Use of natural instabilities for generation of streamwise vortices in a laminar channel flow

Moradi, Hadi; Budiman, Alexander Christantho; Floryan, J. M.

doi:10.1007/s00162-016-0418-5

Cited by 8 publications

(1 citation statement)

References 35 publications

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“…A fluid flow instability mechanism in the form of counter-rotating streamwise vortices has been known for its potential to improve the overall heat and mass transfer in the industrial applications (Chamoli et al, 2017;Cheng et al, 2020;Girgis and Liu, 2002;Moradi et al, 2017). Naturally developed counter-rotating vortices could be found in various conditions, such as Görtler vortices due to the curvature of the concave surface, Dean vortices in fully developed flow in curved pipes and curved rectangular cross-section ducts, as well as in flow between concentric cylinders and rough surfaces.…”

Section: Introductionmentioning

confidence: 99%

Visualization of Induced Counter-Rotating Vortices for Electric Vehicles Battery Module Thermal Management

Budiman¹,

Hasheminejad²,

Sudirja³

et al. 2022

Front. Heat Mass Transf.

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Streamwise development of counter-rotating vortices induced by three different types of chevron Vortex Generators (VGs) placed upstream an Electric Vehicles (EV) dummy battery module is experimentally visualized using a smoke-wire method. From the single chevron reference case, the mushroom-like vortices do not collapse until passing the module. When more chevrons are used in line, the vortices become more prominent. It can also be observed that the vortex sizes and shapes are significantly influenced by the spanwise base length of the chevron. The induced vortices from all three VGs suggest a potential heat transfer augmentation for the EV battery module application.

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Section: Introductionmentioning

confidence: 99%

Visualization of Induced Counter-Rotating Vortices for Electric Vehicles Battery Module Thermal Management

Budiman¹,

Hasheminejad²,

Sudirja³

et al. 2022

Front. Heat Mass Transf.

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Reduction of pressure losses and increase of mixing in laminar flows through channels with long-wavelength vibrations

Floryan

Zandi

2019

J. Fluid Mech.

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Pressure losses and mixing in vibrating channels were analysed. The vibrations in the form of long-wavelength travelling waves were considered. Significant reduction of pressure losses can be achieved using sufficiently fast waves propagating downstream, while significant increase of such losses is generated by waves propagating upstream. The mechanisms responsible for pressure losses were identified and discussed. The interaction of the pressure field with the waves can create a force which assists the fluid movement. A similar force can be created by friction, but only under conditions leading to flow separation. An analysis of particle trajectories was carried out to determine the effect of vibrations on mixing. A significant transverse particle movement takes place, including particle trajectories with back loops. The downstream-propagating out-of-the phase waves provide a large reduction of pressure gradient and significant potential for mixing intensification. Analysis of energy requirements demonstrates that it is possible to identify waves which reduce power requirements, i.e. the cost of actuation is smaller than the energy savings associated with the reduction of pressure gradient. The fast forward moving waves provide an opportunity for the development of alternative propulsion methods which can be more efficient than methods based on the pressure difference.

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Drag reduction and instabilities of flows in longitudinally grooved annuli

Moradi

Floryan

2019

J. Fluid Mech.

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The primary and secondary laminar flows in annuli with longitudinal grooves and driven by pressure gradients have been analysed. There exist geometric configurations reducing pressure losses in primary flows in spite of an increase of the wall wetted area. The parameter ranges when such flows exist have been determined using linear stability theory. Two types of secondary flows have been identified. The first type has the form of the classical travelling waves driven by shear and modified by the grooves. The axisymmetric waves dominate for sufficiently large radii of the annuli while different spiral waves dominate for small radii. The secondary flow topology is unique in the former case and has the form of axisymmetric rings propagating in the axial direction. Topologies in the latter case are not unique, as spiral waves with left and right twists can emerge under the same conditions, resulting in flow structures varying from spatial rings to rhombic forms. The most intense motion of this type occurs near the walls. The second type of secondary flow has the form of travelling waves driven by inertial effects with characteristics very distinct from the shear waves. Its critical Reynolds number increases proportionally to $S^{-2}$, where $S$ denotes the groove amplitude, while the amplification rates increase proportionally to $S^{2}$. These waves exist only if $S$ is above a well-defined minimum and their axisymmetric forms dominate, with the most intense motion occurring near the annulus mid-section. Geometries that give preference to the latter waves have been identified. It is shown that the drag-reducing topographies stabilize the classical travelling waves; these waves are driven by viscous shear, so reduction of this shear decreases their amplification. The same topographies destabilize the new waves; these waves are driven by an inviscid mechanism associated with the formation of circumferential inflection points, and an increase of the groove amplitude increases their amplification. The flow conditions when the presence of grooves can be ignored, i.e. the annuli can be treated as being hydraulically smooth, have been determined.

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Use of natural instabilities for generation of streamwise vortices in a laminar channel flow

Cited by 8 publications

References 35 publications

Visualization of Induced Counter-Rotating Vortices for Electric Vehicles Battery Module Thermal Management

Visualization of Induced Counter-Rotating Vortices for Electric Vehicles Battery Module Thermal Management

Reduction of pressure losses and increase of mixing in laminar flows through channels with long-wavelength vibrations

Drag reduction and instabilities of flows in longitudinally grooved annuli

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