Enhancement of temperature drop behind cylinders by acoustic synchronization

Although the temperature drop behind a cylinder immersed in a flow was discovered in the late 1930s, the exact mechanism of the cooling has remained unresolved. While the shedding of the Kármán vortex street has long been thought to be the cause, this has never been proven conclusively.

Acoustic synchronization—resonance between the cylinder vortex shedding and the normal wind tunnel acoustic modes (the resonance unrelated to structural vibration of the cylinder)—is used as a noninvasive means of intensifying the vortex street and, therefore, the associated temperature drop. Proper design of the physical dimensions of the test apparatus allows this to take place at the low Mach number of 0.21.

At the three lowest resonances, the measured spanwise response of the temperature and pressure at the rear of the cylinder agrees well with the theoretical expectations. The Kármán vortex street is concluded to be indeed the cause of the temperature drop.

Although this investigation is confined to a circular cylinder, the results are expected to be applicable to other bluff bodies since the characteristics of the Kármán vortex street for any body shape are similar.