Single Swirl Research Articles

Effect of anvil roughness on the flow patterns and hardness development in high-pressure torsion

Two sets of anvils having different surface roughness were used to systematically investigate the flow patterns developed on the top and bottom surfaces of stainless steel discs with an anvil misalignment of 100 µm during high-pressure torsion. It is shown that the flow patterns on the disc surfaces have different variation tendencies depending on whether the anvils have rough or smooth surfaces. Double-swirl flow patterns were observed on the top and bottom surfaces of discs after 1 and 5 turns when using an anvil with a smooth surface. In contrast, when using an anvil with a rough surface the double-swirl flow patterns appeared only on the top surface after 1 turn and a single swirl appeared on both surfaces after 5 turns. Hardness measurements on the top surfaces showed that discs processed using an anvil with a rough surface have greater hardness than discs processed using an anvil with a smooth surface. There was no obvious hardness difference on the bottom surfaces for discs processed using anvils with rough or smooth surfaces.

UV-Visible Emission Spectroscopy of the Combustion Process in a Common Rail Cl Engine Fulled with N-Butanol - Diesel Blends

This paper is focused on the study of the effects of the injection strategy and fuel blends on spray combustion and soot formation in compression ignition engines. UV-visible natural emission spectroscopy was applied in the combustion chamber of a single cylinder high swirl compression ignition engine equipped with a common rail multi-jet injection system. The engine was fuelled with low-sulphur neat diesel and blended with 20 and 40% by volume of n-butanol. For all the fuels, the evolution of radical species, such like OH and soot was followed during the spray combustion processes examining different pilot-main dwell timings. Optical data were correlated to engine parameters and exhaust emissions.

Single Inlet Pressure Swirl Nozzle Stationary Wave Pattern and Quality Optimization

A kind of single inlet swirl atomizer is set to adjust the inlet location and the length of the outlet for an optimization spray angle and uniformity in this literature.Stationary wave theory is used to describe the results of spray quality.Experimental and theoretical analysis show that using property machining process size, single inlet swirl nozzles can achieve the optimized quality of atomization (spray cone angle of 55 °and more, skewness of spray cone center below 5 ° ).

Fuzzy Modeling for Optical Sensor for Diagnostics of Pulverized Coal Burner

Abstract The premise for the exploration of new sensors and methods of diagnostics of the combustion process are the difficulties encountered during the implementation of low emission combustion technology. Averaging and delay are the main drawbacks of traditional methods of measurement of the majority of combustion parameters. There is a lack of method that allows measurement of output parameters of an individual burner. It is therefore necessary to use indirect optical methods. They are noninvasive, virtually not delayed and additionally spatially selective. Although they provide large amounts of information, their interpretation requires the use of complex data processing techniques. The authors prove that it is possible to obtain quantitative information, in the article it is demonstrated on the example of nitrogen oxides. The paper describes the use of processing methods with a relatively small computational complexity. Tests were made using 1:10 scale rig with single swirl burner.

Simulation of a GOX–kerosene subscale rocket combustion chamber

In view of future film cooling tests at the Institute for Flight Propulsion (LFA) at Technische Universitat Munchen, the Astrium in-house spray combustion CFD tool Rocflam-II was validated against first test data gained from this rocket test bench without film cooling. The subscale rocket combustion chamber uses GOX and kerosene as propellants which are injected through a single double swirl element. Especially the modeling of the double swirl element and the measured wall roughness were adapted on the LFA hardware. Additionally, new liquid kerosene fluid properties were implemented and verified in Rocflam-II. Also the influences of soot deposition and hot gas radiation on the wall heat flux were analytically and numerically estimated. In context of reviewing the implemented evaporation model in Rocflam-II, the binary diffusion coefficient and its pressure dependency were analyzed. Finally simulations have been performed for different load points with Rocflam-II showing a good agreement compared to test data.

