Abstract
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.
Highlights
The challenges faced in computational flow analysis of turbocharger turbines include unsteady flow through a complex geometry, the need for high-resolution flow representation near the rotor surface, high Reynolds numbers, and multiscale flow behavior
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
One of the main computational challenges encountered in turbocharger-turbine flow analysis is the multiple time scales involved
Summary
The challenges faced in computational flow analysis of turbocharger turbines include unsteady flow through a complex geometry, the need for high-resolution flow representation near the rotor surface, high Reynolds numbers, and multiscale flow behavior. Computations with time-dependent representation of the Computational Mechanics (2019) 64:1403–1419 intake/exhaust cycle require long-durations in the turbine time scale. The parts of these challenges faced in turbine computations in a more general context have been addressed by other researchers, with approaches ranging from using a single blade with spatially-periodic boundary conditions (see, e.g., [1,2,3,4,5,6,7,8]) to “sliding interfaces” (see, e.g., [9,10,11,12]). The core computational method is the space–time variational multiscale (ST-VMS) method [17,18,19], and the other key methods are the ST Slip Interface (ST-SI) method [20,21], ST Isogeometric Analysis (ST-IGA) [13,17,22], ST/NURBS Mesh Update Method (STNMUM) [22,23,24,25], and a general-purpose NURBS mesh generation method for complex geometries [14,15]
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