Liquid crystal thermography in high speed flows

This thesis concerns the development and application of liquid crystal thermography to high speed, in particular hypersonic, flows. Thermochromic liquid crystals provide a repeatable and reversible colour change with temperature. This optical response can be calibrated, and utilised to provide high spatial resolution surface heat transfer data for liquid crystal coated models.A quantitative transient liquid crystal thermography technique has been developed, and applied to wind tunnel models with emphasis on interference heating interactions, where the flow over the model is disturbed by a fin or jet, creating a complex flowfield with regions of enhanced heat transfer. The liquid crystal heat transfer measurement technique and its application are described along with results for the three types of flowfield investigated.Tests were conducted on a flat plate with a transverse sonic jet in hypersonic laminar flow (M = 6.7, unit Re = 7.6 x 106 m-1). Four different jet gases were investigated. The resultant interaction created a complex interference flowfield containing a number of horseshoe vortices close to the jet. Regions of enhanced heating were observed on the flat plate surface and in some cases regions of cooling, extending upstream of the jet, were also present.Heat transfer measurements were obtained, for Matra BAe Dynamics, on a non-axisymmetric generic missile forebody containing an angled sensor window set back from the leading edge. These experiments took place in the BAe Guided Weapons Wind Tunnel at M = 3 and 4, with unit Re = 3.2 x 107 m-1 and 3.7 x 107 m-1 respectively. The effect of incidence and sideslip on the forebody upper surface heating were also investigated. Results show that the heat transfer over the forebody is reasonably uniform, with an increase over the window. For nose up incidence, vortices separating from the nose impinge on the window region creating symmetrical peaks in heat transfer about the forebody centre line.