• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2000년도 춘계학술대회 논문집(Proceeding of the KOSME 2000 Spring Annual Meeting)
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• pp.127-133
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• 2000

In the present study flow characteristics of turbulent pulsating flow in a square-sectional 180。 curved duct are investigated experimentally. in order to measure axial velocity and secondary flow distributions experimental studies for air flow are conducted in a square-sectional $180^{\circ}$ curved duct by using the LDV system with the data acquisition and the processing system of the Rotating Machinery Resolver (RMR) and the PHASE software. The experiment is conducted on seven sections form the inlet(${\phi}=180^{\circ}$) at $30^{\circ}$ intervals of the duct. The results obtained from the experimentation are summarized as follows : In the axial velocity distributions of turbulent pulsating flow when the ratio of velocity amplitude(A1) is less than one there is hardly any velocity change in the section except near the wall and any change in axial velocity distribution along the phase. The secondary flow of turbulent pulsating flow has a positive value at the vend angle of $150^{\circ}$ without regard to the ratio of velocity amplitude. The dimensionless value of secondary flow becomes gradually weak and approaches zero in the region of bend angle $180^{\circ}$ without regard to the ratio of velocity amplitude.

• 대한기계학회논문집B
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• 제25권11호
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• pp.1561-1568
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• 2001

In the present study, flow characteristics of turbulent pulsating flow in a square-sectional 180$^{\circ}$curved duct were experimentally investigated. The experimental study for air flows in a curved duct are carried out to measure axial velocity profiles, wall shear stress distributions and entrance length in a square-sectional 180$^{\circ}$curved duct by using the Laser Doppler Velocimeter(LDV) system and the data acquisition. Velocity profiles are obtained using the Rotating Machinery Resolver(RMR)and PHASE software in case of turbulent pulsating flow. Finally, it was plotted by the ORIGIN software. The experiment was conducted in seven sections from the inlet (ø = 0$^{\circ}$) to the outlet (ø=l80$^{\circ}$) at 3 0$^{\circ}$intervals of the duct.

• Journal of Advanced Marine Engineering and Technology
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• 제24권6호
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• pp.15-23
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• 2000

In the present study, flow characteristics of turbulent pulsating flow in the square-sectional $180^{\circ}$curved duct are investigated experimentally. In order to measure axial direction velocity and secondary flow distributions, experimental studies for air flow are conducted in the square-sectional $180^{\circ}$curved duct by using the LDV system with the data acquisition and the processing system of the Rotating Machinery Resolver (RMR) and the PHASE software. The experiment is conducted on seven sections form the inlet($\phi=0^{\circ}$) to the outlet($\phi=180^{\circ}$) at $30^{\circ}$intervals of the duct. The results obtained from the experimentation are summarized as follows : In the axial direction velocity distributions of turbulent pulsating flow, when the ratio of velocity amplitude (A1) is less than one, there is hardly any velocity change in the section except near the wall and in axial velocity distribution along the phase. The secondary flow of turbulent pulsating flow has a positive value at the bend angle of $150^{\circ}$regardless of the ratio of velocity amplitude. The dimensionless value of secondary flow becomes gradually weak and approaches zero in the region of bend angle $180^{\circ}$without regard to the ratio of velocity amplitude.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.765-770
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• 2000

Hot-wire measurements are reported on the developing turbulent flows subject to plane rate of strain in a rotating $90^{\circ}$ dog bend. The cross-section of the bend varies from $100mm{\times}50mm$ rectangular shape at the bend inlet gradually to the $50mm{\times}100mm$ shape at the bend outlet with remaining a constant area. Data signals from the rotating test section are transmitted through a slip ring to the personal computer which is located at the outside of the rotating disc. 3-dimensional velocity and 6 Reynolds stress components were calculated from the equations which correlate the fluctuating and mean voltage values measured with rotating a slant type hot-wire into 6 orientations. The effects of Coriolis and centrifugal forces on the mean motions and turbulence structures are investigated with respect to rotational speed.

• 대한기계학회논문집
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• 제19권9호
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• pp.2223-2236
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• 1995

0The fields of turbomachinery and electrical generators provide many examples of flow through rotating internal passages. At the practicing Reynolds number, most of the flow motion is three dimensional and highly turbulent. The proper understanding for the characteristics of these turbulent flow is necessary for the design of thermo-fluid machinery of a good efficiency. The flow characteristics in the rotating duct with curvature are very complex in practice due to the curvature and rotational effect of the duct. The understanding of the effect of the curvature on the structure and rotational effect of the duct. The understanding of the effect of the curvature on the structure of turbulence in the curved passage and the characteristics of the flow in a rotating radial straight channel have been well studied separately by many workers. But the combined effects of curvature and rotation on the flow have not been well understood inspite of the importance of the phenomena in the practical design process. In this study, the characteristics of a developing turbulent flow in a square sectioned 90.deg. bend rotating at a constant angular velocity are measured by using hot-wire anemometer to seize the rotational effects on the flow characteristics. As the results of this study, centrifugal forces associated with the curvature of the bend and Coriolis forces and centripetal forces associated with the rotational affect directly both the mean motion and the turbulent fluctuations.

