Hole Shape Research Articles

Experimental investigation of the full coverage film cooling effectiveness of a turbine blade with shaped holes

The film cooling effectiveness of two turbine blades at different turbulence intensities (0.62% and 16.00%) and mass flux ratios (2.91%, 5.82%, 8.73% and 11.63%) is studied by using the Pressure-Sensitive Paint (PSP) measurement technique. There are a baseline and an improved turbine blade in current work, and their film cooling hole position distribution is the same. But the hole shape on suction surface and pressure surface is changed from cylindrical hole (baseline) to laid-back fan-shaped hole (improved blade). Both blades have 5 rows of cylindrical holes at the leading edge and 4 rows of cooling-holes on the suction surface and the pressure surface. The experimental results show that the film cooling effectiveness of the improved blade is much better than the baseline. The increase in turbulence intensity will reduce the cooling effectiveness on the surface of turbine blade, but the effect of turbulence intensity becomes weaker with an increase in the mass flux ratio. Compared with the multiple rows of cylindrical holes, the cooling effectiveness of shaped holes is more influenced by the turbulence intensity at low mass flux ratio.

Experimental study on heat transfer and throughflow losses characteristics of single/triple-row holes with an engine-representative density ratio

In present study, the heat transfer and the throughflow losses characteristics of single/triple-row of fan-shaped and cylindrical film cooling holes with a fixed outlet width are studied experimentally with an engine-representative density ratio. The pressure-sensitive paint (PSP) measurement technology is utilized to test the film cooling performance. The film cooling holes with the inclination angle α which ranged from 20° to 30° and the diffusion angle β which ranged from 0° to 15° are considered. The heat transfer and flow resistance characteristics of film cooling holes under the engine-representative density ratio, DR, of 1.52 as well as the blowing ratio, BR, which ranged from 0.3 to 2.0 are studied. The critical blowing ratios of the secondary flow detaches from wall surface of each hole shape and the hole shape parameters which acquire the highest span-wise averaged adiabatic film cooling efficiency are obtained. Moreover, the experimental results indicate that, within the scope of the investigative parameters pondered in present study, the discharge coefficient and the film cooling performance of the cylindrical hole are significantly lower than that of the fan-shaped film cooling holes. The coolant jet which ejects from the fan-shaped holes does not blow off from the wall surface when BR ≤ 1.5. However, when BR = 2.0, a part of coolant jet begins to detach from the wall surface. In addition, when BR ≤ 1.5, the fan-shaped film cooling hole with the hole shape parameters of α = 20°, β = 15° generates the highest film cooling effectiveness. However, when BR > 1.5, the highest film cooling effectiveness is obtained by the fan-shaped hole with hole shape parameters of α = 25°, β = 10°. Importantly, the discharge coefficient does not change monotonously with the variation of the hole shape parameters. In addition, the fan-shaped film cooling holes with the hole shape parameters of α = 25°, β = 13° as well as those with α = 30°, β = 10° offer the highest discharge coefficient. Finally, the correlations for the discharge coefficients of different hole shape parameters are developed.

Opportunities in Jet-Impingement Cooling for Gas-Turbine Engines

Impingement heat transfer is considered one of the most effective cooling technologies that yield high localized convective heat transfer coefficients. This paper studies different configurable parameters involved in jet impingement cooling such as, exit orifice shape, crossflow regulation, target surface modification, spent air reuse, impingement channel modification, jet pulsation, and other techniques to understand which of them are critical and how these heat-transfer-enhancement concepts work. The aim of this paper is to excite the thermal sciences community of this efficient cooling technique and instill some thoughts for future innovations. New orifice shapes are becoming feasible due to innovative 3D printing technologies. However, the orifice shape variations show that it is hard to beat a sharp-edged round orifice in heat transfer coefficient, but it comes with a higher pressure drop across the orifice. Any attempt to streamline the hole shape indicated a drop in the Nusselt number, thus giving the designer some control over thermal budgeting of a component. Reduction in crossflow has been attempted with channel modifications. The use of high-porosity conductive foam in the impingement space has shown marked improvement in heat transfer performance. A list of possible research topics based on this discussion is provided in the conclusion.

