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Articles de revues sur le sujet « Overexpanded flow »

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Auteur : Grafiati
Publié le 14 mars 2023

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1

Moore, J., et K. M. Elward. « Shock Formation in Overexpanded Tip Leakage Flow ». Journal of Turbomachinery 115, no 3 (1 juillet 1993) : 392–99. http://dx.doi.org/10.1115/1.2929266.

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Shock formation due to overexpansion of supersonic flow at the inlet to the tip clearance gap of a turbomachine has been studied. The flow was modeled on a water table using a sharp-edged rectangular channel. The flow exhibited an oblique hydraulic jump starting on the channel sidewall near the channel entrance. This flow was analyzed using hydraulic theory. The results suggest a model for the formation of the jump. The hydraulic analogy between free surface water flows and compressible gas flows is used to predict the location and strength of oblique shocks in analogous tip leakage flows. Features of the flow development are found to be similar to those of compressible flow in sharp-edged orifices. Possible implications of the results for high-temperature gas turbine design are considered.
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2

Verma, S. B., et Oskar Haidn. « Flow Characteristics of Overexpanded Rocket Nozzles ». International Journal of Aerospace Innovations 2, no 4 (décembre 2010) : 259–77. http://dx.doi.org/10.1260/1757-2258.2.4.259.

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3

MIYAZATO, Yoshiaki, Masashi KASHITANI, Hiroshi KATANODA et Kazuyasu MATSUO. « Characteristics of Overexpanded Flow in a Supersonic Nozzle ». Journal of the Visualization Society of Japan 15, Supplement2 (1995) : 23–26. http://dx.doi.org/10.3154/jvs.15.supplement2_23.

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4

Chung, Chan-Hong, Kenneth J. De Witt, Robert M. Stubbs et Paul F. Penko. « Simulation of overexpanded low-density nozzle plume flow ». AIAA Journal 33, no 9 (septembre 1995) : 1646–50. http://dx.doi.org/10.2514/3.12812.

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5

Silnikov, M. V., et M. V. Chernyshov. « Supersonic flow gradients at an overexpanded nozzle lip ». Shock Waves 28, no 4 (13 novembre 2017) : 765–84. http://dx.doi.org/10.1007/s00193-017-0772-2.

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6

Sharma, H., A. Vashishtha, E. Rathakrishnan et P. Lovaraju. « Experimental study of overexpanded co-flowing jets ». Aeronautical Journal 112, no 1135 (septembre 2008) : 537–46. http://dx.doi.org/10.1017/s0001924000002499.

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Abstract An experimental investigation was carried out to find the effect of an annular co-flow jet on the primary supersonic jet from Mach 2 nozzle at different levels of overexpansion. In this study, a convergent-divergent circular nozzle of exit Mach number 2, surrounded by an annular convergent circular nozzle with an annular gap of 4·4mm was used. Nozzle pressure ratios (NPRs) 3, 4, 5, 6, 7 are investigated for overexpanded states of the primary jet and NPR 8 is investigated for almost correctly expanded state. The centreline pressure distributions were taken at all NPRs for both with and without co-flow case, to investigate the supersonic core extent and mixing activity in the jet field. In the radial direction pitot pressure at different axial locations at all NPRs for both the cases are measured to find the jet development and shadowgraph visualisation of jet structure was done to visualise the shock structure in near-field. It is found that the co-flow acts as mixing inhibitor at all levels of overexpansion for Mach 2 nozzle.
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7

SHIMSHI, E., G. BEN-DOR et A. LEVY. « Viscous simulation of shock-reflection hysteresis in overexpanded planar nozzles ». Journal of Fluid Mechanics 635 (10 septembre 2009) : 189–206. http://dx.doi.org/10.1017/s002211200900771x.

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A computational fluid dynamics simulation of the flow in an overexpanded planar nozzle shows the existence of Mach-reflection hysteresis inside the nozzle. Previous simulations have dealt only with the flow outside the nozzle and thus concluded that the hysteresis phenomenon takes place outside the nozzle even when viscous effects are introduced. When including the geometry of the nozzle in the simulation it becomes evident that flow separation will occur before the transition from regular to Mach reflection for all relevant Mach numbers. The simulation reveals complex changes in the flow structure as the pressure ratio between the ambient and the jet is increased and decreased. The pressure along the nozzle wall downstream of the separation point is found to be less than the ambient pressure, and a modification of the Schilling curve fit is suggested for cases of extensive flow separation.
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8

Zebiri, B., A. Piquet, A. Hadjadj et S. B. Verma. « Shock-Induced Flow Separation in an Overexpanded Supersonic Planar Nozzle ». AIAA Journal 58, no 5 (mai 2020) : 2122–31. http://dx.doi.org/10.2514/1.j058705.

