Home – Home – Jornals – Thermophysics and Aeromechanics 2020 number 2

Here, we consider the empirical relationships presented earlier in the literature that describe the thermophysical properties of H₂O + Al₂O₃ nanofluids, such as viscosity and heat conductivity coefficients. The main parameters affecting these properties of nanofluid are considered to be the volume fraction of particles φ, fluid temperature T, and particle size d_p. The suitability of approximation formulas for calculating the viscosity and heat conductivity coefficients is determined by comparing the data calculated by these formulas with the experimental results. The behavior of the analytical curves of thermophysical coefficients is analyzed in the following ranges of influencing parameters: 0 < φ &8804; 0.1, 280 K &8804; Т &8804; 360 K, 1 nm &8804; d_p &8804; 100 nm. Estimates of the degree of dependence of calculation results on the values of these parameters are given. Conclusions on the qualitative and quantitative reliability of the correlation formulas proposed in the literature, as well as on the limits of their applicability in the ranges of variation of the influencing parameters are drawn.

The results of a parametric study of hydrodynamic stability in linear formulation of the Blasius boundary layer stability over two-layer compliant coatings are presented. In the calculations, experimental data for real silicon rubbers of several types on the elasticity modulus and the loss factor as functions of deformation frequency are used. Eight pairs of the coatings have been considered. The effect of coating layer thickness and external flow velocity on flow stability, in particular, on the behavior of the critical Reynolds number, has been studied parametrically. The regions of the critical Reynolds number of nonmonotonic nature, characteristic of most of coatings under consideration, have been found. A qualitative explanation of this effect is given. An analysis of the behavior of the critical Reynolds number allows determination of the optimal ratio of coating thicknesses for interaction with the flow.

The results of investigating the physical and chemical processes in the wall boundary layer on graphite specimens in a nitrogen flow are reported. The effect of the catalytic wall on the heat flux is considered. The emphasis is on analyzing the distribution of the chemical species concentrations across the boundary layer based on a detailed consideration of the mechanism of heterogeneous catalytic reactions under the surface mass flux conditions. The distributions of the chemical species concentrations over the boundary layer thickness at the stagnation point of a blunted graphite body for a particular flight path segment are presented.

The paper presents a theoretical study for a supersonic boundary layer over a flat plate in a stream of air at Mach number M = 2 under the conditions of surface sublimation. The sublimation-prone material is naphthalene (C₁₀ H₈ ). Calculations demonstrated that at a higher surface temperature the mass flowrate of naphthalene evaporation is increasing. This reduces the wall temperature in comparison with a similar flow without sublimation. The high molecular mass of naphthalene (vs. air) and reduction of wall temperature due to the wall material evaporation creates a higher density of the binary gas mixture (air and naphthalene vapor) near the wall. This modification of the boundary layer profiles induces a significant reduction of instability growth rate. This fact was confirmed by calculations based on the linear stability theory. It was found that boundary layer stabilization occurs for growing sublimation surface temperature; it becomes a maximum near the triple point temperature of the coating material. The e^N method gives the estimates of the Reynolds number for laminar-turbulent transition. This shows a theoretical possibility of extension of the laminar boundary layer above a model with sublimation coating.

The mathematical model of unsteady heat transfer in the thermionic thermal protection system during high-enthalpy heating is studied numerically. The effect of evaporation of electrons from the emitter surface on reduction of the temperature of the multilayered shell of the thermionic thermal protection system is demonstrated. The influence of some heat transfer agents in the composite shell on the regimes of heat transfer in the body is considered. Qualitative agreement of the calculated results with available data is obtained.

Results of a physical experiment aimed at measuring the profile of relative excess pressure on a control surface in the near zone of the disturbed region of a schematized model of supersonic passenger aircraft (SPA) are reported. Tests in the test section of the T-313 wind tunnel, aimed at identification of the optimum mounting of SPA-model suspension and ensuring measurements of the full profile of the disturbed-pressure wave involving the leading, intermediate, and closing shock waves, were carried out. Comparisons of calculated data with experimental results are presented. Using the revealed optimum model suspension, measurement results in good agreement with the results of numerical calculations are obtained. The numerical solution to the problem about the flow around the geometric model was obtained and the necessary measurements in the experiment were carried out at freestream Mach number M_¥ = 2.04 and angle of attack a = 4°.

The paper studies turbulent mixing in thermoviscous fluid flow in a 3D cubic domain which is extended periodically in two directions (X and Y). The flow turbulization develops under the impact of two-dimensional chaotic disturbances at mass average Reynolds number Re₁ = 4704. The vortex field structure is discussed in terms of an isosurface of Q-criterion and local enstrophy z_l. For the advanced stages of flow evolution, the study considers Eulerian correlation coefficients for velocity fluctuations (auto-correlation functions) and the cross-correlations of pressure and temperature. The Eulerian correlation coefficient is split for analysis of correlation characteristics in periodicity and wall-normal directions. The integral scale is evaluated depending on the distance to the walls. The flow analysis is performed in the terminology of viscous scale. The mesh resolution is evaluated for the flow regions corresponding to the logarithmic boundary layer and the near-wall thermal layers.

