• Title/Summary/Keyword: 곡관 유동

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An Experimental Study on Flow Characteristics of Turbulent Pulsating Flow in a Curved Duct by using LDV (LDV에 의한 곡관덕트에서 난류맥동유동의 유동특성에 관한 실험적 연구)

  • Lee, Hong-Gu;Son, Hyun-Chul;Lee, Haeng-Nam;Park, Gil-Moon
    • Proceedings of the KSME Conference
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    • 2000.11b
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    • pp.397-403
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    • 2000
  • In the present study, flow characteristics of turbulent pulsating flow in a square-sectional $180^{\circ}$ curved duct were experimentally investigated. Experimental studies for air flows were conducted to measure axial velocity and wall shear stress distributions and entrance length in a square-sectional $180^{\circ}$ curved duct by using the LDV with the data acquisition and the processing system. The experiment was conducted in seven sections from the inlet (${\phi}=0^{\circ}$) to the outlet (${\phi}=180^{\circ}$) at $30^{\circ}$ intervals of the duct. The results obtained from the experimentation were summarized as follows ; (1) When the ratio of velocity amplitude ($A_1$) was less than one, there was hardly any velocity change in the section except near the wall and any change in axial velocity distributions along the phase. When the ratio of velocity amplitude ($A_1$) was 0.6, the change rate of velocity was slow. (2) Wall shear stress distributions of turbulent pulsating flow were similar to those of turbulent steady flow. The value of the wall shear stress became minimum in the inner wall aid gradually increased toward the outer wall where it became maximum. (3) The entrance length of turbulent pulsating flow reached near the region of bend angle of $90^{\circ}$, like that of turbulent steady flow. The entrance length was changed by the dimensionless angular frequency (${\omega}^+$).

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Application of Numerical Model for the Effective Design of Large Scale Fire Calorimeter (화재발열량계의 효율적 설계를 위한 수치해석 모델의 적용)

  • Kim, Sung-Chan
    • Fire Science and Engineering
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    • v.24 no.6
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    • pp.28-33
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    • 2010
  • The present study develops a numerical model based on the computational fluid dynamics technique to analyse the thermal flow characteristics of large scale fire calorimeter and examine the characteristics of primary parameters affecting on the uncertainty of heat release rate measurement. ANSYS CFX version 12.1 which is a commercial CFD package is used to solve the governing equations of the thermal flow field and the eddy dissipation combustion model and P-1 radiation model are applied to simulate the fire driven flow. The numerical results shows that the horizontal duct system with $90^{\circ}$ bend duct was shown relatively high deviated asymmetric flow profiles at the sampling location and the deviation of the velocity field was higher than that of the temperature and species quantities. The present study shows that the computational model can be applicable to optimize the design process and operating condition of the large scale fire calorimeter based on the understanding of the detail flow field.

A study on the heat transfer characteristics of swirling flow in a circular sectioned $180^{\circ}C$bend with uniform heat flux (균일 열플럭스가 있는 $180^{\circ}C$ 원형단면 곡관의 선회유동 열전달특성 연구)

  • Lee, Sang-Bae;Gwon, Gi-Rin;Jang, Tae-Hyeon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.5
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    • pp.615-627
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    • 1997
  • An experiment was performed to local heat transfer coefficient and Nusselt number in the circular duct of 180.deg. bend for Re=6*10$^{4}$, 8*10$^{4}$ and 1*10$^{5}$ at swirling flow and non-swirling flow conditions. The test tube with circular section was made by stainless which has curvature ratio 9.4. The wall of test tube was heated directly by electrical power to 3.51 kw and swirling motion of air was produced by a tangential inlet to the pipe axis at the 180 degree. Measurements of local wall temperatures and bulk mean temperature of air are made at four circumferential positions in the 16 stations. The wall temperatures show particularly reduced distribution curve at bend for non-swirling flow but this effect does not appear for swirling flow. Nusselt number distributions for swirling flow which was calculated from the measured wall and bulk temperatures were higher than that of non-swirling flow. Average Nusselt number of swirling flow increased about 90 ~ 100% than that of non-swirling flow whole through the test tube. The Nu/N $u_{DB}$ values at the station of 90.deg. for non-swirling flow and swirling flow are respectively about 2.5 and 4.8 at Re=6*10$^{4}$. Also that is good agreement with Said's result for non-swirling flow. flow.

Basic Design of High Pressure LOx Lines for a Liquid Rocket Engine (액체로켓엔진 액체산소 고압 배관부 기본설계)

  • Moon, Il-Yoon;Yoo, Jae-Han;Moon, In-Sang
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2009.11a
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    • pp.107-110
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    • 2009
  • A basic design for a Technical Development Model (TDM) of liquid oxygen lines from the turbopump exit to the oxidizer valves of the combustion chamber and the gas generator was conducted to develop a turbopump-fed liquid rocket engine. The TDM is composed of straight lines, elbows, bellows, a branch, an orifice, flanges and a heat insulator. Materials were determined by consideration of operation conditions, weight constraint and manufacturing procedures. The size and the location of each component were determined by flow analysis of the required flowrate and the pressure loss. Basic designs of the components were conducted by consideration of the operating temperature and the maximum expectation operating pressure. The safety factors were evaluated by structural analysis of design of each component.