A Novel Manufacturing Process for Glass THGEMs and First Characterisation in an Optical Gaseous Argon TPC

This paper details a novel, patent pending, abrasive machining manufacturing process for the formation of sub-millimetre holes in THGEMs, with the intended application in gaseous and dual-phase TPCs. Abrasive machining favours a non-ductile substrate such as glasses or ceramics. This innovative manufacturing process allows for unprecedented versatility in THGEM substrates, electrodes, and hole geometry and pattern. Consequently, THGEMs produced via abrasive machining can be tailored for specific properties: for example, high stiffness, low total thickness variation, radiopurity, moisture absorption/outgassing and/or carbonisation resistance. This paper specifically focuses on three glass substrate THGEMs (G-THGEMs) made from Schott Borofloat 33 and fused silica. Circular and hexagonal hole shapes are also investigated. The G-THGEM electrodes are made from indium tin oxide (ITO), with a resistivity of 150 Ω/Sq. All G-THGEMs were characterised in an optical (EMCCD) readout GArTPC and compared to a traditionally manufactured FR4 THGEM, with their charging and secondary scintillation (S2) light production behaviour analysed.

Scouring of sand beds by short impinging turbulent jets

Laboratory experiments were carried out to study the scouring of sand beds by vertically impinging submerged circular turbulent water jets with short impinging height of 5.5 times the jet diameter. Measurements of the profiles of the static scour hole at different times were made along with the dynamic scour depths using a novel experimental arrangement. It was found that the asymptotic characteristic lengths of the scour hole can be predicted using the erosion parameter, Ec, of short impinging jet experiments. The ratio of the dynamic to static scour depths in asymptotic state varies between 2.1 and 4.3, for Ec ranges between 3 and 28. Semi-empirical prediction equations are developed for the asymptotic lengths and empirical equations are developed for the temporal development of the characteristic lengths. These equations show good correlations, with the coefficient of correlation (R2) varying beween 0.83 and 0.98. The shape of the dimensionless asymptotic scour hole is found to be different for short and long impinging jets. A general equation for its shape is developed considering the shape as a function of the submerged angle of repose of the bed material.

Structural Optimization and Application Research of Alkali-Activated Slag Ceramsite Compound Insulation Block Based on Finite Element Method

The research and application of new wall materials have been attracting increasing attention owing to the continuous promotion of sustainable development in the building industry. An alkali-activated slag ceramsite compound insulation block (AASCCIB) is used as the research object. Based on the finite element method, the effects of different numbers of hole rows and hole ratios on the thermal and mechanical performances of AASCCIBs are analyzed using ANSYS CFX. On this basis, the AASCCIB with the optimal comprehensive performance is determined by a multi-objective optimization analysis. Finally, the improvement effect of the AASCCIB wall on the indoor thermal environment relative to an ordinary block (OB) wall is quantitatively analyzed using ANSYS CFX. The results show that the von Mises equivalent stress and heat transfer coefficient of the AASCCIB decrease with the increase in the hole ratio when the hole shape and number of hole rows are constant. AASCCIB B1 has the optimal comprehensive performance among six AASCCIBs, with the heat transfer coefficient and average von Mises equivalent stress of 0.446 W/(m2∙K) and 9.52 MPa, respectively. Compared with the indoor lowest and average temperatures of the building with the OB wall, those of the building with the AASCCIB wall increased by at least 1.39 and 0.82 °C on the winter solstice, respectively. The indoor temperature difference decreased by at least 0.83 °C. In addition, the indoor highest temperature, average temperature, and temperature difference decreased by at least 1.75, 0.79, and 1.89 °C on the summer solstice, respectively.

