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A systemic and validated model was developed to predict ultraviolet spectra features from the shock layer of near-space hypersonic vehicles in the “solar blind” band region. Computational procedures were performed with 7-species thermal non-equilibrium fluid mechanics, finite rate chemistry, and radiation calculations. The thermal non-equilibrium flow field was calculated with a two-temperature model by the finite volume technique and verified against the bow-shock ultra-violet (BSUV) flight experiments. The absorption coefficient of the mixture gases was evaluated with a line-by-line method and validated through laboratory shock tube measurements. Using the line of sight (LOS) method, radiation was calculated from three BSUV flights at altitudes of 38, 53.5 and 71 km. The investigation focused on the level and structure of ultraviolet spectra radiated from a NO band system in wavelengths of 200–400 nm. Results predicted by the current model show qualitative spatial agreement with the measured data. At a velocity of 3.5 km/s (about Mach 11), the peak absolute intensity at an altitude of 38 km is two orders of magnitude higher than that at 53.5 km. Under the same flight conditions, the spectra structures have quite a similar distribution at different viewing angles. The present computational model performs well in the prediction of the ultraviolet spectra emitted from the shock layer and will contribute to the investigation and analysis of radiative features of hypersonic vehicles in near space.

1-D cavity modes in 1-D resonators, such as strips, have been used to design multiband metamaterial perfect absorbers. As for 2-D resonators, such as squares and crosses, most studies still focus on exciting the 1-D cavity modes. In this paper, a symmetry-breaking idea is proposed for 2-D cavity mode excitation. An asymmetric sword-shaped notched square resonator is proposed to excite a new 2-D (1, 1) cavity mode, in addition to the 1-D (1, 0) and (3, 0) cavity modes. Thus, a triple-band MPA was successfully produced with average absorptivity of 98.8% in the infrared range. The 2-D cavity mode provides better performance as a biosensor than the 1-D cavity modes do. To obtain more absorption bands, a six-band metamaterial perfect absorber with average absorptivity of 97.2% was successfully produced by combining two sword-shaped notched square resonators with different sizes. A nine-band metamaterial perfect absorber was successfully produced with average absorptivity of 94.5% by combining three sword-shaped notched square resonators with different sizes.

Hypersonic vehicles emit strong infrared radiation signatures that can be treated as a detecting source for object identification and routine diagnosis. This paper is aimed at examining the intrinsic radiation characteristics of a Boost-Glide Vehicle (BGV) under the condition of various angles of attack (AOA). A two-temperature model considering the thermal and chemical non-equilibrium effects is coupled with Navier–Stokes equations solved by the finite volume technique. A gas-solid conjunction heat transfer model is also added into the fluid solver to simulate the surface temperature of the vehicle. Gas absorption coefficients are evaluated through Line-by-Line (LBL) method and the radiative transfer equation is solved with line of sight (LOS) algorithm. Each part of the numerical modules is validated separately. The computational results for a Hypersonic Technology Vehicle 2 (HTV-2) type vehicle show that radiances emitted from gas are at least three orders of magnitude lower than that from the surface. The presence of AOA results in different distributions in surface temperature and therefore changes infrared radiation characteristics in intensity and spectral band. Two group simulations are performed in the steady and transient states, these results indicate that the variation of AOA does have a great effect on the infrared radiance and closely relates to observation angle, spectral band, angle size, angular velocity and time history. A low AOA rate of change is beneficial to reduce the radiance in the side view, but increase the radiance in the upward view. AOA rate of change has little effect on radiation intensity-time variations in the top view.

Comparing to the 1-D resonators like strips, the 2-D resonators, such as squares, can excite the higher-order 2-D magnetic plasmon (MP) modes in addition to the fundamental and higher-order 1-D MP modes. However, the low absorptivity of 2-D MP modes greatly limits its applications. We propose and demonstrate an idea utilizing the near-field coupling of electromagnetic fields accumulated around the tips of 2-D square resonators (near-field-coupled lighting-rod effect) to enhance the electromagnetic fields intensity and the emissivity or absorptivity of 2-D MP modes. The tip-tip coupling structure is formed by rotating the square resonators array 45 degrees. The experiment demonstrates the 4.5 times absorptivity enhancement of higher-order 2-D (1, 2) MP mode from 12.5% to 55.8% in addition to the fundamental MP10 and higher-order 1-D MP30 modes with high absorptivity. Our proposed near-field-coupled lighting-rod effect is strongly dependent on the formation of tip-tip coupling structure and the coupling distance.

To achieve a detailed understanding of underexpanded supersonic jet structures influenced by afterburning and other flow conditions, the underexpanded turbulent supersonic jet with and without combustions are investigated by computational fluid dynamics (CFD) method. A program based on a total variation diminishing (TVD) methodology capable of predicting complex shocks is created to solve the axisymmetric expanded Navier–Stokes equations containing transport equations of species. The finite-rate ratio model is employed to handle species sources in chemical reactions. CFD solutions indicate that the structure of underexpanded jet is typically influenced by the pressure ratio and afterburning. The shock reflection distance and maximum value of Mach number in the first shock cell increase with pressure ratio. Chemical reactions for the rocket exhaust mostly exist in the mixing layer of supersonic jet flows. This tends to reduce the intensity of shocks existing in the jet, responding to the variation of thermal parameters.

