Experimental investigation of particle concentration profiles in a turbulent channel flow
Creators: Islam, Saqeeb
Publisher: name: University of Alberta Library
Year: 2024

<p>The purpose of this thesis is to obtain a better understanding of the behavior of particles within a particle-laden turbulent channel flow, as well as evaluate the suitability of the flow facility to measure particle-laden flows. Suitability of the flow loop for measurements of particle-laden flows is determined by whether there is significant error in the loops ability to produce a consistent flow field. Particle-laden flows are prevalent across many industries, and so knowing how the particles act within the flow can aid in increasing process accuracy and efficiency. For this thesis the target of analysis is the concentration profile of the particles in the flow, and how the profile varies with Stokes number. To start, the streamwise and wall-normal velocity profiles for the unladen flow were measured using particle image velocimetry at Reynolds numbers starting from 10 000 up to 80 000. The velocity profiles were measured at the midplane of the channel, as well as at 30mm and 45mm offsets from the midplane in both spanwise directions of the channel, and finally at a midplane location upstream of the test section. These velocity profiles were plotted against the channel height and were used to evaluate the flow conditions with respect to the existing literature. <br>
This study examined the concentration profiles of three different types of spherical particles; 420µm polystyrene particles (Stokes numbers from 0.218 to 1.74), 420µm glass particles (Stokes numbers of 0.549 to 4.39), and 1.2mm polystyrene particles (Stokes numbers from 1.86 to 14.9). The polystyrene particles were approximately neutrally buoyant, while the glass particles have a density of approximately 2511 kg/m3. For all particle types, multiple particle concentrations were considered across the same Reynolds numbers as the unladen flow. Observations at the channel midplane for the 420µm glass particles show a general trend that most of the particles accumulate near the bottom of the channel even as the Stokes number is increased. This is contrary to the 420µm polystyrene particles. For all Stokes numbers these particles demonstrate a core-peaking profile for low concentrations and an upper wall peak for the higher 0.5% concentration. Lastly, the 1.2mm particles also show a similar trend at all Stokes numbers, with the plots showing a core peaking profile at lower concentrations, and an upper wall-peaking profile as the concentration is increased. <br>
In addition to the measurements at the channel midplane, the concentration profiles for the 420µm polystyrene particles were also measured at 30mm and 45mm offset locations in each spanwise direction, at a concentration of 0.1%. The observations generally show a core peaking profile as well in the positive spanwise direction, but a wall-peaking profile in the negative spanwise direction for all Stokes numbers, indicating some variation in the particles detected along the spanwise direction. Finally, the 1.2mm particles were measured at the midplane of the test section, as well as a section further upstream. In the test section, for most concentrations, the concentration profile peak moves towards the top of the channel as the Stokes number is increased. At the upstream channel location, for a concentration of 0.1% the concentration profiles were consistently flatter for all Stokes numbers. These observations indicate that the flow loop is suitable for particle laden flow measurements, and the results obtained here are consistent with other observations discussed in various literature. </p>