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

  • T. Morel

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 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notation

A

projected frontal area

AR

aspect ratio of the slanted surface;width/length

CD

drag coefficient ≡ drag force/(ρ/2 U2A)

CL

lift coefficient ≡ lift force/(ρ/2 U2A)

Cp

pressure coefficient ≡ (p -p)/ρ/2 U2)

Cpb

base-pressure coefficient

D, d

body diameter

Deq

equivalent diameter ≡ \(\sqrt{4\text{ area/}\pi }\)

H, h

height

e

body dimension in the stream direction

LS

length of a slanted surface

p

static pressure

p

free-stream static pressure

ReD

Reynolds number ≡ UD/v

r

radius

SD

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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Copyright information

© Plenum Press, New York 1978

Authors and Affiliations

  • T. Morel
    • 1
  1. 1.General Motors Research LaboratoriesWarrenUSA

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