Underlying mechanism of numerical instability in Large-Eddy Simulation of turbulent flows

Ida, Masato; Taniguchi, Nobuyuki*

Physical Review E, 69(4), p.046701_1 - 046701_9, 2004/04

https://doi.org/10.1103/PhysRevE.69.046701

This paper extends our recent theoretical work concerning the feasibility of stable and accurate computation of turbulence using a large eddy simulation. In our previous paper, it was shown, based on a simple assumption regarding the instantaneous streamwise velocity, that the application of the Gaussian filter to the Navier-Stokes equations can result in the appearance of a numerically unstable term. In the present paper, based on assumptions regarding the statistically averaged velocity, we show that in several situations, the shears appearing in the statistically averaged velocity field numerically destabilize the fluctuation components because of the derivation of a numerically unstable term that represents negative diffusion in a fixed direction. This finding can explain the problematic numerical instability that has been encountered in large eddy simulations of wall-bounded flows. The present result suggests that if there is no failure in modeling, the resulting subgrid-scale model can still have unstable characteristics.

Verification of models for bubble turbulent diffusion and bubble diameter in multi-dimensional two-fluid model

Onuki, Akira; Akimoto, Hajime

Proceedings of the 8th International Symposium on Flow Modeling and Turbulence Measurements (FMTM2001) (CD-ROM), 7 Pages, 2001/12

Multi-dimensional analyses have been expected with expanding computation resources for gas-liquid two-phase flow. We recently developed models for bubble turbulent diffusion and bubble diameter to predict the phase distribution by a multi-dimensional two-fluid model. This study was performed to verify our model. The verification was performed using databases under diameter; 9 mm to 155 mm, pressure; atmospheric to 4.9 MPa, flow rate; superficial gas velocity = 0.01 to 5.5 m/s and superficial liquid one = 0.0 to 4.3 m/s, fluid combination; air-water or steam-water. Through the assessments, our model was found to be applicable to the wide range of flow conditions including the effect of pipe diameter. The shape of phase distribution and the average void fraction are predicted well qualitatively and quantitatively. Since the model is established using the ratio of bubble diameter to eddy size as a key-parameter, the ratio is one of important parameters to develop the constitutive equations in the multi-dimensional two-fluid model.

Development of an atmospheric dispersion and dose calculation code for real-time response by using small-scale computer

Chino, Masamichi; Hayashi, Takashi; Ishikawa, Hirohiko; Yokokawa, Mitsuo

JAERI-M 90-173, 23 Pages, 1990/10

JAERI-M-90-173.pdf:1.42MB

no abstracts in English

Effectiveness of an adaptive acceleration method for inner iterations in some neutron diffusion codes

; *

Nuclear Science and Engineering, 77, p.360 - 367, 1981/00

https://doi.org/10.13182/NSE81-A19845

no abstracts in English