Slot Holes Research Articles

Analysis of the power during machining of Inconel 718 for different geometrical profiles and the development of power prediction models using multisensor data

This article presents analyses and prediction of machining power during end milling of Inconel 718 for different geometric features namely angular slot, half slot, square pocket, rectangular pocket, and blind hole. The experimental study revealed that among the machining features examined, angular slot required the highest specific cutting energy, while blind holes consumed the least, across different machining conditions. A 40% increase in cutting speed raised specific cutting energy by 4–9%, while a similar increase in feed rate lowered specific cutting energy by 40–44% across all profiles. Doubling depth of cut reduced specific cutting energy by 50% for angular slots, half slots, square pockets, and rectangular pockets, but increased it for blind holes. Power prediction models were developed using multisensor data, employing two machine learning and two deep learning architectures. The performance of the four power prediction models was compared for all geometric profiles using both raw data and statistical feature data extracted from machining signals from force dynamometer, accelerometer, and acoustic emission (AE) sensors. Long–Short-Term Memory model outperformed other models in case of raw data for all geometric profiles. The Random Forest Regression method consistently fared better for power predictions models developed based on feature-extracted data. Predictive models trained without AE sensor data performed better than those trained with AE.

Experimental analysis of pressure deviation-induced film cooling effectiveness deviation in pressure sensitive paint measurement

The use of the Pressure Sensitive Paint (PSP) measurement method allows for obtaining dense, completely adiabatic film cooling effectiveness (η) results. In order to adapt to the increasing trend of high-speed and complexity in the application scenarios of film cooling, the pressure deviation-induced film cooling effectiveness deviation in PSP measurements needs to be quantified and corrected. Initially, two different jets of specific materials were injected into a dual-hole flat plate test piece. The pressure difference at corresponding positions of the two jet flows was measured to demonstrate that, compared to air, a ternary oxygen mixed gas better simulated the pressure field of the foreign gas. This illustrates the feasibility of the Test3-OM correction method. Building upon this, the influence of pressure deviation on the accuracy of measurement results was quantitatively evaluated in various scenarios, including a flat circular hole, film holes with a compound angle, a converging slot hole, and film holes at three positions on the blade. The results indicate that the pressure deviation-induced η deviation is non-negligible under conditions of high blowing ratios in most positions. Particularly in the low η region, there is a higher sensitivity to pressure deviation. Generally, there is a negative deviation region near the hole downstream, and a positive deviation region slightly downstream. The generation of deviations stems from variations in density, resulting in different flow patterns of the jet near the wall surface.

Effects of Ribbed Crossflow Channel in a Turbine Blade on Film Cooling Performance of Diffusion Slot Holes with Various Cross Section Orientations

Abstract This paper investigates the influence of ribbed crossflow on the film cooling performance of a turbine rotor blade. A pressure-sensitive paint measurement technique was employed to measure the effectiveness of film cooling. The discharge coefficients were also measured to determine the flow resistance. A row of film holes was positioned at the pressure surface or suction surface with a spanwise hole spacing of 7.5D, which is half of the rib spacing. The experiments were carried out at a mainstream Reynolds number of 520,000, a turbulence intensity of 3.6%, and a density ratio of 0.97. The crossflow inlet velocity was 45% of the cascade inlet velocity. A fan-shaped hole with a 14 deg expansion angle (Fans-14), a horizontally oriented slot cross section diffusion hole with a 14 deg expansion angle (H1.7-14), and two vertically oriented slot cross section diffusion holes with 14 deg (V1.7-14) and 20 deg (V1.7-20) expansion angles were tested with/without crossflow. The results indicated that the slot cross-sectional orientation significantly changes the flow patterns inside the holes. H1.7-14 has stronger lateral expansion and better surface adhesion, while V1.7-14 and V1.7-20 yield more uniform lateral velocity distributions. Regardless of crossflow, H1.7-14 produces the highest film effectiveness and discharge coefficient on the pressure surface, while it changes to V1.7-20 on the suction surface. The ribbed crossflow increases the film effectiveness on both the pressure surface and suction surface, except for V1.7-20, as it is almost unaffected by the crossflow.

