Turbulent Swirling Jet Research Articles

Direct Numerical Simulations of the Evaporation of Dilute Sprays in Turbulent Swirling Jets

The effects of swirled inflows on the evaporation of dilute acetone droplets dispersed in turbulent jets are investigated by means of direct numerical simulation. The numerical framework is based on a hybrid Eulerian–Lagrangian approach and the point-droplet approximation. Phenomenological and statistical analyses of both phases are presented. An enhancement of the droplet vaporization rate with increasing swirl velocities is observed and discussed. The key physical drivers of this augmented evaporation, namely dry air entrainment and swirl-induced centrifugal forces acting on the droplets, are isolated with the aid of additional simulations in which the inertial properties of the droplets are neglected. The correlation between swirl and dry air entrainment rate is found to be responsible for the increase of the global evaporation rate and the spray penetration length reduction, while swirl-induced centrifugal forces are found to be effective only in the jet shear layer, close to the injection orifice, for the analyzed cases.

Numerical investigation of heat transfer from a plane surface due to turbulent annular swirling jet impingement

The heat transfer characteristic of an annular turbulent swirling jet impingement on a heated plane surface is investigated numerically. The annular jet configuration causes instabilities and fluctuations in the flow. Depending on the combinations of different parameters, the annular jet impingement may have positive or negative effects on the heat transfer from the impingement surface. Swirl, on the other hand, introduces vorticity and fluid mixing in an impinging jet, which is desirable in some applications. The axisymmetric two-dimensional flow domain on a radial-axial plane is considered in the numerical model. Both non-swirling and swirling jet impingement is studied. The numerical computations are performed using the ANSYS Fluent CFD code. The Realizable k-ε turbulence model with enhanced wall treatment is used in the computation. The computational process is validated against other published data on similar flow configuration for non-swirling annular impinging jets. The flow and geometric parameters are the jet exit Reynolds number, Re (5000 to 25,000), the swirl strength Sw (0–0.77), the jet exit to the impingement surface distance, H (0.5–4.0), and the moderate blockage ratio of the annular jet, BR (0.4–0.6). The thermal-hydraulic field in the domain is computed for various combinations of these parameters. The effects of these parameters on the Nusselt number distribution on the impingement surface are analyzed. For short separation distance (H = 0.5), the swirling motion positively affects the overall heat transfer, and the average Nu is increased as high as 8% for certain combinations of Re, Sw, and BR; compared to the non-swirling annular jet impingement. For higher separation distances, the average and peak Nusselt number is initially reduced and then increased with increasing swirl strength.

Spatial Structure of a Reacting Turbulent Swirling Jet Flow with Combustion of a Propane–Air Mixture

Results of an experimental study of the spatial structure of a reacting flow during combustion of a propane–air mixture in a turbulent swirling jet escaping into atmospheric air are presented. The fuel-to-air equivalence ratio is φ = 0.7, and the Reynolds number of the jet is Re = 5 · 103. The time-averaged spatial distributions of velocity, local density, and concentrations of the main species of the gas mixture are measured in low-swirl and high-swirl flows. In both cases, the flame front is stabilized in the internal mixing layer formed by the axial region of jet retardation, where hot combustion products are concentrated. In a high-swirl flow, the temperature distributions in the cross section y/d = 0.5 show that the region with the maximum temperature of the gas is located at the periphery of the central recirculation zone. Moreover, in the case of a high-swirl flow, there exists a recirculation zone at the axis, and the CO2 concentration is twice higher than in a low-swirl jet. The opposite situation is observed for O2.

Corrections of dual-wire CTA data in turbulent swirling and non-swirling jets

Constant Temperature Anemometers provide opportunities for high data rate in relation to velocity and turbulence measurements in gaseous jets. The application of dual-wire probes in turbulent non-swirling and swirling jets is, however, challenging due to the need to correct for directional responses, velocity gradients and probe misalignments with the mean flow direction. Although swirl flow measurements have been conducted in the past using dual-wire probes, the literature does not include clear methodologies to compensate for both gradient effects and changes to the mean flow direction, particularly in flow regions with high shear and strong swirl over a range spanning (S=0–1.05). As a result, this paper presents an overview of the methodology needed to apply dual-wire probes and accommodate changes to the resultant velocity (mean flow) angle (α) through orienting the probe (ψ). Results show that both velocity gradient effects as well as probe misalignments are strongly affected by radial location, Reynolds number and swirl intensity. This study demonstrates a setup methodology that orients CTA X-wire probes for improved data yield and accuracy for turbulent swirling jets.

Scalar Mixing and Large-Scale Coherent Structures in a Turbulent Swirling Jet

The paper presents large eddy simulations of co-annular swirling jets into an open domain. In each of the annuli a passive scalar is introduced and its transport is computed. If the exit of the pilot jet is retracted strong coherent flow structures are generated which substantially impact on the transport and mixing of the scalars. Average and instantaneous fields are discussed to address this issue. A conditional averaging technique is devised and applied to velocity and scalars. This allows to quantify the impact of the coherent structures on the mixing process.

Momentum and Heat Transfer in a Buoyant Turbulent Swirling Jet

Solutions are presented for a three-parameter model of turbulence for axisymmetric turbulent buoyant swirling jet flows in uniform and stagnant surroundings. The exit swirl number has a significant effect on the flow characteristics. The predicted results are in good agreement with experimental data. A discussion is provided for the effects of swirl and buoyancy on the growth of the jet width, the axial decay of mean flow properties, and the mass flow rates.

Vortex flow model for the blade-vortex interaction problem

Young, A. D. and Rao, K. N., Some Low Speed Results on the Effects of Swirl and Velocity Distribution on an Axisymmetric Jet, Aerospace Quarterly, Vol. 29, 1978, p. 4. Morse, A. P., Some Experiments on the Turbulent Swirling Jet with and without External Stream, Ph.D. Thesis, Imperial College, London, 1979. Samet, M. and Einav, S., The Directional Pressure Probe, Review of Scientific Instruments, 1984, pp. 582-588.