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Thermophysics and Aeromechanics

2019 year, number 6

Experimental investigation of freestream disturbances across an oblique shock wave via modal analysis with a wedge hot-film

M. Krause1, U. Gaisbauer1, E. Kraemer1, A.D. Kosinov2
1Institute of Aerodynamics and Gas Dynamics, Stuttgart, Germany
2Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: диаграммный метод, клиновидный пленочный датчик, диаграмма пульсаций, косой скачок уплотнения, modal analysis, wedge hot-film, fluctuation diagram, oblique shock

Abstract >>
An experimental fluctuation analysis is usually conducted via thermal anemometry with hot-wires. However, in the vicinity of oscillating shock waves, this kind of sensor can be destroyed due to strong mechanical loads. On the basis of a sufficient modelling, a wedge-shaped hot-film can be suitable for a quantitative fluctuation analysis across a shock wave. Within this study, the modal analysis according to Kovásznay and Morkovin was adapted from hot-wires to the used wedge hot-film. Additionally, 3-dimensional fluctuation diagrams were derived for the separate as well as for mixed modes. The freestream fluctuations were detected across an oblique shock wave with a wedge hot-film in a constant-temperature mode. The shock was caused by a ramp with a 10° ramp angle placed in a flow with a Mach number of M = 2.5 and a unit Reynolds number of Reunit = 4.96×106×m-1. The recorded perturbations were decomposed according to the modal analysis and found to be dominated by the acoustic mode. The fluctuations' amplification across the shock wave and the subsequent decay could clearly be detected. They are in good agreement with the literature.

The impact of weak shock waves on the flow in the boundary layer of a flat plate with a variable sweep angle of the leading edge

V.L. Kocharin1, A.D. Kosinov1,2, A.A. Yatskikh1,2, Yu.G. Ermolaev1,2, N.V. Semionov1, M.V. Piterimova1,2, S.G. Shevelkov3, O.P. Minin3
1Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
3PAO Tupolev, Moscow, Russia
Keywords: сверхзвуковой пограничный слой, N-волна, скользящая пластина, затупленная передняя кромка, эксперимент, продольный вихрь, термоанемометр, supersonic boundary layer, N-wave, swept plate, leading blunt edge, longitudinal vortex

Abstract >>
The impact of weak shock waves on the boundary-layer flow of a flat blunt plate installed along the stream was experimentally studied for different sweep angles of the leading edge of the plate at Mach number 2. The shock waves in the incoming flow in the form of an N-wave were generated by 150´7´0.13-mm two-dimensional roughness provided on the side wall of the T-325 wind tunnel. It was confirmed that, when an N-wave was incident onto the plate leading edge with zero sweep angle, generation of longitudinal vortices accompanied by an increase in the pulsation level and by a change in the spectral composition of perturbations, was observed in the boundary layer. Anemometric data showed that, when the sweep angle of the leading edge changed from 0 to 25 degrees under the impact of the “catching-up” incident weak shock wave, the widening of the vortex in the supersonic boundary layer occurred.

Turbulization of a wake behind the double roughness elements in a hypersonic boundary layer

P.A. Polivanov, Yu.V. Gromyko, A.A. Maslov
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: пограничный слой, гиперзвуковые скорости, ламинарно-турбулентный переход, одиночная и парная шероховатости, развитие возмущений, boundary layer, hypersonic velocities, laminar-turbulent transition, single and double roughness elements, disturbance development

Abstract >>
The study of the effect of close placing of two individual elements of roughness with the cylindrical shape on the nature of laminar-turbulent transition were performed. Experiments were performed for a blunt conical model with the radius 9 mm at Mach number М = 5. These double elements of roughness with different heights and divergence angles between elements were allocated at the blunted nose of the tested model. Measurements with a hot-wire anemometer provided information about the averaged and unsteady parameters of the boundary layer in the wake behind the roughness elements. For all types of roughness, we confirmed existence of an effective height of roughness; for the heights above the effective one, we observe deformation of the boundary layer margin and the growth of nonequilibrium in the wake. Process of turbulization behind a double roughness element (similar to the case of single roughness) is accompanied by the generation of longitudinal vortices and by the deformation of the velocity profile. Depending on this deformation, pulsations in the wake either enhance or decline. In contrast to the single roughness configuration, the double element roughness decreases the mass flowrate for a narrow range of angles (and fullness of the boundary layer profile is more significant). Meanwhile, flow turbulization occurs right behind the single element of turbulization, for the case of double element turbulization, the main gain in the mass flowrate occurs with the wake (developing from the boundary between twin elements). Roughness has significant influence on unsteady characteristics of the boundary layer (when the height of roughness element is lower than the effective height). The wake downstream the double elements roughness exhibits the interaction between vortices, and this reduces the effective Reynolds number (compared to the case of single roughness).

