Author: Andrew Laban
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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The objective of this research is to investigate the effects of nozzle spacing on the mean velocity and higher order turbulent statistics of free round twin jets produced from sharp contraction nozzles. The experiments were performed in an air chamber for four nozzle spacing ratios, S/d = 2.8, 4.1, 5.5 and 7.1 and at a fixed Reynolds number of 10,000. A planar particle image velocimetry system was used to conduct the velocity measurements. The results show that downstream of the potential core, a reduction in spacing ratio leads to an earlier and more intense interaction between the jets, indicated by enhanced half-velocity width spread rate in the inner shear layers and a significant rise of turbulent intensities and vorticity thickness along the symmetry plane. A reduction in spacing ratio, however, diminishes the ambient fluid entrainment along the inner shear layers leading to reduced core jet velocity decay rate. A closer proximity of the jets also leads to the suppression of Reynolds stresses in the inner shear layers but not in the outer shear layers, suggesting that there exists no significant communication between the inner and outer shear layers. The Reynolds stress ratios along the jet centerline reveals the highest anisotropy in the potential core region. Skewness and flatness factors are used to examine the asymmetry and intermittency of the velocity fluctuations, while two-point correlation analysis is employed to investigate the effects of nozzle spacing ratio on the spatial coherence of large-scale vortical structures.
Author: Chidiebere Felix Nwaiwu
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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The effects of nozzle geometry on the mean and turbulent characteristics of submerged twin jets were experimentally investigated. The experiments were conducted at fixed Reynolds number and offset height ratio of 4,400 and h⁄d=2, respectively. The jets were produced from three nozzle geometries: round, square, and rectangle, with the rectangular nozzle geometry oriented in the minor (rect_min) and major (rect_maj) planes. The twin nozzles of each geometry type were aligned parallel to the free surface, and the separation ratio between the twin jets was fixed at G⁄d=2.3 for all cases. Velocity measurements were obtained using a particle image velocimetry (PIV) technique, and analyses of various quantities such as the instantaneous, mean, and surface velocities, as well as the turbulent statistics were performed. The jet-free surface interaction was examined using mean and turbulent surface velocities at the free surface, velocity defect, and vorticity thickness. Two-point velocity correlation and joint probability density function revealed the dynamics of the turbulent structures. Results from the velocity contours showed that the shear layer expansion was most rapid in twin jets produced from the rect_min nozzle geometry, which resulted in the shortest attachment length to the free surface. The instantaneous velocity field showed the most prograde and retrograde vortices in the rect_min nozzle geometry, accounting for the fastest shear layer expansion. Surface-normal profiles of the Reynolds stress ratio showed an enhancement of about 60% at the free surface and that the Townsend structure parameter was dependent on nozzle geometry. The mean surface velocity revealed that the free surface was in a state of strain due to alternating velocity gradient and was most intense in the rect_min jet. Large-scale structures produced along the centreline of the jet father away from the free surface (jet B) showed a larger streamwise extent compared to those along the centreline of the jet closer to the free surface (jet A) and were independent of nozzle geometry. Analysis of the joint probability density function of the streamwise and surface-normal velocity fluctuations showed that within the shear layer, the Reynolds shear stress producing events were dominated by slow entrainment and fast ejection events, and the damping effect of the free surface was least on the rect_min jets.