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9

Satyajit, De, et Ethirajan Rathakrishnan. « Experimental study of supersonic co-flowing jet ». Proceedings of the Institution of Mechanical Engineers, Part G : Journal of Aerospace Engineering 233, no 4 (9 janvier 2018) : 1237–49. http://dx.doi.org/10.1177/0954410017749866.

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A detailed experimental study was carried out to investigate the behaviour of a Mach 2 primary jet in the presence of a Mach 1.6 annular co-flow. The lip thickness of the inner nozzle was 7.75 mm. The characteristics of jets were investigated at nozzle pressure ratios 3 to 8, in steps of 1. At nozzle pressure ratios 3 to 7, the centre jet is overexpanded; and at nozzle pressure ratio 8, it is marginally underexpanded. Both primary and secondary jets were operated at the nozzle pressure ratio. Centreline pressure distribution was measured to examine the supersonic core length of the centre jet in the presence and absence of the co-flow at all nozzle pressure ratios. It is found that the co-flow reduces the core length of the primary jet at all overexpanded states. A maximum core length reduction of about 61% is at nozzle pressure ratio 4, whereas the core increases by 5% at the marginally underexpanded state corresponding to nozzle pressure ratio 8. The co-flow jet merges with the primary jet at 4 D, at nozzle pressure ratio 3, and at 8 D for nozzle pressure ratios above 4. Shadowgraph images of the jet in the presence and absence of co-flow reveal that the waves in the core of the jet are strongly influenced by the co-flow.
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10

Moiseev, M. G., E. A. Nikulicheva et V. S. Suminova. « Convergent-Divergent Nozzle under Highly Overexpanded Conditions ». Fluid Dynamics 39, no 3 (mai 2004) : 503–10. http://dx.doi.org/10.1023/b:flui.0000038569.29058.7e.

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11

Sellam, Mohamed, et Amer Chpoun. « Numerical Simulation of Reactive Flows in Overexpanded Supersonic Nozzle with Film Cooling ». International Journal of Aerospace Engineering 2015 (2015) : 1–15. http://dx.doi.org/10.1155/2015/252404.

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Reignition phenomena occurring in a supersonic nozzle flow may present a crucial safety issue for rocket propulsion systems. These phenomena concern mainly rocket engines which use H2gas (GH2) in the film cooling device, particularly when the nozzle operates under over expanded flow conditions at sea level or at low altitudes. Consequently, the induced wall thermal loads can lead to the nozzle geometry alteration, which in turn, leads to the appearance of strong side loads that may be detrimental to the rocket engine structural integrity. It is therefore necessary to understand both aerodynamic and chemical mechanisms that are at the origin of these processes. This paper is a numerical contribution which reports results from CFD analysis carried out for supersonic reactive flows in a planar nozzle cooled with GH2film. Like the experimental observations, CFD simulations showed their ability to highlight these phenomena for the same nozzle flow conditions. Induced thermal load are also analyzed in terms of cooling efficiency and the results already give an idea on their magnitude. It was also shown that slightly increasing the film injection pressure can avoid the reignition phenomena by moving the separation shock towards the nozzle exit section.
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12

Luchikhina, E. A., et L. E. Tonkov. « Detached eddy simulations of side-loads in an overexpanded nozzle flow ». IOP Conference Series : Materials Science and Engineering 158 (novembre 2016) : 012064. http://dx.doi.org/10.1088/1757-899x/158/1/012064.

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13

Abdol-Hamid, K. S., Alaa Elmiligui et Craig A. Hunter. « Numerical Investigation of Flow in an Overexpanded Nozzle with Porous Surfaces ». Journal of Aircraft 43, no 4 (juillet 2006) : 1217–25. http://dx.doi.org/10.2514/1.18835.

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14

YONEZAWA, Koichi, Tsuyoshi MORIMOTO, Yoshinobu TSUJIMOTO, Yasuhide WATANABE et Kazuhiko YOKOTA. « A Study of an Asymmetric Flow in an Overexpanded Rocket Nozzle ». Journal of Fluid Science and Technology 2, no 2 (2007) : 400–409. http://dx.doi.org/10.1299/jfst.2.400.

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15

YONEZAWA, Koichi, Yukinori YAMASHITA, Yoshinobu TSUJIMOTO, Yasuhide WATANABE et Kazuhiko YOKOTA. « Effect of Nozzle Contour on Flow Separation in Overexpanded Rocket Nozzles ». Journal of Fluid Science and Technology 2, no 1 (2007) : 97–108. http://dx.doi.org/10.1299/jfst.2.97.

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16

YONEZAWA, Koichi, Yukinori YAMASHITA, Yoshinobu TSUJIMOTO, Yasuhide WATANABE et Kazuhiko YOKOTA. « Effect of Nozzle Contour on Flow Separation in Overexpanded Rocket Nozzles ». Transactions of the Japan Society of Mechanical Engineers Series B 71, no 707 (2005) : 1789–97. http://dx.doi.org/10.1299/kikaib.71.1789.