The paper presents a study of the slip velocity for almost spherical bubbles in a downward laminar tube flow. The local slip velocity is defined as a difference between the mean liquid velocity (measured with electrodiffusional method) and the mean bubble velocity (measured with a modified LDA tool with a small size of measurement volume). The law for slip velocity for downward flow is significantly different from a similar law for upward flow. This reveals that the bubble flow motion is rather random than structured in the downward flow.

The flow modes of a vapor-drop mixture in a regasifier-heater of liquefied natural gas are numerically studied on the basis of the model that takes into account polydispersity, power and thermal interaction of phases, processes of breakup, coalescence, evaporation of droplets and condensation of steam. The dynamics of the carrier medium is described by the system of Navier-Stokes equations for a compressible gas, taking into account the exchange of mass, momentum, and energy with a dispersed phase that includes several fractions differing in the size of droplets. Each fraction is described by a system of equations consisting of the continuity equation for the average density, the conservation equations for the momentum components, and the thermal energy conservation equation, taking into account the interfacial exchange of mass, momentum, and energy with the carrier medium. Systems of equations of motion for the carrier medium and fractions of the dispersed phase are solved by the explicit McCormack method with the spatial operator splitting in directions and a scheme of nonlinear correction. At each time step, the main part of the computational algorithm is supplemented with models of breakup, coalescence, evaporation of droplets and vapor condensation, followed by correction of the hydro- and thermodynamic parameters of the mixture. The calculation of the flow modes of the vapor-drop mixture0020in the channel of the regasifier-heater of liquefied natural gas is performed based on the described model.

Results of a study of the air-plasma spraying of cavitation- and hydroabrasive-resistant coatings from powder materials are reported. A method of laboratory (bench) testing of coatings for resistance under pulsed impact loads is proposed. The bench is a laboratory impact tester that strikes an indenter brought in permanent contact with the sample. A measure of the damage inflicted to the surface hardened by a wear-resistant coating is the diameter of the hole produced by the indenter. The moment of coating destruction is the time at which cracks appear in the coating or the peeling occurs. The developed technique of the bench tests for the pulsed impact loading of wear-resistant coatings imitates the operating conditions of the blades of a high-speed propeller of a water-jet propulsion device in shallow water. The method of air-plasma spraying of powder materials as protective coatings was successfully tested when hardening the propeller blades of a water-jet propulsor of a KS-101D river ship.

A method for rapid determination of diffusion coefficients of polar solvents in anisotropic porous materials, making it possible to control the state of products prepared from such materials without destruction, is reported. For implementation of the proposed method, no preliminary calibration of the local solvent concentration in solid phase for the used converter and each new “porous material-solvent” system is required; that circumstance largely increases the research productivity of the method. The method possesses flexibility in terms of the possibility for measuring the values involved in the calculation expression on curve sections with a high sensitivity to parameter changes and in the range with a stable and noise-protected output signal of the concentration converter, which fact ensures an in-creased control accuracy.

This paper presents the results of numerical simulation of air flow with suspended particles through a human nasal cavity. The stationary and nonstationary problem statements were considered. Within the nonstationary case, two variants were studied: for the first variant, the breath cycle is taken with symmetric inhale/exhale, and for the second variant, we modelled a real asymmetric breath cycle. The solution was based on Navier-Stokes equations for laminar flow of incompressible gas. Particle flow is described using the Lagrangean approach with account for Brownian motion. Numerical simulation results were compared with experimental and simulation data from other authors. Results for different variants of problem statement were compared. Asymmetry of breath cycle should be accounted in calculation of particle deposition efficiency. A simple rule was found that replaces the computation-consuming nonstationary calculation with three stationary flow calculations.

A new method is described for measuring the average void fraction of a one-component two-phase flow moving in a channel with a fixed porous aggregate. The known method of cutting off the flow is used but, in contrast, the vapor phase in the cut-off volume is transferred to the condensed state, and the released space is filled with the measured amount of additional fluid. The result of verification using this method is presented for the previously proposed formula for calculating the void fraction of the adiabatic steam-water flow in a channel with a fixed bed of spherical particles.

The enthalpy increment of the CsBi alloy in the temperature range of 432-1127 K of the solid and liquid states has been measured by the mixing method on an isoperibolic calorimeter. Approximation equations have been obtained, and the isobaric heat capacity and enthalpy changes on phase transitions have been determined. The estimated errors of the data on enthalpy and heat capacity of the melt are 0.75 and 1.5-2.0%, respectively. The enthalpy of the alloy formation in the liquid state has been determined. The obtained results have been compared with the calculations based on the laws of ideal solutions.