Effect of Wall Shape and Real Gas Properties on Dual Bell Nozzle Flowfields

Dual bell nozzle permits two different operating modes, which provide higher performance than conventional bell nozzles, when applied to rocket engines operating from sealevel. During the highly overexpanded mode the separation line is located near the geometrical discontinuity of the nozzle wall, in a region characterized by a negative value of the wall pressure gradient as in conventional nozzle and where side loads may occur. The characteristics of this region in hot full-scale applications are addressed by means of numerical simulations, and scaling laws are sought for cold sub-scale side loads experiments. In addition, because of the possible effect of wall cooling on the wall pressure gradient and thus on side loads, the relevant role of film cooling is discussed in detail