Fluid Dynamics最新文献

Rapid development of the anomalous enhancement of separated turbulent Re = 6000 air flow and heat transfer in an in-line single-row package of 31 inclined grooves, 0.2 in dimensionless depth, in a singled-out longitudinal region of the wall of a narrow channel is studied. It is due to the interference of vortex wakes behind the grooves and the acceleration in the channel flow core with the formation of a zone of ultrahigh longitudinal velocity. The wave-shaped parameter characteristics are stabilized in the region of approximately 15th groove, whereupon the oscillation amplitudes are moderately reduced. The return flows in the grooves are enhanced with distance from the entry section, the minimum negative friction diminishing from −2 to −4. The total relative heat removal from the structured region increases at q = const by a factor of approximately 2.75 and by the factor of two at T = const with increase in the relative hydraulic losses by the factor of 1.7, as compared with the case of a plane–parallel channel. The relative heat removal from the surface bounded by the contour of the 20th inclined groove amounts to 3.7 (q = const) with increase in the hydraulic losses by the factor of 2.2. An increase in the local maximum of the longitudinal velocity up to a factor of 1.5, as compared with the mean-mass velocity, can be observable.

The results of numerical study of the interaction of a formed cellular detonation wave propagating in a plane channel occupied by a quiescent stoichiometric hydrogen-air mixture with multiple obstacles (barriers) located on the inner surface of the channel are given. The study is carried out to determine the conditions that ensure suppression of detonation. The influence of geometric parameters of the area with obstacles on wave propagation is studied. It is found that localization of the obstacles in a recess in the channel wall leads to a decrease in their destructive effect on detonation. Quenching of detonation combustion by the layer of a non-reacting gas located along the channel wall, limited by single barriers, is considered. The effect of gas composition on the interaction of the detonation wave with the layer is studied. Non-reacting gas mixtures, which, being filled into the area with obstacles, enhance the destructive effect of barriers on the detonation wave are proposed.

The problem of injection of Newtonian fluid at a constant flow rate through an injection well into an initially undisturbed infinite reservoir with an erosive vertical main fracture of constant width is considered. Using the Laplace transform method, analytical solutions are obtained for the pressure fields in the fracture and reservoir, the flow velocity in the fracture, as well as the equations for fluid trajectories in the reservoir and in the main fracture are derived. The solutions obtained are also applicable to the problem of fluid withdrawal into a production well intersected by a vertical main fracture. Nonstationary two-dimensional pressure fields in the reservoir, as well as the pressure and velocity fields in the fracture, are constructed.

Ice slurry has a huge application in the field of refrigeration and space cooling due to its high energy storage and transport capability. During transportation of ice slurry, various bends, junctions, and bifurcations are the essential parts of any pipeline network. In the present study, numerical simulation has been carried out on ice slurry flow through a horizontal T-shaped pipe of 23 mm diameter. The length of each section of the T-shaped pipe (inlet and both bifurcated branches) are equal to 50 times of the pipe diameter. The Eulerian granular multiphase model with the per phase k–ε turbulence model have been adopted for simulation. The investigation has been performed for the flow velocity that varied from 1 to 3 m/s and the ice concentrations ranging from 10 to 30%. The velocity and ice distribution contours are also presented in various planes near the bifurcation region to comprehend the fluid flow characteristics. It has been observed that a high-pressure zone is created on the outer wall of the T-junction as fluid strikes the wall and got deflected along the bifurcated branches. In addition, a low-pressure zone is also formed in the neighborhood of corner of the T-section. Due to that, secondary flow is induced in the bifurcated branch which results in flow separation. The velocity and the ice concentration distribution are also significantly affected near the bifurcation section. However, flow is again redeveloped towards the outlet of the bifurcated pipe branches. The results show that the ice concentration and velocity profiles at the outlet are almost homogeneous and fully developed, respectively. It is also concluded that the length of redeveloped zone in the bifurcated branch also increases with the flow velocity. Further, the influence of flow velocity on the pressure drop is more crucial as compared to the ice concentration.

To elucidate the influence of curvature on the mechanism governing stable detonation waves, this study delves into the experimental and numerical exploration of gaseous detonations within an annular channel utilizing a 2H₂/O₂/3Ar mixture. The investigation encompasses both empirical observations of the cellular structure of the detonation wave through a soot-coated stainless-steel plate and numerical simulations employing advanced methodologies. To capture the intricacies of the detonation phenomenon, the second-order additive semi-implicit Runge–Kutta method and the fifth-order weighted essentially non-oscillatory (WENO) scheme are adeptly employed for discretizing the time and spatial derivatives, respectively. The underlying chemical reactions during detonation are meticulously modeled using a detailed reaction mechanism. The pressure and velocity contours unveiling a nuanced picture are extracted using a numerical analysis. The inner wall divergence effect emerges as a critical determinant, weakening the detonation strength and consequently yielding the larger cellular structures. Contrarily, the outer wall convergence effect significantly amplifies the strength yielding the smaller cellular structures. This intricate interplay causes the detonation velocity to increase progressively along the radial direction. Furthermore, near the inner wall the detonation wave manifests periodic phases of augmentation and attenuation, resulting in oscillations in both the velocity and the pressure. A granular scrutiny of the flow field finer attributes underscores the continuous regeneration and dissolution of triple points along the wave front. Notably, triple point regeneration predominantly occurs near the outer wall surface, while their dissipation is more proximate to the inner wall. In the context of the stable detonation wave, equilibrium between triple point regeneration and decay sustains a constant triple point count on the wave front. This pivotal equilibrium enables the self-sustaining propagation of detonation within the annular channel.

