Drag coefficient of a sphere in a non-stationary flow: new results

Abstract

The drag coefficient of a sphere placed in a non-stationary flow is studied experimentally over a wide range of Reynolds numbers in subsonic and supersonic flows. Experiments were conducted in a shock tube where the investigated balls were suspended, far from all the tube walls, on a very thin wire taken from a spider web. During each experiment, many shadowgraph photos were taken to enable an accurate construction of the sphere's trajectory. Based on the sphere's trajectory, its drag coefficient was evaluated. It was shown that a large difference exists between the sphere drag coefficient in steady and non-steady flows. In the investigated range of Reynolds numbers, the difference exceeds 50%. Based on the obtained results, a correlation for the non-stationary drag coefficient of a sphere is given. This correlation can be used safely in simulating two-phase flows composed of small spherical particles immersed in a gaseous medium.

Visualization of water droplet deformation and breakup in a continuously accelerating flow field

“…The problem is a non-stationary problem and transient effects need to be considered. Accelerating and decelerated non-uniform flow fields have only been studied for non-deformable spheres [9,10], or droplets that are small enough to neglect deformation [11] and it has proved to be a very complex problem since there still exist contratdicting results. Therefore, one of the novelties of this work is to study the aerobreakup of droplets in a non-stationary flow.…”

Theoretical model for droplet deformation and trajectory in continously accelerating flows

“…Because of their relevance for the present work, it is important to discuss in some detail the studies presented by Temkin and Metha (1982), Takayama (1993), andJourdan et al (2007). The article by Temkin and Metha (1982) presents an experimental study on the motion of water droplets inside accelerating and decelerating flows.…”

“…Although many theoretical and experimental studies (based, mostly, on shock tube type facilities) have been carried out in conditions of constant, or nearly constant, flow velocity, certain applications of engineering interest are characterized by either accelerating or decelerating flow profiles. In this specific area, relevant references are the works of Temkin and Metha (1982), Igra and Takayama (1993) and Jourdan et al (2007).…”

“…In their conclusions, the authors reported unsteady drag values about 50 % larger than the corresponding steady values in these shock tube conditions. More recently, Jourdan et al (2007) have presented another quite comprehensive experimental study based, also, on a shock tube type test rig. They also used non deformable spheres (made of either polystyrene or nylon) with diameters ranging from 500 m to 6.6 mm.…”

Water droplet deformation and breakup in the vicinity of the leading edge of an incoming airfoil

“…Another quite comprehensive article regarding non-stationary flows was the one of Jourdan et al in 2007 [46], where an experimental study on the drag coefficient of spheres in a multi-phase variable inclination shock tube was conducted. They used spheres of diameter between 0.29 mm and 6.5 mm made of polystyrene, polymer ATE-CA, polypropylene and nylon.…”