Effect of turbulence-driven secondary flow on particle preferential concentration and clustering in turbulent square duct flows

We have performed direct numerical simulations of turbulent flows in a square duct considering a range of Reynolds numbers spanning from a marginal state up to fully developed turbulent states at low Reynolds numbers. The main motivation stems from the relatively poor knowledge about the basic physical mechanisms that are responsible for one of the most outstanding features of this class of turbulent flows: Prandtl's secondary motion of the second kind. In particular, the focus is upon the role of flow structures in its generation and characterization when increasing the Reynolds number. We present a two-fold scenario. On the one hand, buffer layer structures determine the distribution of mean streamwise vorticity. On the other hand, the shape and the quantitative character of the mean secondary flow, defined through the mean cross-stream function, are influenced by motions taking place at larger scales. It is shown that high velocity streaks are preferentially located in the corner region (e.g. less than 50 wall units apart from a sidewall), flanked by low velocity ones. These locations are determined by the positioning of quasi-streamwise vortices with a preferential sign of rotation in agreement with the above described velocity streaks' positions. This preferential arrangement of the classical buffer layer structures determines the pattern of the mean streamwise vorticity that approaches the corners with increasing Reynolds number. On the other hand, the centre of the mean secondary flow, defined as the position of the extrema of the mean cross-stream function (computed using the mean streamwise vorticity), remains at a constant location departing from the mean streamwise vorticity field for larger Reynolds numbers, i.e. it scales in outer units. This paper also presents a detailed validation of the numerical technique including a comparison of the numerical results with data obtained from a companion experiment.

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Computation of turbulent flow in a square duct: aspects of the secondary flow and its origin

Computers & Fluids ◽

10.1016/0045-7930(94)90033-7 ◽

1994 ◽

Vol 23 (1) ◽

pp. 157-176 ◽

Cited By ~ 3

Author(s):

F.M. Wang ◽

Y.T. Chew ◽

B.C. Khoo ◽

K.S. Yeo

Keyword(s):

Turbulent Flow ◽

Secondary Flow ◽

Square Duct

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514 Turbulence Structures and Secondary Flow in a Square Duct

The Proceedings of Conference of Kansai Branch ◽

10.1299/jsmekansai.2008.83._5-21_ ◽

2008 ◽

Vol 2008.83 (0) ◽

pp. _5-21_

Author(s):

Genta KAWAHARA ◽

Atsushi SEKIMOTO ◽

Markus UHLMANN ◽

Alfredo PINELLI

Keyword(s):

Secondary Flow ◽

Square Duct ◽

Turbulence Structures

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The Torsion Effect on Fully Developed Laminar Flow in Helical Square Ducts

Journal of Fluids Engineering ◽

10.1115/1.2910138 ◽

1993 ◽

Vol 115 (2) ◽

pp. 292-301 ◽

Cited By ~ 8

Author(s):

Wen-Hwa Chen ◽

Ray Jan

Keyword(s):

Laminar Flow ◽

Secondary Flow ◽

Friction Factor ◽

Stokes Equations ◽

Axial Flow ◽

Outer Wall ◽

Square Duct ◽

Torsion Effect ◽

Inclined Angle ◽

Curvature And Torsion

The continuity equation and Navier-Stokes equations derived from a non-orthogonal helical coordinate system are solved by the Galerkin finite-element method in an attempt to study the torsion effect on the fully developed laminar flow in the helical square duct. Since high-order terms of curvature and torsion are considered, the approach is also applicable to the problems with finite curvature and torsion. The interaction effects of curvature, torsion, and the inclined angle of the cross section on the secondary flow, axial velocity, and friction factor in the helical square duct are presented. The results show that the torsion has more pronounced effect on the secondary flow rather than the axial flow. In addition, unlike the flow in the toroidal square duct, Dean’s instability of the secondary flow, which occurs near the outer wall in the helical square duct, can be avoided due to the effects of torsion and/or inclined angle. In such cases, a decrease of the friction factor is observed. However, as the pressure gradient decreases to a small value, the friction factor for the toroidal square duct is also applicable to the helical square duct.

