| OCR Text |
Show generator. The swirling flow enters a 400 mm diameter, 4000 mm long cyl i ndrical chamber (Df=400mm), via a sudden expansion. The blockage ratio of the bluff body Db/a, equals to 0.5. The inside diameter of inlet throat, a, equals to 190 mm. The quar1 and furnace confinements are made of transparent plastic and have measuring slot on their side wall. The flow is contracted at the exit of the furnace via a gradual convergent . quarl. The Reynolds number of the air is 5.0x10 4 . Simultaneously axial and azimuthal, mean and fluctuation velocity measurements were made using the 2-dimensional backward-scattering laser-Doppler anemometer (LOA) system show in Fig.2 LOA uses the optical Doppler effect to determine the velocity of the fluid which offers the advantage of calibration-free, nonintrusive velocity measurements. The beam from a 4w Argon-ion laser (Coherent Innova Model 70-4) was passed through a prism to separate the various wavelengths. blue (488 The two most intense beams, green (514 nm) and nm), were polarized and split into two beam of equal intensity 40mm . apart. A 20 MHz frequency shift was applied to one of each pair of beams to detect high turbulence and reverse flow. Four beams were then focused through a 1000 mm lens to a point within the test section. Receiving o~tics consisted of a 500 mm lens focused on to a 1 mm dimeter photomultiplier tube aperature where the light signals are converted to electric signals. These optics were placed by backward scatter which resulted in a probe volume of 0. 022 mm3. Signal validation was obtained using two counter processor (Aerometrics PDP 3200) directly to computer system (Aerometrics Data Management System Model DMS-4000). |
