Daniel C. Vaz

On the Stability Range of a Cylindrical Combustor for Operation in the FLOX Regime

The implementation of flameless combustion in gas turbines is a recent research topic motivated by the potential for ultra-low NOx emissions and improvement of the combustion acoustics. This paper presents preliminary results of the implementation of flameless oxidation in a laboratory model of a cylindrical combustor (in view of stationary and micro gas turbines). Guidelines are given for the start-up of this combustion system. The experimental study then assesses, for atmospheric conditions, the combined effect of the air-to-fuel ratio, wall temperature and jet velocity on combustion stability. Global volumetric heat releases up to 16 MW/m3 , and air pre-heat up to 265°C are attained. The numerical simulations give insight into the recirculating pattern of the flow and the state of mixing of reactants and products in the near-nozzle region. The turbulence-chemistry interaction is accounted for by means of the non-premixed flamelet-PDF approach (including finite rate chemistry and scalar dissipation rates up to the extinction limit).Copyright

Technique to Locate Key Points in Recirculating Flows, Using Pitot Tubes

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.