摘要 :
Based on a quantitative analogy between developing laminar flows in curved pipes and orthogonally rotating straight pipes, a corresponding analogy of forced convective heat transfer in the entry regions of the pipes is described t...
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Based on a quantitative analogy between developing laminar flows in curved pipes and orthogonally rotating straight pipes, a corresponding analogy of forced convective heat transfer in the entry regions of the pipes is described through similarity arguments and computational studies. Three-dimensional developments of these flows are characterized by secondary flows due to the centrifugal or the Coriolis forces. Similarity considerations taking the secondary flow into account suggest a remarkable Effect of the Prandtl number or the heat transfer structure, which is demonstrated by The computational results. When the curvature parameter large, it is shown that the Development of the temperature fields and the Nusselt numbers of the two flows are Similar when the governing parameters and the Prandtl numbers of he two flows are Equal.
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Buoyancy-induced secondary flows in a heated pipe rotating about a parallel axis are similar to those in a stationary horizontal heated pipe. The effect of buoyancy on fully developed laminar flows and heat transfer in rotating pi...
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Buoyancy-induced secondary flows in a heated pipe rotating about a parallel axis are similar to those in a stationary horizontal heated pipe. The effect of buoyancy on fully developed laminar flows and heat transfer in rotating pipes and in horizontal pipes in studied by similarity analysis and computations. The similarity analysis reveals that the flows are characterized by a new fundamental parameter, K_LB, and the Prandtl number, P_r; K_LB plays a role of Peclet number in the cross-section and P_r determines the sensitivity of the axial primary flow to secondary flow.
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The mechanism of three-dimensional rotational flow in a curved duct caused by distorted inflow is investigated numerically. The steady, laminar flow of viscous, incompressible fluid in a 90-deg. curved duct with a square cross sec...
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The mechanism of three-dimensional rotational flow in a curved duct caused by distorted inflow is investigated numerically. The steady, laminar flow of viscous, incompressible fluid in a 90-deg. curved duct with a square cross section is simulated by the pseudo-compressibility method. A uniform velocity gradient is assumed at the entrance of the computational domain.
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Fully developed laminar flow in a curved square duct rotating about a center of curvature is investigated by similarity arguments, computational studies and use of experimental data. Similarity arguments suggest that the flow char...
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Fully developed laminar flow in a curved square duct rotating about a center of curvature is investigated by similarity arguments, computational studies and use of experimental data. Similarity arguments suggest that the flow characteristic are governed by four parameters: the Dean number K_LC, the body force ratio F, the curvature parameter λ and the Rossby number Ro. By using the computed flow patterns, the flow structure is elucidated for a wide range of these parameters.
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A visualization study has been made to investigate the secondary flow induced in an oscillatory laminar flow in the entrance region of a curved pipe with a curvature ratio of 9.8. The experiments were performed under the condition...
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A visualization study has been made to investigate the secondary flow induced in an oscillatory laminar flow in the entrance region of a curved pipe with a curvature ratio of 9.8. The experiments were performed under the condition of a moderate Womersley number a=10, which is a physiologically interesting nondimensional frequency, and a Dean number D=300. The secondary flow motion was rendered visible by means of a tracer method using nylon particles, and photographs were taken at four phases in one cycle and at axial locations from the upper stream tangent to the downstream in the curved pipe.
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The fluid flowing in rotating heated curved pipes is subjected to three body forces: centrifugal, Coriolis and buoyant forces. Fully developed laminar flow in rotating coiled pipes is investigated through similarity arguments and ...
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The fluid flowing in rotating heated curved pipes is subjected to three body forces: centrifugal, Coriolis and buoyant forces. Fully developed laminar flow in rotating coiled pipes is investigated through similarity arguments and computational studies. The thermal boundary conditions at the wall are uniform wall heat flux axially and uniform wall temperature peripherally. Flow and heat transfer characteristics are elucidated for the case when they are governed by four parameters: Dean number, Prandtl number, body force ratio and buoyancy parameter. Detailed structures of Velocity and temperature fields are shown for wide range of these parameters.
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Linear stability of wall-bounded shear layers modified by distributed suction has been considered. Wall suction was introduced in order to simulate distributed surface roughness. In all cases studied, i.e. Poiseuille and Couette f...
