# The Effect of Base Slant on the Flow Pattern and Drag of Three-Dimensional Bodies with Blunt Ends

## Abstract

The paper describes an experimental investigation concerning the effects of slanting the blunt base of three-dimensional bodies having either an axisymmetric or a rectangular cross section. It was found that base slant can have a very dramatic effect on body drag, particularly in a relatively narrow range of slant angles where the drag coefficient exhibits a large local maximum (overshoot).

Detailed study of the flow showed that the drag maximum is related to the existence of two very different separation patterns at the rear of either body. One pattern is similar to that found behind axisymmetric bodies with no base slant, and its main feature is the presence of a closed separation region adjacent to the base. The other pattern is highly three-dimensional with two streamwise vortices approximately parallel to the slanted surface, one at each side of the body. The drag coefficient maximum occurs in the slant-angle range where a changeover from one flow pattern to the other takes place. The observed phenomenon may be thought of as being associated with a broader category of “critical geometries,” which is tentatively defined and discussed.

## Keywords

Critical Angle Strouhal Number Lift Coefficient Streamwise Vortex Side Edge## Notation

- A
projected frontal area

- AR
aspect ratio of the slanted surface;width/length

- C
_{D} drag coefficient ≡ drag force/(ρ/2 U

^{2}A)- C
_{L} lift coefficient ≡ lift force/(ρ/2 U

^{2}A)- C
_{p} pressure coefficient ≡ (p -p

_{∞})/*ρ/*2 U^{2})- C
_{pb} base-pressure coefficient

- D, d
body diameter

- D
_{eq} equivalent diameter ≡ \(\sqrt{4\text{ area/}\pi }\)

- H, h
height

- e
body dimension in the stream direction

- L
_{S} length of a slanted surface

- p
static pressure

- p
_{∞} free-stream static pressure

- Re
_{D} Reynolds number ≡ UD/

*v*- r
radius

- S
_{D} Strouhal number ≡ fD/U

- t
thickness

- U
free-stream velocity u′ rms turbulence intensity

- u′
width

- W
streamwise coordinate

- α
angle of inclination of a slanted base away from the normal to the stream direction

*v*kinematic viscosity

*ρ*density

*θ*momentum thickness

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## References

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