급확대-축소 연결부 주변의 원관 난류유동에 관한 실험적 연구

Abstract

The flow structure in a sudden expansion-contraction joint in a pipe is experimentally investigated. The turbulent velocity field is measured by using a single channel LDV system. Mathematical relations between forward-scattered signals from incident beams at three different angles permit measurements of Reynolds stress components, u2, v2 and uv. The static wall pressure distribution in the streamwise direction is also measured by tapping a number of small pressure holes in the expansion-joint wall. The expansion-joint length(L) to step height(H) ratios were L/H=5.45, 10.9 and 16.4. For the cases, L/H=5.45 and 10.9, the flows turn out to have cavity-like flow structure, whereas in the last case, L/H=16.4, the mean flow reattaches at about the distance 10.5 times the difference in radii of two pipes from the sudden expansion, and shortly later re-separates again to reach the exit of the expansion-joint. The profiles of the Reynolds normal stresses, u2 and v2, and the shear stress, -uv, are discussed in details in comparison with those of other axisymmetric sudden expansion flows.