We develop and apply various laser and optical diagnostics to study the behavior of complicated fluid flows. Some of our capabilities include particle image velocimetry, laser induced fluorescence, laser Rayleigh scattering, thermographic phosphor thermometry, laser Raman scattering, and chemiluminescence. We have capabilities to perform these measurements at repetition-rates up to 1 MHz and in three spatial dimensions (using tomography).
We particularly specialize in applying diagnostics to challenging environments, such as high pressure combustors, very turbulent flows, or plasmas. Some current research interests include high-resolution 3D velocimetry, filtered Rayleigh scattering, improving tomography algorithms, and THz-frequency diagnostics.
Nearly all practical combustion occurs under turbulent flow conditions. Turbulent combustion involves multi-scale, multi-physics interactions between fluid mechanics, transport, and chemistry. We use laser diagnostics to study the fundamental dynamics of turbulent combustion, in order to build physically grounded models that can be used to simulate practical combustion devices. Current interests include the impact of small-scale chemistry on the evolution of the turbulent microscales, inter-scale energy transfer, and reaction rate controlling processes in high-speed flames.
Combustion dynamics refers to large scale unwanted changes in the fluid/chemical/thermal state, including thermoacoustic oscillations, blow-out, and flashback. These dynamics can cause problems ranging from reduced efficiency to catastrophic failure of combustion systems. All combustion dynamics involve some form of coupling between combustion and fluid mechanics. Our high-frequency laser diagnostics are able to resolve these interactions, thus unraveling the causes of combustion dynamics. Examples of projects include identifying the feedback pathways driving oscillations in advanced aeronautical gas turbine combustors, understanding the effects of fuel composition and operating conditions on blow-out, and detecting early warning signs of impending flashback. These projects often partner with leading manufacturers of gas turbine engines.
Gas turbine engines are the main power source for aviation and a large component of the power generation system. However, the physical and chemical processes occurring inside of gas turbine combustors remains relatively opaque. We use our advanced diagnostics to measure important parameters -- such as the flow field, spray, and heat release rate -- in realistic combustors operating at realistic conditions (high pressure, high temperature, etc.). These experiments provide novel insight into the physical phenomena that limit the operation and critical data for comparison against computational and heuristic design methods. Research in this area partners closely with industry, such as GE, Pratt & Whitney, and Siemens.
Experimental and computational simulations of combustion systems have traditionally interacted in a relatively simple manner; experiments provide data against which computational results are validated (or invalidated). Research in this area aims to create stronger links between the physical and digital versions of these systems. These links can be used in various manners, from correcting for model inaccuracies, to adjustment of simulation boundary conditions, to improving experimental sensor location. Areas of interest include data assimilation for improved state- and parameter-estimation in simulations, optimal experimental design to provide maximum information to simulations, reduced order modeling, and virtual sensors.
Utilization of supercritical CO2 as the working fluid (in place of air) in power generation gas turbine engines has the potential to improve the cycle efficiency. This arises due to high sensitivity of thermodynamic properties around the critical point. Direct firing of these systems requires combustion to occur at extremely high pressures (around 300 atmospheres), at which fluid, chemical, and thermodynamic phenomena are not well understood. Furthermore, it is very hard to measure anything at these conditions. Research in this area aims to measure mixing and combustion properties in a oxygen-fuel combustor for supercritical CO2 cycles using both emissions and absorption diagnostics.