Estimation of velocity fields from the axial wire-mesh sensor data

The paper presents briefly the design of the axial sensor and the HIPE test loop that was used in the experiments. The sensor enables the study of the two-phase flow in high resolution (10,000 frames/s, 3 mm × 3 mm resolution). In this paper, the main emphasis is on the study of the different methods that can be applied for the estimation of the velocity fields from the axial wire-mesh sensor data. Two methods have been tested: traditional Time-of-Flight (ToF) estimation and optical flow method. The Time-of-Flight estimation relies on the cross-correlation of the time series of the void fraction values from the different locations. The velocities can be calculated from the Time-of-Flight estimates and the distances between the particular locations. The optical flow methods can be used to evaluate the motion of the objects between the two sequential images. The estimation of the velocity fields from the axial sensor data is analogous to the calculation of the velocity fields from the Particle Image Velocimetry (PIV) images. Now, the same methods are applied to process the axial WMS data. The paper discusses the pros and cons of the different approaches and gives some general recommendations on how and when they should be applied for the WMS data. The velocity fields from the axial sensor experiments are compared to the experiments conducted with the two cross-sectional WMS (32 × 32 sensors). One aim of the studies on axial sensor is to utilize the sensor in research dealing with swirling flows generated by different mechanisms.