A study published in Aerospace proposed a method to study aero-optical effects in hypersonic vehicles based on the interaction between gas molecules and photons. This method can explain the energy dissipation and optical distortion induced by aero-optical effects at the microscopic level.
Study: A new method for analyzing the aero-optical effects of hypersonic vehicles based on a microscopic mechanism. Image Credit: Naeblys/Shutterstock.com
Importance of aero-optical effects in hypersonic vehicles
Hypersonic vehicles have attracted a lot of interest due to their ability to attack quickly. The demand for autonomous navigation systems in these vehicles is increasing.
A celestial navigation system (CNS) offers remarkable advantages over conventional navigation systems in hypersonic vehicles, including excellent anti-interference ability, non-cumulative error, and high reliability.
However, the implementation of CNS in hypersonic vehicles is hampered by measurement errors of optical sensors due to aero-optical effects. The aero-optic effect can induce angle measurement errors of up to 400 rad in dynamic high-speed environments. Understanding aero-optical effects is crucial for CNS error correction of hypersonic vehicles.
Aero-optical effects include the coupling of the light field and the high velocity flow field. A complex flow field produced between an incoming flow and an optical head cover, together with aero-optical effects, generates transmission interference in the imaging detection system, resulting in jitter, image drift, blurring and loss of energy.
Limits of current research on aero-optic effects
Despite significant experimental advances in the study of the aero-optic effect, research on their microscopic processes has stagnated. Current research on aero-optical effects mainly focuses on the modification of the turbulent density field along the optical path.
In these studies, the ray tracing technique examines the refractive index field near the turbulent boundary layer (TBL) to study the phase distortion imposed by a high velocity flow field.
However, these studies were unable to adequately quantify the energy loss of light transmission in turbulence since their methodologies on the deflection effects of large-scale turbulent vortex formations on light transmission were limited to the macro characteristic level.
Some researchers have used wave theory to describe aero-optical phenomena, but the change in amplitude has been largely neglected and simple Maxwell’s equations have been used to model the transmission of light in turbulence.
Investigate aero-optic effects using photon theory
Aero-optical effects can be understood using photon theory. When a uniform gas or laminar flow is used as the study target, microscopic effects such as absorption and scattering are not visible and could be studied directly using geometric optics.
However, when the turbulent changes become more severe, the large-scale particles reach the dissipation zone and transform into small-scale particles. At this time, the speed and density of the turbulence and the distribution of molecules in the excited and ground states vary considerably.
However, analysis of actual aero-optical effects is impossible by simply considering the refraction effect. Therefore, photon transmission in turbulence is necessary to study the microscopic mechanism of aero-optical effects.
Analysis of aero-optical effects based on the interaction between photons and gas molecules
Researchers have used the photon transport mechanism to perform the first-ever microscopic examination of aero-optic effects.
A modeling technique based on microscopic mechanisms was designed by generating a photon transmission model in turbulence. Photon perspective reveals the microscopic structure of aero-optical effects, which are based on the interaction between gas molecules and photons in a high-velocity flow environment.
The effectiveness of the proposed microanalysis at the macro scale has been verified by comparing physical quantities of standard aero-optical effects with optical distortion parameters developed from the photonic point of view.
Important Study Findings
The core of aero-optical effects at the microscopic level is revealed for the first time from the photon perspective using a photonic transmission mechanism.
Current aero-optical simulation tools cannot examine energy dissipation in the transmission process. However, this research develops a simulation analysis technique to explain the energy dissipation and optical distortion induced by aero-optic phenomena at the microscopic level.
The energy dissipation ratio and photon energy divergence of photons closer to the optical window are larger, indicating that turbulent molecules absorb and scatter photons more as the transmission distance increases. The photon energy divergence and the energy dissipation ratio grow linearly with the thickness of the photon simulation threshold.
Although the energy dissipation rate is reduced, the energy loss rates of photons at various locations are variable, affecting the identification of the center of mass when calculating the offset angle with the conventional method of 5 .56%.
By describing the distortion characteristics of photons in various turbulent scale structures and evaluating the energy in aero-optical effects, the proposed method transcends the constraints of conventional geometrical optical methods.
Reference
Yang, B.; Yu, H.; Liu, C.; Wei, X.; Fan, Z.; Miao, J. A new method for analyzing the aero-optical effects of hypersonic vehicles based on a microscopic mechanism. Aerospace. https://www.mdpi.com/2226-4310/9/10/618
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