Combustion & Gas Dynamics

Processes that involve combustion and high-speed, compressible flow (gas dynamics) are important in numerous aeropropulsion and energy conversion applications. We focus on the study of the vaporization and combustion of liquid oxygen droplets in a gaseous hydrogen environment, a problem relevant to combustion processes in rockets using cryogenic liquate propellants. This research is being conducted both experimentally in microgravity using a drop tower and by numerical modeling.

Liquid Oxygen Droplet Combustion

In collaboration with the Center of Applied Space Technology and Microgravity (ZARM) at the University of Bremen in Germany, and the IPHT Leibnitz-Institute for Photonic Technologies in Jena, Germany, we are studying the combustion of liquid oxygen droplets in a hydrogen environment. This combustion problem is relevant to rocket combustion chambers utilizing cryogenic hydrogen/oxygen propellants. We conduct combustion tests both in the laboratory and in microgravity using the ZARM Drop Tower. We develop optical diagnostics in collaboration with the IPHT. We are developing analytical and numerical modeling of the droplet evaporation and combustion processes. The research is primarily funded by the German Aerospace Center (DLR) and the US Fulbright Program.

Microgravity Science

Microgravity science involves the study of physical phenomena in which the normal force of gravity present on earth is greatly reduced. This can be done by the use of parabolic-trajectory aircraft, drop towers, sounding rockets, and by conducting experiments in space. Microgravity research involves a broad range of disciplines, including materials, fluid dynamics, combustion, and biological systems. Combustion research is greatly facilitated by the removal of buoyant convection in microgravity, which can result in geometric simplifications, and increased time scales, which greatly aid both the experimental investigation and numerical modeling of combustion processes.

Conducting experiments in microgravity can also unmask important behaviors in fluids undergoing phase-change processes. These mechanisms can include the action of thermocapillary forces, the recoil associated with ejected vapor, the effects of non-uniform vaporization or condensation, and the impact of these forces on the stability and structure of the evaporating film.

Our microgravity research activities and interests focus on fluid physics and combustion, including the study of the vaporization / combustion of cryogenic propellants in microgravity conditions and film evaporation processes in normal and reduced gravity.

Multiphase Flow and Heat Transfer

Fluids undergoing phase change (such as evaporation, condensation) are of great importance in many engineering problems. These include cooling, fuel vaporization, power generation systems, and many industrial processes that rely on evaporation and/or condensation, such as coatings, crystal growth in semiconductors, polymer processing, magnetic storage devices, and more. As technologies advance and push the limits of traditional thermal management, however, a more thorough understanding of the coupled fluid and thermal transport phenomena is needed. Our particular research interests are the behavior of evaporating films under non-stationary conditions and the phase-change and heat transfer behavior associated with cryogenic liquid propellants. We also research the non-equilibrium processes that can result from very rapid evaporation processes.

Superheated Droplet Vaporization

The research investigates the explosive vaporization of liquid droplets at the superheat limit by computational modeling combined with experiments. The boiling of liquid at high temperatures can be explosive and destructive, and poses a potential hazard for a host of industrial processes. Direct Numerical Simulation (DNS) computations are performed at Southern Illinois University, Carbondale; with companion experiments conducted at the UW. The UW research involves superheating liquid droplets in a heated liquid column, allowing for the initiation of explosive vaporization, and employing high-speed image to visualize the dynamic vaporization behavior, the subsequent droplet oscillations and instabilities, and also detecting and analyzing the accompanying pressure signatures. This research is supported by the National Science Foundation.

Phase-change phenomena in cryogenic propellants

The long-term storage of cryogenic propellants on-orbit is a limiting technology for manned deep-space exploration missions. A joint, NASA-Sponsored program between Michigan Technological University, the UW, and the National Institute for Standards and Technology (NIST) is studying the evaporation and condensation behavior of liquid hydrogen and liquid methane propellants. The accommodation coefficients of evaporating cryogenic hydrogen-methane propellant mixtures are measured at NIST using neutron imaging. MTU is performing a numerical simulation of the evaporating films; the UW component of the research involves computational thermal modeling of the experimental assembly/evaporating film configuration.

Recently Completed Research

Stability, Cellular Structure and Heat Transfer of Evaporating Films

We conducted comprehensive laboratory experiments that revealed the evolution of the convective structure in quasi-steady and transient evaporating thin films and the corresponding impact on heat transfer. The experiment was flown in zero-gravity at NASA Johnson Space Center in May, 2012. The work was supported by NASA.