Cylinders

The drag reduction by vortex fusion was investigated. A comparison of flow over a bundle of cylinders in uniform and in disturbed currents was performed in a water channel. The model was subjected to cross flow. A thin cylindrical wire located nearby upstream and leveled at half the height of the test model was used as a source of disturbance. A hydrogen bubble technique was utilized to observe the flow pattern. The accumulation of vortices at stagnating regions in front of a bundle of cylinders transformed into a counter-rotated curl at leading edges of each leading cylinder in the bundle. Measurements were carried out by a computerized data acquisition system. Drag coefficient measurements, digital spectral and fourier analyses were also performed. Results have shown that a drag reduction can be obtained by introducing a thin cylindrical wire in front of the stagnation.

An experimental study of the vortex response to interaction with and cutting by a thin flat
plate or circular cylinders of various diameters has been performed. The direction of
motion of the flat plate (or circular cylinder) is normal to the vortex axis in the experiments.
The vortex is generated by withdraw of fluid at an orifice at the bottom of an "inner
cylinder" immersed in a rectangular tank, and the flow field is visualized with both water
soluble and immiscible dyes. In the experiments with circular cylinders, the bending of
the vortex is compared to computational predictions from [15], and the mechanism of
subsequent breakup of the vortex as it gets closer to the cylinder is studied. The vortex is
observed to bend farther without breakup for larger forward speeds of the circular cylinder.
Very little bending is observed when the vortex interacts with the flat plate, except for
angles of attack exceeding the stall limit Following cutting of the vortex by the flat plate or
circular cylinder, a vortex shock is observed to form and propagate up the vortex axis. No
vortex shock is observed on the opposite side of the blade. The various forms of these
vortex shocks have been photographed, and they appear very similar to travelling vortex
breakdowns. The propagation speed of the shocks is compared to an analytical solution for
instantaneous vortex cutting by a flat plate of zero thickness.

This paper studies the stress concentrations at the root of the threads of a cylinder. A photoelastic analysis using the stress freezing procedure is used to calculate the stress along the cylinder and the stress concentrations at the root of the threads. These values are compared to that of similar cylinders with different threaded configurations. A finite element model is built by using the photoelastic data to find a suitable load distribution along the threaded region. The finite element model predicted results similar to the photoelastic analysis and showed a method of reducing the stress concentrations on the threads by redesigning a pressure ring on the cylinder.