Experimental investigation of freestream disturbances across an oblique shock wave via modal analysis with a wedge hot-filmKrause, M.; Gaisbauer, U.; Kraemer, E.; Kosinov, A. D.
2019 Thermophysics and Aeromechanics
doi: 10.1134/S0869864319060015
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 edgeKocharin, V. L.; Kosinov, A. D.; Yatskikh, A. A.; Ermolaev, Yu. G.; Semionov, N. V.; Piterimova, M. V.; Shevelkov, S. G.; Minin, O. P.
2019 Thermophysics and Aeromechanics
doi: 10.1134/S0869864319060027
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 layerPolivanov, P. A.; Gromyko, Yu. V.; Maslov, A. A.
2019 Thermophysics and Aeromechanics
doi: 10.1134/S0869864319060039
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 M = 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 non-equilibrium 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 turbulenceHrebtov, M. Yu.; Bobrov, M. S.; Zhakebaev, D. B.; Karzhaubaev, K. K.
2019 Thermophysics and Aeromechanics
doi: 10.1134/S0869864319060040
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 layerBoiko, A. V.; Dovgal, A. V.; Sorokin, A. M.
2019 Thermophysics and Aeromechanics
doi: 10.1134/S0869864319060052
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 designsDmitriev, S. M.; Gerasimov, A. V.; Dobrov, A. A.; Doronkov, D. V.; Pronin, A. N.; Solntsev, D. N.; Khrobostov, A. E.; Shvetsov, Yu. K.; Shipov, D. L.
2019 Thermophysics and Aeromechanics
doi: 10.1134/S0869864319060064
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.
Flow of liquid films over a single element of structured packing. Comparison of microtextures of various typesTrifonov, Yu. Ya.
2019 Thermophysics and Aeromechanics
doi: 10.1134/S0869864319060088
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 pressureNigmatulin, R. I.; Aganin, A. A.; Toporkov, D. Yu.
2019 Thermophysics and Aeromechanics
doi: 10.1134/S086986431906009X
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 µm. 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-µm 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).