Author: Ramin Naseri Oskouie
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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An experimental study was performed to investigate the effects of the spacing ratio between the nozzles on the evolution and interaction of twin rectangular jets. The velocity measurements were conducted using particle image velocimetry (PIV) technique. The measurements were performed on the symmetry plane of the rectangular jets. A total of 5 test cases of S/de = 1.8, 2.8, 3.7, 5.5 and 7.3 were examined with Reynolds number being fixed and equal to Rede = 10,000. The effects of the spacing ratio on the mean flow in terms of its mixing characteristics (e.g., decay and spread rates) and turbulence statistics (e.g., turbulence intensities and Reynolds stresses) were investigated. The focus was then on large-scale structures (LSS). The evolution of LSS was studied along the shear layers and the symmetry line in order to investigate the effects of nozzle spacing and interactions. For doing so, various techniques such as Galilean decomposition, two-point correlation and swirling strength were applied on the flow field. The conditionally-averaged mean streamwise velocity profiles were also extracted around the turbulent/non-turbulent interface (TNTI) and results were compared with twin round jet counterpart. The results showed that changing the spacing ratio directly affects some characteristics of the mean flow, turbulence statistics and LSS. For instance, it was observed that increasing the spacing ratio, linearly increases the streamwise locations of the merging and combined points though with different slopes. Turbulence intensity profiles along the symmetry line showed a peak downstream of the merging point, where its value decreased as the spacing ratio increased. Also, interestingly for S/de ≤ 3.7, the peak of the transverse component was larger than the streamwise component. Regarding the integral length scale of turbulence along the symmetry line, a linearly increasing trend was observed. Whilst no effects of nozzle spacing was observed on the streamwise component, the trend for the transverse component showed to increase by increasing the spacing ratio. Due to the importance of the shear layers in free shear flows, a special attention was paid to the inner and outer shear layers. In the converging region, jet half-velocity widths were identical for the shear layers. In the merging region however, while the outer shear layer continued to spread similarly to its single jet counterpart, the half-velocity width of the inner shear layer rapidly increased before becoming unstable by the interactions. Study of coherent structures showed that the effects of interactions become more pronounced as the inner shear layer develops in the merging region. For instance, 0.1de downstream of the merging point, the streamwise spatial correlation of the outer and inner shear layers were identical. By progressing into the merging region however, this reduced for the inner shear layer while expectedly increased for the outer shear layer. In a similar fashion, at the TNTI the difference between conditionally- and unconditional- averaged profiles of mean streamwise velocity increased as the inner shear layer developed in the merging region. As a result, the conditional profile jumped to a larger value upon entering the turbulent region.
Author: Ella Morris
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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The effects of nozzle orientation on the mixing and turbulent characteristics of elliptical free triple and twin jets were studied experimentally. The experiments were conducted using modified contoured nozzles with a sharp linear contraction. The centers of the nozzle pair had a separation ratio of s/d = 5.5 for twin jets and s/d = 4.1 for triple jets. For the twin-jet system, two nozzle configurations were tested, twin nozzles oriented along the minor plane (Twin_Minor) and twin nozzles oriented along the major plane (Twin_Major) and the results were compared with single jet. For the triple-jets system, three nozzle configurations were tested. The first configuration had each nozzle oriented along the minor plane (3_Minor), the next had two nozzles oriented along the minor plane and one along the major plane (Min_Maj_Min) and the last configuration had one nozzle oriented along the minor plane and two along the major plane (Maj_Min_Maj). In each case, the Reynolds number based on the maximum jet velocity and the equivalent diameter was 10,000. A planar particle image velocimetry system was used to measure the velocity field in the jet symmetry plane. The velocity decay, jet spread, merging point, combined point and potential core length were used to characterize the effects of nozzle orientation on the mixing performance. For both twin jets and triple jets, it was observed that the velocity decay rate is not sensitive to nozzle orientation. However, the spread rate was approximately 35% higher in the minor plane for each configuration. In addition, the potential core length for 3_Minor was approximately 42% shorter than Twin_Minor. Furthermore, contour plots of swirling strength, Reynolds shear stress and turbulent intensities revealed significant differences between the minor and major plane for both twin and triple jets. One-dimensional plots revealed that jets approached self-similarity at a faster rate in the major axis.
Author: Suvanjan Bhattacharyya
Publisher: Springer Nature
ISBN: 9811962707
Category : Science
Languages : en
Pages : 628
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Book Description
This book presents the select proceedings of the 48th National Conference on Fluid Mechanics and Fluid Power (FMFP 2021) held at BITS Pilani in December 2021. It covers the topics such as fluid mechanics, measurement techniques in fluid flows, computational fluid dynamics, instability, transition and turbulence, fluid‐structure interaction, multiphase flows, micro- and nanoscale transport, bio-fluid mechanics, aerodynamics, turbomachinery, propulsion and power. The book will be useful for researchers and professionals interested in the broad field of mechanics.
