Fan-shaped Holes Research Articles

Effect of hole configurations on film cooling performance

This study aims to investigate the cooling performance of various film cooling holes, including combined hole, cylinder hole, conical hole, and fan-shaped hole. For film cooling technology, a novel combined hole configuration is first proposed to improve the cooling protection for gas turbine engines. This combined hole consists of a central cylinder hole (an inclination angle of 35°) and two additional side holes (a lateral diffusion angle of 30°). Film holes for four-hole configurations have the same inlet diameter of 8 mm. The adiabatic film cooling effectiveness for each hole configuration is analyzed for varying blowing ratios (M = 0.25, 0.5, 0.75, and 1.0). Results show that the best cooling performance for the conical and fan-shaped holes is obtained at the blowing ratio of 0.75. In addition, the combined hole configuration provides a more uniform cooling protection and a better cooling performance than the other hole configurations.

The characteristics and divergence of fan-shaped and cylindrical holes on the suction side of a turbine blade under rotating conditions

Detailed film cooling effectiveness for fan-shaped and cylindrical holes on the suction side of a turbine blade under rotating conditions was obtained by experimental measurements. The experiments were conducted using a 1-stage turbine installed in a closed-loop, low-speed, thermal wind tunnel. The turbine section was designed to rotate at different settled speeds, and the velocity of the mainstream was adjusted to achieve a zero-incidence angle. In the experiments, a steady-state thermochromic liquid crystal (TLC) technique was used to evaluate the film cooling performance. The row hole was situated at an axial location of 8% with an injection angle of 45°. The diameter of the cylindrical hole was 0.8 mm, and the length-to-diameter ratio was 6. For the fan-shaped hole, the forward expansion angle and the lateral diffusion angle were 12° and 10°, respectively. The effects of blowing ratio (M), rotation speed (Ω) and density ratio (DR) on the film cooling performance were analyzed. The blowing ratio was varied from 0.5 to 2.0 with three rotation speeds, 300 rpm, 450 rpm and 600 rpm. CO2 and N2 acted as coolants to achieve the two density ratios of 1.47 and 0.98, respectively. The results showed that the row of fan-shaped holes had better film cooling performance under most operating conditions and especially at low blowing ratios. The length of the coolant trace first increases and then decreases along the spanwise direction, from hub to tip, at all operating conditions. With an increase in the rotation speed, the lateral averaged film cooling effectiveness of both hole geometries decreases. However, fan-shaped holes have better film cooling performance at low rotation speed. In addition, the results for the density ratio showed that CO2, which has a higher density ratio, achieves higher film cooling performance for fan-shaped holes, while the length of the coolant trace is almost constant between the two density ratios.

Combined Experimental and CFD Investigation of Flat Plate Film Cooling through Fan Shaped Holes

The present paper reports the results of an experimental and computational investigation of flat plate film cooling jets discharged from three fan-shaped holes. Measurements have been carried out at near unity density ratio in a low-speed wind tunnel, at low inlet turbulence intensity, with blowing ratios (BR) of 1 and 2. Aerodynamic results have shown that the jet stays attached to the flat plate. Thermal measurements have revealed that film cooling effectiveness decreases downstream of the holes, and BR equal to 1 provides the best trade-off between cooling air consumption and thermal protection. Consequently, BR = 1 was selected for assessing the performance of different turbulence models, implemented in STAR-CCM+, according with the steady Reynolds-averaged Navier–Stokes (RANS) approach. Predictions from realizable k-ε (RKE), shear stress transport k-ω (SST KW) and Reynolds stress model (RSM) were compared against measurements of laterally averaged and centerline adiabatic effectiveness, as well as off-the-wall velocity maps and profiles of stress components. RSM provided the most accurate predictions.

Performance evaluation of a converging-diverging film-cooling hole

A converging-diverging film-cooling hole was designed by combining a converged inlet with a fan-shaped exit. The performance of the proposed design was analyzed numerically and compared to that of a fan-shaped hole. The film-cooling effectiveness was evaluated using three-dimensional Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model. The numerical results for fan-shaped and cylindrical holes were compared with previous experimental data. Compared to the fan-shaped hole, the converging-diverging hole improved the spatially averaged film-cooling effectiveness by 4.3%, 5.9%, and 9.9% at blowing ratios of 0.5, 1.0, and 1.5, respectively. These improved film-cooling performances were achieved by reducing the size of the separation bubble in the hole, thus increasing the thickness of the coolant layer downstream of the hole.

