A. A. Dekterev

Measuring the heat-transfer coefficient of nanofluid based on copper oxide in a cylindrical channel

The heat-transfer coefficient of nanofluid during its flow in a cylindrical channel is studied experimentally. The studied nanofluid was prepared based on distilled water and CuO nanoparticles. Nanoparticle concentration varied in the range from 0.25 to 2% in the volume. The nanofluid was stabilized using a xanthane gum biopolymer the mass concentration of which did not exceed 0.03%. Considerable intensification of heat transfer was found. The nanofluid appeared to be Newtonian when particle concentrations exceeded 0.25%. Estimates for rheological parameters of the nanofluid and thermal conductivity coefficient have been obtained.

Mathematical modeling of low-frequency pressure fluctuations in hydroturbine ducts

The results of the modeling of unsteady three-dimensional flows in the hydroturbine ducts of two high-head hydroelectric stations are presented. The flow structure behind the turbine wheel is analyzed and its effect on the frequency and the intensity of unsteady processes in the duct is shown. The individual features and the general tendencies in the behavior of the fluctuation characteristics of both turbines are established.

Modeling of swirling flows with coherent structures using the unsteady Reynolds stress transport model

Swirling flows are investigated using an unsteady model based on the Reynolds stress transport equations. Swirling flows with vortex core precession are considered, namely, the swirling flow behind an abrupt expansion and the swirling flow in a burner with an annular fuel inlet. The method under consideration is shown to well reproduce the recirculation flow formed as a result of the vortex core precession, with respect to both mean and fluctuation parameters. At the same time, the calculations in accordance with the unsteady model prolong the central recirculation zone. It is established that the contributions made by the resolvable and modeled components of the Reynolds stress tensor to the turbulent transport are comparable.

Comparative study of different combustion models for turbulent gas flames

Several popular turbulent combustion models have been tested in a computational study of three experimentally well-documented non-swirling and swirling jet flames. Different combinations of turbulence, combustion and reaction mechanisms models were considered. It is shown that the eddy- dissipation concept (EDC) and the probability-density function (PDF) of flamelet combustion models with detailed kinetics mechanisms provide the best results for all flames examined. For some cases, a combination of RANS turbulence models and less costly combustion approaches (Hybrid or EDC with 4 reactions) also gives acceptable results.