditions. A computational baseline was established using data previously collected at the Pratt and Whitney Canada High-Speed Wind Tunnel at Carleton University near design conditions using the Reynolds-Averaged Naiver-Stokes shear stress transport k − ω turbulence model with γ transition. The effects of inflow conditions on aerodynamic performance were examined by varying incidence by ± 20°, mainstream turbulence intensity from 5 to 20% and mainstream turbulent length scale from 1 to 100% of the airfoil pitch. Quantitative data of mass-flow averaged Mach numbers, mass-flow averaged flow angles, surface isentropic Mach number distributions and mass-flow averaged total pressure loss coefficients were collected and are presented alongside flow visualizations of numerical Schlieren images to allow for a detailed description of the entire flow domain. Similar to previous experimental work the limit loading pressure ratio and the mass-flow averaged outlet flow angle were strongly correlated with the airfoil outlet metal angle. The influence of inflow conditions was minimal on the exit flow profile with the exception of the mass-flow averaged total pressure loss coefficients. Results show incidence variation to change the total pressure loss coefficient depending on the airfoil, whereas, turbulence intensity and turbulent length scale predicted a drastic increase in loss with increased turbulence level for all airfoils considered.

Numerical analysis of vane endwall film cooling and heat transfer with different mainstream turbulence intensities and blowing ratios

In present study, effects of mainstream turbulence intensity and blowing ratio on the endwall film cooling and heat transfer are numerically investigated. Upstream double-row streamwise cylindrical holes with inclination angel (θ) of 30 deg is applied. Four blowing ratios (M = 0.5, 1.0 1.5, 2.0) and three turbulence intensities (Tu = 5%, 15%, 25%) are studied. Distributions of film cooling effectiveness and heat transfer coefficient are presented together with vortex structure. Results show that with the increasing of blowing ratio, the strength of horseshoe vortex is significantly weakened and the level of film cooling effectiveness is obviously improved. In addition, the low heat transfer zone downstream the holes and upstream the leading edge is enlarged because of the increased momentum, while the high heat transfer zone at the exit of passage gradually shrinks. With the increasing of turbulence intensity, the variation of film cooling effectiveness is very limited, but the level of heat transfer near the pressure side in the second half of the vane passage obviously decreases. Moreover, a more uniform film coverage and heat transfer distribution is obtained at high turbulence intensities.

Direct and Inverse Model for Single-Hole Film Cooling With Machine Learning

Abstract The direct prediction model for adiabatic film cooling effectiveness distribution and inverse prediction model for design parameters are studied in this article. Convolutional neural networks (CNNs) are trained on a set of simulated adiabatic film cooling effectiveness contours parameterized by blowing ratio, density ratio, mainstream turbulence intensity, injection angle, and compound angle. The direct model and the inverse model are able to approximate the data in the test set with plausible accuracy. The absolute error of spatial averaged effectiveness no larger than 0.03 could be obtained in the test set by a direct model with time consumption less than 1 ms for a single case. The inverse model is the first model of its kind, which accomplished the inverse mapping from contours to parameters. It has been demonstrated that the concatenation of inverse model with the pretrained direct model, which can be treated as a complex loss function, has preferable approximation performance compared with simple mean squared error (MSE) loss function in the training of the inverse model, thus confirming the necessity of adopting specialized modeling strategies for inverse problems.

Experimental Study on Film Cooling Effectiveness of Blade With Chevron-Shaped Holes Under Wake Influence

Abstract Gas turbines have been widely used. With the continuous improvement of the performance of gas turbines, the turbine inlet temperature has greatly exceeded the heat-resistance limit of the turbine blade material, so advanced cooling technology is required. The film cooling effectiveness distribution over the blade under the effect of wake was obtained by the pressure-sensitive paint (PSP) technique. The test blade has five rows of chevron film holes on the pressure side, three rows of cylindrical film holes on the leading edge, and three rows of chevron film holes on the suction side. The mainstream Reynolds number is 130,000 based on the blade chord length, and the mainstream turbulence intensity is 2.7%. The upstream wake was simulated by the spoken-wheel type wake generator. The film cooling effectiveness was measured at three wake Strouhal numbers (0, 0.12, and 0.36) and three mass flux ratios (MFR1, MFR2, and MFR3). The results show that the increase of mass flux ratio leads to a decrease of the film cooling effectiveness on the suction surface. In the wake condition, the effect of mass flux ratio is weakened. Wake leads to a marked decrease of the film cooling effectiveness over most blade surface except for the surface near leading edge on the pressure surface. In the high mass flux ratio condition, the effect of wake on the film cooling effectiveness is weakened on the suction surface and strengthened on the pressure surface.

