Browsing by Author "Zhang, Yutong"

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    Computational Flow Analysis of a Cyclone Vacuum Cleaner
    (2019-04-17) Zhang, Yutong; Tezduyar, Tayfun E
    Computational flow analysis of a cyclone vacuum cleaner can provide valuable fluid mechanics information for efficient design and operation. The vacuum cleaner is made of multiple cones, each with a rotational flow field that facilitates the dust collection. Reliable computational analysis requires both accurate representation of the complex geometry and high-resolution representation of the boundary layers near the internal surfaces of the cones. We address these computational challenges with the Space–Time Variational Multiscale (ST-VMS) method and isogeometric discretization, using NURBS basis functions. The ST framework has higher-order accuracy in general, and the VMS feature of the ST-VMS addresses the challenge created by the turbulent nature of the flow. The isogeometric discretization provides a more accurate representation of the geometry and increased accuracy in the flow solution. We conduct our studies for both single-cone and multi-cone configurations, and the comparison of the results from the two helps us discern the reasonableness of using single-cone flow analysis in place of full-machine flow analysis.
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    Space–time VMS flow analysis of a turbocharger turbine with isogeometric discretization: computations with time-dependent and steady-inflow representations of the intake/exhaust cycle
    (Springer, 2019) Otoguro, Yuto; Takizawa, Kenji; Tezduyar, Tayfun E.; Nagaoka, Kenichiro; Avsar, Reha; Zhang, Yutong
    Many of the computational challenges encountered in turbocharger-turbine flow analysis have been addressed by an integrated set of space–time (ST) computational methods. The core computational method is the ST variational multiscale (ST-VMS) method. The ST framework provides higher-order accuracy in general, and the VMS feature of the ST-VMS addresses the computational challenges associated with the multiscale nature of the unsteady flow. The moving-mesh feature of the ST framework enables high-resolution computation near the rotor surface. The ST slip interface (ST-SI) method enables moving-mesh computation of the spinning rotor. The mesh covering the rotor spins with it, and the SI between the spinning mesh and the rest of the mesh accurately connects the two sides of the solution. The ST Isogeometric Analysis enables more accurate representation of the turbine geometry and increased accuracy in the flow solution. The ST/NURBS Mesh Update Method enables exact representation of the mesh rotation. A general-purpose NURBS mesh generation method makes it easier to deal with the complex geometries involved. An SI also provides mesh generation flexibility in a general context by accurately connecting the two sides of the solution computed over nonmatching meshes, and that is enabling the use of nonmatching NURBS meshes in the computations. The computational analysis needs to cover a full intake/exhaust cycle, which is much longer than the turbine rotation cycle because of high rotation speeds, and the long duration required is an additional computational challenge. As one way of addressing that challenge, we propose here to calculate the turbine efficiency for the intake/exhaust cycle by interpolation from the efficiencies associated with a set of steady-inflow computations at different flow rates. The efficiencies obtained from the computations with time-dependent and steady-inflow representations of the intake/exhaust cycle compare well. This demonstrates that predicting the turbine performance from a set of steady-inflow computations is a good way of addressing the challenge associated with the multiple time scales.