Tham khảo tài liệu 'turbo machinery dynamics part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | COMBUSTION SYSTEM 343 FIGURE Double concentric burner outlet region Gupta Lewis and Daurer 2000 . Gupta Lewis and Daurer 2000 . A 30 swirler for annulus 1 and 50 and -50 swirlers for annulus 2 are used to investigate flames produced from the change of swirl direction in the annuli. The arrangement with both swirlers having positive angles is referred to as producing coswirl flame while angles of opposite directions have a counterswirl flame. Figure provides a diagram of the burner outlet where the flame stabilization zone occurs and Fig. shows details of the swirling flow field and the regions of a swirl-stabilized premixed flame Marshall 1996 . High-frequency temperature measurements are taken with a microthermocouple probe with a wire diameter small enough not to cause interference on the flame s structure while providing rigidity for the probe. At every location in the flame the signal is amplified and digitized for a sampling time of 30 s to allow averaging over low-frequency temperature measurements and to assure a good statistical representation of the thermal field. Large variations in the temperature are present at any location in the flame. The sampling frequency used is 10 kHz which is high enough to resolve small thermal time scales in the flame. Direct flame photographs taken during the tests provide data about the overall features of the flame and its stability. Negative images of the photographs determine the size of the flame in proportion to the burner. Raw temperature data have to be compensated for radiation losses and thermal inertia effects of the thermocouple. Radiation losses can be significant particularly at high temperatures. Similarly the level of fluctuations obtained without compensating the thermocouple output can be considerable. Fluctuating temperatures are lower by as much as 250 C at some locations in the flame without compensation. Qi Gupta and Lewis 1997 provide a method for making corrections. The compensated mean
