Application of digital speckle pattern interferometry for fluid velocimetry in wind tunnel flows

This paper shows the feasibility of using digital speckle pattern interfero metry (DSPI) as a fluid velocimetry technique in high speed gaseous flows. The light scattered from an illuminated plane was recorded with a CCD camer a at the same time as a uniform reference beam. A fibre optic was used to b ring this reference beam from the laser cavity to the CCD camera. The compa rison of two subsequent frames gives information about the velocity field. DSPI was applied to a Von Karman street flow set up in a wind tunnel. Parti cle image velocimetry (PIV) measurements were also obtained for comparison with the information provided by DSPI. A system for increasing the measurem ent region when using short coherence length lasers is proposed.