Instantaneous density measurement in two-dimensional gas flow by high speed differential interferometry

The aim of this paper is to present an experimental set-up using a Wollaston prism differential interferometer producing up to twenty successive short exposure white light interferograms at a high framing rate. It is shown that, through optical component calibration, the interferograms can be analysed to yield the instantaneous density field. This method has been successfully tested in the two-dimensional unsteady flow generated by the interaction of a mixing layer and a cavity.List of symbols h height of the downstream edge of the cavity - H height of backward facing step - M Mach number - t time - t time interval between two successive frames - N frequency - double-prism median plane - birefringence angle - _p pressure fluctuation - C_p pressure coefficient - biprism abscissa corresponding to any colour - ₀ biprism reference abscissa corresponding to background colour - _y deviation of light rays - R radius of curvature of spherical mirror - L virtual distance from the middle of the test section to the spherical mirror - E optical thickness - E_e optical thickness corresponding to background colour - d_E difference of optical thickness - d_x abscissa difference - gas density - ₀ stagnation gas density - _e gas density of background colour