Study of gas-saturated turbulent streams using a laser doppler velocity meter

Microbubble skin friction reduction on an axisymmetric body

“…Based on simple extrapolation of the flat plate studies [1][2][3][4][5][6][7], the observation of larger drag reduction at the higher tunnel speeds is an unexpected result. The differing results are apparently due to the differing influence of buoyancy in each geometry.…”

“…(This, of course, presupposes that the bubble concentration profiles can be made to peak in the near wall region and persist there, independent of the geometry of the boundary layer.) It is apparent from all the experimeats done to date that large reductions in skin friction [1][2][3][4][5][6][7] and total drag [8] may be obtained by using gas injection in a liquid turbulent boundary layer, provided that a sufficient concentration of (sufficiently small) bubbles can be maintained in the near wall region. The extrapolation of these results to practical geometries at practical Reynolds number, as well as calculations of the gas flow rate necessary, is very much dependent on the dynamics of the bubbles in these situations.…”

“…The injection of a gas (to form microbubbles) into a liquid turbulent boundary layer has been shown, in several studies [1][2][3][4][5][6][7][8], to reduce drag. For the most part, these studies have looked at the skin friction reduction obtainable in a flat plate geometry [1][2][3][4][5][6][7].…”

“…For the most part, these studies have looked at the skin friction reduction obtainable in a flat plate geometry [1][2][3][4][5][6][7].…”

“…While the key to a fundamental understanding of the phenomenon would appear to lie in an understanding of bubble dynamics in a boundary layer flow, it seems plausible from the computational work [9], when taken in concert with some bubble concentration profile measurements [4][5][6], that the bubbles provide a mechanism for increasing the kinematic viscosity near the buffer region, thereby destroving some of the turbulent production. A similar mechanism has been postulated for the polymer drag reduction phenomenon [111.…”