Numerical simulations of laminar pipe and channel flows were carried out: (i) to understand the effect of inlet conditions, viz., flat inlet and streamtube inlet, on entry lengths, and (ii) to investigate the flow development in radial/transverse locations. Results show that hydrodynamic entry lengths from the streamtube inlet simulations are significantly lower compared to the entry lengths from the flat inlet simulations for low Reynolds numbers. Moreover, results from the current study (Newtonian flow with no-slip) as well as the results from the literature (non-Newtonian flow with no-slip) showed that for many flow situations, the slowest development of axial velocity in the transverse location happens to be very near to the wall. For the above cases, the existing entry length criteria (centerline as well as global entry length) are not appropriate to define the entry length. We have proposed a new entry length criterion based on the displacement thickness which is an integral measure of the velocity profile. A new entry length correlation using the displacement thickness criterion is proposed for Newtonian flows in pipe and channel based on simulations with the streamtube inlet condition.
Entry Lengths of Laminar Pipe and Channel Flows
Indian Institute of Space
Science and Technology,
Thiruvananthapuram 695547, India
Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received July 27, 2017; final manuscript received November 12, 2017; published online February 14, 2018. Assoc. Editor: Riccardo Mereu.
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Joshi, Y., and Vinoth, B. R. (February 14, 2018). "Entry Lengths of Laminar Pipe and Channel Flows." ASME. J. Fluids Eng. June 2018; 140(6): 061203. doi: https://doi.org/10.1115/1.4038668
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