Delayed-Action Mechanism of Buckling-Restrained Brace Using Gusset Plates with Multiple Slot Holes

Delayed-Action Mechanism of Buckling-Restrained Brace Using Gusset Plates with Multiple Slot Holes

A Numerical Investigation of Particle Swarm Optimization to Improve Film-Cooling Effectiveness from Converging Slot Hole

A Numerical Investigation of Particle Swarm Optimization to Improve Film-Cooling Effectiveness from Converging Slot Hole

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.

Experimental verification of novel double-wall structure with pin-fins and slots

This Letter proposes a novel double-wall structure with pin-fins and slot holes. The overall cooling effectiveness and characteristics of flow field at the slot outlet are verified by infrared thermal imager and particle image velocimetry technology. The results indicate that when the overall cooling effectiveness is nearly identical, the coolant consumption of the double-wall structure proposed in this study is 33.3% lower than that of conventional impingement/effusion structures. Our findings indicate the presence of counter-rotating vortex pairs within the slot film coverage. This phenomenon is expected to result in the accumulation and uplift of coolant downstream of the vortex pairs.

Experimental and numerical investigations on film cooling performance of converging slot holes in plate and turbine conditions

Based on the heat-mass transfer analogy, the Pressure Sensitive Paint (PSP) technique was used to explore the film cooling characteristics of converging slot holes on the plate model and the actual turbine endwall model conditions. Meanwhile, the numerical calculation was also adopted to pursue the flow field details. The width of the converging slot hole exit is a key geometry affecting cooling performance. On the plate model condition, three widths of exit slot Lw (1.7d, 2.3d, 2.9d) were chosen to obtain the optimal exit width. The case with Lw = 2.3d obtained the highest level of adiabatic effectiveness from spanwise and streamwise views. This case operated as a two-dimensional slot and produced a more uniform cooling jet film relative to other cases. Nevertheless, the cooling performance decreased significantly as the converging slot hole width increased to Lw = 2.9d. Then the cooling performance of three patterns of film holes was further investigated in the turbine endwall. Laid-back fan-shaped holes and converging slot holes could improve the film cooling performance effectively compared to the cylindrical holes. Converging slot holes with Lw = 2.3d improved the uniformity of the cooling jet outflow through rows of upstream film holes, and also effectively avoided the phenomenon of coolant blowing away or high-temperature gas entering the film hole, resulting in high film cooling effectiveness performance. Compared to cylindrical holes, the area-averaged adiabatic effectiveness was increased by 216.5 % for the endwall with cylindrical holes with the momentum ratio I = 0.25. Overall, converging slot holes improved cooling performance among all studied film hole configurations.

Experiments on heat transfer and film cooling characteristics of double-wall cooling structure with novel slot holes and pin-fins

The influences of blowing ratio, mainstream velocity, density ratio and jet Reynolds number on the heat transfer and film cooling properties of double-wall cooling cell (DWCC) with slot holes, impingement and diamond-shaped pin-fins were studied by means of pressure sensitive paint and transient liquid crystal. The simulation obtained the flow characteristic at a jet Reynolds number of 20000. The results indicated that with the increase of blowing ratio, the film cooling performance of DWCC structure also increased, and there was no film lift-off phenomenon which occurred in the cylindrical hole. The presence of pin-fins created a spike-shaped film in the slot outlet. Therefore, when studying the DWCC structure, it was important to consider the couple effects of impingement, pin-fins, and slot hole. As the density ratio decreased and the mainstream velocity increased, the film cooling effectiveness (FCE) gradually decreased. When jet Reynolds number increased from 20,000 to 60,000 under a density ratio of 2.0, the area-averaged FCE increased from 0.308 to 0.435, with an increase of up to 41.2%. The convective heat transfer level of impingement stagnation point was much higher than that of pin-fins region. Due to the transition between the impinging jet and the wall jet, the heat transfer coefficient (HTC) had a multi-peak distribution. In addition, several low heat transfer zones similar to wing-shaped, eye-shaped, and crescent-shaped were observed on the target surface and bottom surface inside the cooling cell. The DWCC structure studied in this paper is more efficient in cooling performance compared to traditional cooling structures. This makes it suitable for use in various fields such as heat transfer of turbine blades and electrical equipment.

