1 Issues Regarding the Measurement of Turbulence Properties in Bubble Plumes Fabián A. Bombardelli 1, 2 , Carlos M. García 1 , Mariano I. Cantero 1 , Lucas Rincón 1 , Andy Waratuke 1 , Chris R. Rehmann 1 and Marcelo H. García 1 1 Ven Te Chow Hydrosystems Laboratory, Dept. of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Ave., IL 61801, USA 2 On leave from Instituto Nacional del Agua, Argentina Abstract This paper discusses different issues that appear when characterizing turbulence in two-phase, air-water flows, in relatively deep containers. The flows correspond to bubble plumes with relatively large bubble diameters. Results of velocity time series obtained with the help of Acoustic Doppler Velocimeters (ADVs) are presented and analyzed. The post-processing of those signals is discussed in detail, presenting a methodology to separate air velocity from water velocity using ADV. Turbulence statistics, obtained from the time series, are also presented. Specifically, spatial distributions for the turbulent kinetic energy are analyzed. An interpretation of the behavior of the plume in the tank is also provided. Introduction Bubble plumes have been the subject of a large amount of works during the last three decades. Yet, the understanding of turbulence in bubble plumes is not complete. This fact is true even for bubble plumes in homogeneous water bodies, which constitute the most commonly investigated set of cases, as opposed to situations with stratification. One of the applications of bubble plumes is related to their use as aerators and as mixers. Gases are dissolved in the water column as bubbles go up and, thus, the plume contributes to prevent anaerobic conditions in the vessel. At the same time, currents generated by the plume help in establishing differential velocities, therefore producing mixing. As part of the Chicagoland Tunnel and Reservoir Plan, the U.S. Army Corps of Engineers plans to build several reservoirs to store combined storm water and raw sewage during large floods. The objective of this action is to store the combined effluent, and hence to avoid any release to the waterways in the Chicago area, an event that presently takes place several times a year. Once the storm has ended, the effluent can be pumped back into the wastewater treatment plant, at the rate that the plant is able to handle. To prevent the combined sewage in the reservoir from becoming anoxic (with the undesirable known effect of bad odors in a very populated area), different mechanisms are under analysis to incorporate air into the liquid. One of the alternatives consists in installing an array of bottom bubble diffusers, so as to provide oxygen to the effluent. The design of these systems of diffusers introduces a host of new technical issues as well as scientific questions. Turbulence in bubble plumes is one of them. The importance of turbulence in the present application is apparent: the mass transfer of oxygen and nitrogen to the effluent