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17

YONEZAWA, Koichi, Tsuyoshi MORIMOTO, Yoshinobu TSUJIMOTO, Yasuhide WATANABE et Kazuhiko YOKOTA. « A Study of an Asymmetric Flow in an Overexpanded Rocket Nozzle ». Transactions of the Japan Society of Mechanical Engineers Series B 72, no 717 (2006) : 1241–48. http://dx.doi.org/10.1299/kikaib.72.1241.

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18

Dehane, Rabie, Khatir Naima, Abdelkrim Liazid, Mustafa Inc, Abdallah Benarous, Hijaz Ahmad et Younes Menni. « Impact of the convergent geometric profile on boundary layer separation in the supersonic over-expanded nozzle ». Open Physics 20, no 1 (1 janvier 2022) : 1080–95. http://dx.doi.org/10.1515/phys-2022-0185.

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Abstract This article aims to conduct a numerical investigation of phenomena induced by gas expansion in chemical propulsion nozzles. A numerical simulation of full-scale flat convergent-divergent nozzle geometry using the finite volume method on structured meshes is performed to predict the change in the convergent geometry on the boundary layer separation resulting from a shock/shock and shock/boundary layer. Two turbulence models are tested, namely, the k−ε and k−ω shear-stress transport (SST) models. Three steps are considered to achieve this work. First, 10 numerical schemes are tested to select the accurate one. The findings of the first step are used to predict the boundary layer separation in a supersonic overexpanded nozzle. The available experimental data from the NASA Langley Research Center are used to validate the results. The third step concerns investigating the impact of the convergent geometric profile on the downstream flow of the nozzle. The obtained results are analyzed and compared with the experimental data. These results show that convergent geometry may cause the formation of different shock structures and different points of flow separation and modifies several parameters of the flow and nozzle performance downstream the throat. The findings indicated that the convergent profile must be considered during the design phase when focusing on the problem of boundary layer separation in the supersonic overexpanded regime nozzles.
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19

Menon, Shyam, et Mohana Gurunadhan. « Droplet behavior in overexpanded supersonic two-phase jets ». International Journal of Multiphase Flow 152 (juillet 2022) : 104076. http://dx.doi.org/10.1016/j.ijmultiphaseflow.2022.104076.

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20

Luchikhina, E. A., et L. E. Tonkov. « Detached eddy simulations of the side-loads in an overexpanded nozzle flow ». Vestnik Udmurtskogo Universiteta. Matematika. Mekhanika. Komp'yuternye Nauki 27, no 1 (mars 2017) : 121–28. http://dx.doi.org/10.20537/vm170110.

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21

Hamed, A., et C. Vogiatzis. « Overexpanded Two-Dimensional-Convergent-Divergent Nozzle Flow Simulations, Assessment of Turbulence Models ». Journal of Propulsion and Power 13, no 3 (mai 1997) : 444–45. http://dx.doi.org/10.2514/2.5183.

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22

Silnikov, Mikhail V., et Mikhail V. Chernyshov. « Incident shock strength evolution in overexpanded jet flow out of rocket nozzle ». Acta Astronautica 135 (juin 2017) : 172–80. http://dx.doi.org/10.1016/j.actaastro.2016.11.025.

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23

Чернышов, М. В., et Л. Г. Гвоздева. « Дифференциальные характеристики поля течения перерасширенной газовой струи в окрестности кромки сопла ». Журнал технической физики 89, no 4 (2019) : 483. http://dx.doi.org/10.21883/jtf.2019.04.47300.2533.

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AbstractA parametric study of the features of the flow field of a plane and axisymmetric overexpanded ideal gas jet in the vicinity of the nozzle edge has been conducted over the entire theoretically admissible range of determining parameters (nozzle divergence angles, exhaust Mach numbers, jet incalculabilities, and gas adiabat indicators). The exhaust parameters that correspond to the extremes of the differential characteristics of a shockwave falling (descending) from the edge and the flow field behind it have been revealed. A significant difference in the character of changes in the characteristics of the shockwave and the flow field behind it depending on the type of symmetry of the gas jet has been found and studied.
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24

Hamed, A., et C. Vogiatzis. « Overexpanded Two-Dimensional Convergent-Divergent Nozzle Performance, Effects of Three-Dimensional Flow Interactions ». Journal of Propulsion and Power 14, no 2 (mars 1998) : 234–40. http://dx.doi.org/10.2514/2.5272.

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25

Malik, T. I., et R. K. Tagirov. « Semiempirical method of calculating overexpanded turbulent separated flow in a conical laval nozzle ». Fluid Dynamics 23, no 6 (1989) : 851–56. http://dx.doi.org/10.1007/bf01051818.

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26

Chutkey, K., M. Viji et S. B. Verma. « Effect of clustering on linear plug nozzle flow field for overexpanded internal jet ». Shock Waves 27, no 4 (25 janvier 2017) : 623–33. http://dx.doi.org/10.1007/s00193-017-0707-y.

