Swirl Stream Research Articles

Employing a novel crimped-spiral rib inside a triple-tube heat exchanger working with a nanofluid for solar thermal applications: Irreversibility characteristics

This research attempts to study the performance of employing an innovative crimped-spiral rib within a triple-pipe heat exchanger (TPHE) operated with an alumina–water nanofluid regarding the second law viewpoint. The numerical analyses are carried out using the two-phase mixture model, and turbulence modeling is done via the Reynolds Stress Model (RSM). The parameters consist of the rib height ratio (0.23, 0.38, and 0.53), crimped intensity (2, 4, 6), rib pitch ratio (0.1, 0.2, and 0.3), and the nanofluid volume fraction (1, 2, and 3%). The nanofluid is the hot fluid flowing inside the intermediate tube, while the two other fluids are water. This paper underlines the lowest energy degradation to design a more efficient TPHE. The outcomes indicate that the idea of utilizing crimped-spiral rib is effective such that the nanofluid’s thermal entropy generation reduces about 22.92% using rib with higher crimped intensity because of the stronger swirl stream. The total entropy generation and total exergy destruction decline by the volume fraction increment, rib pitch ratio decrement, and by an increment in either crimped intensity or rib height ratio. The second law efficiency is found to be high for all the cases such that it is greater than 0.6.

The Phenomenon of Hysteresis in a Swirling Stream

The article considers a swirling current with a sudden expansion. As a result of an experimental study, it was found that two flow modes can exist under these conditions. In the first case, there is an intense twist at the outlet of the vortex device, a zone of return currents and precessional oscillations. In the second case, there is no zone of return currents and precession. At the same time, the gas flow through the device increases abruptly

Experimental Study on Coaxial Swirling Flows

The experimental investigation of a swirling jet and an annular swirling stream issuing from coaxial cylinders is presented. The objective is to contribute to the research on the combined flow field close to vortex breakdown conditions. The two swirling water streams are interacting in the extension of the outer cylinder. Swirl is generated by two rotating impellers, located in the inner tube and the annular duct, just before the merging of the two streams. Controlled flow parameters comprise the flow rates of the streams and the angular velocities of the impellers. The flow field is monitored by means of Stereoscopic 3D-PIV, providing the velocity components on an axial, central plane. Four typical test cases were investigated comprising four combinations of inlet conditions. Two dimensionless numbers were utilized to interpret the experimental results, a modified Rossby number and the velocity ratio ζ, along with the Reynolds numbers of the internal and annular stream, respectively. The most important coherent structure developed, is a recirculation region formed downstream of the exit of the internal swirl nozzle. A bubble type vortex breakdown occurs when the appropriate flow conditions are applied. The alterations of the flow field were discussed with respect to the changes of the inlet conditions. The flowrates of the two streams and the combined swirl strength applied through the rotating impellers appear to be crucial for the onset of the vortex breakdown. Comparisons were drawn with previous work.

Temperature and reaction zone imaging in turbulent swirling dual-fuel flames

Gaseous and liquid dual-fuel flames present both a practical approach to emissions reduction and a challenge to current state-of-the-art combustion modelling. This paper uses simultaneously imaged temperature and normalised OH signal fields to investigate flame structure and provide experimental data for model validation across a range of swirl-stabilised n-heptane spray flames. These data are obtained by non-linear excitation regime two-line atomic fluorescence (NTLAF) of indium, and planar laser-induced fluorescence (OH-PLIF), respectively. Swirling gas streams are varied by flowrate (63–88% of blow-off), premixed equivalence ratio (including air-only), and by type of gaseous fuel (natural gas and hydrogen). Results are used to describe how hot combustion products interact with the fuel spray: heating and diluting the region above the apex of the spray cone at low air flowrates but drawing fuel into outer branches of the flame with increasing air flowrates. Adding natural gas to the swirling air stream, at a concentration below the lean flammability limit, gives rise to a temperature increase in the outer branches with little effect on the hot region above the apex of the spray, along the burner centreline. The size of this region is significantly reduced; however, using hydrogen. As the concentration of gaseous fuel increases towards the lean flammability limit, peak temperatures shift towards the outer branch of the flame. Exceeding the lean flammability limit, an additional reaction zone begins to form in the premixed swirling stream, adjacent to the outer branch of the swirl flame. Stable outer branches of the swirl flame, however, become less prevalent and the peak temperatures of the spray flame return to burner centreline. This study provides insight into the complex behaviour of dual-fuel flames, a complementary dataset to related, PLIF-only studies and validation data for the development of numerical modelling tools.