Influence of Transversal Acoustic Excitation of the Burner Approach Flow on the Flame Structure

Modern large gas turbines for power generation have multiple burners, which are distributed around the circumference of the engine and which generate flames in combustors of either annular or can-annular geometry. In both cases, considering only the axial modes has proven to be insufficient for the assessment of the thermoacoustic stability. An adequate analysis requires consideration of the circumferential acoustic coupling generated by the acoustic field in the upstream and downstream annuli and the open passages between the cans, respectively. As in annular combustors, the particularly critical eigenmodes with low frequencies are predominantly of circumferential nature; the stability of annular combustors is often governed by the onset of circumferential acoustic oscillations. To determine the influence of these circumferential acoustic modes on the dynamic flame behavior, a new single burner test rig was developed. The unique acoustic properties of the test rig allow the exposure of a single swirl burner to a two-dimensional acoustic field that resembles the circumferential mode in an annular combustor. Measurements were performed for axial as well as transversal excitation of the burner and the combination of both. To investigate the dynamic flame structure, phase-resolved flame images have been evaluated in terms of amplitude and phase distribution. Under transversal excitation, the flame structure becomes highly asymmetrical. A region of higher OH∗ intensity is generated in the combustion chamber, which rotates with the excitation frequency. From phase-resolved particle image velocimetry (PIV) measurements of the isothermal flow, it is concluded that the transversal excitation modulates the swirl generation leading to an asymmetrical velocity distribution in the burner nozzle and the combustion chamber.

Characteristics of the Suppression of Sloshing in a Vessel by a Bulkhead

This paper investigates the characteristics of the suppression of sloshing in a vessel by a bulkhead that divides the vessel vertically into two sections but allows communication between two sections at the lower part of the vessel. The sloshing behavior is thus separated into a U-tube sloshing mode and a sloshing mode confined to each of the separated compartments. The effect of the aperture height beneath the bulkhead and the amplitude of the excitation on the characteristics of the suppression of the U-tube sloshing mode is investigated experimentally. As a result, the following phenomena are clarified. Three types of flow patterns were observed: flow pattern A, with unsteady vortices, flow pattern B, with a single swirl and a vortex, and flow pattern C, with twin swirls. The flow pattern changes from A to B or C as the amplitude of the excitation increases. The damping ratio with the bulkhead is much larger than that without the bulkhead. The damping generated by the bulkhead depends on the amplitude of the excitation. The flow pattern plays an important role in the dissipation of the energy of the sloshing. In particular, the vortices and swirls increase the rate of energy dissipation of the sloshing.

Effect of Co- and Counterswirl on Noise from Swirling Flows and Flames

Overall and spectral sound pressure levels radiating from swirling flows and flames were measured and correlated with simultaneous plenum pressure fluctuations measurements. Single swirler and co- and counter-rotating double swirlers were used. Generic radial-entry swirlers with straight vanes and a convergent-divergent nozzle were employed. At the same Reynolds number and Mach number, precessing-vortex-core frequency, spectral amplitude at that precessing-vortex-core frequency, and overall sound pressure levels for flows were the highest for the single swirler, followed by the co- and counter-rotating double swirlers. Rates of increase in precessing-vortex-core frequency and overall sound pressure levels with Reynolds number and Mach number were also in the same order. Sound spectra for single and corotating double swirlers contained precessing-vortex-core-related strong tonal components. However, for counter-rotating double-swirler flows, amplitude of the tonal component was reduced considerably. Double-swirler configurations exhibited dual precessing-vortex-core frequencies. The addition of a second swirler slowed down precessing-vortex-core and reduced its upstream transmission to the plenum and the transmission of plenum modes to the sound field. The counter-rotation configuration was more effective in slowing down the precessing vortex core and acting as a transmission barrier than the corotation configuration. Compared to flow, partially premixed flame,Φ=1.15, produced 5-10 dB higher overall sound pressure levels. However, the flame had a lower Mach number exponent than the flow. Flames inhibited the transmission of high-frequency tones across them. At the sameΦand Reynolds number, the corotating flame was the least noisy and the counter-rotating flame was the noisiest. Premixed flames withΦ= 0.98 were compared with the flows by keeping an identical pressure differential across the premixer. The counter-rotating double swirlers produced higher overall sound pressure levels than the corotating double swirlers, which generated more overall sound pressure levels than the single swirler.

