High-Speed Measurements of Flame-Stabilization Processes in Vitiated Augmentor Environments for Understanding Screech, Rumble, and Blowoff

ABSTRACT: The Phase-I research is to demonstrate high-speed (up to 10 kHz) burst-mode tomographic PIV measurements of velocity in turbulent reacting shear flows in afterburners, which allow complete determination of the nine-component strain rate tensor, the vorticity vector and the strain rate upstream the flame front. High-speed Tomo-PIV measurements will be correlated with two-color OH-PLIF thermometry to shed insights onto key physicochemical processes in turbulent combustion, flame stabilization and combustion instabilities in afterburners. Different from high-speed planar stereo-PIV measurements and hot-wire measurements, high-speed measurements of volumetric velocity with Tomo-PIV enable turbulence analyses without resorting to Taylors hypothesis of frozen turbulence, particularly suitable for studying turbulence evolution in spatially-developing flows. Data and analyses will be made available to AFRL personnel and combustion researchers to guide development and validation of turbulent closure models for numerical simulation of turbulent combustion and optimize design and operation of afterburners.; BENEFIT: Combustion instabilities and blowoff are two major technical challenges facing design and operation of afterburners and other high-performance combustion and propulsion systems. To shed insights on combustion instabilities and blowoff and guide afterburner design and operation, high-speed burst-mode Tomo-PIV measurements will be correlated with temperature measurements via two-color OH-PLIF thermometry and synchronized with HCO measurements via CH2O/OH PLIF (if time permits) to resolve flame/turbulence/acoustics interactions along the separating shear layer in afterburners within a large range of length and time scales.1. Immediate benefits to the Air Force: The proposed high-speed measurements of turbulent combustion and data analyses are of immediate relevance to design and operation of afterburners with enhanced performance, operability, reliability and sustainability.2. Scientific discoveryHigh-speed Tomo-PIV measurements allow complete determination of the strain rate tensor, the vorticity vector and the strain rate upstream the flame front, and enable turbulence analyses without resorting to Taylors hypothesis of frozen turbulence. High-speed Tomo-PIV measurements correlated with temperature measurements and/or synchronized with HCO measurements spatially, temporally and fully resolve flame/turbulence/acoustics interactions within a large range of length and time scales. Benchmark data will be used for development and validation of turbulence closure models, including unsteady flamelet models.3. Economic security and prosperityThe proposed research on turbulent combustion, flame stabilization and combustion instabilities sheds insights onto fundamental mechanisms and key physicochemical processes in flame/turbulence/acoustics interactions, which are of immediate relevance to R&D of advanced combustion and propulsion systems, including but not limited to afterburners, gas turbine engines, internal combustion engines, ramjet engines, rockets and even industrial furnaces. This is a huge market throughout US and the world.