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Computational Analysis of Air Flow Over a Powder Hill

Jena, Satyasreet
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1733841817000342

Abstract Details

2024, MS, University of Cincinnati, Engineering and Applied Science: Mechanical Engineering.
In industries such as mining and powder handling, workers are at risk of exposure to inhaling particulates as the powder can get aerosolized in their work environments. It is critical to characterize the dustiness or propensity of powders to get aerosolized to quantify workers’ health risks. The Venturi Dustiness Tester (VDT) is widely used for this purpose. The aerosolization process in this device starts at the powder holding tube, where a dome or hill of powder is exposed to very high flow rate and the aerosol gets sucked into the measurement chamber where it is sampled for dustiness characterization. The process of powder hill aerosolization occurring in VDT is very complex as the obstruction caused by the dome leads to vortex shedding and the shape of the hill changes with aerosolization. To keep the problem tractable, a simplified model problem of flow over a solid hemisphere attached to a horizontal substrate in a rectangular duct is analyzed in this thesis. While this model does not account for changing shape of the hill during the aerosolization process, flow features like vortex shedding and their effect of shear and lift forces acting on the dome surface are captured. This information will be useful in understanding how particulate in a powder hill are likely to be affected by the flow. The flow dynamics in the simplified configuration were explored for different flow speeds, including creeping flow (Re<<1), laminar flow, and turbulent flow using computational fluid dynamics techniques. To obtain the inlet velocity profile to provide the inlet boundary condition for the unsteady simulations of flow over the solid dome, a set of steady-state empty duct simulations were performed first. A grid convergence study was carried out at Re = 1000 to establish grid-independent results for the unsteady simulations. The optimized grid was then used for all Reynolds numbers. In the creeping flow regime, the flow was found to be symmetric around the hemisphere as the viscous forces were dominant. Next, Re = 10 case was explored where signs of a recirculation zone were evident. As the flow was ramped up to Re = 100, turbulent model was required to obtain a converged solution. Turbulent flow simulations at Re = 1000 captured vortex shedding on the finer grid. At Re = 10000, the flow became highly turbulent. This case is the closest to the operation of VDT. Many simulations were conducted initially with larger time steps, but the vortex shedding was initially not captured. This was because the larger time step led to averaging over the finer unsteady features. As the timestep was shortened, the velocity and vorticity contour plots showed signs of vortex shedding. A Q-criterion iso-surface was used to visualize the vortex shedding in 3D. Q-criterion plot showed that a vortex sheet had been set up with vortices being shed from the top of the dome and two on either side of the dome. These simulations showed that the correct choices of the grid size and timestep are crucial in accurately capturing the flow dynamics. Vorticity and pressure were tracked in time at the apex of the hemisphere and at the half height of the hemisphere, which showed clear periodic oscillations. The period of oscillations was found to be 1.6×10-4s. Based on this, a calculation of Strouhal number yielded a value of 0.195 for the flow over the hemisphere. This helped to determine the fundamental periodicity of the configuration. The simulations provided a time scale of vortex shedding as well as the required time step to capture this phenomenon. These will be valuable in developing a computational model of aerosolization of a particulate dome in the future.
Milind Jog, Ph.D. (Committee Chair)
Leonid Turkevich, Ph.D. (Committee Member)
Je-Hyeong Bahk, Ph.D. (Committee Member)
Urmila Ghia, Ph.D. (Committee Member)
76 p.
Mechanical Engineering
Computational analysis; Powder hill aerosolization; Turbulent flow

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Citations

  • Jena, S. (2024). Computational Analysis of Air Flow Over a Powder Hill [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1733841817000342

    APA Style (7th edition)

  • Jena, Satyasreet. Computational Analysis of Air Flow Over a Powder Hill. 2024. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1733841817000342.

    MLA Style (8th edition)

  • Jena, Satyasreet. "Computational Analysis of Air Flow Over a Powder Hill." Master's thesis, University of Cincinnati, 2024. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1733841817000342

    Chicago Manual of Style (17th edition)

ucin1733841817000342
© 2024, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.