Slot Holes Research Articles

Experimental Investigation on the Effects of a Large Recirculating Area on the Performance of an Effusion Cooled Combustor Liner

An experimental analysis of a realistic engine cooling scheme was performed on a test article replicating a slot injection and an effusion array with a central large dilution hole. A test section consists of a rectangular cross-section duct with a flat plate comprised of 270 effusion holes arranged in 29 staggered rows (D = 1.65 mm, Sx/D = 7.6, Sy/D = 6, L/D = 5.5, α = 30 deg) and a dilution hole (D = 18.75 mm) located at the 14th row. Both effusion and dilution holes are fed by a channel replicating a combustor annulus, which allows to control of cold gas side cross-flow parameters, especially in terms of Reynolds number of both annulus and effusion holes. Upstream the first row, a 6 mm high slot ensures the protection of the very first region of the liner. In order to simulate the combustor flowpath, a backward facing step was installed upstream the slot to generate a large recirculating area. Adiabatic effectiveness, heat transfer coefficient and net heat flux reduction were evaluated and compared with non- recirculating experiments. Measurements were performed by means of a steady-state Thermochromic liquid crystals (TLC) technique with a thin Inconel heating foil for the heat transfer measurements. A data reduction procedure based on a finite element approach has been developed to take into account the non uniform heat generation and conduction due to the large amount of holes. Experiments were carried out considering the combined effects of slot, effusion and dilution holes. Three different effusion blowing ratios (BR = 3-5-7) are investigated, keeping constant the slot flow parameters (BR = 1.3). Results highlight that the presence of the step leads to a general reduction of effectiveness while does not have effects on the heat transfer coefficient.

Simulations of a two-stream backward-wave oscillator with a slot-hole structure

We study a two-stream backward-wave oscillator with a slot-hole structure at short millimeter waves with the help of a three-dimensional particle-in-cell simulation. In order to increase the interaction region of the electron beam, the efficiency and the output power, a slot-hole loaded rectangular waveguide structure used as the high-frequency system is proposed. Based on the mechanism of the backward-wave oscillator, a slow-wave oscillator with a frequency of 0.14 THz is designed. The simulations show that the output power and the efficiency of the oscillator can be enhanced due to the coupling between the two beams through the slot holes. The interaction efficiency is 5.18%, and the starting current density is below 5 A · cm−2 for the two beams. These attractive results indicate that, based on the two-stream backward-wave oscillator, we can get short millimeter wave sources with high power and low current density.

Fracture Mechanism and Ductility Construction of Joints of H-Style Beam-Square Tubular Column

Numerical simulation and fracture analysis were performed on conventional joint of H-style beam-square steel tubular column based on suggested elliptical yield model. The modified coefficient of elliptical fracture model was obtained by equivalently calculating the effects of residual stress and flaws. Using the elliptical fracture model with equivalently calculating the effects of residual stress and disfigurement for evaluation, the parameters of slot holes and horizontal haunch at beam flanges on failure mode of joints of H-style steel beam-square steel tubular column were studied by finite element method. The results indicate that the plastic rotation of joints of H-style beam-square steel tubular column with slot holes and horizontal haunch at beam flanges reach 0.03rad and meet with the requirement of the interim guidelines FEMA, and the loading capacity decrease within 15% compared with that of the conventional joint.

Fracture Mechanism and Ductility Construction of Joints of H-Style Beam-Square Tubular Column

Numerical simulation and fracture analysis were performed on conventional joint of H-style beam-square steel tubular column based on suggested elliptical yield model. The modified coefficient of elliptical fracture model was obtained by equivalently calculating the effects of residual stress and flaws. Using the elliptical fracture model with equivalently calculating the effects of residual stress and disfigurement for evaluation, the parameters of slot holes and horizontal haunch at beam flanges on failure mode of joints of H-style steel beam-square steel tubular column were studied by finite element method. The results indicate that the plastic rotation of joints of H-style beam-square steel tubular column with slot holes and horizontal haunch at beam flanges reach 0.03rad and meet with the requirement of the interim guidelines FEMA, and the loading capacity decrease within 15% compared with that of the conventional joint.

