A method utilizing circular arcs to generate the divergence contour in a supersonic nozzle is presented. Comparison of the arc-based geometry with existing contours demonstrated that an average reduction in length of 7.5% can be expected when the arcbased design is applied to a core stage nozzle. Two arc-based and conventional nozzles were evaluated numerically across the entire range of pressure operating conditions to compare calculated thrust and flow parameters with existing data. The thrust coefficient and flow behavior in the arc-based design was equivalent to the conventional nozzle at all conditions tested. The result indicates that a reduction in nozzle length independent of calculated thrust can be achieved when the arc-based method is applied to high area nozzle contour design. NomenclatureTurbulent kinetic energy (m 2 s -2 ) L = Nozzle contour length (m) Ma = Mach number P = Static pressure (Pa) r = Radius (m) x = Horizontal distance (m) y = Vertical distance (m) ε = Turbulent dissipation rate (m 2 s -3 ) θ = Angle (°) ω = Specific dissipation rate (s -1 ) Subscripts 0 = Stagnation condition 1 = Inflection point, conventional contour 2 = End point, conventional contour C = Coarse mesh c = Conical nozzle e = Nozzle exit F = Fine mesh i = Arbitrary contour point i j = Arbitrary contour point j m = Inflection point, simplified contour n = End point, simplified contour S = Standard mesh t = Nozzle throat 1 PhD Candidate, kyll.schomberg@unsw.edu.au, Student Member AIAA. 2 Lecturer, Member AIAA. 3 Lecturer. Downloaded by UNIVERSITY OF NEW SOUTH WALES on August 13, 2015 | http://arc.aiaa.org |

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The effect of nozzle geometry on the thrust efficiency of the linear expansion-deflection (ED) nozzle concept has been investigated at highly overexpanded flow conditions. A new design method for generation of the ED nozzle contour is introduced and a factorial-based approach used to determine the effect of nozzle geometry on thrust coefficient. An area ratio of 17.6 was selected to represent a core stage nozzle and eight geometric parameters compared across sixteen separate configurations. Thrust coefficient was determined numerically from a time-dependent model using dry air as the working fluid. The numerical model was verified with respect to viscous effects and dimensional grid parameters, and then validated against experimental results to quantify sources of numerical error. Results were obtained for pressure ratios ranging from 5-50 to replicate highly overexpanded conditions where flow separation would occur in an equivalent conventional nozzle. Thrust coefficient in all ED nozzle configurations relative to the conventional nozzle ranged between 105-190% at low pressures and 90-120% at high pressures. The conclusions from the factorial analysis of ED nozzle contour geometry suggested that low curve radii and high inflection angles would further improve thrust coefficient for the flow conditions tested. The results show that an improvement in thrust relative to a conventional design can be expected at highly overexpanded flow conditions through the use of an ED nozzle configuration. NomenclatureA = Area (m 2 ) R = Specific gas constant (kJkg -1 K -1 ) C = Contraction ratio r = Radius (m) C F = Thrust coefficient v = Velocity (ms -1 ) C F,% = Thrust efficiency x = Longitudinal direction (m) G t = Throat gap (m) y = Lateral direction (m) ̇ = Mass flow rate (kgs -1 ) γ = Ratio of specific heats P = Static pressure (Pa) θ = Wall angle (°) Subscripts 0 = Stagnation conditions e = Pintle contour point e a = Pintle contour point a i = Arbitrary contour point i amb = Local ambient conditions j = Arbitrary contour point j b = Pintle contour point b m = Nozzle contour point m c = Pintle contour point c n = Nozzle contour point n d = Pintle contour point d t = Throat region 1 PhD Candidate, kyll.schomberg@unsw.edu.au, Student Member AIAA.

An experimental and numerical analysis of a low-angle annular expander nozzle is presented to observe the variance in shock structure within the flow field. A RANS-based axisymmetric numerical model was used to evaluate flow characteristics and the model validated using experimental pressure readings and schlieren images. Results were compared with an equivalent converging-diverging nozzle to determine the capability of the wake region in varying the effective area of a low-angle design. Comparison of schlieren images confirmed that shock closure occurred in the expander nozzle, prohibiting the wake region from affecting the area ratio. The findings show that a low angle of deflection is inherently unable to influence the effective area of an annular supersonic nozzle design.

A computational analysis of an annular converging-diverging (CD) and an altitude adaptive expansion-deflection (ED) nozzle is presented. Numerical results were generated using a 2D axisymmetric, pressure-coupled solver in conjunction with the Spalart-Allmaras turbulence closure model and second order spatial discretisation schemes. Results were recorded over a theoretical altitude range and compared to experimental static pressure readings and schlieren images. The correlation between numerical and experimental static pressure values was high for all cases. Comparison of schlieren imagery outlined the large variety of flow regions within the ED nozzle flow field. The interactions between these regions were highly sensitive to turbulence and reinforced that conventional inviscid analytical techniques are unable to accurately describe behaviour within the ED nozzle flow field. The results highlight the salient effect of viscous effects within the ED nozzle flow field and justify a continued approach utilising computational fluid dynamics to increase understanding of the ED nozzle concept.