Pipe Inlays to Shorten the Development Lengths of Laminar Pipe Flows: A Numerical Study

Experimental investigations of fully developed laminar pipe flows, at very high Reynolds numbers and diameters of about 30 mm and more, are nowadays considerably hampered by requirements of long pipe lengths to reach the fully developed states of the flows. The literature shows this for flow cases with constant inlet velocity profiles and the present paper refers to this work. The authors´ own numerical predictions show, that the states of fully developed pipe flows can be reached, at much shorter development lengths, by modifying the inlet velocity profiles. Numerical computations are presented to prove this finding. Knowledge is extracted from these computations, to construct practically realizable inlays for the inlet regions of pipes. Two- and three-dimensional numerical computations are performed to show that appropriately chosen inlays allow development lengths of laminar pipe flows to be considerably shortened. Suggestions are made to use such inlays to carry out experimental investigations of fully developed pipe flows at high Reynolds numbers and larger pipe diameters, without the need to use long pipes. These studies show that, with such inlays, the required pipe lengths can be shortened by factors of over 200 in comparison with development lengths obtained for constant inlet velocities.