Performance evaluation of film holes used for cooling the optical window of a sensor probe

In this paper, three types of film holes (namely cylindrical hole, round-to-slot hole, slot hole) are applied to provide cooling protection for a sensor probe’s optical window while considering the structural size limitations. The film cooling performance, discharge coefficients and pressure drop of three types of film holes are discussed and compared in terms of both the blowing ratios and the outlet heights of the film holes through numerical simulation. The results demonstrate that, compared to the cylindrical holes, the round-to-slot holes and slot holes exhibit significantly improved film coverage performance. Among these, the RTSH-0.6 hole exhibits the best comprehensive performance, the film cooling effectiveness of the RTSH-0.6 hole is higher than 0.99 under all three blowing ratios with the lowest pressure drop ratio less than 0.5.

Comparative analysis of reinforcement addition techniques on fabricated hybrid surface composite of AA7075-T651/WC/BN through friction stir processing

In the present work, three reinforcement addition techniques such as the slot method (SM), hole method (HM), and zig-zag hole method (ZZHM), are selected to make the hybrid surface composite of AA7075-T651/BN/WC through FSP. The comparative assessment of each method is thoroughly assessed through microstructure, mechanical, and tribological characteristics. Material flow, particle spreading, zone development and phase formation were examined using optical microscopy (OM), field emission scanning electron microscopy (FESEM) with energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). Furthermore, the microhardness and wear characteristics were measured and compared. Based on the findings, ZZHM reveals enhanced material flow and more even particle spreading in the nugget zone than SM and HM. The higher grain refinement and excellent interfacial bonding without any reaction between AA7075-T651 and reinforcement particles (BN and WC) are due to higher DRX and severe plastic deformation (SPD) caused by the tool in ZZHM. The composite made with ZZHM had greater hardness and wear resistance due to the reduction in clusters, even the spreading and lubricating effect of particles and a significant reduction in grain size. This study revealed that the ZZHM is superior to the SM and HM for adding reinforcement and fabricating the hybrid surface composite.

Enhancing Steel Wheel Ventilation Efficiency Through Multi-Objective Optimization

This study focuses on the optimization of ventilation hole design in steel wheels used for heavy commercial vehicles. The primary objective is to reduce the weight of the wheel while ensuring compliance with radial fatigue and cornering fatigue test requirements. Four distinct ventilation types were parametrized using ANSYS Mechanical, with the von Mises stress on the disk, number of ventilations, and wheel weight serving as design parameters. Stress analysis and weight comparisons were performed between wheels featuring different ventilation types and an ellipse ventilation wheel. Incorporating the design of experiment (DoE) and response surface optimization (RSO) module in ANSYS Workbench 2022 R1 was employed to compare and evaluate the obtained values. Subsequently, the multi-objective genetic algorithm (MOGA-II) method was employed for optimization, aiming to identify the optimal design. The optimization process, utilizing a maximum of 20 iterations, a convergence stability percentage of 2%, and a maximum allowable Pareto percentage of 70%, yielded 1, 3, 3, and 3 candidate design points for round, slot, trapezoid, and halfmoon-type ventilation holes, respectively. Among the various ventilation types considered, the halfmoon-type ventilation hole exhibited the most promising results. Compared to the current design, the optimized wheel achieved a weight reduction of 0.9 kg (2.05%). This outcome demonstrates the effectiveness of the proposed methodology. Although lighter designs were not attainable while maintaining the same stress values for the other three ventilation types, the halfmoon-type ventilation hole was ultimately selected as the preferred design.

Failure analysis and numerical drive structure optimization design of Cr12Mo1V1 electrical connection die

A type of Cr12Mo1V1 electric connection die occured brittle fracture after 200 times of service, and its life was much lower than the design life of the die. In this paper, the 5M1E failure analysis method was adopted, combined with the characteristics of Cr12Mo1V1 cold-work die steel, scanning electron microscopy, direct reading spectrometer, Rockwell hardness tester, metallographic microscope and other means were used to analyze and test the macro fracture morphology, material composition, mechanical properties and microstructure of Cr12Mo1V1 electric connection die. The crimping process of the die was simulated by Deform software. The results show that the material composition is not up to standard, the strength is too low, the internal eutectic carbide is not uniform, the size of carbide exceeds the standard and so on are the root causes of the short life and brittle fracture of the die. In addition, the unreasonable designs of the crack slot and round hole of the die lead to excessive stress concentration in the crimping process of the die, which is too the main reason for the brittle fracture failure of the die. In view of the above factors, the paper puts forward some measures to prolong the life of the electric connection die from the aspects of raw materials, heat treatment, forging process and die structure design.