Computational research on film cooling performance of different shaped holes with backward and forward injection

The present work has been performed to evaluate the effect of three shaped holes (cylindrical hole, expansion-shaped hole and fan-shaped hole) with forward injection and backward injection on film cooling effectiveness on the adiabatic wall flat plate. All the cases are computed under eight blowing ratios (M) = [0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75 and 2.0]. The results show that for film cooling hole structure with backward injection, a pair of rotating vortex is formed at the outlet of film cooling hole. Differing from the classical counter rotating vortex pair (CRVP) found in each hole with forward injection, the vortexes are expanded away from the test wall under the function of transverse main flow and are broken quickly. It indicates that the rotating vortex pair does not promote the mixing of main flow and jet flow. The uniformity of local film cooling effectiveness of the hole with backward injection is higher than that of the hole with forward injection. In terms of the spatially averaged film cooling effectiveness with a certain hole shape, the value under backward injection exceeds that under forward injection at a certain point: (1) M=0.5 for cylindrical hole, (2) M=0.75 for expansion-shaped hole and (3) M=1.25 for fan-shaped hole. The comparison of the calculation results of different holes with backward injection shows that in the case of high blowing ratio, a uniform distribution with higher film cooling effectiveness is easier to achieve with fan-shaped hole.

Uncertainty Quantification of the Effects of Small Manufacturing Deviations on Film Cooling: A Fan-Shaped Hole

The film cooling holes in the blade of modern gas turbines have commonly been manufactured by laser drilling, Electric Discharge Machining (EDM), and Additive Manufacturing (AM) in recent years. These manufacturing processes often result in small geometric deviations, such as conical angles, filleted edges, and diameter deviations of the hole, which can lead to deviations on the distribution of adiabatic cooling effectiveness (η) values, the value of the discharge coefficient (Cd), and the characteristic of the in-hole flow field. The current study employed flat plate fan-shaped film cooling holes with length-to-diameter values (L/D) equal to 3.5 and six to investigate the effects of these manufacturing deviations on the distribution of η values, the value of Cd, and the characteristic of in-hole flow field. An Uncertainty Quantification (UQ) analysis using the Polynomial Chaos Expansion (PCE) model was carried out to quantify the uncertainty in the values of η and Cd. The statistical characteristics (mean values, standard deviation (Std) values, and Probability Density Function (PDF) values) of η and Cd were also calculated. The results show that conical angle deviations exert no visible changes on the value of η. However, the Cd value decreases by 6.2% when the conical angle changes from 0–0.5°. The area averaged adiabatic cooling effectiveness ( η = ) decreases by 3.4%, while the Cd increases by 15.2% with the filleted edge deviation existing alone. However, the deviation value of η = is 7.6%, and that of Cd is 25.7% with the filleted edge deviation and the diameter deviation existing.

Optimization of the configuration of the laidback fan-shaped film cooling hole with a lateral expansion angle of 10 degrees

Film cooling techniques have been widely applied to gas turbine engines to protect the components from hot combustion gas. In this study, the shape of the laidback fan-shaped hole with a lateral expansion angle of 10 degrees was optimized through the Reynolds Averaged Navier-Stokes (RANS) analysis. Results by numerical analysis were validated with the corresponding experimental results obtained by the pressure sensitive paint technique (PSP). For optimal hole shape derivation, the design points were selected through the Latin Hypercube Sampling (LHS) method for three design variables: injection angle, metering length, and forward expansion angle. The overall averaged effectiveness was used as the objective function. Results showed that the overall film cooling effectiveness of the optimal holes derived by the response surface method and the Kriging method were higher than that of the reference hole by 4.5% and 7.5%, respectively. Generally, holes with a higher area ratio (AR) showed higher overall film cooling effectiveness. However, the interaction between each shape parameter should be considered to derive the optimal hole shape.

