A Conditional-Sampling Study Of The Interaction Of Two Turbulent Wakes

Abstract

Measurements were taken of a developing complex turbulent flow formed by the merging of two far turbulent wakes of equal cylinders. The lower wake only was slightly heated, permitting the use of the conditional-sampling technique to study the interaction of the two wakes in detail. A special four-wire probe (Fabris 1978) enabled simulataneous uncontaminated measurement of all three instantaneous velocity components and temperature. The single-wake data of Fabris (1979) served as a reference. The interaction of the two single turbulent wakes resulted in a striking enhancement of the lateral transfer of heat. Undulations of the thermal interface are significantly wider laterally, but shorter streamwise than in the basic single wake. Lateral velocities of the heated and the unheated intermittent lumps are amplified two- to threefold by the interaction process. Levels of all three components of the kinetic energy of turbulence reach their highest relative maxima in the heated zones as they cross the upper cold wake. These maxima are higher than appropriate conventional or conditional maxima in the single wake. In addition to physical insights into the phenomena of turbulent flow, the data should be useful in refining and validating predictive methods, possibly spurring their further development.