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27

Omel’chenko, A. V., V. N. Uskov et M. V. Chernyshev. « An approximate analytical model of flow in the first barrel of an overexpanded jet ». Technical Physics Letters 29, no 3 (mars 2003) : 243–45. http://dx.doi.org/10.1134/1.1565647.

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28

Murugesan, Priyadharshini, A. R. Srikrishnan, Akram Mohammad et Ratna Kishore Velamati. « Numerical Study of Wall Heat Transfer Effects on Flow Separation in a Supersonic Overexpanded Nozzle ». Energies 16, no 4 (10 février 2023) : 1762. http://dx.doi.org/10.3390/en16041762.

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In this study, numerical simulations have been carried out to analyze the effect of convective heat transfer on flow separation occurring in a DLP-PAR nozzle. Heat transfer coefficient (0, 200 and 1000 w/m2K) was applied to the nozzle wall to incorporate the cooling effect for different gas inlet temperatures ranging from 1000 to 1500 K. The impact of the cooling effect was analyzed based on nozzle wall temperature and wall static pressure. The wall static pressure distribution also characterizes movement of the separation point. For an inlet temperature of 1000 K, a detailed heat transfer study was carried out for four different nozzle pressure ratios (14, 22, 30 and 40). Significant amount of heat transfer was observed for pressure ratio 14, which in turn had an impact on flow separation. The wall cooling resulted in a shift of the point of separation towards the nozzle exit. For the nozzle pressure ratio of 14, this shift was by about 8.8%, indicating that the flow separation can be delayed by way of cooling for the considered inlet temperature. For higher inlet temperatures, the effect of heat transfer on flow separation seems to be negligible. The current study concludes that the separation point can be controlled by convective cooling for inlet gas temperatures below 1500 K so that the optimal performance of the nozzle can be achieved.
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29

Prasad, J. K., R. C. Mehta et A. K. Sreekanth. « Experimental study of overexpanded supersonic jet impingement on a double wedge deflector ». Aeronautical Journal 97, no 966 (juillet 1993) : 209–14. http://dx.doi.org/10.1017/s0001924000026245.

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AbstractExperiments have been conducted to study the impingement fiowfield, over a double wedge deflector, produced by the impingement of an overexpanded supersonic jet. The jet has an exit Mach number of 3.1 and an expansion ratio of 0.81. The distance between the nozzle exit and deflector apex was varied from 2 to 5 times the nozzle exit diameter. The experiment consisted of schlieren flow visualisations and measurements of pressure distribution. Load coefficient has been obtained by integrating the measured pressure distributions. Boundary layer thickness and skin friction coefficient on the deflector surface have been calculated by solving compressible turbulent boundary layer equations, using moment integral and moment-of-momentum integral equations in conjunction with the measured surface pressure distributions.
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30

de Cacqueray, Nicolas, et Christophe Bogey. « Noise of an Overexpanded Mach 3.3 Jet : Non-Linear Propagation Effects and Correlations with Flow ». International Journal of Aeroacoustics 13, no 7-8 (décembre 2014) : 607–32. http://dx.doi.org/10.1260/1475-472x.13.7-8.607.

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31

Moshfegh, Abouzar, Mehrzad Shams, Reza Ebrahimi et Mohammad Ali Farnia. « Two-way coupled simulation of a flow laden with metallic particulates in overexpanded TIC nozzle ». International Journal of Heat and Fluid Flow 30, no 6 (décembre 2009) : 1142–56. http://dx.doi.org/10.1016/j.ijheatfluidflow.2009.09.001.

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32

Sainte-Rose, B., N. Bertier, S. Deck et F. Dupoirieux. « Numerical simulations and physical analysis of an overexpanded reactive gas flow in a planar nozzle ». Combustion and Flame 159, no 9 (septembre 2012) : 2856–71. http://dx.doi.org/10.1016/j.combustflame.2012.04.001.

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33

Chernyshov, M. V., et L. G. Gvozdeva. « Differential Characteristics of the Overexpanded Gas Jet Flow Field in the Vicinity of the Nozzle Edge ». Technical Physics 64, no 4 (avril 2019) : 441–48. http://dx.doi.org/10.1134/s106378421904008x.

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34

Sureshkumar, A., et B. T. N. Sridhar. « Experimental Studies on Decay and Spread Characteristics of an Overexpanded Triangular Supersonic Jet ». Fluid Dynamics 54, no 5 (septembre 2019) : 629–39. http://dx.doi.org/10.1134/s0015462819050082.

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35

Saleem, Mohammad, Omar L. Rodriguez, Aatresh Karnam, Ephraim Gutmark et Junhui Liu. « Optical-acoustics source analysis of supersonic jet noise reduction using micro vortex generators ». Journal of the Acoustical Society of America 152, no 4 (octobre 2022) : A221. http://dx.doi.org/10.1121/10.0016074.

