The experimental and numerical studies of the boundary layer diffusion flame over a porous plate have been conducted. In order to know the effect of separation on the flow field, flows in the presence and absence of separation region are considered. For these cases, flow visualization, measurements of mean velocity, r.m.s value of velocity fluctuations, species concentration and temperature have been made. The modified Falkner Skan transformation including the effect of chemical reaction have been established. By using this transformation, several; important assumptions used in the other numerical researches have been examined. And also, the detailed structures of local acceleration in the boundary layer diffusion flame have been investigated in the numerical calculation by using the elliptic type governing equations.
The main conclusions are summarized as follows; For the case without separation, the velocity overshoot is clearly observed near the flame zone for all flow conditions. On the while, for the case with separation, the velocity overshoot is observed only at lower free stream velocity and higher fuel injection velocity. The r.m.s. value of velocity fluctuations is significantly decreased by combustion for the case with separation. But for the case without separation, it is increased near the visible flame zone in comparison with cold flow. In both cases, the peak values of r.m.s. of velocity fluctuations appear near the visible flame zone.
The velocity distorsion and velocity overshoot could be explained by the mechanism of local acceleration for the case without separation. Local acceleration is rapidly changed near the starting station of the fuel injection in its role and magnitude, while local acceleration at downstream station acts positive on the fluid so that the velocity overshoot could be seen. For the case with separation, the effect of chemical reaction suppresses the tendency for flow separation. In the case of a lower fuel mass flux, a less active chemical reaction does not overcome the influence of flow separation, therefore separation bubble still exists and velocity overshoot could not be observed. On the other hand, a more active chemical reaction in the case of a higher fuel mass flux changes the pressure distribution as the favorable gradient so that the positive local acceleration makes the velocity overshoot downstream.