Цистоскопічні особливості вічок сечоводів у дітей з міхурово-сечовідним рефлюксом

Purpose – to establish cystoscopic prognostic criteria for vesicoureteral reflux (VUR) in children. Materials and methods. Clinical material covers 270 patients with VUR II–IV grades aged 9 months to 14 years and 22 healthy children. The study included patients with VUR in the period of clinical and laboratory remission without symptoms of neurogenic bladder. During cystoscopy, the condition of the bladder mucosa was assessed; location, shape, hydrodistention degree, and ureteral orifices contractility. Results. Patients with VUR were diagnosed ureteral orifices in the form of: horseshoes – 127 (47.04%) patients, stadium – 106 (39.26%) and golf holes – 37 (13.7%). They were in the zones: A – 13 (4.81%) children, B – 154 (57.04%), C – 67 (24.81%), D – 36 (13.33%), and were characterized by the hydrodistention degree: H0 – 7 (2.59%) patients, H1 – 173 (64.07%), H2 – 60 (22.22%) and H3 – 30 (11.11%). In children with VUR, sluggish peristalsis of the ureter orifices clearly prevailed – 252 (93.33%) cases, relative to active peristalsis in only 18 (6.67%) patients. Conclusions. For ureteral orifices in the form of a stadium and with more pronounced signs of deepening, which are shifted to zone B and laterally to the sidewall of the bladder, with a hydrodistention degree above H1 has a positive association with VUR at the highest specificity of tests. Unfavorable prognostic diagnostic markers for effective minimally invasive interventions in patients with VUR should be considered ureteral orifices, which combine such morpho-topographic characteristics as pronounced signs of deepening to the shape of a golf hole, lateralization to the sidewall of the bladder in zone D, and hydrodistention H3 degree. The research was carried out in accordance with the principles of the Helsinki declaration. The study protocol was approved by the Local ethics committee of all participating institution. The informed consent of the patient was obtained for conducting the studies. No conflict of interest was declared by the authors. Key words: vesicoureteral reflux, ureteral orifice, cystoscopy, children.

Experimental Study of Perfobond Rib Shear Connector under Lateral Force

A series of full-scale pushed out tests were performed on the Perfobond rib shear connector. The tests were designed to examine the performance of the Perfobond rib shear connector under different rib hole sizes and shapes, reinforcing bar sizes, rib thicknesses, as well as the presence of lateral forces. It has been revealed from the test results that the rib hole size and reinforcement diameter may not act independently, and the influence of one’s size is actually dependent on the size of the other one. The lateral forces also affect the performance of the shear connector; for example, the capacity of the shear connector would be larger under compression than under tension. The existence of transverse pretension stress accelerated the cracking of concrete, leading to the strength and stiffness of concrete, perforated plate, and reinforcing rebars unable to fully exert their effect. In addition, the constraint effect of transverse stress improved the strength and stiffness of concrete and delayed the concrete cracking, bringing the strength and stiffness of concrete, perforated plate, and reinforcing rebars into full play, and resulting in a significant improvement in the shear capacity of Perfobond rib shear connectors.

Evaluation of hetro-stacked target plate response toward different nose shaped projectile impact

Detailed experimental and numerical investigations were carried out for evaluating the dynamic response of the stacked target plates toward moderate (100–250 m/s) velocity projectile impact. A single stage gas gun was utilized to launch the hemispherical and the blunt projectile toward two different hetro-stacked configurations (Al-St and St-Al). A comprehensive experimental (high speed 3D-DIC) and numerical (FE) evaluation was conducted to obtain the transient and post-impact behavior of the target plates. Influence of different projectile shapes on the full-field transient deformation profiles of different stacking configurations was studied in detail. Also, typical perforation parameters like plug size, shape, and perforation hole diameters were carefully measured and analyzed. A comprehensive error measure was utilized to quantify the similarity between the experimental and simulation results, a very good agreement was observed.