Film Cooling Measurements for a Laidback Fan-Shaped Hole: Effect of Coolant Crossflow on Cooling Effectiveness and Heat Transfer

Internal coolant passages of gas turbine vanes and blades have various orientations relative to the external hot gas flow. As a consequence, the inflow of film cooling holes varies as well. To further identify the influencing parameters of film cooling under varying inflow conditions, the present paper provides detailed experimental data. The generic study is performed in a novel test rig, which enables compliance with all relevant similarity parameters including density ratio. Film cooling effectiveness as well as heat transfer of a 10–10–10 deg laidback fan-shaped cooling hole is discussed. Data are processed and presented over 50 hole diameters downstream of the cooling hole exit. First, the parallel coolant flow setup is discussed. Subsequently, it is compared to a perpendicular coolant flow setup at a moderate coolant channel Reynolds number. For the perpendicular coolant flow, asymmetric flow separation in the diffuser occurs and leads to a reduction of film cooling effectiveness. For a higher coolant channel Reynolds number and perpendicular coolant flow, asymmetry increases and cooling effectiveness is further decreased. An increase in blowing ratio does not lead to a significant increase in cooling effectiveness. For all cases investigated, heat transfer augmentation due to film cooling is observed. Heat transfer is highest in the near-hole region and decreases further downstream. Results prove that coolant flow orientation has a severe impact on both parameters.

Numerical assessment of round-to-slot film cooling performances on a turbine blade under engine representative conditions

Numerical simulations are carried out to address further insights into the effects of round-to-slot film cooling holes on a multi-row film-cooled turbine blade under representative engine-simulated conditions by adopting both adiabatic and conjugate heat transfer CFD models. In the current study, only the alteration of film-hole shape at suction and pressure sides is concerned while the showerhead film cooling holes at the leading edge remain cylindrical or baseline shape. Four film-hole shapes are taken into consideration, including converging round-to-slot hole (RTSH-1), equivalent-area round-to-slot hole (RTSH-2), diffusing round-to-slot hole (RTSH-3) and fan-shaped hole (FSH). Beside, a series of computations are also performed to the individual single-row film cooling by setting the coolant-feeding condition as its corresponding one in the multi-row film cooling situation. Viewed from the comprehensive influence of film-hole shape on film cooling performance, such as coolant feeding usage amount, enthalpy loss coefficient and cooling effectiveness, it is suggested that RTSH-2 should be the most favourable shape. RTSH-1 leads to the smallest coolant usage and enthalpy loss coefficient but its cooling effectiveness is low. Although RTSH-3 could present the highest cooling effectiveness, it produces the largest coolant usage and cascade enthalpy loss coefficient.

팬 형상 막냉각 홀이 위치한 평판 막냉각 유동에 대한 대와류 모사해석

팬 형상 막냉각 홀이 위치한 평판 막냉각 유동에 대한 대와류 모사해석

Combined effects of unsteady wake and free-stream turbulence on turbine blade film cooling with laid-back fan-shaped holes using PSP technique

Detailed film cooling effectiveness distribution for a gas turbine blade under the effects of unsteady wakes and oncoming free-stream turbulence intensities was obtained using pressure sensitive paint (PSP) technique. Tests were performed on a linear cascade at Reynolds number of 3.85 × 105 based on the blade chord at cascade exit. Upstream unsteady wakes were simulated using a spoke-wheel type wake generator. The test blade has three rows of compound angled cylindrical film holes at the leading edge, five rows of laid-back fan-shaped holes on the pressure surface and three rows of laid-back fan-shaped holes on the suction surface. The wake Strouhal number was varied from 0 to 0.36 and three mass flux ratios were determined. The oncoming free-stream turbulence intensities are 2.7% and 26.9%, respectively. Results show that the effect of the mass flux ratio on the film cooling effectiveness decreases under the high turbulence intensity and unsteady wake conditions. In most regions of the blade surface, the film cooling effectiveness decreases with the increase of wake Strouhal number, and the free-stream turbulence superimposed on the unsteady wake reduces the film cooling effectiveness further. The effect of the unsteady wake decreases under the high free-stream turbulence conditions.

Heat transfer mechanisms of inclined jets in cross flow with different holes

Film cooling is one of the key techniques to improve the thermal performance of hot sections in gas turbines. Heat transfer coefficient is an important parameter to quantify the thermal performance, which is often analyzed based on the time averaged flow field. Nevertheless, in the case of film cooling, the mixing between the coolant and the main flow is inherently unsteady. To understand the mechanism of heat transfer, the current study uses large eddy simulation (LES) method to investigate the heat transfer coefficient of inclined jets in crossflow. The angle between the hole and the main flow is 35°. Two different geometric holes, namely a cylindrical hole and a fan-shaped hole are investigated at a blowing ratio of 0.5, which is a typical value for film cooling application. Both the time averaged and the instantaneous flow characteristics are analyzed. The mechanism of heat transfer distribution is analyzed in detail. Near the surface, the streamwise fluctuated variables u′T′‾ has a large effect on the heat transfer coefficient. Compared with the cylindrical hole, the heat transfer downstream of the fan-shaped hole is highly unsteady and streamwise fluctuated variables u′T′‾ is larger, so the heat transfer coefficient is higher.

