Diffuser Influence on the Mixing of Coaxial Swirling Jets

2014 ◽  
Author(s):  
Teresa Parra-Santos ◽  
Ruben Perez-Dominguez ◽  
Gonzalo Lorenzo Esteban ◽  
Robert Z. Szasz ◽  
Artur N. Gutkowski ◽  
...  
Keyword(s):  
Mechanical Energy ◽  
Flow Characteristics ◽  
Area Ratio ◽  
Sudden Expansion ◽  
Swirl Number ◽  
Swirling Jets ◽  
Annular Jet ◽  
Turbulence Regime ◽  
Recirculation Zones ◽  
Minimum Residence Time

Numerical results depicting the effects of diffusers on confined isothermal high-swirl jets are presented. The aim is analyze the mixing between a non-swirling inner jet (natural gas) and a swirling annular jet (primary air). This simple setup is widely used in burners to promote stabilized flames of lean mixtures. Flow patterns for sudden-expansion and diffusers are contrasted for swirl number of 1 and expansion area ratio of 4 in a transitional turbulence regime. Diffusers have important influence on size and location of recirculation zones. Hence knowledge of flow characteristics is a prerequisite in the design process. The criteria to establish the optimum diffuser would be better mixing as well as minimum residence time in the recirculation zones to prevent the formation of NOx in the future burner. The dissipated mechanical energy is not important in burner applications.

Topological Flow Structures of Annular Swirling Jets

2001 ◽  
Vol 17 (3) ◽  
pp. 131-138
Author(s):  
Feng Chin Tsai ◽  
Rong Fung Huang
Keyword(s):  
Vortex Breakdown ◽  
Swirling Flow ◽  
Single Bubble ◽  
Flow Structures ◽  
Complex Flow ◽  
Swirl Number ◽  
Recirculation Bubble ◽  
Annular Jet ◽  
Ring Mode ◽  
Dual Ring

AbstractThe effects of blockage and swirl on the macro flow structures of the annular jet past a circular disc are experimentally studied through the time-averaged streamline patterns. In the blockage-effect regime, the flows present multiple modes, single bubble, dual rings, vortex breakdown, and triple rings, in different regimes of blockage ratio and swirl number. The topological models of the flow structures are proposed and discussed according to the measured flow fields to manifest the complex flow structures. The single bubble is a closed recirculation bubble with a stagnation point on the central axis. The dual-ring flow is an open-top recirculsation zone, in which a pair of counter-rotating vortex rings exists in the near wake. The fluids in the dual rings are expelled downstream through a central jet-like swirling flow. A vortex breakdown may occur in the central jet-like swirling flow if the exit swirl number exceeds critical values. When the vortex breakdown interacts with the dual rings, a complex triple-ring flow structure forms. Axial distributions of the local swirl number are presented and discussed. The local swirl number increases with the increase of the exit swirl number and attains the maximum in the dual-ring mode. At large exit swirl numbers where the vortex breakdown occurs, the local swirl number decreases drastically to a low value.

The Effect of Red Cell Dynamics on Platelet Spatial Distribution in Sudden Expansion

2007 ◽  
Author(s):  
Rui Zhao ◽  
Joie Marhefka ◽  
Marina Kameneva ◽  
James Antaki
Keyword(s):  
Spatial Distribution ◽  
Sudden Expansion ◽  
Red Cell ◽  
Common Complication ◽  
Complex Flow ◽  
Cell Dynamics ◽  
Stagnation Points ◽  
Recirculation Zones

Thrombosis is a common complication associated with blood contacting devices [1]. Platelets often (or preferably) deposit in specific regions which contain complex flow featuring separations, recirculation zones and stagnation points [2, 3].

Effect of Cavities in Suddenly Expanded Flow at Supersonic Mach Number

CFD letters ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 57-71
Author(s):  
Atifatul Ismah Ismail
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Mach Number ◽  
Pressure Ratio ◽  
Area Ratio ◽  
Base Pressure ◽  
Sudden Expansion ◽  
Expansion Level ◽  
Computational Fluid Dynamics Cfd ◽  
Base Drag

