Vortex Detachment Research Articles

A comprehensive experimental investigation of tubular entry flow of viscoelastic fluids: Part I. Vortex characteristics in stable flow

AbstractThe characteristics of a vortex found at the entry of a 2:1 and 4:1 contraction for viscoelastic fluids is investigated. Two distinct flow regimes are identified in the contraction flow field: a vortex growth regime and a divergent flow regime. In the vortex flow regime, rheological forces are found to dominate the flow, with the vortex detachment length being a linear function of the Weissenberg number. In the divergent flow regime, the flow is found to diverge at the center line upstream of the vortex detachment plane, and the vortex size decreases with increasing flow rates. Inertial forces are important in the divergent flow regime. The entry flow characteristics for the 2:1 and 4:1 contraction are quantified in terms of the vortex detachment length as a function of Reynolds and Weissenberg number over the range of 0:2 < N′Re < 200 and 0.10 < NWS < 0.7.

Periodic Discontinuities in the Acceleration of Spheres in Free Flight

The trajectories of unrestrained spheres being accelerated from rest behind a normal shock wave in a shock tube have been recorded by high-speed stroboscopic photography, and precise measurements of the particle positions made with an optical comparator. Data of sufficient precision were obtained to permit the accurate determination of the second time derivative of the particle trajectories. The experiments were conducted in air with plastic spheres ranging in diameter from 0.7 to 2.4 mm and with specific gravities from 0.7 to 1.5. Particle Reynolds numbers from 1 × 104 to 5 × 104 were obtained, and absolute particle accelerations from 1 × 106 to 5 × 106 ± 0.16 × 106 cm/s2 were measured. The relative velocities were all subsonic; relative Mach numbers ranged from 0.3 to 0.6. The values of the particle acceleration, when plotted as a function of time, were found to contain periodic abrupt changes similar to a mathematical discontinuity. It is postulated that the associated abrupt changes in the forces exerted on the particles are caused by periodic detachment of low-pressure centers of vorticity which form behind the spheres. Values of the drag coefficients determined from the data similarly exhibit periodic abrupt changes. These changes appear, in the way they consistently increase during each cycle of the period and fall at the point of “discontinuity,” to be compatible with the postulate that the periodic behavior is caused by formation and abrupt detachment of low-pressure vortices in the wake. Values of the drag coefficients were found to vary from 10 percent to 30 percent above steady-state values at comparable Reynolds numbers—the range of the computed values of the drag coefficient being caused by the periodic nature of the quantity.

On a rotational flow disturbed by gravity

We examine a rapidly rotating flow that exhibits periodic vortex detachment. Specifically, the rotation/symmetry axis of a fluid-filled cylinder is set perpendicular to gravity. A free buoyant cylindrical float placed within the container is acted upon by both centrifugal and gravitational forces, the competition of which causes fluid motion and, in certain parameter ranges, flow instability. The motion is determined, a criterion for separation is advanced, preliminary experiments and data are described and the relationship of this phenomenon to other examples of vortex shedding in rotating fluids is discussed.

Vortex trails behind a cylinder in ox blood1

It has long been known that a cylindrical obstacle placed in a moving fluid generates a vortex trail. The frequency of vortex detachment is related to the non-dimensional Strouhal number, S . For Newtonian fluids S = 0.14 at Reynolds number R = 60 an