Analysis of Influence of Masks Flow on Intake Valve of Gas and Oil Fuel Engine Based Simulation

Turbulent flow in the combustion chamber affects the combustion process which also affects the engine performance. The turbulent flow intensity can increase the duration of combustion, but too much turbulent turbulent flow leads to a tap. In addition, turbulent flow also contributes to the gas-water mixing process. There are two types of turbulent flow that occur inside the machine, which is a current vortex and a falling current. The current whirl is better known as the swirl flow and the falling current is better known as the tumble flow. The fluid flow in the combustion chamber can be adjusted by optimizing the engine components and developing the engine design. A review has been made of the vortex and Tumble flow on a luminous spark machine and its effect on turbulence and fire propagation. From several journals available to create tumble and swirl streams in the combustion chamber, they use modifications to the intake valve by adding vin to create a swirl stream and adding a mask to create a tumble stream. to know the experiment was successful or not, first modeling and then perform simulation using CFD Ansys Fluent. for the variables choose 3mask, 4mask, and 5mask (for addition of mask) which later dilih air flow formed by the addition of mask.

Scalar dissipation rate statistics in turbulent swirling jets

The scalar dissipation rate statistics were measured in an isothermal flow formed by discharging a central jet in an annular stream of swirling air flow. This is a typical geometry used in swirl-stabilised burners, where the central jet is the fuel. The flow Reynolds number was 29 000, based on the area-averaged velocity of 8.46 m/s at the exit and the diameter of 50.8 mm. The scalar dissipation rate and its statistics were computed from two-dimensional imaging of the mixture fraction fields obtained with planar laser induced fluorescence of acetone. Three swirl numbers, S, of 0.3, 0.58, and 1.07 of the annular swirling stream were considered. The influence of the swirl number on scalar mixing, unconditional, and conditional scalar dissipation rate statistics were quantified. A procedure, based on a Wiener filter approach, was used to de-noise the raw mixture fraction images. The filtering errors on the scalar dissipation rate measurements were up to 15%, depending on downstream positions from the burner exit. The maximum of instantaneous scalar dissipation rate was found to be up to 35 s−1, while the mean dissipation rate was 10 times smaller. The probability density functions of the logarithm of the scalar dissipation rate fluctuations were found to be slightly negatively skewed at low swirl numbers and almost symmetrical when the swirl number increased. The assumption of statistical independence between the scalar and its dissipation rate was valid for higher swirl numbers at locations with low scalar fluctuations and less valid for low swirl numbers. The deviations from the assumption of statistical independence were quantified. The conditional mean of the scalar dissipation rate, the standard deviation of the scalar dissipation rate fluctuations, the weighted probability of occurrence of the mean conditional scalar dissipation rate, and the conditional probability are reported.

Validation of LES Predictions of Scalar Mixing in High-swirl Fuel Injector Flows

A combined experimental and computational study is described, aimed at validation of LES predictions of the flow and mixing fields created by a fuel injector which incorporates a single, radially-fed annular swirl stream surrounding a central axial jet flow. The focus of this work was on turbulent mixing processes, so an isothermal (water flow) experiment was carried out, using a representative injector geometry operated at appropriate Reynolds and Swirl Numbers. Combined SPIV and PLIF instrumentation allowed simultaneous instantaneous measurements of velocity vector and a conserved scalar introduced into the fuel stream. For the first time in such a flow, all 3 components of the turbulent scalar flux were available for validation of LES-based CFD predictions. A careful assessment of experimental errors was carried out. Very close to the injector exit plane (x/DS < 0.1), the measured data were prone to larger errors (~20%). Further downstream (x/DS = 0.2 − 1.5), spatial filtering errors were much smaller (~5 − 10%). Comparison of LES predictions with experimental data showed very good agreement for both 1st and 2nd moment statistics, as well as spectra and scalar pdfs. It is particularly noteworthy that comparison between LES computed and measured scalar fluxes was very good; this represents successful validation of the simple (constant Schmidt No.) SGS model used for this complex and practically important flow.

Numerical simulation of flow around square cylinder using different low-Reynolds number turbulence models

ABE-KONDOH-NAGANO, ABID, YANG-SHIH and LAUNDER-SHARMA low-Reynolds number turbulence models were applied to simulating unsteady turbulence flow around a square cylinder in different phases flow field and time-averaged unsteady flow field. Meanwhile, drag and lift coefficients of the four different low-Reynolds number turbulence models were analyzed. The simulated results of YANG-SHIH model are close to the large eddy simulation results and experimental results, and they are significantly better than those of ABE-KONDOH-NAGANO, ABID and LAUNDER-SHARMR models. The modification of the generation of turbulence kinetic energy is the key factor to a successful simulation for YANG-SHIH model, while the correction of the turbulence near the wall has minor influence on the simulation results. For ABE-KONDOH-NAGANO, ABID and LAUNDER-SHARMA models satisfactory simulation results cannot be obtained due to lack of the modification of the generation of turbulence kinetic energy. With the joint force of wall function and the turbulence models with the adoption of corrected swirl stream, flow around a square cylinder can be fully simulated with less grids by the near-wall.

