A new model heating capability and study of wall temperature effects in hypersonic boundary layer transitio

Imagine traveling from the United Kingdom to Australia in less than five hours. Or imagine a round-trip flight aboard a commercial spaceplane to a space hotel for the same price as flying executive class nowadays. More than half a century after the technological marvels that led Humankind to set foot on the Moon, both concepts still seem somewhat distant from reality. However, this can become the norm if sustainable hypersonic capabilities are to be developed. High-speed, efficient transportation systems embolden the vision of a highly interconnected civilization, attending to the requirements of an inherently globalized society for the 21st century. For this to become a reality, one must be able to confidently simulate and predict flow behaviour. This is extremely difficult since aerodynamic effects become coupled with thermodynamics and chemistry at such speeds, and are dependent on a multitude of parameters. Whether cruising the atmosphere at five times the speed of sound, or performing a planetary re-entry, when designing a vehicle, parameters such as wall temperature and surface roughness become extremely important.

The first objective of this research is to develop a mechanism to increase surface temperatures of test models to better match hypersonic flight conditions, a capability that is currently lacking at the Oxford Thermofluids Institute. During real hypersonic flights, wall temperatures can reach values in excess of 1200 C, which is difficult to replicate in wind tunnels. Heating up the incoming gas in a wind tunnel is not an option since it usually leads to high noise levels, and the test times are so short the model would not be able to reach steadily reach required temperatures. At Oxford, heating techniques have been used in the past but were only able to reach 600 K, which is not enough to properly encapsulate the flow field at hypersonic speeds. As such, a survey needs to be conducted to assess what heating techniques could be used inside of the available hypersonic wind tunnels at the Oxford Thermofluids Institute to achieve meaningful wall temperatures (e.g., electrical heating, plasma heating, laser heating, etc.). Ultimately, once a choice is made, this research will focus on building, testing and validating said system, starting with benchtop tests. This will also be of great benefit for any future research in hypersonics where wall temperature effects want to be studied with further detail, since the infrastructure and knowledge on how to heat up a model will remain with the university.

The second main objective of this research is to study the effect of wall temperature and surface gas blowing on boundary layer transition, using the selected heating technique mentioned above. The idea is to understand how these effects, coupled together, can trigger transition from laminar to turbulent flow, and contribute to the current literature with new correlations and methods for this phenomena. This is fundamental for hypersonic vehicle design, as it is currently a field of study with high levels of uncertainty. While many parameters that influence this transition have been studied while coupled, there is currently no literature (to the best of the researcher's knowledge) that analyses the effect of wall temperature and surface gas blowing combined; therefore this would be a significant contribution to said literature. This will require designing and building a new test campaign, possibly building up on previous test campaigns done at the Oxford Thermofluids Institute.

This project falls within the EPSRC Fluid dynamics and aerodynamics research area.