We describe laboratory experiments which reproduce characteristic signals observed on spacecraft, believed to be caused by dust impact. A simulated spacecraft, including an antenna system using a facsimile of the preamplifier electronics from the STEREO/WAVES instrument, was bombarded by 10 km/s submicron‐sized dust at the University of Colorado Institute for Modeling Plasma, Atmospheres, and Cosmic Dust accelerator facility. Signal variation was investigated as a function of the DC potentials of both the spacecraft and the antennas. We observed (1) signals corresponding to modification of the spacecraft body potential, an important process believed to be responsible for the so‐called “triple hit” antenna signals on STEREO, (2) a few‐eV energy distribution for the electrons and ions released in the impact leading to (3) signals corresponding to direct recollection of a substantial fraction of the impact charge by the spacecraft antennas, even at modest antenna bias potentials. We also observe (4) an unexpected class of fast antenna signals, which do not appear to be caused by charge recollection by either the spacecraft or the antennas and may be induced by charge separation in the expanding plasma cloud. Similar signals are also commonly observed by the STEREO/WAVES instrument but have not previously been analyzed.
Transonic high-Reynolds-number flows through channels which are so narrow that the classical boundary-layer approach fails locally are considered in the presence of a weak stationary normal shock. As a consequence, the properties of the inviscid core and the viscosity-dominated boundary-layer region can no longer be determined in subsequent steps but have to be calculated simultaneously in a small interaction region. Under the requirement that the core-region flow should be considered to be one-dimensional to the leading order the resulting problem of shock–boundary-layer interaction is formulated by the means of matched asymptotic expansions for laminar flows of dense gases (Bethe–Zel'dovich–Thompson, or BZT, fluids). Such fluids have the distinguishing feature that the fundamental derivative of gas dynamics can become negative or even change sign under the thermodynamic conditions to be considered. The regularizing properties of the mechanism of viscous–inviscid interactions on the different anomalous shock forms possible in the flow of dense gases with mixed nonlinearity, namely rarefaction, sonic, double-sonic and split shocks, will be discussed. To this end we show the consistency of the resulting internal-shock profiles because of strong shock–boundary-layer interaction with a generalized shock admissibility criterion formulated for the case of purely inviscid flows. Representative solutions for the internal-shock structures are presented, and the importance of such flow phenomena in technical applications in the near future are shortly discussed by considering estimates of the actual dimensions of the interaction region for a specific representative situation in which the BZT fluid PP10 (C13F22) has been selected.
On présente une approche numérique et expérimentale du problème de la convection mixte entre deux plans horizontaux à températures différentes. L'approche numérique consiste en une simulation par différences fi nies des équations de la convection, elle est réalisée pour 2000 < Ra < 12 000, l < Re < 9, et pour Pr= 0,7. Cette étude a permis de mettre en évidence un écoulement sous la forme de rouleaux transversaux se déplaçant dans le sens du mouvement d'ensemble de l'écoulement. Les résultats expér imentaux obtenus avec l'air montrent une structuration de l'écoulement sous forme de rouleaux trans versaux pour les faibles valeurs du nombre de Reynolds. Des rouleaux longitidinaux apparaissent pour des nombres de Re plus élevés. 'IHCJIEHHOE H 3KCilEPHMEHTAJibHOE HCCJIE,r(OBAHHE CMEIIlAHHOA KOHBEKUHH ME)K)J.Y)J.BY MJI rOPl130HTAJibHbIMH IlJIACTHHAMH IlPH PA3J1UllHOA TEMilEPATYPE AlmoT8Qll1t-Hpoee)leHo ICOMllJleICCHOe 'IHCJieHHOe H)ICCnepHMeHTaJlhHOe HCCJJe)lOBaHHe CMCWaHHOH JJaMHHapHOH ICOHBeICIUIH Mel!C)ly ropH3OHTaJJhHhlMH napaJJJJeJJhHhlMH D JJaCTHHaMH. Koae'IHO pa3HOCTHhlM MeTO)lOM noJJy'leHhl peweHHII)lJIII)lHaml3OHOB 'IHCCJI P3JJCJI OT 2000)lO 12 000, 'IHCCJI PeHHOJlh)lca OT 1)lO 9 H 'IHCJia IlpaHJlTJlll 0,7. H3 'IHCJJeHHhlX pe3yJihTaTOB CJICllYeT, 'ITO nonepe'!Hhle BaJJhl nepeMeW:a!OTCII B aanpaBJJeHHH Te'ICHHII, a H3)ICCnepHMeHTaJJhHh!X HCCJIC)lOBaHHH)lJIJI B03)lyxa yCTaHOBJieHO cym:eCTBaHHe nonepe'IHhlX BaJJOB npH HH31CHX 'IHCJJax PeHHOJih.!{Ca H npo,!lOJlhHOro BHXpll npH BhlCOICHX 'IHCJlaX PeHHOJihJJ,Ca.
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