正四角斷面덕트 內에서 遷移非定常流動 特性에 關한 硏究

최주호 朝鮮大學校 1988 국내박사

덕트내에서의 소음은 사무실, 스튜디오 그리고 반도체 공장등 정숙한 환경을 필요로 하는 장소에 있어서 큰 문제가 되어 왔다. 덕트계의 소음제어는 흡음제를 이용한 수동 소음제어방식이 주류를 이루고 있으나 소음 감쇄 성능이 500㎐ 이상의 중고음 영역에서 유효아여 그 이하의 주파수에서는 소음 감쇄 성능이 떨어져 많은 소음기를 직렬로 사용해야하는 문제점이 있어 500㎐이하의 저주파 소음에 대해 소음원 위상과 180도 차이가 나고 동일한 크기의 2차음을 스피커로 부가하여 상호의 간섭효과로 소음을 제거하는 소위 능동 소음제어 방식이 효과적이다. 본 연구에서는 제어 스피커와 오차 마이크로폰 사이에 존재하는 보조 경로의 2차 경로 전달함수를 적응 모델링하고 이를 보상함으로써 능동 소음제어 시스템의 성능을 향상시킬 수 있는 적응 능동 소음 제어기법을 토대로 LMS 알고리즘을 이용하여 능동 소음 제어기를 설계하고 컴퓨터 시뮬레이션을 행하여 설계한 제어기가 소음의 크기를 크게 감쇄시키는것을 확인하였다. In the present study, the detailed structure and characteristics of steady flow, oscillatory flow and pulsating flow in a square duct are investigated analytically and experimentally in the range of transitional flow. A system of conservation equations for steady, oscillatory and pulsating duct flows are solved analytically by using the linearization of non-linear convective term and adoption of eddy viscosity from empirical correlations. Analytical solutions of velocity profiles and shear stress for these flows are obtained in the form of infinite series. The experimental study for the air flow in a square duct with ratio of 1 (40mm × 40mm)and 4000mm long is carried out to measure the velocity profiles and other parameters by using a hot-wire anemometer with data acquisition and processing system. The study on major characteristics for the flows such as the classification of flow patterns, determination of critical Reynolds number, velocity profiles and shear stress is accomplished from the results of both studies. The results obtained from analytical and experimental studies are summarized as follows: (1) The critical Reynolds numbers for steady, oscillatory, and pulsating flow depend on cross-sectional mean velocity, hydraulic diameter, fluid kinematic viscosity, dimensionless frequency and velocity amplitude ratio. The critical Reynolds numbers obtained are Re_(st cr) ≒ 1700 in the steady flow, Re_(os cr) ≒ 380 ω^(+) and Re_(os cr) ≒ 2700 in oscillatory flow, and Re_(ta cr) ≒ 1900 in pulsating flow, respectively. (2) The steady, oscillatory, and pulsating duct flows are classified into laminar, transitional, and turbulent flow regions, respectively, by the velocity waveforms obtained by the hot-wire anemometer. These three flow regions differ in axial positions and positions in z-direction. The amplitude of the velocity waveforms near the wall is smaller than that of the center line, and puffs occur in transitional square duct. (3) The friction factors for the square duct are smaller than those of the circular duct for the same Reynolds number. The friction factor of the transitional steady flow is λ_(st) ≒ 4.4 × 10^(-5) Re_(st)^(0.894) in the range of Re_(st) ≒ 1700∼2500. The instantaneous friction factor for the transitional oscillatory flow region is λu(t) ≒ 0.2877 / (Re_(os)(t))^(0.25) in the range of Re_(os) ≒ 2700~8200. The instantaneous friction factor for the transitional pulsating flow region is λu(t) ≒ 0.3925/ (Re_(ta)(t))^(0.25) in the range of Re_(ps) ≒ 1900~4100. (4) The veloctiy profiles of the transitional steady, oscillatory, and pulsating square duct flow decrease abruptly in z' ≒ 0.7∼1.0. The amplitude of the veloctiy (| u_(m os a) |) near the wall is smaller than that of the center line. The results of analytical study are in good agreement with the results of experimental study, quantitatively. (5) The distributions of shear stress for the transitional steady flow oscillatory flow, and pulsating flow increase abruptly in z' ≒ 0.8∼1.0. The shear stresses of inflow and outflow for the oscillatory and pulsating flows are symmetrical, the largest at ωt / (π/6)= 3 and 9, and the smallest at ωt / (π/6)=0 and 6. The variations in △p/ℓ, τ_(os) and τ_(ps) over one cycle for the transitional oscillatory and pulsating flows are in the form of a sine wave.

