A nonlinear streamwise traveling-wave solution is obtained by homotopy for square duct flow. For a particular symmetry of the perturbations, this wave comes into existence at about Re(b)=600 (based on half-duct width and bulk speed) for a streamwise wave number alpha=0.85 . The resulting four-vortex mean flow resembles the transitional flow structures observed in previous simulations.

Flow visualization techniques using tracer markers such as die, smoke, hydrogen bubbles, etc., have been widely used in experimental investigations of large scale structures of a variety of flow fields. They have played an important role in understanding the physics of the coherent structures' formation and evolution in the transitional as well as the turbulent regions of the flow fields. Howev...

Transitions are the glue that holds a paper together. These cohesive allies are needed when a paper “does not flow,” is “choppy,” or seems unrelated to the thesis of their parent essay. Transitions can be simple, such as the following: moreover, therefore, nevertheless, despite, consequently, instead, also. However (that’s another transition), it is better to use transitional phrases, rather th...

Laminar and turbulent natural convection inside concentric spherical shells with isothermal cold and hot boundaries is numerically investigated up to Rayleigh number values Ra 6 10 and Pr = 0.71. The study utilizes direct numerical simulation (DNS), large eddy simulation (LES) and Reynolds averaged Navier– Stokes (RANS) approaches for investigation of the laminar, transitional and fully develop...

This paper presents direct comparisons of related visualization and hot film measurement studies of the nonlinear, late stages of transition in a boundary layer. The preceding nonlinear stages of the transition process are well documented in previous studies. Both the visualizations and measurements were performed with controlled disturbance conditions excited by an instability wave in a flat-p...

Horizontal-tube, falling-film heat exchangers are used in many air-conditioning and refrigeration systems. Depending on the geometry, flow rate and fluid properties, when a liquid film falls over a series of horizontal tubes several distinct flow patterns can be manifested: the droplet mode, the jet mode, and the sheet mode. A thermodynamic analysis is undertaken to predict the transitions betw...

Laser-Doppler velocity measurements adjacent to the bounding walls of three-dimensional (3-D) backward-facing step flow are performed for the purpose of mapping the boundaries of the reverse flow regions that develop in this geometry (adjacent to the sidewalls, the flat wall and the stepped wall) as a function of the Reynolds number. The backward-facing step geometry is configured by a step hei...

This work addresses the simulation of transitional flow over airfoils under low Reynolds number conditions (Rec ≤ 60000). The flow solutions are obtained by means of an Implicit Large Eddy Simulation (ILES) using a newly developed unstructured, parallel solver that employs the high-order spectral difference (SD) method for spatial discretization. The calculations are performed on the SD7003 air...

In this paper, we propose a theoretical model to simulate microbial growth on contaminated air filters and entrainment of bioaerosols from the filters to an indoor environment. Air filter filtration and antimicrobial efficiencies, and effects of dust particles on these efficiencies, were evaluated. The number of bioaerosols downstream of the filter could be characterized according to three phas...