Abstract

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INVERSE DESIGN OF NACELLES USING MULTI-BLOCK NAVIER STOKES

CODES

D. A. Naik

ViGYAN, Inc., Hampton, Virginia 23666

S. E. Krist, R. L. Campbell, and V. N. Vatsa

NASA Langley Research Center, Hampton, Virginia 23681

P. G. Buning

NASA Ames Research Center, Moffett Field, California 94035

and

L. M. Gea

McDonnell Douglas Aerospace, Long Beach, California 90810

Abstract

The objective of this work is to reshape a nacelle to achieve a specified nacelle pressure distribution.

The nacelle may be either isolated or installed on an airplane. There are no restrictions on the attitude

(toe, incidence, and roll) and position of the nacelle. The design algorithm is coupled to two different

multi-block 3-D Navier Stokes flow solvers. The coupling between design and analysis is automated to

the point where the design proceeds with minimal user input.

Nomenclature

C - Local nacelle or wing chord.

CDISC - Constrained DISC.

Cp - Coefficient of pressure.

DISC - Direct Iteration Surface Curvature.

O(..) - Order of magnitude.

R - Local nacelle radius.

X - Streamwise coordinate.

theta - Angle running from the nacelle crown through the keel (outboard side) and back up to the crown

(inboard side).

Introduction

Given the harsh reality of placing capital intensive products in the modern marketplace, it is an ongoing

quest to improve the operational efficiency and cost effectiveness of any commercial airplane. The

emergence of the current generation of large turbofans, in the 80,000 to 100,000 pound thrust class,

presents anew the opportunity to optimize or reduce the drag associated with the outer surface of the

engine nacelle. These large nacelles could account for a good portion of airplane drag.

The problem of external cowl design may be broadly placed in two separate, yet complementary

categories: (1) the design of an isolated cowl immersed in a uniform flow; and, (2) the design of an

installed cowl with the attendant non-uniform flow. The former should enable the designer to derive a

cowl geometry starting from a fairly rudimentary first guess. The resulting design will be inherently

symmetrical about the vertical plane, thus allowing for a universal nacelle that can be installed on either

side of the airplane. On the other hand, the inverse design of an installed nacelle will always result in a

nacelle that is non-symmetric about the vertical plane, unless the designer can invoke special options to

force symmetry.