Time Resolved Multiparameter Flow Diagnostic for Engine Exhaust Plumes

High temperature jet plumes emanating from aircraft engines and missiles produce effects that are of interest for threat detection, environmental noise, and engine development purposes. Optical and infrared emissions from plumes are sources of light and heat signatures, respectively, that can potentially be used for tracking or targeting vehicles in flight.  Acoustic noise from jet plumes can potentially give away a vehicle’s position or can cause unwanted disturbances to the environment. Much effort has gone into characterizing high speed jets through experimentation and computational simulations, yet there still remains significant uncertainty in many aspects of modeling aircraft jet plume phenomena.  A contributing factor to this uncertainty is a lack of data from high-temperature and high-velocity exhaust plumes, due to measurement difficulties. Time-resolved measurements of temperature and species concentrations can also be important indicators of engine health and efficiency and are necessary to better understand transient phenomena including startup and shut down sequences, combustion instabilities, and flow nonuniformity. However, exhaust plumes present a uniquely challenging measurement environment. Intrusive sensors, such as thermocouples and pressure transducers, degrade rapidly in reactive, particle-laden, high-temperature, high-velocity plume flows, emphasizing a need for nonintrusive measurement approaches. Even optical techniques are challenged by the sometimes optically thick flows with large density gradients and high levels of thermal emission in full-scale aircraft engine exhaust flows. Thus, an innovative measurement system for temperature and species concentration that avoids the effects of beam steering, background emission, and acoustic noise is needed for high-temperature high-velocity exhaust plumes. In the proposed effort, the team of MetroLaser and Stanford University will develop an innovative noninvasive sensor designed to provide quantitative, two-dimensional spatial distributions of temperature and water vapor concentrations in a full-scale aircraft exhaust with anticipated measurement uncertainties of better than +/- 5%. The sensor system will take advantage of MetroLaser’s expertise in the application of tomographic measurements in industrial burners and by Stanford in a wide range of propulsion related flows over the last four decades.