Effect of volume energy supply on swirled flows in a subsonic cocurrent stream

The results of a numerical investigation of the effect of thermal energy supply on a swirling viscous heat-conducting gas flow in a subsonic cocurrent stream are presented. The initial stage of development of the swirling flow in the neighborhood of the vortex axis with constant circulation in the outer flow region is considered for two different distributions of the streamwise velocity vector component which simulate a swirling jet-type flow and a wake flow with a streamwise velocity deficit. The effect of local volume energy supply in the neighborhood of the vortex axis, the circulation of the azimuthal velocity component, and the longitudinal pressure gradient in the inviscid stream on the development of the swirling flow and the process of breakdown of cocurrent vortex flows is investigated. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, pp. 47–53, November–December, 1998. The work was carried out with financial support from the Russian Foundation for Basic Research (project No. 96-01-00586).     

Behaviour of carbon dioxide jets in a confined swirling flow

An investigation of jet mixing in confined swirling flow, using carbon dioxide as the jet fluid, was carried out. In order to compare the present results with previous measurements by So et al¹ on homogeneous and helium jet mixing, the experiments were carried out in the same facility and under the same test conditions. Contrary to the flow characteristics found in helium jet mixing in confined swirling flow, density difference and swirl combined to give rise to an accelerated decay of the jet and increased mixing between jet and swirling air. Consequently, the second reversed flow region observed in the swirling flow was only slightly displaced downstream. This contrasted with a radial displacement of the second reversed flow region by the helium jets and a complete destruction of the reversed flow regions by the air jets.     

Reynolds stress modelling of jet and swirl interaction inside a gas turbine combustor

Influences of the inlet swirl levels on the interaction between the dilution air jets and the swirling cross‐flow to the interior flow field inside a gas turbine combustor were investigated numerically by Reynolds stress transport model (RSTM). Due to the intense swirl and jet interaction, a high level of swirl momentum is transported to the centreline and hence, an intense vortex core is formed. The strength of the centreline vortex core was found to depend on the inlet swirl levels. For the higher swirling inlet, the decay of the swirling motion causes strong streamline variation of pressure; and consequently leads to an elevated level of deceleration of its axial velocity. Predictions contrasted with measurements indicate that the stress model reproduces the flow correctly and is able to reflect the influences of inlet swirl levels on the interior flow structure. Copyright © 1999 John Wiley & Sons, Ltd.     

On the self-similar solution to the Euler equations for an incompressible fluid in three dimensions

The equations for a self-similar solution to an inviscid incompressible fluid are mapped into an integral equation that hopefully can be solved by iteration. It is argued that the exponents of the similarity are ruled by Kelvin's theorem of conservation of circulation. The end result is an iteration with a nonlinear term entering a kernel given by a 3D integral for a swirling flow, likely within reach of present-day computational power. Because of the slow decay of the similarity solution at large distances, its kinetic energy diverges, and some mathematical results excluding non-trivial solutions of the Euler equations in the self-similar case do not apply.     

Radial jet in rotating outer flow

The rotating radial jet formed by fluid introduced radially outwards into a rotating environment is studied by the momentum integral method and by perturbation for weak swirl, assuming incompressible laminar flow. For non-swirling outer fluid, the results slightly extend previously published results. For swirling outer fluid, the jet is characterized by a finite radial penetration distance. Its development over that distance is divided into three regions: an initial adjustment, a central pseudo-similarity region, and a final decay.     

