4각덕트의 입구영역에서 난류진동유동의 유동특성에 관한 연구

박길문,조병기,고영하 조선대학교 동력자원연구소 1996 動力資源硏究所誌 Vol.18 No.1

The flow characteristics of developing turbulent oscillatory flow are investigated experimentally in the entrance region of a square duct (40 ㎜ X 40 ㎜ and 4,000 ㎜). Experimental results of mean velocity profiles, turbulence intensity and entrance length are measured by using a hot-wire anemometer system together with data acquisition and processing systems. For turbulent oscillatory flow, the turbulent components in the velocity waveforms increase as the dimensionless transverse position approaches the wall. Velocity distribution are not change fully developed region. Inflow and outflow are nearly symmetrical form in the fully developed region such as x/D_h≥40. 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 developing turbulent oscillatory flows. The entrance length of the turbulent oscillatory flow is about 40 times as large as the hydraulic diameter in the present experimental conditions.

曲管에 있어서 熱傳達에 관한 硏究

朴吉文 조선대학교 동력자원연구소 1984 動力資源硏究所誌 Vol.6 No.1

An experimental study of steady and unsteady heat transfer process in helical coiled tubes has been conducted. The heat transfers were studied using a helical coil with a ratio of curvature of 0.053, and distilled water for laminar flow and turbulent flow regimes. The ration of the heat transfer coefficient for the helical coil to that for the straight tube higher in the laminar flow regime than in the turbulent flow regime. The axial temperature distributions show large oscillations with axial distance, which damp out in the fully developed region. The value of resonant frequency agrees with the analytical results of Mori andNakayama.

정4각단면 덕트 내에서 비정상 천이유동에 관한 연구

박길문,박선종,최주호,유영태,Park, G.M.,Park, S.J.,Choi, J.H.,Yoo, Y.T. 대한설비공학회 1989 설비공학 논문집 Vol.1 No.3

A system of conservation equations for steady, oscillatory and pulsating duct flows are solved analytically by linearizing non-linear convective terms. Analytical solutions of velocity profiles for these flows are obtained in the form of infinite series. The experimental study for the air flow in a square duct ($40mm{\times}40mm$ and 400 mm long) is carried out to measure velocity profiles and other parameters by using a hot-wire anemometer with data acquisition and processing system. Major characteristics of the flows such as the classification of flow patterns, determination of critical Reynolds number and velocity profiles is accomplished from the experismental results.

원형관로내 층류 맥동유동의 속도와 압력 분포에 관한 연구

박길문,유영태,위광환,이충주,정지철 조선대학교 생산기술연구소 1996 生産技術硏究 Vol.18 No.2

In this study basic equations for the pulsatile laminar flow in a circular rigid pipe containing a slightly compressible fluid are derived and analytical solutions for the distributions of wave propagation factor K, cross-sectional mean velocity u_(m) and pressure P are schematically developed and confirmed experimentally. The pulsatile flow with 0 ≤ f ≤ 48Hz and 0 ≤ Re ≤ 2500 generated by summing the oscillatory flow made by ball valve into steady one. The wave form of pulsatile flow is described as a longitudinal wave and particle velocities measured experimentally are group velocities of the wave packet which are always smaller than phase velocities which are approximate to the sonic velocity C when the radial dispersion and wall friction are negligible. Therefore wave number is approximated to k = ω/c for high angular velocity region. The axial pressures and centerline velocities were measured by strain-gage type pressure transducers and Pito-static tubes, respectively. The cross-sectional mean velocities calculated from centerline velocities with the parabolic distributions of the laminar flow and confirmed by using the ultrasonic flowmeter. We knew that axial distributions of oscillatory velocity and pressure coincide with thoeretical and depend on the Reynolds number and angular velocity.

곡관 덕트내 난류 비정상유동의 압력분포

박길문,이행남,백대우,손현철 朝鮮大學校 機械技術硏究所 2000 機械技術硏究 Vol.3 No.1

In this study, Flow characteristics of turbulent unsteady flows in a square-sectional 180°curved duct were experimentally investigated. Experimental studies for air flow were conducted to measure pressure distributions in the square-sectional 180°curved duct by using a magnehelic differential pressure gage. The experiment were conducted in nineteen sections from the inlet (ø=0°) to the outlet(ø=180°) of the duct at 10°intervals. The results obtained from the experimentation are summarized as follows. (1) In the turbulent oscillatory flow, the pressure distribution was the largest in the accelerating and decelerating region of the bend angle of 90°and the pressure difference of the inner and outer walls was the largest before and after the bend angle of 90°. (2) In the turbulent pulsating flow, the pressure difference was the largest near the region of bend angle of 90°in the case of the middle region, and since then the pressure difference of the inner and outer walls became smaller.

曲管部 뒤에 이어진 直管部의 流動現象에 對한 考察

朴吉文 조선대학교 생산기술연구소 1978 生産技術硏究 Vol.1978 No.-

Flow phenomena in straight parts after helically coiled capillary tubes is studied experimentally. Coiled capillary copper tubes are 1.7mm I.D and 942mm length, and then experimental curvature ratio are d/D =O.0340(D×n=50mm×6 turns), 0.0170(100×3), O.0057(300×1). The Secondary flow was attributed of the effect of the centrifugal pressure gradient in the main flow of coiled tubes, and these variations are due to the oscillatory changes in the secondary circulation discovered here. Since the damping effect of viscous and main flow on the oscillation is large, it tends to decrease the period. The secondary circulation was sometime disappeared in the straight regions after coiled capillary tubes. The experimental results with water agreed with White formula in the laminar rigions and Ito formula in the Tubulent regions.

