Daniel Vaz

Abstract Saddle points (SPs), recirculation centres (RCs), and reattachment points (RPs) are examples of key points of the flow, also called critical or stationary points. Finding the location of these null velocity points is essential to the understanding of a flow pattern and may even spare measurements of the whole flow field. To that purpose, laser based techniques may render inappropriate, especially because of the difficulty in conveying seed particles to the vicinity of those points. The article details an original technique based on the measurement of pairs of profiles with Pitot tubes and finding their intersection. Two flows are taken as case-studies. These consist of jets emanating from the base of a cylindrical chamber: multiple jets arranged in a circular crown and a single central jet. While the location of SP and RP could be done in a single step, due to the symmetry of the flow, pinpointing RCs required an iterative procedure, in which the radial and longitudinal coordinates were determined alternately. The location of the RP was the least accurate. The technique has pedagogical value and will particularly interest young researchers and practicing engineers without access to elaborate and expensive techniques such as particle image velocimetry. © 2013, Society for Experimental Mechanics.