An automatic static masking technique using Particle Image Velocimetry image ensembles

A robust and easy-to-apply automatic static mask generation technique for PIV images is described. The technique is used after background removal operations and requires an image ensemble with sufficient number of single-frame or double-frame PIV images. The technique does not require any prior knowledge of the flow, illumination conditions, the bounding surface, or static object geometry. The technique categorically marks the fluid phase by exploiting the simple fact that PIV seeding particles reside in the flow medium. There may be a combination of stationary and moving objects in the ensemble, and the technique is not affected by the presence of moving objects, i.e. dynamic masking techniques can still be applied after the static masking operation described here. The generation of static masks of the fluid phase is important as these masks are used to improve accuracy and spatial resolution close to the walls during the evaluation steps of the advanced PIV algorithms. In order to demonstrate the efficiency and limitations of the technique we use several examples including the microfluidics case (Case A) and the flow over periodic hills case (Case B) in the 4th international PIV challenge.