This dissertation conducts a systematic study of the hydrodynamics of a small single bubble in turbulent horizontal channel flow. The effects of Reynolds number on bubble formation and its shape, velocity, and trajectory were investigated experimentally. A Shack Hartman wavefront sensor and a high-speed video camera were used to collect images at various points downstream from the bubble injection point. This provided information on bubble size, velocity, and spatial location as a function of Reynolds number. Particle image velocimetry (PIV) was used to measure both mean and turbulent liquid velocity statistical profiles. The data collected using PIV coupled with the analysis of the three-dimensional trajectory of a single bubble completely characterizes the flow.
As a result, the optimal parameters for bubble formation in a horizontal channel are found in terms of the bubble injection velocity at the injection nozzle, and the necessary bubble volume for stabilization. Specifically, it is found that the bubble shape near the injection nozzle (x=2H, where H is the width of the channel) is not stable but becomes more stable in terms of its shape and orientation in the central section in the vertical direction of the experimental pipe. Investigations of bubble trajectory show that at a distance equal to the channel width from the injection nozzle, the buoyancy force is dominant and, as a result, the bubble trajectory is sufficiently stable and independent of the Reynolds number. Thus, it can be described by equations of motion resulting in a parabolic function. Further away from the nozzle, turbulent effects dominate over the buoyancy force and the bubble trajectory cannot be predicted with certainty for Reynolds numbers greater than 74000. A critical regime was found for the current geometry where a detailed investigation of the streamwise and vertical bubble velocities was conducted to assess the dominant forces controlling them. It is found that the previously mentioned velocity components depend on the Reynolds number. Also, drag and buoyancy forces, in addition to the turbulence dispersion force, are the main factors affecting the bubble velocity. An experimental study of the continuous phase (bubble carrier) velocities allows one to establish a correlation between the turbulent eddies and the bubble motion. The use of a stochastic turbulence force for predicting the bubble trajectory is proposed. This idea is implemented in a numerical model to simulate the bubble trajectory in turbulent pipe flow. It is shown that this model reflects the experimental data within the parameters investigated sufficiently well. Overall, the present study presents a thorough description of bubble formation and behaviour for different Reynolds numbers. All results are given using non-dimensional parameters for researcher’s convenience to reproduce experiments.