No abstract

Numerical calculations on the pipe flow with wall blowing was conducted using LES methodology to capture the intrinsic changes of axial small-scale vortices and radial fluctuating motions near the flow surface upon the insertion of diaphragm. The special attentions were devoted to the relation between the flow characteristics of variant turbulent vortices over the diaphragm and the analysis of combustion characteristics by introducing 'Reynolds analogy' theory. Numerical results as well as streak line analysis showed that large-scale vortex over a diaphragm interfered with the existing vortices near the surface. The growth of the small-scale vortices was suppressed until large-scale vortex shed in the downstream pseudo-periodically. In addition, POD (Proper Orthogonal Decomposition) analysis revealed that inserting a diaphragm decreased the energy content in the primary flow mode, and reallocated flow energy in the lower modes 2-5. The increase of flow energy in the lower modes 2-5 was found to be directly associated with the experimentally observed local increase in regression rate after a diaphragm. Finally, the estimation of skin friction coefficient in the flow with a diaphragm showed a very good qualitative agreement with the axial profile of regression rate obtained both by numerical and experimental studies.