Numerical study of the interaction of vortex ring and background turbulence

M.Yu. Hrebtov1, M.S. Bobrov1, D.B. Zhakebaev2, K.K. Karzhaubaev3
1Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
2Al-Farabi Kazakh National University, Almaty, Kazakhstan
3National Engineering Academy of the Republic of Kazakhstan, Almaty, Kazakhstan
Keywords: турбулентность, прямое численное моделирование, плавучесть, каскад турбулентности, turbulence, direct numerical simulation, buoyancy, turbulence cascade

Abstract >>
The article presents the results of direct numerical simulation of a turbulent vortex ring with a moderate Reynolds number, interacting with the field of external turbulent fluctuations. The ring is formed by buoyancy forces from a spherically-shaped volume of elevated temperature. We consider the interaction of the ring with the field of turbulent fluctuations (of temperature and velocity) located in the form of a horizontal layer in front of the ring. The effect of separation of vortices by the sign of vorticity in a layer of fluctuations (with respect to the rotation of the ring) during the passage of the ring through this field has been found. This effect first causes the ring to slow down when the fluctuations pass outside the ring, and then to accelerate with decreasing radius when the fluctuations pass through its center. Due to buoyancy effects in the fluctuations layer, the separation of hot and cold air occurs. During the interaction with the ring, this leads to the accumulation of the reduced temperature in the core of the ring, while the increased temperature is accumulated near the axis. This temperature distribution results in a baroclinic vorticity generation leading to the reduction of the ring radius.

Stability of space-periodic flow with separation of a laminar boundary layer

A.V. Boiko1,2, A.V. Dovgal1, A.M. Sorokin1
1Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
2Tyumen State University, Tyumen, Russia
Keywords: отрыв пограничного слоя, пространственно периодическое течение, гидродинамическая устойчивость, boundary layer separation, space-periodic flow, hydrodynamic stability

Abstract >>
An unstable laminar flow over a wavy region of a plate placed parallel to the oncoming air flow is studied. The results have been obtained by the hot-wire method in a low-turbulent wind tunnel at low subsonic velocities. Flow near a wall with transverse undulation, whose amplitude is sufficiently large and can contribute to the formation of local regions of boundary layer separation, is considered. The external harmonic (acoustic) forcing of the periodic flow leads to the suppression of perturbations that dominate in the spectrum of velocity disturbances near the model surface. The results of this work may be useful in developing methods for controlling spatially inhomogeneous flows.

Hydrodynamics and mixing of a coolant in the core of the VVER with fuel assemblies of different designs

S.M. Dmitriev1, A.V. Gerasimov1, A.A. Dobrov1, D.V. Doronkov1, A.N. Pronin1, D.N. Solntsev1, A.E. Khrobostov1, Yu.K. Shvetsov2, D.L. Shipov2
1Nizhny Novgorod State Technical University n.a. R.E. Alekseev, Nizhny Novgorod, Russia
2OKBM Afrikantov JSC, Nizhny Novgorod, Russia
Keywords: активная зона, тепловыделяющая сборка, дистанционирующие и комбинированные дистанционирующие решетки, межкассетное взаимодействие, гидродинамика теплоносителя, active zone, fuel assembly, spacer and combined spacer grids, inter-assembly interaction, hydrodynamics of the coolant

