Thermophysics and Aeromechanics最新文献

Supersonic underexpanded air jet modeling based on the QGD algorithm is carried out. The process of jet flow evolution and the formation of unsteady flow regions are investigated to obtain a good qualitative and quantitative agreement of the results with experimental and simulation data, known from the literature. The QGD algorithm is shown to enable studies of the structure of shock-wave cells at the initial region of the flow and to describe the general character of the turbulent jet.

In the presented work, the process of heat and mass transfer inside an original design nozzle for a catalytic reformer of diesel fuel in a low-mass-flux mode is investigated by direct numerical simulation using Open FOAM open-source code. The main goal of a new nozzle design is to increase the rate and degree of fuel evaporation, as well as to improve the mixing characteristics of diesel fuel with superheated water vapor before the reaction mixture passes through the catalyst. Inside the nozzle, there are two regions where flows with opposite swirl directions are created; this leads to a strong velocity shear inside the nozzle, intensifying the mixing processes. Simulations were carried out in the Eulerian-Lagrangian formulation, taking into account the processes of evaporation of fuel droplets. The simulation results show that the flow at the outlet of the nozzle has a good uniformity of the mixture composition and provides a high degree of fuel evaporation at the early stages of flow development.

The present study is aimed at searching for mechanisms of wave interaction in a supersonic boundary layer on a flat plate with the flow being distorted by a streamwise disturbance generated on a sharp leading edge by a pair of weak shock waves. The space and time distributions and the frequency-wave spectra of oscillations and their wave characteristics in the linear and weakly nonlinear phases of wave train development in a nonhomogeneous boundary layer under conditions of a fixed power of the local source of controlled disturbances are analyzed. Based on experimental results, possible variants of wave interaction in a supersonic boundary layer on a flat plate in the region of the longitudinal wake generated by an N-wave are proposed.

The analysis was performed for input condition sensitivity of hemodynamic simulation performed for a zone of abdominal aortic aneurysm. We took three versions of patient-specific configurations of aneurysm decease and computed the haemodynamics with different spatial and velocity profiles at the aorta inlet. Their impact on hemodynamic characteristics was evaluated. At total, the study was performed for three spatial variants (uniform, parabolic, and parabolic-and-secondary-flow velocity profiles) and three versions of time behavior of velocity profiles: this produces nine cases for every of three chosen geometries. The study demonstrated that one can neglect the impact of the spatial profile for inlet velocity (including the non-coaxial velocity vector components). Meanwhile, the value of reverse diastolic flow is significant for the solution. However, simulation in the zone of abdominal aortic aneurysm does not demonstrate great differences in simulation results for the values of wall shear stress and velocity for the data averaged over a cardiac cycle. For the distribution of the oscillation index of shear, the maximum deviation from the basic solution is about ∼ 10 %, which is quite acceptable for clinical applications.

Numerical simulation of the final viscous stage of degeneration of a momentumless turbulent wake behind a sphere in an isotropic turbulent flow is performed using a modified e ∼ ε turbulence model. The laws of degeneration are consistent with those for a momentumless turbulent wake at absent turbulent background.

The effect of icing on the kinematic and power parameters of the working element of a wind generator blade was experimentally studied using a modified laser Doppler anemometry method. Arctic conditions were modeled in a specially designed aerodynamic climatic setup based on an optically transparent plexiglass tube with a square cross section of 200×200 mm with the following parameters: flow velocity of up to 20 m/s, temperature of up to −20 °C, and relative humidity of up to 90 %. The flow was saturated with moisture by fine aerosol generators. Aerosol generator flows were optimized using laser Doppler anemometry. The following parameters were measured: flow velocities at distances of up to 400 mm behind the trailing edge of the blade and power characteristics of the blade element subjected to icing. The effect of icing on aerodynamic and power characteristics is shown.

The flow in the vicinity of the source of controlled harmonic non-stationary perturbations of a gas medium, applicable for generating Görtler vortices in a compressible boundary layer, is studied. The source has a flat surface with linearly arranged cylindrical channels, leading alternately to two cavities of variable volume. Various configurations of the source are considered: with separate channel outlet openings and with a slit opening above them. Numerical simulation is performed in the Solid Works Flow Simulation package, and experimental measurement of gas velocity is realized by the PIV method. The developed source is shown to create periodic velocity fluctuations with an amplitude of up to 2 m/s at a frequency of 1 kHz near the surface. The shapes of the profiles of velocity normal to the surface along the source are close to sinusoidal in both time and space.

An experimental method is proposed for determining the frequency response of a hot-wire and hot-film system using short-pulse laser action on a sensor. The possibility to obtain frequency response by this method is demonstrated. The frequency response is obtained from constant temperature anemometers of two manufacturers with two types of sensors: surface thin-film and wire.

It is shown that the vibration transfer and working medium pressure pulsations through vibration-isolating pipeline junctions of various plants may increase by two or three orders of magnitude with an increase in the vibration frequency and in the presence of incompressible working fluid. The results of research of the found physical models that determine this phenomenon are presented. The experimental results for a spatial three-component broadband active vibration-protection system (AVS) for vibration damping beyond the vibration isolation junction with liquid are considered. An experimental plant scheme for studying the simultaneous spatial active damping of dynamic forces, vibrations and pressure pulsations downstream from the junction has been given. Calculated dependences of the maximum efficiency of considered AVS on frequency are obtained. Efficient active damping of forces is shown to be attainable in an open loop without feedback. While damping in an open loop at the experimental plant, the efficiency of active damping of dynamic forces is obtained in three directions up to 10 dB or more in the frequency range from 5 to 800 Hz (more than seven octaves). The analysis of scientific publications reveals the uniqueness of this result. In this case, there are no zones of negative efficiency outside the active damping frequency range, which appear while using other methods of active damping.

Influence of streamwise slots with the orientation angle φ = 0 and various depths h (corresponding Reynolds number Re_h = 0–2000) on the stability of the supersonic (M = 2) flat-plate boundary layer with relation to natural disturbances of the first (vorticity) instability mode driving laminar-turbulent transition was investigated experimentally. Experiments shown that such kind of disturbances can be stabilized by small-depth streamwise slots, wherein the maximum stabilization occurs at the Reynolds number (based on the slot depth) of about Re_h ≈ 1000.