Disks wakes

Fig. 6.2 Wake lengths for spheroids and disks. Numerical predictions for spheroids (M4, P5) flow visualization for disks (K2).

The calculated impedance I/Q is represented in Fig. 5-3. The curves in solid line correspond to the behaviour previously calculated for the rotating disk electrode (see Section 3.1) and in reference [57], for the isolated microelectrode. The different curves in dots and dashes were obtained for the microelectrode in the wake of the large electrode. The first two curves (solid line) show only a monotonic decrease with increasing frequency. The controlled microelectrode curves display, at variance, nonmonotonic evolutions with two characteristic frequency domains ... 

Air from the compressor enters the mixing chamber of the atomizer at sonic velocity and, after interaction with the liquid kerosene stream, emerges as a two-phase mixture, directed vertically upwards. The air flow from the annular stream forms a recirculation zone in the wake of the stabilizer disk. The flame is ignited by an external gas stream and subsequently bums independently as a flame in the open atmosphere. Droplets are initially confined to the air jet from the atomizer nozzle, but some of the finer droplets are taken up by the reverse flow of the stabilizer disk recirculation zone. Previous studies on spray combustion and details of atomizer design are reviewed by Chigier (J). 

Reverse flow measurements in the wake of a stabilizer disk show increases in size and magnitude of the maximum reverse flow velocities within the recirculation zone as a result of combustion. Evidence was found of initial pilot burning in the recirculation zone from combustion of flne droplets transported by the reverse flow. 

The curve of Cj, versus for an infinitely long cylinder normal to the flow is much like that for a sphere, but at low Reynolds numbers, does not vary inversely with because of the two-dimensional character of the flow around the cylinder. For short cylinders, such as catalyst pellets, the drag coefficient falls between the values for spheres and long cylinders and varies inversely with the Reynolds number at very low Reynolds numbers. Disks do not show the drop in drag coefficient at a critical Reynolds number, because once the separation occurs at the edge of the disk, the separated stream does not return to the back of the disk and the wake does not shrink when the boundary layer becomes turbulent. Bodies that show this type of behavior are called bluff bodies. For a disk the drag coefficient Cj, is approximately unity at Reynolds numbers above 2000. 

Carmody, T. (1964). Establishment of the wake behind a disk. Journal of Basic Engineering ASME 86(4) 869-882. 

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