A comprehensive three-dimensional computational analysis is undertaken to track the droplet dynamics along with the heat transfer characteristics throughout the spreading and recoiling phases. Notably, the simulation results are compared within the frameworks of the static contact angle (SCA) and dynamic contact angle (DCA) models. The study uses the volume of fluid (VOF) technique within the ANSYS Fluent platform, incorporating the dynamic contact angle model. The simulation outcomes exhibit a reasonable degree of agreement with experimental results, both in quantitative and qualitative terms. The SCA model closely approximates the DCA model during the initial spreading phase, but, as the process progresses, the results based on the SCA model significantly deviate from the results of the DCA model as well as from the experimental observations. The presence of air trapped between the droplet and the solid surface acts as a barrier, impeding the heat transfer from the droplet to the surface. The heat flux attains the global maxima about the triple phase contact line region.

The behavior of an ice cover on the surface of an ideal incompressible fluid of finite depth under the action of a pressure domain that moves rectilinearly at a constant velocity in the presence of a current with velocity shift in the upper layer is studied. It is assumed that the ice deflection is steady in the coordinate system moving with the load. The Fourier transform method is used within the framework of the linear wave theory. The critical velocities, the deflection of ice cover, and the wave forces are studied depending on the current velocity gradient, the shear layer thickness, the direction of motion, and the compression ratio.

Continuum models of media with zero pressure are widely used in various branches of physics and mechanics, including studies of a dilute dispersed phase in multiphase flows. In zero-pressure media, the particle trajectories may intersect, “folds” and “puckers” of the phase volume may arise, and “caustics” (the envelopes of particle trajectories) may appear, near which the density of the medium sharply increases. In recent decades, the phenomena of clustering and aerodynamic focusing of inertial admixture in gas and liquid flows have attracted increasing attention of researchers. This is due to the importance of taking into account the inhomogeneities in the impurity concentration when describing the transport of aerosol pollutants in the environment, the mechanisms of droplet growth in rain clouds, scattering of radiation by dispersed inclusions, initiation of detonation in two-phase mixtures, as well as when solving problems of two-phase aerodynamics, interpretation of measurements obtained by LDV or PIV methods, and in many other applications. These problems gave an impetus to a significant increase in the number of publications devoted to the processes of accumulation and clustering of inertial particles in gas and liquid flows. Within the framework of classical two-fluid models and standard Eulerian approaches assuming single-valuedness of continuum parameters of the media, it turns out impossible to describe zones of multi-valued velocity fields and density singularities in flows with crossing particle trajectories. One of the alternatives is the full Lagrangian approach proposed by the author earlier. In recent years, this approach has been further developed in combination with averaged Eulerian and Lagrangian (vortex-blob method) methods for describing the dynamics of the carrier phase. Such combined approaches made it possible to study the structure of local zones of accumulation of inertial particles in vortex, transient, and turbulent flows.

This article describes the basic ideas of the full Lagrangian approach, provides examples of the most significant results which illustrate the unique capabilities of the method, and gives an overview of the main directions of further development of the method as applied to transient, vortex, and turbulent flows of “gas-particle” media. Some of the ideas discussed and the results presented below are of a more general interest, since they are also applicable to other models of zero-pressure media.

Anomalous heat transfer enhancement in turbulent separated air flow over a long groove of moderate depth made in a plate inclined at an angle of 45° to the freestream is revealed both experimentally and numerically. The region under investigation includes a rectangle heated to 100°C by saturated water vapor. The Reynolds number varied from 10³ to 3 × 10⁴. Using the gradient heatmetry the twofold increase, as compared with the case of a flat plate, of the heat transfer coefficient on the groove bottom is established at the Reynolds number Re = 3 × 10⁴. The relative Nusselt number in different regions of the groove is determined both in the physical experiment and in the RANS calculations with the application of multiblock computational technologies and the SST model in the VP2/3 software package. The results are in good agreement in the turbulent flow regime at Re = (5, 10, and 30) × 10³.

The initial and boundary value problem for the equations of free internal inertia-gravity waves in an unconfined basin of constant depth is numerically calculated in the Boussinesq approximation in the presence of a two-dimensional, vertically-inhomogeneous flow. The boundary value problem for the vertical velocity amplitude includes complex coefficients and is solved both numerically and within the framework of perturbation theory. With reference to the example of the calculations of the decay rate of internal waves and wave-induced momentum fluxes it is shown that the exact numerical calculations provide considerably better estimates than those obtained using the perturbation method. In particular, at minimum disagreement of the dispersion curves obtained using the two calculation methods the imaginary parts of the wave frequency interpreted as the decay rates can differ by two-three orders. The vertical wave-induced momentum fluxes are comparable with turbulent fluxes and can be even greater than those. In this case, the results obtained using numerical methods are almost an order smaller than those calculated by the method of perturbation theory.