• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.9
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• pp.2206-2222
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• 1995

In this study, the characteristics of the three-dimensional turbulence flow in a rotating square sectioned 90.deg. bend were investigated by numerical simulation. And a dimensionless number, Coriolis force ratio, primarily subjected to the feature of the flow in the rotating 90.deg. bend was obtained as a result of one-dimensional theory. In the simulation study, low Reynolds number ASM developed by Kim(1991) in the square sectioned 180.deg. bend flow was modified in order to consider the rotational effects in the testing flows. In the near wall region of low Reynolds number, four turbulence models were employed and compared in order to find the most appropriate model for the analysis of the rotating 90.deg. bend flow. By comparison of the results with the experimental data, it is shown that low Reynolds number Algebraic Stress Model with rotating terms reflects most correctly the rotational effects. As the results of this study, centrifugal forces associated with the curvature of the bend and Coriolis forces and centripetal forces associated with the rotation affect directly both the mean motion and the turbulent fluctuations. Their actions on the mean flow are to induce a secondary motion while their effects on turbulence are to modify the pressure strain.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.9
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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.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2000.05a
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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.

• Journal of Biomedical Engineering Research
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• v.17 no.4
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• pp.515-524
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• 1996

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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.2
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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.