Flow field characteristics in the near field region of particle-laden coaxial jets

2005 ◽  
Vol 39 (5) ◽  
pp. 885-894 ◽  
Author(s):  
Reza Sadr ◽  
Joseph C. Klewicki
Keyword(s):  
Flow Field ◽  
Near Field ◽  
Field Region ◽  
Coaxial Jets ◽  
Flow Field Characteristics

Aerodynamics of Linearly Arranged Rad-Rad Swirlers, Effect of Number of Swirlers and Alignment

2013 ◽  
Author(s):  
Yi-Huan Kao ◽  
Samir B. Tambe ◽  
San-Mou Jeng
Keyword(s):  
Flow Field ◽  
Swirling Flow ◽  
Near Field ◽  
Aerodynamic Characteristics ◽  
Field Region ◽  
Clockwise Rotation ◽  
Swirling Jets ◽  
Entire Flow ◽  
High Turbulence ◽  
Series Of Experiments

A series of experiments have been conducted to study the aerodynamic characteristics of a confined swirling flow generated by multiple rad-rad swirlers arranged linearly. The rad-rad swirlers used in this study are identical, and consist of an inner, primary swirler generating counter-clockwise rotation and an outer, secondary swirler generating clockwise rotation. A two-component Laser Doppler Velocimetry (LDV) system was employed to measure the velocity in the flow field. Initial measurements were conducted on unconfined and confined flow generated by a single swirler to serve as the baseline reference for the multi-swirler arrangements. Tests were conducted for 3 and 5 swirlers arranged in a line, with a spacing of 2D between the swirler centers, where D is the swirler exit diameter. An additional 5 swirler configuration was tested, where the exit plane of the center swirler was shifted 3.2 mm (1/8 inch) in the streamwise direction. The flow field generated by the multi-swirler arrangement is very complex, due to the interaction between the swirling jets of adjacent swirlers. The number of swirlers is seen to have a clear impact on the entire flow structure, as well as each recirculation zone. For the 3 swirler arrangement, a weak CTRZ is observed for the center swirler, whereas strong CTRZs are observed for the two outer swirlers. For the 5 swirler arrangement, the CTRZ pattern for the 3 inner swirlers is the same strong-weak-strong as seen for the 3 swirler arrangements, with weak CTRZs observed for the two outer swirlers. Higher interaction between swirlers is observed for the 5 swirler arrangement, as compared to the case with 3 swirlers. Since the swirlers are identical, the region between swirlers features merging of two opposing swirling jets, producing high turbulence intensity in the near field region. For the case with the offset center swirler, the swirling jet from this swirler did not merge with its neighbors in the near field region. This resulted in strong CTRZ for the center swirler, accompanied by weaker CTRZs at its immediate neighbors, which is reverse of the CTRZ strength pattern observed for the initial 5 swirler arrangement.

scholarly journals Coaxial Circular Jets—A Review

Fluids ◽  
2021 ◽  
Vol 6 (4) ◽  
pp. 147
Author(s):  
René van Hout ◽  
Sudharson Murugan ◽  
Abhijit Mitra ◽  
Beni Cukurel
Keyword(s):  
Flow Field ◽  
Near Field ◽  
Mixing Layer ◽  
Flow Characteristics ◽  
Fine Tuning ◽  
Nozzle Geometry ◽  
Jet Flows ◽  
Coaxial Jets ◽  
Static Pressure Distribution ◽  
Circular Jets

This review article focuses on the near-field flow characteristics of coaxial circular jets that, despite their common usage in combustion processes, are still not well understood. In particular, changes in outer to inner jet velocity ratios, ru, absolute jet exit velocities and the nozzle dimensions and geometry have a profound effect on the near-field flow that is characterized by shear as well as wake instabilities. This review starts by presenting the set of equations governing the flow field and, in particular, the importance of the Reynolds stress distributions on the static pressure distribution is emphasized. Next, the literature that has led to the current stage of knowledge on coaxial jet flows is presented. Based on this literature review, several regions in the near-field (based on ru) are identified in which the inner mixing layer is either governed by shear or wake instabilities. The latter become dominant when ru≈1. For coaxial jets issued into a quiescent surrounding, shear instabilities of the annular (outer) jet are always present and ultimately govern the flow field in the far-field. We briefly discuss the effect of nozzle geometry by comparing the flow field in studies that used a blockage disk to those that employed thick inner nozzle lip thickness. Similarities and differences are discussed. While impinging coaxial jets have not been investigated much, we argue in this review that the rich flow dynamics in the near-field of the coaxial jet might be put to an advantage in fine-tuning coaxial jets impinging onto surfaces for specific heat and mass transfer applications. Several open questions are discussed at the end of this review.

scholarly journals Coupled Fluid–Solid Numerical Simulation for Flow Field Characteristics and Supporting Performance of Flexible Support Cylindrical Gas Film Seal