사각형 및 원형 출구 Synthetic Jet의 유동 특성에 대한 수치적 연구

사각형 및 원형 출구 형상 synthetic jet의 수치적 연구를 통하여 유입류가 존재할 경우 평판에서의 유동 구조 및 유동 제어 효과를 분석하였다. 사각형 출구 형상의 경우, jet 직후에 강한 vortex가 생성되지만 주변에 적은 momentum을 공급하기 때문에 유입류 방향으로 갈수록 유동제어 효과가 감소하게 된다. 원형 출구 형상의 경우, 규칙적인 vortex의 형태가 slot 중앙부터 끝까지 나타나고 보다 멀리까지 jet vorticity의 영향이 미치게 된다. 유동제어 효과를 예상하기 위하여 위치 별 wall shear stress를 비교하였다. 이에 원형 출구 형상이 사각형 출구 형상보다 유동제어 효과가 더 클 것으로 판단된다. 또한 최적의 원형 출구 형상을 도출하기 위하여, hole gap과 diameter의 변화에 따른 유동 구조 및 유동 제어 효과를 비교 분석하였다. 그 결과, hole diameter와 gap를 고려하여 원형 출구 형상을 설계할 경우 유동제어 효과를 극대화 할 수 있음을 밝혔다. The flow characteristics of synthetic jet depending on rectangular and circular jet exit configuration are investigated using numerical computation with cross flow. In rectangular slot, synthetic jet generates the strong vortex but supplies fewer momentum and effectiveness of flow control is reduced along flow direction. In circular slot, regular vortex is formed from slot center to end. It affects the wider region than rectangular slot. The distribution of wall shear stress is considered in order to indicate the effectiveness of flow control device for flow separation delay. Consequently, circular slot is a more suitable candidate for delaying flow separation. In order to derive the optimal shape of a circular slot exit, hole gap and diameter that affect the flow structure and flow control were analyzed. As a result, consider the hole diameter and gap of circular slot exit design, effectiveness of the flow control can be increased.

Experimental and Numerical Investigation on the Film Cooling of Waist-Shaped Slot Holes Comparing With Converging Slot Holes

Film cooling performance of a new shaped hole, waist-shaped slot hole, is studied in this paper. Experimental measurement and numerical simulation are carried out to investigate the film cooling character and physics of this new shaped hole. And comparisons between the waist-shaped slot hole and two kinds of console holes are also performed. Both the cooling effectiveness distribution and the heat transfer coefficient distribution of the waist-shaped slot hole are similar with those of the console hole with a large divergence angle because of the effect of the waist-shaped slot hole’s structure. The middle constriction structure of the waist-shaped slot hole and the coupled vortices makes jets from the waist-shaped slot holes produce higher cooling effectiveness in the midspan region between adjacent holes. And also due to the effect of the middle constriction structure, the heat transfer coefficient of the waist-shaped slot hole is very high in the upstream midspan region between adjacent holes. However, the heat transfer coefficient in the downstream midspan region is lower than that in the region near the hole centerline because of the effect of the coupled vortices. The waist-shaped slot holes provide the surface with very good thermal protection, especially in the upstream region. Although the console holes with small a exit-entry area ratio provide better thermal protection than the waist-shaped slot holes due to small turbulence intensity, the flow resistance characteristic of the waist-shaped slot hole, which has a larger exit-entry area ratio, is much better.

Analysis of Fringe Effect of MEMS Comb Capacitor with Slot Structures

For a super high precision MEMS sensor with the comb capacitor structure, the fringe effect of capacitors can not be neglected. In this paper, directing at the comb capacitor structure with slot holes, the effects of the non-overlap parts of comb capacitor, the distance between two slot holes in comb electrodes and slot depth aspect ratio on sensing capacitance are simulated by 3D finite element method of ANSOFT Maxwell software. The results show that when the width H and thickness t of sensing electrode plate are fixed, the fringe effect becomes larger for a smaller length L. The fringe effect is very small as non-overlap length is between 100 μm and 180 μm for 500 μm≤L≤1200 μm. The capacitance error caused by the fringe effect is the smallest for the slot distance 35 μm, slot depth 25 μm and slot width 20 μm. The error of sensing displacement caused by the fringe effect of the comb capacitor is 0.61% obtained by MATLAB Simulink.

