Investigation of fluid-thermal-structural coupling for hypersonic control surface design

Project Description

The structural design of a control surface affects temperature distribution and warping, which change the aerodynamic performance, therefore, the methodology to design such surfaces becomes vital for the controllability of hypersonic vehicles, where the flow physics, thermal environment, and structural behaviour are all coupled [1]. These three coupled interactions are difficult to model and hard to effectively design optimised geometries for.

In hypersonic flows, temperatures inside the boundary layer and close to the surface of a vehicle (wall temperature) are relatively high, therefore, the surface warps and deforms. This in turn changes the surrounding flow physics, such as shock structure and heating, and so on. The project aims to develop understanding of this fluid-thermal-structural coupling for control surface applications.

Additionally, the project addresses the design and testing methodology of a hypersonic fin while considering coupled aerodynamics with thermal-structural constraints. This project falls within the EPSRC Continuum Mechanics, Fluid Dynamics and Aerodynamics, and Engineering Design research areas. A scaled fin model will be experimentally tested in the Oxford High Density Tunnel at Mach 5 using different angles of attack to determine relevant boundary conditions.

The surface heat flux and pressure distributions will be measured with thermography, pressure sensitive paint, and surface-mounted sensors, while Schlieren imaging will visualise the flowfield. These measured distributions will be used as boundary conditions in a thermal-mechanical simulation, leading to an optimised internal architecture to be used for the fin test subject that will be subsequently manufactured.

The resulting fin-surface temperature distribution is used to determine the flight-equivalent wall-to-total temperature ratio, which will be vital to use as a similarity parameter for experimental testing, alongside flight-equivalent Reynolds number. The wall-to-total temperature ratio and the resulting thermal gradient within the boundary layer have been shown to impact the transition process [2].

In a subsequent experimental test campaign, this ratio is realised by locally cooling the fin model with liquid nitrogen from the inside. To achieve the precise wall temperature at the different points along the test subject surface, necessary for maintaining a flight-equivalent wall-to-total temperature ratio, the wall thickness will be varied to change the cooling rates accordingly.

This enables coupling between temperature and velocity boundary layers, to study the aerodynamic performance (lift, drag, flowfield structure). This in-the-loop approach can be iterated until a best fin design is found. The project looks to further understanding of fluid-thermal-structural coupling for hypersonic control surface applications and addresses the need for an integrated design methodology of hypersonic vehicle components, aiming to demonstrate that capability through new experimental and simulation-based procedures.

[1] J. D. Anderson, Hypersonic and High-Temperature Gas Dynamics, Third Edition. 2019.

[2] T. Hermann, M. Mcgilvray, C. Hambidge, and L. Doherty, "TOTAL TEMPERATURE MEASUREMENTS IN THE OXFORD HIGH DENSITY TUNNEL Oxford OX2 0ES, United Kingdom D . Buttsworth School of Mechanical and Electrical Engineering, University of Southern Queensland."