While the term "rocket scientist" gets tossed around rather loosely these days, Dr. Josette Bellan, a senior research scientist at NASA's Jet Propulsion Laboratory, is the genuine article, spending much of her time pondering the mysteries of propellants at high pressures and temperatures.
Bellan is currently leading research to help better understand the intricacies of high-pressure fluid behavior, which could help in the eventual use of powerful computers to simulate what goes on in combustion chambers. That could result in significant cost savings over the current rocket design standard, which is primarily based on hardware testing.
Bellan and one of her associates, JPL's Dr. Kenneth Harstad, are about to publish a paper in the International Journal of Multiphase Flow that may provide researchers with key elements needed to unlock the mystery of high-pressure fluid behavior.
The work, titled "An All-Pressure Fluid Drop Model Applied To a Binary Mixture: Heptane in Nitrogen," due to be published this spring, documents the accuracy of their model of a single hydrocarbon droplet in a high-pressure environment, emulating the conditions that propellants endure in combustion chambers. It also pinpoints differences between low- and high-pressure fluid behavior.
The model highlights the importance of a previously neglected quantity, the "thermal diffusion factor," describing how a highly localized change in temperature within a mixture of fluids can give rise to a flow of one ingredient in that mixture compared to the rest of the ingredients. Conversely, this factor describes how local changes in ingredients can give rise to local changes in temperature.
While typically playing no role at ordinary atmospheric pressure, the thermal diffusion factor becomes important at high pressures.
"Because this factor is usually unimportant, quantifying it has not been a high priority in the past," said Bellan, who holds a Ph.D. in aerospace and mechanical sciences from Princeton University and now conducts research in JPL's Thermal and Propulsion Engineering Systems section. Reared in France, she earned a master of science in applied mathematics from the University of Sciences in Paris.
"Our research shows that if we want to understand propellant behavior under high pressure, knowing this factor is in fact very important," she adds.
She points out that this model brings scientists a step closer to creating realistic computer simulations of rocket, jet and diesel engine combustion chambers. Long-term benefits will likely include cost savings and greater design accuracy.
Those simulations may well lead to new estimates of the ideal size of combustion chambers, because those simulations will now include the thermal diffusion factor, whose importance has been proven by this model.
This research has been supported by the Advanced Subsonic Technology Program at the NASA Glenn Research Center, Cleveland, OH, and by the NASA Marshall Space Flight Center, Huntsville, AL.
The Jet Propulsion Laboratory is a division of the California Institute of Technology, Pasadena, CA.
News Media ContactJohn G. Watson