PDA and Neural Network Investigation of Swirl Spray Interaction Phenomena

AbstractExperiments are performed to investigate the atomization characteristics of mixed‐interaction regions of sprays of two swirl injectors installed side by side. Both droplet size and velocity distributions on a plane perpendicular to the axes of the injectors are measured using a PDA system. As a result of the interaction phenomenon, a region of secondary atomization is identified that differs significantly from the hollow region spray of a single swirl injector. A neural network algorithm is used to reconstruct the entire spray field for both droplet size and velocity distribution in extrapolation regimes for injector spacing as well as three dimensional spatial coordinates. Excellent agreement between the predicted values and the measurements is obtained. It is observed that points on the extrapolation regime of the neural network can be predicted with an accuracy of 93 % using a training data set with less than 50 % of the number of data points to be predicted. The results indicate the capability of performing design‐ and optimization studies for pressure‐swirl injectors, with sufficient accuracy, by applying a modest amount of data in conjunction with an overall optimized value for the width of the probability.

The Effect of Swirl on Flow Stability in Spray Dryers

The effect of varying the amount of inlet air swirl on the stability of the flow patterns in a small-scale, co-current spray dryer has been investigated. The objective of this work was better understanding of the effect of the vane angle on the flow patterns and to determine whether a particular vane angle provided superior performance. The dryer studied was a cylinder on cone unit, with a drying chamber 0.8 m in diameter and 1.61 m tall, and fitted with adjustable swirl vanes tightly surrounding a Delavan GA1 two-fluid atomiser. Swirl vane angles between 0° and 45°, in 5° increments, were investigated using a complementary combination of flow visualisation and laser Doppler velocimetry (LDV) techniques. No single swirl vane angle resulted in behaviour that was clearly steady throughout the dryer, but a swirl vane angle of about 25° was considered to be an appropriate selection. This vane angle, corresponding to a Swirl number of approximately 0.45, gave an observable degree of stability in much of the flow domain and good air-spray mixing without excessive spreading of the spray cloud and wall deposition. The introduction of spray had a significant effect on the flow behaviour, so that air-only studies did not adequately represent the flow conditions with spray.

Suppression Characteristics of Sloshing in a Recutangular Vessel by a Bulkhead.

This paper deals with suppression characteristics of sloshing in a rectangular vessel by a bulkhead which divides the vessel vertically into two sections. The sloshing mode is separated into two modes by the bulkhead ; the one is the sloshing mode of liquid column in a U-tube, and the other is the sloshing mode in the separated tank. The effect of aperture height of the bulkhead and exciting amplitude on the suppression characteristics of U-tube mode sloshing is examined experimentally. And the flow patterns of the fluid In the vessel are visualized. As a result, following phenomena are clarified. (1) There are three types of flow pattern. The one is the flow pattern (A) with unsteady vortexes, and another is the flow pattern (B) with single swirl and a vortex, and the other is the flow pattern (C) with twin swirls. (2) The flow pattern changes from pattern (A) to (B) or (O with increasing the exciting amplitude. (3) The damping ratio of the sloshing with the bulkhead is much larger than that without the bulkhead. (4) The damping produced by the bulkhead is dependent on the exciting amplitude and it's damping ratio increases with increasing the exciting amplitude. (5) The flow pattern plays an important role for dissipation of the energy of the sloshing. In particular, the vortexes and swirls increase the energy dissipation of the sloshing.

An experimental estimation of mean reaction rate and flame structure during combustion instability in a lean premixed gas turbine combustor

The interactions between the local flame structure produced by a premixed swirl-stabilized injector with combustion instabilities were experimentally studied for a model gas turbine combustor operating at high pressure and temperature. The model gas turbine combustor studied utilizes a sudden-expansion dump combustor with a single swirler and bluff body for enhancing mixing rate and flame stabilization, respectively. Laser-based measurements were made for both stable and unstable operating conditions. The local flame front structure was visualized using planar laser-induced fluorescence (PLIF) from the OH⊙, and the global heat release zone was interpreted from flame emission measurements. For stable combustion conditions, the mean reaction rate estimated independently from both OH-PLIF and OH * chemiluminescence measurements showed good agreement, thereby indicating confidence in the use of OH-PLIF measurements for extracting the local mean reaction rate. For unstable combustion conditions, the flamefront characteristics, including flame surface density and mean reaction rate, were evaluated together with the information from the OH * chemiluminescence measurements to identify the boundary of the heat release region at discrete phases of the unstable flame. Analysis of the flame structures during combustion instability indicated significant variations during different phases of the instability. The heat release flow field, particularly in the recirculation regions appearing at the corner and inner face of the dump plane, varied substantially. Rayleigh index information indicated that the recirculation zones play an important part in driving the instability. In contrast, the high shear layer formed along the interface between reactants and hot products produced a region where the instability was damped due to a lowering of the heat release.

