Large Eddy and Reynolds-Averaged Navier - Stokes Simulations of Turbulent Flow Over an Airfoil

The use of implantable pumps for cardiac support (Ventricular Assist Devices) has proven to be a promising option for the treatment of advanced heart failure. Avoiding blood damage and achieving high efficiencies represent two main challenges in the optimization process. To improve VADs, it is important to understand the turbulent flow field in depth in order to minimize losses and blood damage. The application of the Large-eddy simulation (LES) is an appropriate approach to simulate the flow field because turbulent structures and flow patterns, which are connected to losses and blood damage, are directly resolved. The focus of this paper is the comparison between an LES and an Unsteady Reynolds-Averaged Navier-Stokes simulation (URANS) because the latter one is the most frequently used approach for simulating the flow in VADs. Integral quantities like pressure head and efficiency are in a good agreement between both methods. Additionally, the mean velocity fields show similar tendencies. However, LES and URANS show different results for the turbulent kinetic energy. Deviations of several tens of percent can be also observed for a blood damage parameter, which depend on velocity gradients. Possible reasons for the deviations will be investigated in future works.

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PANS Turbulence Model for Seamless Transition Between RANS and LES: Fixed-Point Analysis and Preliminary Results

Volume 2: Symposia, Parts A, B, and C ◽

10.1115/fedsm2003-45336 ◽

2003 ◽

Cited By ~ 40

Author(s):

Sharath S. Girimaji ◽

Ravi Srinivasan ◽

Euhwan Jeong

Keyword(s):

Fixed Point ◽

Navier Stokes ◽

Control Parameters ◽

Preliminary Results ◽

Point Analysis ◽

Large Eddy ◽

Seamless Transition ◽

Bridging Model ◽

Reynolds Averaged Navier Stokes ◽

Initial Results

Partially-averaged Navier-Stokes (PANS) approach has been recently developed as a possible bridging model between Reynolds-averaged Navier-Stokes (RANS) method and large-eddy simulations (LES). The resolution control parameters in PANS are the fractions of unresolved kinetic energy (fk) and unresolved dissipation (fε). We investigate the fixed-point behavior of PANS and present some preliminary results obtained using this model. By comparing the fixed-point behavior of PANS and URANS (unsteady Reynolds-averaged Navier-Stokes) methods, the possible advantage of the former over the latter is explained. Initial results from two-dimensional simulations of flow past square results are also presented.

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Large-eddy simulations of tip leakage and secondary flows in an axial compressor cascade using a near-wall turbulence model

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1243/09576509jpe825 ◽

2009 ◽

Vol 223 (6) ◽

pp. 645-655 ◽

Cited By ~ 12

Author(s):

D Borello ◽

G Delibra ◽

K Hanjalić ◽

F Rispoli

Keyword(s):

Secondary Flows ◽

Tip Clearance ◽

Navier Stokes ◽

Wall Region ◽

Compressor Cascade ◽

Tip Leakage ◽

Computational Mesh ◽

Large Eddy ◽

Reynolds Averaged Navier Stokes ◽

Near Wall

This paper reports on the application of unsteady Reynolds averaged Navier—Stokes (U-RANS) and hybrid large-eddy simulation (LES)/Reynolds averaged Navier—Stokes (RANS) methods to predict flows in compressor cascades using an affordable computational mesh. Both approaches use the ζ— f elliptic relaxation eddy-viscosity model, which for U-RANS prevails throughout the flow, whereas for the hybrid the U-RANS is active only in the near-wall region, coupled with the dynamic LES in the rest of the flow. In this ‘seamless’ coupling the dissipation rate in the k-equation is multiplied by a grid-detection function in terms of the ratio of the RANS and LES length scales. The potential of both approaches was tested in several benchmark flows showing satisfactory agreement with the available experimental results. The flow pattern through the tip clearance in a low-speed linear cascade shows close similarity with experimental evidence, indicating that both approaches can reproduce qualitatively the tip leakage and tip separation vortices with a relatively coarse computational mesh. The hybrid method, however, showed to be superior in capturing the evolution of vortical structures and related unsteadiness in the hub and wake regions.

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