正四角斷面덕트 入口區域에서의 層流非定常流動 特性

박길문 高麗大學校 1987 국내박사

正四角덕트의 流動特性에 관한 實驗的 硏究

김태혁 조선대학교 1999 국내석사

Heat engine and fluid machinery in the plant have to linked with various ducts network and the corresponding design have to be concerned about effectiveness and stability of system of plant. To optimum control and design system concerning stability, economization, operating effectiveness, we have to exact analysis flow properties of a duct applying to fluid machinery, heat exchanger, cooling machine, air conditioning equipment. Therefore, it is necessary to research the duct, heat transfer equipment, for increasing overall effectiveness of air conditioning system by suggesting basic data of the duct resulting from organic research. So we can contribute to technical development of the duct. In case of speeding up the flow rate of the duct, lots of wave velocity components are occurred, the value of boundary layer resulting from developing the boundary layer at both walls of duct.

正四角덕트 入口領域에서 코너流動에 관한 硏究

이충주 朝鮮大學校 大學院 1997 국내석사

The corner flow characteristics of a square duct is applied to a miniature, high effectiveness, automatic control of mechanical facilities and architectural facilities on the industrial scenes. It is necessary to analyze exactly the flow characteristics of a square duct using 5-hole pitot tube. Because these can be applied to energy problem of air conditioning system. The governing equations(Continuity & Navier-Stokes equations) are solved theoretically by using a torodial coordinate system in a square duct. The experimental study using air in a square duct carried out to measure the corner flow characteristics by 5-hole pitot tube with 3-D traverse system, blower pressure transducers, A/D converter, amplifiers, power supply and oscilloscope. According to ratios of x/D_(h) in the a square duct, the following results was suggested. 1. Its is shown exactly symmetrical velocity distributions along a corner bisector 2. As the unsteady flows in the entrance region is developed at the downstream, boundary layer is developed because of viscosity at the wall and potential flow is disappeared when x/D_(h) reach 16. Thus, we can form clear definition the fully developed region from the point. 3. As flow go by downstream, that uniform velocity line is wrenched shows the increased intensity of secondary flows. 4. The velocity is decreased in caused by friction in the entrance region. The energy loss quantity is large because the velocity gradient become bigger. But, it become the uniform flow in the fully developed region and relatively, loss quantity owing to collision of air particle shows largely.

正四角덕트 入口領域에서 亂流脈動流動의 連度分布와 亂流特性에 관한 硏究

윤기수 朝鮮大學校 産業大學院 1990 국내석사

In the present study, the velocity distribution and turbulent characteristics of turbulent pulsatile flows in a square duct are investigated experimentally and the entrance length of developing turbulent pulsatile flows is determined in a square duct. The experimental study for the air flow in a square duct(40mm × 40mm and 4000mm long) is carried out to measure velocity profiles and distributions by using a hot-wire anemomenter with data acquisition and processing system. The results obtained from experimental studies are summarized as follows (1) Turbulence intensity of the development turbulent pulsating flow is smaller in the accelerating than in the decelerating region. (2) The development of the turbulent pulsating flow is faster in the decelerating phase than in the accelerating phase. (3) The time averaged velocity profiles agree appoximately with the one-seventh power law of fully developed steady dust flows, and turbulence intensity increases in the fully developed flow region and near the wall of the duct (4) For the turbulent pulsating flow, the entrance length is a function of the time-averaged Reynolds number(Re_(□)), the dimensionless angular frequency(ω'), and the velocity amplitude ratio(A_(1)). The entrance length correlation in the present study is L_(□)/D_(h) ≒ 40.