Abstract >>
The study presents the experimental results for inter-assembly interaction of coolant flows in the core of the VVER consisting of fuel assemblies TVSA-T and TVSA-T.mod.2. The coolant flowing in fuel assemblies (FA) was modeled on an aerodynamic stand. The studies were carried out on the model of the VVER core fragment and consisted in measuring the velocity vector modulus in the characteristic zones of both the TVSA and the inter-assembly space of the VVER core. Measurements were carried out by a five-channel pneumometric probe. The analysis of the spatial distribution of the projections of the absolute flow velocity allowed detailing the pattern of streamlining of the spacer, mixing and combined spacer grids of the TVSA by the coolant flow. Results of investigation of inter-assembly interaction of the coolant between adjacent fuel assemblies TVSA-T and TVSA-T.mod.2 were adopted for practical use in JSC "OKBM Afrikantov" to assess the thermal reliability of VVER cores and included in the database to verify the programs of computational fluid dynamics (CFD-codes) and to provide a detailed cell calculation of the VVER core.

Simulating nonlinear wavy flow modes developing in a thin horizontal layer of heavy liquid entrained by a gas flow

O.Yu. Tsvelodub1,2
1Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
Keywords: горизонтальный слой вязкой жидкости, газовый поток, модельная система, эволюционное уравнение, устойчивость, horizontal layer of viscous fluid, gas flow, model system, evolution equation, stability

Abstract >>
The paper considers nonlinear waves generated on a surface of a horizontal liquid layer put into an assigned stress field at the gas-liquid interface. The nature of branching for wavy modes from the undisturbed flow was studied. To accomplish this, the solution of a model nonlinear equation written for the deviation of the layer thickness from the undisturbed layer is found. Analytical solutions were constructed for nonlinear steady state-travelling solutions of this equation with the wavenumbers belonging to the vicinity of neutral wavenumbers. Steady state-travelling periodic solutions for the first family were simulated for the case of wavenumbers beyond this vicinity.

Flow of liquid films over a single element of structured packing. Comparison of microtextures of various types

Yu.Ya. Trifonov
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: пленочное течение вязкой жидкости, крупное гофрирование и микротекстура, структурированные насадки, film flow of viscous liquid, coarse corrugation and microtexture, structured packing

Abstract >>
The paper deals with the theoretical analysis of viscous liquid films flowing down along a single element of a structured packing with large ribs and microtexture in the form of a wavy two-dimensional surface or three-dimensional surface of the “undulating” type. The effect of inertia forces, surface tension, coarse corrugation, and fine texture geometry on the averaged characteristics of the film flow is considered. New equations for calculating a three-dimensional film flow along a plate with double corrugation structure are obtained. In the calculations, the main attention is paid to the effect of various types of microtextures on film spreading. The type, amplitude, angle of fine texture inclination, and Reynolds number of liquid are varied. It is found that the microtexture of three-dimensional “undulating” type has a small effect on liquid film spreading over a single element of the structured packing; the averaged liquid flow rates along and across large ribs depend weakly on the amplitude and inclination angle of fine texture of this type. It is revealed that only the average film thickness is sensitive to a change in the amplitude of microsurface of the “undulating” type. This is very different from the effect that a wavy two-dimensional microtexture has on film spreading along and across the large ribs. In this case, the effect of waviness on spreading hydrodynamics depends substantially on fine texture amplitude and inclination angle.

Dependence of vapor bubble collapse in hot tetradecane on its pressure

R.I. Nigmatulin1,2,3, A.A. Aganin1, D.Yu. Toporkov1
1Institute of Mechanics and Engineering KazanSC RAS, Kazan, Russia
2Shirshov Institute of Oceanology RAS, Moscow, Russia
3Tyumen ITAM SB RAS, Tyumen, Russia
Keywords: акустическая кавитация, коллапс пузырька, кумуляция, сходящиеся ударные волны, acoustic cavitation, bubble collapse, cumulation, converging shock waves