Endwall film cooling holes design upstream of the leading edge of a turbine vane

Endwall film cooling upstream of the leading edge (LE) of a vane presents a relatively complex flow phenomenon due to the horseshoe vortices (HVs) generated at the LE region. Upstream of the LE region, the coolant flow has difficulties to eject out. This research work focuses on controlling the jet holes coolant coverage upstream of the LE region. Compound angle holes in staggered arrangement are introduced and applied in the LE region to increase the coolant coverage. Six different arrangements of cooling holes are designed, with variations from one row or two rows arrangements, parallel or staggered arrangements, normal cylindrical holes or compound angle holes. Besides cooling holes with different shapes and arrangements, effect of the blowing ratio (BR) and turbulence intensity (TI) are also considered. The BR ranges from 1 to 3 and TI ranges from 1.3% to 15%. The calculated results show that the film cooling holes upstream of the LE of a vane have significant cooling effects on both the vane surfaces and the endwall. At small BRs, the film cooling effectiveness (η) on the endwall is considerable. When the BR is increased, the η on the vane surfaces is increased more quickly and becomes dominant. The coolant coverage in the vane-endwall junction region are not affected by the mainstream turbulence intensity and almost keep the same with the varied turbulence intensities. A single row of cylindrical holes (Case 1) and two rows of compound angle holes with staggered arrangement (Case 5) have relatively high overall averaged cooling effectiveness compared with other cases at different BRs. In addition, the high averaged cooling effectiveness on the endwall and vane surfaces by Case 5 is not affected by a change of the BRs.

Experimental study of free-stream turbulence intensity effect on overall cooling performances and solid thermal deformations of vane laminated end-walls with various internal pin–fin configurations

Experimental investigations of mainstream turbulence intensity (Tu) effect on conjugate heat transfer performances, total pressure loss and solid thermal deformations of vane laminated cooling end-walls (LCEs) have been carried out under two engine-near mainstream-to-coolant temperature ratios of 1.4 and 2.0. Influences of parameters of internal elements of LCEs were discussed. A servicing film cooling end-wall (FCE) was chosen as a reference. Two typical Tus were designed, 2.2% and 10.1% (in the engine range). Measurements of fluid-thermal-solid coupling characteristics of cooled end-walls were implemented in a hot wind tunnel based on matched engine Biot number under three mass flow ratios. Generally, the elevated Tu exhibited a negative influence on overall cooling effectiveness and component reliability of cooled end-walls, total pressure loss in cascade and slight thermal deformations of LCEs. Moreover, the elevated Tu displayed a negative effect on the remarkable benefit of LCEs over FCE. The shape and diameter of pin-fins and the impingement-hole size played complex roles on overall effectiveness, surface thermal gradient, aerodynamic loss and component weight. However, the Tu effect on the aforementioned roles was slight. Overall, the LCE with diamond-shaped pin-fins and large impingement-holes was the most optimal design.

A tip region film cooling study of the fan-shaped hole using PSP

Suction side tip region film cooling of fan-shaped hole was investigated experimentally. In the experiments, the cylindrical hole film cooling performance is also studied for comparison. The experiments were completed in a cascade, which is constituted by five rotor blades with the tip clearance of 1.0 mm. The film hole was located at 7/8 height of the total blade. The adiabatic film cooling effectiveness contours were obtained by the pressure sensitive paint (PSP) technology. Inlet velocity was controlled by the inlet and outlet valves. Simultaneously, the averaged pressure at the outlet was measured. The mainstream turbulence intensity was controlled within 3.2%–5.6%. In this paper, the blowing ratio effects, the density ratio effects, the tip structure effects and the Reynolds number effects were studied. The results showed the fan-shaped hole film cooling performance is worse than that of the cylindrical hole. As the blowing ratio increases the fan-shaped hole film coverage area increases while that of the cylindrical hole decreases gradually. Finally, for the results of M = 2.0, they both decreases greatly. The film deflection angle of the fan-shaped hole is much higher. The density ratio experiments show the low density ratio jet has bigger momentum to resist the passage vortex. High Reynolds number weakens influences of leakage flow and passage vortex on the film. At last, the single squealer tip reduces the pressure gradient near the film, promoting the jet-off.

A Parametric Investigation of Vane Showerhead Film Cooling by Pressure-Sensitive Paint Technique

Abstract In this study, a parametric analysis of the thermal performance of a nozzle vane cascade with a showerhead cooling system made of four rows of cylindrical holes was carried out by using the pressure-sensitive paint (PSP) technique. Coolant-to-mainstream blowing ratio (BR), density ratio (DR), main flow isentropic exit Mach number (Ma2is), and turbulence intensity level (Tu1) were the considered parameters. The cascade was tested in an atmospheric wind tunnel at Ma2is values ranging from 0.2 to 0.6, with an inlet turbulence intensity level of 1.6% and 9%, at variable injection conditions of BR = 2.0, 3.0, 4.0. Moreover, the influence of the DR on the leading-edge film-cooling performance was investigated: the testing was carried out at DR = 1.0, using nitrogen as foreign gas, and DR = 1.5, with carbon dioxide serving as a coolant. In the near-hole region, higher BR and Ma2is resulted in higher effectiveness, while higher mainstream turbulence intensity reduced the thermal coverage in between the rows of holes, whatever the BR is. Further downstream along the vane pressure side, the effectiveness was negatively affected by rising the BR but positively influenced by lowering the mainstream turbulence intensity. Moreover, a decrease in the DR caused a reduction in the film-cooling performance, whose extent depends on the injection condition.