The contribution from the base drag due to the sub-atmospheric pressure is significant. It can be more than two-thirds of the net drag. There is a need to increase the base pressure and hence decrease the base drag. This research examines the effect of Mach Number on base pressure. To accomplish this objective, it controls the efficacy in an enlarged duct computed by the numerical approach using Computational Fluid Dynamics (CFD) Analysis. This experiment was carried out by considering the expansion level and the aspect cavity ratio. The computational fluid dynamics method is used to model supersonic motion with the sudden expansion, and a convergent-divergent nozzle is used. The Mach number is 1.74 for the present study, and the area ratio is 2.56. The L/D ratio varied from 2, 4, 6, 8, and 10, and the simulated nozzle pressure ratio ranged from 3 to 11. The two-dimensional planar design used commercial software from ANSYS. The airflow from a Mach 1.74 convergent-divergent axi-symmetric nozzle expanded suddenly into circular ducts of diameters 17 and 24.5 mm with and without annular rectangular cavities. The diameter of the duct is taken D=17mm and D=24.5mm. The C-D nozzle was developed and modeled in the present study: K-ε standard wall function turbulence model was used with the commercial computational fluid dynamics (CFD) and validated. The result indicates that the base pressure is impacted by the expansion level, the enlarged duct size, and the passage’s area ratio.

A New Tailpipe Design for GE Frame-Type Gas Turbines to Substantially Lower Pressure Losses

2003 ◽  
Vol 125 (1) ◽  
pp. 128-132
Author(s):  
Richard Golomb ◽  
Vivek Sahai ◽  
Dah Yu Cheng
Keyword(s):  
Power Systems ◽  
Gas Turbines ◽  
Large Angle ◽  
Flow Characteristics ◽  
Exhaust System ◽  
Sudden Expansion ◽  
Pressure Losses ◽  
Turbine Efficiency ◽  
Fluid Systems ◽  
Large Pressure

Many GE frame gas turbines have a unique 90-deg tailpipe exhaust system that contains struts, diffusers, and turning vanes. As confirmed in a recent report by GE and other authors, it is known in the industry that this tailpipe design has large pressure losses. In this recent report a pressure loss as high as 60 in. of water (0.15 kgs/sqcm) was cited. Due to the flow separations they create, the report indicates that the struts can cause very high-pressure losses in the turbine. The report also states that these pressure losses can vary with different turbine load conditions. Cheng Fluid Systems and Cheng Power Systems have conducted a study aimed at substantially reducing these pressure losses. Flow control technology introduced to the refinery industry, i.e., the Cheng Rotation Vane (CRV) and the Large Angle Diffuser (LAD) can be used to mitigate the flow separation and turbulence that occurs in turns, bends, and large sudden expansions. Specifically the CRV addresses the flow separations in pipe turns, and the LAD addresses the flow problems that occur with large sudden expansion areas. The paper will introduce the past experience of the CRV and LAD, and will then use computer simulations to show the flow characteristics around a new design. First, the study meticulously goes through the entire GE exhaust system, starting with the redesign of the airfoil shape surrounding the struts. This new design has a larger angle of attack and minimizes the flow separations over a much wider operating range. Second, the pros and cons of the concentric turning vanes are studied and it is shown that they are more flow restrictive, rather than flow enhancing. Third, it is shown that the highly turbulent rectangular box-type exhaust ducting design, substantially contributes to high noise levels and pressure losses. In this paper a completed design will be shown that incorporates a new airfoil shape for the struts, and by using CRV flow technology in combination with the LAD flow technology, the pressure recovery can be enhanced. If the pressure losses could be reduced by 40 inches of water (0.10 kgs/sqcm), the turbine efficiency could be increased by 5%, and the power output could be increased by 6%.

Shaping Air Flow Characteristics of a High-Speed Rotary-Bell Sprayer for Automotive Painting Processes

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
Ch. Stevenin ◽  
Y. Béreaux ◽  
J.-Y. Charmeau ◽  
J. Balcaen
Keyword(s):  
High Speed ◽  
Vortex Breakdown ◽  
Flow Behavior ◽  
Air Flow ◽  
Flow Characteristics ◽  
Rotation Frequency ◽  
Zone Length ◽  
Swirling Jets ◽  
Automotive Parts

Electrostatic rotary bell sprayers (ERBS) are widely used in automotive painting applications. These processes involve complex airflows to shape paint sprays and transport droplets toward automotive parts to be coated. Despite the importance of shaping airflow on global spray characteristics, a detailed characterization of this aerodynamic flow is still missing. For this purpose, an experimental study was conducted on the influence of some ERBS operating parameters on the development and characteristics of shaping airflow. Results show that, for low swirl numbers, the flow behavior is close to that of annular swirling jets and a good agreement is found between ERBS flow characteristics and data available in literature. When rotational speed of the bell cup is sufficiently fast, a change of regime is observed with a shift in the longitudinal flow development and an increase of recirculation zone length. This change of regime is attributed to vortex breakdown instability, known to occur when high swirl strength is beyond a critical value. Experimental results obtained in this study put forward a clear link between the shaping air flow rate and the rotation frequency on the aerodynamics and also provide valuable leads to design shaping air flow in modern ERBS.

