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171.
《中国航空学报》2021,34(5):350-363
The interaction of an impinging oblique shock wave with an angle of 30° and a supersonic turbulent boundary layer at Ma∞=2.9 and Reθ = 2400 over a wavy-wall is investigated through direct numerical simulation and compared with the interaction on a flat-plate under the same flow conditions. A sinusoidal wave with amplitude to wavelength ratio of 0.26 moves in the streamwise direction and is uniformly distributed across the spanwise direction. The influences of the wavy-wall on the interaction, including the characterization of the flow field, the skin-friction, pressure and the budget of turbulence kinetic energy, are systematically studied. The region of separation grows slightly and decomposes into four bubbles. Local peaks of skin-friction are observed at the rear part of the interaction region. The low-frequency shock motion can be seen in the wall pressure spectra. Analyses of the turbulence kinetic energy budget indicate that both diffusion and transport significantly increase near the crests, balanced by an amplified dissipation in the near-wall region. Proper orthogonal decomposition analyses show that the most energetic structures are associated with the separated shock and the shear layer over the bubbles. Only the bubbles in the first two troughs are dominated by a low-frequency enlargement or shrinkage. 相似文献
172.
Salvatore Mancuso Alessandro Bemporad 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
We report on the analysis of two fast CME-driven shocks observed with the UltraViolet Coronagraph Spectrometer (UVCS) on board the Solar and Heliospheric Observatory (SOHO). The first event, detected on 2002 March 22 at 4.1 R⊙ with the UVCS slit placed in correspondence with the flank of the expanding CME surface, represents the highest UV detection of a shock obtained so far with the UVCS instrument in the corona. The second one, detected on 2002 July 23 at 1.6 R⊙ with the UVCS slit placed in correspondence with the front of the expanding CME surface, shows an anomalous deficiency of ion heating with respect to what observed in previous CME/shocks observed by UVCS, possibly reflecting the effect of different coronal plasma conditions over the solar cycle. From the two different sets of observations we derived an estimate for the shock compression ratio X, which turns out to be X = 2.4 ± 0.2 and X = 2.2 ± 0.1, respectively, for the first and second event. Comparison between the two events provides complementary perspectives on the dynamical evolution of CME-driven shocks. 相似文献
173.
C. Jacobi G. Stober D. Kürschner 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(9):1429-1434
Scale height, H, estimates are calculated from the decrease/increase of ionospheric virtual reflection heights of low-frequency (LF) radio waves at oblique incidence in suitably defined morning intervals around sunrise during winter months. The day-to-day variations of H qualitatively agree with daily mean temperature variations around 90 km from meteor radar measurements. Since mesospheric long-period temperature variations are generally accepted to be the signature of atmospheric planetary waves, this shows that LF reflection height measurements can be used for monitoring the dynamics of the upper middle atmosphere. The long-term variations of monthly mean H estimates have also been analysed. There is no significant trend, which is in agreement with other measurements of mesopause region temperature trends. 相似文献
174.
G.N. Kichigin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
The paper discusses the possibility of particle acceleration up to high energies in relativistic waves generated by various explosive processes in the interstellar medium. We propose to use the surfatron mechanism of acceleration (surfing) of charged particles trapped in the front of relativistic waves as a generator of high-energy cosmic rays (CRs). Conditions under which surfing in the waves under consideration can be made are studied thoroughly. Ultra-high-energy CRs (up to 1020 eV) are shown to be obtained due to the surfing in relativistic plane and spherical waves. Surfing is supposed to take place in nonlinear Langmuir waves excited by powerful electromagnetic radiation or relativistic beams of charged particles, as well as in strong shock waves generated by relativistic jets or spherical formations that expand fast (fireballs). 相似文献
175.
E.I. Astafyeva E.L. Afraimovich S.V. Voeykov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(9):1459-1462
By using data from GPS receivers we detected huge-amplitude solitary large-scale traveling acoustic-gravity waves (LS AGW) which manifested themselves as perturbations of total electron content (TEC) of duration of about 40 min. Originated in the auroral area after significant alterations of geomagnetic field intensity during geomagnetic storms on 29–30 October 2003, LS disturbances propagated with a velocity about 1000–1200 m/s and caused generation of secondary small-scale (SS) waves with time period of 2–10 min. Such SS structure followed the solitary intensive AGW at a distance more than 4000 km. However, we observed such phenomenon only within the territory with high values of “vertical” TEC and steep gradients of TEC. Apparently, these conditions are necessary for generation of SS waves due to propagation of LS AGW. 相似文献
176.
I.R. Petrova V.V. Bochkarev R.R. Latipov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
We present results of the spectral analysis of data series of Doppler frequency shifted signals reflected from the ionosphere, using experimental data received at Kazan University, Russia. Spectra of variations with periods from 1 min to 60 days have been calculated and analyzed for different scales of periods. The power spectral density for spring and winter differs by a factor of 3–4. Local maxima of variation amplitude are detected, which are statistically significant. The periods of these amplitude increases range from 6 to 12 min for winter, and from 24 to 48 min for autumn. Properties of spectra for variations with the periods of 1–72 h have been analyzed. The maximum of variation intensity for all seasons and frequencies corresponds to the period of 24 h. Spectra of variations with periods from 3 to 60 days have been calculated. The maxima periods of power spectral density have been detected by the MUSIC method for the high spectral resolution. The detected periods correspond to planetary wave periods. Analysis of spectra for days with different level of geomagnetic activity shows that the intensity of variations for days with a high level of geomagnetic activity is higher. 相似文献
177.
Soft X-ray (SXR) waves, EIT waves, and Hα Moreton waves are all associated with coronal mass ejections (CMEs). The knowledge of the characteristics about these waves is crucial for the understanding of CMEs, and hence for the space weather researches. MHD numerical simulation is performed, with the consideration of the quiet Sun atmosphere, to investigate the CME/flare processes. On the basis of the numerical results, SXR, EUV, and Hα images of the eruption are synthesized, where SXR waves, EIT waves, and Hα Moreton waves are identified. It confirms that the EIT waves, which border the expanding dimmming region, are produced by the successive opening (or stretching) of the closed magnetic field lines. Hα Moreton waves are found to propagate outward synchronously with the SXR waves, lagging behind the latter spatially by ~27 Mm in the simulated scenario. However, the EIT wave velocity is only a third of the Moreton wave velocity. The synthesized results also suggest that Hα± 0.45Å would be the best off-band for the detection of Hα Moreton waves. 相似文献
178.
The surface wave induced magnetic reconnection (SWIMR) model based on Alfven Resonance theory will be discussed briefly both
for collisional and collisionless plasmas. It is shown that the spatial scales and time delays associated with Flux Transfer
Events and Pulsed Ionospheric Flows, as observed by satellites and SuperDARN radars and the magnetic bubbles, observed at
the high latitude boundary of the magnetopause, can be explained by the SWIMR model.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
179.
One of the most ubiquitous indicators of the state and topology of the magnetosphere are ultra-low frequency (ULF) waves.
These may be continuously and inexpensively monitored from the ground using networks of magnetometers. The most robust measurable
quantity provided by magnetometer networks is signal phase and this paper emphasizes the usefulness of this parameter in a
variety of ULF wave diagnostic processes ranging from equatorial to high latitudes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
180.