정사각단면 $180^{\circ}$ 곡관덕트의 입구영역에서 비정상층류유동의 유동특성에 관한 연구

박길문,모양우,조병기,Park, G.M.,Mo, Y.W.,Cho, B.K. 대한의용생체공학회 1996 의공학회지 Vol.17 No.4

The flow characteristics of developing unsteady laminar flow in a square-sectional $180^{\circ}$ curved duct are experimentally investigated by using laser doppler velocimerty (LDV) system with data acquisition and processing system of rotating machinery resolver(RMR) and PHASE software. The major flow characteristics of developing laminar pulsating flows are presented by mean velocity profilel velocity distribution of secondary flow, wall shear stress distributions, entrance lengths according to dimensionless angular frequency($\omega^+$), velocity amplitude ratio($A^1$), and time-averaged Dean number($De_ta$). The velocity profiles and wall shear stress distribution of laminar pulsating flow with dimensionlessangular frequency show the flow characteristics of the quasi-steady laminar flow in a curved duct. The developing region of laminar pulsatile flows in a square-sectional $180^{\circ}$ curved duct is extended to the curved duct angle of approximately $120^{\circ}$ under the present experimental condition.

정4각단면덕트 입구영역에서 층류맥동유동 유동특성에 관한 연구

박길문 대한기계학회 1991 대한기계학회논문집 Vol.15 No.5

본 연구에서는 정4각단면덕트 입구영역에서 층류맥동유동(laminar pulsating flows)의 유동특성을 이론 및 실험적으로 규명하기 위하여, 이론적 방법으로 덕트 입 구영역에서의 층류맥동유동에 대한 운동량방정식을 유도한 후 비선형인 대류항을 선형 화 시켜서 라플라스변환으로 속도분포식의 해를 구하였고, 실험적인 방법으로는 시험 덕트 크기는 횡단면의 가로*세로가 40mm*40mm이고, 길이가 4000mm인 정4각단면덕트 입구영역에서 송풍기에 의한 공기흡입유동으로 층류진동유동을 발생하며 이들 두유동 을 합성시켜 발생한 층류맥동유동에 대하여 열선유속계의 열선신호로부터 얻어진 속도 파형을 고찰하여 덕트내의 맥동유동에 대한 임계레이놀즈수를 결정하고 속도분포를 측 정하였다. 그리고 이론적으로 얻어진 속도분포식과 열선유속계로 측정한 속도분포를 비교검토하여 정확성을 검증하고, 이들 해석결과로 부터 층류맥동유동의 입구길이(en- trance lenght)식을 결정하여 제안하였다.

4각 덕트의 입구영역에서 천이 정상유동의 입구길이에 관한 연구

박길문,유영태,고영하,Park, G.M.,Yoo, Y.T.,Koh, Y.H. 대한설비공학회 1990 설비공학 논문집 Vol.2 No.1

In the present study, the entrance length, velocity profiles and waveforms of developing transitional steady flows in a square duct are investigated analytically and experimentally. The systems of conservation equations for transitional steady duct flows are solved analytically by linearizing non-linear convective terms and adoption of modified eddy viscosity from empirical correlations. Analytical solutions of velocity profiles for developing transitional steady flow were obtained in the form of infinite series. The experimental study for transitional steady flow in a square duct with $40mm{\times}40mm{\times}4000mm$($width{\times}height{\times}length$) was carried out to measure velocity profiles and other parameters by using a hot-wire anemometer with data acquisition and processing system. The entrance length of developing transitional steady flows in a square duct was $L_e{\fallingdotseq}0.02{\cdot}Re,st{\cdot}D_h$, and the overshoot was occured at about 30 times of hydraulic diameter because of the effect of external velocity of boundary layer and instantaneous acceleration.

정사각단면 $180^{\circ}C$ 곡덕트에서 층류진동유동의 유동 특성에 관한 연구

박길문,조병기,봉태근,Park, Gil-Mun,Jo, Byeong-Gi,Bong, Tae-Geun 대한기계학회 1998 大韓機械學會論文集B Vol.22 No.2

In the present study, the flow characteristics of developing laminar oscillatory flows in a square -sectional 180 deg. curved duct are investigated experimentally. The experimental study using air in a square-sectional 180 deg. curved duct is carried out to measure velocity distributions with a data acquisition and LDV (Laser Doppler Velocimetry) processing system. In this system, Rotating Machinery Resolver (RMR) and PHASE program are used to obtain the results of unsteady flows. The major flow characteristics of developing oscillatory flows are found by analyzing velocity curves, mean velocity profiles, time-averaged velocity distribution of secondary flow, wall shear stress distributions, and entrance lengths. In a lower dimensionless angular frequency, the axial velocity distribution of laminar oscillatory flow in a curved duct shows a convex shape in a central part and axial symmetry. The maximum value of wall shear stress in a lower dimensionless angular frequency is located in an outside wall, but according to increasing the dimensionless angular frequency, the maximum of wall shear stress is moved to inner wall. The entrance lengths of laminar oscillatory flows in a square-sectional 180 deg. curved duct is obtained to 90 deg. of bended angle of duct in this experimental conditions.