Surface roughness and diametral consistency of holes drilled into DDGS/phenolic resin blends

In this study, corn-based distillers dried grains with solubles (DDGS) has been utilized as a filler and blended with phenolic resin. The blends were compression molded into rectangular test specimens, into which holes have been machined using a standard 9.52 mm (3/8 in) diameter, two-fluted twist drill. A series of tests was then conducted to examine the effects of DDGS content, cutting speed, and feed rate upon the surface finish (roughness) of the interior hole slot, as well as the consistency of the drilled hole diameter. DDGS content was 0, 25, 50, and 75%, by weight. Cutting speed was 17, 30, and 46 m/min (55, 100, and 150 ft/min). Feed rate was 0.025, 0.152, and 0.279 mm/rev (0.001, 0.006, and 0.011 in/rev). Results indicate that as the DDGS content increased, roughness exhibited a weak but statistically significant decrease. When the cutting speed increased, roughness increased slightly. However, when feed rate increased, roughness increased at a greater rate than that due to cutting speed. In terms of diametral consistency, the effect of adding DDGS resulted in holes with diameters less than the nominal drill size. As cutting speed increased, the holes tended to be oversized. Based on the cutting speed and feed rate levels used, optimal machining conditions which would reduce roughness occurred for 75% DDGS, cutting speed of 17 m/min (55 ft/min), and feed rate of 0.025 mm/rev (0.001 in/rev). However, to maintain consistent hole diameter, optimal conditions were found to be 40% DDGS, 30 m/min (100 ft/min), and 0.152 mm/rev (0.006 in/rev) and would produce a drilled hole with a diameter of 9.52 mm (0.375 in). As the use of biofillers in plastic composites evolves, it will become increasingly important to examine the machinability of these novel materials.

New development of the turbulent Prandtl number models for the computation of film cooling effectiveness

This paper presents the new development on the turbulent Prandtl number distribution models which are used to improve the computation accuracy of film cooling effectiveness distribution in the frame of the isotropic turbulence models. In the new developed turbulent Prandtl number distribution models, the turbulent Prandtl number varies with some characteristic quantity of the film cooling to make the models applicable for more film cooling cases effectively. A new VTG-Pr t model is developed for the computation of film cooling cases in which the wall is mainly influenced by the mixing layer region between the jet core and the mainstream. The Pr t value in this model varies with dimensionless temperature gradient which is suggested to be the characteristic quantity of the mixing layer region. The VTG-Pr t model has been used in the computations of long cylindrical hole film cooling, short cylindrical hole film cooling, compound angle cylindrical hole film cooling and expansion shaped hole film cooling in the present paper. And it is validated to be an effective and easy way to obtain accurate film cooling effectiveness distributions for this kind of film cooling. But for the kind of film cooling, in which the wall is mainly influenced by the jet core region and the influence of heat diffusion in the mixing layer region on the cooling effectiveness is very small, the VTG-Pr t model is disabled. Another turbulent Prandtl number distribution model, named VT-Pr t model, is developed for this kind of film cooling in the present paper. The Pr t value in this model varies with dimensionless temperature which is suggested to be the characteristic quantity of the jet core region. Good agreement between the computed and measured results is obtained through the use of VT-Pr t model in the computation of converging slot hole film cooling.

Computational Analysis for Dynamic Characteristics of Drilling Shaft System in Deep Slot Hole Drilling

In this article, the nonlinear dynamic responses of drilling shaft system with hydrodynamic forces of cutting fluid were analyzed in deep slot hole drilling. A numerical method is presented to observe the states of the drilling shaft system. Using the proposed method, the periodic orbit of the drilling shaft motion and its period are calculated when the design parameters of drilling shaft system are subject to change, then the stability for dynamic responses of the drilling shaft system can be determined by the Floquet theory. According to the physical character of cutting fluid, the variational constraint approach is introduced to continuously revise the variational form of Reynolds equation at every step of iteration process. The nonlinear hydrodynamic forces of cutting fluid and their Jacobian are solved simultaneously without the increasing of computing efforts. The numerical examples show that the scheme of this study saves computing efforts but also is good precision, and can make a good reference for the dynamic design of drilling shaft system in deep slot hole drilling.

Investigation into the effect of nozzle shape on the nozzle discharge coefficient and heat and mass transfer characteristics of impinging air jets

High velocity impinging air jets are commonly used for heating, cooling and drying, etc. because of the high heat and mass transfer coefficients which are developed in the impingement region. In order to provide data for the designers of industrial equipment, a variety of slot nozzles were tested to determine the effect on heat transfer of both nozzle shape and slot width. A large multi-nozzle rig was also used to measure average heat and mass transfer characteristics under arrays of both slot nozzles and circular holes. As a necessary preliminary to the heat transfer investigation, the discharge coefficients of the nozzles were measured. Then, the experimental results are compared with the simplified flow model. A good agreement was found between the theoretical and experimental results. From the tests, it was also found that the heat transfer results from differently shaped nozzles could be satisfactorily correlated provided that the effective slot width or hole diameter was used to characterize the nozzle shapes.

