The results of the numerical investigation of flow regimes in the axisymmetric inlets of internal compression at a supersonic flow around them are presented in the work. The main attention is paid to the determination of the ranges of the duct geometric convergence, in which a supersonic inflow in the inlet realizes. The investigation has been carried out at high supersonic freestream velocities corresponding to the Mach numbers М = 2-8 by the example of the frontal conical (funnel-shaped) inlets with the angles of the internal cone wall inclination δw = 7.5-15° under the variation of the relative area of the throat cross section. The flow structure alteration was studied and the critical relative areas of the inlet throat were determined, at which either there is no starting of the inlet in the process of flow steadying at the initial subsonic flow in it or a flow breakdown occurs in the process of flow steadying at an initial supersonic inflow. Numerical computations of the axisymmetric flow were done on the basis of the solution of the Navier–Stokes equations and the k-ω SST turbulence model.
Based on full unsteady compressible Navier–Stokes equations a direct numerical simulation of the linear and nonlinear stages of the laminar-turbulent transition in boundary layer of a flate plate at the freestream Mach number M = 2 is carried out.
Results of life firing tests of a dual-mode ramjet engine intended for operation in the speed range М = 3-6 are discussed. The tests were carried out on a test bench under freestream conditions typical of Mach 6 flight at 27.6-km altitude. In the tests, the adopted design and technological solutions were verified, and efficient operation of the ramjet engine with kerosene combustion during 110 s was demonstrated.
Measured data on the filtration velocity of air in highly porous cellular materials under conditions of high filtration velocities and reduced air densities are reported. The viscosity and inertia coefficients entering the quadratic dependence of pressure gradient as a function of filtration velocity in porous materials for various flow conditions in the pores are evaluated.
The intensification of the fragmentation and vaporization of liquid droplets in two-phase flows with the gas stagnation temperature Тg= 800-2500 K is an important scientific and technological problem. One should note that despite a high practical importance the mechanism of the vaporization of droplets with their preliminary gas-dynamic fragmentation in high-enthalpy flows has been studied insufficiently completely and requires additional research. The paper presents a mathematical model and the results of the computations of the fragmentation and vaporization of liquid droplets in subsonic and supersonic flows with a high stagnation temperature. A comparison of the obtained data with the experiments of other authors has been done. The extension of the regions of the gas-dynamic fragmentation and droplet vaporization in flow ducts with a variable distribution of parameters has been estimated. The found peculiarities may be used at the design of energy installations of the promising samples of the aerospace technology and gas-dynamic pipes.
The mathematical model is developed and the swirling two-phase flow behind a sudden tube expansion is simulated numerically using the model of Reynolds stress transport. The gas phase is described by the three-dimensional RANS-equations taking into account the back effect of particles on transport processes in gas. To calculate the dispersed phase dynamics in a swirling confined flow, the Euler approach are used. It is found that with an increase in size, the particle are not involved into the separated flow and keep a positive value of the averaged axial velocity along the computational domain. Due to inertia of particle, the zone of reverse flows for the dispersed phase is noticeably smaller than the recirculation zone of gas phase. Performance of the developed mathematical model for description of the swirling two-phase flows in the presence of detachment areas is shown.
The model and the computer code FDS, albeit widely used in engineering practice to predict fire development, is not sufficiently validated for fire suppression by fine water sprays. In this work, the effect of numerical resolution of the large scale turbulent pulsations on the accuracy of predicted time-averaged spray parameters is evaluated. Comparison of the simulation results obtained with the two versions of the model and code, as well as that of the predicted and measured radial distributions of the liquid flow rate revealed the need to apply monotonic and yet sufficiently accurate discrete approximations of the convective terms. Failure to do so delays jet break-up, otherwise induced by large turbulent eddies, thereby excessively focuses the predicted flow around its axis. The effect of the pressure drop in the spray nozzle is also examined, and its increase has shown to cause only weak increase of the evaporated fraction and vapor concentration despite the significant increase of flow velocity.
The two-phase flow in the narrow short horizontal rectangular channels 1 millimeter in height was studied experimentally. The features of formation of the two-phase flow were studied in detail. It is shown that with an increase in the channel width, the region of the churn and bubble regimes increases, compressing the area of the jet flow. The areas of the annular and stratified flow patterns vary insignificantly.
Two-layer gas-liquid flows and evaporation intensity at the interface were studied. The influence of gas flow rate, longitudinal gradient of temperature, the Soret effect on the nature of flow and transfer processes was demonstrated. Experimental and theoretical results were compared; they show dependence of evaporation at the interface on gas flow rates.
The scheme of an integrated coal gasification combined-cycle power plant with small capacity is proposed. Using the built mathematical model a feasibility study of this unit was performed, taking into account the kinetics of physical and chemical transformations in the fuel bed. The estimates of technical and economic efficiency of the plant have been obtained and compared with the alternative options.
