The effect of sudden expansion and contraction joint in turbulent flow field of a pipe was investigated experimentally. Reynolds number is 73000 at entrance of control volume in wind tunnel. The expansion and contraction joint length is main parameter by which the internal flow field is varied.
The wall pressure distribution, the mean velocity, velocity fluctuation are measured by pressure transducer and LDV system using dual beam mode and forward scattering technique. The length to diameter ratio in this experiment were 1.37, 2.73, 4.11, the former two case were cavity flow and in the last case appeared the reattachment in the joint tube where its length is longer than in backward facing step flow with same expansion ratio resulting from high pressure gradient. When the reattachment arose the seperated bubble just upstream of contraction is relatively very small than downstream bubble of expansion joint. The developing rate of velocity field in joint part is high compared with backward step flow.
