A study of curved duct flows associated with side-dump combustor and artery disease

• Main Author: 廖津均
• Other Authors: Liou,Tong-Miin
• Format: Others
• Language: en_US
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/43820619586013730690

博士 === 國立清華大學 === 動力機械工程學系 === 85 === The flowfields in the three-dimensional side-dump combustor inlet and chamberwith various numbers of inlet guide-vanes have been characterized using laser-Doppler velocimetry. The Reynolds number based on the bulk mean velocity andhydraulic diameter of the curved combustor inlet and the combustor chamber were25300 and 26000, respectively. Four significant changes of the flow features inthe curved combustor inlet occur through insertion of the guide vanes. The firstis the reduction and suppression of the flow reversal region; the separatedflow rergion along the inner wall decreases with increasing guide-vane numberand vanishes through installing three guide vanes. In addition, the criticalReynolds number at which flow separation is absent in the curved combustor inletis found to decrease with increasing product of radius and aspect ratios. Thesecond event is that the turbulence levels are lowered and more isotropic; inmost regions, all three turbulence intensity components, and the turbulentkinetic energy decrease with increasing guide-vane number. The third is asignificant reduction of the velocity differences between the inner and outerwalls and, hence, a more uniform distribution of the velocity ahe passages nearthe exit of the curved combustor inlet. The last is the peak frequency of theradial velocity power spectra is found to increase with increasing product ofradius and aspect have no such a trend. In the dome region of the combustor inlet-jet plane, there is one pair ofcounter-rotating vortices for the no-vane, one-vane, and two-vane cases and twopairs of counter-rotating vortices for the three-vane case, respectively. Thistrend is reversed in the combustor impinging plane. The combustor flowfielddownstream of the Xc*=2.5 station is insensitive to the variation of theguide-vane number arranged in the side-inlet duct. For the combustor withside-inlet guide vanes, it is suggested that more fuel injection positionshould locate adjacent to the upstream side of the side-inlet duct in order tomake more of the side-inlet injected fuel recirculating upstream into the domeregion and increase the fuel residence time in the combustor. The presentedturbulence level, vortex strength in the dome region, pressure loss, andpressure oscillation tend to suggest that the curved combustor inlet with twoguide vanes is beneficial to the successful performance of the combustor. Pulsatile and steady flowfields in a lateral aneurysm model arising from theparent vessel with radius of curvature to vessel diameter ratios of 2.5, 5, andoo are presented in terms of particle tracking velocimetry (PTV) measurementsand flow visualization. The steady-flow case has a Reynolds number of 600 andthe pulsatile-flow one has a Womersley number of 3.9 and Reynolds number of600. The intra-aneurysmal flow velocity, vorticity, and wall shear stressesincrease with increasing curvature of the parent vessel. It is suggested thatthe lateral aneurysm arising from a straight or small-curvature parent vesselhas a tendency to thrombosis whereas the lateral aneurysm arising from alarge-curvature parent vessel is more risky. Although an increase of theWormersley number or Reynolds number does not qualitatively change the flowpattern in the aneurysm sac, it is found that in the circumstance of highheartbeat rate, i.e. , high Wormersley and Reynolds numbers, the aneurysm sacis filled with higher-velocity and -vorticity fluids, and the intra-aneurysmalwall is undergone higher level of wall shear stresses. In addition, the effectof the parent vessel curvature on the flow activity and the wall shearstress is larger than that of the Wormersley and Reynolds numbers, especiallyfor the large curvature case, and the effect of the Reynolds number is theleast among these three effects.