Hypersonic flight is currently an area of research with a lot of emerging technological developments that are aiming towards making hypersonic propulsion vehicles a viable means of high speed flight. One of the most viable methods used at current to model hypersonic flight, is through the use of a shock tunnel. Due to the mechanisms by which a shock tunnel operates, once the test gas reaches the test section it is often at high temperatures, and speeds much greater than the speed of sound. As a result, high temperature gas effects, such as excitation of vibrational energy modes, causes a change in flow characteristics that is not accounted for by analytical modelling methods such as Rayleigh Pitot pressure equations.
The aims of this thesis are to understand the influence of thermal, and chemical non-equilibrium on flow conditions towards stagnation due to the presence of a Pitot tube. The influence of these high temperature gas effects on stagnation pressure was then used to determine the relative accuracy of Rayleigh Pitot pressure methods. In order to understand the mechanisms of thermal relaxation, and to provide preliminary results for comparison, an inviscid numerical solver was developed that assumed chemically frozen flow. Further testing was completed through the use of CFD package ‘US3D’, allowing the inclusion of chemical effects and flow viscosity. A parametric study was completed by altering the flow conditions to isolate the effects of individual flow characteristics, for example by running simulations with thermal effects on, followed by thermal effects off. Testing was completed for two different nozzles and input conditions; M8 nozzle, and M6 nozzle.
Due to the development of a shock wave upstream from the Pitot tube contributing to almost 90% of pressure rise within the flow, the subsonic region towards stagnation contributed to the remaining 10%. As flow is considered both chemically and thermally frozen across a shock wave, all test cases had a good coherence for post shock pressure. When thermal effects and chemical effects were isolated, their influence on stagnation pressure was found to be less than 1% for all test cases. It was determined that the accuracy of Rayleigh Pitot and Rayleigh Pitot Simplified methods were within 2% and 3% respectively when compared to CFD results. Based on the two nozzles tested, it was deemed possible to apply the Rayleigh Simplified method with an adjusted coefficient in order to predict stagnation pressure within 1% of the actual pressure modelled by CFD under ‘real gas’ test conditions.