Film-Cooling effectiveness of combined hole slot geometries on a turbine rotor blade surface

A film cooling experiment was conducted for a novel hole structure, namely, the combined hole slot. The basic geometric shape of the combined hole slot is connecting adjacent sidewalls of two parallel diffuser holes internally to form a continuous slot exit. Two combined hole slot geometries constructed based on circular and vertical slot cross-sections were tested and compared with a conventional fan-shaped hole. The film-cooling effectiveness was measured on a turbine rotor blade surface using a linear cascade and pressure sensitive paint technique. The mainstream Reynolds number was 520,000 based on the cascade outlet velocity and the axial chord length. The mainstream turbulence intensity was 3.6%. Coolant-to-mainstream density ratios of 1.5 and 1.0 were tested under five blowing ratios ranging from 0.5 to 2.5. Although an obvious bifurcation occurs at the hole exit, both combined hole slot geometries remarkably increase the film-cooling effectiveness relative to that of the fan-shaped hole, in which the case based on a vertical slot cross-section performs better than the case based on a circular cross-section, regardless of the density ratio. In comparison, the increase in film effectiveness on the suction surface due to the combined hole slot geometries is greater than that on the pressure surface, especially for medium to high blowing ratios. The combined hole slot geometry is generally more suitable for using branch holes with a weak lateral expansion, in which a tighter merging effect can be achieved at the centerline.

Research on optimization of combustor liner structure based on arc-shaped slot hole

Research on optimization of combustor liner structure based on arc-shaped slot hole

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.

Experimental study on cooling characteristics of an air-cooled evaporative flame holder under combustion conditions

The flame holder needs an integrated design with the cooling structure in advanced ramjet or afterburner combustors. Experimental studies were carried out on the air-cooled evaporative flame holder with impingement-film-slot composite cooling structure under combustion conditions. The effects of blowing ratio M (0.54–2.74) and fuel-air ratio FAR (0.0016–0.0027) on the cooling characteristics of the flame holder were studied under mainstream inlet temperature T = 600 K, inlet Mach Number Ma = 0.15 and on-duty combustion conditions. The results show that the air-cooled evaporative flame holder can stabilize the flame after adding cold air. When the blowing ratio M increases, the wall temperature decreases and the cooling effectiveness increases. The average cooling effectiveness is only 0.237 at M = 0.54 and can reach 0.595 at M = 2.74. The distribution of cooling effectiveness on the inner surface of the flame holder is similar at different blowing ratios. Along the flow direction of the inner surface, the first row of cooling structure A uses the impingement jet and the guide ring to form the initial cooling film. The cooling effectiveness of the first row A is from 0.352 to 0.433 at M = 1.89. The next row B downstream the impingement holes and guide ring uses discrete film holes and has a high cooling effectiveness ranging from 0.578 to 0.815 at M = 1.89. The row C with discrete film holes downstream of B is close to the combustion recirculation zone and has a higher heat load. The cooling effectiveness of row C is 11.7%–23.5% lower than that of row B. The last row D with slot holes is at the trailing edge heated by the hot gas in the recirculation zone. The protective effect of the cooling film is poor in row D and the cooling effectiveness is only about 0.268–0.276 at M = 1.89. In the spanwise direction, the cooling effectiveness is higher near the cold air inlet and lower away from the cold inlet. The increase of the fuel-air ratio (FAR) mainly affects the combustion temperature and wall temperature, and has little effect on the cooling effectiveness. When the fuel-air ratio increases from 0.0016 to 0.0027, the average cooling effectiveness varies from 0.502 to 0.558. As the fuel-air ratio increases, the distribution pattern of cooling effectiveness at all measuring points has little change.

