Application of an algebraic turbulent heat flux model to a backward facing step flow at low Prandtl number

2018 ◽  
Vol 117 ◽  
pp. 32-44 ◽  
Author(s):  
Andrea De Santis ◽  
Afaque Shams
Author(s):  
I. Otic´ ◽  
G. Gro¨tzbach

Results of direct numerical simulation (DNS) of turbulent Rayleigh-Be´nard convection for a Prandtl number Pr = 0.025 and a Rayleigh number Ra = 105 are used to evaluate the turbulent heat flux and the temperature variance. The DNS evaluated turbulent heat flux is compared with the DNS based results of a standard gradient diffusion turbulent heat flux model and with the DNS based results of a standard algebraic turbulent heat flux model. The influence of the turbulence time scales on the predictions by the standard algebraic heat flux model at these Rayleigh- and Prandtl numbers is investigated. A four equation algebraic turbulent heat flux model based on the transport equations for the turbulent kinetic energy k, for the dissipation of the turbulent kinetic energy ε, for the temperature variance θ2, and for the temperature variance dissipation rate εθ is proposed. This model should be applicable to a wide range of low Prandtl number flows.


Author(s):  
A. Shams ◽  
F. Roelofs ◽  
E. Baglietto ◽  
S. Lardeau ◽  
S. Kenjeres

2013 ◽  
Vol 181 (1) ◽  
pp. 144-156
Author(s):  
M. Pellegrini ◽  
H. Endo ◽  
E. Merzari ◽  
H. Ninokata

Author(s):  
Vera Papp ◽  
Andrea Pucciarelli ◽  
Medhat Sharabi ◽  
Walter Ambrosini

This work proposes simulations of heat transfer under supercritical pressure conditions showing improvements with respect to previous works. This is obtained by the introduction of the Algebraic Heat Flux Model (AHFM) for evaluating the turbulent heat flux in turbulence production terms, using the in-house code THEMAT and the STAR-CCM+ code. The first code makes use of the AHFM also in the energy balance equations, while for the commercial code simplifying assumptions are considered in the implementations. Custom sets of parameters for every condition of inlet temperature and internal diameter are tuned in some cases, driven by the opinion that a single set of parameters cannot be suitable in every flow conditions, considering the complexity of the variables that concur in the heat transfer deterioration phenomenon. The AHFM model gives promising results with new sets of parameters in order to model the deterioration and the recovery phases because of its term related to the variance of temperature.


Author(s):  
Haomin Yuan ◽  
Elia Merzari

The flow characteristic of fluid at low Prandtl number is of continued interest in the nuclear industry because liquid metals are to be used in the next-generation nuclear power reactors. In this work we performed direct numerical simulation (DNS) for turbulent channel flow with fluid of low Prandtl number. The Prandtl number was set to 0.025, which is representative of the behavior of liquid metals. Constant heat flux was imposed on the walls to study heat transfer behavior, with different boundary conditions for temperature fluctuation. The bulk Reynolds number was set as high as 50,000, with a corresponding friction Reynolds number of 1,200, which is closer to the situation in a reactor or a heat exchanger than used in normally available databases. Budgets for turbulent variables were computed and compared with predictions from several RANS turbulence models. In particular, the Algebraic Heat Flux Model (AHFM) has been the focus of this comparison with DNS data. The comparisons highlight some shortcomings of AHFM along with potential improvements.


Sign in / Sign up

Export Citation Format

Share Document