Effects of Upstream Nozzle Geometry on Rectangular Free Jets PDF Download
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Author: Tanmay J. Tipnis
Publisher:
ISBN:
Category : Jet engines
Languages : en
Pages :
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This study is aimed at understanding the effects of changing the upstream nozzle geometry on the development of rectangular free jets. An existing converging rectangular nozzle with an exit aspect ratio of 4 and a circular inlet (AR4 nozzle) has been used as the basic configuration for this work. The study is primarily based on the results of numerical simulations wherein the internal geometry variation is accomplished by changing the inlet aspect ratio (AR,) and the length of the converging section, expressed as a ratio with respect to the length of the nozzle (called 'converging section ratio*, CSR); all the other parameters are kept constant. The results from LDA experiments done on the AR4 nozzle are presented and used as validation data for the CPD simulations. Analyses of the numerical results help in understanding the variation of the jet spreading for different combinations of AR, and CSR. Two parameters are identified for describing the jet development: the cross-over point (XC), defined as the location downstream of the exit where the jet half-velocity-widths (B) along the major and minor axes are equal, and the difference in the half-velocity-widths at 30 nozzle equivalent diameters (Dm) from the exit (AB30), to ascertain the occurrence of axis-switching. For a given AR, XC varies linearly with CSR; the variation of XC is non-linear with AR, for a constant CSR. The A1330 variation is non-linear with both AR, and CSR; the other variable being kept constant. The data obtained from the simulations are further used to propose two parametric models which can be used to predict the occurrence of axis-switching, within the scope of this work. The parametric models are validated and future work is proposed.
Author: Tanmay J. Tipnis
Publisher:
ISBN:
Category : Jet engines
Languages : en
Pages :
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Book Description
This study is aimed at understanding the effects of changing the upstream nozzle geometry on the development of rectangular free jets. An existing converging rectangular nozzle with an exit aspect ratio of 4 and a circular inlet (AR4 nozzle) has been used as the basic configuration for this work. The study is primarily based on the results of numerical simulations wherein the internal geometry variation is accomplished by changing the inlet aspect ratio (AR,) and the length of the converging section, expressed as a ratio with respect to the length of the nozzle (called 'converging section ratio*, CSR); all the other parameters are kept constant. The results from LDA experiments done on the AR4 nozzle are presented and used as validation data for the CPD simulations. Analyses of the numerical results help in understanding the variation of the jet spreading for different combinations of AR, and CSR. Two parameters are identified for describing the jet development: the cross-over point (XC), defined as the location downstream of the exit where the jet half-velocity-widths (B) along the major and minor axes are equal, and the difference in the half-velocity-widths at 30 nozzle equivalent diameters (Dm) from the exit (AB30), to ascertain the occurrence of axis-switching. For a given AR, XC varies linearly with CSR; the variation of XC is non-linear with AR, for a constant CSR. The A1330 variation is non-linear with both AR, and CSR; the other variable being kept constant. The data obtained from the simulations are further used to propose two parametric models which can be used to predict the occurrence of axis-switching, within the scope of this work. The parametric models are validated and future work is proposed.
Author: Allan Ross Werbow
Publisher:
ISBN:
Category :
Languages : en
Pages : 154
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Author: Vern G. Rollin
Publisher:
ISBN:
Category : Aerodynamics
Languages : en
Pages : 22
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Author: Seyed Sobhan Aleyasin
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ISBN:
Category :
Languages : en
Pages : 0
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An experimental study was designed to investigate the effects of Reynolds number and nozzle geometry on the development and the structures of free turbulent single and twin jets. The velocity measurements were performed using a particle image velocimetry (PIV). Measurements were conducted in the symmetry planes of single round, elliptic, rectangular, triangular, cross, daisy, star and square jets, and the Reynolds number studied ranged from 2500 to 20000. The effects of the initial conditions on the jets' properties are studied using the mean velocities, Reynolds stresses and triple velocity correlations. Also, several methods are employed to extract and examine the turbulent structures of the jets which are responsible for their different mixing performance. The results show that noncircular jets have shorter potential core length, faster growth of centerline turbulence intensity and higher velocity decay and spread rates. Due to the specific topology of the daisy and triangular jets, the normalized profiles of mean velocity and higher order turbulent statistics in their minor and major planes are close to each other, therefore, the turbulent kinetic energy can be approximated by k=0.5((u^2 )+2(v^2 )). In addition, proper orthogonal decomposition (POD) analysis shows that the fractional and cumulative energy of turbulent structures in both minor and major planes of the triangular jet are almost identical. In the elliptic and rectangular jets, the statistical quantities in the minor and major planes differ significantly. The swirling strength analysis shows that the vortical structures in the minor plane of the elliptic and rectangular jets are more intense compared to those in their major plane as well as in the round and square jets leading to a higher jet spreading in the minor planes. It is observed that an increase in Reynolds number decreases the decay and spread rates, however, at Re > 10000 they become asymptotic. The joint probability density function (JPDF) and weighted joint probability density function (WJPDF) analysis demonstrate that the dominant events that contribute towards the Reynolds shear stress are different upstream of the axis-switching point in the minor and major planes of the elliptic jet. Consequently, a sign change occurs in the distribution of the Reynolds shear stress in the major plane but not in the minor plane. In twin jets, upstream of the merging point, the levels of turbulence intensities and Reynolds shear stress are higher in the inner shear layers, but the opposite trend is observed downstream of the merging point. The swirling strength analysis reveals that the vortical structures are more intense in the inner shear layers upstream of the merging point, their strengths are equal at the merging point and eventually more intense in the outer shear layers after the merging point. The analysis performed at the turbulent/non-turbulent interface of the jets reveals no Reynolds number effect on conditional streamwise velocity and spanwise vorticity distribution. However, the values of conditional transverse velocity are significantly larger at the lowest Reynolds number. The two-point correlation functions point out that the turbulent structures in the outer shear layers are larger compared to the inner shear layers.
Author: I. WYGNANSKI
Publisher:
ISBN:
Category :
Languages : en
Pages : 29
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The asymmetric-jet created by the mixing of a wall-jet with quiescent surrounding fluid downstream of a trailing edge is considered. The method of analytic continuation, developed by Goldstein is extended to provide a series solution for the asymmetric jet. The different boundary conditions as well as the extension to turbulent flow reveal some new aspects which are discussed in detail. In particular, the conservation of momentum downstream of the trailing edge enables one to determine the location of a jet with respect to the y-coordinate. In turbulent flow the analysis has been supplemented by experiment, providing a fair agreement between the two. (Author).
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 994
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Author: Hylton Ratliffe Murphy
Publisher:
ISBN:
Category : Aerodynamics, Transonic
Languages : en
Pages : 376
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Author: Ramin Naseri Oskouie
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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:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 904
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Author:
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ISBN:
Category :
Languages : en
Pages : 458
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