VENTILATED FLOW BETWEEN COROTATING DISKS WITH LARGE OBSTRUCTIONS IN AFIXED CYLINDRICAL ENCLOSURE

Time-resolved laser-Doppler velocimeter measurements of the circumfere ntial velocity component were obtained for the flow between the center pair of four disks of common radius R(2) corotating at angular veloci ty hi in a fixed, cylindrical enclosure. Mean and rms profiles of this velocity component were obtained for two disk rotation speeds (300 an d 3600 rpm), two relatively thick tapered obstructions (long and short ) placed radially inward midway between each pair of disks, and three ventilation conditions (unventilated, blowing, and sucking) resulting from an imposed inter-disk radial throughflow. The profiles were deter mined at four circumferential locations downstream of the respective o bstructions; radially along the midplane, and axially at selected radi al locations. The profiles for the unventilated flow case show that th e circumferential component of motion significantly accelerates near t he hub, in the region between the tip of the obstruction and the rotat ing hub. Elsewhere, this component of motion is significantly decelera ted. The presence of ventilation, whether directed radially outward or inward, significantly affects the flow field only in the region immed iately around the hub, and far downstream of the obstruction where it increases both the mean and rms velocities. Analysis of the time recor ds suggests that the observed increases in the rms values are due to t he circumferentially periodic nature of the radial ventilation conditi on. These observations are, for the most part, independent of the disk speed of rotation and the length of the obstructions. A comparison of present unventilated flow results with the corresponding results of U sry et al. (1993), who used much thinner obstructions, reveals the ext ent to which increasing the obstruction blockage ratio induces larger levels of flow unsteadiness.