Comparison of Turbulent Jets Issuing From Various Sharp Contoured Nozzles

2017 ◽  
Author(s):  
Seyed Sobhan Aleyasin ◽  
Nima Fathi ◽  
Mark Francis Tachie ◽  
Mikhail Koupriyanov
Keyword(s):  
Cross Sections ◽  
Turbulent Transport ◽  
Flow Characteristics ◽  
Turbulent Jets ◽  
Decay Rates ◽  
Nozzle Geometry ◽  
Strength Analysis ◽  
Linear Contraction ◽  
Turbulence Structures ◽  
Swirling Strength

An experimental study was conducted to investigate nozzle geometry effects on mixing characteristics and turbulent transport phenomena in the near and intermediate regions of free jets issuing from modified contoured nozzles (contoured nozzle with a sharp linear contraction). The cross-sections examined were round, square, equilateral triangle as well as ellipse and rectangle with aspect ratio of 2. For each nozzle shape, detailed velocity measurements were made using particle image velocimetry at a Reynolds number of 10000. It was observed that noncircular jets have shorter potential cores than their round counterparts and their lengths are comparable with those of orifice jets. In addition, the spread and decay rates and the levels of turbulence intensities are the highest in the jets issuing from the elliptic and rectangular nozzles, implying enhanced mixing in these jets. The results from the swirling strength analysis revealed that the rotational motions induced by vortices within the minor planes of the elliptic and rectangular jets are more intense than those observed in the other jets. Furthermore the obtained data indicate distinctly different flow characteristics in the major and minor planes of elliptic, rectangular and triangular jets due to their asymmetric shapes. The size of turbulence structures in all the jets studied increases with streamwise distance and the elliptic and rectangular jets contain the largest structures.

Experimental-Numerical Analysis of Turbulent Incompressible Isothermal Jets

2017 ◽  
Author(s):  
Seyed Sobhan Aleyasin ◽  
Nima Fathi ◽  
Mark Francis Tachie ◽  
Peter Vorobieff ◽  
Mikhail Koupriyanov
Keyword(s):  
Reynolds Number ◽  
Near Field ◽  
Turbulent Transport ◽  
Reynolds Numbers ◽  
Nozzle Geometry ◽  
System Response ◽  
Potential Core ◽  
Turbulence Structures ◽  
Round Jets ◽  
Core Length

An experimental investigation was conducted to study the effects of Reynolds number on mixing characteristics and turbulent transport phenomena in the near and intermediate regions of free equilateral triangular and round jets issuing from modified contoured nozzles (nozzles with sharp linear contractions). Detailed velocity measurements were made using a particle image velocimetry at Reynolds numbers of 6000, 10000, 13800 and 20000. Computational fluid dynamics (CFD) was also applied to understand the flow behaviors in different Reynolds numbers. We applied standard k-ε turbulence model in an axisymmetric domain to conduct the numerical simulation of the round jet cases. The potential core length was the system response quantity to evaluate our simulation against the experimental results. The geometrical comparative study shows enhanced mixing in the near field of the triangular jets compared to the round jets, regardless of Reynolds number. This conclusion is supported by shorter potential core length and faster growth of turbulence intensity on the centerline of the triangular jets. The obtained data in the round jets exhibit that the jet at the lowest Reynolds number has the most effective mixing with the ambient fluid, while increase in Reynolds number reduces the mixing performance. In the triangular jets almost there is no Reynolds number effect on the measured quantities including the length of the potential core, the decay rate and the axis-switching locations. The results revealed that the asymptotic values of the turbulence intensities on the jet centerline are not only independent of the Reynolds number but also they are the same for both the round and triangular jets. Due to the specific shape of the triangular nozzle, a skewed flow pattern is observed in the near field region in the major plane while the jet is absolutely symmetric in the minor plane. The turbulence structures in all the jets studied become larger as streamwise distance increases, while there is no considerable Reynolds number or nozzle geometry effects on the size of the structures on the jet centerline.

scholarly journals Effect of nozzle geometry on the dynamics and mixing of self-similar turbulent jets

2021 ◽  
Author(s):  
Pourya Nejatipour ◽  
Babak Khorsandi
Keyword(s):  
Mass Flow ◽  
Cross Sections ◽  
Turbulent Jets ◽  
Nozzle Geometry ◽  
Entrainment Rate ◽  
Radial Profiles ◽  
Self Similar ◽  
The Mean ◽  
Elliptical Jet ◽  
Velocity Variances