Particle image velocimetry investigation of the flow-field of a 3D turbulent annular swirling decaying flow induced by means of a tangential inlet

Particle image velocimetry (PIV) has been used in order to measure the three mean components and turbulence intensities of the velocity vector in a swirling decaying flow induced by a tangential inlet in an annulus. This kind of flow motion is found to be very complex, exhibiting three-dimensional and non-axisymmetric characteristics coupled with a free decay of the swirling intensity along the flow path, thereby making it difficult to study. A method allowing the measurement of the three components of the velocity flow-field with a standard PIV system with two-dimensional acquisitions, is presented. The evolution of each velocity component between the inlet and the outlet of the annulus is obtained. Furthermore, the PIV technique is extended to the measurement of turbulent characteristics such as turbulent intensities and dimensionless turbulent energy. The main characteristics of the swirling flow are discussed and the swirl number is estimated as a function of the axial distance from the tangential inlet. Received: 6 July 1998/Accepted: 20 March 1999     

Experimental study of an impinging jet with different swirl rates

A stereo PIV technique using advanced pre- and post-processing algorithms is implemented for the experimental study of the local structure of turbulent swirling impinging jets. The main emphasis of the present work is the analysis of the influence of swirl rate on the flow structure. During measurements, the Reynolds number was 8900, the nozzle-to-plate distance was equal to three nozzle diameters and the swirl rate was varied from 0 to 1.0. For the studied flows, spatial distributions of the mean velocity and statistical moments (including triple moments) of turbulent pulsations were measured.

The influence of the PIV finite spatial resolution on the measured dissipation rate and velocity moments was analyzed and compared with theoretical predictions. For this purpose, a special series of 2D PIV measurements was carried out with vector spacing up to several Kolmogorov lengthscales.

All terms of the axial mean momentum and the turbulent kinetic energy budget equations were obtained for the cross-section located one nozzle diameter from the impinging plate. For the TKE budget, the dissipation term was directly calculated from the instantaneous velocity fields, thereby allowing the pressure diffusion term to be found as a residual one. It was found that the magnitude of pressure diffusion decreased with the growth of the swirl rate. In general, the studied swirling impinging jets had a greater spread rate and a more rapid decay in absolute velocity when compared to the non-swirling jet.     

Hot flow analysis of swirling sudden-expansion dump combustor

Hot flow of a sudden-expansion dump combustor with swirling is analysed by employing an infinite chemical reaction rate. Turbulence properties are closed using one type of algebraic Reynolds stress model and two types of κ–? model. One of the κ–? models includes a swirling effect modification to the ε-equation. Computations have been performed by the SIMPLE-C algorithm with a power-law scheme. The calculated results of the momentum fields and turbulence quantities for swirling flow are compared with the available experimental data. It is shown that the standard κ–? model gives poor prediction of the mean velocity, particularly the tangential velocity. For the hot flow analysis of a sudden-expansion dump combustor with swirling flow it is suggested that it is necessary to use the modified κ–? model or algebraic Reynolds stress model.     

Determination of principal characteristics of turbulent swirling flow along annuli: Part1: Measurement of time mean parameters

Turbulent swirling flows along the annulus formed between two concentric stationary cylinders have been studied. Hot-wire anemometry was used to detect radial variations of velocity components and the data presented in Part 1 of the investigation describes time mean measurements. Pressure measurements along the length of the outer, concave, cylindrical surface were obtained from wall tappings attached to a pressure transducer. Flow visualization using tufts indicated general swirl decay phenomena and these have been confirmed by the traverse data. The swirl flow rig was designed to incorporate suction systems to remove boundary layers from all walls preceding the test section. In this way the essentially free vortex generated by a circumferentially disposed set of guide vanes in the inlet bellmouth of the apparatus could be efficiently transferred to the test section entry region. This feature has not been incorporated by other workers and so their reported results depend on the upstream boundary layer flow, making correlation of data difficult. The data shown in this paper indicate the complex nature of swirling flow development in an annulus although it is not yet possible to be precise about the initial phases     

A self-similar solution for a weakly swirling jet

A study is made of the laminar flow of a viscous incompressible fluid in a swirling jet that is produced by the action of a point source which transmits to the medium surrounding it a finite momentum flux. The limit of large Reynolds numbers is investigated under the assumption that the circulation of the azimuthal component of the velocity is a constant quantity at large distances from the jet axis. The boundary layer equations are solved asymptotically for the case of small circulation. It is shown that in the case of weak swirling of the jet the interaction of the azimuthal and axial motions is basically nonlinear.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 45–50, July–August, 1984.     

