• 대한기계학회논문집B
• /
• 제22권9호
• /
• pp.1255-1266
• /
• 1998

Effects of a length-to-diameter ratio, L/D, on the three-dimensional flow and aerodynamic loss within an injection hole, which is normally oriented to the mainflow, have been investigated by using a straight five-hole probe. The length-to-diameter ratio of the injection hole is varied to be 0.5 and 2.0 for blowing ratios of 0.5, 1.0 and 2.0. Regardless of the blowing ratio, flows within the hole and at the jet exit are strongly affected by the length-to-diameter ratio. In the case of L/D=0.5, the inside flow is considerably influenced by the mainflow, and the exit flow variation is found to be the greatest. The aerodynamic loss in this case is usually attributed to jet -mainflow interactions. In the case of L/D=2.0, the flow separation and reattachment in the inlet region are completely separated from the complicated exit flow, and the aerodynamic-loss production is mainly due to the inlet flow separation.

• 대한조선학회지
• /
• 제3권1호
• /
• pp.11-18
• /
• 1966

In a polarized light field, triangular plate bracket specimen of CR-39 with lightening hole were subjected to tension. The variables of the models used in the experiment were taken in the range of length-depth $ratio=0.583{\sim}1.715$, eccentricity of lightening hole from the geometrical center of $bracket=-1/4"{\sim}+1/4"$, and the lightening hole $diameter=1/2"{\sim}2"$. The isoclinics were drawn and from those the stress trajectories were constructed. Then the distributions of boundary stress around the lightening holes were determined from the isochromatic fringe pattern. The conclusions reached in this investigation are as follows: 1. Maximum stresses of the hole boundary are gradually increased when the diameter of the lightning hole increase. 2. Maximum stresses of the lightning hole boundary are decreased gradually when the eccentricity of the lightning hole from the geometrical center of the bracket to the farther side from the free end. 3. If the minimum distances from the free end of the brackets to the lightening hole boundaries are equal, the variation of the maximum stresses are in a small range for the change of lightening hole diameter and its location. 4. When the length-depth ratios are smaller than 0.8, the maximum stresses increase steeply. In the range of $0.8{\sim}1.2$ maximum stresses increase gradually and thereafter increase rapidly when the length-depth ratio of the bracket increase for the same diameter of a lightening hole.

• 한국정밀공학회지
• /
• 제22권7호
• /
• pp.47-53
• /
• 2005

Microholes with high aspect ratio are required in microstructures. Among various methods for producing the microhole, micro electrical discharge machining (MEDM) is very effective and useful process. But, it is difficult to machine the high aspect ratio holes below $100\;{\mu}m$ in diameter because machining condition becomes unstable due to bad removal of debris at deep hole. In this paper, ultrasonic vibration is applied to MEDM work fluid to make a high aspect ratio micro hole. It is shown that the vibration is effective in circulating the debris and increasing the machining rate. As a result, produced was a micro hole with $92\;{\mu}m$ entrance diameter, $81\;{\mu}m$ exit diameter and aspect ratio 23.

• 대한기계학회논문집B
• /
• 제27권7호
• /
• pp.948-955
• /
• 2003

Pressure coefficient in rotating discharge hole was measured to gain insight into the influence of rotation to the discharge characteristics of rotating discharge hole. Pressure measurements were done by the telemetry system that had been developed by the authors. The telemetry system measures static pressure using piezoresistive pressure sensors. Pressure coefficients in rotating discharge hole were measured in longitudinal direction and circumferential direction with various rotating speed and 3 pressure ratios. From the results, the pressure coefficient, and therefore the discharge coefficient, is known to decrease with the increase of Ro number owing to the increase of flow approaching angle to the discharge hole inlet. However, there exists critical Ro number where the decrease rate of discharge coefficient with the increase of Ro number changes abruptly; flow separation occurs from the discharge hole exit at this critical Ro number. Critical Ro number increases with the increase of length-to-diameter ratio, but the increase is small where the length-to-diameter ratio is higher than 3. The decrease rate of discharge coefficient with the increase of Ro number depends on the pressure recovery at the discharge hole, and the rate is different from each length-to-diameter ratio; it has tendency that the short discharge hole shows higher decrease rate of discharge coefficient.

• Steel and Composite Structures
• /
• 제21권6호
• /
• pp.1211-1226
• /
• 2016

In this study, free vibration and damping characteristics of composite beams with holes are investigated, experimentally and numerically. Two types of samples with different fabrics are used: unidirectional and woven. The effects of diameter, number and location of circular holes on the vibration characteristics of composite beams are examined. The effects of rotation angle and minor to major diameter ratio of the elliptical hole are also investigated numerically. Moreover, the mode shapes of all types of beams are obtained numerically. According to the results, the natural frequency decreases with increasing hole diameter but increases very little with increasing the distance between the hole center and the clamped end. Damping ratio decreases by increasing the diameter of hole. But it fluctuates by increasing the diameters of holes of beam having three holes. Furthermore it decreases by increasing the distance between hole center and clamped end except for the range 50 mm to 100 mm.

