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81.
临近空间螺旋桨低雷诺数高效翼型数值分析 总被引:1,自引:0,他引:1
针对临近空间翼型边界层变厚更容易发生分离的特点,在修正了湍流模型后,通过分析比较13种低雷诺数翼型的升阻系数得到了比较适合用于临近空间螺旋桨叶素的高效翼型。结果显示,攻角在-6°~8°、8°~14°、14°~22°三种工况下,分别采用SST k-ω、RNG k-ε、Realizable k-ε湍流模型,可以得到与国外实验比较接近的合理结果;工况条件对翼型气动性能好坏的影响很大,翼型S-1223和FX63-137在所研究的工况内都具有较好的气动性能;因此可以选择这两种翼型作为临近空间螺旋桨用高效翼型。 相似文献
82.
低雷诺数涡轮叶片边界层转捩及分离特性测量 总被引:7,自引:5,他引:2
低雷诺数工作条件下涡轮流场特征及其控制设计,是航空发动机低压涡轮部件设计的难点和重点。针对低雷诺数涡轮叶栅流场开展了实验研究工作,利用油流显示、表面静压、边界层压力探针等测量手段研究了涡轮叶片边界层的分离和转捩。结果表明雷诺数降低导致了流动损失的增大,且存在一个临界雷诺数。当雷诺数小于临界雷诺数时,发生在吸力面的流动分离是开式的层流分离泡,不会再附与叶片;当雷诺数大于临界雷诺数时,分离流会在尾缘前重新附着于叶片吸力面,形成闭式分离泡。随着雷诺数的减小,出口尾迹变宽,出口流动损失、出口速度亏损和出口气流角偏离增大,尾迹中心向吸力面方向移动。 相似文献
83.
N. Mridula Tarun Kumar PantC. Vineeth K. Kishore Kumar 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
The general features of occurrence of an additional layer on the bottom side of F region, referred to as F0.5 layer in the pre noon period, over the magnetic equatorial location of Trivandrum (8.5° N; 77° E; dip lat of 0.5° N) in India during the period from 2004 to 2007 are presented using ionosonde observations. The F0.5 layer has a June (northern summer) solsticial maximum probability of occurrence with secondary maxima during December (northern winter) solstice. The seasonal as well as the day-to-day variability in the occurrence of F0.5 layer as mentioned in this paper seems to be a result of the variations in the amplitude and phases of the tides and gravity waves, and inventory of the metallic ions of meteoric origin. This study brings out an important manifestation of morning time F layer base region dynamics. 相似文献
84.
M. Pietrella M. PezzopaneC. Bianchi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Hourly systematic measurements of the highest frequency reflected by the sporadic-E layer (foEs) recorded from January 1976 to June 2009 at the ionospheric stations of Rome (Italy, 41.8°N, 12.5°E) and Gibilmanna (Italy, 37.9°N, 14.0°E) were considered to carry out a comparative study between the sporadic E layer (Es) over Rome and Gibilmanna. Different statistical analysis were performed taking into account foEs observations near the periods of minimum and maximum solar activity. The results reveal that: (1) independently from the solar activity, Es develops concurrently over extended regions in space, instead of being a spatially limited layer which is transported horizontally by neutral winds over a larger area; especially during summer months, when an Es layer is present at Rome, there is a high probability that an Es layer is also present over Gibilmanna, and vice versa; (2) Es layer lifetimes of 1–5 h were found; in particular, Es layers with lifetimes of 5 h both over Gibilmanna and Rome are observed with highest percentages of occurrence in summer ranging between 80% and 90%, independently from the solar activity; (3) latitudinal effects on Es layer occurrence emerge mostly for low solar activity during winter, equinoctial, and summer months, when Es layers are detected more frequently over Gibilmanna rather than Rome; (4) when the presence of an Es layer over Rome and Gibilmanna is not simultaneous, Es layer appearance both over Rome and Gibilmanna confirms to be a locally confined event, because drifting phenomena from Rome to Gibilmanna or vice versa have not been emphasized. 相似文献
85.
N. Zolotukhina N. Polekh E. Romanova A. Polyakova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
We report work utilizing 15-min resolution ionospheric data obtained with DPS-4 digisonde in 2003–2011 to study the seasonal variations in amplitudes and phases of the most powerful spectral components of the F2 layer critical frequency (foF2) and peak height (hmF2) fluctuations over Irkutsk (52.5°N, 104.0°E). We show that fluctuations of both parameters contain quasi-harmonic components with periods of Tn = 24/n h (n = 1–7). The number of distinct spectral peaks varies from 3 in summer to 7 in winter. Amplitude and phase characteristics of the diurnal (n = 1) and semidiurnal (n = 2) components is studied using the data sets extracted from the original data sets with band-pass filter. It has been found that the amplitudes of diurnal/semidiurnal foF2 and diurnal hmF2 components are maximum in winter and minimum in summer. Amplitudes of the diurnal components vary gradually; those of the foF2 semidiurnal one, abruptly, thus forming a narrow winter maximum in November–January. The phase (local time of maximum) of the diurnal foF2 component increases gradually by 4–6 h from winter to summer. The phase of the semidiurnal foF2 component is nearly stable in winter/summer and sharply decreases (increases) by 2–3 h near the spring (autumn) equinox. The phase of the diurnal component of hmF2 (local time of minimum) varies slightly between 1130 and 1300 LT; that of the semidiurnal one decreases (increases) by 4–6 h from January to March (from September to November). The results obtained show that the main features of seasonal variations in the diurnal and semidiurnal components of the mid-latitude F2 layer parameters recur consistently during the solar activity growth and decline phases. 相似文献
86.
87.
双模态超燃冲压发动机由于压力扰动可能发生不起动现象,造成推力严重下降,对飞行稳定性与飞行安全具有很强的破坏性.不起动初始阶段主要受到激波与边界层相互作用引起的流动分离影响,希望通过控制分离达到改善流动的目的.采用5阶特征型WENO(weighted essentially non-oscillator)格式与3阶TVD(total variation diminishing)型Runge-Kutta(R-K)格式的高精度数值方法,求解三维Navier-Stokes(N-S)方程,研究与分析了凸起物和被动吹吸两种被动控制方法对激波与边界层相互作用导致的高超声速流动分离现象的控制效果.结果表明:凸起物通过诱导流向涡形成,改变空间压力分布,减弱二次分离,影响分离结构;吹吸方式的被动控制技术通过平衡分离区与再附区之间的高低压差,降低逆压梯度,使压力分布与分离区域发生改变. 相似文献
88.
A numerical simulation of shock wave turbulent boundary layer interaction induced by a 24° compression corner based on Gao-Yong compressible turbulence model was presented.The convection terms and the diffusion terms were calculated using the second-order AUSM (advection upstream splitting method) scheme and the second-order central difference scheme,respectively.The Runge-Kutta time marching method was employed to solve the governing equations for steady state solutions.Significant flow separation-region which indicates highly non-isotropic turbulence structure has been found in the present work due to intensity interaction under the 24° compression corner.Comparisons between the calculated results and experimental data have been carried out,including surface pressure distribution,boundary-layer static pressure profiles and mean velocity profiles.The numerical results agree well with the experimental values,which indicate Gao-Yong compressible turbulence model is suitable for the prediction of shock wave turbulent boundary layer interaction in two-dimensional compression corner flows. 相似文献
89.
90.