• 대한기계학회논문집B
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• 제22권2호
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• pp.139-152
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• 1998

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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.627-632
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• 2000

Developing turbulent flows in a rotating 90 degree bend with square cross-section were measured by a hot-wire anemometer. The six orientation hot-wire technique was applied to measured the distributions of 3 mean velocities and 6 Reynolds stress components. Effects of Coriolis and centrifugal forces caused by the curvature and rotation of bend on the mean motion and turbulence structures were experimentally investigated Productive addition of Coriolis and centrifugal forces to the outward radial direction in the entrance region of bend increases the secondary flow intensity according to the rotational speeds. However, after 45 degree of bend, centrifugal force due to the rotation of bend may promote the break down of counter rotating vortex pair into multi-cellular pattern, thereby decreasing the production rate of turbulence energy and Reynolds stresses.

• 대한기계학회논문집B
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• 제28권4호
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• pp.441-448
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• 2004

A numerical study was conducted to show the effect of aspect ratio on the analogy of the developing laminar flows between in orthogonally rotating straight duct and in a stationary curved duct of rectangular cross-section. In order. to clarify the similarity of two nows, dimensionless parameters (equation omitted) and Rossby Ro= $w_{m}$$\Omega$ $d_{h}$, in a rotating straight duct were used as a set corresponding to Dean number, (equation omitted), and curvature ratio, λ=R/ $d_{h}$, in a stationary curved duct. Four. different aspect ratios A=0.25, 0.5, 2 and 4 were considered. Under the condition that the magnitudes of Ro and λ were large enough to satisfy the 'asymptotic invariance property' and the aspect ratio was larger than 1, there were strong quantitative similarities between the two flows such as flow patterns, friction factors, and maximum axial velocity magnitudes fur the same values of $K_{LR}$ and $K_{LC}$ . On the other hand, as the aspect ratio decreased below 1 (A=0.25 and 0.5), the difference of the secondary flow intensity between these two flows was enhanced and therefore the analogy of two flows was not so evident as that of the larger aspect ratio (A=2 and 4). 4).nd 4).

• 설비공학논문집
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• 제27권7호
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• pp.344-353
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• 2015

In the present study the characteristics of turbulent oscillatory flows in a square-sectional $180^{\circ}$curved duct were investigated experimentally. A series of experiments for air flow were conducted to measure axial velocity profiles, secondary flow velocity profiles and pressure distributions. The measurements were made by a Laser Doppler Velocimeter (LDV) system with a data acquisition and processing system which includes Rotating Machinery Resolve (RMR) and PHASE software. The results from the experiment are summarized as follows. (1) The maximum velocity moved toward the outer wall from the region of a bend angle of $30^{\circ}$. The velocity distribution had a positive value extended over the total phase in the region of a bend angle of $150^{\circ}$. (2) Secondary flows were generally proportional to the velocity of the main flow. The intensity of the secondary flow was about 25% as much as that in the axial direction. (3) Pressure distributions were effects of the oscillatory Dean number and respective region.

• 대한기계학회논문집B
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• 제26권10호
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• pp.1378-1386
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• 2002

In the present study, velocity profile and wall shear stress distributions of developing turbulent oscillatory flows in an oscillator connected to straight duct located in exit region of a curved duct was investigated experimentally. The experimental study for air flows was conducted to measure axial velocity profiles, shear stress distributions by using the Laser Doppler Velocimetry(LDV) system with the data acquisition and processing system of Rotating Machinery Resolver(R.M.R) and PHASE software. The results obtained from experimental studies are summarized as follows. The critical Reynolds number for a change from transitional oscillatory flow to turbulent flow was about 7500, in the 60region of dimensionless axial position which was considered as a fully developed flow region. The turbulent oscillatory flow, velocity profiles of the inflow period in the entrance region were gradually developed, but those of the outflow period were not changed nearly. Velocity profiles of inflow and outflow were shown as a symmetric form in a fully developed flow region. The wall shear stress distributions of turbulent oscillatory flow increase rapidly as the flow proceeds to downstream and flow was in good agreement with the theoretically.