Flow structures in solid-liquid suspensions in mixing and confined jets
This thesis investigates the influence of solid particles on different liquid flow systems.
Large-scale periodic fluctuations such as macro instability (MI) phenomena in a mixing
vessel and jet flows in a confined jet were experimentally analyzed by means of LDV. The
influences of different sized (0.5mm-2mm) glass particles (0%vol - 6.2%vol) on the velocity
and turbulence distribution in a jet were investigated, as well as the effects of varying the
amounts of solid particles (up to 11.8%vol) on the frequency and amplitude of macro instabilities.
Two component LDV measurements were conducted at different locations in the
jet and in the mixing vessel. The values were evaluated using the Lomb algorithm to obtain
frequency spectra of the liquid flow. The average axial and lateral velocities, as well as
RMS distributions, were determined together with the integral length scale in the confined
jet to analyse particle effect. The particle Stoke number was evaluated for the different sized
particles and the different flow situations.
The results showed that the MI frequency is not influenced by the addition of solids. However,
the MI amplitude was reduced by the addition of the solid phase although still detectable
up to the highest concentration measured (11.8 %vol). The particles (1.5mm) with
a Stokes number of 1.1, related to the time scale of MI phenomena, caused an increase in
MI strength at intermediate solids loading. This phenomenon could not be observed for
No change in the rate of decrease of the centreline velocity or the jet expansion ratio could
be observed in the confined jet configuration. The RMS values in the jet increased at high
particle loadings; the increase was particularly pronounced in the shear layer close to the
nozzle. With increasing particle size a greater effect on the RMS values could be observed.
The frequency spectra of the flow and the strength of the large-scale instabilities were only
affected by the suspension with the 2mm particles. The 2mm particles had a stabilizing
effect on the jet and moved the instability further downstream while the frequency was
integral length scale