Abstract The effect of nozzle geometry on the dynamics and mixing of turbulent jets is experimentally investigated. The jets with a Reynolds number of 13,000 were issued from four different pipes with circular, elliptical, square and triangular cross sections. The velocity field was measured in the self-similar region of the jets using an acoustic Doppler velocimeter. Statistical parameters, such as the mean velocities, velocity variances, spreading rates, mass flow rates, and entrainment rates are presented. The results show that despite having approximately similar decay rates for the mean centerline velocities, the radial profiles of the axial mean velocity varied in jets with different nozzle cross sections and were widest for elliptical jets and narrowest for the triangular ones. On the other hand, velocity variances were greatest for the triangular jet when compared to the jets released from cross sections of other geometries. Furthermore, the spreading rate, mass flow rate, and entrainment rate were highest for the elliptical jet, and lowest for the triangular jet. From this it can be inferred that the elliptical jet has the highest mixing and dilution. The results of this study could help to improve the initial mixing of pollutants by optimizing the initial conditions.

Flow and Energy Loss Downstream of Rectangular Sharp-Crested Weirs for Free and Submerged Flows

2021 ◽  
Author(s):  
Mahmud R. Amin ◽  
Nallamuthu Rajaratnam ◽  
David Z. Zhu
Keyword(s):  
Energy Loss ◽  
Flow Regime ◽  
Analytical Study ◽  
Flow Characteristics ◽  
Turbulent Jets ◽  
Flow Regimes ◽  
Impinging Jet ◽  
Relative Energy ◽  
Surface Flow ◽  
Upper Stage

Abstract This work presents an analytical study of the flow and energy loss immediately downstream of rectangular sharp-crested weirs for free and submerged flows, using the theory of plane turbulent jets and the analysis of some relevant studies. The flow regimes downstream of the sharp-crested weir is characterized as the impinging jet and surface flow regimes. Based on the flow characteristics and the downstream tailwater depths, each flow regime is further classified, and the relative energy loss equation is developed. It is found that significant energy loss occurs for the regime of supercritical flow and the upper stage of impinging jet flow. The energy loss for the submerged flow regime is minimal.

Investigations on Flow Characteristics in Diffuser-Discharge-Channel of Volute Casing

2018 ◽  
Author(s):  
Yandong Gu ◽  
Ji Pei ◽  
Shouqi Yuan ◽  
Jinfeng Zhang ◽  
Ernst Nikolajew ◽  
...  
Keyword(s):  
Cross Sections ◽  
Discharge Channel ◽  
Transient Flow ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Centrifugal Pumps ◽  
Discharge Pipe ◽  
Hydraulic Design ◽  
Flow Loss ◽  
Two Sides

The volute casing used in centrifugal pumps is efficient for the transformation of kinetic energy into pressure energy, however, its asymmetric hydraulic design makes the flow in diffuser-discharge-channel (DDC) inhomogeneous, resulting in unsatisfactory flow patterns. In this study, the unsteady numerical simulations are carried out to investigate the transient flow characteristics in DDC. The accuracy of numerical results is found to agree well with experimental performance and pressure fluctuations. It is observed that the flow in DDC is significantly uneven. At the elbow of DDC, the static pressure on the volute left side (VL) is larger than the volute right side (VR) due to the flow impact and flow separation respectively. Thereby, this high-pressure gradient induces the secondary flow on the cross sections of DDC. Further, there is an obvious dependency of pressure fluctuations in the discharge pipe on the strong interaction between the impeller and tongue, in which four small peaks and four large peaks can be observed. At each moment, the pressure on VL gradually decreases from the inlet of discharge pipe to the pump outlet, while it increases on VR, finally, two sides tend to be the same. The pressure fluctuation intensity gradually becomes equivalent-distributed. In particular, it should be noticed that the energy loss in the diffuser part is larger than the discharge pipe, which requires a redesign concerning hydraulic performance. This study can help to better understand the transient flow characteristics and provide guidance for reducing flow loss in the volute casing.

