| OCR Text |
Show In a previous paper (Edwards, 1988), we reported results of the macroscopic structure of the flame under various operating conditions. In the present study, a single operating condition has ~en chosen for more detailed study. A key component of the detailed description of this flame 1S knowledge of the velocity field of the flame. The objective of this paper is to provide a coml;>lete description of the gas phase aerodynamics of the flame; a description suitable to, proVIde both physical insight into the flame structure, and quantitative boundary conditions and comparative data for numerical modeling. APPARATUS AND PROCEDURES Research Furnace F aciIity The optical access research furnace used in this study is the same as used in previous work (Edwards, 1988). Figure 1 shows the significant features of the furnace while Table I summarizes the operating conditions of this study. The furnace is octagonal in cross section, providing a compromise between the experimental requirement of planar window surfaces for optical diagnostics and the need to provide a ne~ ru(1symmetric cross section for modeling. It is oriented vertically with the burner at the bottom so that buoyancy forces are aligned with the axis of symmetry, and the products of combustion are carried away from the flame zone. Fuel and atomizing air enter the burner at the bottom and travel through the nozzle support tube to the atomizing nozzle located flush with the furnace entrance plane. The main air supply is introduced into the swirler assembly and flows through the annulus around the nozzle support tube. Angular momentum of the main air supply is varied by introducing it into the swirler assembly through four nozzles with delivery angle variable between radially inward (no swirl) and tangential to the flow (maximum swirl). The atomizer employed in this study is a modified form of the Parker Hannifin Research Simplex-Air (RSA) atomizer producing a hollow cone spray with a nominal included angle of 60-. This nozzle uses swirl in both the atomizing air and fuel streams. Atomizing air swirl is imparted by a 45- vane-type swirler just before the exit of the nozzle. Fuel swirl is imparted by tangential entry upstream of the fuel filming surface. This nozzle was operated at a fixed fuel flowrate of 1.4 g/s (approximately 60 kw heat release) with a mass-based atomizing-air/fuel ratio of one. The total air flow rate to the furnace was chosen so as to deliver 50% excess air to the flame while the main air swirler nozzles were adjusted to provide a swirl number2 of one, measured at the entrance plane of the furnace. Orientation of the main air swirl and atomizing air swirl was the same--counterclockwise when looking down at the nozzle. Laser Doppler Velocimeter The Laser Doppler Velocimeter used in this study was a single component, dual scattering system utilizing a combination of commercial (TSI Inc.) and in-house components. Figure 2 shows the layout of the optical components of the system while Table II summarizes the operating conditions. 2The swirl number reported here is defined as the axial flux of angular momentum divided by the product of the axial flux of axial momentum and the throat radius (see, for example, Gupta et al. 1984). Note that in evaluation of the swirl number for this flow, possible contributions due to correlated velocity fluctuations and pressure gradients have been neglected. - 2- |
