in a relatively simpler establishment of geometrical dimensions. However, it is not simple engineering at elevated temperatures and for suppressing noise levels.

The nozzle exit plane is at the end of the engine. Its length from the turbine exit plane is 0.8 to 1.5 times the fan-face diameter. The nozzle-exit-area diameter is roughly half to three fourths of the intake-throat diameter in this study.

10.9.3 Coursework Example of Civil Aircraft Nacelle Design

For coursework on the Bizjet, the following factors are taken from the turbofan class and type:

Uninstalled TSLS = 15.6 kn (3,500 lb)

Bare engine length = 1.547 m (5.07 ft)

Maximum diameter = 1.074 m (3.52 ft)

Engine airmass flow at takeoff = 66.2 kg/s (146 lb/s)

Engine airmass flow at maximum cruise rating ≈ 20 kg/s (44 lb/s)

BPR = 4

Fan-face diameter = 0.716 m (2.35 ft)

This results in the following nacelle dimensions (factors are from industrial experience).

Intake Geometry (see Section 10.8.1)

Highlight diameter = 0.9 × 0.716 m = 0.644 m (2.11 ft)

Throat diameter (use the contraction ratio 1.12) = 0.575 m (1.89 ft), ATH = 0.26 m2 (2.8 ft2)

Check air velocity at the throat for the maximum cruise condition at Mach 0.74

(716 ft/s) and at 41,000-ft altitude (p∞ = 17,874 N/m2, T∞ = 216.65 K, and ρ∞ = 0.284 kg/m3)

Therefore, VTH = 20/(0.284 × 0.26) = 270 m/s (689 ft/s); i.e., Mach 0.922 is a preferred number

This could result in low diffuser length: Ldiff = 0.65 × Dfan = 0.65 × 0.716 = 0.465 m (1.5 ft)

Lip Section (Crown Cut)

Use (b + d) = 0.18 × Ldiff = 0.18 × 0.465 = 0.0837 m (0.275 ft)

Use b = 1.4 × d; this results in b = 0.05 m (0.164 ft) and d = 0.0337 m (0.11 ft)

Use a lower-lip fineness ratio of a/b = 2; this gives a = 0.1 m (0.328 ft)

Use an upper-lip fineness ratio of c/d = 4; this gives c = 0.134 m (0.44 ft)

The intake length from the highlight (low-speed aircraft) = 0.465 + 0.1 = 0.565 m (1.85 ft)

The LFB is about 1 m from the highlight, which is 1.4 times Dfan = 1.4 × 0.716 = 1 m (3.28 ft)

The crown-cut radius at LFB is 1.15 times Rfan = 1.1 × 0.716/2 = 0.41 m (1.34 ft)

Lip Section (Keel Cut)

This book keeps the internal contour of the intake circular to fit with the rotating circular fan face; even the constrained Boeing 737 with a flat keel section must be circular at the fan face. Therefore, the internal contour of the keel cut is the mirror