Pulsatility role in cylinder flow dynamics at low Reynolds number

• Published in: Physics of fluids (1994) Vol. 24; no. 8
• Main Authors: QAMAR, Adnan, SAMTANEY, Ravi, BULL, Joseph L
• Format: Journal Article
• Language: English
• Published: Melville, NY American Institute of Physics 01.08.2012
• Subjects: Anesthesia. Intensive care medicine. Transfusions. Cell therapy and gene therapy; Biological and medical sciences; Collapse; Cylinders; Dynamics; Emergency and intensive respiratory care; Fluid dynamics; Fluid flow; Fluids; Intensive care medicine; Medical sciences; Separation; Vortices; Numerical simulation; Low Reynolds number; Artificial lung; Modeling; Respiratory support; Pulsating flow
• ISSN: 1070-6631; 1089-7666
• DOI: 10.1063/1.4740504

We present dynamics of pulsatile flow past a stationary cylinder characterized by three non-dimensional parameters: the Reynolds number (Re), non-dimensional amplitude (A) of the pulsatile flow velocity, and Keulegan-Carpenter number (KC = Uo/D omega c). This work is motivated by the development of total artificial lungs (TAL) device, which is envisioned to provide ambulatory support to patients. Results are presented for 0.2 less than or equal to A less than or equal to 0.6 and 0.57 less than or equal to KC less than or equal to 2 at Re = 5 and 10, which correspond to the operating range of TAL. Two distinct fluid regimes are identified. In both regimes, the size of the separated zone is much greater than the uniform flow case, the onset of separation is function of KC, and the separation vortex collapses rapidly during the last fraction of the pulsatile cycle. The vortex size is independent of KC, but with an exponential dependency on A. In regime I, the separation point remains attached to the cylinder surface. In regime II, the separation point migrates upstream of the cylinder. Two distinct vortex collapse mechanisms are observed. For A < 0.4 and all KC and Re values, collapse occurs on the cylinder surface, whereas for A > 0.4 the separation vortex detaches from the cylinder surface and collapses at a certain distance downstream of the cylinder. The average drag coefficient is found to be independent of A and KC, and depends only on Re. However, for A > 0.4, for a fraction of the pulsatile cycle, the instantaneous drag coefficient is negative indicating a thrust production.