Vortex Breakdown in Swirling Fuel Injector Flows

It is well known that the process of vortex breakdown plays an important role in establishing the near-field aerodynamic characteristics of fuel injectors, influencing fuel/air mixing and flame stability. The precise nature of the vortex breakdown can take on several forms, which have been shown in previous papers to include both a precessing vortex core (PVC) and the appearance of multiple helical vortices formed in the swirl stream shear layer. The unsteady dynamics of these particular features can play an important role in combustion induced oscillations. The present paper reports an experimental investigation, using particle image velocimetry (PIV) and hot-wire anemometry, to document variations in the relative strength of PVC and helical vortex patterns as the configuration of a generic fuel injector is altered. Examples of geometric changes that have been investigated include: the combination of an annular swirl stream with and without a central jet; variation in geometric details of the swirler passage, e.g., alteration in the swirler entry slots to change swirl number, and variations in the area ratio of the swirler passage. The results show that these geometric variations can influence: the axial location of the origin of the helical vortices (from inside to outside the fuel injector), and the strength of the PVC. For example, in a configuration with no central jet (swirl number S=0.72), the helical vortex pattern was much less coherent, but the PVC was much stronger than when a central jet was present. These changes modify the magnitude of the turbulence energy in the fuel injector near field dramatically, and hence have an important influence on fuel air mixing patterns.

An experimental study of the under-expanded swirling jet with secondary coaxial stream

The present study addresses experimental results for investigating the details of the near field flow characteristics produced in an under-expanded, dual, coaxial, swirling jet. The under-expanded swirling jet is discharged from a sonic inner nozzle. An outer annular nozzle produces co- and counter-swirling streams relative to the inner primary swirling jet. The interaction between both the outer annular swirling stream and inner under-expanded swirling jet is quantified by impact and static pressure measurements, and visualized by using the shadowgraph method. Experiments are performed for several different pressure ratios. The results show that the outer secondary co-swirling jet significantly changes the structure of the inner under-expanded swirling jet, such as the shock structures and the recirculation region generated at the jet axis. The effect of the outer secondary stream on the major structures of the inner primary swirling jet is strongly dependent on the pressure ratio of the inner swirling jet, regardless of the swirl direction of the outer stream.

An experimental study of underexpanded sonic, coaxial, swirl jets

The present study addresses experimental investigations of the near-field flow structures of an underexpanded sonic, dual, coaxial, swirl jet. The swirl stream is discharged from the secondary annular nozzle and the primary inner nozzle provides the underexpanded free jets. The interactions between the secondary swirl and primary underexpanded jets are quantified by a fine pitot impact and static pressure measurements and are visualized using a shadowgraph optical method. The pressure ratios of the secondary swirl and primary underexpanded jets are varied below 7.0. Experiments are conducted to investigate the effects of the secondary swirl stream on the primary underexpanded jets, compared with the secondary stream of no swirl. The results show that the presence of an annular swirl stream causes the Mach disc to move further downstream, with an increased diameter, and remarkably reduces the fluctuations of the impact pressures in the underexpanded sonic dual coaxial jet, compared with the case of the secondary annular stream with no swirl.

An Experimental Study of the Supersonic, Coaxial Jet with Swirl

The present study addressed an experimental investigation of the near field flow structures of supersonic, dual, coaxial, swirl jet. The swirl stream was discharged from the secondary annular nozzle and primary inner nozzle provided the sonic and supersonic free jets. The pressure ratios of the secondary swirl and primary sonic/supersonic jets were varied below 7.0. Experiments were conducted to investigate the effects of the secondary swirl stream on the primary sonic and supersonic jets, compared with the secondary stream of no swirl. The results showed that the presence of annular swirl stream causes the Mach disk to move more downstream, with the increased diameter, and remarkably reduces the fluctuations of the Pitot pressures in the supersonic dual coaxial jet, compared with the case of the secondary annular stream of no swirl.

Interaction between a jet and an annular swirling stream

The problem of the interaction between axisymmetric flows with a swirl distributed over the radius is numerically investigated. Various flow regimes with the formation of axial recirculation zones are obtained.