Investigation of the influence of the conditions of swirling on the structure of a two-phase flow in an expanding channel

Both experimental and theoretical investigations show that the main feature in the structure of sufficiently strongly swirling gas flows is the presence in then of reverse circulation regions whose configuration depends very strongly both on the law of swirling of the flow and the conditions at the entrance as well as on the channel geometry [1–6]. In expanding channels, the occurrence of such regions is most probable in the axial region [7, 8]. In short annular channels for which the characteristic transverse and longitudinal dimensions are of the same order, reverse flow arises in the exit part of the channel along its inner wall [6, 9]. Hitherto, the investigations have been made for single-phase gas flows. The present paper reports a numerical investigation of the influence of particles of a condensed phase on the intensity of the reverse flow and the structure of the gas flow in an annular expanding channel under conditions of thermal, mass, and mechanical interaction of the phases. The method of stabilization was used to solve the boundary-value problem. The system of equations describing the axisymmetric unsteady flow of the two-phase medium was integrated by means of Godunov's difference scheme [10, 11]. The calculations were made for different conditions of injection of the particles of the condensed phase into the channel.     

Advantageous swirling flow in 45° end-to-side anastomosis

The effects of swirling flow on the flow field in 45° end-to-side anastomosis are experimentally investigated using a particle image velocimetry technique to reveal fluid dynamic advantages of swirling flow in the vascular graft. Non-swirling Poiseuille inlet flow unnecessarily induces pathological hemodynamic features, such as high wall shear stress (WSS) at the ‘bed’ side and large flow separation at the ‘toe’ side. The introduction of swirling flow is found to equalize the asymmetric WSS distribution and reduces the peak magnitude of WSS. In particular, the intermediate swirling intensity of S = 0.45 induces the most uniform axial velocity and WSS distributions compared with weaker or stronger swirling flows, which addresses the importance of proper selection of swirling intensity in the vascular graft to obtain optimum flow fields at the host vessel. In addition, swirling flow reduces the size of flow separation because it disturbs the formation of Dean-type vortices in secondary flow and inhibits secondary flow collision. The beneficial fluid dynamic features of swirling flow obtained in this study are helpful for designing better vascular graft suppressing pathological hemodynamic features in the recipient host vessel.     

A differential-pressure probe for velocity measurements in swirling air flows

For measuring air velocities in swirling flows a differential pressure probe of small axial length was developed. The determination of the velocity is based on measuring the difference between the stagnation pressure and the base pressure of a circular disk whose surface is perpendicular to the main flow direction.     

Effect of swirling flow on platelet concentration distribution in small-caliber artificial grafts and end-to-end anastomoses

Platelet concentration near the blood vessel wall is one of the major factors in the adhesion of platelets to the wall.In our previous studies,it was found that swirling flows could suppress platelet adhesion in small-caliber artificial grafts and end-to-end anastomoses.In order to better understand the beneficial effect of the swirling flow,we numerically analyzed the near-wall concentration distribution of platelets in a straight tube and a sudden tubular expansion tube under both swirling flow and normal flow conditions.The numerical models were created based on our previous experimental studies.The simulation results revealed that when compared with the normal flow,the swirling flow could significantly reduce the near-wall concentration of platelets in both the straight tube and the expansion tube.The present numerical study therefore indicates that the reduction in platelet adhesion under swirling flow conditions in small-caliber arterial grafts,or in end-to-end anastomoses as observed in our previous experimental study,was possibly through a mechanism of platelet transport,in which the swirling flow reduced the near-wall concentration of platelets.     