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A new supersonic jet noise reduction technology has been developed using Micro Vortex Generators (MVGs) by the collaboration between the University of Cincinnati and the Naval Research Laboratory. MVGs are used on model scale nozzles that are representative of GE F404 engine nozzles. Noise reductions up to −10 dB have been observed in both laboratory measurements and LES simulations at conditions related to take off in the overexpanded regime. Analysis of the acoustic field and flow field using Schlieren visualization reveal the noise reduction mechanisms associated with MVGs. Direct visualization of the changes in shock cell spacing, Large Coherent Structures (LCS) formation, and their convective velocity are identified and those changes modify the downstream propagating hydrodynamic waves and the upstream propagating acoustics waves. Spectral Proper Orthogonal Decomposition (SPOD) is utilized to examine the flow sources at frequencies associated with the noise components observed in the acoustic spectra to explain the noise reduction mechanisms of MVGs.
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36

GARELLI, L., G. RIOS RODRIGUEZ, R. PAZ et M. STORTI. « ADAPTIVE SIMULATION OF THE INTERNAL FLOW IN A ROCKET NOZZLE ». Latin American Applied Research - An international journal 44, no 3 (31 juillet 2014) : 267–76. http://dx.doi.org/10.52292/j.laar.2014.451.

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This work is a first step in the understanding of the interaction process between internal shock waves and the flow transition inside of a rocket nozzle that develops during the engine start-up phase or when the nozzle is operated at overexpanded conditions. In many cases, this transition in the flow pattern produces side loads in the nozzle due to an asymmetric pressure distribution on the wall, being harmful for the rocket’s integrity. To understand this phenomenon, a numerical simulation is performed by solving the three-dimensional Euler equations on unstructured tetrahedral meshes. With this model the computational cost to solve the equations significantly increases, therefore parallel processing is required. Also, an unsteady h-adaptive refinement strategy is used jointly with a Streamline Upwind Petrov-Galerkin and a discontinuity capturing scheme, both to keep the size of the fluid flow problem bounded and to sharply resolve the shock wave pattern. The mesh adaptation strategy is introduced. Since its performance is a major concern in the solution of unsteady flow problems, some implementation issues about the data structure chosen to represent the mesh are discussed. Average pressure distributions computed at the wall and the axis of the nozzle for various pressure ratios are analyzed based on experimental and numerical results from other authors.
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37

Bae, Dae Seok, Hyun Ah Choi, Ho Dong Kam et Jeong Soo Kim. « A Computational Study on the Shock Structure and Thrust Performance of a Supersonic Nozzle with Overexpanded Flow ». Journal of the Korean Society of Propulsion Engineers 18, no 4 (1 août 2014) : 1–8. http://dx.doi.org/10.6108/kspe.2014.18.4.001.

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38

Deck, Sébastien. « Delayed detached eddy simulation of the end-effect regime and side-loads in an overexpanded nozzle flow ». Shock Waves 19, no 3 (8 avril 2009) : 239–49. http://dx.doi.org/10.1007/s00193-009-0199-5.

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39

Tkacik, P. T., R. G. Keanini, N. Srivastava et M. P. Tkacik. « Color Schlieren imaging of high-pressure overexpanded planar nozzle flow using a simple, low-cost test apparatus ». Journal of Visualization 14, no 1 (24 octobre 2010) : 11–14. http://dx.doi.org/10.1007/s12650-010-0056-8.

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40

Брыков, Н. А., К. Н. Волков, В. Н. Емельянов et И. В. Тетерина. « Flows of ideal and real gases in channels of variable cross section with unsteady localized energy supply ». Numerical Methods and Programming (Vychislitel'nye Metody i Programmirovanie), no 1 (28 février 2017) : 20–40. http://dx.doi.org/10.26089/nummet.v18r103.

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Проводится моделирование течений газа в технических устройствах, в которых протекают процессы, связанные с нестационарным локализованным подводом энергии. Для численного моделирования нестационарных сопловых течений с интенсивным энергоподводом используется метод конечных объемов и векторизованный подход к расчету потоков. Для моделирования термодинамических процессов в высокотемпературных потоках воздуха применяется приближенная модель равновесной термодинамики воздуха. Приводятся результаты численного моделирования одномерных и двумерных сопловых течений с подвижной зоной энерогоподвода. На основе данных численного моделирования обсуждается качественная картина газодинамических и тепловых процессов в сопле при нестационарном подводе энергии. Устанавливается зависимость расходных характеристик сопла, а также смещение соплового скачка уплотнения при перерасширенном истечении газа из сопла от интенсивности и цикличности энергоподвода в дозвуковой части сопла. Gas flows are simulated in technical devices where processes associated with unsteady localized energy supply are proceeded. The finite volume method and the vectorized approach to the calculation of numerical fluxes are applied to the simulation of unsteady nozzle flows with intense energy supply. An approximate model of equilibrium thermodynamics of air is used to simulate thermodynamic processes in high-temperature air flows. The numerical results obtained for one-dimensional and two-dimensional nozzle flows with moving zones of energy supply are analyzed. A qualitative picture of gasdynamic and thermal processes in a nozzle with unsteady energy supply is discussed on the basis of the results of numerical simulation. A dependence of the nozzle flow rate and the displacement of nozzle shock wave on the intensity and cyclicity of energy supply is considered for overexpanded nozzle flow.
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Yu, Y., J. Xu, J. Mo et M. Wang. « Numerical investigation of separation pattern and separation pattern transition in overexpanded single expansion ramp nozzle ». Aeronautical Journal 118, no 1202 (avril 2014) : 399–424. http://dx.doi.org/10.1017/s0001924000009192.

