Home – Home – Jornals – Thermophysics and Aeromechanics 2016 number 2

Various issues of numerical simulation of supersonic gas flows with allowance for thermochemical nonequilibrium on the basis of fluid dynamic equations in the two-temperature approximation are discussed. The computational tool for modeling flows with thermochemical nonequilibrium is the commercial software package ANSYS Fluent with an additional user-defined open-code module. A comparative analysis of results obtained by various models of vibration-dissociation coupling in binary gas mixtures of nitrogen and oxygen is performed. Results of numerical simulations are compared with available experimental data. 

The aim of this study is to investigate numerically the effects of four vortices on the dynamic, scalar, and turbulent fields of the hydrogen jet. These vortices, which appear in the vicinities of the nozzle, are created by the vortex generators (VGs), and they are assembled with periodicity or symmetry in order, respectively, to give four vortices of the same or opposite direction. A second-order Reynolds stress model is used to investigate asymmetric turbulent jet. The results indicate that the presence of the vortex near the emission jet section noticeably enhances mixing to ensure a good combustion.

A supersonic air flow in a plane channel with a transverse turbulent jet of hydrogen injected through a slot on the bottom wall is simulated. The algorithm for solving the Favre-averaged NavierStokes equations for the flow of a perfect multispecies gas on the basis of the WENO scheme is proposed. The main attention is paid to the interaction of the shock-wave structure with the boundary layers on the upper and lower duct walls under the conditions of an internal turbulent flow. Namely, a detailed study of the structure of the flow is done, and separation and mixing depending on the jet slot width are investigated. It is found that in addition to well-known shock-wave structures produced by the interaction of the free stream with the transverse jet and the bow shock interaction with the boundary layers near the walls, an additional system of shock waves and the flow separation arise on the bottom wall downstream at some distance from the jet. The comparison with the experimental data is performed.

Recent years many flight control systems and industries are employing PID con-trollers to improve the dynamic behavior of the characteristics. In this paper, PID con-troller is developed to improve the stability and performance of general aviation aircraft system. Designing the optimum PID controller parameters for a pitch control aircraft is important in expanding the flight safety envelope. Mathematical model is developed to describe the longitudinal pitch control of an aircraft. The PID controller is designed based on the dynamic modeling of an aircraft system. Different tuning methods namely Zeigler–Nichols method (ZN), Modified Zeigler–Nichols method, Tyreus–Luyben tuning, Astrom–Hagglund tuning methods are employed. The time domain specifications of different tuning methods are compared to obtain the optimum parameters value. The results prove that PID controller tuned by Zeigler–Nichols for aircraft pitch control dynamics is better in stability and performance in all conditions. Future research work of obtaining optimum PID controller parameters using artificial intelligence techniques should be carried out.

A method of formation and heating of СО₂ as a test gas in the settling chamber of a hotshot wind tunnel is considered. To form and heat СО2, the chamber is filled with a source gas mixture of СО, О₂, and СО₂, and after initiation, these substances participate in an exothermic chemical reaction in accordance with the formula СО + 0.5 О₂ + х СО₂ = (1 + х)СО₂. A stoichiometric ratio of the concentrations of carbon monoxide CO and oxygen is used. Variation of the number of moles x of ballast CO₂ in the left part of the chemical formula allows changing the temperature of the resultant test gas in a wide range. Experiments in the IT-302M hotshot wind tunnel carried out at ITAM SB RAS have shown that a pressure increase during an isochoric process in the settling chamber due to the joint effect of heat released in the reaction СО + 0.5 О₂ and an electric charge provides the completeness of CO combustion almost equal to unity. The time of reaction completion at its initiation by an electric arc is no more than several milliseconds.

In the present paper, results of numerical simulation of single-phase flows of heat carrier through square and triangular rod bundles are reported. The simulations were aimed at the determination of parameters involved in an integral model of turbulence being developed for modeling nuclear-reactor cores and heat exchangers in anisotropic porous-body approximation.

The paper deals with the numerical study of heat and mass transfer in the process of direct evaporation air cooling in the laminar flow of forced convection in a channel between two parallel insulated plates with alternating wet and dry zones along the length. The system of Navier–Stokes equations and equations of energy and steam diffusion are being solved in two-dimensional approximation. At the channel inlet, all thermal gas-dynamic parameters are constant over the cross section, and the channel walls are adiabatic. The studies were carried out with varying number of dry zones (n = 0–16), their relative length (s/l = 0–1) and Reynolds number Re = 50–1000 in the flow of dry air (j₀ = 0) with a constant temperature at the inlet (T₀ = 30 °C). The main attention is paid to optimization analysis of evaporation cell characteristics. It is shown that an increase in the number of alternating steps leads to an increase in the parameters of thermal and humid efficiency. With an increase in Re number and a decrease in the extent of wet areas, the efficiency parameter reduces.

A horizontal water layer of 0.29÷0.44 mm thickness, locally heated from the substrate, is investigated. The value of thermocapillary deformation occurring at local heating is measured by an inverted laser scanning confocal microscope Zeiss LSM 510 Meta. The heater in the form of strip of 0.5-mm width, 40-mm length, and 0.5-mm height made of indium oxide is sputtered on a sapphire substrate. The water temperature from the side of the substrate is measured using the infrared scanner Titanium 570M. We studied in detail the effect of the initial layer thickness and heating power on the value of thermocapillary deformation and temperature field. It is shown that defor-mation increases with an increase in thermal capacity and decrease in the layer thick-ness. Results of numerical simulation are in good qualitative agreement with the measurement results.

