Estimate of Pressure Losses in Steady and Pulsatile Flows through Sudden Expansion and Contraction of Pipes

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  • 拡大管・縮小管を通る定常及び脈動流れにおける圧力損失
  • カクダイカン シュクショウカン オ トオル テイジョウ オヨビ ミャクドウ ナガレ ニ オケル アツリョク ソンシツ

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Steady and unsteady pressure losses in sudden expansion and sudden contraction in pneumatic piping systems are studied. An experimental study for steady state loss coefficients was carried out with pipes having expansion ratios (=pipe diameter ratio) of 1.2, 1.5 and 2.0, and contraction ratios of 5/6, 2/3 and 1/2. The Reynolds number downstream of the sudden cross section changes lies between about 5,000 and 36,000. The difference between the obtained loss coefficient and commonly known data that were obtained with water is about 10%. After steady-state measurement, pressure losses due to the cross-section changes in pulsatile flow are estimated and compared with the experiments. The estimate was made ignoring the compressibility of the fluid, and assuming the same value of loss coefficient as in the steady flow. The experiments were carried out using the same expansion and contraction pipes used in the steady-state experiment. The frequency of the pulsation is 1∼30[Hz]. The mean Reynolds numbers of the pulsatile flows were 12,000∼26,000 and the amplitude Reynolds numbers were about 27% of the corresponding mean Reynolds numbers. Differences between the estimates and the experiments are within 3% with contraction pipes, up to 15% with expansion pipes.

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