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An Experimental Study of Turbulent Uniform Shear Flow in a Nearly Two-Dimensional $90^{\circ}$ Curved Duct (II) - Turbulent Flow Field- (2차원 $90^{\circ}$ 곡관에서 균일전단류의 특성에 대한 실험적 연구 (2) -난류유동장-)

  • 임효재;성형진;정명균
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.3
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    • pp.846-857
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    • 1995
  • An experimental study is made of turbulent shear flows in a nearly two-dimensional 90.deg. curved duct by using the hot-wire anemometer. The Reynolds normal and shear stresses, triple velocity products, integral length scales, Taylor micro length scales and dissipation length scales are measured and analyzed. For a positive shear at the inlet, the afore-mentioned turbulence quantities are all suppressed. However, when the inlet shear flow is negative, they are augmented, i.e., the convex curvature suppresses the turbulence whereas the concave curvature augments it. It is found that the curvature effects are rather sensitive to the triple velocity products than the Reynolds stresses. The evolution of turbulence under the curvature with the different shear conditions is well described by the modified curvature parameter S' and the non-dimensional development time ${\tau}$.'

A Simulation for the Natural Frequencies of Curved Pipes Containing Fluid Flow with Various Elbow Angles (시뮬레이션에 의한 유체 유동 파이프 계의 곡관부의 각도 변화에 따른 고유진동수 고찰)

  • 최명진;장승호
    • Journal of the Korea Society for Simulation
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    • v.10 no.1
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    • pp.63-65
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    • 2001
  • To investigate the natural frequencies of curved piping systems with various elbow angles conveying flow fluid, a simulation is performed considering Initial tension due to the inside fluid. The system is analyzed by finite element method utilizing straight beam element. Elbow part is meshed using 4 elements, and the initial tension is considered by inserting equivalent terms into the stiffness matrix. Without considering the initial tension, the system becomes unstable, that is, the fundamental natural frequency approaches to zero value fast, as the flow velocity reaches critical value. With the initial tension terms, the system becomes stable where there is no abrupt decrease of the fundamental natural frequency. The change rate of the natural frequency with respect to the flow velocity reduces. As elbow angle increases, the system becomes stiffer, then around 150 degrees of the elbow angle the natural frequency has the largest value, the value decreases after the angle of the largest natural frequency. When angle is between 170 degrees and 179 degrees, the natural frequency is very sensitive. This means that small change of angle results in great change of natural frequency, which is expected to be utilized in the control of the natural frequency of the piping system conveying flow fluid.

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Flows Characteristics of Developing Turbulent Pulsating Flows in a curved Square Duct (곡관덕트내의 입구영역에서 난류 맥동유도의 유동특성)

  • 봉태근
    • Journal of Advanced Marine Engineering and Technology
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    • v.23 no.4
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    • pp.533-542
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    • 1999
  • In this study the flow characteristics of developing turbulent pulsating flows in a square-sec-tional 180。 curved duct are investigated experimentally. The experimental study of air flow in a square-sectional curved duct is carried out to measure axial velocity distribution secondary flow velocity profiles and wall shear stress distributions by using a Laser Doppler Velocimetry system with the data acquisition and processing system of Rotating Machinery Resolver (RMR) and PHASE software at the entrance region of the duct which is divided into 7 sections from the inlet(${{\o}}=0_{\circ}$) to the outlet (${{\o}}=180_{\circ}$) in $30_{\circ}$ intervals. The results obtained from the study are summarized as follows: (1) The time-averaged critical Dean number of turbulent pulsating flow(De ta, cr) is greater than $75{\omega}+$ It is understood that the critical Dean number and the critical Reynolds number are related to the dimensionless angular frequency in a curved duct. (2) Axial velocity profiles of turbulent pulsating flows are of an annular type similar to those of turbulent stead flows. (3) Secondary flows of trubulent pulsating flows are strong and complex at the entrance region. As velocity amplitudes(A1) become larger secondary flows become stronger. (4) Wall shear stress distributions of turbulent pulsating flows in a square-sectional $180_{\circ}$ curved duct are exposed variously in the outer wall and are stabilized in the inner wall without regard to the phase angle.

