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Vaz, D. C. "Technique to locate key points in recirculating flows, using pitot tubes." Experimental Techniques. 39 (2015): 55-68. AbstractWebsite

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.

Vaz, D.C.a b, Van Kampen Van Buijtenen Kok J. F. c J. "Experimental characterization of the combustion roar in a gas turbine combustor model operating in the flame and flameless oxidation regimes." 12th International Congress on Sound and Vibration 2005, ICSV 2005. Vol. 2. 2005. 1657-1664. Abstract

Most investigations on the implementation of flameless oxidation in gas turbines have been focused on the emissions aspects while the demonstration of the combustion acoustiCS improvement has been hardly ever addressed experimentally. The present experimental study provides insight into the differences of combustion generated noise between the conventional flame and flameless oxidation regimes. Results include noise levels measured in both combustion regimes, for different air-to-fuel ratios, and show an increased noise output in flame mode as compared to flameless oxidation. The paper also explains the acoustic precautions taken to allow comparison between cases.

Vaz, D.C.a b, Van Buijtenen Borges Spliethoff J. P. a A. "On the stability range of a cylindrical combustor for operation in the flox regime." Proceedings of the ASME Turbo Expo 2004. Vol. 1. 2004. 511-516. Abstract

The implementation of flameless combustion in gas turbines is a recent research topic motivated by the potential for ultra-low NO x 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/m 3, and air preheat 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).