Outflow velocity variation from the filter surface with longitudinal position of the filter l0 was measured using a hotwire
velocimeter. The measurements were conducted for filter I with the S-85 core panel at l0¼0.3 m, 0.8 m, and 1.3 m.
In each region, outflow velocities were measured at thirty points within 710 cm in the longitudinal and 75 cm in the
circumferential direction every 1 cm (see Fig. 21(a)). The measurement results are presented in Fig. 21(b). As shown in the
figure, the flow velocity was almost the same in the both circumferential and the longitudinal directions at each measured
region, and the outflow velocity increased with increases in l0; this suggested that the outflow volume from the filter
surface was larger in the tip region of the filter.