A. G. Sudakov

Bio: A. G. Sudakov is an academic researcher from Saint Petersburg State University. The author has contributed to research in topics: Vortex & Turbulence. The author has an hindex of 9, co-authored 47 publications receiving 246 citations. Previous affiliations of A. G. Sudakov include Saint Petersburg State University of Civil Aviation & Saint Petersburg State Polytechnic University.

Suppression of the Karman vortex street and reduction in the frontal drag of a circular cylinder with two vortex cells

Abstract: Numerical analysis of an unsteady-state two-dimensional incompressible flow at a Reynolds number of 40000 around a circular cylinder with two vortex cells is carried out on the basis of the finite-volume solution of the Reynolds equations closed by the Menter’s shear-stress transport model. The vortex cells are fitted with slots that ensure suction into the central channel via a fan located and through outflow of a low-pressure jet. It is shown that the suction in small-size cells intensifies the circulatory flow inside it and leads to the rearrangement of a large-scale structure of the flow around the cylinder accompanied by suppression of the Karman vortex street and a slightly symmetrical stabilization of the wake. The frontal drag of the cylinder decreases almost by three times with an optimal coefficient of the sucked air rate.

Numerical simulation and experiments on turbulent air flow around the semi-circular profile at zero angle of attack and moderate Reynolds number

Abstract: Two-dimensional flow around a semi-circular profile at the zero angle of attack and at Re = 50000 on the self-oscillatory period is extensively studied by the URANS method involving the standard semi-empirical SST turbulence models, the SST turbulence model with the correction for streamline curvature modified within the Rodi-Leschziner-Isaev and Smirnov-Menter approaches, as well as involving Hanjalic's four-parameter eddy viscosity elliptic relaxation model and its analog - eddy viscosity elliptic blending model proposed in the present work. This has been done with the use of different-structure grids (multiblock with structured overlapping and unstructured composite). Different numerical approximation methods realized in six codes (VP2/3, SigmaFlow, Fluent, CFX, OpenFOAM, and StarCCM+) are used. An underestimation (up to 30%) of time-averaged integral aerodynamic loads is revealed by means of the standard near-wall SST model. This is explained by the high vortex viscosity production in the profile wake. Wind tunnel tests show that the location of cutoff washers on the semi-circular profile provides a quasi-two-dimensional flow around it and allows applying measurement data to verify two-dimensional turbulent flow. The best agreement of experimental results and numerical predictions when comparing the Strouhal number and time-averaged surface pressure coefficient distributions is achieved using both the modified SST model with the correction for streamline curvature and the modified eddy viscosity elliptic blending model. When the SST model with the correction for streamline curvature, modified within the Rodi-Leschziner-Isaev, Smirnov-Menter and Durbin approaches, is used, all the above codes yield close predictions of a vertical aerodynamic load on the oscillation period.

Numerical simulation of the lowering of the drag of a cylinder containing vortex cells with the use of a control system for the turbulent boundary layer

Abstract: a of eat Using a factorized finite-volume method of solving th Reynolds equations closed by a two-parameter dissipa model of turbulence, we analyze the lowering of the fron drag of a cylinder containing vortex cells when the bound layer is controlled by utilizing provisions for the suction fluid at the central shaft of the cell. Methods of decreasing the drag of a profile by contr ling the turbulent boundary layer by the blowing and suct of fluid in the wall layers are well known in aerodynamic For practice purposes, however, these methods have not developed very far. The growing interest in vortex traps curvilinear surfaces of objects has stimulated the use of tion of the fluid as an instrument for intensifying the flow these traps. In the present study we employ numerical simulati methods to pose and solve the related problem of the in ence of large-scale trapped vortex structures on the turbu flow of an incompressible viscid fluid around an object a on the aerodynamic drag of an object of classic geometry a circular cylinder — for different positions of a circular ce with respect to the center of the cylinder ~Fig. 1a!. The vortex cells under discussion have a central shaft of the s geometry, with provisions for suction of the fluid over th entire contour of the shaft ~Fig. 1b and 1c !. The algorithm that was devised is based on the fin volume method of solving the Reynolds-averaged Navi Stokes equations closed with a high-Reynolds two-param dissipative model of turbulence, utilizing the concept of d composition of the computational region and the genera in substantially different-scale subregions of overlapp multigrid oblique-angle meshes of the same type ~viz., of the O type!. The system of initial equations is written in dive gence form for the increments of the dependent variables covariant components of the velocity and pressure. Such approach is characterized by a more exact representatio the flows through the faces of the computational cells. In the approximation of a source term, which in the ca of the steady-state problem is the right-hand side of the eq tions for the momentum, convective flows were calcula with a one-dimensional counterflow quadratic interpolat scheme, which was proposed by Leonard. 1 It should be noted that the Leonard scheme should be applied not to the c riant but to the Cartesian components of the velocity, oth wise failure of the ‘‘uniform flow’’ test could occur. For this reason, and for convenience of computer programming