Numerical aspects of calculation of confined swirling flows with internal recirculation

Predictions were performed for two different confined swirling flows with internal recirculation zones. The convection terms in the elliptic governing equations were discretized using three different finite differencing schemes: hybrid, quadratic upwind interpolation and skew upwind differencing. For each flow case, calculations were carried out with these schemes and successively refined grids were employed. For the turbulent flow case the k-ε turbulence model was used. The predicted cases were a laminar swirling flow investigated by Bornstein and Escudier, and a turbulent low-swirl case studied by Roback and Johnson. In both cases an internal recirculation zone was present. The laminar case is well predicted when account is taken of the estimated radial velocity component at the chosen inlet plane. The quadratic upwind interpolation and skew upwind schemes predict the main features of the internal recirculation zone also with a coarse grid. The turbulent case is well predicted with the coarse as well as the finer grids, the skew upwind and quadratic upwind interpolation schemes yielding results very close to the measurements. It is concluded that the skew upwind scheme reaches grid independence slightly before the quadratic upwind scheme, both considerably earlier than the hybrid scheme.     

Stability of a viscous subsonic swirl flow

The results of calculating the stability of a three-dimensional swirl flow of a viscous heat-conducting gas are presented. The stability characteristics are determined using the linear time-dependent theory of plane-parallel flow stability. The main undisturbed axisymmetric vortex flow was determined numerically using a quasi-cylindrical approximation for the complete set of Navier-Stokes equations. The circulation of the peripheral velocity in the cocurrent flow surrounding the viscous vortex core was assumed to be constant. In analyzing the stability, nonaxisymmetric perturbations in the shape of waves traveling along the vortex axis with both positive and negative wavenumbers were considered; in these two cases the perturbation rotation is either the same or opposite in sense to the rotation in the vortex core. Neutral stability curves are determined for various values of the swirling parameter and the cocurrent flow Mach number. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 50–59, May–June, 1998.     

Numerical analysis of swirling turbulent droplet-laden flow and heat transfer in a sudden pipe expansion

The effect of swirling intensity on the structure and heat transfer of a turbulent gas–droplet flow after a sudden pipe expansion has been numerically simulated. Air is used as the carrier phase, and water, ethanol, and acetone are used as the dispersed phase. The Eulerian approach is applied to simulate the dynamics and heat transfer in the dispersed phase. The gas phase is described by a system of Reynolds-averaged Navier-Stokes (RANS) equations, taking into account the effect of droplets on mean transport and turbulent characteristics in the carrier phase. Gas phase turbulence is predicted using the second-moment closure. A swirling droplet-laden flow is characterized by an increase in the number of small particles on the pipe axis due to their accumulation in the zone of flow recirculation and the action of the turbulent migration (turbophoresis) force. A rapid dispersion of fine droplets over the pipe cross-section is observed without swirling. With an increase in swirling intensity, a significant reduction in the length of the separation region occurs. The swirling of a two-phase flow with liquid droplets leads to an increase in the level of turbulence for all three types of liquid droplets investigated in this work due to their intensive evaporation. It is shown that the addition of droplets leads to a significant increase in heat transfer in comparison with a single-phase swirling flow. The greatest effect of flow swirling on heat transfer intensification in a two-phase gas-droplet flow is obtained for the droplets of ethanol and water and smallest effect is for the acetone droplets.     

Laminar boundary layer in a swirling flow

The spatial non-self-similar boundary layer in a compressible gas in a swirling flow is studied. Boundary-layer equations are written in variables ensuring constancy of the coefficients of first derivatives and are solved by the finite-difference method. Boundary-layer peculiarities in the presence of a return circulation region in the channel are clarified.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 43–49, January–February, 1976.     

Hydrodynamics of swirling flow in a circular tube with sudden increase in cross-section and of the flow through a borda mouthpiece

By applying the mass, momentum, and angular momentum conservation laws and the maximum flow rate principle to swirling, effectively inviscid, incompressible flows in a circular tube with a sudden expansion and in direct-flow and reversed-flow Borda mouthpieces the dependence of the flow rate coefficient and mechanical energy losses on the radius ratio and nondimensional circulation is obtained. Several calculating approaches with potential and helical motion are introduced and investigated. In the case of helical motion, as the swirl decreases the axial core of the flow is found to close with a sudden change of the flow parameters.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.3, pp. 51–66, May–June, 1994.