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Pressure and Flow Characteristics in a Rotating Two-Pass Square Duct With 45° Angled Ribs

Volume 5: Turbo Expo 2003, Parts A and B ◽

10.1115/gt2003-38346 ◽

2003 ◽

Cited By ~ 3

Author(s):

Tong-Miin Liou ◽

Guang-Yuan Dai

Keyword(s):

Secondary Flow ◽

Pressure Coefficient ◽

Flow Characteristics ◽

Operating Conditions ◽

Laser Doppler Velocimeter ◽

Main Stream ◽

Height Ratio ◽

Mean Velocity ◽

Square Duct ◽

Pressure Transducers

Measurements are presented of the local velocity and wall static-pressure distributions by using laser-Doppler velocimeter and pressure transducers, respectively, in a rotating two-pass square duct with ribs placed on the leading and trailing walls at an angle of 45° to the main stream. The ribs were square in cross-section and in a parallel mode of arrangement. The rib-height/duct-height ratio and the pitch/rib-height ratio were 0.136 and 10, respectively. The duct Reynolds number was 1×104 and rotation number Ro ranged from 0 to 0.2. Results are addressed in terms of the evolutions of both main flow and cross-stream secondary flow and the distributions of the pressure coefficient, which are lacking in the published literature for ducts ribbed with 45° ribs and under rotation. In addition, the relationships between the regional averaged Nusselt number, transverse and convective mean velocity component, and turbulent kinetic energy are documented. The 45° ribs are found to reduce the pressure loss to 60% of the 90° ribs for rotating duct under same operating conditions. For CFD reference, the fully developed flow condition is absent for the rotating ducts investigated. The measured evolution of complex secondary flow vortices is believed to be a challenge to numerical simulations.

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Effects of Rotation on Transient Fluid Flow and Heat Transfer Through a Curved Square Duct: The Case of Negative Rotation

International Journal of Applied Mechanics and Engineering ◽

10.2478/ijame-2021-0048 ◽

2021 ◽

Vol 26 (4) ◽

pp. 29-50

Author(s):

Mohammad Sanjeed Hasan ◽

Md. Tusher Mollah ◽

Dipankar Kumar ◽

Rabindra Nath Mondal ◽

Giulio Lorenzini

Keyword(s):

Heat Transfer ◽

Fluid Flow ◽

Secondary Flow ◽

Flow Behavior ◽

Square Duct ◽

Curvature Effects ◽

Flow And Heat Transfer ◽

Curved Duct ◽

Wide Range ◽

Mechanical Devices

Abstract The fluid flow and heat transfer through a rotating curved duct has received much attention in recent years because of vast applications in mechanical devices. It is noticed that there occur two different types of rotations in a rotating curved duct such as positive and negative rotation. The positive rotation through the curved duct is widely investigated while the investigation on the negative rotation is rarely available. The paper investigates the influence of negative rotation for a wide range of Taylor number (−10 ≤ Tr ≤ −2500) when the duct itself rotates about the center of curvature. Due to the rotation, three types of forces including Coriolis, centrifugal, and buoyancy forces are generated. The study focuses and explains the combined effect of these forces on the fluid flow in details. First, the linear stability of the steady solution is performed. An unsteady solution is then obtained by time-evolution calculation and flow transition is determined by calculating phase space and power spectrum. When Tr is raised in the negative direction, the flow behavior shows different flow instabilities including steady-state, periodic, multi-periodic, and chaotic oscillations. Furthermore, the pattern variations of axial and secondary flow velocity and isotherms are obtained, and it is found that there is a strong interaction between the flow velocities and the isotherms. Then temperature gradients are calculated which show that the fluid mixing and the acts of secondary flow have a strong influence on heat transfer in the fluid. Diagrams of unsteady flow and vortex structure are further sketched and precisely elucidate the curvature effects on unsteady fluid flow. Finally, a comparison between the numerical and experimental data is discussed which demonstrates that both data coincide with each other.

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