WIDECARS multi-parameter measurements in premixed ethylene-air flames using a wavelength stable ultrabroadband dye laser.

Width-increased dual-pump enhanced coherent anti-Stokes Raman spectroscopy (WIDECARS) measurements were used to determine the temperature and major species mole fractions in laminar, premixed, ethylene-air flames operating at atmospheric pressure. Conventional ultrabroadband dye lasers for WIDECARS, which use Pyrromethene dyes, have historically suffered from day-to-day wavelength shifting. To overcome this problem, a new ultrabroadband dye laser was developed in this study to provide a stable wavelength and power generation. A new dye laser pumping scheme and a mixture of Sulforhodamine 640, Kiton Red 620, and Rhodamine 640, was used to generate the desired FWHM ${\sim}{15}\;{\rm nm}$∼15nm (${410}\;{{\rm cm}^{ - 1}}$410cm-1) bandwidth. The WIDECARS measured mole fraction ratios of ${{\rm CO}_2}$CO2, CO, and ${{\rm H}_2}$H2 with ${{\rm N}_2}$N2 agreed well with chemical equilibrium calculations.

Development of a three-legged, high-speed, burst-mode laser system for simultaneous measurements of velocity and scalars in reacting flows.

We report the development of a three-legged, high-speed, high-energy, burst-mode laser system for the simultaneous measurement of velocity and key combustion species in turbulent reacting flows. The laser system is designed to simultaneously amplify a four-pulse sequence [including a doublet pulse for particle image velocimetry (PIV) measurements] with variable pulse separations at a repetition rate up to 500 kHz and a burst duration of 1-10 ms. With the three-legged, burst-mode laser system, we demonstrate simultaneous measurements of velocity using PIV and planar laser-induced fluorescence imaging of hydroxyl and formaldehyde in a turbulent jet flame.

High-repetition-rate interferometric Rayleigh scattering for flow-velocity measurements.

High-repetition-rate interferometric-Rayleigh-scattering (IRS) velocimetry is implemented and demonstrated for non-intrusive, high-speed flow-velocity measurements. High temporal resolution is obtained with a quasi-continuous burst-mode laser that is capable of providing bursts of 10-msec duration with pulse widths of 10-100 nsec, pulse energy > 100 mJ at 532 nm, and repetition rates of 10-100 kHz. Coupled with a high-speed camera system, the IRS method is based on imaging the flow field though an etalon with 8-GHz free spectral range and capturing the Doppler shift of the Rayleigh-scattered light from the flow at multiple points having constructive interference. The seed-laser linewidth permits delivery of a laser linewidth of < 150 MHz at 532 nm The technique is demonstrated in a high-speed jet, and high-repetition-rate image sequences are shown.

Experimental and computational study of pulsatile flow characteristics in Romanesque and gothic aortic arch models.

Romanesque and Gothic are two types of deformed aortic arch geometries after surgical repair of coarctation of the aorta. The abnormal arch geometry and hemodynamics are associated with late systemic hypertension, aortic aneurysms, and other cardiovascular complications. To understand the fluid dynamic signatures of such flow, a combined experimental and computational fluid dynamic (CFD) study has been conducted to quantitatively compare the main (axial) and secondary flow characteristics. In the experiments, a pulsatile flow simulator was used to generate the pulsatile flow conditions. Phase-locked planar and tomographic particle image velocimetry techniques were employed to quantitatively study the flow fields. Three-dimensional CFD simulations were also performed and compared with the experimental data. The results show that in the Romanesque arch, the flow first accelerates along the inner wall and then becomes more uniform in the cross-section after the peak systole. A pair of wall vortices and Dean-type vortices develop during the systolic phase. The coherent structures are continuously extended into the descending aorta and persist throughout the cycle. In comparison, the Gothic arch exhibits a highly skewed velocity distribution with high velocity around the arch apex. The sharp curvature causes flow separation, jet impingement, and stagnant flow near the top. The coherent structures in the Gothic arch are less continuous in the descending aorta, which also differ from those observed in the Romanesque model. The distinct flow characteristics of the Gothic arch lead to more temporal and spatial variations of wall shear stress in the descending aorta, implying hemodynamic risks for aortic complications.