Flutter-enhanced mixing in small-scale mixers

Abstract

Enhancement of mixing via flow-induced flutter of a flexible membrane is explored for small-scale mixers that operate at low Reynolds numbers. Flow induced flutter and mixing in a duct flow is simulated using fully coupled fluid-structure-scalar interaction simulations including two-way coupling between the fluid and structure. The fluid and structural dynamics are analyzed and their impact on the mixing performance is characterized. The sensitivity of the system to the Reynolds number and to the membrane’s size and shape are also examined. It is shown that these flutter mixers create complex vortex structures even at low Reynolds numbers and these vortex structures lead to complex stretching and folding of fluid interfaces resulting in rapid mixing.

Bioprosthetic aortic valve diameter and thickness are directly related to leaflet fluttering: Results from a combined experimental and computational modeling study

“…This section develops a simple scaling model that relates the fluttering frequency with the orifice area (characterized by PDVA) and tip displacement. Previous studies of fluttering in other systems have characterized the fluttering frequency by the Strouhal number, defined as St = fL/U , in which f is the fluttering frequency, L is a characteristic length, and U is a characteristic speed 21 - 24 For a given body thickness, the Strouhal number exhibits only relatively small variations over a large range of Reynolds numbers, 23 - 26 including those considered here. We propose a scaling model as a function of valve diameter using this relationship.…”

Unsteady flow regimes in arrow-shaped micro-mixers with different tilting angles

“…4 Many active or passive methods have been proposed to promote mixing. [5][6][7][8][9] The active ones need ultrasounds, electric fields, pressure pulses, and so on as an extra energy input, while the passive ones want to break the symmetry of the flow through a favorable design of the geometry of the mixer without any external energy input.…”

Flow-induced instabilities of springs-mounted plates in viscous flows: A global stability approach

“…Historically, these different types of vibrations were mostly observed on large-scale objects surrounded by high-speed flows -plane wings, helicopter blades, tall buildings, bridges, etc -where they put at risk the integrity of the structure. In the recent years however, several new and smaller-scale applications have been proposed that take advantage of flow-induced vibrations for energy harvesting purposes 9 or for improving the performance of small-scale mixers 10,11 and heat exchangers 12,13 . For these applications, the objective is generally to design the system so as to maximize the vibrations.…”

“…For coupled-mode flutter, a classical choice is to resort to potential flow theories 15,21,22 , such as the Theodorsen model 27 , that have encountered a great success for the computation of aeroelastic stability of aircraft 28 . However, in contrast to aircraft applications that naturally yield high-Reynolds-number flows, energy harvesting or micro-scale mixing typically involve low-to-moderate Reynolds numbers 10,11,18,[21][22][23][24][25][26] , ranging from Re = 10 1 to Re = 10 5 . For these Reynolds numbers, the validity of the potential flow assumption must be questioned, as shown by Bruno and Fransos 29 or Brunton and Rowley 30 for the case of thin plates forced in heaving or pitching motions.…”