An experimental study of compressible jet flows has been undertaken in a small transonic wind tunnel. The aim of this investigation was to realize a jet simulator in the framework of wing/nacelle integration research and to characterize the jet flow behavior. First, free jet configuration, and subsequently jet flow in co-flowing air stream configuration were analyzed. Flow conditions were those encountered in a typical flight condition of a generic transport aircraft. i.e, fully expanded sonic jet flows interacting with a compressible external flowfield. Conventional experimental techniques were used to investigate the jet flows-Schlieren visualization and two-component Laser Doppler Velocimetry (LDV). The mean and fluctuating properties were measured along the jet centerline and in the symmetric plane at various downstream locations. The results of two configurations show remarkable differences in the mean and fluctuating components and agree well with the trend observed by other investigators. Moreover, these experiments enrich the database for such flow conditions and verify the feasibility of its application in future aerodynamic research of wing/nacelle interactions.
Measurements have been made in an automotive HV AC blower for two different centrifugal fans. This work is directed at improving the performance of a conventional forward-curved centrifugal fan for a given small blower casing. Mean velocities and pressure have been measured using a miniature five-hole probe and a pressure scanning unit connected to an online data acquisition system. First, we obtained the fan performance curves versus flow rates showing a significant attenuation of unstable nature achieved with the new fan rotor in the surging operation range. Second, aerodynamic characterizations were carried out by investigating the velocity and pressure fields in the casing flow passage for different fan operating conditions. The measurements showed that performance coefficients are strongly influenced by flow characteristics at the throat region. The main flow features were common in both fans, but improved performance is achieved with the new fan rotor, particularly in lower flow rate regions. Based on the measured results, design improvements were carried out in an acceptable operation range, which gave considerable insight into what features of flow behavior were most important.
The topological structure of an underexpanded Mach 2·5 jet injected into a Mach 0·75 crossflow are studied experimentally and numerically. The structure of the skin friction pattern is examined in detail by localising precisely the topological singularities. Oil-flow visualisations reveal the complex nature of the wall flow and its strong three-dimensionality. Four vortical structures appear in the vicinity of the wall, where two are essentially parallel to the wall (horseshoe vortex and boundary-layer vortices) and the other two are directed perpendicular to the wall (wake vortices). Comparison of computation with experiment shows good agreement for the complex separated-flow surface shear pattern and the pressure distribution. The crossflow Mach number plays an important role in the separation mechanisms. Significant differences in the topology occur with a Mach 0·3 crossflow whereas above Mach 0·6 the mean structure of the interaction is almost conserved, except that the secondary wake vortices disappear.
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