UNSTEADY ENTRANCE FLOW DEVELOPMENT IN A STRAIGHT TUBE

The entrance conditions for pulsatile flow are important in the unders tanding blood flow out of the heart and in developing regions at branc hes. The pulsatile entrance flow was solved using a spectral element s imulation of the full unsteady Navier-Stokes equations. A mean Reynold s number of 200 and a range of Womersley parameters from 1.8 to 12.5 w as used for a sinusoidal inlet flow waveform 1 + sin (omega ($) over b ar). Variations in the entrance length were observed during the pulsat ile cycle. The amplitude of the entrance length variation decreased wi th an increase in the Womersley parameter. The phase lag between the e ntrance length and the inlet flow waveform increased for Womersley par ameter alpha up to 5. 0 and decreased for alpha larger than 5.0. For l ow alpha, the maximum entrance length during pulsatile flow was approx imately the same as the steady entrance length for the peak flow. For high alpha, the pulsatile entrance length was more uniform during the cycle and fended to the entrance length for the mean flow. The wall sh ear rate reached its far downstream value after only about half of the entrance length and also exhibited a dependence on alpha. The results quantify the entrance conditions typically encountered in studies of the arterial system.