In-process measurement of a keyhole using a low-coherence interferometer with a high repetition rate.

The shape of an instance hole (keyhole) created via a high-power laser was measured using a low-coherence interferometer with the following parameters: repetition rate, 10 MHz; center wavelength, 1550 nm; absolute spatial resolution, 10 µm; and measurement range, 5 mm. The keyhole was created on a 3-mm-thick stainless-steel plate using a high-power laser with 8-kW peak power and 1070-nm center wavelength. The cross-sectional area of the keyhole was measured to be 0.42 mm × 0.78 mm (width × depth) using the interferometer, and its side dimension was 0.46 mm × 0.78 mm (width × depth).

Holes' Parameters Analysis of a Perforated Thin-Walled Lipped Beam Buckled Under a Bending Load

This work studied the effects of holes on the buckling characteristic of an open thin-walled lipped channel beam under a bending load. A nonlinear finite element method was utilised to examine the buckling behaviour of the beam. Experimental works were carried out to verify the finite element simulation. Three factors were chosen to examine their influence on the buckling of the beam. These factors namely, the holes’ shape, perforated ratio (hole length to beam height) and spacing ratio (centre to centre distance between holes to beam height). The finite elements output was analysed by implementing the Taguchi method to distinguish the best group of three parameters collections for optimal strength of buckling. Whereas the analysis of variance technique (ANOVA) method was applied to specify the impact of each parameter on critical buckling load. Outcomes showed that the combination of parameters that gives the best buckling strength is the hole with a hexagonal shape, perforated ratio =1.7 and spacing ratio =1.3, and the holes’ shape is the most effective factor. In addition, the study demonstrated that the hole's shape factor has the greatest influence on the buckling capacity. While the perforated ratio factor is the least influential.

The Hole Size that the Japanese Marten (Martes melampus) can Pass through

The Japanese marten (Martes melampus) invades houses through holes and causes excrement problems. These holes should be covered to prevent the marten's intrusion into houses. However, there is no information about what size of hole they can squeeze through. Therefore, we investigated the sizes of the holes that they could pass through using three reared individuals in summer and winter. We put a bait in an experimental box with a replaceable front panel, which had a square or round hole. The minimum passable sizes were recorded in summer. For a square hole the minimum size was 5.0 cm for each side, and for a round hole the minimum sized hole had a diameter of 5.5 cm. It is necessary to cover holes of these sizes or more to prevent their house invasion. The body weight and the hole shape had no significant effect on the minimum passable area. On the other hand, the season had a significant effect on the minimum passable areas. The shoulder seems to be the limiting factor for whether the martens can pass through the holes. Therefore, the seasonal change in the body size around the shoulder may affect the minimum passable area of holes.

Seismic behavior of bolted truss-to-column joint with oversized or slotted bolt hole

Bolted connections are preferred in prefabricated steel structures because of the convenience for construction and quality control. A prefabricated steel structural system with truss beams and bolted joints were proposed, and enlarged bolt holes were adopted in the joints for easier assembly and better energy dissipations. A series of 6 truss-to-column joint specimens, with oversized or slotted bolt holes, were tested under cyclic loads. The resistance, the hysteresis behaviour, the ductility, the energy dissipation capacity, and the slipping behaviour of the tested joints were analysed, and the influences of the bolt hole dimensions and shapes were evaluated. Finite element models were established and validated for further investigation of the joint performances. According to the results, the enlarged bolt holes would slightly decrease the slipping resistance, but would significantly improve the joint ductility and energy dissipation capacity. The slippages in the joints with oversized or slotted bolt holes could make 38%∼59% of the contributions to the energy dissipation capacity, proving that the slippages could be utilized in seismic design. Based on the investigations, the diameters of the oversized bolt holes are recommended to be 4 mm larger than the nominal bolt diameter, and a 0.3 mm-thick copper plate is recommended to be adopted between the connected plates to obtain stable slip behaviours. Simplified calculation methods for the slipping resistance and the yield resistance of the investigated joints were proposed and evaluated to have acceptable accuracy for resistance prediction and design.