正四角斷面덕트의 入口領域에서 亂流非正常流動의 流動特性에 關한 數植解析

양광열 朝鮮大學校 大學院 1993 국내석사

The flow characteristics of turbulent pulsating flows are investigated numerically in the entrance region of a square duct (40 mm × 40 mm and 4,000 mm). The numerical analysis are incorporated by finite-volume discretization with staggered grid system and SIMPLE algorithm. The numerical solution are compared with experimental results of mean velocity profiles, turbulence intensity, pressure distribution, shear stress distribution and entrance length. Time-averaged velocity profiles of the turbulent pulsating flows follow the one-seventh power law profile in the fully developed flow region. Turbulence intensity increases as the dimensionless transverse position increases from the center to the wall of the duct, and is slightly smaller in the accelerating phase than in the decelerating phase for the turbulent pulsating flows. Shear stress distribution show maxmun when angular frequency is about 3 and minimum when angular frequency is about 0. The entrance length of the turbulent pulsating flow is about 40 times as large as the hydraulic diameter under the present numerical solution.

正四角덕트의 90°分岐管內 流動特性에 관한 實驗的 硏究

金龍才 朝鮮大學校 大學院 1998 국내석사

Heat engine and fluid machinery in the plant have to linked with various ducts net and the corresponding design have to be concerned about effectiveness and stability of system of plant. To optimum control and design system concerning stability, economization, operating effectiveness, we have to exactly analysis flow properties of duct applying to fluid machinery, heat exchanger, cooling machine, air conditioning equipment. Therefore, it is necessary to research the duct, heat transfer equipment, for increasing overall effectiveness of air conditioning system by suggesting basic data of duct resulting from organic research. So we can contribute to technical developement of duct. According to the experiment on working properties, we can conclude as followings 1) The flow from the upstream of main duct outflows toward the branch duct after carring out complicated vortex flow, but the flow appearance is extremely complex. The flux of branch duct passed by about 20% of straight duct flux and others, 80% flux of straight duct, passed by through the main duct. 2) In case of speeding up the flow velocity of the duct, lots of wave velocity component is occured, the value of wave velocity component is large by the mixture of two boundary layers resulting from developing the boundary layer at both walls of duct.

正4角斷面덕트 內에서의 定常流動 特性에 關한 硏究

朴政均 國民大學校 1990 국내석사

정사각덕트 입구영역에서 난류파동유동에 속도분포와 난류특성에 관한 연구

윤기수 朝鮮大學校 1990 국내석사

正四角덕트내 코너영역에서의 流動特性에 관한 硏究

최윤철 朝鮮大學校 大學院 1997 국내석사

The role of building facilites is creating a pleasant space to maintain every sences of residents with in the satisfying range. For this role, many researches on air conditioning system have been in progress by to many researchers. Recently, building facilites part has been satisfied human demand in living space serving as intelligent building for the result. Therefore, it is needed rearches and concerin on a duct, heat transport device. For presenting primary date, we made a experimental duct and tested in size of x/D. In this experimental study, we conclude as the following : 1. It is shown exactly symmetrical velocity distributions along the corner bisector. 2. As flows go by downstream, that uniform velocity line is wrenched shows the increased intensity of secondary flows. 3. The velocity is decreased in caused by friction in the entrance region. The energy loss quantity is large because the velocity gradient become bigger. But, it become the uniform flow in the fully developed region and relatively, loss quantity owing to collision of air particle shows largely. 4. It is distinguished portential flow domain and boundary flow domain by viscosity force which cause the developement of boundary layer on surface of duct when uniformity flow proceeds from the approoch to the end of duct. There is not absolute uniformity flow for alteration velocity element however in the fully developed flow region, velocity profiles show parabulic distribution at laminar flow and show velocity distribution of a seventh of principle at turbulent flow.