Turbulence and Combustion Research Laboratory - Research
Research
High-Speed Imaging in Turbulent Flows
Turblent flows vary in both space and time and exhibit high levels of spatio-temporal intermittency. In order to track fundamental physical processes (i.e., vorticity, fluid strain, scalar/particle transport, mixing, etc.) in "real time", measurement capabilities are needed that have both high spatial and temporal resolution.
The use of a custom high-energy pulse burst laser system (HEPBLS) facilitates novel studies of turbulence and combustion dynamics. The system as described in [1, 2] produces the unprecidented combination of high laser pulse energy and high repetition rates. This allows many non-intrusive gas-phase diagnostics to be extended from sampling rates of a few Hz to multi-kHz. This feature is especially important for scalar measurements. Examples include kHz-rate planar Rayleigh scattering, Raman scattering, and planar-laser induced fluorescence (PLIF) diagnostics.
Below are a few of the many applications of the HEPBLS
References (with HEPBLS Applications)
[1] Fuest, F., Papageorge, M.J., Lempert, W.R., Sutton, J.A., “Ultra-High Laser Pulse Energy and Power Generation at 10 kHz,” Optics Letters, 2012, 37(15), 3231-3133
[2] McManus, T.A., Papageorge, M., Fuest, F., Sutton, J.A., “Spatio-Temporal Characteristics of Temperature Fluctuations in Turbulent Non-Premixed Jet Flames,” Proceedings of the Combustion Institute, 2015, 35(2), 1191-1198.
[3] Papageorge, M., Sutton, J.A., Intrusive Effects of Repetitive Laser Pulsing in High-Speed Tracer-LIF Measurements, Experiments in Fluids, 2017, 58(5), 40.
[4] Papageorge, M., Sutton, J.A., "Statistical Convergence and Processing of Finite-Duration Time-Series Measurements in Turbulent Flows", Experiments in Fluids, 2016, 57(8), 126
[5] Arndt, C.M., Papageorge, M., Fuest, F., Sutton, J.A., Meier, W., Aigner, W., "The Role of Temperature, Mixture Fraction, and Scalar Dissipation Rate on Transient Methane Injection and Auto-Ignition in a Jet-in-Hot-Coflow Burner", Combustion and Flame, 2016, 167, 60-71.
[6] Papageorge, M., Arndt, C.M., Fuest, F., Meier, W., Sutton, J.A., “Erratum to: High-Speed Mixture Fraction and Temperature Imaging of Pulsed, Turbulent Fuel Jets Auto-Igniting in Vitiated Co-Flows,” Experiments in Fluids, 2016, 57(1), 14.
[7] Papageorge, M., Arndt, C.M., Fuest, F., Meier, W., Sutton, J.A., “High-Speed Mixture Fraction and Temperature Imaging of Pulsed, Turbulent Fuel Jets Auto-Igniting in Vitiated Co-Flows,” Experiments in Fluids, 2014, 55(7), 1763.
[8] Papageorge, M., McManus, T.A., Fuest, F., Sutton, J.A., “Recent Advances in High-Speed Planar Rayleigh Scattering in Turbulent Jets and Flames: Increased Record Lengths, Acquisition Rates, and Image Quality,” Applied Physics B, 2014, 115(2), 197-213.
[9] Patton, R.A., Gabet, K.N., Jiang, N., Lempert, W.R., Sutton, J.A., “Multi-kHz Temperature Imaging in Turbulent Non-Premixed Flames Using Planar Rayleigh Scattering”, Applied Physics B: Lasers and Optics, 2012, 108, 377-392.
[10] Gabet, K.N., Patton, R.A., Jiang, N., Lempert, W.R., Sutton, J.A., “High-Speed CH2O PLIF Imaging in Turbulent Flames Using a Pulse Burst Laser System”, Applied Physics B: Lasers and Optics, 2012, 106(3), 567-575.
[11] Patton, R.A., Gabet, K.N., Jiang, N., Lempert, W.R., Sutton, J.A., “Multi-kHz Mixture Fraction Imaging in Turbulent Jets Using Planar Rayleigh Scattering”, Applied Physics B: Lasers and Optics, 2011, 106(2), 457-471.
[12] Jiang, N., Patton, R.A., Lempert, W.R., Sutton, J.A., “Development of High-Repetition Rate CH PLIF Imaging in Turbulent Nonpremixed Flames”, Proceedings of the Combustion Institute, 2011, 33(1), 767-774.
[13] Gabet, K.N., Jiang, N., Lempert, W.R., Sutton, J.A., “Demonstration of High-Speed 1D Raman Scattering Line Imaging”, Applied Physics B: Lasers and Optics 2010, 101 (1-2), 1-5.
Dynamics of Transient Fuel Injection, Mixing, and Auto-Ignition
The transient behavior of auto-ignition under turbulent fuel injection is of great importance for several engineering applications, including diesel and HCCI engines and scramjets. Understanding auto-ignition also is required for situations where such events are undesired (e.g. gas turbines, SI engines) and could lead to a catastrophic failure. Autoignition in turbulent environments is a complex phenomenon, where the chemical time scales responsible for ignition are on the same order as the fluid mechanic time scales and thus both chemical kinetics and turbulence play a major role in the events that lead to ignition and flame stabilization.
