Nozzle Afterbody Research Articles

Inverse Design Method on Scramjet Nozzle with Full Geometrical Constraints for Nozzle–Afterbody Integration

AbstractA design method on scramjet nozzles is proposed to satisfy the requirements of nozzle positions and geometrical constraints. The proposed method adopts the inverse design concept and maximu...

Civil turbofan engine exhaust aerodynamics: Impact of bypass nozzle after-body design

It is envisaged that the next generation of civil large turbofan engines will be designed for greater bypass ratios when compared to contemporary architectures. The underlying motivation is to reduce specific thrust and improve propulsive efficiency. Concurrently, the aerodynamic performance of the exhaust system is anticipated to play a key role in the success of future engine architectures. The transonic flow topology downstream of the bypass nozzle can be significantly influenced by the after-body geometry. This behavior is further complicated by the existence of the air-flow vent on the nozzle after-body which can have an impact on the performance of the exhaust system. This paper aims to investigate the aerodynamics associated with the geometry of the bypass nozzle after-body and to establish guidelines for the design of separate-jet exhausts with respect to future large turbofan engines. A parametric geometry definition has been derived based on Class-Shape Transformation (CST) functions for the representation of post-nozzle-exit components such as after-bodies, plugs, and air-flow vents. The developed method has been coupled with an automatic mesh generation and a Reynolds Averaged Navier–Stokes (RANS) flow solution method, thus devising an integrated aerodynamic design tool. A cost-effective optimization strategy has been implemented consisting of methods for Design Space Exploration (DSE), Response Surface Modeling (RSM), and Genetic Algorithms (GAs).The combined approach has been deployed to explore the aerodynamic design space associated with the bypass nozzle after-body geometry for a Very High Bypass Ratio (VHBR) turbofan engine with separate-jet exhausts. A detailed investigation has been carried out to expose the transonic flow mechanisms associated with the effect of after-body curvature combined with the impact of the air-flow vent. A set of optimum curved after-body geometries has been obtained, with each subsequently compared against their respective conical representation. The obtained results suggest that no significant performance improvements can be obtained through curving the nozzle after-body relative to the case of a conical design. However, it is shown that the application of surface curvature has the potential to unlock new parts in the design space that allow analysts to reduce the required after-body length without any loss in aerodynamic performance. The developed approach complements the existing tool-set of enabling technologies for the design and optimization of future large aero-engines, consequently leading to increased thrust and reduced Specific Fuel Consumption (SFC).

Applications of Algebraic Reynolds Stress Turbulence Models Part 2: Transonic Shock-Separated Afterbody

The ability of the three-dimensional Navier – Stokes method PAB3D code to simulate the effect of Reynolds number variation using nonlinear explicit algebraic Reynolds stress turbulence modeling was assessed. Surface pressure coefŽ cient distributions and integrated drag predictions on an axisymmetric nozzle afterbody were compared with experimental data at Reynolds numbers from 10 to 130 3 10. There was generally good agreement of surface static pressure coefŽ cients between the computational  uid dynamics (CFD) and measurement. The change in pressure coefŽ cient distributions with varying Reynolds number was similar to the experimental data trends, though the CFD slightly overpredicted the effect. The computational sensitivity of viscous modeling and turbulence modeling are shown. Integrated afterbody pressure drag was typically slightly lower than the experimental data. The change in afterbody pressure drag with Reynolds number was small, both experimentally and computationally, even though the shape of the distribution was somewhat modiŽ ed with the Reynolds number.

Axisymmetric afterbody experiments for CFD validation

SummaryAn experiment is described which was undertaken specifically to provide CFD validation data for the case of transonic flow over nozzle afterbodies. The tests were undertaken with the AGARD standard 10° and 15° axisymmetric boat-tail geometries. Onset Mach numbers in the range 0·80-0·99 and subsonic and under-expanded jet plumes were employed in the tests. Test conditions were selected which provided a range of afterbody flow features from largely attached to shock-induced separated flows. A uniquely detailed set of surface pressure and flowfield data are presented. The flow data were acquired with a two-component laser Doppler anemometer (LDA) and define the mean and fluctuating flow components at about 500 spatial locations for each of these complex transonic flowfields. Additional information was recorded which fully defines the required computational boundary conditions.Also presented is a detailed study of the necessary attributes of windtunnel CFD validation data. It is demonstrated that relatively high blockage experiments using cost-effective windtunnels can be used to generate CFD validation data if proper account is taken of the model/tunnel interference.

Comparison of computational and experimental jet effects

Computations were made for transonic flow over a nozzle afterbody with a real plume. The effects of parameters such as nozzle pressure ratio, plume stagnation temperature, and interior nozzle shape on afterbody drag were quantified and compared with available experimental data. Remarkable agreement between the computational and experimental results is demonstrated, including the drag minimum associated with low nozzle pressure ratios and the absolute dependence of drag on temperature. The computer program used for the calculations is an axisymmetric modification of Deiwert's planar Navier-Stokes program and utilizes a mixed explicit-implicit MacCormack algorithm with an algebraic turbulence model.

Calculation of Separated Turbulent Flows on Axisymmetric Afterbodies Including Exhaust Plume Effects

A calculative method is presented for turbulent boundary-layer, inviscid flow interactions for axisymmetric configurations of the type used for isolated nozzle afterbody models. The method is applicable to flows with subsonic freestreams, including slightly supercritical flows, and to bodies with high-pressure exhaust plumes or solid plume simulators. Integral boundary-layer and plume entrainment methods are coupled iteratively with a finite-difference inviscid flow method through a boundary-layer plume displacement thickness. Results are presented which indicate that the procedure provides an accurate engineering prediction method for boattail flowfield with moderately underexpanded exhaust flows and for bodies with solid plume simulators.

Measurement of drag from interaction of jet exhaust and airframe.

An investigation was undertaken with a wind-tunnel model specifically designed to measure the drag arising from the interaction of jet exhaust and the surrounding airframe. Three basic nozzle configurations were tested at Mach numbers ranging from 0.60 to 2.48. A onecomponent axial force balance measured the nozzle afterbody drag. A second one-component balance measured the nozzle thrust minus afterbody drag. This balance was bridged with two air supply lines through a bellows system, which minimized the bridging effects. The model was strut-mounted through the side walls of the transonic and supersonic test sections in the McDonnell Polysonic Wind Tunnel. Cold air, piped into the model through the two strut supports, was used for the jet simulation. Test results were very satisfactory with excellent repeatability and permitted valid configuration comparison.