In-Situ Fracturing Induced Caving of a Hard Orebody and Its Application

In-situ fracturing induced caving is proposed as a solution to the problem that it is difficult to form the cutting slot required by conventional mining to achieve sublevel caving stoping in a broken orebody affected by high-stress fracturing. This method involves the creation of a limited blasting compensation space through the construction of roadways, and then the formation of an in situ fractured area with the use of fan-shaped beam hole enhanced blasting technology, thus improving ore cavability. When the undercut area at the bottom satisfies the conditions of continuous caving, induced caving mining of a high-stress hard orebody can be achieved. This method adopts super-extrusion blasting technology in a limited blasting compensation space to fragment the ore through the combination of stress and blasting, changing the characteristic parameters of endogenic joints and fissures, and utilizes fan-shaped beam hole enhanced blasting technology to guide the design of the blasting parameters. The method also establishes a multichannel ground pressure monitoring system based on acoustic emission technology to monitor changes in ground pressure in real time during in situ fracturing induced caving mining and to guarantee mine safety. The corresponding key technologies have been applied successfully for caving mining area II of orebody no. 92 in Tongkeng mine, which provides useful theoretical and technical references for efficient blasting and mass mining at other locations where there is limited space.

Multi-objective optimization of laidback fan-shaped film cooling hole on Turbine Vane Suction Surface

A CFD-based multi-objective optimization is performed for improving the film cooling performance of the laidback fan-shaped holes on the suction surface of a turbine guide vane under a typical blowing ratio of M = 1.5. Among the main geometric parameters, the inclination angle (α), lateral expansion angle (β) and forward expansion angle (γ) are selected as the design variables, with respective lower and upper bounds of (25°, 55°), (10°, 20°) and (3°, 15°) in turns. Two independent objective functions that are simultaneously optimized are selected as the spatially-averaged adiabatic film cooling effectiveness (ranging from s/d = 0 to s/d = 12) and the discharge coefficient. By using a variant of non-dominated sorting genetic algorithm (NSGA-II) coupled with the RBFNN-based surrogate model, the Pareto front of optimal solutions is obtained, providing a variety of options for seeking the maximum spatially-averaged adiabatic film cooling effectiveness, the maximum discharge coefficient, or the compromise of both aspects. The optimized results show that the optimal geometers of (α, β, γ) are (50.3°, 19.5°, 9.8°), (25°, 18.7°, 11.8°) and (27.3°, 19°, 5.1°) for achieving the most maximum film cooling effectiveness, the most maximum discharge coefficient and the compromise of both aspects, respectively. In general, a large lateral expansion angle of the laidback fan-shaped film-cooling hole is necessary in the shape optimization for all of the optimal options. However, with regard to the other design variables, their selections are very distinct following the optimal option. Further, the influence role of optimal fan-shaped geometry on the film cooling performance is illustrated according to the detailed flow and thermal behaviors.

35-7-10 팬형상 막냉각 홀의 복합설치각도가 막냉각 효율에 미치는 영향

35-7-10 팬형상 막냉각 홀의 복합설치각도가 막냉각 효율에 미치는 영향

A Novel Method for Designing Fan-Shaped Holes With Short Length-to-Diameter Ratio in Producing High Film Cooling Performance for Thin-Wall Turbine Airfoil

An experimental investigation of the geometrical parameter effects on the film cooling performance of a fan-shaped hole was conducted on a low speed flat-plate facility. The pressure sensitive paint (PSP) technique and steady liquid crystal (SLC) technique were employed to determine the adiabatic film cooling effectiveness and heat transfer coefficients, respectively, for a blowing ratio ranging from 0.3 to 3 and a density ratio of DR = 1.5. Several geometrical parameters were investigated, including lateral expansion angle, length-to-diameter ratio, and hole entrance shape. Local, laterally averaged, and area-averaged adiabatic film cooling effectiveness, heat transfer coefficients, and net heat flux reduction (NHFR) were shown to provide a comprehensive understanding on the geometrical parameter effects on the thermal performance. A novel method was proposed for designing a fan-shaped hole with short length-to-diameter ratio to design to achieve high film cooling performance. The original and optimized fan-shaped holes were compared in terms of adiabatic film cooling effectiveness, heat transfer coefficients, and NHFR. Results showed that the optimized fan-shaped hole with short length-to-diameter ratio, large lateral diffusion angle, and slot hole entrance shape obtained highest overall thermal performance. It demonstrated the feasibility of adopting the proposed design method to design fan-shaped holes applied in thin wall gas turbine blades.