Experimental research on the thermal performance of converging slot holes with different divergence angles

Thermal performances of two kinds of converging slot-hole ( console) with different divergence angles have been measured using transient liquid crystal measurement technique which can process the nonuniform initial wall temperature. Four momentum ratios are tested. Consoles with different divergence angles produce different cooling effectiveness distributions in the upstream region. However, the cooling effectiveness distributions of the two consoles are similar in the downstream. The laterally averaged cooling effectiveness results show that the differences between the two consoles are very small and the best momentum ratio for both consoles’ cooling effectiveness distribution is around two. With the momentum ratio increasing, the normalized heat transfer coefficient h/ h 0 of both consoles increases, but the h/ h 0 value of small divergence case is higher and becomes progressively higher than that of large divergence case. Moreover, the effect of the couple vortices on the heat transfer coefficient distributions is more significant for the large divergence case. Both consoles provide the surface a certain degree of thermal protection, especially in the upstream region. The distributions of heat flux ratio q/ q 0 are similar with those of η because the influence of η on q/ q 0 is much larger than that of h/ h 0 on q/ q 0.

Two-Phase Flow Simulation of Mist Film Cooling on Turbine Blades With Conjugate Internal Cooling

Effective cooling of gas turbine combustor liners, combustor transition pieces, turbine vanes (nozzles), and blades (buckets) is a critical task to protect these components from the flue gas at extremely high temperature. Air film cooling has been successfully used to cool these hot sections for the past half century. However, the net benefits from the traditional methods seem to be incremental, but the temperature of working gas is continuously increasing to achieve high thermal efficiency. Therefore, new cooling techniques need to be developed. One of the promising techniques is to enhance film cooling with mist injection. While the previous study reported the effect of mist on the cooling effectiveness with an adiabatic wall, this paper focuses on the effect of mist injection on heat transfer of film cooling with a nonadiabatic flat wall, using the commercial computational fluid dynamics software package FLUENT. Both 2D and 3D cases are considered with a 2D slot and diffusive compound-angle holes. Modeling of the interaction of a droplet with a uniformly cooled wall as well as conjugate heat conduction inside the solid base are conducted. Different mist droplet sizes and mist concentrations are adopted. Conditions both in a gas turbine operating environment (15 atm and 1561 K) and in a laboratory environment (1 atm and 450 K) are considered. Results show that injecting 2–10% mist reduces the heat transfer coefficient and the wall temperature. Especially, mist has the prolonged effect of cooling the region downstream for 15 jet hole diameters, where conventional air film cooling is not effective.

Parameters Affecting Turbulent Film Cooling-Reynolds-Averaged Navier-Stokes Computational Simulation

Film cooling of surfaces appears in many applications. For instance, it is one of the most effective methods to improve the efficiency of gas turbines. As a fundamental study, two different types of film cooling (slot and discrete holes injections) are numerically simulated here. A flat surface is used to model a small portion of a gas turbine blade. Incompressible, stationary, viscous, turbulent flow is assumed using the STAR-CD software with the standard k‐e model and a cell-centered finite volume method on a nonuniform structured grid. The jet flow Reynolds number, based on the jet’s hydraulic diameter, is 4.7 × × 103. The study of the injection angle and the velocity ratio shows that the optimum film cooling occurs at jet angle of about 30 deg. However, the optimal velocity ratios of about 1.5 for slot injection and about 0.5 for discrete holes injection have been obtained. On the other hand, the study of jet-exit aspect ratio in discrete holes injection shows that stretching the hole in spanwise direction increases the film-cooling effectiveness. Also, the study of jet spacing in spanwise direction shows that decreasing the jet spacing increases the film-cooling effectiveness, but not as much as the jet aspect ratio.

Type II superconductors with applied current and magnetic field:effects of geometry and London depth

It is shown how the previous continuum theory of type II superconductorswith and without vortex pinning, of various shapes and in an applied magneticfield, is generalized to account for an applied transport current and a finiteLondon penetration depth λ. This extension is particularly importantat low inductions B, where the transition to the Meissner state is nowdescribed correctly, and for films with thickness comparable to or smallerthan λ. The finite width of the surface layer with screening currentsand the correct dc and ac responses in various geometries follow naturallyfrom an equation of motion for the current density in which the integralkernel now accounts for finite λ. Also considered is the geometry of`washers', i.e. thin-film squares with a slot and central hole as used forSQUIDs.