Author: Sudev Das
Publisher: Springer Nature
ISBN: 981995990X
Category : Technology & Engineering
Languages : en
Pages : 840
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Book Description
This book comprises the proceedings of the 1st International Conference on Fluid, Thermal and Energy Systems. The contents of this book focus on phase change heat transfer, advanced energy systems, separated flows, turbulence and multi-phase modeling, computational fluid flow and heat transfer, thermal energy storage systems, integrated energy systems, nuclear thermal hydraulics, heat transfer in nanofluids, etc. This book serves as a useful reference to researchers, academicians, and students interested in the broad field of thermo-fluid science and engineering.
Author: Antonio Carcaterra
Publisher: Springer Nature
ISBN: 3030410579
Category : Science
Languages : en
Pages : 2200
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Book Description
This book gathers the peer-reviewed papers presented at the XXIV Conference of the Italian Association of Theoretical and Applied Mechanics, held in Rome, Italy, on September 15-19, 2019 (AIMETA 2019). The conference topics encompass all aspects of general, fluid, solid and structural mechanics, as well as mechanics for machines and mechanical systems, including theoretical, computational and experimental techniques and technological applications. As such the book represents an invaluable, up-to-the-minute tool, providing an essential overview of the most recent advances in the field.
Author: Morris D. Rousso
Publisher:
ISBN:
Category : Atmospheric temperature
Languages : en
Pages : 39
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Book Description
Investigations have been conducted to determine by means of total-pressure surveys the boundaries of single and twin jets discharging through convergent nozzles into quiescent air. The jet boundaries for the region from the nozzle outlets to a station 6 nozzle diameters downstream are presented for nozzle pressure ratios ranging from 2.5 t o 16.0 and for twin-Jet nozzle center-line spacings ranging from 1.42 to 2.50 nozzle diameters. The effects of these parameters on the interaction of twin Jets are discussed.
Author: Jan Lepicovsky
Publisher:
ISBN:
Category : Boundary layer
Languages : en
Pages : 0
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Book Description
An experimental investigation of the effects of nozzle operating conditions on the development of nozzle-exit boundary layers of highly heated air free jets is reported in this paper. The total pressure measurements in the nozzle-exit boundary layer were obtained at a range of jet Mach numbers from 0.1 to 0.97 and jet total temperatures up to 900 K. The analysis of results shows that the nozzle-exit laminar boundary-layer development depends only on the nozzle-exit Reynolds number. For the nozzle-exit turbulent boundary layer, however, it appears that the effects of the jet total temperature on the boundary-layer integral characteristics are independent from the effect of the nozzle-exit Reynolds number. This surprising finding has not yet been reported. Further, laminar boundary-layer profiles were compared with the Pohlhausen solution for a flat-wall converging channel and an acceptable agreement was found only for low Reynolds numbers. For turbulent boundary layers, the dependence of the shape factor on relative Mach numbers at a distance of one momentum thickness from the nozzle wall resembles Spence's prediction. Finally, the calculated total pressure loss coefficient was found to depend on the nozzle-exit Reynolds number for the laminar nozzle-exit boundary layer, while for the turbulent exit boundary layer this coefficient appears to be constant.
Author: Yaw Yeboah Afriyie
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
An experimental investigation was conducted using particle image velocimetry to study the effect of nozzle geometry on turbulent free orifice jets. The nozzle geometries studied include the round, cross, flower, star, rectangular and elliptical nozzles (aspect ratio 2). The spread rate of the rectangular nozzle was 61% greater than the square nozzle while the elliptical nozzle was 45% greater than the round nozzle using the conventional half velocity width. The superior mixing capacity of the rectangular and elliptical nozzles is attributed to the axis-switching mechanism. Evaluation of the energy budget showed a higher level of production of turbulence and convection of the mean flow for the rectangular nozzle compared with the round nozzle. Two-point auto-correlation function revealed larger structures in the non-circular nozzles and in particular the rectangular nozzle. The Kolmogorov and Taylor microscales however, did not show any significant dependency on nozzle geometry.