Experimental and unsteady numerical investigations on cooling characteristics of trailing-edge cutback with effect of upstream film holes

This paper investigates the influence of film cooling characteristics of pressure-side film hole on trailing-edge cutback in the high-pressure vane of gas turbines. This paper employs the Pressure Sensitive Paint (PSP) technique and Particle Image Velocimetry (PIV) technique to obtain the time-averaged adiabatic film cooling effectiveness and details of the mixing region, respectively. Numerical simulations with the DDES turbulence model are also used to predict the flowfields. Two configurations are examined: one with a cutback without pressure-side film holes (Config A) and another with a cutback that includes pressure-side film holes (Config B). This paper investigates eight blowing ratios (Mslot = 0.3–1.2) of slot coolant in cutback for Config A and a suitable blowing ratio (Mhole = 0.4) of film holes for Config B, using both experimental and numerical methods. The results of both experiments and simulations for Config A and B show good agreement and reveal a non-monotonic trend of film cooling effectiveness with increasing blowing ratio. The non-monotonic trend observed in Config A is attributed to an increase in the velocity gradient in the boundary layer on the coolant side with increasing blowing ratio, which leads to a different shedding vortex structure. The results for Config B show that the coolant from the pressure-side film holes changes the mixing structure downstream of the lip by rebuilding the mainstream's shear layer on the mainstream side. Adiabatic film cooling effectiveness increases significantly under low and moderate slot blowing ratios, but non-monotonicity is maintained. The Fast Fourier Transform method is used to investigate the impact of the jet stream, which affects only the area downstream of the film holes, while other regions along the pitch-wise direction are less affected. This paper also attempts to combine the effectiveness empirical correlations of 2D slot and film holes using the superposition model to quantitatively analyze the deterioration of cooling effectiveness resulting from the mixing of coolant and mainstream.

Aerothermal characteristics of thin double-wall effusion cooling systems with novel slot holes and cellular architectures for gas turbines

Double-wall effusion cooling system is a promising cooling solution for next-generation gas turbines. Thinning the blade wall can bring the coolant closer to the hot stream, thereby enhancing overall cooling effectiveness. However, a thin blade wall creates film cooling holes with a short length-to-diameter ratio, which increases jet-crossflow mixing and reduces coolant attachment, inevitably degrading film cooling performance. Herein, we constructed a new thin double-wall effusion cooling system by integrating novel short slot holes for better coolant attachment and triply periodic minimal surface (TPMS) based cellular architectures for improved internal heat transfer. The effects of wall thickness, film hole shape, and internal turbulators configurations were numerically studied. Adiabatic and overall film cooling effectiveness, vortex structures, and aerodynamics loss were comprehensively assessed. The results demonstrate that the novel slot hole significantly improves the overall film cooling effectiveness under thin wall conditions by enhancing the attachment of kidney vortices to walls. Notably, compared to the short fan-shaped hole (scheme B), the novel slot hole (scheme C) shows an improvement in the averaged overall cooling effectiveness of over 20% and a reduction in the total pressure loss coefficient by 60%. Furthermore, three TPMS-based cellular architectures produce similar overall film cooling effectiveness and reduction of total pressure loss coefficient in the range of 0.57-0.81 and 23%-53%, respectively. This work provides guidance for designing thin double-wall effusion cooling systems for next-generation gas turbines.

Large eddy simulation of film cooling flow from diffusion slot hole with crossflow coolant configuration

A three-dimensional compressible large eddy simulation (LES) method was performed to explore the flow and heat transfer characteristics in the hole and mixing zone of a crossflow film cooling model. A traditional cylindrical hole and diffusion slot hole were selected as the cases for the film hole. The characteristics of the crossflow film flow-field and the influence of the internal crossflow on the film cooling of the diffusion slot hole were explained by the vortex flow in the hole and the instantaneous/time-averaged jet mixing. The results showed that helical motion is easily induced in the holes under the influence of crossflow. Asymmetric outlet flow behavior is the main reason for the asymmetric characteristics downstream of the hole. The difference in the blowing ratio results in the difference in the strength of the spiral vortex and the central vortex tube inside the hole. For the diffusion slot hole, the high-speed zone caused by the crossflow effect at the hole-inlet gradually evolves into strip shapes under the combined action of axial extrusion and spanwise diffusion. With the disappearance of the helical structure, the high-speed areas gradually converge on both sides of the hole exit in the span direction, and the streamline at the exit develops relatively smoothly. The inlet crossflow and the crossflow Reynolds number have little effect on the film cooling effectiveness of the diffusion slot hole. With an increase in the blowing ratio, the lateral diffusion capacity of the film is gradually enhanced. Furthermore, compared with the cylindrical hole, the instantaneous film fluctuation region of the diffusion slot hole case is smaller in range and more symmetrical in distribution. These findings advance the understanding of the film cooling of diffusion slot holes.