SIMILARITIES OF TURBULENCE STRUCTURE IN A CONICAL DIFFUSER WITH OTHER WALL-BOUNDED FLOWS

Experiments were conducted in a conical diffuser with a total divergence angle of 8 deg and an area ratio of 4:1 with fully developed turbulent pipe flow at entry. The results of previous research have shown that diffuser flow can be separated into two regions, i.e., the wall region where u2 varies linearly with distance from the wall and an inner core region starting where u reached a maximum. Detailed experiments were performed to show the similarities of diffuser flow with boundary-layer flow (and pipe flow). Such flows have recently been thoroughly researched with the aid of flow visualization. The probability density of instantaneous velocity, the behavior of the ejection, sweep, wallward and outward interaction events, and the highly intermittent nature of the fine structure near the wall in the diffuser flow are similar to the flows in other wall-bounded flows, e.g., pipe, channel, and boundary-layer flows. Measurements of fine structure parameters such as the spectra of ( u/ t)2 also show that in the wall region for the diffuser the spectra have a dual slope similar to that shown by Ueda and Hinze, clearly suggesting structure similarity. © 1979 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.