A number of different proven nozzle configurations are available today. This section describes their geometries and performance. Other chapters (6, 8, 11, 14, and 16) discuss their materials, heat transfer, or application, and mention their requirements, design, construction, and thrust vector control. Nozzles and chambers are usually of circular cross section and have a converging section, a throat at the narrowest location (minimum cross section), and a diverging section. Nozzles can be seen in Figs. \-<\, 1-5, 1-8, 2-1, 3-11 to 313, 3-15, 10-2 to 10-5, 10-16, 11-1 to 11-3, and 14-6 to 14-8. Refs. 3-5 and 3-8 describe many nozzle configurations.
The converging nozzle section between the chamber and the nozzle throat has never been critical in achieving high performance. The subsonic flow in this section can easily be turned at very low pressure drop and any radius, cone angle, wall contour curve, or nozzle inlet shape is satisfactory. A few small attitude control thrust chambers have had their nozzle at 90 degrees from the combustion chamber axis without any performance loss. The throat contour also is not very critical to performance, and any radius or other curve is usually acceptable. The pressure gradients are high in these two regions and the flow will adhere to the walls. The principal difference in the different nozzle configurations is found in the diverging supersonic-flow section, as described below. The wall surface throughout the nozzle should be smooth and shiny to minimize friction, radiation absorption, and convective heat transfer due to surface roughness. Gaps, holes, sharp edges, or protrusions must be avoided.
Six different nozzle configurations are shown in Fig. 3-12 and each will be discussed. The first three sketches show conical and bell-shaped nozzles. The other three have a center body inside the nozzle and have excellent altitude compensation. Although these last three have been ground tested, to date none of them has flown in a space launch vehicle. The lengths of several nozzle types are compared in Fig. 3-13. The objectives of a good nozzle configuration are to obtain the highest practical Is, minimize inert nozzle mass, and conserve length
Contoured or bell-full length
Contoured or bell shape, shortened
Plug or aerosplke full length
Plug or aerospike, truncated or cut off
Flow with underexpanslon at altitude
^ Diffused boundaries with air
Flow with overexpansion (sea level)
Jets contract outside nozzle
Jets contract outside nozzle
Mass flow distribution at exit or tip
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