Fluid Dynamics最新文献

Mathematical modeling of a supersonic gas flow around a delta wing is carried out for M = 2. A wing made of a conventional solid material is compared to a wing whose leading edge is made of a porous material with a porosity coefficient of 0.6. The influence of a permeable edge on the flow structure and thermal regime is studied.

We present the results of the numerical modeling of the formation and motion of a blown solitary pulsed turbulent gas-droplet jet under the conditions approximately corresponding to human cough. The calculations are performed for the pulse duration t = 0.6 s and the greatest velocity of the gas phase of 20 m/s at the mass fraction of droplets M_L1 = 1%. The drop phase in the exit section is monodisperse, while the initial dimension of particles in the calculations varied in the range D₁ = 5‒30 μm. Two zones of elevated vorticity are formed within the cloud in the initial period of motion. They are situated in the mixing layer and in the region of deceleration of two-phase pulsed jet. The greatest levels of the longitudinal velocity and the kinetic energy of turbulence are attained in the interval of pulse blow-on. At the subsequent moments of time the turbulence velocity and level monotonically decrease. The vortex cloud produced by the solitary pulse exists for a fairly long time (t ≈ 4 s) and has a time to penetrate into the surrounding space at a distance greater than 3 m.

Two-layer flow of a density-stratified fluid with mass transfer between the layers is considered. In the Boussinesq approximation, the equations of motion are reduced to a homogeneous quasilinear system of partial differential equations of mixed type. The flow parameters in the intermediate mixed layer are determined from the equilibrium conditions in a more general model of three-layer flow of a miscible fluid. In particular, the equilibrium conditions imply the constancy of the interlayer Richardson number in velocity-shift flows. A self-similar solution to the problem of breakdown of an arbitrary discontinuity (the lock-exchange problem) in the domain of hyperbolicity of the system under consideration is constructed. The transcritical flow regimes over a local obstacle are studied and the conditions under which the obstacle determines the upstream flow are determined. A comparison of steady-state and time-dependent solutions with the solutions obtained for the original three-layer models of miscible fluid flow is carried out.

This paper studies an actual problem of the appearance of a deposit on walls of heat-exchange devices. An improved deposit formation number is presented that describes the heat and electrochemical nature of any deposit. A new criterion equation for the free convection of air when a salt deposit appears on a heated-up surface is successfully obtained and shown in the paper. New methods of the heat transfer calculation during the formation of deposits based upon the improved heat transfer similarity criterion of deposit formation are developed.

The dynamics of unstable sound waves in a nonequilibrium vibrationally excited gas is considered with allowance for viscosity and thermal conductivity. A numerical model has been constructed and a computational tool has been developed to study the linear and nonlinear stages of the development of acoustic instability in a nonequilibrium gas with different models of relaxation, heating, and cooling times. The numerical model has a high spatial resolution and second order accuracy. It is shown that at the initial stage small disturbances generated by a sound source grow exponentially in accordance with conclusions of the linear theory. At the nonlinear stage of the development of acoustic instability, a sawtooth system of weak shock waves (SWs) is first formed; then, due to the interaction (merging) of SWs, a quasi-stationary system of high-intensity shock wave pulses (SWPs) is formed.

The spatial problem of supersonic flow past the MSL descent space vehicle in the dense layers of the Martian atmosphere is solved using the perfect gas model. The system of Reynolds-averaged Navier-Stokes (RANS) equations is numerically integrated together with the Baldwin-Lomax algebraic turbulent mixing model. In addition to studying the flow field patterns in the vicinity of the descent vehicle for real trajectory conditions, the calculated data on convective heating of the surface on the windward and leeward sides are analyzed. Change in the heating conditions during laminar-turbulent transition near the surface is taken into account. A comparison with flight data is presented.

A technique for modeling the radiation of shock-heated oxygen by the direct simulation Monte Carlo (DSM) method is described, taking into account the rates of chemical reactions and excitation of vibrational, rotational, and electronic degrees of freedom of oxygen molecules. The simulation results are compared with the experimental data on the measurement of the radiation of shock-heated oxygen in the shock tube of the Institute of Mechanics of Moscow State University.

The problems associated with the formation of an external cluster flow that we previously discovered, which is formed in the external field of a traditional supersonic jet and called the cluster wake, are discussed. The reasons for the long-term anomalous glow of the cluster wake are studied. The results of a spectral study of the induced radiation of a supersonic clustered argon flow in the region of particle excitation (on an electron beam) and beyond are presented. The anomalies in the glow of a traditional spindle-shaped jet and a flow of heavy clusters are discussed. The possible causes of the observed anomalous phenomena are presented based on the above comparisons of the results obtained. The role of the energy exchange between clusters and the background gas in the afterglow of a cluster wake is established. The wavelengths and corresponding transitions in Ar_I and Ar_II that are responsible for the anomalous emission are determined. The lifetimes of particles in the excited state in the central part and on the periphery of the clustered flow are determined.

The anomalous enhancement of laminar separation flow and heat transfer (AELSFHT) is studied in a channel with two rows of 26 densely packed grooves inclined at angles of ±45° in the case of uniform flow at the entry and the Reynolds number Re varying from 1000 to 5500. The local flow acceleration is validated, when the greatest flow velocity becomes of the order of 1.8 in dimensionless units and the wall layer becomes thinner above the spherical entry segments. In this case, the longitudinal velocity increases to a value of 1.4 at a distance y = 0.005 from the wall for Re = 2500. The interrelation between the local acceleration at the channel center and the AELSFHT is established, the minimum value of the negative acceleration amounting to –25 at Re = 5500 and the relative heat removal from the structured region of the channel reaching up to 5.2.

The results of an experimental investigation and physical modeling of self-induced displacement and rotation of an ice disk on the still water surface are presented. The dependence of the ice specimen rotation velocity on the water salinity and the depth of the experimental container is measured. It is shown that the reason for observable motions over the still water surface is the cellular convective flow generated by the ice melting process.