Vortical Structures and Mixing Characteristics of Flow in Randomly Packed Porous Media During Transition to Turbulence

2021 ◽  
Author(s):  
Reza M. Ziazi ◽  
James A. Liburdy
Keyword(s):  
Porous Media ◽  
Scale Effects ◽  
Turbulent Transport ◽  
Flow Characteristics ◽  
Transition Process ◽  
Industrial Applications ◽  
Transition To Turbulence ◽  
Vortical Structures ◽  
Macro Scale ◽  
Mixing Characteristics

Abstract Transition to turbulence in randomly arranged porous media is observed in nature and industrial applications. The flow characteristics of these flows during transition are not well identified. This work describes the parameters influencing on overall mixing during the transition process from the perspective of scale of vortical structures and dispersion characteristics by addressing the following questions: (a) what are the dominant mechanisms evolution of scale of vortices, and (b) how does the inertial effects of vortical structures enhance the flow transport properties through tortuosity and dispersion. Time-resolved PIV is used to investigate the flow in the macro-scale Reynolds numbers from 100 to 1000 to show the pore- versus macro-scale effects on the scale of the flow dispersion, and their contribution in interpreting the overall flow mixing. Lagrangian mixing characteristics based on Eulerian local pore velocity variances is used to demonstrate the bed characteristics for flow in randomly distributed porous media flows. The dispersion asymptotically approaches 0.085 % of VintDH longitudinally which shows the turbulent transport is increased by enhancing the Reynolds number that matches very well with the literature.

Nozzle Geometry Effect on Twin Jet Flow Characteristics

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Muthuram A ◽  
Thanigaiarasu S ◽  
Rakesh Divvela ◽  
Rathakrishnan Ethirajan
Keyword(s):  
Mach Number ◽  
Flow Characteristics ◽  
Nozzle Geometry ◽  
Ambient Atmosphere ◽  
Free Jets ◽  
Twin Jets ◽  
Equivalent Area ◽  
Nozzle Configuration ◽  
Jet Nozzle ◽  
Nozzle Geometries

AbstractEffect of nozzle geometries on the propagation of twin jet issuing from nozzles with circle-circle, circle-ellipse, circle-triangle, circle-square, circle-hexagon and circle-star geometrical combinations was investigated for Mach numbers 0.2, 0.4, 0.6 and 0.8. In all the cases, both jets in the twin jet had the same Mach number. All the twin jets of this study are free jets, discharged into stagnant ambient atmosphere. The result of the twin jets issuing from circle-circle nozzle is kept as the reference in this study. For all the twin jet nozzles, the inter nozzle spacing; the distance between the nozzle axes (S) was 20 mm and all the nozzles had an equivalent area of 78.5 mm2. Thus for all the cases of the present study, S/D ratio is 2. The results show that the mixing of the combined jet, after the merging point is strongly influenced by the combined effect of the nozzle geometry and jet Mach number. Among the six different twin jet nozzle configuration studied, circle-square combination is found to be the most superior mixing promoter.

The Sensitivity of Inner Nozzle Flow in Gasoline Direct Injection Injector to the Nozzle Geometry Parameters

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Xinhai Li ◽  
Yong Cheng ◽  
Xiaoyan Ma ◽  
Xue Yang
Keyword(s):  
Structural Parameters ◽  
Direct Injection ◽  
Large Diameter ◽  
Small Diameter ◽  
Flow Characteristics ◽  
Gasoline Direct Injection ◽  
Nozzle Geometry ◽  
Nozzle Flow ◽  
Nozzle Length ◽  
Injector Nozzle

The inner-flow of gasoline direct injection (GDI) injector nozzles plays an important role in the process of spray, and affects the mixture process in gasoline engine cylinder. The nozzle structure also affects the inner-flow of GDI injector. In order to obtain uniform performance of GDI injector, the size consistency of injector nozzle should be ensured. This paper researches the effect of nozzle length and diameter on the inner flow and analyzes the sensitivity of inner flow characteristics to these structural parameters. First, this paper reveals the process of inception, development, and saturated condition of cavitation phenomenon in injector nozzle. Second, the inner-nozzle flow characteristics are more sensitive to small diameter than large diameter under the short nozzle length, while the sensitivity of the inner-nozzle flow characteristics to large nozzle diameter becomes strong as the increase of the nozzle length. Finally, the influence of nozzle angle on the injection mass flow is studied, and the single nozzle fuel mass will increase as the decrease of nozzle angle α. And the sensitivity of inner-flow characteristic to nozzle angle becomes strong as the decrease of α.

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