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Numerical calculation of turbulent flow in symmetric two-dimensional diffusers

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Summary

This study presents numerical predictions on the fluid flow characteristics for turbulent flow in symmetric two-dimensional diffusers. The grids are established by employing the nonorthogonal bodyfitted coordinate system and associating them with the multi-block to handle the complex geometry. The turbulent governing equations are solved by the control-volume-based finite-difference method. The parameters studied include the entrance Reynolds numbers of the diffusers (Re=6000, 9000 and 12000), the diffusion angle (θ=22.5°, 30°, 60° and 90°), and the diffusers expansion ratioER=3. The numerical results show that the influence on the size of the recirculation region for turbulent flow was ambiguous with Reynolds numbers effect, but evident with the change of diffusion angles. From the streamline contours, it can be seen that there is a large recirculation region on the top wall, and a small recirculation region is formed at the corner of the bottom wall, but the recirculation region of the bottom wall is ambiguous at θ=22.5°. In addition, with increasing Reynolds numbers of diffusion angle the pressure recovery coefficientC PR decreases.

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Abbreviations

C 1,C 2,C μ :

turbulent constant

C P :

pressure coefficient

C PR :

pressure recovery coefficient

ER :

expansion ratio

f 1,f 2,f μ :

empirical constants for low Reynolds number turbulence model

G :

generation rate of turbulent kinetic energy

H :

height of the diffuser

k :

turbulent kinetic energy

Re:

Reynolds number (U S W 1)/⋎

S ϕ :

source term

U S :

maximum velocity upstream of the diffuser

W 1 :

height of the upstream channel

W 2 :

height of the downstream channel

\(\overline {u'\upsilon '} ,\overline {u'u'} ,\overline {\upsilon '\upsilon '}\) :

Reynolds stress

ξ, η:

axes of nonorthogonal curvilinear coordinate system

ϕ:

transported scalar

ϱ:

density

μ l , μ t :

laminar and turbulent viscosity

⋎:

kinematic viscosity

θ:

diffusion angle

ε:

turbulent energy dissipation rate

σ k , σε :

empirical constants in turbulence model equations

Γφ :

diffusion coefficient

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Author notes

  1. Y. T. Yang & C. F. Hou

    Present address: Department of Mechanical Engineering, National Cheng Kung University, 701, Tainan, Taiwan

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    1. Y. T. Yang
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    2. C. F. Hou
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    Yang, Y.T., Hou, C.F. Numerical calculation of turbulent flow in symmetric two-dimensional diffusers. Acta Mechanica 137, 43–54 (1999). https://doi.org/10.1007/BF01313143

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