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Heat/Mass Transfer Characteristics in A Rotating Duct with $180^{\circ}$ Turn ($180^{\circ}$ 곡관부를 가지는 회전 덕트에서의 열/물질전달 특성)

  • Won, Chung-Ho;Lee, Sei-Young;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.3
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    • pp.405-413
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    • 2001
  • The present study investigates convective heat/mass transfer and flow characteristics inside a rotating two-pass rectangular duct. A naphthalene sublimation technique is employed to determine the detailed local heat transfer coefficients using the heat and mass transfer analogy. The objective of this study is to determine the effects of turning geometry with rotation for 0.0$\leq$Ro$\leq$0.24. The results reveal that the sharp-turn corner has the larger pressure drop and lower heat transfer in the post-turn region than those of the round-turn corner. The strong secondary flow enhances heat transfer for the round-turn corner. Coriolis force induced by the rotation pushes the high momentum core flow toward the trailing wall in the first passage with radially outward flow and toward the leading wall in the second passage with radially inward flow. Consequently, the high heat transfer rates are generated on the trailing surface and the leading surface in the first and second passage, respectively. However, the strong secondary flow due to the turning dominates the flow pattern in the second passage, thus the heat transfer differences between the leading and trailing surfaces are small with the rotation.

Effects of Rotation Speed on Heat Transfer and Flow in a Coolant Passage with Turning Region ( I ) - Cross Ribbed Duct - (곡관부를 가지는 내부 냉각유로에서 회전수 변화에 따른 열전달 및 유동 특성 ( I ) - 엇갈린 요철배열 덕트 -)

  • Kim Kyung Min;Kim Yun Young;Rhee Dong Ho;Cho Hyung Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.6 s.237
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    • pp.737-746
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    • 2005
  • The present study investigates heat/mass transfer and flow characteristics in a ribbed rotating passage with turning region. The duct has an aspect ratio (W/H) of 0.5 and a hydraulic diameter ($D_h$) of 26.67 mm. Rib turbulators are attached in the cross arrangement on the leading and trailing surfaces of the passage. The ribs have a rectangular cross section of $2\;mm\;(e){\times}\;mm\;(w)$ and an attack angle of $70^{\circ}$. The pitch-to-rib height ratio (p/e) is 7.5, and the rib height-to-hydraulic diameter ratio ($e/D_h$) is 0.075. The rotation number ranges from 0.0 to 0.20 while the Reynolds number is constant at 10,000. To verify the heat/mass transfer augmentation, internal flow structures are calculated for the same conditions using a commercial code FLUENT 6.1. The heat transfer data of the smooth duct for various Ro numbers agree well with not only the McAdams correlation but also the previous studies. The cross-rib turbulators significantly enhance heat/mass transfer in the passage by disturbing the main flow near the surfaces and generating one asymmetric cell of secondary flow skewing along the ribs. Because the secondary flow is induced in the first-pass and turning region, heat/mass transfer discrepancy is observed in the second-pass even for the stationary case. When the passage rotates, heat/mass transfer and flow phenomena change. Especially, the effect of rotation is more dominant than the effect of the ribs at the higher rotation number in the upstream of the second-pass.

Effects of Rotation Speed on Heat Transfer and Flow in a Coolant Passage with Turning Region (II) - Parallel Ribbed Duct - (곡관부를 가지는 내부 냉각유로에서 회전수 변화에 따른 열전달 및 유동 특성 (II) - 평행한 요철배열 덕트 -)

  • Kim Kyung Min;Kim Yun Young;Lee Dong Hyun;Cho Hyung Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.8 s.239
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    • pp.911-920
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    • 2005
  • The present study investigates heat/mass transfer and flow characteristics in a ribbed rotating passage with turning region. The duct has an aspect ratio (W/H) of 0.5 and a hydraulic diameter ($D_h$) of 26.67 mm. Rib turbulators are attached in the parallel arrangement on the leading and trailing surfaces of the passage. The ribs have a rectangular cross section of 2 m (e) $\times$ 3 m (w) and an attack angle of $70^{\circ}$. The pitch-to-rib height ratio (p/e) is 7.5, and the rib height-to-hydraulic diameter ratio (e/$D_h$) is 0.075. The rotation number ranges from 0.0 to 0.20 while the Reynolds number is constant at 10,000. To verify the heat/mass transfer augmentation, internal flow structures are calculated for the same conditions using a commercial code FLUENT 6.1. The results show that a pair of vortex cells are generated due to the symmetric geometry of the rib arrangement, and heat/mass transfer is augmented up to $Sh/Sh_0=2.9$ averagely, which is higher than that of the cross-ribbed case presented in the previous study for the stationary case. With the passage rotation, the main flow in the first-pass deflects toward the trailing surface and the heat transfer is enhanced on the trailing surface. In the second-pass, the flow enlarges the vortex cell close to the leading surface, and the small vortex cell on the trailing surface side contracts to disappear as the passage rotates faster. At the highest rotation number ($R_O=0.20$), the turn-induced single vortex cell becomes identical regardless of the rib configuration so that similar local heat/mass transfer distributions are observed in the fuming region for the cross- and parallel-ribbed case.