The approximate analytic solution of the problem of temperature field in a rectangular plate with an internal temperature-dependent source is obtained by the method of fast expansions. The critical value of a parameter characterizing heat release, which fun-damentally affects the analytic solution form, is found. The maximum solution error is shown to amount to 0.02 at the consideration of the first three terms of the Fourier series in fast expansion. Temperature fields are presented, and an analysis of the influence of the plate sizes and the heat release magnitude on their formation is given. Recommendations on the plate shape choice are given.

The density and the thermal expansion of liquid lithium–lead alloys with Pb content of 83.0 and 84.3 at. % was measured using gamma-ray attenuation technique over the temperature range from liquidus to 1000 K. The density change during solid–liquid phase transition was directly measured for the first time for Li_15.7Pb_84.3 alloy. A comparison of the obtained results with literature data has been carried out.

Thermoelectric materials have attained importance because of the gargantuan energy crisis the world faces today. A thermoelectric material can be used efficiently and frequently, provided, its figure of merit ZT is increased. Also, easy availability, manufacturing, and low cost are the other factors to be considered for a novel ther-moelectric material. A theoretical model is proposed in this paper for the enhancement of the figure of merit of thermoelectric materials.

In the present study, a model for the heating of inert-matrix-hosted metal nano-particles with laser radiation taking into account the melting processes is examined. The calculations were performed using the characteristics of gold and pentaerythritol tetranitrate materials. The kinetic dependences of the temperature and molten-layer thickness on nanoparticle surface were calculated. The main non-dimensional govern-ing parameters of the model were identified. An expression for the maximum thickness of molten layer was obtained. The results can be used in predicting the stability of nonlinear-optics devices with hosted gold nanoparticles, in raising the efficiency of hyperthermia cancer therapy, and in optimizing the optical detonators.

Radiation heat loss is an important type of heat loss in thermal systems. In this work, a numerical study of the transient response of two circular radiation heat shields in-serted between two parallel and circular surfaces of emissivities ε1 and ε2 is pre-sented. The same dimensions have been assumed for the two main radiating surfaces and the two radiation shields. The radiation shields are assumed to have different emissivities on their top (ε3 and ε5) and bottom (ε4 and ε6) surfaces, and both are as-sumed to be different but linear functions of temperature. A specific configuration is investigated in detail to highlight the transient temperature and heat transfer characte-ristics of the system. Some new results for the transient temperature and heat transfer characteristics of the system such as the effect of shield location, shield emissivities, the temperature dependence of shield emissivities, system dimensions, temperatures of the hot and cold surfaces and emissivities of the hot and cold surfaces are pre-sented for future references. It has been observed that increasing the temperature of the first radiation shield by changing a parameter such as surface emissivity or dis-tance between the radiation shield or the temperature of the hot surface, will not nec-essarily decrease the temperature of the second radiation shield.

The paper considers using a differential method for thermal calculation of a furnace with finding the thermal and aerodynamic parameters within the radiation chamber of a tube furnace. The furnace is equipped with acoustic-type burners allocated in three tiers on the lateral walls. The method implies joint numerical solution of 2D radiation transfer equations using the S2-approximation of the discrete ordinate method, of energy equations, flow equations, k-ε turbulence model, and single-stage modeling of gas fuel combustion. Typical results of simulation are presented.

A new approach has been developed to solve the optimization problems of conti-nuous parameters of thermal power plants. It is based on such organization of opti-mization, in which the solution of the system of equations describing thermal power plant, is achieved only at the endpoint of the optimization process. By the example of optimizing the parameters of a coal power unit for ultra-supercritical steam parame-ters, the efficiency of the proposed approach is demonstrated and compared with the previously used one, in which the system of equations was solved at each itera-tion of the optimization process.

We discuss the method of comparing pulse detonation engines (PDE) and engines with combustion in subsonic flow (ramjet) by means of their specific impulse used by the “Center of Pulse-Detonation Combustion” (CPDC). We demonstrate that the method used by CPDC to calculate the performance of PDE overstates the value of specific impulse relative to its actual value by a factor of at least two. In contrast, the values of specific impulse for ramjet are understated. As a result, the specific impulse of PDE significantly exceeds that of ramjet or is close to it. We investigate these misleading conclusions, and demonstrate their complete failure.

The paper reports on shape of a three-dimensional coherent structure in a velocity field of a high-swirl turbulent jet with the bubble-type vortex breakdown. A set of the 3D instantenous velocity fields was measured by using the tomographic particle image velocimetry (tomographic PIV) technique and processed by the proper orthogonal decomposition (POD) method. The detected intensive coherent velocity component corresponded to a helical vortex core of the swirling jet and two secondary spiral vortices. The entire coherent structure was rotating around the jet axis in compliance with the direction of the flow swirl. From the 3D data it is concluded that the dynamics  of the strsucture can be described by a traveling wave equation: Re[A(y, r)×e^{i(mθ + ky − ωt)}] with the number of the spiral mode m = +1 for positively defined k and ω.

The influence of combustion effect on unsteady vortex structure in the form of precessing vortex core was studied using the non-intrusive method of laser Doppler anemometry and special procedure of extracting the non-axisymmetric mode of flow fluctuations. The studies show that combustion has a significant effect on the parameters of such a core, reducing the amplitude (vortex deviation from the burner center) and increasing precession frequency. At the same time, the acoustic sensors detect almost an order reduction in the level of pressure pulsations generated by the precessing vortex core. Moreover, distributions of tangential velocity fluctuations and cross-correlation analysis show that vortex precession is quite pronounced even under the combustion conditions, bringing a significant coherent component to distributions of velocity fluctuations.

On March 12, 2016 a famous Russian scientist in the field of thermophysics, Doctor of Technical Sciences, Professor Ivan I. Gogonin became 80 years of age.