Optimization of the Shapes of Holes in a Quasiorthotropic Plate under Biaxial Tension

Optimization of the Shapes of Holes in a Quasiorthotropic Plate under Biaxial Tension

Direct fabrication and characterization of gold nanohole arrays.

We demonstrate a one-step fabrication method to realize desired gold (Au) nanoholes arrays by using a one-photon absorption based direct laser writing technique. Thanks to the optically induced thermal effect of Au material at 532 nm excitation wavelength, the local temperature at the laser focus area can reach as high as 600°C, which induces an evaporation of the Au thin film resulting in a metallic nanohole. By controlling the laser spot movement and exposure time, different two-dimensional Au nanoholes structures with periodicity as small as 500 nm have been demonstrated. This allows obtaining plasmonic nanostructures in a single step without needing the preparation of polymeric template and lift-off process. By this direct fabrication technique, the nanoholes do not have circular shape as the laser focusing spot, due to the non-uniform heat transfer in a no-perfect flat Au film. However, the FDTD simulation results and the experimental measurement of the transmission spectra show that the properties of fabricated plasmonic nanoholes arrays are very close to those of ideal plasmonic nanostructures. Actually, the plasmonic resonance depends strongly on the periodicity of the metallic structures while the heterogeneous form of the holes simply enlarges the resonant peak. Furthermore, it is theoretically demonstrated that the non-perfect circular shape of the Au hole allows amplifying the electromagnetic field of the resonant peak by several times as compared to the case of perfect circular shape. This could be an advantage for application of this fabricated structure in laser and nonlinear optics domains.

Investigation of shape effects and dead layer thicknesses of a coaxial HPGe crystal on detector efficiency by using PHITS Monte Carlo simulation

In gamma-ray spectrometry, the full energy peak efficiency can be determined by experimental, or by Monte Carlo (MC) simulation methods. In experimental methods, reference standard materials including a large number of gamma emitters or mixed gamma emitters in different geometries are requested to determine the efficiency curves. Besides, simulation by MC methods has advantages of modelling any geometries and energy range of interest. However, by simulation it is not easy to determine the efficiency curves due to the lack of information supplied from manufacturers. In this work, it is focused on the effect of dead layer thickness and other geometric parameters of detector crystal on the efficiency of the detector. The general-purpose MC code PHITS and specific-purpose MC code GESPECOR are used to simulate the detector. The experiments are performed by single gamma point sources at a 12.5 cm distance from the end cap of the detector. The results showed that the physical parameters of the detector are different from those provided by the manufacturer. After 15 years of operation of the detector, it is observed that the dead layer thickness increased from 0.7 mm to 1.29 mm. It causes a decrease in the efficiency by a reduction in the active volume of the detector. In addition, it is showed that the round shape of the front edge and bullet shape of the inner hole of the detector crystal have an undeniable effect on efficiency of detector especially for low energy photons. The study shows that the PHITS MC simulation program can be successfully used in obtaining efficiency calibration of HPGe detectors and determining the dead layer thickness.

Recent Patents on Electrochemical Machining of Shaped Holes

Background: Electrochemical Machining (ECM) can machine most conductive materials and is not limited by physical properties of materials such as strength, hardness and toughness. However, the process of ECM is unstable as the structure of tool electrode, electrolyte composition and the machining device of ECM will affect machining accuracy and stability of shaped holes. Therefore, people pay more and more attention to the development trend of ECM of shaped holes. Objective: In order to increase machining accuracy and machining stability of ECM of shaped holes, ECM method has been constantly improved. Methods: This paper reviews various representative patents and papers on ECM of shaped holes at home and abroad. Results: By summarizing a large number of patents and papers about ECM of shaped holes, this paper analyzes the structure of tool electrode, electrolyte composition and the machining device of ECM, and the development trend of ECM of shaped holes is also discussed. Conclusion: The optimization of the technological equipment and process of ECM of shaped holes is beneficial to improve the machining accuracy and the machining stability of shaped holes. More interrelated patents on ECM of shaped holes will be invented later.

