Inverse method using infrared thermography for surface temperature and heat flux measurements

Temperature measurements, for the direct identification of the surface heat flux, are not always possible considering an aggressive environment or an inaccessible zone. That is why an inverse method has been developed: the direct problem with the unknown boundary condition (wall heat flux) is solved by adding an observation equation given by temperature measurements on the opposite face of the wall. In order to estimate spatiotemporal variations of the surface heat flux, an inverse non linear three-dimensional unsteady model has been developed. The resolution is based on the minimisation of a function representing the sum of the differences between the observations (measured surface temperatures) and the calculated temperature at the same position. A compression method using DCT is used to filter the temperature measurements and reduce the number of heat flux components to be estimated. First a numerical validation of the inverse model has been conducted: a flat plate submitted to a specified spatiotemporal heat flux evolution. Then two validation experiments have been developed: impact of a moving laser beam on a flat steel plate and flame-wall interaction. The estimation of high resolution unsteady heat flux cartographies have been demonstrated.