Transient Behavior of Wake Length around a Decelerated Cylinder.

Abstract

Flows around a decelerated circular cylinder are studied with BFC-MAC scheme for a moving frame of reference. The main results are given for Reynolds number lower than Re=36.5 as in the previous experimental measurements. Typical behaviors of wake length are predicted at a range of deceleration as in the experiment. That is, histories of wake-length: S, if they are plotted against instantaneous Reynolds number, are almost similar for relatively large deceleration α. Such 'Similarity' with respect to α is attempted to be interpreted with a model equation based on approximate estimation of arrival time of the wake-end. In contrast at small deceleration the transient variation of wake-length depends upon α. The mechanisms are discussed such as the fact that the smaller deceleration parameters, the larger delay in elongation of wake length. For large deceleration the proposed model equation, which utilizes the BFC-MAC results on the rear symmetry line at an arbitrary couple of time-steps, successfully illuatrates wake-length history versus instantaneous Reynolds number from start to termination of deceleraton.