Aerospace ◽  
2021 ◽  
Vol 8 (4) ◽  
pp. 97
Author(s):  
Junfeng Sun ◽  
Meihong Liu ◽  
Zhen Xu ◽  
Taohong Liao ◽  
Xiangping Hu ◽  
...  
Keyword(s):  
Flow Field ◽  
Film Thickness ◽  
Fluid Dynamic ◽  
Structural Characteristics ◽  
Structural Parameters ◽  
Equivalent Stress ◽  
Three Dimensional ◽  
High Rotational Speed ◽  
Flexible Support ◽  
Flow Field Characteristics

A new type of cylindrical gas film seal (CGFS) with a flexible support is proposed according to the working characteristics of the fluid dynamic seal in high-rotational-speed fluid machinery, such as aero-engines and centrifuges. Compared with the CGFS without a flexible support, the CGFS with flexible support presents stronger radial floating characteristics since it absorbs vibration and reduces thermal deformation of the rotor system. Combined with the structural characteristics of a film seal, an analytical model of CGFS with a flexible wave foil is established. Based on the fluid-structure coupling analysis method, the three-dimensional flow field of a straight-groove CGFS model is simulated to study the effects of operating and structural parameters on the steady-state characteristics and the effects of gas film thickness, eccentricity, and the number of wave foils on the equivalent stress of the flexible support. Simulation results show that the film stiffness increases significantly when the depth of groove increases. When the gas film thickness increases, the average equivalent stress of the flexible support first decreases and then stabilizes. Furthermore, the number of wave foils affects the average foils thickness. Therefore, when selecting the number of wave foils, the support stiffness and buffer capacity should be considered simultaneously.

scholarly journals Experimental observation of asymmetrical microwave jets and far-field distribution generated by a dual-material system

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
B. Varghese ◽  
O. Shramkova ◽  
P. Minard ◽  
L. Blondé ◽  
V. Drazic ◽  
...  
Keyword(s):  
Near Field ◽  
Microwave Frequency ◽  
Far Field ◽  
Material System ◽  
Field Region ◽  
Edge Diffraction ◽  
Jet Behavior ◽  
Electric Field Profile ◽  
Dual Material ◽  
Plane Wave Diffraction

AbstractIn this paper, we report the experimental and numerical investigation of plane wave diffraction by an all-dielectric dual-material cuboid. Edge diffraction by a cuboid leads to the generation of a narrow, high intensity beam in the near-field region called a photonic jet. We examine the dependence of the jet behavior and orientation on the materials and dimensions of constitutive parts in the microwave frequency domain. The possibility to shift and deviate the resultant microwave jet in the near-field region of such a structure depending on the size of constitutive parts is demonstrated numerically. Experimentally, we observe a shift in the spatial position of the jet. The experimental asymmetric electric field profile observed in the far-field region is attributed to the input of multiple edge waves generated by the dual-material cuboid. The presented results may be scaled at different frequency bands such as optical frequencies for designing nanostructures enabling the focusing and deviation functionality and creation of new optical devices which would satisfy the needs of emerging nanophotonic applications.

scholarly journals Influence of Vortex Finder Structure on Separation Performance of Double-Overflow Three-Product Hydrocyclones

Separations ◽  
2021 ◽  
Vol 8 (6) ◽  
pp. 79
Author(s):  
Yuekan Zhang ◽  
Jiangbo Ge ◽  
Lanyue Jiang ◽  
Hui Wang ◽  
Junru Yang ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Experimental Research ◽  
Separation Efficiency ◽  
Structural Parameters ◽  
Separation Performance ◽  
Insertion Depth ◽  
Flow Field Characteristics ◽  
Vortex Finder ◽  
Fine Classification

In view of the difficulty of traditional hydrocyclones to meet the requirements of fine classification, a double-overflow three-product (internal overflow, external overflow and underflow) hydrocyclone was designed in this study. Numerical simulation and experimental research methods were used to investigate the effects of double-overflow flow field characteristics and structural parameters (i.e., internal vortex finder diameter and insertion depth) on separation performance. The research results showed that the larger the diameter of the internal vortex finder, the greater the overflow yield and the larger the cut size. The finest internal overflow product can be obtained when the internal vortex finder is 30 mm longer than the external vortex finder. The separation efficiency is highest when the internal vortex finder is 30 mm shorter than the external vortex finder.

scholarly journals Design of a Double-Nozzle Air Spray Gun and Numerical Research in the Interference Spray Flow Field

Coatings ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 475
Author(s):  
Yin-An Wang ◽  
Xiao-Peng Xie ◽  
Xiao-Hui Lu
Keyword(s):  
Flow Field ◽  
Central Region ◽  
Interference Effect ◽  
Thickness Distribution ◽  
Computational Domain ◽  
Coating Film ◽  
Discrete Phase Model ◽  
Spray Painting ◽  
Flow Field Characteristics ◽  
Spray Gun

