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• Uncertainty qualification of IR signatures from rocket exhaust plume was analyzed. • A point collocation nonintrusive polynomial chaos method was utilized. • Influences of nozzle exit conditions on IR signatures were clarified. • Sensitivity of plume IR radiations using Sobol's indices was discussed. In this study, an uncertainty analysis for the infrared radiation characteristics of rocket exhaust plumes at representative trajectory points is performed. Owing to the instability of the rocket motor's working characteristics, numerical rocket plume infrared radiation predictions possess significant uncertainties. In this study, four epistemic uncertain variables (freestream velocity, nozzle exit pressure, temperature, and velocity) are considered for uncertainty and sensitivity analyses. Based on the infrared signature analysis tool, the response surface of statistical samples is established through the point collocation nonintrusive polynomial chaos expansion method. Polynomial chaos expansion coefficients are solved using the quadrature method to calculate the statistical characteristics and uncertainty of random input variables. The tensor-product quadrature sparse grid method is utilized to reduce the number of samples for multiple input variables. Based on these models, the uncertainty quantification of infrared radiation for Atlas-IIA rocket plumes is analyzed, including the flows, radiation images, spectra, and radiance. The results show that the uncertainty mainly results from afterburning at low altitude, and the nozzle exit velocity has a significant influence on the radiation intensity of the plume. With an increase in altitude, the uncertainty of infrared radiation owing to the afterburning effect decreases, and the influence of the freestream velocity increases. In addition, the proportion of radiation intensity in the 4.3-μm band is higher than that in the 2.7-μm band, and the corresponding uncertainty band is gradually widened. The nozzle exit temperature is the dominant factor that affects the radiation characteristics of the plume at high altitudes. These results of uncertainty and sensitivity analyses are helpful for improving numerical models of the plume infrared signature. [ABSTRACT FROM AUTHOR]

• Developed Semi-analytic Monte Carlo Method for solid rocket plume polarized radiation. • Simulated solid rocket plume polarized characteristics. • The effects of different light sources on the polarized characteristics of the plume were analyzed. Polarization optical detection has been widely used in the detection and identification of particle containing media such as clouds, aerosols, fire plumes, and volcanic smoke. Solid rocket plume is a typical high-temperature gas–solid two-phase medium. Polarization optical detection of solid rocket plume has attracted much attention in recent years. The polarized radiation transfer mechanism of solid rocket plume is complex, especially in the infrared band, with both the scattering radiation transfer from external incident light and the scattering radiation transfer from the high-temperature region inside the jet flame to the outside. The research on the polarization scattering characteristics of solid jet flame still needs to be further developed. Therefore, this study focuses on modeling the infrared polarization scattering mechanism and the simulation of polarization transfer characteristics of a solid rocket gas–solid two-phase plume, which can guide the usability analysis of solid rocket plume polarization detection. A novel model based on Semi-analytic Monte Carlo Method is proposed to simulate polarized radiation transfer of solid rocket plume. The wavelength and angle dependence of the self-radiation polarization characteristic of a solid rocket plume is simulated based on the proposed model. Note that the overall polarization degree of the plume shows wavelength selectivity and angle sensitivity at different wavelengths. The spatial distribution of polarization degree at 1.55 μm, 2.2 μm, and 2.75 μm shows that the plume edge's polarization degree is higher than the plume center. The findings suggest that the ratios of the relative contribution of self-radiation, direct solar radiation, and background polarization radiation components to the total polarization characteristics are 0.47 %, 70.50 %, 29.03 % at 1.55 μm and 20.43 %, 79.55 %, 0.02 % at 2.75 μm. [ABSTRACT FROM AUTHOR]

• Rapid calculation of atmospheric molecular absorption characteristics in the frequency range of 0.3-30THz. • A fitting coefficient table of exponential kernel is established to rapidly calculate the absorption coefficient • The relative contribution of absorptive capacity of eight atmospheric molecules compared to H 2 O molecules was studied. This paper focuses on rapidly calculating atmospheric molecular absorption properties in the 0.3–30 THz frequency range of terahertz waves. It conducts research related to spectral radiation models and fast computation model databases. Based on the latest version of the High-resolution transmission molecular absorption database-2020, in conjunction with the line-by-line (LBL) spectral radiative calculation method, the spectral absorption characteristics of nine atmospheric molecules (H 2 O, CO 2 , O 3 , NO, N 2 O, NO 2 , NH 3 , SO 2 , CH 4) are analyzed. The relative contributions of the eight other gas molecules absorption abilities in the terahertz range are examined, with H 2 O molecule serving as the reference. Taking into account the non-gray absorption properties of atmospheric molecules and the need for fast computation, this study divides the frequency range of 0.3–30 THz into 24 calculation bands based on the spectral absorption distribution characteristics of atmospheric molecules. Utilizing LBL calculations with a resolution of 0.01 cm−1, a non-correlated wideband K-distribution model (WBK) is developed, which achieves nearly the same computational accuracy as LBL. Furthermore, the WBK radiation calculation model is validated under both uniform and non-uniform atmospheric conditions based on earth atmospheric environmental parameters. An exponential kernel fitting coefficient table for the rapid calculation of atmospheric molecular absorption coefficients is established based on the WBK radiation calculation model to improve computational efficiency further. This database enables fast calculation of 24 broadband absorption coefficients (corresponding to 7 Gaussian integration points) within 0–100 km altitude in earth atmosphere. [ABSTRACT FROM AUTHOR]

