Experimental investigation on turbulent flow in a square-sectioned 90-degree bend

Sudo, Kozo; Sumida, Masaru; Hibara, Hideki

doi:10.1007/s003480000157

Cited by 72 publications

(44 citation statements)

References 4 publications

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“…3͑b͔͒. Similar vertical k profiles have been measured in channel bends and meanders by Tamai and Ikeya, 15 Anwar, 16 Muto, 17 and Sudo et al 18 While in straight uniform flow the ratio ͗k͘ / ͗K͘ would be constant ͑about 0.03͒ in the two-dimensional ͑2D͒ flow zone away from the banks, the opposite patterns of K and k in our experiment result in a pronounced variation of ͗k͘ / ͗K͘ over the cross-section. Towards the centerline, ͗k͘ / ͗K͘ is of the expected order of magnitude, but it then decreases, down to 0.01 in most of the outer bend, only to increase strongly in the region affected by bank friction.…”

Section: -13supporting

confidence: 63%

Turbulence characteristics in sharp open-channel bends

Blanckaert¹,

Vriend

2005

Physics of Fluids

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In spite of its importance, little is known about the turbulence characteristics in open-channel bends. This paper reports on an experimental investigation of turbulence in one cross section of an open-channel bend. Typical flow features are a bicellular pattern of cross-stream circulation ͑secondary flow͒ and a turbulence activity in the outer bend that is significantly less than in the equivalent straight uniform shear flow. Measured distributions are given of the turbulent kinetic energy, its production, the mixing coefficients, some parameters characterizing the turbulence structure, and the fourth-order correlations of the turbulent velocity fluctuations. The transport equation for the turbulent kinetic energy is evaluated term by term, on the basis of the measured data. The results show that the turbulence structure is different from straight uniform flow, in that the Reynolds stress tensor is more diagonally dominant. This is shown to be the main cause of the observed reduction of turbulence activity in the outer bend. The usual two-equation turbulence closure models include a transport equation for the turbulent kinetic energy, but they do not account for this modified turbulence structure. The departures of the measured turbulence structure from its equivalent in straight uniform shear flow are related to a curvature-flux-Richardson number R f which includes the streamline curvature. Such a relation may be useful to improve simple turbulence closure models for curved open-channel flow.

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Section: -13supporting

confidence: 63%

Turbulence characteristics in sharp open-channel bends

Blanckaert¹,

Vriend

2005

Physics of Fluids

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“…It is estimated that this longitudinal vortex is generated by the centrifugal force that arises due to the curvature of the streamlines of the flow entering from the branch. This mechanism of vortex generation is similar to that in a flow through a 90-deg bend (9) . At X/B = 4, the longitudinal vortex disappears because the curvature of the streamline becomes quite small as recognized from Fig.…”

Section: Secondary Flowsupporting

confidence: 55%

Three-Dimensional Structure of Turbulent Flow in Mixing T-junction

Hirota

Asano

Nakayama

et al. 2006

JSME international journal. Ser. B, Fluids and thermal engineer

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Experimental results on the turbulent mixing of hot and cold airflows in a T-junction are reported, which simulates the HVAC unit used in an automobile air conditioning system. Experiments are conducted keeping Reynolds number and temperature of the main flow at 2.5 × 10 4 and 12• C, respectively, and the velocity of the branch flow (60 • C) is changed for three velocity ratios of 0.5, 1 and 2. The flow from the branch is separated at the edge of the T-junction and forms a large separation bubble. Longitudinal vortices are formed around this separation bubble, thus the flow field has a three-dimensional structure. In spite of such a complex flow field, the mean temperature in the thermal mixing layer shows quite uniform distributions in the spanwise direction, and the strong turbulence produced around the separation bubble does not work effectively to the thermal mixing of hot and cold airflows.

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“…Moreover, their results showed the development of the pressure-driven secondary motion in the corner region which eventually leads to the formation of a longitudinal vortex on the convex wall. Sudo et al [9], using the method of an inclined hot-wire obtained mean velocity and Reynolds stress measurements for turbulent air ow through a square-sectioned 90…”

Section: Introduction Developing Turbulent Ow Through 90mentioning

confidence: 99%

Prediction of developing turbulent flow in 90°-curved ducts using linear and non-linear low-Rek–ɛ models

Raisee

Alemi

Iacovides

2006

Int. J. Numer. Meth. Fluids

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SUMMARYThis paper reports the outcome of applying two di erent low-Reynolds-number eddy-viscosity models to resolve the complex three-dimensional motion that arises in turbulent ows in ducts with 90• bends. For the modelling of turbulence, the Launder and Sharma low-Re k-model and a recently produced variant of the cubic non-linear low-Re k-model have been employed. In this paper, developing turbulent ow through two di erent 90• bends is examined: a square bend, and a rectangular bend with an aspect ratio of 6. The numerical results indicate that for the bend of square cross-section the curvature induces a strong secondary ow, while for the rectangular cross-section the secondary motion is conÿned to the corner regions. For both curved ducts, the secondary motion persists downstream of the bend and eventually slowly disappears. For the bend of square cross-section, comparisons indicate that both turbulence models can produce reasonable predictions. For the bend of rectangular cross-section, for which a wider range of data is available, while both turbulence models produce satisfactory predictions of the mean ow ÿeld, the non-linear k-model returns superior predictions of the turbulence ÿeld and also of the pressure and friction coe cients.

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Experimental investigation on turbulent flow in a square-sectioned 90-degree bend

Cited by 72 publications

References 4 publications

Turbulence characteristics in sharp open-channel bends

Turbulence characteristics in sharp open-channel bends

Three-Dimensional Structure of Turbulent Flow in Mixing T-junction

Prediction of developing turbulent flow in 90°-curved ducts using linear and non-linear low-Rek–ɛ models

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