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Linear stability of wall-bounded shear layers modified by distributed suction has been considered. Wall suction was introduced in order to simulate distributed surface roughness. In all cases studied, i.e. Poiseuille and Couette flows and Blasius boundary layer, wall suction was able to induce a new type of instability characterized by the appearance of streamwise vortices. Results of calculations show that a linear model of suction-induced flow modifications provides a sufficiently accurate representation of the basic state. The effects of an arbitrary suction distribution can, therefore, be assessed by decomposing this distribution into Fourier series and carrying out stability analysis on a mode-by-mode basis, i.e. once and for ever. [References: 25]
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A Numerical analysis has been carried out of developing turbulent flow in S-shaped duct with a square cross section at a Reynolds number of 4 x 10~4. The S-duct was formed from two 22.5 degree bends with 40mm hydraulic diameter an...
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A Numerical analysis has been carried out of developing turbulent flow in S-shaped duct with a square cross section at a Reynolds number of 4 x 10~4. The S-duct was formed from two 22.5 degree bends with 40mm hydraulic diameter and 280mm mean radius of curvature. Straight ducts with hydraulic diameters of 7.5 and 50 are attached to the inlet and outlet planes of the S-duct, respective- ly. In calculation, an algebraic Reynolds stress model was adopted in order to predict anisotropic turbulence precisely, and boundary-fitted corrdinate system was introduced as the method of coordi- nate transformation.
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Pulsating flow through bifurcations are of general interest. In the human body such flows are also very common; for example in blood vessels and the respiratory tract. The characteristics of the flow in arteries have been related ...
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Pulsating flow through bifurcations are of general interest. In the human body such flows are also very common; for example in blood vessels and the respiratory tract. The characteristics of the flow in arteries have been related to the process of atherogenesis, based on the observation that the initial manifestation of the process is observed at certain common locations, i.e., near bifurcations in vessels of certain size. In-spite of these observations there is no direct understanding between the flow itself and the pathological process. In fact, the flow itself is rather complex since it is unsteady and transitional. The paper considers both unsteady- and steady-flow through a three generation system of (non-symmetric) bifurcations. The geometry consists of a 90°. bifurcation followed by two sets of consecutive symmetric bifurcations. The aim of the paper is to investigate the effects of the bifurcations on the flow and mass transport in such a geometrical configuration that is often found in physiological situations. Additionally, the effects of different inlet velocity conditions have been considered. The different inlet conditions are aimed at studying the sensitivity to variations of inflow conditions; variations found under normal physiological conditions. The results show that the geometrical asymmetry affects the velocity distribution even after a second bifurcation downstream. Two generations down this asymmetry does not have a significant effect anymore. The different inlet conditions affect the flow to the next generation of branches during parts of the cycle. At peak flow and further downstream in the system the effects are negligible. It is also found that over a cycle the mass flow distribution through the outlets can be affected by the inlet velocity conditions. The distribution of a passive scalar is not uniform but depends on the inlet conditions and the Schmidt number (i.e., molecular diffusion).
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An in-house fully three-dimensional general-purpose finite element model is applied to solve the hydrodynamic structure in a periodic Kinoshita-generated meandering channel. The numerical model solves the incompressible Reynolds-a...
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An in-house fully three-dimensional general-purpose finite element model is applied to solve the hydrodynamic structure in a periodic Kinoshita-generated meandering channel. The numerical model solves the incompressible Reynolds-averaged Navier-Stokes equations for mass and momentum, while solving the k-ε equations for turbulence. The free surface is described by the rigid-lid approximation (using measured water surface data) for flat (smooth-bed) and self-formed (rough-bed) conditions. The model results are compared against experimental measurements in the 'Kinoshita channel', where three-dimensional flow velocities and turbulence parameters were measured. This validation was carried out for the upstream-valley meander bend orientation under smooth (flat bed) conditions. After validation, several simulations were carried out to predict the hydrodynamics in conditions where either it was not possible to perform measurements (e.g. applicability of the laboratory acoustic instruments) and to extrapolate the model to other planform configurations. For the flat smooth-bed case, a symmetric (no skewness) planform configuration was modeled and compared to the upstream-skewed case. For the self-formed rough-bed case, prediction of the hydrodynamics during the progression of bedforms was performed. It appears that the presence of bedforms on a bend has the following effects: (i) the natural secondary flow of the bend is disrupted by the presence of the bedforms, thus depending on the location of the dune, secondary flows might differ completely from the traditional orientation; (ii) an increment on both the bed and bank shear stresses is induced, having as much as 50% more fluvial erosion, and thus a potential increment on the migration rate of the bend. Implications on sediment transport and bend morphodynamics are also discussed in the paper.
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