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Abstract Flow separation results in many problems to single expansion ramp nozzle (SERN) and hypersonic vehicle. However, little research has been conducted on the separation patterns and their effects on SERN’s performance. In the present paper, the numerical simulation is adopted to get the intuitive results and help to analyse the separation phenomena in SERN thoroughly. The main separation pattern is the restricted shock separation (RSS) in SERN, and the free shock separation (FSS) only appears in a small range of the nozzle pressure ratio (NPR), which is much different from the axisymmetric rocket nozzle. Further CFD results show that the separation pattern transition makes great effects on the performance of SERN, especially the lift. Moreover, the performance of SERN has an extreme in the separation pattern transition because of the main jet impinging on the expansion ramp. The transitions occur in both the startup and shutdown processes but the critical nozzle pressure ratios of the separation pattern transitions are different, which leads to a hysteresis loop of SERN performance.
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42

Uskov, V. N., et M. V. Chernyshov. « Differential characteristics of the flow field in a plane overexpanded jet in the vicinity of the nozzle lip ». Journal of Applied Mechanics and Technical Physics 47, no 3 (mai 2006) : 366–76. http://dx.doi.org/10.1007/s10808-006-0064-6.

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Chai, Xiaochuan, Prahladh S. Iyer et Krishnan Mahesh. « Numerical study of high speed jets in crossflow ». Journal of Fluid Mechanics 785 (13 novembre 2015) : 152–88. http://dx.doi.org/10.1017/jfm.2015.612.

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Large-eddy simulation (LES) and dynamic mode decomposition (DMD) are used to study an underexpanded sonic jet injected into a supersonic crossflow and an overexpanded supersonic jet injected into a subsonic crossflow, where the flow conditions are based on the experiments of Santiago & Dutton (J. Propul. Power, vol. 13 (2), 1997, pp. 264–273) and Beresh et al. (AIAA J., vol. 43, 2005a, pp. 379–389), respectively. The simulations successfully reproduce experimentally observed shock systems and vortical structures. The time averaged flow fields are compared to the experimental results, and good agreement is observed. The behaviour of the flow is discussed, and the similarities and differences between the two regimes are studied. The trajectory of the transverse jet is investigated. A modification to Schetz et al.’s theory is proposed (Schetz & Billig, J. Spacecr. Rockets, vol. 3, 1996, pp. 1658–1665), which yields good prediction of the jet trajectories in the current simulations in the near field. Point spectra taken at various locations in the flowfield indicate a global oscillation for the sonic jet flow, wherein different regions in the flow oscillate with a frequency of $St=fD/u_{\infty }=0.3$. For supersonic jet flow, no such global frequency is observed. Dynamic mode decomposition of the three-dimensional pressure field obtained from LES is performed and shows the same behaviour. The DMD results indicate that the $St=0.3$ mode is dominant between the upstream barrel shock and the bow shock for the sonic jet, while the roll up of the upstream shear layer is dominant for the supersonic jet.
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Kumar, Bholu, Suresh Kant Verma et Shantanu Srivastava. « Mixing Characteristics of Supersonic Jet from Bevelled Nozzles ». International Journal of Heat and Technology 39, no 2 (30 avril 2021) : 559–72. http://dx.doi.org/10.18280/ijht.390226.

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The present study focuses on the effect of nozzle exit inclination on the mixing characteristics of Mach 2.17 overexpanded jets at the NPR 5, NPR 6 and NPR 7, using commercial software package ANSYS Fluent. The convergent-divergent nozzles, investigated are circular nozzle and bevel nozzle with bevel angle 300, and bevel angel 450. The nozzles are constructed with equal throat-to-exit area ratio, in order to maintain uniform Mach number at the nozzle exit. From the results, it was found that, the bevelled nozzles effectively reduce the jet core as much as 46%, indicating enhanced jet mixing. It was also observed that at lower NPR, i.e., at NPR 5, the Bevel30 nozzle is found superior over Bevel45 and circular nozzle and at the intermediate NPR, both of the Bevel30 and Bevel45 nozzle reduces the jet core with the same rate. However, at highest NPR of the present study, the Bevel45 nozzle exhibits the highest mixing enhancement. An early axis switching is seen for the Bevel30 jet at NPR 5 and for the Bevel45 jet at NPR 7.
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Halynskyi, V. P. « Calculation of the interaction of a supersonic jet with a flat obstacle inclined off the jet axis ». Technical mechanics 2020, no 4 (10 décembre 2020) : 72–81. http://dx.doi.org/10.15407/itm2020.04.072.

