A numerical study of the influence of the Basset force on the statistics of LDV velocity data sampled in a flow region with a large spatial velocity gradient

Abstract

 The motion of small particles, such as those typically used as seeding particles for tracer particle flow velocity measurement techniques, is studied numerically for a flow region with a large spatial velocity gradient. The influence of the Basset history integral on the statistics of results of particle motion calculations which are based on multi-disperse particle size distributions is investigated. The biasing of the measured velocity data, with regard to the actual flow velocity, which results as a consequence of such particle size distributions is discussed. It is found that the net effect of the Basset integral on the calculations is indeed to reduce the maximum RMS deviation associated with the multi-disperse distribution and that the relative reduction increases with a decreasing particle density. The main result of this study is, thus, that it is desirable to use light tracer particles not only because they more readily adjust to a changed flow velocity but in particular also because they tend to contribute less to the overall RMS deviation of velocity data sampled in a region with a large spatial gradient of the flow velocity.