Turbulence Intensity Effects on a Leading-Edge Separation Bubble of Flat Plate Wing at Low-Reynolds Numbers

In this study, we experimentally investigate the effects of mainstream turbulence intensity (Ti) on a leading-edge separation bubble under low-Reynolds number (Rec) conditions range of 2.0 × 104 to 6.0 × 104. We used a flat plate to fix a separation point at the leading edge. Also, we visualized the behavior of the leading-edge separation bubble using the smoke wire technique and Particle Image Velocimetry (PIV) measurement. Furthermore, we measured the effect of Ti on the turbulent transition process in the separated shear layer using a hot-wire anemometer. The results indicate that the bypass transition for large Ti causes the turbulent transition, and so accelerates the reattachment of the separated shear layer. The results show that the bypass transition promotes the reattachment of the separated shear layer to maintain the leading-edge separation bubble on the upper surface even at high angles of attack, increasing the stall angle.

Investigations of flow field around two-dimensional simplified models with wind tunnel experiments

The effect of topographic features on wind velocity and turbulence intensity was evaluated by conducting wind tunnel experiments with Particle Image Velocimetry (PIV) system. In this study, to simulate the natural wind characteristics, the active turbulence grids and boundary layer generation frame were installed in the wind tunnel. The mean wind velocity, the velocity vector diagram and the turbulence intensity around the two-dimensional single simplified models were investigated. As a result, the flow was separated at the simplified model tip in all cases of models, and the countercurrent flow field was generated at the downstream side. Moreover, the clockwise circulation flow also moved to the upstream side in the case of large radius R. RX was followed by the name given the radius value of X. For the mainstream turbulence intensity, the ranges of high turbulence intensity were z/H < 2.8 for R1 model, z/H < 2.6 for R3 model, z/H < 2.5 for R6 model, z/H < 2.4 for R11 model, z/H < 2.2 for R20 model, z/H < 2.0 for R23 model, z/H < 1.9 for R25 model in the vertical direction. The quantitative measurement results of this paper provided a database for the validation of the wind velocity distributions of atmospheric turbulent flow in the hill and mountain regions.

Effects of Mainstream Turbulence Intensity and Coolant-to-Mainstream Density Ratio on Film Cooling Effectiveness of Multirow Diffusion Slot Holes

Abstract Multirow film cooling is widely used in gas turbine airfoils cooling to cope with extremely high inlet temperature. The film cooling effectiveness of diffusion slot holes was measured in multirow arrays at a flat plate experimental facility using the pressure sensitive paints (PSP) technique. Emphasis was focused on the influence mechanism of mainstream turbulence intensity (Tu) and coolant-to-mainstream density ratio (DR) on film cooling effectiveness of multirow arrays with wide exit holes. The diffusion slot hole with exit width of 3.7D and 4.0D was, respectively, tested in three staggered arrays of P/D = 6 and S/D = 30, P/D = 6 and S/D = 20, and P/D = 9 and S/D = 20. Four blowing ratios varied from M = 0.5 to 2.0. The baseline condition (Tu = 3.5%, DR = 1.38) was compared with an increased Tu condition (Tu = 8.4%) and a decreased DR condition (DR = 0.97). The results showed that in two P/D = 6 arrays, increasing Tu decreased the multirow effectiveness considerably under all blowing ratios, but increasing Tu prominently restrained the film coalescence. The influences of Tu were more intense for the arrays with larger exit width holes and larger S/D. Decreasing DR increased multirow effectiveness obviously. The influences of DR tended to consistent for all arrays and the influences were relatively weak for high blowing ratios. In the P/D = 9 array, the superiority of large exit width hole disappeared completely, regardless of Tu and DR variations.

Overall effectiveness of film-cooled leading edge model with normal and tangential impinging jets

This paper investigates the overall effectiveness of film-cooled leading edge model with normal and tangential impinging jets. The leading edge has three rows of cylindrical film cooling holes, located at the stagnation line (0°) and ± 40° measured from the stagnation line. Film cooling holes are at an inclined angle of 25° relatives to the surface. The normal jet has one row of normal jet impinging holes and the tangential jet has two rows of tangential jet impinging holes. Mainstream Reynolds number based on the leading edge cylinder external diameter is about 100,000, and the mainstream turbulence intensity is about 7%. Three blowing ratios of 0.77, 1.54, and 2.31 are considered. Pressure sensitive paint technique is applied to measure the adiabatic effectiveness with the density ratio of 0.97. Liquid crystal technique is used to obtain the overall effectiveness with the density ratio of 0.94. Numerical simulations using realizable k-ɛ (RKE) turbulence model with enhanced wall treatment were applied to calculate the adiabatic effectiveness and overall effectiveness. Compared with experiments, numerical simulations overpredict overall effectiveness about 20% to 30% between the 0° row and the 40° row, and the difference between simulations and experiments is about 10% to 20% after the 40° row. The results provide baseline information for turbine blade leading edge film cooling design and heat transfer analysis.