Annular Swirling Flow Research Articles

Computations of recirculation zones of a confined annular swirling flow

Computations of recirculation zones of a confined annular swirling flow

Isothermal Flow Visualization for Flows near Swirl Burners.

Isothermal annular swirling flows with a central jet stream were investigated using a flow visualization technique in order to clarify flow structures near pulverized coal-fired swirl burners. The experiments revealed that the behavior of the central nonswirling jet is significantly affected by the downstream flow system geometry. For flows with a divergent burner tile, observed flow patterns were classified into four categories : type A to D in order of the swirl strength. Type A is a simple jet flow. Type B flows can be seen for the swirl numbers less than 1. 2-1. 3, and are characterized by the way that the primary jet stream rotates around the central recirculation zone. For higher swirl numbers, types C and D, which are steady and axisymmetrical unlike type B, can be seen. The observation revealed that for a certain range of swirl number the flow becomes unsteady and three dimensional, suggesting that time mean figures in terms of transport phenomena should be carefully treated for such flows.

Electrochemical study of mass transfer in decaying annular swirl flow Part II: Correlation of mass transfer data

This paper presents correlations of local mass transfer at the inner rod and the outer wall in annular decaying swirl flow generated by axial vane swirl generators. Four swirl generators with vane angles in the range 15–60° to the duct axis were used and experiments were carried out in a Reynolds number range 3300–50000 and at a Schmidt number of 1650. The results were correlated in the general form Shx = 0.0204 Rex0.86 (1 + tan θi)0.53Sc1/3, for the inner rod, and Shx = 0.0224 Rex0.86 (1 + tan θo)0.55Sc1/3, for the outer pipe. Comparison is made with heat transfer data for work with a similar entry configuration.

Electrochemical study of mass transfer in decaying annular swirl flow

This paper describes an investigation of local mass transfer behaviour at the inner rod and outer pipe wall of an annular test section in decaying annular swirl flow generated by axial vane-type swirl generators. Four swirl generators with vane angles of between 15–60° to the axis of the duct were used. The experiments were carried out in the Reynolds number range 3300–50 000 and at a Schmidt number of 1650. The axial distribution of the local mass transfer coefficients at both the inner rod and the outer wall were measured using an electrochemical technique. Current fluctuations were also recorded to gain information on the turbulence characteristics in the vicinity of the local electrodes.

Hydrodynamics and mass transfer in decaying annular swirl flow

This paper reports an electrochemical study of local mass transfer behaviour in decaying annular swirl flow. Initially, flow visualisation experiments were conducted to observe the general behaviour of the flow. It was found that the swirl angle decays exponentially along the tube. Measurements of pressure drop across the vaned swirl generators were correlated in terms of the inverse of the square of the tangent of the vane angle and approximately the square of the mean fluid velocity for vane angles of 30° and over. Measurements of the axial distribution of local mass transfer coefficient for the inner rod were carried out using the electrochemical limiting diffusion current technique and results were correlated for each swirl generator, in the Reynolds number range 3300–50000. It was found that the relative enhancement of mass transfer in swirl flow increases as the vane angle increases and Reynolds number decreases.

The effects of inlet conditions on mass transfer in annular swirling decaying flow

Wall to liquid mass transfer coefficients are experimentally investigated, with an electrochemical method, in an annular swirling flow generated by a tangential inlet. Attention is focused on the influence of the ratio of the annular thickness e to the inlet diameter φ e . According to the value of this ratio, three categories of flow regimes are obtained: the pure swirl flow, for φ e = e, the contraction swirl flow, for φ e > e and the expansion swirl flow, for φ e < e. The other parameters of the study are the mean axial distance of the mass transfer surfaces, to characterize the swirl decay, the Reynolds number based on the hydraulic diameter and the geometric factors of the annulus. Correlations of the experimental data, taking into account the aforementioned parameters, are proposed for laminar and turbulent swirling flows.

Near-field aerodynamics of swirl burners. (Part 3; Isothermal annular swirling flows with and without primary air injection).

Isothermal annular swirling flows were investigated to clarify the effects of a bluff body and a nonswirled central air jet upon the characteristics of swirl-induced recirculation zones. The velocity measurement using an LDA system revealed that the use of a bluff body increased the rate of recirculating mass flow and also the mass flow brought back into the quarl (or expansion) section. For flows with a primary air jet, two distinct flow patterns were observed: (I) ordinary IRZ (Internal Recirculation Zone) and (II) IRZ with primary air jet penetration. The IRZ strength could be determined by the combined parameter, Sa(D1/Do)2, where the swirl number is Sa and the vortex diameter expansion ratio is D1/Do.

Mean Flow and Turbulence Measurements of Annular Swirling Flows

This paper presents the results of a detailed experimental investigation of swirling flows in a cylindrical annulus. Flows having nominal swirl angles of 0, 15, 30, and 45 degrees were measured. Mean velocity components, total and static pressures, wall shear and Reynolds stresses were measured. Mixing length and eddy viscosity distributions were deduced from the data. The majority of the flow field measurements were made with single-sensor hot-wire anemometer probes; six independent readings, each with a different sensor orientation, were made at each point. Consistency checks were applied wherever possible and indicate that the data are of high quality.

Asymmetric Swirling Flows in Turbomachine Annuli

An analytical and experimental investigation of asymmetric annular swirling flows is presented. It is shown that, in contrast to the situation in nonswirling flow, the different types of flow disturbances (pressure and vorticity) are not separable in a swirling flow but are strongly coupled. The flows that occur due to this coupling are inherently three-dimensional and exhibit new features not seen in the nonswirling case. The theoretical predictions are in good agreement with experimental measurements carried out in an annular swirl rig.