3D numerical analysis of thermal-hydraulic behaviors of turbulent flow inside twisted square ductsPromthaisong, P.; Chuwattanakul, V.; Eiamsa-ard, S.
2020 Thermophysics and Aeromechanics
doi: 10.1134/S086986432003004X
Heat transfer, local distributions of Nusselt number, flow structure, and friction characteristics of twisted square ducts are presented. Numerical analysis was carried out to investigate the influence of the twist ratio (TR = p/D = 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, and 6.0) on the thermal-hydraulic performance of twisted square ducts under constant wall heat flux condition for Reynolds numbers based on the hydraulic diameter of the twisted square duct ranging from 3000 to 20 000. The straight square duct was also analyzed for comparison. The numerical results showed that the twisted square ducts were more efficient in heat transfer than the straight square ducts because the swirl flow helped to increase fluid mixing and reduce thermal layer boundary thickness. The decrease of the twist ratio led to the increase in the Nusselt number and friction factor due to the higher frequency of swirl flow. As compared to the straight square duct, the twisted square ducts with TR = 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, and 6.0 improved heat transfer by 52, 49.82, 45.85, 42.22, 39.54, 35.41, and 31.77 %, respectively. Among the studied twisted ducts, the ones with twist ratio TR = 3.5 offered the maximum thermal enhancement factor of 1.42 at Re = 3000. In addition, the results also revealed that the twisted square ducts are thermo-hydraulically superior to the straight square ducts.
Blockage effect induced by an airfoil model in the low-velocity wind tunnel test sectionKornilov, V. I.; Popkov, A. N.
2020 Thermophysics and Aeromechanics
doi: 10.1134/S0869864320030051
The results of computational and experimental studies of the flow around a symmetric airfoil with a relative thickness of 12% in the free stream and in a low-velocity wind tunnel with a closed test section are presented. The experiments are performed for the Reynolds number Rec = 0.7·106−2·107 and angles of attack a = −12°÷12°. The problem is numerically solved in a 2D formulation by using the ANSYS Fluent software package. The mathematical model of the flow includes steady Reynolds equations closed by different turbulence models, including the k-ω SST model, which is a superposition of the k-ε and k-ω models. A significant effect of blockage of the wind tunnel test section with limited dimensions by the airfoil on the flow character and aerodynamic characteristics of the airfoil even if the blockage coefficient is only 5.7% is demonstrated.
Magneto-convection inside a tilted enclosurePirmohammadi, M.; Salehi-Shabestari, A.
2020 Thermophysics and Aeromechanics
doi: 10.1134/S0869864320030063
In this study, laminar magneto-convection flow of a viscous fluid in an inclined enclosure is considered. The temperature gradient is applied on two opposing walls while the other two walls are maintained adiabatic. In order to solve the governing non-linear differential equations, an in-house developed code based on the finite volume method is utilized. The fluid of interest is molten sodium whose thermal and electrical properties such as heat capacity, thermal and electrical conductivity are temperature dependent. Representative results illustrating the effects of the enclosure inclination angle on the contour maps of the streamlines and temperature are reported and discussed. In addition, results for the midsection velocity profile and the average Nusselt number at the hot wall of the enclosure are presented and discussed for various inclination angles and Hartmann numbers. It is observed that for Hartmann number of 600, an increase in the inclination angle leads to the growth of the number of vortices in the enclosure.
Rheology model for turbulent suspension flow through a horizontal channelGavrilov, A. A.; Shebelev, A. V.
2020 Thermophysics and Aeromechanics
doi: 10.1134/S0869864320030075
A model was developed for solids-liquid flow with any solids concentrations. The model includes the two-phase flow equations for the entire flow. It includes also the rheology law and the particle transfer equation with account for interphase slipping. The statistical model of turbulence accounts for the turbulence modulation by particles. The model was tested on a problem about a steady state flow with suspended heavy particles in a horizontal pipe. Comparison with experimental data and other accurate simulations demonstrated that this new model is useful for predicting the features of turbulent suspension flows. The secondary flows in a pipe show three-layered structure of the two-phase flow.
Experimental study of momentum transfer in a cellular flame of rich and lean propane-butane/air mixtureBoyarshinov, B. F.; Fedorov, S. Yu.
2020 Thermophysics and Aeromechanics
doi: 10.1134/S0869864320030099
To simulate a cellular flame, rich (equivalent ratio Φ = 1.4) and lean (Φ = 0.9) propane-butane/air mixtures were used in a burner, which forms a stationary flame with a single cell. Experimental data on the temperature fields were obtained using the coherent anti-Stokes Raman scattering (CARS) method; the velocity components were measured using PIV (Particle Image Velocimetry) equipment. The terms of friction stress and static pressure in the momentum transfer equations were calculated using the balance method. It is shown that the equality of dynamic and static pressures associated with the thermal expansion of the combustion products is satisfied on the cellular flame surface. Flameout occurs when the magnitude of the pressure head becomes greater than the magnitude of a static pressure change. The shear stress profiles contain extrema, whose coordinates are associated with streamline curvatures and are close to the position of the heat release region at combustion of lean and rich mixtures.
Numerical simulation in the diffraction approximation of laser radiation interaction with a stream of microparticlesStatsenko, P. A.; Khomyakov, M. N.
2020 Thermophysics and Aeromechanics
doi: 10.1134/S0869864320030105
In laser cladding, the interaction of laser radiation with the powder flow and the substrate plays a key role. Surface heating depends on the distribution of radiation on the surface of the material, which is determined by the interaction of radiation with the flow of the powder microparticles. Usually, in models for calculating laser beam attenuation, the interaction of radiation with microparticles is limited to a simple geometric consideration based on the ratio of the cross-section area of the particles to the total area of the cross section under consideration, without taking into account the influence of diffraction. Radiation propagation is also considered in epy geometric approximation. The presented model allows taking into account the phenomenon of diffraction on powder microparticles. The results obtained using the model with radiation propagation in the geometric approximation are compared with the model with radiation propagation in the diffraction approximation proposed by the authors. It is shown that the numerical model of radiation attenuation and propagation in the diffraction approximation is applicable for complex analysis of the interaction between a laser beam, a particle stream, and a surface. The model allows estimating the beam attenuation due to interaction with the flow of microparticles and obtaining the intensity distribution on the surface of the substrate.