Radiative heating of a Mars entry capsule was evaluated along a reconstruction trajectory. Reactive flows were computed using a three-dimensional computational fluid dynamics (CFD) solver. Based on the narrow-band k-distribution (NBK) method, a new seven-point radiative property database was established relying on the line-by-line (LBL) approach. The CFD solver and the radiative model were verified by use of the experimental data. Some issues were numerically studied including flow field parameters, radiative heat fluxe (RHF) at forebody and afterbody, and contribution of radiative heating to aero-heating. The results reveal that the high RHF region is distributed in the windward side of the forebody and the leeward side of the afterbody. A comparison between the RHF and the convective heat flux (CHF) shows that the contribution of the RHF has a noticeable increase at low-altitude trajectory points. The maximum increase of the RHF reaches up to 45% of the total heat flux. In addition, the computational results without the angle-of-attack (AOA) indicate that the AOA has a less than 20% influence on the maximum RHF. These computational results provide a guide for the design of the thermal protection system (TPS) of Mars entry capsules.

Optical design parameters for a ground-based infrared sensor rely strongly on the target’s optical radiation properties. Infrared (IR) optical observability and imaging simulations of an Earth entry vehicle were evaluated using a comprehensive numerical model. Based on a ground-based IR detection system, this model considered many physical mechanisms including thermochemical nonequilibrium reacting flow, radiative properties, optical propagation, detection range, atmospheric transmittance, and imaging processes. An orbital test vehicle (OTV) was selected as the research object for analysis of its observability using a ground-based infrared system. IR radiance contours, maximum detecting range (MDR), and thermal infrared (TIR) pixel arrangement were modeled. The results show that the distribution of IR radiance is strongly dependent on the angle of observation and the spectral band. Several special phenomena, including a strong receiving region (SRR), a characteristic attitude, a blind zone, and an equivalent zone, are all found in the varying altitude MDR distributions of mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) irradiances. In addition, the possible increase in detectivity can greatly improve the MDR at high altitudes, especially for the backward and forward views. The difference in the peak radiance of the LWIR images is within one order of magnitude, but the difference in that of the MWIR images varies greatly. Analyses and results indicate that this model can provide guidance in the design of remote ground-based detection systems.

The bandwidths of thermal-tunable metamaterial perfect absorbers (MPAs) based on the phase change materials such as Ge2Sb2Te5 and VO2 are usually hundreds of nanometers at near-infrared frequency. Amorphous silicon (a-Si) provides the approach to achieve linearly thermal-tunable ultra-narrowband MPAs, if the absorption band is narrow enough. Four-nanorod-coupled a-Si resonators are proposed in this Letter. An absorption band at 1064 nm is obtained with ultra-narrow bandwidth (FWHM) only 1.4 nm by exciting the coupled magnetic dipole (CMD) mode, which exhibits great linearity to the temperature. In addition, the thermo-optical sensitivity (S=Δλ/ΔT) is about 0.08 nm/°C. The figure of merit of the thermal tunability performance FOM=S/FWHM=0.06. As a modulator, the critical temperature of absorptivity at 1064 nm is only 40°C, which is much lower than the Ge2Sb2Te5 (GST) and VO2. In addition, the modulation depth is up to 82% at near-infrared frequency.

Plasmonic resonances in metal-dielectric-metal structures have shown strong electric and magnetic fields enhancement in the sub-wavelength region, which can significantly boost the performance of plasmon-based metamaterial absorbers. Square resonators (SR) and ring resonators (RR) are both the most common blocks for designing metamaterial perfect absorbers (MPAs) by exciting fundamental electric dipole plasmonic modes. Actually, they can also excite the higher-order electric sextupole plasmonic modes but the absorptivity is very low, which are not available for the design of MPAs. In this paper, the near-field-coupling idea is introduced to enhance the absorptivity of higher-order electric sextupole modes. We propose the outer-square inner-ring coupled resonators (OSIRCR) made of the Ag and ZnS. When the coupling distance has decreased from 70 to 10 nm, the electric field intensity has increased 10.8 times from 55 to 594, which leads to a 5.4 times increase in absorptivity of higher-order electric sextupole modes of the outer-square from 17.6% to 95.3%. In addition to the higher-order electric sextupole modes, the OSIRCR can also excite the fundamental electric dipole modes of the outer-square and the inner-ring. Then a six-band polarization-independent MPA in the infrared range is designed with an average absorptivity of 91.5% utilizing two different sized OSIRCRs.

plan Abstract: The valve cooling system of converter station plays a very important role in the DC transmission project, and it is important to keep the system stable running. It is found that great scaling difference appeared among three spray towers of the valve cooling system in Tianshengqiao converter station during overhaul, and this phenomenon seriously affects the stability and effective operation of valve cooling system. Through theoretical analysis and experimental study, this paper reveals the main reason of the scaling difference of the surface of heat exchanger coil, and puts forward the control strategy for the Tianshengqiao converter station. After one year of running, the scaling difference of the surface of heat exchanger coil significantly reduced, and this shows that the effect of improvement is good.