Tracer particle momentum effects in vortex flows

Abstract

The measurement of vortex flows with particle-image velocimetry (PIV) is particularly susceptible to error arising from the finite mass of the tracer particles, owing to the high velocities and accelerations typically experienced. A classical model of Stokes-flow particle transport is adopted, and an approximate solution for the case of particle transport within an axisymmetric, quasi-two-dimensional Batchelor q-vortex is presented. A generalized expression for the maximum particle tracking error is proposed for each of the velocity components, and the importance of finite particle size distributions is discussed. The results indicate that the tangential velocity component is significantly less sensitive to tracking error than the radial component, and that the conventional particle selection criterion (based on the particle Stokes number) may result in either over-or under-sized particles for a specified allowable error bound. Results were demonstrated by means of PIV measurements carried out in air and water using particles with very different properties.

On the mechanisms of secondary flows in a gas vortex unit

“…The magnitude of the radial and axial velocities in the bulk flow are so low that they may be in the inaccuracy range of SPIV measurements (3% for azimuthal velocities). It is known from literature that the SPIV error can be high for radial velocity measurements in highly swirling flows . In the bulk region, the centrifugal force on a gas element is balanced by the radial pressure gradient (Eq.…”

“…It is known from literature that the SPIV error can be high for radial velocity measurements in highly swirling flows. 34 In the bulk region, the centrifugal force on a gas element is balanced by the radial pressure gradient (Eq. 13).…”

Influence of Upstream Total Pressure Profiles on S-Duct Intake Flow Distortion

“…These uncertainty figures account for no particle tracking errors due to centrifugal forces caused by the flow to the particles. As shown by Birch and Martin [28] and Raffel et al [27], the in-plane circumferential velocity component is far less susceptible to particle momentum errors than the radial velocity.…”

Calibration and Use of n-Hole Velocity Probes

“…Furthermore, because they can provide local measurements of the three components of fluid velocity as well as of the local static and total pressure, they are of particular use in wake surveys (see [1,2,3,4] and references cited therein), for which optical methods may present difficulties owing to the potential flow interference arising from particle injection [5] and particle momentum effects [6].…”