Abstract >>
Specific features of the phenomenon of vapor bubble collapse in hot tetradecane (with a temperature of 663 K) are considered for various values of pressures in the liquid in the range from 13 to 100 bar. At the beginning of the collapse, the vapor in the bubble is in the state of saturation with a pressure of 10.3 bar, and with the initial radius of the bubble to equal 500 mm. It is shown that, at a liquid pressure lower than 13 bar, a nearly-uniform vapor compression is realized in the bubble, whereas at higher pressure values, compression is realized by means of radially converging isentropic waves (at 14-18 bar) and shock waves (starting from 19 bar). The degrees of vapor compression, estimated from the vapor pressure, density and temperature at the boundary of a small central region of the bubble of 0.25-mm radius, are compared with the degrees of vapor compression realized when a similar vapor bubble collapses in cold acetone at a temperature of 273 K (as in known experiments on acoustic cavitation of deuterated acetone). It is found that the degrees of compression comparable with those achieved in the case of acetone at a pressure of 15 bar, equal to the amplitude of the acoustic action exercised in the mentioned experiments, are achieved in the case of tetradecane at a pressure of 70 bar. In the latter case, the maximum rate of bubble collapse in tetradecane is 10 times lower than that in acetone (110 m/s versus 1100 m/s).

Acoustic streaming in a cylindrical cavity at variation of its radius and boundary conditions

A.A. Gubaidullin1,2, A.V. Pyatkova1,3
1Tyumen Department ITAM SB RAS, Tyumen, Russia
2University of Tyumen, Tyumen, Russia
3Institute of Mechanics and Engineering KazanSC RAS, Kazan, Russia
Keywords: акустическое течение, цилиндрическая полость, радиус полости, термические граничные условия, свободные колебания, средняя за период температура, acoustic streaming, cylindrical cavity, cavity radius, thermal boundary conditions, free oscillations, period average temperature

Abstract >>
Acoustic streaming in a vibrating air-filled cylindrical cavity is numerically investigated. Adiabatic and isothermal boundary conditions are considered, as well as the case in which adiabatic and isothermal boundary conditions are set respectively at the ends of the cavity and on its lateral surface. The value of the cavity radius at which the axial component of acoustic streaming velocity attains its maximum is found. The influence of the radius of the cavity and boundary conditions at its ends on the free oscillations, at the initial stage of the process, on the period average temperature, and on the acoustic streaming pattern is described.

Fluid flow in an enclosed cavity of rotational bioreactor for bone tissue engineering

P.M. Larionov1, V.L. Ganimedov2, N.A. Maslov2, E.O. Tsibulskaya2
1Novosibirsk State University, Novosibirsk, Russia
2Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: математическое моделирование, вычислительный алгоритм, ротационный биореактор, вихри Тейлора, уравнения Навье-Стокса, ламинарный режим течения, касательное напряжение, коаксиальные цилиндры, скаффолд, mathematical simulation, numerical algorithm, rotational bioreactor, Taylor’s vortices, Navier-Stokes equations, laminar flow, shear stress, coaxial cylinders, scaffold

Abstract >>
The developed mathematical model was applied for study of fluid dynamics in a rotational bioreactor for bone tissue engineering by in vitro technology. The research goal is finding an optimal mode for rotation ensuring proper cyclic loading from fluid upon the cell-seeded biomaterial. The basis for developing a mathematical model of a bioreactor was a design of rotational type biological reactor used in medical research; the liquid flow is generated through viscosity mechanism due to surface rotation. Mathematical description of flow in a reactor cavity was performed with Navier-Stokes equations. It was assumed that flow regime in the boundary layer is laminar. Numerical algorithm was accomplished using a fluid flow solver “Fluent” in the code package ANSYS-12. Four variants of generating the rotational motion in the reactor cavity were considered. A series of parametric computations was performed for the rotation frequency f in the range 0.05 £ f £ 0.25 Hz. The paper offers visualization of velocity fields in the vertical plane. The distributions for shear stress and pressure in the working zone of reactor were calculated and analyzed. Simulations demonstrated that a method of fluid rotation by driving the outer cylinder with an offset axis is the best for arranging a cyclic pressure and cyclic shear stress on the biological material.

