Lobed mixers are widely used in gas turbine engines to increase mixing between hot and cold streams and consequently reduce jet noise. CFD predictions are presented for a simplified experimental configuration of a planar, three lobe geometry. Results are shown for a standard linear k–ε turbulence model, the same model with a time scale limitation invoked and a non-linear quadratic model also employing a time scale limitation. Comparisons are presented between the three models for axial velocity, velocity vectors, shear stress and turbulence kinetic energy at a selected plane in the mixing region. The non-linear model was found to have little influence on the mean flow but some effect on the turbulence structure was observed. Comparison with measurements showed that all major features were reproduced but detail differences were evident. The use of a time scale limit reduced peak values of predicted turbulence quantities by 20-30%. As compared to the standard linear model, the time scale limited non-linear model moved the position of the zero streamwise circulation location by about one lobe wavelength upstream so giving better agreement with experiment.

This paper describes an evaluation of the longitudinal flying qualities of a generic blended-wing-body (BWB) transport aircraft at low speed flight conditions. Aerodynamic data was obtained from several sources and integrated into the equations of motion of a typical BWB configuration in order to provide a reasonable basis for flying qualities assessment. The control requirements to trim are enumerated for a representative range of cg position and static margin over the typical range of approach speeds for both stable and unstable configurations. The linear dynamic characteristics of the unaugmented airframe are also described for the same range of stability margin. Subsequent work describes the development of a rate command-attitude hold command and stability augmentation system configured to comply with representative modern handling criteria. Finally, the flight dynamics of the augmented aircraft are described after refinement of the control law by means of piloted simulation in a fixed base flight simulator.

In this paper we study large angle rotational manoeuvres of spacecraft. The problem of attitude control is formulated and solved through potential functions, thus simplifying frequent reorientation manoeuvres. A combination of gas jet and FEEP thrusters is employed in order to obtain short settling times while meeting stringent pointing requirements. In this way, spacecraft reorientation is achieved in two integrated steps by means of a discrete/continuous control law. Autonomous avoidance of undesired space orientations is obtained and constraints due to the solar array pointing requirements are satisfied. A case study is discussed where the methodology is applied to a large space telescope.

This paper looks at active control of the swept shock wave/turbulent boundary-layer interaction using smart flap actuators. The actuators are manufactured by bonding piezoelectric material to an inert substrate to control the bleed/suction rate through a plenum chamber. The cavity provides communication of signals across the shock, allowing rapid thickening of the boundary-layer approaching the shock, which splits into a series of weaker shocks forming a lambda shock foot, reducing wave drag. Active control allows optimum control of the interaction, as it would be capable of positioning the control region around the original shock position and control the rate of mass transfer.

The effects on the wall pressure of the plate caused by the introduction of a gap near the ground and the flaps were investigated experimentally. The mean pressure on the plate surface was found to decrease with the size changing of the gap near the ground when the gap size (g) is larger than the flap height (h), but the one in the recirculation region increase with the size of the gap when the gap size is about 0 ≤ g ≤ 2h. Three kinds of flow structure appear with increasing the gap sizes, and the transit point is at g/h = 0·2, 0·8 respectively. For the zigzag flap (d/h = 0·19, d is the height of the zigzag), the variation of wall pressure with g/h is similar to the flat flap in general. The zigzag affects the mean wall pressure in the region of 0 ≤ x/h ≤ 20 (the recirculation zone) and can decrease the fluctuating pressure in the region of x/h > 20 downstream.

The influence of flap-end geometry modifications on the near-field wake behind a generic high-lift wing/flap configuration is investigated experimentally with a single-tube yawmeter. It is found that flap-end additions tend to split the concentrated area of streamwise vorticity shed by the flap into two less intense regions, associated with the tips of the flap and the addition. For shorter additions, these regions tend to roll up together, resulting in a slightly more diffuse flap vortex of almost unchanged circulation. For larger additions, the outer region is captured by the tip vortex, which correspondingly gains in circulation at the expense of the flap vortex. In all cases, the vorticity centroid of the rolled-up wake is shifted outboard, and the overall circulation slightly increased. However, the associated lift increase implies a decrease in overall circulation at a given lift coefficient.