We are currently investigating auto-ignition using advanced optical and laser-based diagnostics in canonical configurations to isolate the relative roles of flow turbulence, turbulent mixing, and reaction chemistry on auto-ignition processes of turbulent fuel jets injected into a high-temperature, vitiated oxidizer stream.
Below we show a schematic of the OSU auto-ignition burner (AIB) and video of the transient operation. Each "burst" is less than 50 ms and we collect more than 1000 individual sequences at each operating condition.
Auto-ignition Experiment in Motion
We have examined the role of mixing rate fluctuations on auto-igntion. Below is a sample image sequence of time-resolved mixture fraction, temperature, and OH* (representing the onset of combustion) in a Re = 40,000 DME fuel jet issuing into a T = 1330 K coflow. Each image sequence corresponds to approximately 5 ms of real time.
Results show that for the current fuels and thermodynamic conditions, auto-igntion occurs in very lean regions with low values of scalar dissipation rate [1, 2]
References
[1] Papageorge, M., Arndt, C.M., Fuest, F., Meier, W., Sutton, J.A., “High-Speed Mixture Fraction and Temperature Imaging of Pulsed, Turbulent Fuel Jets Auto-Igniting in Vitiated Co-Flows,” Experiments in Fluids, 2014, 55(7), 1763.
[2] Arndt, C.M., Papageorge, M., Fuest, F., Sutton, J.A., Meier, W., Aigner, W., "The Role of Temperature, Mixture Fraction, and Scalar Dissipation Rate on Transient Methane Injection and Auto-Ignition in a Jet-in-Hot-Coflow Burner", Combustion and Flame, 2016, 167, 60-71.
[3] Saksena R., Sutton, J.A., "Transient and Steady-State Behavior of Auto-Igniting Propane and Dimethyl Ether Fuel Jets in High-Temperature Vitiated Coflows", accepted, Proceedings of the Combustion Institute
[4] Arndt, C.M, Papageorge, M., Fuest, F., Sutton, J.A., Meier, W., "Experimental Investigation of the Auto-Ignition of a Transient Propane Jet-In-Hot-Coflow", accepted, Proceedings of the Combustion Institute
We have used simultaneous time-resolved conserved scalar and velocity measurements to investigate the spatial and temporal interaction and coupling between the flow turbulence and scalar mixing in gas-phase turbulent jets. Our results indicate that scalar fluctuations de-correlate at the same rate as the velocity fluctuations yielding nearly identical integral length and time scales. Additional space-time cross correlation analysis shows that the peak correlation between the conserved scalar and velocity occurs at zero time lag, indicating zero phase delay. Physically, this implies that scalar fluctuations are almost a direct response to velocity fluctuations, indicating their passivity. Results in reacting flows do not show this behavior!
Quantitative velocity measurements underpin fluid dynamics research and paramount for understanding flow physics. Over the last 30 years of application and refinement, particle image velocimetry (PIV) has become a well-established and the most utilized technique for measuring velocity in fluid flows. PIV relies on seeding small tracer particles into the flow and collecting the scattered light from two closely spaced, temporally sequential laser sheets onto a camera. Image pairs are processed using statistical correlation algorithms to produce the most probable displacement of groups of particles (within an interrogation window) and the velocity.
While PIV can be considered as the de facto standard for velocity measurements in fluid flows, it produces a non-dense estimate of the velocity field since only one velocity vector per interrogation window is calculated. The relatively poor spatial resolution can lead to challenges with the interpretation of correlation-based PIV velocity results in flows with strong gradients such as turbulent flows. With access to only a single vector per interrogation window, the true small-scale velocity gradient information is not preserved and the estimated velocity gradients can be underestimated significantly.
In this work, an alternative approach for ultra-high-resolution and high-accuracy velocity imaging is used based on a wavelet-based optical flow (WOF) method. This approach has the advantage of producing a dense velocity vector field; that is, one velocity vector at each pixel in the collected images.
Optical flow methods rely on the conservation of intensity, I(x,t) (commonly referred to as “brightness”), between a pair of images and uses the time and spatial variations of I(x,t) to infer the underlying motion. More specifically, optical flow methods seek to estimate the multi-dimensional motion that leads an image at time t to evolve to its state at time t+Dt.
While the theory behind this method is being uploaded, please enjoy some of our more recent results using synthetic particle fields generated from a DNS of isotropic turbulence. Please note that is all situations, the WOF method produces a more accurate and higher resolution result. In particular, the results of vorticity and the energy spectrum are quite striking!
We have developed a new laser diagnostic method to measure fuel vapor and gas phase mixing in the presence of droplets in turbulent sprays using Filtered Rayleigh Scattering (FRS). Our FRS method provides a gas-phase measurement without inteference from the dispersed phase.
We are currently applying the diagnostic in a new high-pressure/temperature spray facility
Reference
Allison, P.M., McManus, T.A., Sutton, J.A., "Quantitative Fuel Vapor/Air Mixing Imaging in Droplet/Gas Regions of an Evaporating Spray Flow Using Filtered Rayleigh Scattering," Optics Letters, 2016, 41(6), 1074-1077.
Accordions
The research performed within the TCRL is made possible by the following funding sources:
Air Force Office of Scientific Research (AFOSR)
National Science Foundation (NSF)
American Chemical Society (ACS) Petroleum Research Fund
Ohio Board of Regents (OBOR) Action Fund
Department of Energy (DoE)
Army Research Office (ARO)
many SBIR and STTR collaborations with small businesses
