Laser technology is extensively used in various fields, including additive manufacturing, removal processing, and laser weaponry. This technology has the potential to revolutionize battlefield dynamics through defensive and offensive applications. Research on laser irradiation under high-speed airflow provides a theoretical basis for efficient damage strategies and the protection of aircraft, this is crucial for deploying military laser systems. However, conducting real-scale model tests for large-scale engineering structures is challenging due to equipment limitations and testing environments. Additionally, wind tunnel tests with real-scale models are prohibitively expensive and time-consuming, preventing extensive testing. Consequently, scaled-model tests are often relied upon for regularity studies. Therefore, establishing a similarity relationship in the thermomechanical responses between real and scaled models under laser irradiation and high-speed airflow is a practical approach. Significant efforts have been made to understand the similarity theory of laser-induced thermomechanical behavior under static air conditions. Nonetheless, due to the complex fluid-thermal-structural interactions in high-speed airflow, the similarity criteria for thermomechanical responses in an airflow environment significantly differ from those in static air. In this study, we propose new similarity criteria and scaling laws suitable for the thermomechanical responses of a metal plate subjected to high-speed airflow and laser irradiation.
To clarify the similarity relation of thermomechanical responses for metal plates under coupling conditions, the effects of the tangential airflow were equivalently converted to the structural force and thermal load boundary conditions using the approximate equivalence method, and the dimensionless governing equations of the coupling problem were established. Thus, combined with the analysis of dominant factors, the similarity criteria and scaling laws suitable for the thermomechanical responses of the metal plate under the combined action of a high-speed airflow and laser were determined. According to the similarity criteria, there is a contradiction in the similarity relationship between the thermal boundary condition and force boundary condition under the fluid-thermal-structural coupling effects, which cannot be satisfied simultaneously. Considering that the thermal stress induced by the temperature gradient is much greater than the mechanical stress due to the aerodynamic force under the combined action of high-speed airflow and laser irradiation, this study focused on the similarity of aerodynamic heat transfer, ignored that of the aerodynamic force, and established the corresponding scaling law. Then, a fluid-thermal-structural coupling numerical example of a metal plate irradiated by a high-power laser under tangential flow was conducted to verify the scaling law under different scale ratios and Mach numbers.
The similarity criteria and scaling laws for the fluid-thermal-structural coupling analysis of the metal plate subjected to laser irradiation and high-speed airflow are presented in Tables 1 and 2, respectively. A numerical example of the fluid-thermal-structural coupling of a metal plate irradiated by a high-power laser under a tangential flow is conducted to verify the scaling law. The results show that under different scale ratios and Mach numbers, the predicted response errors between the scaled and original models are within 1%, which proves the reliability and accuracy of the scaling law. Simultaneously, with the increase in scale ratios or Mach numbers, the aerodynamic heat transfer effect is enhanced, making the thermal-mechanical response difference between the scaled model and real model more obvious when the aerodynamic similarity criteria are not considered.
In this study, similarity criteria and scaling laws suitable for the thermomechanical responses of a metal plate under the combined action of a high-speed airflow and laser are determined. Several numerical examples are conducted and compared to verify the proposed similarity criteria and scaling laws. The main conclusions are as follows: (1) Using the approximate equivalence method and analysis of dominant factors, the effects of the tangential airflow are equivalently converted to structural force and thermal load boundary conditions, and the similarity criteria and scaling laws are determined. Considering that the thermal stress induced by the temperature gradient is significantly greater than the mechanical stress caused by the aerodynamic force, this study focusses on the similarity of the aerodynamic heat transfer and ignores the similarity of the aerodynamic force. (2) A fluid-thermal-structural coupling numerical example of a metal plate irradiated by a high-power laser under tangential flow was conducted to verify the scaling laws under different scale ratios and Mach numbers. The results show that the predicted response errors between the scaled and original models are within 1%, which proves the reliability and accuracy of the scaling laws. (3) However, the scope of application of the proposed similarity criteria should be emphasized in the following aspects: the similarity criteria are applicable for calorically perfect gases. For hypersonic flows, complex chemical reactions occur at high temperatures, and the similarity criteria are no longer applicable. The similarity criteria are applicable for the plate flow condition. However, for the non-plate flow, such as the flow around a blunt-nosed bodies, the similarity criteria are no longer applicable. The similarity criteria are applicable to the thermal-mechanical responses of the metal structure before melting. When melting is involved, similarity criteria are no longer applicable.
