Drag ratio spheroids

Ol). Results for thin disks are obtained in the limit as 0. Approximate relationships, obtained by treating the spheroid as a slightly deformed sphere (H3, SI), are also given. The drag ratio may conveniently be expressed as the ratio of the resistance of the spheroid to that of the sphere with the same equatorial radius a ... 

Fig. 4.3 Drag ratios for spheroids in axisymmetric flow. Drag ratio — Exact —- Approximate ------Drag Component (1) Friction (2) Form.

Fig. 4.5 Drag ratios for spheroids compared to volume-equivalent spheres.

Analytic results for cylinders comparable to those discussed for spheroids are not available. However, Heiss and Coull (H4) reported accurate experimental determinations for cylinders, spheroids, and rectangular parallelepipeds, and developed a general correlation for settling factors. In terms of the volume drag ratio,, their results may be written ... 

Fig. 6.5 Ratio of skin friction to form drag for spheroids in axial flow. Numerical predictions of Masliyah (M4).

Figure 4.5 shows the variation of A with E for flow parallel and normal to the axis, and averaged over random orientations. Except for disk-like particles, the dependence of A on aspect ratio is rather weak. In axial motion, a somewhat prolate spheroid experiences less drag than the volume-equivalent sphere A passes through a minimum of 0.9555 for E = 1.955. For motion normal to the axis of symmetry, A 2 takes a minimum of 0.9883 at = 0.702. However, the average resistance A is a minimum for a sphere. 

Fig. 6.6 Ratio of drag on oblate spheroid or disk to drag on sphere of same equatorial radius.

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