Toward Excellence in Turbomachinery Computational Fluid Dynamics: A Hybrid Structured-Unstructured Reynolds-Averaged Navier-Stokes Solver

[+] Author and Article Information
Hong Yang, Dirk Nuernberger

Institute of Propulsion Technology, German Aerospace Center (DLR), Linder Hoehe, 51147 Cologne, Germany

Hans-Peter Kersken

Simulation and Software Technology, German Aerospace Center (DLR), Linder Hoehe, 51147 Cologne, Germany

J. Turbomach 128(2), 390-402 (Feb 01, 2005) (13 pages) doi:10.1115/1.2162182 History: Received October 01, 2004; Revised February 01, 2005

A three-dimensional hybrid structured-unstructured Reynolds-averaged Navier-Stokes (RANS) solver has been developed to simulate flows in complex turbomachinery geometries. It is built by coupling an existing structured computational fluid dynamics (CFD) solver with a newly developed unstructured-grid module via a conservative hybrid-grid interfacing algorithm, so that it can get benefits from the both structured and unstructured grids. The unstructured-grid module has been developed with consistent numerical algorithms, data structure, user interface and parallelization to those of the structured one. The numerical features of the hybrid RANS solver are its second-order accurate upwind scheme in space, its SGS implicit formulation of time integration, and its accurate modeling of steady/unsteady boundary conditions for multistage turbomachinery flows. The hybrid-grid interfacing algorithm is essentially an extension of the conservative zonal approach that has been previously applied on the mismatched zonal interface of the structured grids, and it is fully conservative and also second-order accurate. Due to the mismatched grids allowed at the block interface, users would have great flexibility to build the hybrid grids even with different structured and unstructured grid generators. The performance of the hybrid RANS solver is assessed with a variety of validation and application examples, through which the hybrid RANS solver has been demonstrated to be able to cope with the flows in complex turbomachinery geometries and to be promising for the future industrial applications.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Schematic of hybrid-grid interface

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Figure 2

Hexahedral grid around flat plate

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Figure 3

Comparison of convergence for flat plate computations (y+=1, CFL No. =20)

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Figure 14

Radial distributions of circumferentially averaged total pressure, Mach number, and flow angle at the entry and exit of the rotor (design point)

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Figure 4

Comparison of nondimensional eddy viscosity νT∕ν0 contours in the boundary layer of flat plate (y+=1, scaling factor x:y=1:5). (top) Unstructured solver and (bottom) structured solver.

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Figure 5

Comparison of skin friction factor on flat plate

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Figure 6

Comparison of velocity profile at the middle of flat plate

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Figure 7

The simulated flat-plate boundary layer across the hybrid-grid interface (contours of the eddy viscosity νT∕ν0, y+=1, scaling factor x:y=1:5)

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Figure 8

The skin friction factor on flat plate from the hybrid-grid simulation (y+=1 case)

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Figure 9

Subsonic flow in the bump channel – grids, Mach number contours, and Mach number at walls (Mainflow=0.5). (top) Hybrid grid, (middle) structured grid, and (bottom) Mach number at walls.

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Figure 10

Grids in the bump channel, supersonic case. (top) Hybrid grid (6957 faces on viewing plane) and (bottom) structured grid (4400 faces on viewing plane).

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Figure 11

Comparison of convergence on the structured and hybrid grids for the subsonic flow in the bump channel (CFL No. =20)

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Figure 12

Mach number contours for the supersonic flow in the bump channel (Mainflow=1.4) (top) with hybrid grid and (bottom) with structured grid

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Figure 13

Numerical model of the 1.5-stage compressor using hybrid grid in rotor tip clearance gap

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Figure 15

Comparison of predicted and measured pressure distributions on stator blade surfaces at 90% span (design point). (left) Stator 0 and (right) stator 1.

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Figure 16

Comparison of the simulated results with the experimental data at operating point BP2. (left) Total pressure at rotor entry and exit and (right) isentropic Mach number on stator-1 blade surfaces at 90% span.

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Figure 17

Numerical model of moving-bar experiment using hybrid grids

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Figure 18

Pressure coefficient distributions along blade surfaces

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Figure 19

Instantaneous distribution of nondimensional eddy viscosity νT∕ν0

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Figure 20

Scaled mass flowrate versus time step at entry and exit boundaries

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Figure 21

FFT spectrum of unsteady mass flow signal in the wake of the moving bar

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Figure 27

Comparison of computed pressure contour distributions—close-up around the interface of the intake and the IGV. (left) Hybrid and (right) structured.

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Figure 28

Comparison of pressure contours at the main exit of the intake—a rear view. (left) Hybrid and (right) structured.

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Figure 22

Comparison of unsteady hot-film signals (left) and predicted suction-side skin friction (right) over three wake passing periods

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Figure 23

Hybrid grid model of the intake and IGV

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Figure 24

Structured grid model of the intake and IGV

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Figure 25

Mass flowrate versus time step for the hybrid grid simulation of the intake and IGV

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Figure 26

Comparison of pressure flooded contours at outer boundaries—a global view for overall. (left) Hybrid and (right) structured.




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