Design, construction and calibration of a transonic wind tunnel

A transonic wind tunnel was designed, constructed and calibrated in order to provide a valuable \ntool for the study of transonic flow phenomena. The wind tunnel makes use of flow properties \nsurrounding the propagation of a shock wave along a tube in order to create the transonic flow. \nAs a result, the wind tunnel is a modified shock tube, with its layout being optimised for \nmaximum flow time. The flow times are dependent on the Mach number of the transonic flow \nbeing created, with the longest realistic flow time being approximately sixty milliseconds. The \nmajority of the shock tube was built from commercially available steel construction tubing which \nwas then attached to a pressure vessel of similar cross sectional dimension. A test section \ncontaining windows was constructed and placed in a position along the length of the tube to \nmaximise the available test flow time. The position optimisation was calculated based on standard \nshock wave theory. The incident shock wave, as well as any resulting flow features, were \nvisualised using schlieren photography. The test piece was designed to be set at angles of attack \nof up to ten degrees, both positive and negative. The main purpose of the testing carried out was \nto validate the functioning of the wind tunnel rather than obtaining more data on the test piece. \nAn RAE2822 aerofoil was used as the test piece due to the large amount of aerodynamic data \navailable on it, especially in the transonic flow region, thus making it an excellent tool for \nvalidation. In addition, the Fluent computational fluid dynamics package made use of the same \naerofoil to validate their numerical results when the package was under development. This meant \nthat for any numerical result obtained for the RAE2822 aerofoil using the Fluent package, there \nwas a high degree of confidence. This fact provided a great tool for comparing results obtained \nexperimentally in the wind tunnel with results obtained numerically. The short duration testing \ntime was found to be adequate for establishing semi-steady state flow at any transonic flow Mach \nnumber. The bursting of the weak diaphragm at the end of the driven section of the shock tube \nresulted in the upstream propagation of a disturbance with a much lower velocity than would be \nseen if the incident shock wave reflected off a solid boundary and thus its arrival at the test \nsection was delayed, resulting in a significant increase in testing time. \nThe results obtained experimentally compared well to results obtained numerically. Transonic \nshock waves that were set up on the test piece had very similar shapes, features and chord-wise \npositions in both experimental and numerical results, showing that the geometric layout of the test \nsection was correct. Furthermore, it was shown that a short duration flow time wind tunnel could \nbe constructed using a shock tube and that accurate results could be obtained through its use.