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This paper presents results of a numerical solution of the model problem of the interaction of a plane supersonic jet with a semiinfinite flat plate inclinable off the jet axis. The paper is devoted to the study of the flow parameters in the jet flow field and the pressure distribution over the plate surface as a function of the plate inclination. The aim of the paper is to obtain the flow parameters in the jet flow field and the pressure distribution over the plate surface as a function of the plate inclination angle and front edge position. To obtain numerical results, marching algorithms in the inviscid gas and viscous layer approximation were used. At specified values of the supersonic underexpanded/overexpanded jet parameters, calculations were conducted in the plate inclination angle range of 0 to 20?. The position of the plate front edge was specified by two coordinates: a longitudinal and a transversal one, and in the parametric calculations the transversal coordinate was varied at a fixed longitudinal one. The cross-section at which the nonuniform jet field starts to interact with the plate was determined as a function of both the plate front edge position and the plate inclination. The numerical study showed the following: with increasing plate inclination angle, the oscillation frequencies of the flow parameters in the jet flow field and on the plate surface decrease, while their oscillation amplitudes increase, and the position of the maximum pressure point on the plate surface depends on the initial position of the plate front edge and may not coincide with the cross-section at which the jet–plate interaction starts. The results obtained may be used in qualitative estimation of the effect of different parameters in the jet flow field.
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Carlton, D. P., J. J. Cummings, R. G. Scheerer, F. R. Poulain et R. D. Bland. « Lung overexpansion increases pulmonary microvascular protein permeability in young lambs ». Journal of Applied Physiology 69, no 2 (1 août 1990) : 577–83. http://dx.doi.org/10.1152/jappl.1990.69.2.577.

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To study the effects of inflation pressure and tidal volume (VT) on protein permeability in the neonatal pulmonary microcirculation, we measured lung vascular pressures, blood flow, lymph flow (QL), and concentrations of protein in lymph (L) and plasma (P) of 22 chronically catheterized lambs that received mechanical ventilation at various peak inflation pressures (PIP) and VT. Nine lambs were ventilated initially with a PIP of 19 +/- 1 cmH2O and a VT of 10 +/- 1 ml/kg for 2-4 h (base line), after which we overexpanded their lungs with a PIP of 58 +/- 3 cmH2O and a VT of 48 +/- 4 ml/kg for 4-8 h. QL increased from 2.1 +/- 0.4 to 13.9 +/- 5.0 ml/h. L/P did not change, but the ratio of albumin to globulin in lymph relative to the same ratio in plasma decreased, indicating altered protein sieving in the pulmonary microcirculation. Seven other lambs were mechanically ventilated for 2-4 h at a PIP of 34 +/- 1 cmH2O and a VT of 23 +/- 2 ml/kg (base line), after which their chest and abdomen were bound so that PIP increased to 54 +/- 1 cmH2O for 4-6 h without a change in VT. QL decreased on average from 2.8 +/- 0.6 to 1.9 +/- 0.3 ml/h (P = 0.08), and L/P was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)
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Sousa, Ana E., Ana F. Chaves, Manuela Doroana, Francisco Antunes et Rui M. M. Victorino. « Kinetics of the Changes of Lymphocyte Subsets Defined by Cytokine Production at Single Cell Level During Highly Active Antiretroviral Therapy for HIV-1 Infection ». Journal of Immunology 162, no 6 (15 mars 1999) : 3718–26. http://dx.doi.org/10.4049/jimmunol.162.6.3718.

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Abstract The effects of highly active antiretroviral therapy on cytokine imbalances associated with HIV-1 infection have not been characterized. Using single cell analysis by flow cytometry, we show that a significant recovery in the frequency of IL-2-producing cells was only observed in patients with a sustained control of viral replication and that the overexpanded CD8 T cell population of CD28− IFN-γ+ cells was not significantly reduced after 1 yr of effective therapy. Moreover, a detrimental role of IL-4 is suggested by the association between an enhanced proportion of IL-4-producing cells within the CD4 and particularly the CD8 subset and viral load rebound. Finally, the kinetics of changes of cell subsets assessed for simultaneous production of different cytokines supports the view that cell reconstitution during highly active antiretroviral therapy is initially due to redistribution of terminally differentiated cells, followed by peripheral expansion of less differentiated ones and a late progressive increase of the proportion of functionally defined naive/memory precursor lymphocytes. These data bring new support for the role of cytokine imbalances in AIDS pathogenesis and may be relevant for the definition of immunointervention targets.
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P., Arun Kumar, et E. Rathakrishnan. « Triangular tabs for supersonic jet mixing enhancement ». Aeronautical Journal 118, no 1209 (novembre 2014) : 1245–78. http://dx.doi.org/10.1017/s0001924000009969.

