ABSTRACT
The stagnation-point fl ow has been extensively used for stretched fl ame analysis, because the fl ow fi eld is well defi ned and often can be represented by a single parameter, namely the stretch rate. Notable stagnationfl ow confi gurations that have been widely used in premixed combustion experiments include fl ow impinging on a surface or single jet-wall (e.g., Refs. [1,2]), porous burner in uniform fl ow or Tsuji burner (e.g., Refs. [3,4]), opposing jets or counterfl ow (e.g., Refs. [5,6]), tubular fl ows (e.g., Refs. [7-9]), etc. In the single jet-wall geometry, a premixed reactant fl ow from a nozzle impinges on to a fl at stagnation plate. If the premixed fl ame front
is situated suffi ciently far away from the stagnation plate, then the downstream heat loss from the fl ame to the plate has a minimal effect on the fl ame propagation. In the Tsuji burner, a cylindrical or spherical porous body is placed horizontally in a wind tunnel. A premixed reactant mixture is injected out uniformly from the upstream portion of the porous body. The stretch rate in the forward stagnation region is proportional to U/R, where U is the forced fl ow velocity in the tunnel and R is the radius of the cylinder or sphere. Unlike the stagnation-fl ow fi eld produced between the two counterfl owing coaxial jets, in a tubular burner, the inlet fl ow is directed radially, while the exhaust fl ow is axial. The tubular premixed fl ame formed in a tubular fl ow is subjected to the combined effects of fl ame stretch and fl ame curvature; whereas, for the planar fl ame established in the opposed-jet confi guration, the effect of aerodynamic straining on the fl ame response can be studied without complications owing to fl ame curvature. Although the above-mentioned stagnation-point fl ow confi gurations
in the laboratory practice are generally multidimensional in nature owing to the inevitable edge effects, the existence of stagnation-fl ow similarity for most part of the fl amelet, when valid, would greatly facilitate the associated mathematical analysis and computation with detailed chemistry in that the fl ame scalars, such as temperature and species concentrations, can be assumed to depend on only one independent variable.