Theory of type-II superconductors with finite London penetration depth

Previous continuum theory of type-II superconductors of various shapes with and without vortex pinning in an applied magnetic field and with transport current, is generalized to account for a finite London penetration depth lambda. This extension is particularly important at low inductions B, where the transition to the Meissner state is now described correctly, and for films with thickness comparable to or smaller than lambda. The finite width of the surface layer with screening currents and the correct dc and ac responses in various geometries follow naturally from an equation of motion for the current density in which the integral kernel now accounts for finite lambda. New geometries considered here are thick and thin strips with applied current, and `washers', i.e. thin film squares with a slot and central hole as used for SQUIDs.

The variation of heat transfer coefficient, adiabatic effectiveness and aerodynamic loss with film cooling hole shape.

The heat transfer coefficient and adiabatic effectiveness of cylindrical, fan shaped holes and a slot are presented for the region zero to 50 diameters downstream of the holes. Narrow-band liquid crystals were used on a heated flat plate with heated air coolant. These parameters have been measured in a steady state, low speed facility at engine representative Reynolds number based on hole diameter and pressure difference ratio (ideal momentum flux ratio). The aerodynamic loss due to each of the film cooling geometries has been measured using a traverse of the boundary layer far downstream of the film cooling holes. Compared to the cylindrical holes, the fan shaped hole case showed an improvement in the uniformity of cooling downstream of the holes and in the level of laterally averaged film cooling effectiveness. The fan effectiveness approached the slot level and both the fan and cylindrical hole cases show lower heat transfer coefficients than the slot and non film cooled cases based on the laterally averaged results. The drawback to the fan shaped hole was that the aerodynamic loss was significantly higher than both the slot and cylindrical hole values due to inefficient diffusion in the hole exit expansion.

Aerodynamic Characteristics of Pressure-Pad Air Bars

Air-flotation ovens are widely used for noncontact support and drying of coated paper and plastic films (generically called webs). The main components in typical air-flotation ovens are air bars which have slot nozzles or holes through which hot air jets are ejected. Problems in air-flotation drying techniques include sideward motion of the web, web flutter, and contact between the web and air bars. The key to analyzing these problems is to determine the aerodynamic forces on the web. This paper discusses the aerodynamic forces generated by pressure-pad-type air bars, each of which has two slot nozzles. Ground-effect theories, which were originally developed for the design of hovercraft, are re-examined. The theories are compared with the measured values of the aerodynamic forces for typical air bars. It is shown that ground effect theories can be applied to pressure-pad-type air bars if we properly define the equivalent values of the ground effect variables, which include thickness of the air jet, flotation height, ejection angle of the air jet, and the effective total pressure of the air jet. [S0021-8936(00)02801-4]

Development of 17‐in. “pure flat” color‐monitor tube

Abstract— A perfectly flat‐face color‐monitor tube with 0.24‐mm‐pitch stripe screen has been developed. The anisotropically tensioned mask with slot holes has made it possible. The bonded front glass plate with conductive A/R (anti‐reflection) coating satisfies TCO regulation and the high performance new DQ‐DAF electron gun has been introduced. This tube is combined with newly developed deflection yoke which maintains self‐convergence function for multi‐scanning application in the display monitors. For the first time, the system includes three criteria for the next‐generation color‐monitor tube: perfectly flat screen, stripe phosphor arrangement, and multi‐scanning function.

Electron Microscopic Methods for Determining Changes in the Density of Synaptic Input to Neurons in the Aging Brain

Changes in the synaptic input to aging neurons can best be evaluated using electron microscopy (EM). Immunocytochemistry is used to identify neuronal populations and to distinguish the chemical identity of their synaptic input, using a double-label protocol (e.g., diaminobenzidine for the sites of the first antigen/antibody complexes and tetramethylbenzidine for the second). In preparing tissue for EM examination, neurons are sectioned in the plane of the nucleus at 70 nm and sections collected on slot hole grids. Photographic montages of neurons are made at a minimum of 3 depths of section, with about 1 μm intervening. The original micrographs are taken at 10,000× and printed at 25,000×. Morphometric analyses are performed using the Bloquant program (R&M Biometrics) and an IBM computer. The perikaryal membrane is outlined on an X-Y digitizing pad, and regions along which there is synaptic modification are measured. These synaptic regions are expressed as a percentage of the perikaryal membrane measured. Data are tested using a non-parametric statistic (Mann-Whitney U, P < 0.05). In some cases, the entire neuronal soma is serially sectioned in order to determine whether synapses are randomly distributed over the neuronal surface.