Browsing by Author "Mei, Sen"

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    Computational Analysis of Flow in a Turbocharger Turbine with Pulsating Inflow
    (2016-08-30) Mei, Sen; Tezduyar, Tayfun E.
    The turbine of an automobile turbocharger commonly operates under pulsating inflow, which leads to an undesired “hysteresis” performance. This study is to investigate this phenomenon by presenting a computational flow analysis that can capture the pulsating flow physics in a turbocharger turbine. We use a method of higher-order accuracy, and the key techniques include: (i) the Space–Time Variational Multiscale (ST-VMS) method, which is a stabilized formulation and a turbulence model, (ii) the ST Slip Interface (ST-SI) method, which maintains the solution quality near rotor surface, (iii) the Isogeometric Analysis (IGA), where we use NURBS basis functions in space and time, and (iv) weakly-imposed Dirichlet boundary conditions, which can give accurate mean flow solutions on a coarse mesh with unresolved boundary layers. The geometric model is from a realistic turbocharger turbine. The pulsating inflow conditions are taken from a 1D engine-cycle simulation. The computations are carried out with an incompressible-flow solver. The results show that the turbine is likely to operate far from nominal conditions under pulsating inflow, and geometric features such as exhaust manifold and vanes play a significant role in improving the performance. The techniques show a good potential for solving difficult turbomachinery problems.
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    Turbocharger turbine and exhaust manifold flow computation with the Space-Time Variational Multiscale Method and Isogeometric Analysis
    (Elsevier, 2019) Otoguro, Yuto; Takizawa, Kenji; Tezduyar, Tayfun E.; Nagaoka, Kenichiro; Mei, Sen
    We address the computational challenges encountered in turbocharger turbine and exhaust manifold flow analysis. The core computational method is the Space–Time Variational Multiscale (ST-VMS) method, and the other key methods are the ST Isogeometric Analysis (ST-IGA), ST Slip Interface (ST-SI) method, ST/NURBS Mesh Update Method (STNMUM), and a general-purpose NURBS mesh generation method for complex geometries. The ST framework, in a general context, provides higher-order accuracy. The VMS feature of the ST-VMS addresses the computational challenges associated with the multiscale nature of the unsteady flow in the manifold and turbine, and the moving-mesh feature of the ST framework enables high-resolution computation near the rotor surface. The ST-SI 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-IGA enables more accurate representation of the turbine and manifold geometries and increased accuracy in the flow solution. The STNMUM enables exact representation of the mesh rotation. The general-purpose NURBS mesh generation method makes it easier to deal with the complex geometries we have here. An SI also provides mesh generation flexibility in a general context by accurately connecting the two sides of the solution computed over nonmatching meshes. That is enabling us to use nonmatching NURBS meshes here. Stabilization parameters and element length definitions play a significant role in the ST-VMS and ST-SI. For the ST-VMS, we use the stabilization parameters introduced recently, and for the ST-SI, the element length definition we are introducing here. The model we actually compute with includes the exhaust gas purifier, which makes the turbine outflow conditions more realistic. We compute the flow for 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. The computation demonstrates that the methods we use here are very effective in this class of challenging flow analyses.