An integrated approach to expansion deflection nozzle analysis
Expansion Deflection (ED) nozzles have long been considered as an alternative to conventional
bell and conical designs. The ED nozzle has two primary benefits over such nozzle
configurations, being shorter, and with the potential for altitude compensation. However,
the difficulties involved with modelling the complex flow interactions within the nozzle type
have thus far prevented the creation of a reliable method for its design and analysis.
The work presented within this dissertation makes use of a combination of several different
approaches to flow solution to provide a more complete analysis than previously
achieved. The primary advance is the use of a CFD scheme to analyse the transonic throat
region, the results of which are used as input to a Method of Characteristics based algorithm
for the solution of the inviscid supersonic flow-field. This method is both efficient, and
allows contour optimisation through the calculus of variations. The viscous flow region is
treated in a partially or fully empirical manner, depending upon ambient pressure.
The results of this analysis reveal several previously unidentified flow-field behaviours
and design parameter interactions. Careful selection of the variables used to define the throat
region is shown to be of considerable importance, as they effect not just the thrust produced,
but also whether a real flow through such a nozzle may' exist. Secondly, the high probability
of shock wave formation and interaction with the nozzle wall within length optimised ED
nozzles is demonstrated. This has consequences for both the design and analysis of the ED
Overall, a framework is established which allows the flow behaviour and performance
characteristics of the nozzle type to be estimated in greater detail than previously possible.
The performance increments demonstrated over conventional bell nozzles include an approximately
25 to 50 percent length reduction for nozzles designed for solely high altitude
operation, and a similar reduction in length plus a noticeable increase in low altitude thrust
for trans-atmospheric nozzles. However, before application of the ED nozzle concept to a
real system becomes possible, several areas of uncertainty must be addressed, and these are
highlighted at the end of this dissertation.