On the Digital Image Correlation Technique

This study has been focused in the introduction of the theoretical and practical foundations of the Digital Image Correlation DIC technique to undergraduate students at EPN through the implementation of a Laboratory DIC practice. In the experimental test, an elastomer with different hole shapes is used as a test specimen, which should have a pattern of random speckles/dots in its surface, where the load applied is sequential or staggered to obtain images. The project evaluates three specialized image correlation packages: Digital Image Correlation Engine (DICe), Matlab's open source 2D Digital Image Correlation software Ncorr, and finally the GOM correlate software. The stress concentrator values result around different hole shapes are compared with analytically solutions of theory of elasticity and other formulas found in literature. Finally, a numerical simulation is carried out on a commercial FEA software to further compare experimental dossier. Data suggest a good agreement between procedures of analysis that allow the correct introduction of theoretical and experimental foundations of the Digital Image Correlation DIC among EPN community.

Microfabric features of microbial carbonates: experimental and natural evidence of mold holes and crusts

Results of our study based on examination of induced precipitation of carbonate by a cyanobacterium, Lyngbya in the laboratory, and the analyses of microphotographs of both modern and ancient microbial carbonates, demonstrated the importance of recognition of mold holes and carbonate crusts in understanding microbial carbonates. In the experiment, only cyanobacteria Lyngbya can induce precipitation of carbonate, forming scattered grains on the surface of Lyngbya filaments. Carbonate crusts enclosing the old parts of the filaments were formed through aggregation of these scatter grains while mold holes were formed after decay of the filaments. Mainly based on the experiment, six different ways of microbial carbonate formation were recognized: (1) trapping without mold holes, (2) trapping with mold holes, (3) particle-forming induced-precipitation of carbonate, (4) discrete crust-forming induced-precipitation of carbonate, (5) induced precipitation, forming tangled crusts that build a porous construction, and (6) induced precipitation, forming a dense construction. And mold holes and crusts can form in ways (4), (5), and (6). Examination of both modern microbial carbonates from the Shark Bay of Australia, Highborne Cay of Bahamas and the atoll of Kiritimati and the microbialites from the Cambrian dolostone sequence in Tarim, Xinjiang, China all demonstrated the limitation of recognizing only mesofabric features and importance of examining microfabric features for understanding of the genesis of the microbial carbonates and their proper classification. The shape, size and arrangement of the mold holes, crusts, and the features of the minerals filling in pores between the crusts, which are referred as the microfabric features here, are keys to better understand the formation and environments of both modern and ancient microbial carbonates.

Numerical simulation of flow and heat transfer characteristics of nanofluids in built-in porous twisted tape tube

For enhancing the heat transfer efficiency of heat exchanger, silica-water (SiO2-H2O) nanofluids were used as a working medium in this study. Further, the effects of tube structure, twisted tape hole spacing, and hole shape on the flow and heat exchange characteristics of nanofluids in the tube were systematically researched by numerical simulation. The results displayed that a triangular tube exhibited larger flow resistance, better heat transfer effect and more comprehensive performance compared to the round tube. The conclusion also showed that the highest comprehensive evaluation index (PEC) was obtained by producing open circular holes on the twisted tape. The usage of porous twisted tape, nanofluids, and triangular tube could significantly improve the system economy and enhance the heat exchange ability. At the same time, the flow in the tube was disordered and accompanied with the increase in entropy. The maximum improvement of heat exchange efficiency of nanofluids in round tube and triangular tube with porous twisted tape was 74.80 and 55.97%, respectively.