• Plume infrared signatures were studied from the phenomenological point of view. • A methodology to characterize the rocket altitude from several spectral bands was proposed. • Effects of afterburning on the radiation phenomena were studied. • Effects of atmospheric attenuation and observation angles were discussed. Rocket exhaust plume treated as a significant radiation source has been widely used in space-based detection. In this paper, infrared radiation signatures of plumes were studied in the view of the phenomenon. The reacting plume flows were calculated by an axisymmetric computational fluid dynamics (CFD) solver. Radiative properties of gases were evaluated with the statistical narrow-band (SNB) model by relying on the NASA-3080 database. The line-of-sight (LOS) based on the single-line-group (SLG) approximation was employed for radiative transfer computations. The numerical model was validated against reference data. Based on this model, radiation characteristics of Atlas-II liquid rocket plumes were computed and analyzed in aspects of afterburning, atmospheric attenuation, spectral bands and observation angle. Results show that afterburning has a significant improvement in the wavelengths of 1.5–6.0 μm. Also, the atmospheric attenuation greatly decreases the plume radiance at low altitudes but it can be ignored above 40 km. Radiance is strongly dependent on the spectral bands. The altitude-varying spectral dependency can contribute to the rocket altitude estimation. The effect of the observation angle on the radiance distributions is varying with the spectra band and the flight altitude. These results are helpful for the design of the rocket motors and the application of the infrared detecting system. [ABSTRACT FROM AUTHOR]

Highlights • Infrared thermal radiation noise of the bow-shock layer was investigated. • A relationship between the radiation intensity and flight conditions was given. • Simulations results were discussed including the LOS, station and direction. • Effects of the dome radius and altitudes on the radiation noise were studied. Abstract To examine the effect of atmospheric trace species on the infrared thermal radiation of a supersonic dome, a series of radiation characteristics with different geometry sizes at near-ground altitudes were investigated numerically. The conjugate heat transfer method was applied to build the heat transfer model of the optical dome. Three major radiating species of H 2 O, CO 2 , and CO were taken into account in the shock layer. A line-by-line (LBL) method was used for evaluating the radiative properties of species. A line-of-sight (LOS) approach was applied to solve the radiative transfer equation (RTE). The simulated and measured results of the dome were also proposed to validate the numerical method. The effects of the dome geometry size, the dome material and the time-varying altitude on the infrared radiation noise were studied in detail. The results show that the altitude-varying radiation intensity along the LOS is related to the ambient density and velocity. The variation of the dome radius is proportional to the total radiation received on the dome surface. It is observed that the maximum radiation intensity along the LOS does not occur in the normal direction of the receiving point, but it is determined by both the flow field parameters and the path length. Also, the radiation increment corresponding to different dome sizes approximately obeys a Gaussian distribution related to the product of density and velocity. [ABSTRACT FROM AUTHOR]

• A laser radar cross-section (LRCS) approach for arbitrarily complex targets in the aero-optical environment is proposed and verified. • The effects of incoming density, incoming Mach number, and material bidirectional reflectance distribution function (BRDF) parameters on LRCS measurements are investigated. • The influence of the aero-optical environmental flow field on the LRCS is characterized by a directional and regional distribution. One of the concerns in the process of measuring laser radar cross-section (LRCS) using optical measurement methods is the aero-optical effect around a high-speed flow field. In this paper, a computational model for LRCS considering supersonic flow in a non-homogeneous medium is presented. First, by taking a typical 15° half-cone blunt cone as the research object, based on CFD calculation, the flow field distribution of the non-uniform medium around the high-speed vehicle is obtained. The ray-tracing method is used to calculate the light transmission in an aero-optical environment. An LRCS approach for arbitrarily complex targets in the aero-optical environment is then proposed, and the method is verified by analytical and numerical methods. Finally, the effects of incoming density, incoming Mach number, and material bidirectional reflectance distribution function (BRDF) parameters on LRCS measurements are investigated, and the errors caused by the steady aero-optical environment are analyzed. The results show that the maximum relative error of the measurement caused by the aero-optical environment in the direction of the shock-wave layer observation is significant when the Fresnel function approximation exponential function parameter is too large or when the root mean square (RMS) of the surface slope is too small in the BRDF parameters of the material. The influence of the aero-optical environmental flow field on the LRCS is characterized by a directional and regional distribution, determined by the incoming Mach number and shock-wave angle, with the influence of the incident flow density on the regional distribution being weakly correlated. The proposed method and calculation results are useful for the simulation, analysis, and calibration of LRCS measurements in complex aero-optical environments. [ABSTRACT FROM AUTHOR]

• A radiative property database was established based on the NBK method. • Thermal effects of the MSL capsule along the reconstructed trajectory were simulated. • The contribution of the radiative heating to aero-heating was compared and analyzed. 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. [ABSTRACT FROM AUTHOR]