Experimental investigation of wall thickness and hole shape variation effects on full-coverage film cooling performance for a gas turbine vane

The effects of wall thickness and hole shape variation on a full-coverage film cooled turbine vane are investigated in a stationary and linear cascade utilizing the pressure sensitive paint technique. The varied wall thickness produces hole length-to-diameter ratio (L/D) in a range from L/D = 2 to 5, and holes tested include simple angle hole, compound angle hole, and fan-shaped hole. Five rows of holes are provided on the pressure side while three rows of holes are provided on the suction side, with six rows of cylindrical holes drilled on the leading edge to construct showerhead film cooling. The tested blowing ratios for the showerhead, pressure side, and suction side range from 0.25 to 1.5, with a density ratio of 1.5. The freestream Reynolds number is 1.35 × 105, based on the axial chord length and the inlet velocity, with a freestream turbulence intensity level of 3.5% at the cascade inlet. The results indicate that the wall thickness variation produces significant influence on the pressure side film cooling effectiveness, while only marginal effect on the showerhead and suction side film cooling. Also observed is that the fan-shaped hole generates the highest film cooling effectiveness on pressure or suction side. Also discussed is the surface curvature effect, combining with effects of wall thickness and hole shape variations, on the film cooling effectiveness in comparison to the flat-plate data.

Large-Eddy Simulations of Inclined Jets in Crossflow with Different Holes

Film cooling is a key technology to improve the thermal performance of high-pressure turbines. The mixing of the cooling air and the main flow is inherently unsteady, but the unsteady flow physics of different cooling holes are seldom investigated. In the current study, the large-eddy simulation method is used to investigate inclined jets in crossflow via a cylindrical hole and a fan-shaped hole. The angle between the hole and the main flow is 35 deg, and the blowing ratio is 0.5, which are representative for film cooling. First, the results are analyzed in a traditional way using counter-rotational vortices based on the time-averaged results. Then, the instantaneous flowfield is presented. The mixing of the injected flow with the main flow is highly related to the unsteady coherent vortices. The results showed that the instantaneous flowfield can provide a better explanation of the distribution of film-cooling effectiveness than the time-averaged flowfield. The effects of instantaneous vortices on the temperature distribution for different cooling hole geometry are discussed in detail.

Impact of wall boundary condition on scaling film cooling performance from near ambient to engine temperatures

The present work computationally examines the scaling of a fan-shaped hole's film-cooling performance from a near ambient temperature to an engine temperature on a flat plate. Heat flux distributions for both film-cooled and non-film-cooled cases were computed for several isothermal boundary conditions. Cases with engine representative freestream temperatures and near ambient temperatures were examined.This study first shows that the adiabatic wall temperatures interpolated from the isothermal results were higher than those measured directly using an adiabatic wall boundary condition. This was due to the presence of a thermal boundary layer in the isothermal results, which would not develop for the adiabatic case. As a result, the adiabatic effectiveness found with adiabatic models will not represent the true thermal condition found in the engine. Finally, this study shows that both the adiabatic effectiveness interpolated from the isothermal results and Net Heat Flux Reduction can be scaled from low temperature to high temperature by proper non-dimensional matching.

Investigation of boundary layer thickness and turbulence intensity on film cooling with a fan-shaped hole by direct numerical simulation

Effects of the mainstream boundary layer thickness and the turbulence intensity on film cooling under low Reynolds number conditions are studied in this work by the direct numerical simulation (DNS). In other to solve low-speed compressible flow problems, several methods of Roe scheme, preconditioning, dual time stepping, and LUSGS are adopted to solve governing equations. Results reveal that a horseshoe vortex appears with a thicker mainstream boundary layer, and thus the lateral coverage of the coolant fluid has increased significantly. In addition, the existence of turbulence intensity eliminates the blow-off phenomenon, which happens in a thin mainstream boundary layer condition and enhances the film cooling effectiveness.