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AbstractThe mixing promoting capability of right-angled triangular tab with sharp and truncated vertex has been investigated by placing two identical tabs at the exit of a Mach 2 axi-symmetric nozzle. The mixing promoting efficiency of these tabs have been quantified in the presence of adverse and marginally favourable pressure gradients at the nozzle exit. It was found that, at all levels of expansion of the present study though the core length reduction caused by both the tabs are appreciable, but the mixing caused by the truncated tab is superior. The mixing promoting efficiency of the truncated tab is found to increase with increase of nozzle pressure ratio (that is, decrease of adverse pressure gradient). For all the nozzle pressure ratios of the present study, the core length reduction caused by the truncated vertex tab is more than that of sharp vertex tab. As high as 84% reduction in core length is achieved with truncated vertex right-angled triangular tabs at moderately overexpanded level, corresponding to expansion levelpe/pa= 0·90. The corresponding core length reduction for right-angled triangular tabs with sharp vertex and rectangular tabs are 65% and 31%, respectively. The present results clearly show that the mixing promoting capability of the triangular tab is best than that of rectangular tabs at identical blockage and flow conditions.
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T., Thillaikumar, Tamal Jana et Mrinal Kaushik. « Experimental Assessment of Corrugated Rectangular Actuators on Supersonic Jet Mixing ». Actuators 9, no 3 (17 septembre 2020) : 88. http://dx.doi.org/10.3390/act9030088.

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To improve the stealth capability of a military aircraft, the reduction in core length is essential to reduce the heat signature and the noise characteristics of the engine exhaust. The efficacy of rectangular vortex generators in achieving these objectives has been demonstrated by several researchers, owing to their simplicity. One way of producing the mixed-size vortices is by providing corrugations on the edge of the tab (actuator). Therefore, in the current study, two tabs of aspect ratio 1.5, mounted diametrically opposite to each other at the outlet of a Mach 1.73 circular nozzle, are examined at varying levels of expansions, ranging from overexpanded to underexpanded jet states. In addition, to generate the mixed-size vortices, three corrugation geometries, i.e., rectangular, triangular, and semicircular, are configured along the tab edges. Both quantitative and qualitative investigations are carried out by using the pitot probe to measure the stagnation pressures and by utilizing a shadowgraph technique to visualize the flow field. The corrugated tabs generated a significant mixing, and among them, the tabs with triangular corrugations are found to be most effective. A maximum reduction of about 99.7% in the supersonic core is obtained with triangular corrugated tabs at near-correct-expansion, corresponding to nozzle pressure ratio (NPR) 5. Interestingly, the semicircular corrugated tab significantly reduces the asymmetry near the nozzle exit plane. The shadowgraph images confirm the efficacy of different corrugated tabs in reducing the strength of the waves, prevalent in the supersonic core.
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Ranjan, Abhash, Mrinal Kaushik, Dipankar Deb, Vlad Muresan et Mihaela Unguresan. « Assessment of Short Rectangular-Tab Actuation of Supersonic Jet Mixing ». Actuators 9, no 3 (21 août 2020) : 72. http://dx.doi.org/10.3390/act9030072.

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This work explores the extent of jet mixing for a supersonic jet coming out of a Mach 1.8 convergent-divergent nozzle, controlled with two short rectangular vortex-generating actuators located diametrically opposite to each other with an emphasis on numerical methodology. The blockage ratio offered by the tabs is around 0.05. The numerical investigations were carried out by using a commercial computational fluid dynamics (CFD) package and all the simulations were performed by employing steady Reynolds-averaged Navier–Stokes equations and shear-stress transport k−ω turbulence model on a three-dimensional computational space for more accuracy. The numerical calculations are administered at nozzle pressure ratios (NPRs) of 4, 5, 6, 7 and 8, covering the overexpanded, the correctly expanded and the underexpanded conditions. The centerline pressure decay and the pressure profiles are plotted for both uncontrolled and the controlled jets. Numerical schlieren images are used to capture the barrel shock, the expansion fans and the Mach waves present in the flow field. Mach contours are also delineated at varying NPRs indicating the number of shock cells, their length and the variation of the shock cell structure and strength, to substantiate the prominent findings. The outcomes of this research are observed to be in sensible concurrence with the demonstrated exploratory findings. A reduction in the jet core length of 75% is attained with small vortex-generating actuators, compared to an uncontrolled jet, corresponding to nozzle pressure ratio 5. It was also seen that the controlled jet gets bifurcated downstream of the nozzle exit at a distance of about 5 D, where D is the nozzle exit diameter. Furthermore, it was fascinating to observe that the jet spread increases downstream of the nozzle exit for the controlled jet, as compared to the uncontrolled jet at any given NPR.
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