The presence of numerical noise in engineering design optimisation problems inhibits the use of many gradient-based optimisation methods. This numerical noise may result in the inaccurate calculation of gradients which in turn slows or prevents convergence during optimisation, or it may promote convergence to spurious local optima. The problems created by numerical noise are particularly acute in aircraft design applications where a single aerodynamic or structural analysis of a realistic aircraft configuration may require tens of CPU hours on a supercomputer. The computational expense of the analyses coupled with the convergence difficulties created by numerical noise are significant obstacles to performing aircraft multidisciplinary design optimisation. To address these issues, a procedure has been developed to create noise-free algebraic models of subsonic and supersonic aerodynamic performance quantities, for use in the optimisation of high-speed civil transport (HSCT) aircraft configurations. This procedure employs methods from statistical design of experiments theory and response surface modelling to create the noise-free algebraic models. Results from a sample HSCT design problem involving ten variables are presented to demonstrate the utility of this method.

Windtunnels are generally used for testing models of solid, aerodynamic objects, such as aircraft. The test articles are generally manufactured to have a representative external profile but provide sufficient strength to survive the harsh windtunnel environment without damage to the test article or tunnel. It is somewhat unusual, however, to test lightweight, high drag, fabric models (i.e. parachutes) in supersonic flow.

This paper describes the testing carried out on the parachutes for the Huygens probe, the techniques developed for the testing and the lessons learned.

Tests were carried out to characterise the drag coefficient of the parachute designs throughout the Mach range of 0.05 to 1.5, and the stability coefficients at incidences of up to 15° at low Mach numbers.

The unsteady flowfield in a twin side-by-side intake arrangement arising as a result of a surge in one of the engines has been studied numerically by solving the Euler equations. Unsteadiness was introduced by prescribing a pressure disturbance at the exit plane of one of the intakes. The two cases considered correspond to static ground-running of the engines and a flight Mach number of 0.6 with a single rapidly increasing exit plane pressure disturbance representative of a pop surge. The amplitude of the imposed pressure disturbance varied between 100% and 200% of the mean exit static pressure. In the cases considered, the results indicate that static pressure attenuation of the propagating hammer shock occurs upstream of the intake entry plane, resulting in a relatively weak rarefaction wave travelling down the adjacent intake. No evidence of increased dynamic flow distortion likely to lead to a complementary surge in the adjacent engine was observed. These conclusions have been confirmed by available test data thus demonstrating the value of CFD techniques for modelling complex unsteady transient flow phenomena of this type.

A critical revision is made of the classic power-law expressions that describe the effect of the Prandtl number on laminar heat transfer and temperature recovery for Pr near one, by applying a perturbation analysis to the energy equation for constant-property flow. In this way, the Pr dependence is obtained as a systematic asymptotic expansion up to any desired order, which provides a more accurate and convenient procedure than classic curve-fitting methods. The effect of pressure gradient and flow sweep are examined for self-similar yawed wedge flows.

This paper derives innovative techniques for use in the trimming and stability analysis of advanced rotorcraft simulations. It begins by exploiting the symmetry of the rotor to produce an efficient definition of periodic trim which is applicable to rotorcraft simulations. This definition is then expanded to produce a trimming algorithm which is capable of concurrently ascertaining the initial conditions and control inputs necessary to trim latest generation simulation models to a specified periodic trim state. The algorithm is based on a periodic shooting approach with Newton-Raphson iteration and exploits the symmetry of the rotor to minimise computational workload. The definition of periodic trim is then further developed to produce a technique by which the stability characteristics of rotorcraft can be ascertained from advanced simulation models. This technique is based on a Floquet approach and again exploits the symmetry of the rotor to reduce computational burden. The paper concludes by presenting results obtained when the stability characteristics of a tiltrotor simulation model are investigated.

Two major technologies in aeronautics promise substantial improvements in the fields of economy and ecology. One is laminar flow technology and the other arises from new developments related to aircraft turbofan engines. The trend in turbofan engine development is towards engines possessing higher bypass ratios. This, however, entails larger engine dimensions, leading not only to an increase in the skin friction drag but also to negative engine-airframe interactions. As a consequence, the need for laminar flow nacelles becomes all the more important as part of the general process of engine-air-frame integration optimisation for advanced transport aircraft.

This paper deals with some results obtained from flight tests with a laminar flow nacelle demonstrator and specifically addresses the topic of aerodynamics of intakes and nozzles. The results described relate to a European collaborative programme in which a natural laminar flow (NLF) nacelle was flight tested. Results of the effect of the angle of yaw on the static pressure distribution on the fan cowl including the intake of an NLF nacelle are presented for the maximum cruise flight condition. At zero yaw, a comparison of Euler calculations with flight test data is made. Measured flow variables of the fan nozzle flow directly downstream of the fan nozzle exit, exemplified by the Mach number and the flow density distributions, are also presented for the condition of maximum cruise.