Wake phenomena behind solid and liquid particles

While detailed information is available about the nature and the phenomenology of the wake, there is a distinct lack of useful and quantitative information about the size of the wake behind individual fluid particles and those in a swarm. Many studies have been performed on the wake behind individual particles, yet the results are not only fragmentary, i.e., of little relevance for the operating regime of bubble columns, but also beset with surprisingly large discrepancies. These considerable differences are of a systematic nature and due, in part, to insufficient elimination of surfactant effects, in part, to different boundary effects of the experimental equipment, and, in part, to differing techniques of measurements. Experimental results for the wake in swarms of droplets and bubbles in the relevant regimes of operation are still completely lacking.