The rate of decay of swirl in turbulent pipe flow

An experimental study is performed for the development of the mean velocity field of swirling turbulent flows in straight pipes with a smooth wall. Swirl intensities were selected in a range that can be expected to occur in large piping systems. Measurements were taken for two different Reynolds numbers, and two widely different initial conditions. Although the swirl intensity can best be expressed by the axial flow of angular momentum, a representation by a single swirl angle seems to be satisfactory for the final decay process. While the difference between the initial conditions persists during a considerable part of the decay process, the decay rates are not essentially different. The rate of decay appears to vary with the Reynolds number in the same way as the friction factor does.

Characteristics of a Power Station Boiler

An experimental investigation of the flow patterns in a model of a power station boiler has been carried out under isothermal conditions, to produce data for computational fluid dynamic code validation. Measurements were made in three dimensions on a single swirl burner in isolation, in two dimensions on a bank of 12 burners in a 4 × 3 grid and in the model boiler with this bank installed. The single burner exhibited a central reverse flow zone with high levels of turbulence at its boundaries. The general flow pattern found in the single burner was greatly distorted when interaction with surrounding burners in the bank occurred. Several unexpected secondary flows occurred. The model boiler displayed a complex flow arrangement with recirculation zones and two stagnation points.

Effect of Swirling Flow on Electro-magnetic Flow Meters.

In general, liquid metal fluid flow in externally applied magnetic fields produces induced currents. A study was carried out on the electro-magneto-hydraulic effect of the induced currents on the characteristics of liquid metal electro-magnetic flow meters. Both theoretical analysis and corresponding experimental measurements have been conducted to investigate swirling flow profiles which are produced by upstream arrangements of pipes and bends. The results showed that these arrangements produced two types of flow profiles ; single swirling and double swirling. Based on such flow profiles, the distortion of a potential field was evaluated and the influence on voltage output was estimated with the two-dimensional electro-magnetic analysis code FALCON-2D developed for this study. The analyis showed that the single swirling flow had a larger effect on the voltage output than the double swirling flow.

Dry resistance of a single conical swirl element

Dry resistance of a single conical swirl element

On the Operational Characteristics of a Multi-annular Swirl Burner

Abstract Further experimental results are described from the multi-annular swirl burner (MASB). The burner comprises a plurality of concentric annular divergent nozzles with the inner end of each nozzle aligned substantially with the outer end of the adjacent nozzle. The MASB makes use of the principle that under turbulent conditions high volumetric heat release rates can be achieved by matching the concentrations and directions of flow of reactants in such a way that regions of high fuel concentration overlap regions of large shear stresses in the flow. Wider stability limits and better mixing of reactants are found in this MASB compared to the conventional type of single annular swirl burner. Laser anemometry system was used to obtain the three components of mean and r.m.s. velocity together with the higher moments of turbulence. Results were obtained under non-combustive and combustive conditions both with and without extension tube attached to the burner exit. The results indicate clearly an increase ...

Formation and nature of swirl defects in silicon

Point defect agglomerates in dislocation-free silicon crystals, usually called “swirls”, have been investigated by means of high-voltage electron microscopy. It was found that a single swirl defect consists of a dislocation loop or a cluster of dislocation loops. By contrast experiments it could be shown that these loops are formed by agglomeration of self-interstitial atoms. Generally the loops have a/2〈110〉 Burgers vectors, but in specimens with high concentrations of carbon (∼1017 cm−3) and oxygen (∼1016 cm−3) also dislocation loops including a stacking fault were observed. In crystals grown at growth rates higher thanv=4 mm/min no swirls are observed; lower growth rates do not markedly affect the size and shape of the dislocation loops. With decreasing impurity content (particulary of oxygen and carbon) the swirl density decreases, whereas the dislocation loop clusters become larger and more complex. A model is presented which describes the formation of swirls in terms of agglomeration of silicon self-interstitials and impurity atoms.