Control of spray properties by gas flow turbulence
Abstract
The efficient combustion of liquid fuel spray is of paramount importance for the performance ofnumerous energy systems, including t""he combustors of gas turbine engine. The size, velocity,and trajectory of the atomized droplets play primary roles in determining t""he air-fuel mixtureratios, the ignition and combustion process, and the content of the exha ust emissions. Thereforecontrolling th"e processes of formation and dispersion of the droplets is critical to design the nextgeneration of spray combustion systems. Optim"izing these processes is however difficult becauseof the complexity and interactions among the several involved mechanisms, and sev""eralstrategies have been pursued including: advanced atomizer geometry, acoustic and ultrasonicvibrations applied to the nozzles,"" piezoelectric actuators, and injection of gas bubbles. Here wefocus on one aspect which is believed to be crucial to determine the"" spray droplet properties andbehavior, yet is not well understood: the interaction between the spray drop lets and the gasturbulen""ce. Such interaction has far reaching consequences for the performance of spraycombustion, but a systematic study of the effects of"" the turbulence properties has been lacking.Based on bot h established and novel results on droplet-turbulence interaction, we post""ulate that,by tuning the properties of the gas turbulence, spray performance can be greatly enhanced.Accordingly, our objectives a"re: (i) to reveal the mechanisms by which the different turbulenceproperties of the gas flow influe nce key spray features such as" pe netration, drop let sizedistribution, and gas entrainment; and (ii) to show how the intelligent choice of the turbulenceparame"ters can lead to an enhanced spray performance. To this end we will use a novelexperimental facility built by the PI at the Univers"ity of Minnesota, capable of generating intensegas turbulence over a large volume. This consists of a zero-mean-flow chamber featur""ing 256individually actuated jets, which interact and create intense air turbulence of specified propertiesover a volume of around"" one cubic meter. By using multi-resolution high speed PIV (ParticleImage Velocimetry), PTV (Particle Tracking Velocimetry) and sha""dowgraphy, we willsimultaneously characterize the air flow motion and the spray properties. In particular, we usehigh-power/high-s""peed laser illumination, up to four high-speed cameras, and a telescopicobjective to perform planar and volumetric measurements of"" droplet velocity an size, as well ascapturing the motion of the air flow. Our proposed three-year research efforts will be organiz""edaround three specific questions, for which we will be testing current working hypotheses: (1)How doe s turbulence affect spray p""e netration? Our hypo thesis is that, due to non-linear dragforces, the penetration distance for spray droplets in turbulent gas is" reduced compared to aquiescent or laminar flow environment; (2) How do turbulence properties affect gas entrainmentand mixing? Ou"r hypothesis is that, due to preferential concentration by turbulent edd ies, largerdroplets mix less effectively with the surround""ing gas; (3) How does the droplet size distributionchange in presence of gas turbulence? Our hypothesis is that, due to the prevale""nce of collisioncoalescenceover breakup in regions of higher concentration, the mean droplet size increases forincreasing average" volume fraction. Answering the questions above will provide new andfundamental insight into the physical processes at play in the interaction between spray dropletsand gas turbulence. This is essential for a mechanistic understanding of these complex andhighl"y coupled phenomena, and will pave the way towards a better control of the sprayatomization and combustion performance.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 09, 2017
- Source ID
- N000141712578
Entities
People
- Filippo Coletti
Organizations
- Office of Naval Research
- Regents of the University of Minnesota
- United States Navy