Hydrodynamical instability of newtonian flow of downstream on axisymmetric sudden contraction

Abstract

Measures to reduce energy losses in pipeline transport systems must be implemented already at the design stage. In particular, this also applies to local resistances of pipelines. In the paper, the separation length and separation height downstream of the contraction plane of axisymmetric sudden contraction of the circular pipe of a single-phase Newtonian flow have been investigated. Area ratios 0.250 and 0.321 were considered. After all, measures to reduce energy losses on the axisymmetric sudden contraction must be effective at values of the area ratio not less than 0.250. The separation length and separation height have the extreme dependence with a maximum at the transition of the laminar flow into a turbulent flow one. When the values of the Reynolds number at the laminar flow increase, these sizes increase, and they decrease at the turbulent flow. In the first case, the separation point is shifted downstream from the plane of contraction. The separation length and separation height are proportional to the Reynolds number. This is similar to changing the separation length and separation height of upstream from the plane of contraction. A transition zone be located between 9650 and 40000 and 1200 and 5000 if the Reynolds number is based on smaller pipe diameter and step height correspondingly. The separation length of downstream of the contraction plane are decreased if these sizes are length - smaller pipe diameter ratio, and increase if these sizes are length - step height ratio. The changing of separation height is similar. But the change of the separation length is greater than the change of separation height. There is enough good agreement between the experimental results and the results described in the literature. For taking measures providing decrease in energy losses, the investigation of the separation length and separation height downstream of the contraction plane at different values of area ratio being more than 0.250 is proposed.