Recirculation zones of unconfined and confined annular swirling jets

AIAA Journal ◽  
1996 ◽  
Vol 34 (3) ◽  
pp. 572-579 ◽  
Author(s):  
H. J. Sheen ◽  
W. J. Chen ◽  
S. Y. Jeng
Keyword(s):  
Swirling Jets ◽  
Recirculation Zones

Effect of Swirler Offset on Aerodynamics of Multiswirler Arrays

2014 ◽  
Author(s):  
Prachi Rojatkar ◽  
Yi-Huan Kao ◽  
Milind A. Jog ◽  
San-Mou Jeng
Keyword(s):  
Flow Pattern ◽  
Flow Characteristics ◽  
Computational Domain ◽  
Exit Plane ◽  
Linear Arrangement ◽  
Interesting Phenomenon ◽  
Straight Line ◽  
Recirculation Zones ◽  
Vertical Walls ◽  
Inlet Manifold

Multiple swirlers arranged in an annular fashion are used in modern day gas turbine engines. A section of this annulus can be considered as a straight line or what is referred to in the paper as a linear arrangement of swirlers. Three such linear arrangements are computationally analyzed and results are presented through this study. Study of linear arrangements is crucial and novel to the swirler aerodynamics research as it lays a foundation in understanding the flow physics when swirlers are arranged at a fixed distance next to each other. Swirling flows are complicated and when slight modifications are introduced in physical arrangements the flow is impacted drastically. In the present study observations have been presented on effect of changing the offset of exit plane of swirler from the base wall of confinement when there is a single swirler or a linear arrangement of swirlers. Computational simulations of flow through single and multi-swirler array have been carried out to understand the effect of the distance of exit plane of swirler from the base wall of confinement on the swirler aerodynamics. The swirlers used in this study are radial-radial swirlers with counter rotating vanes. The computational domain extended from the inlet manifold to 12 D downstream from the swirler where D is the diameter of swirler exit. Realizable k-ε turbulence model is used and the computational grid is about 4 million points for a single swirler arrangement, about 12 million points for a three swirler array and up to 22 million for the five swirler arrangement. The computational model is validated by comparing the results with velocity measurements carried out at three different planes downstream of the swirler exit using LDV technique. First, single swirler with the exit plane of swirler with an offset of 0.04 D and 0.02D with the base wall of confinement and that with no offset (swirler exit in-line with base wall of confinement) are analyzed. It is observed that flow development in region close to the swirler exit is highly sensitive to the offset condition. In case of 0.04D and 0.02D offset a strong jet is formed as soon as the air exits the swirler. The flow tends to progress vertically forming recirculation zones in the vicinity of corners of the horizontal and vertical walls. When there is no offset, the flow exiting the swirler tends to align with the base wall and then progresses vertically. Thus for no offset case a jet formation is not observed. Next, multi-swirler arrangements with 0.04D, 0.02D offset as well as no offset configurations are simulated. All the swirlers tend to show similar pattern as single swirler arrangements with a slight difference in intensity of the flow field. For swirlers with offset of 0.04D and 0.02D there is formation of a strong jet exiting the swirler and recirculation zones are formed in corners of the base and vertical walls of the confinement as was observed for the single swirler arrangement. Recirculation zones are also formed in areas between each swirler assembly in the multi swirler arrangement. For the no offset condition it is again observed that flow aligns with the horizontal base wall for each of the swirler assembly. The axial velocity of the flow in this arrangement tends to be lower than the offset case in regions between each swirler. An interesting phenomenon of multi swirler arrangement is an asymmetrical flow pattern that is observed at each swirler. While each swirler geometry is identical, the flow pattern as well as the strength of recirculation zone developed from each individual swirler differs significantly. Results show that alternate swirlers tend to exhibit similar flow characteristics.

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