The contribution of temperature dependence of optical absorption coefficient of the sample to the formation of a thermal field in a photoacoustic cell

T.Kh. Salikhov1, F. Rakhimi2, A. Makhmalatif1, D.M. Sharifov3
1Scientific Research Institute of Tajik National University, Dushanbe, Republic of Tajikistan
2Presidium of the Academy of Sciences of the Republic of Tajikistan, Dushanbe, Republic of Tajikistan
3Gumilev Eurasian National University, Nur-Sultan, Republic of Kazakhstan
Keywords: температурное поле, фотоакустика, тепловая нелинейность, температурная зависимость оптического коэффициента поглощения, temperature field, photoacoustics, thermal nonlinearity, temperature dependence of optical absorption coefficient

Abstract >>
Expressions describing the peculiarities of the temperature field formation in the photoacoustic cell, taking into account the temperature dependence of not only the thermophysical parameters of all layers and the absorptivity, but also of the optical absorption coefficient of the sample have been obtained. A system of nonlinear algebraic equations has been derived to determine the dependence of temperatures of the illuminated layer of the sample and its reverse side on the intensity of the incident beam. As a result of numerical solution of this system, nonlinear dependences of temperatures of both sides of the sample on the beam intensity have been obtained. The sign of the thermal coefficient of the temperature dependence of the optical absorption coefficient has been found to significantly affect the nature of the dependences of the increment of the irradiated surface temperature and the rear side of the sample on the intensity. Significant effect of the substrate on the formation of the temperature field in the photoacoustic cell has been shown as well.

Experimental study of the dynamics of phase changes in a heat storage of thermal control system of electronic equipment

E.N. Vasi’ev, V.A. Derevyanko, M.I. Korkhova
Institute of Computational Modeling SB RAS, Krasnoyarsk, Russia
Keywords: тепловой аккумулятор, теплоаккумулирующий материал, гипертеплопроводящая пластина, теплота плавления, коэффициент теплопроводности, heat storage, heat storage material, hyper-heat-conducting plate, heat of melting, coefficient of thermal conductivity

Abstract >>
A heat storage using the latent heat of the solid-liquid phase change was experimentally investigated. To intensify heat exchange in its design, hyper-heat-conducting plates were used. During the experiments, the temperature values and the volume changes of the working substance (hexadecane) were measured. The analysis of the thermal balance and phase changes in the volume of the heat storage was carried out. The efficiency of the considered design of the heat storage and high heat-distribution capacity of hyper-heat-conducting plates have been confirmed.

Processes of heat and mass transfer in furnace chambers with combustion of thermochemically activated fuel

V.E. Messerle1,2,3, A.S. Askarova1,2, Salmat A. Bolegenova1,2, P. Safarik4, V.Yu. Maksimov1, Symbat A. Bolegenova2, A.O. Nugymanova1
1Al-Farabi Kazakh National University, Almaty, Kazakhstan
2SRI of Experimental and Theoretical Physics, Almaty, Kazakhstan
3Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
4Czech Technical University in Prague, Prague, Czech Republic
Keywords: численное моделирование, тепломассоперенос, скоростные, температурные и концентрационные поля, плазменно-топливные системы, термохимическая активация, numerical modeling, heat and mass transfer, velocity, temperature and concentration fields, plasma-fuel systems, thermochemical activation

Abstract >>
The paper presents the results of numerical studies of the influence of thermochemical activation of pulverized coal flows on the processes of heat and mass transfer occurring in the areas of real geometry (furnaces) with burning power fuel. The aerodynamic flow pattern, velocity, temperature, and concentration fields were obtained, the analysis of which allows the conclusion that plasma activation of fuel increases the efficiency of its combustion and reduces emissions of harmful substances into the atmosphere.

Experimental plasma setup for gasification of organic waste with their discrete supply into gasifier

S.V. Alekseenko, A.S. Anshakov, P.V. Domarov, V.A. Faleev
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: плазменная газификация, органические отходы, дискретная подача, синтез-газ, калорийность, метан, плазмообразующий газ, камера плавления, камера газификации, узел загрузки, plasma gasification, organic waste, discrete supply, synthesis gas, calorie value, methane, plasma forming gas, melting chamber, gasification chamber, loading unit

Abstract >>
The paper describes the design of an experimental setup for plasma gasification of organic waste with its discrete supply to the loading unit. The experimental results of determining the percentage composition of synthesis gas and its calorific value depending on time for gasification of wood sawdust and polyethylene granules are presented. The amount of methane in synthesis gas composition has been calculated depending on temperature and oxygen flow rate. It is shown that when the waste is fed in separate portions, the synthesis gas composition, its yield and calorific value change over time significantly.