Ensuring safe descend of reusable rocket stages - Numerical simulation and experiments on subsonic turbulent air flow around a semi-circular cylinder at zero angle of attack and moderate Reynolds number

Abstract: Two-dimensional flow around semi-circular cylinder at zero angle of attack and at Re = 50000 during the self-oscillatory regime has been extensively studied within the URANS method with the use of different-structure grids (multiblock, structured overlapping, unstructured composite), the SST turbulence model and its versions (1993) and (2003) considering the streamline curvature influence modified within the Rodi–Leschziner–Isaev approach and numerical different-approximation methods realized in two codes (VP2/3, Fluent). Experiments have been made on flow around a semi-circular cylinder in the wind tunnel of the Lomonosov Moscow State University, Institute of Mechanics to obtain data for verification of numerical predictions. The double-mode character of a periodic time history of a drag force caused by a periodically forming and disappearing jet flap and acting upon a body is explained. With increasing compressibility at a Mach number ranging from 0 to 0.5, it is observed that periodic flow around the semi-circular cylinder is restructured, and the time history of the drag force acting upon it is described by a dependence close to a sinusoidal one. It is found that, as the Mach number is increased, pressure field distortions in the form of concentric cylindrical waves propagating from the semi-circular cylinder and the vortex street behind it grow over the infrasonic range.

Numerical Modeling of a Turbulent Incompressible Viscous Flow Along Bodies of a Curvilinear Shape in the Presence of a Mobile Shield

Abstract: Based on the concept of splitting by physical processes the authors synthesize an efficient computational algorithm for the numerical modeling of a turbulent detached incompressible viscous flow along a two-dimensional curvilinear body near a mobile shield applied to the problems of automobile-configuration aerodynamics.

The influence of initial sizes and velocities of water droplets on transfer characteristics at high-temperature gas flow

Abstract: We report the executed experimental investigation of initial sizes and velocities of water droplets movement influence on integral characteristics of its transfer (motion trajectories, velocities, sizes, relative concentration) through high-temperature (more than 1000 K) gas area. It was used the optical methods of two-phase gas–vapor-droplet mixtures diagnostics (“Particle Image Velocimetry” and “Interferometric Particle Imaging”). The limiting values of gas velocities, velocities and sizes of water droplets have been established when the complete droplet evaporation in high-temperature gas mixture is possible. Several modes of droplet motion through the gas flow in intensive evaporation conditions have been singled out and the dependences have been received which allowed to predict these modes.

Vortex heat transfer enhancement in the narrow plane-parallel channel with the oval-trench dimple of fixed depth and spot area

