Combustion, Flow, and Plasma Interaction Laboratory
The work in this lab focuses on the interactions of different plasma sources with combustible and inert flows for both subsonic and supersonic applications. Plasma generation, by means of AC or DV electrical discharges or optical laser breakdown, is used to control the flowfield of simple atmospheric flames, subsonic and supersonic boundary layers, and supersonic base flows. These effects are probed by a variety of optical diagnostics in order to measure velocity, temperature, and species concentrations in order to develop an understanding of the benefits of plasma actuators in these types of flows. Work in the lab is supported by the Army Research Office (ARO), the Air Force Office of Scientific Research (AFOSR), and the U.S. Department of Energy (DOE).
|102 Aerodynamics Research lab
Facility and Equipment Description
Combustion Research Stand
A 3-axis traverse system mounted between optical tables and below the facility exhaust allows for trivial positioning of the test burner with respect to the desired diagnostic. Five flow controllers allow for accurate control of fuel or dilution gases flowing to the burner. Diagnostics performed on the combustion research stand include absorption measurements, spontaneous Raman scatters, CARS, filtered Rayleigh scattering, PIV, and ignition measurements.
Subsonic and Supersonic Wind Tunnels
The LabVIEW-controlled subsonic facility features a 15”x15”x47” test section that exhausts outside the facility with full optical access on both sides and limited optical access from above. The supersonic facility has a 5”x5” square test section with optical access on all 4 sides designed for Mach 4 flows but modular enough to produce Mach 2 flow.
Plasmas generated for flow control in the lab include a pulsed plasma jet actuator, an AC dielectric barrier discharge (DBD) actuator, a nanosecond DC pulsed DBD, and a RF discharge. The plasma from a laser induced breakdown (LIB) is also commonly used as an ignition source for combustion experiments on the test stand and in the subsonic wind tunnel, but also for flow control in the Mach 4 facility.
The lab includes two seeded Nd:YAG lasers, an unseeded Nd:YAG, both a narrowband and broadband dye laser, and four dual-cavity PIV lasers. Detectors include two ICCD cameras, a back-illuminated CCD camera, an EMCCD camera, two high-speed Photron cameras, 6 dual framing cameras for PIV, and 4 cMOS detectors coupled with 4 spectrometers ranging from resolutions of 0.007 nm to 0.38 nm. Diagnostics performed with this equipment include emission spectroscopy, OH and H2O absorption, PIV, spontaneous Raman scattering, filtered Rayleigh scattering, CARS, OH PLIF, H and O TALIF, and high-speed schlieren.
DBD Plasma-assisted Combustion
Ro-vibrational spontaneous Raman scattering provides spatially resolved, time-averaged measurements of vibrational and rotational temperatures. When simultaneously collecting Raman spectra from different species, relative mole fractions are obtained as shown for hydrogen and nitrogen for two different applied potentials (0 and 5 kV peak at 18 kHz) in the hydrogen-air DBD burner. This coupled information of fuel concentration and rotational temperature help describe the average structure of the flame for different DBD operating conditions.
Granted the required optical access, laser induced breakdown (LIB) is a nonintrusive method for ignition of combustible mixtures. Our lab has studied this effect in a low pressure chamber, atmospheric pressure on the combustion stand, and in the low speed wind tunnel as shown with still images of high-speed schlieren photography at different time delays after the initial breakdown event. For this case, the pure hydrogen fuel is injected through the fuel orifice in the turbulent boundary layer of a 5 m/s crossflow. A laser beam is then focused down from the top of the tunnel to just above the fuel orifice causing breakdown and eventual ignition of the hydrogen-air mixture.
Spark Jet Flow Control
Supersonic flow control by means of a pulsed plasma jet is attractive for it’s lack of mechanical components and fast response times. Characterizing this jet by means of mico-PIV as shown demonstrates the ability to generate a high velocity jet for use in supersonic boundary layer studies or base flow experiments in our gas dynamics laboratory.
Laser Induced Breakdown (LIB)
Using a LIB as an ignition source and for flow control is of interest to the group, but studying the LIB process itself is a test of timescales. For the earliest times, imaging the emission onto a streak camera provides insight into the spatial-temporal evolution of the plasma. Gating the emission with an ICCD detector allows for the plasma evolution over 10’s of nanoseconds as shown. Visualization of the resulting blast wave requires Rayleigh scattering or schlieren techniques in the microsecond time frame, followed by the actual ignition of a combustible mixture on the millisecond timescale.