Studies on Fluid-Structure Interactions in Hypersonic Flow

Abstract

Fluid-structure interaction (FSI) represents a critical area of research in aerospace engineering, particularly in the hypersonic flows where aerodynamic and thermal loads significantly impact structural integrity and performance. The global thrust towards the development of hypersonic cruise systems for various applications is leading towards slender configurations with lifting and control surfaces which are thin and complaint and face a hypersonic flow. Hypersonic flows are characterized by large f lowkinetic energy and momentum, which manifests into strong shocks, high temperatures, and associated effects that can cause coupling between the flow, structure, and thermal effects. Therefore, understanding f luid structure interactions in hypersonic flow gains significance, and its predictive modelling is necessary to avoid adverse effects in flight. The majority of literature in supersonic and hypersonic FSI consider low-fidelity modelling using piston theory, two-dimensional FSI computations, and a limited number of experiments on mainly fully clamped flat panels subjected to aerodynamic loads, including shock-boundary layer interactions at supersonic Mach numbers. Studies on cantilevered panels, which are template shapes of control surfaces, at hypersonic Mach numbers are few, and there is a significant need to obtain experimental data to aid physical understanding, validate computational tools and methodology and model the hypersonic FSI phenomena. This motivated the study of three different template flat plate experimental models in the hypersonic shock tunnel HST-2 in the Ludwieg Mode of Operation, which has 35 milliseconds of test time. The freestream Mach number of M=6.6 is incident upon a) a cantilevered panel placed along the direction of the flow, b)a cantilevered panel with an impinging shock, and c)a trapezoidal wing-like shape fixed at the root and placed transverse to the flow. The study aims to enhance the understanding of FSI phenomena, which are paramount for the design and optimization of hypersonic vehicles, such as re-entry capsules and high-speed aircraft. Initially, the experimental setup involves testing the cantilevered plate at two different angles of attack, specifically10 degrees and 20 degrees. By varying the AOA, the study aims to observe how the aerodynamic loading and resultant structural response of the plate change. Furthermore, the study explores the impact of structural thickness on the plate’s response to aerodynamic loading. Plates with two different thicknesses, 2 mm and 4 mm, are tested. This variation in thickness is critical to understanding the role of structural rigidity and compliance in FSI. A set of experiments without and with shock impingement was conducted to compare the structural response in the presence of SBLI. In order to study this more realistic and real-world problem, coupling was also studied on the trapezoidal wings. In addition to the experimental investigations, numerical simulations are conducted to gain a comprehensive understanding and insights on the aeroelastic coupling mechanisms. The numerical results complement the experimental data, providing a detailed picture of the FSI phenomena and validating the experimental observations. The accelerometers measure the structure’s response, while Schlieren imaging captures the instantaneous flow field. The analysis revealed that the panel’s response depends on parameters such as panel thickness,mass ratio, and flow conditions. Spectral analysis of the acceleration data indicates that the dominant frequency of the structure is 89.65 Hz, which is higher than the natural frequency of the structure. For the thinner plate, an increase in the angle of attack causes the dominant frequency to shift towards the panel’s higher modes. In contrast, for the thicker plate, the dominant frequency is lower than the natural frequency as the angle of attack increases. In the case of shock impingement, Schlieren images show a reduction in the separation bubble size for the compliant panel compared to the rigid plate. This reduction is likely due to the deformation of the compliant panel, which mitigates the adverse pressure gradient and shifts the bubble downstream. Numerical simulations were also conducted to gain further insights into the dynamics of the separation bubble.