Boundary Layer Characterization during Impulsive Spin-up and Spin-down Motions of High-Reynolds Number Rotating Flow

International audienceVarious planar and stereo PIV measurements have been conducted for high-Re in a rotating tank during spin-up and spin-down with the purpose to characterize the side-wall boundary-layer development and corresponding vorticity distributions. The effect of Ekman pumping was successfully suppressed with an additional saltwater layer. An algorithm was developed to identify distinct patterns such as Görtler vortices and transition. Despite a linearly stable character, the spin-up showed transition turbulent for high Reynolds numbers. It is hypothesized that shear-layer instabilities trigger the transition process for high velocities combined with extremely small wall curvature

Multicarrier Digital Pre-distortion/ EqualizationTechniques for Non-linear Satellite Channels

Two key advances are envisaged for future missions: (a) spectrally efficienttransmission to meet the increasing demand and (b) sharing of satellite capacityamong different links to meet power/mass requirements. Joint amplification ofmultiple-carrier DVB-S2 signals using a single High-Power Amplifier (HPA) is aparticular application of satellite resource sharing. However, effects specific to sucha scenario that degrade power and spectral efficiencies include (a) an increasedAdjacent Channel Interference caused by non-linear characteristic of the HPA and(b) increased peak to average power ratio. The paper studies signal processingtechniques – digital pre-distortion (DPD) at the gateway and equalization (EQ) atthe User Terminal – to mitigate the non-linear effects and improve power as well asspectral efficiencies. While the algorithms for DPD and EQ are described inliterature, their use in multi-carrier scenario is novel and poses new challenges thatare investigated in the paper.QC 20131218</p