Theoretical and Computational Fluid Dynamics Laboratory
College of Engineering
University of Massachusetts Amherst
13 December 2010
Dr Kshitij Neroorkar’s defense was so smoothly delivered you’d have thought he’d done this a thousand times already. Who knows? Simulation of Flash-Boiling in GDI Injections with Gasoline-Ethanol Fuel Blends might be the kind of hard science topic where 1000 experiments are needed before you get to defend the phd! Being the lone, non-family-member representative of the social sciences present, “How much did you understand?” was the question-du-jour, post-defense. Here comes the test, huh? At least enough to recognize that Dr Neroorkar’s subject matter seemed very similar to Dr Shivasubramanian Golapakrishnan’s dissertation topic, which I distorted metaphorically in a previous blogentry: Language is a Fluid. A big thanks, btw, to Dr Blair Perot, who read and questioned the two-way utility of my analogy:
“Since I understand the fluids, this analogy certainly helps me understand what is important to linguists. I am less sure about if it will help the other way around. Does it really help linguists understand/describe linguistics better to think in terms of fluids?” (I like how he cuts right to the chase!)
Foundation
The site of Dr Neroorkar’s study is in the nozzle part of a fuel-injection system, so its a pretty small physical space. Inside that wee tunnel all kinds of things are going on, one of them being flash-boiling: the violent explosion of liquid into steam (a gas). The better this explosion is controlled, the more usable energy one gets, but it is tricky to maximize the energy potential because, well, all kinds of things are going on! There’s a pressure drop where the fluid enters, certain processes that generate the growth of nucleation bubbles which start out teeny-tiny and expand until they touch each other, and then these bubbles bursting into spray in a process called atomization. The art is to manage the rate and speed (measured by a non-dimensional number – one of those deeply held math secrets engineers bandy about like social scientists bartering philosophical theories). The particular number in this case (that describes nothing in the physical world) is quite effected by the slightest change in temperature. Changes in temperature affect the rate and there’s a whole bunch of modeling that needs to be done to get this whole puppy optimized. Or something like that.
“Then we do some mathematical tricks”
Turns out that with 8-hole injectors, the plumes of vapor generated from each hole merge in a way that needs to be taken into account, and this hasn’t actually been done before, or not so well/thoroughly or otherwise unequivocally established through parametric study. What is the difference, someone asked, from what Dr Gopalakrishnan did before? “Shiva didn’t couple them.” Couple what? The nuances were definitely over my head here, but the two of them did use the same HRM model, which (as Dr Neroorker explained to me later) “assumes the liquid-vapor mixture is one substance, not separate.” Treating the fluid-gas mix as homogeneous rather than heterogeneous (as explained here right at my level) enables an epistemological framework in which the system will relax to equilibrium if given enough time. There are (apparently) problems with the assumptions of cavitation, and the degree of superheat figures in some crucial way, not to mention the influence of specific geometry (90% symmetric) and the composition of the periodic boundary conditions (sounds an awful lot like “context” to me).
Somehow, Dr Neroorkar put all that together in the first validated 3D simulation showing the geometry region, the residence time dominated region, and the vaporization time dominated region, and got a volatility distribution curve showing stuff that matters. With important limitations of course: laminar flows, empirical time scales relevant to one fluid not others, so on and so forth.
Party!
The best part (of course) was the celebration, where I got to pretend to blend in with the relaxing homogenous crowd of Indians (“convenience store not casino” as distinguished by Russell Peters) at Sneha & Kshitij’s cozy apartment. Except for Nidhi (who delivered all her laugh lines in Hindi so I couldn’t understand them), everyone stepped up to being blogged. Partha gave in pretty easy: “We aren’t cited that often.” I had a great conversation with Vikram, who informed me that “helium is helium,” and Upen, “Math is not context-dependent.” Bhooshan mildly admitted that there “are not so many more fundamental reactions to discover [in chemistry]”, which Upen amended, “until they are discovered!” I would have followed up on these topics except Ruchita chimed in, ” This is not the conversation I want to be having!” Oh alrighty then!
Sandeep, meanwhile, was focused: “Where is the biryani?” Pritish arrived a little late and took awhile to catch up, “She’s gonna use my name somewhere?” You know I was amused when Sneha told us “people used to think I was a boy.” And did I ever learn some gossip about somebody’s Victoria’s Secret!
The meal was awesome, the company grand, and the event momentous. Kshitij himself did the honors on the decadent chocolate mousse cake, announcing: “My job is done.”