Hirofumi Hattori

A New Low-Reynolds-Number One-Equation Model of Turbulence

AbstractIn this study, we propose a new Low-Reynolds-Number (LRN)one-equation model, which is derived from an LRN two-equation(k-ε) model. The derivation of the transport equation, in principle, is based on the assumption that the turbulent structure parameter remains constant. However, the relation for the turbulent structure parameter a1(=|−

Direct numerical simulation and modelling of spanwise rotating channel flow with heat transfer

\bar u\bar v

Analysis of Turbulent Heat Transfer under Various Thermal Conditions with Two-Equation Models

|/k) is modified to account for near-wall turbulence. As a result, the present one-equation model contains a term which takes the near-wall limiting behavior explicitly into account. Thus, the present model provides the correct wall-limiting behavior of turbulence in the vicinity of the wall and can be applied to the analysis of heat transfer. The validity of the present model is tested in channel flows, boundary layer flows with and without pressure gradient, plane wall jet, and flow with separation and reattachment. The calculated results showed good agreement with the direct numerical simulation (DNS) and experimental data.

Nonlinear two-equation model taking into account the wall-limiting behavior and redistribution of stress components

In the present study, we construct a turbulence model based on a low-Reynolds-number non-linear k–ϵ model for turbulent flows in a rotating channel. Two-equation models, in particular the non-linear k–ϵ model, are very effective for solving various flow problems encountered in technological applications. In channel flows with rotation, however, the explicit effects of rotation only appear in the Reynolds stress components. The exact equations for k and ϵ do not have any explicit terms concerned with the rotation effects. Moreover, the Coriolis force vanishes in the momentum equation for a fully developed channel flow with spanwise rotation. Consequently, in order to predict rotating channel flows, after proper revision the Reynolds stress equation model or the non-linear eddy viscosity model should be used. In this study, we improve the non-linear k–ϵ model so as to predict rotating channel flows. In the modelling, the wall-limiting behaviour of turbulence is also considered. First, we evaluated the non-l...

Improvement of the nonlinear eddy diffusivity model for rotational turbulent heat transfer at various rotating axes

Rotating flows with heat transfer are encountered in many applications relevant to engineering, such as in turbomachinery. However, it is no easy matter to make fine measurements of rotating flows with heat transfer. As an alternative, a direct numerical simulation (DNS) has been utilized to examine a canonical rotating flow, and a turbulence model has been used for predicting realistic rotating flows. In this study, to explore the turbulent transport mechanism of rotating shear flows with heat transfer, we have conducted the DNS of fully developed turbulent spanwise rotating channel flows with heat transfer at various rotation numbers. Then, using the DNS results, we have assessed the existing linear and nonlinear two-equation heat-transfer models to understand the performance of the models in rotating channel flows with heat transfer. Finally, we have reconstructed a two-equation turbulence model to predict spanwise rotating channel flows with heat transfer. This article is a modified version of the ori...

DNS and Turbulence Modeling for Turbulent Boundary Layers With Various Thermal Stratifications

Two-equation turbulence models for velocity and temperature (scalar) fields are developed to calculate wall shear flows under various flow conditions and related turbulent heat transfer under various wall thermal conditions. In the present models, we make the modified dissipation rates of both turbulent energy and temperature variance zero at a wall, though the wall limiting behavior of velocity and temperature fluctuations is reproduced exactly. Thus, the models assure computational expediency and convergence. Also, the present k- model is construted using a new type of expression for the Reynolds stress ūiūj proposed by Abe et al. [Trans. JSME B 61 (1995) 1714–1721], whose essential feature lies in introducing the explicit algebraic stress model concept into the nonlinear k- formulation, and the present two-equation heat transfer model is constructed to properly take into account the effects of wall thermal conditions on the eddy diffusivity for heat. The models are tested with five typical velocity fields and four typical thermal fields. Agreement with experiment and direct simulation data is quite satisfactory.

Turbulence Model for Wall-Bounded Flow with Arbitrary Rotating Axes

Two-equation turbulence models for velocity and thermal fields are developed to calculate wall shear flows under various pressure gradient conditions and turbulent heat transfer under various wall thermal conditions. In the present models, we make the dissipation rates of both turbulence energy and temperature variance zero at a wall, though the wall limiting behavior of velocity and temperature fluctuations is reproduced exactly. Thus, the models assure computational expediency and convergence. Also, the present models are constructed to properly take into account the effects of pressure gradient on shear layers and of wall thermal conditions on the eddy diffusivity for heat. The models are tested with three typical velocity fields and four typical thermal fields, all of which can be regarded as essential in engineering applications. Agreement with the experiment and the direct simulation data is quite satisfactory.

DNS AND MODELLING OF ROTATING CHANNEL FLOW WITH HEAT TRANSFER

AbstractNonlinear k–ε models have been extensively used in technological applications. It is clear from the assessment of the existing nonlinear k–ε models using DNS databases that the nonlinear models can not satisfy and reproduce exactly the wall-limiting behavior and the anisotropy of Reynolds normal stress components. Especially, the Reynolds normal stress component,