• Journal of Mechanical Science and Technology
• /
• 제15권4호
• /
• pp.482-491
• /
• 2001

An experimental study has been carried out to investigate an I-type sparger-performance in view of pressure oscillation and thermal mixing in a pool. Its pitch-to-hole diameter, P/D, varies from 2 to 5. The test conditions are restricted to the condensation oscillation regime. In the present study, two different hole patterns, staggered and parallel types, are employed under various test conditions. The amplitude of the pressure pulse shows a peak for pool temperatures of 45∼85$\^{C}$, which depends on P/D and the steam mass flux. The effect of hole pattern on the pressure load is smaller than that of P/D. The dominant frequency increases with the subcooling temperature of pool water and P/D. A correlation for the dominant frequency is proposed in terms of the pitch-to-hole diameter ratio and other dimensionless thermal hydraulic parameters.

• Journal of Mechanical Science and Technology
• /
• 제16권12호
• /
• pp.1693-1701
• /
• 2002

The intermittent spray characteristics of a multi-hole and a single-hole diesel nozzle were experimentally investigated. The hole number of the multi-hole nozzle was 5, and the hole diameter of the 5-hole and the single-hole nozzle was the same as d$\_$n/=0.32 ㎜ with the constant hole length to diameter ratio(l$\_$n//d$\_$n/=2.81). The droplet diameters of the spray, including the time-resolved droplet diameter, SMD (Sauter mean diameter) and AMD (arithmetic mean diameter) , injected intermittently from the two nozzles into the still ambient were measured by using a 2-D PDPA (phase Doppler particle analyzer). Through the time-resolved evolutions of the droplet diameter, it was found that the structure of the multi-hole and the single-hole nozzle spray consisted of the three main parts : (a) the leading edge affected by surrounding air. and composed of small droplets; (b) the central part surrounded by the leading edge and mixing flow region and scarcely affected by the resistance of air, (c) the trailing edge formed by the passage of the central part. The SMD decreases gradually with the increase in the radial distance, and the constant value is obtained at the outer region of the radial distance (normalized by hole diameter) of 7-8 and 6 for the 5-hole and single-hole nozzle, respectively. The SMD along the centerline of the spray decrease shapely with the increase in the axial distance after showing the maximum value near the nozzle tip. The SMD remains the constant value near the axial distance(normalized by hole diameter) of 150 and 180 for the 5-hole and the single-hole nozzle, respectively.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2002년도 춘계학술발표대회 논문집
• /
• pp.9-12
• /
• 2002

A parametric study has been conducted to investigate the effect of the geometry on the strength of an unidirectional and fabric hybrid laminated composite joint. Tests are conducted for the specimens with nine different edge-to-hole diameter or width-to-hole diameter ratios. For the finite element analysis, the characteristic length method is used, and the tests for determining the characteristic length are performed additionally. Nonlinear contact problem between the pin and laminate is modeled by the gap element in MSC/NASTRAN. Tsai-Wu failure criteria is applied to the stress on the characteristic curve. The finite element and experimental results shows good agreement in strength of composite joint. Results of the parametric study shows the effect of the geometry is remarkable in the specimens with width-to-hole diameter ratio less than 2.8 and edge-to-hole diameter ratio less than 1.4.

• 한국레이저가공학회지
• /
• 제18권2호
• /
• pp.11-13
• /
• 2015

Pressure-drop in a micro-channel is critical when a hole diameter is less then 100um with the high aspect ratio, more than 40. To minimize these pressure loss for micro-channel applications is important and there would be the best hole diameter, taper angle, and their combinations. In this work, the parametric study for laser drilling of anodized material is conducted to obtain the micro-channel hole with high aspect ratio.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2010년 춘계학술대회논문집
• /
• pp.530-533
• /
• 2010

This paper presents numerical analysis and design optimization of various turbine blade cooling techniques with three-dimensional Reynolds-averaged Navier-Stokes(RANS) analysis. The fluid flow and heat transfer have been performed using ANSYS-CFX 11.0. A fan-shaped hole for film-cooling has been carried out to improve film-cooling effectiveness with the radial basis neural network method. The injection angle of hole, lateral expansion angle of hole and ratio of length-to-diameter of the hole are chosen as design variables and spatially averaged film-cooling effectiveness is considered as an objective function which is to be maximized. The impingement jet cooling has been performed to investigate heat transfer characteristic with geometry variables. Distance between jet nozzle exit and impingement plate, inclination of nozzle and aspect ratio of nozzle hole are considered as geometry variables. The area averaged Nusselt number is evaluated each geometry variables. A rotating rectangular channel with staggered array pin-fins has been investigated to increase heat transfer performance ad to decrease friction loss using KRG modeling. Two non-dimensional variables, the ratio of the eight diameter of the pin-fins and ratio of the spacing between the pin-fins to diameter of the pin-fins selected as design variables. A rotating rectangular channel with staggered dimples on opposite walls are formulated numerically to enhance heat transfer performance. The ratio of the dimple depth and dimple diameter are selected as geometry variables.