Spray painting robots equipped with air spray guns have been widely used in the painting industry. In view of the low efficiency of single-nozzle air spray guns when spraying large targets, a new double-nozzle air spray gun structure was designed in this paper based on the Coanda effect of double jets. Firstly, a 3-D physical model of the double-nozzle air spray gun was built in Solidworks, in which unstructured grids were generated for the computational domain by ICEM. Secondly, the spray painting process was numerically modeled with the help of the computational fluid dynamics (CFD) software ANSYS-Fluent 16.0. The two-phase spray flow was calculated by coupling a discrete phase model (DPM) and the Taylor analogy breakup (TAB) method. The TAB model was applied to predict the secondary break-up. The DPM model was applied to predict the droplet trajectories. The geometry of an air spray gun has a significant influence on the spray flow field characteristics. The influence of the air spray gun geometry on the interference spray flow field characteristics and coating film thickness distribution were investigated by changing the values of the distance between the centers of the two paint holes (L) and the angle between the axes of the two paint holes (θ). Numerical results show that the smaller L and θ are, the stronger the interference effect between the two jets, while the more concentrated the paint is in the central region of the target surface, the easier it is for overspray to occur. With increasing L and θ, the interference effect gradually decreased and the extension distance of the coating film along the x-axis gradually increased. However, if L and θ are too large, the interference effect will become too weak and the shape of the coating film will become a concave, with more paint on both side regions and less paint in the central region, which will cause an uneven coating film. From the simulation results, it can be concluded that a more uniform coating film can be obtained when L = 30 mm and θ = 10°. The effective coating width of the double-nozzle air spray gun was increased by 85.7% compared with the single-nozzle air spray gun, which improved the spraying efficiency.

Effects of Flue Gas Inlet Structure on the Flow Field Characteristics of Multi-Stage Liquid Column Scrubber

2013 ◽  
Vol 773 ◽  
pp. 749-754
Author(s):  
Zhen Ya Duan ◽  
Fu Lin Zheng ◽  
Hui Ling Shi ◽  
Jun Mei Zhang
Keyword(s):  
Flow Field ◽  
Flue Gas ◽  
Static Pressure ◽  
Liquid Column ◽  
Liquid Distribution ◽  
Multi Stage ◽  
Flow Field Characteristics ◽  
Wall Flow ◽  
Two Peaks ◽  
Saddle Shape

In this paper, the numerical model of multi-stage liquid column scrubber was established. The flow field of liquid column scrubber with different inlet structure was respectively simulated by a commercial CFD code, Fluent. Considering the distribution characteristics of static pressure and velocity in the scrubber, this inlet type, single horizontal gas inlet with a notch at the bottom, is regarded as the most reasonable structure. On one hand, that structure has uniform distribution of static pressure. On the other hand, the velocity profile of its field presents saddle shape, i.e. the low central velocity exists between two peaks, which could contribute to weakening wall-flow phenomenon and obtaining uniform gas-liquid distribution.

scholarly journals Instability wave models for the near-field fluctuations of turbulent jets

2011 ◽  
Vol 689 ◽  
pp. 97-128 ◽  
Author(s):  
K. Gudmundsson ◽  
Tim Colonius
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Microphone Array ◽  
Near Field ◽  
Turbulent Jets ◽  
Instability Wave ◽  
Mean Flow ◽  
Velocity Fluctuations ◽  
The Mean ◽  
Scale Structures

AbstractPrevious work has shown that aspects of the evolution of large-scale structures, particularly in forced and transitional mixing layers and jets, can be described by linear and nonlinear stability theories. However, questions persist as to the choice of the basic (steady) flow field to perturb, and the extent to which disturbances in natural (unforced), initially turbulent jets may be modelled with the theory. For unforced jets, identification is made difficult by the lack of a phase reference that would permit a portion of the signal associated with the instability wave to be isolated from other, uncorrelated fluctuations. In this paper, we investigate the extent to which pressure and velocity fluctuations in subsonic, turbulent round jets can be described aslinearperturbations to the mean flow field. The disturbances are expanded about the experimentally measured jet mean flow field, and evolved using linear parabolized stability equations (PSE) that account, in an approximate way, for the weakly non-parallel jet mean flow field. We utilize data from an extensive microphone array that measures pressure fluctuations just outside the jet shear layer to show that, up to an unknown initial disturbance spectrum, the phase, wavelength, and amplitude envelope of convecting wavepackets agree well with PSE solutions at frequencies and azimuthal wavenumbers that can be accurately measured with the array. We next apply the proper orthogonal decomposition to near-field velocity fluctuations measured with particle image velocimetry, and show that the structure of the most energetic modes is also similar to eigenfunctions from the linear theory. Importantly, the amplitudes of the modes inferred from the velocity fluctuations are in reasonable agreement with those identified from the microphone array. The results therefore suggest that, to predict, with reasonable accuracy, the evolution of the largest-scale structures that comprise the most energetic portion of the turbulent spectrum of natural jets, nonlinear effects need only be indirectly accounted for by considering perturbations to the mean turbulent flow field, while neglecting any non-zero frequency disturbance interactions.

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