Abstract: The article is devoted to the analysis of vortex heat transfer enhancement due to the use of oval-trench dimples. The main role in the understanding of this process is associated with the application of the technologies developed in engineering practice thanks to design decisions. As a result, prevailing interest has been paid to a spherical dimple when a spot diameter is chosen as a characteristic size, whereas hydraulic losses depend on the dimple-to-device size ratio. Progress in vortex heat transfer enhancement due to the use of oval dimples is connected with the explanation of the mechanism of generation of both vortex structures in dimples and spiral vortices behind them. An abrupt increase of heat transfer in the vicinity of the spherical dimple due to the restructuring of the flow structure in the dimple with two vortices to that in the dimple with one spiral vortex made it possible to propose a new shape of a surface vortex generator – an oval dimple located at an angle of inclination to the incoming flow and consisting of two spherical dimple halves separated by a cylindrical insert. The generation of vortex structure in this case is rather stable and intense in comparison to spherical dimple. The numerical results for vortex heat transfer enhancement in the turbulent water flow in the rectangular narrow channel with spherical, 10°-truncated conical and oval dimples of the same spot area and depth at the heated wall are presented. In the article, central attention is given to the mechanism of secondary flow restructuring and heat transfer enhancement due to increase in a relative length and width of an oval dimple followed by the formation of a long spiral vortex in it. The change in the length of the oval dimple (in terms of its width) from 1 to 6.78 allowed one to rationally mount spiral vortex surface generators in the narrow channel with high thermal and thermal-hydraulic efficiencies, significantly exceeding the identical characteristics of channels with spherical and conical dimples. In this case, moderate hydraulic losses in the channel with an oval-trench dimple, when its length is increased to 6.78, are comparable to those in the channel with a basic spherical dimple.

Fluid-thermal analysis of aerodynamic heating over spiked blunt body configurations

Abstract: When flying at hypersonic speeds, the spiked blunt body is constantly subjected to severe aerodynamic heating. To illustrate the thermal response of different configurations and the relevant flow field variation, a loosely-coupled fluid-thermal analysis is performed in this paper. The Mesh-based parallel Code Coupling Interface (MpCCI) is adopted to implement the data exchange between the fluid solver and the thermal solver. The results indicate that increases in spike diameter and length will result in a sharp decline of the wall temperature along the spike, and the overall heat flux is remarkably reduced to less than 300 W/cm2 with the aerodome mounted at the spike tip. Moreover, the presence and evolution of small vortices within the recirculation zone are observed and proved to be induced by the stagnation effect of reattachment points on the spike. In addition, the drag coefficient of the configuration with a doubled spike length presents a maximum drop of 4.59% due to the elevated wall temperature. And the growing difference of the drag coefficient is further increased during the accelerating process.

The Lid-Driven Cavity

Abstract: The lid-driven cavity is an important fluid mechanical system serving as a benchmark for testing numerical methods and for studying fundamental aspects of incompressible flows in confined volumes which are driven by the tangential motion of a bounding wall. A comprehensive review is provided of lid-driven cavity flows focusing on the evolution of the flow as the Reynolds number is increased. Understanding the flow physics requires to consider pure two-dimensional flows, flows which are periodic in one space direction as well as the full three-dimensional flow. The topics treated range from the characteristic singularities resulting from the discontinuous boundary conditions over flow instabilities and their numerical treatment to the transition to chaos in a fully confined cubical cavity. In addition, the streamline topology of two-dimensional time-dependent and of steady three-dimensional flows are covered, as well as turbulent flow in a square and in a fully confined lid-driven cube. Finally, an overview on various extensions of the lid-driven cavity is given.

Numerical simulation of the turbulent air flow in the narrow channel with a heated wall and a spherical dimple placed on it for vortex heat transfer enhancement depending on the dimple depth

Abstract: Numerical study is made of heat transfer enhancement in the narrow channel with insulated walls in air steady flow around a heated spherical dimple, when its relative depth is varied from 0 to 0.26 (in terms of spot diameter) at a defined Reynolds number 4 × 10 4 based on bulk velocity and dimple spot diameter. The applicability of multiblock computational technologies for solution of Reynolds and energy equations with the implication of an implicit factorized finite-volume algorithm and overlapping different-scale structured grids of different topology, as well as the verification of the shear stress transfer model (SST model) modified with regard to the streamline curvature within the framework of Leschziner–Rodi–Isaev’s approach is assessed from the comparison of numerical predictions obtained by different SSTM versions. Flow regimes in a spherical dimple, as its depth is increased, are classified on the basis of the analysis of change in the jet–vortex flow structure in the dimple and its wake in the channel. In what follows, special attention is paid to asymmetric flow around a dimple with the greatest vortex heat transfer enhancement.